Methodology and technology of seismic exploration can. Common depth point method 2D seismic survey CDP method

The experience of conducting field seismic exploration using the classical technique and the high-performance Slip-Sweep technique by Samaraneftegeofizik is considered.

The experience of conducting field seismic exploration using the classical technique and the high-performance Slip-Sweep technique by Samaraneftegeofizika is considered.

The advantages and disadvantages of the new technique are revealed. The economic indicators of each of the methods are calculated.

Currently, the productivity of field seismic exploration depends on many factors:

Land use intensity;

Movement of automobiles and railway vehicles through the study area;

Activity on the territory of settlements located in the study area; influence of meteorological factors;

Rough terrain (ravines, forests, rivers).

All of the above factors significantly reduce the speed of seismic exploration.

In fact, during the day there are 5-6 hours of night time left for seismic observations. This is critical and insufficient to complete the volumes within the stipulated time frame, and also significantly increases the cost of work.

The time of work, first of all, depends on the following stages:

Topogeodetic preparation of the observation system - installation of profile pickets on the ground;

Installation and adjustment of seismic receiving equipment;

Excitation of elastic vibrations, recording of seismic data.

One way to reduce the time spent is to use the Slip-Sweep technique.

This technique allows you to significantly speed up the production of the excitation stage - recording seismic data.

Slip-sweep is a high-performance seismic survey system based on the overlapping sweep method, in which vibrators operate simultaneously.

In addition to increasing the speed of field work, this technique allows for the compaction of explosion points, thereby increasing the density of observations.

This improves the quality of work and increases productivity.

The Slip-Sweep technique is relatively new.

The first experience in conducting CDP-3D seismic exploration using the Slip-Sweep technique was obtained in an area of only 40 km 2 in Oman (1996).

As you can see, the Slip-Sweep technique was used mainly in desert areas, with the exception of work in Alaska.

In Russia, in pilot mode (16 km 2), the Slip-Sweep technology was tested in 2010 by the forces of Bashneftegeofizika.

The article presents the experience of conducting field work using the Slip-Sweep method and comparing indicators with the standard method.

The physical basis of the method and the possibility of compacting the observation system simultaneously with the use of Slip-Sweep technology are shown.

The primary results of the work are presented and the shortcomings of the method are identified.

In 2012, Samaraneftegeofizik carried out 3D work using the Slip-Sweep method at the Zimarnoy and Mozharovsky license areas of Samaraneftegaz in the amount of 455 km 2 .

The increase in productivity due to the Slip-Sweep technique at the excitation-recording stage in the conditions of the Samara region occurs due to the use of short-term periods of time allotted for recording seismic data during the daily cycle of work.

That is, the task of performing the largest number of physical observations in a short time is performed by the Slip-Sweep technique most effectively by increasing the productivity of recording physical observations by 3-4 times.

The Slip-Sweep technique is a high-performance seismic exploration system based on the method of overlapping vibration sweep signals, in which vibration installations on different PVs operate simultaneously, registration is continuous. Vibration excitations on different PVs are performed with a time delay, so simultaneously operating vibrators emit elastic vibrations at different frequencies ranges (Fig. 1).

The emitted sweep signal is one of the operators of the cross-correlation function in the process of obtaining a coregram from a vibrogram.

At the same time, in the correlation process, it is also a filter operator that suppresses the influence of frequencies other than the frequency emitted at a given time, which can be used to suppress emissions from simultaneously operating vibrators.

With a sufficient delay time for the operation of vibration installations, their emitted frequencies will be different, thereby completely eliminating the influence of neighboring vibration emissions (Fig. 2).

Consequently, with correctly selected slip-time, the influence of simultaneously operating vibration installations is eliminated in the process of converting the vibrogram into a coregram.

Rice. 1. Slip-time delay. Simultaneous emission of different frequencies.

Rice. 2. Evaluation of the use of an additional filter for the influence of neighboring vibration radiation: A) corellogram without filtering; B) corelogram filtered by vibrogram; B) frequency-amplitude spectrum of filtered (green light) and unfiltered (red color) coregrams.

The use of one vibrator instead of a group of 4 vibrators is based on the sufficiency of the energy of vibration radiation from one vibrator to form reflected waves from target horizons (Fig. 3).

Rice. 3. Sufficient vibration energy from one vibration installation. A) 1 vibration unit; B) 4 vibration units.

The Slip-Sweep technique is more effective when using compaction surveillance systems.

For the conditions of the Samara region, a 4-fold compaction of the observation system was applied. 4-fold division of one physical observation (f.n.) into 4 separate f.n. based on the equality of the distance between the vibrator plates (12.5 m) with a group of 4 vibrators, a PV pitch of 50 m and the use of one vibrator with a PV pitch of 12.5 m (Fig. 4).

Rice. 4. Compaction of the surveillance system with 4-fold separation of physicalobservations.

In order to combine the results of observation using the standard technique and the slip-sweep technique with 4-fold compaction, the principle of parity of the total energies of vibration radiation is considered.

The parity of vibration energy can be assessed by the total time of vibration.

Total time of vibration exposure:

St = Nv * Nn * Tsw * dSP,

where Nv is the number of vibration units in the group, Nn is the number of accumulations, Tsw is the duration of the sweep signal, dSP is the number of f.n. within the basic step PV=50m.

For the traditional method (PV step = 50m, group of 4 sources):

St = 4 * 4 * 10 * 1 = 160 sec.

For the slip-sweep method:

St = 1 * 1 * 40 * 4 = 160 sec.

The result of parity of energies for equality of total time shows the same result in the total Bin of 12.5m x 25m.

To compare methods, Samara geophysicists received two sets of seismograms: 1st set - 4 seismograms processed by one vibrator (Slip-Sweep technique), 2nd set - 1 seismogram processed by 4 vibrators (standard technique). Each of the 4 seismograms of the first set is approximately 2-3 times weaker than the seismogram of the second set (Fig. 3). Accordingly, the signal-microseism ratio is 2-3 times lower. However, a better result is the use of compacted 4 individual seismograms that are relatively weak in energy (Fig. 5).

In the case of joining areas worked out by different methods, using processing procedures oriented to the wave field of the standard method, the result was practically equivalent (Fig. 6, Fig. 7). However, if we apply processing parameters adapted for the Slip-Sweep technique, the result will be time sections with increased time resolution.

Rice. 5. Fragment of the primary summary time section according to INLINE (without filtering procedures) at the junction of two areas developed using the slip-sweep method (left) and standard technique (right).

A comparison of time sections and spectral characteristics of the standard technique and the Slip-Sweep technique shows high comparability of the resulting data (Fig. 8). The difference lies in the presence of higher energies of the high-frequency component of the Slip-Sweep seismic data signal (Fig. 7).

This difference is explained by the high noise immunity of the compacted observation system and the high multiplicity of seismic data (Fig. 6).

Another important point is the point impact of one vibrator instead of a group of vibrators and its single impact instead of the sum of vibration impacts (accumulations).

The use of a point source of excitation of elastic vibrations instead of a group of sources expands the spectrum of recorded signals in the high-frequency region, reduces the energy of near-surface interference waves, which affects the increase in the quality of the recorded data and the reliability of geological constructions.

Rice. 6. Amplitude-frequency spectra from seismograms processed using differentmethods (based on processing results): A) slip-sweep technique; B) Standard technique.

Rice. 7. Comparison of time sections worked out using different methods(based on processing results): A) Slip-sweep technique; B) Standard technique.

Advantages of the Slip-Sweep technique:

1. High productivity of work, expressed in increased productivity of registration of f.n. 3-4 times, increasing overall productivity by 60%.

2. Improved quality of field seismic data due to PV compaction:

High noise immunity of the surveillance system;

High frequency of observations;

Possibility of increasing spatial;

Increasing the share of the high-frequency component of the seismic signal by 30% due to point excitation (vibration).

Disadvantages of using the technique.

Working in the Slip-Sweep technique mode is working in a “conveyor” mode in a streaming information environment with non-stop recording of seismic data. With non-stop recording, the seismic complex operator's visual control over the quality of seismic data is significantly limited. Any failure can lead to mass defects or work stoppage. Also, at the stage of subsequent monitoring of seismic data at the field computer center, the use of more powerful field computing systems for the preparation and preliminary field processing of data is required. However, the costs of purchasing computer equipment, as well as equipment for retrofitting the recording complex, are recouped within the scope of the work contractor’s profit due to a reduction in the time required for their completion. Among other things, more efficient logistical procedures are required for preparing profiles for testing physical observations.

When carrying out work by Samaraneftegeofizika using the Slip-Sweep method in 2012, the following economic indicators were obtained (Table 1).

Table 1.

Economic indicators for comparing work methods.

These data allow us to draw the following conclusions:

1. With the same amount of work, the overall productivity of Slip-Sweep work is 63.6% higher than when carrying out work using the “standard” method.

2. Increased productivity directly affects the duration of work (decrease by 38.9%).

3. When using the Slip-Sweep technique, the cost of field seismic exploration is 4.5% lower.

Literature

1. Patsev V.P., 2012. Report on the implementation of work on the object of field seismic exploration work MOGT-3D within the Zimarny license area of Samaraneftegaz OJSC. 102 pp.

2. Patsev V.P., Shkokov O.E., 2012. Report on the implementation of work on the object of field seismic exploration MOGT-3D within the Mozharovsky license area of Samaraneftegaz OJSC. 112 p.

3. Gilaev G.G., Manasyan A.E., Ismagilov A.F., Khamitov I.G., Zhuzhel V.S., Kozhin V.N., Efimov V.I., 2013. Experience in seismic exploration MOGT-3D using the Slip-Sweep technique. 15 s.

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MINISTRY OF EDUCATION AND SCIENCE OF THE RUSSIAN FEDERATION

Federal Agency for Education

TOMSK POLYTECHNIC UNIVERSITY

Institute of Natural Resources

Course project

on the course "Seismic exploration"

Methodology and technoLogic of seismic exploration works CDP

Completed by: student gr. 2A280

Severvald A.V.

Checked:

Rezyapov G.I.

Tomsk -2012

Introduction
1. Theoretical foundations of the common depth point method

1.1 Theory of the CDP method
1.2 Features of the CDP hodograph
1.3 CDP interference system

2. Calculation of the optimal observation system of the CDP method
2.1 Seismological model of the section and its parameters

2.2 Calculation of the observation system of the CDP method
2.3 Calculation of hodographs of useful waves and interference waves
2.4 Calculation of the delay function of interference waves
2.5 Calculation of parameters of the optimal observing system

3. Field seismic technology

3.1 Requirements for the observation network in seismic exploration
3.2 Conditions for excitation of elastic waves
3.3 Conditions for receiving elastic waves
3.4 Selection of hardware and special equipment
3.5 Organization of field seismic surveys

Conclusion
Bibliography

Introduction

Seismic exploration is one of the leading methods for studying the structure, structure and composition of rocks. The main area of application is the search for oil and gas fields.

The purpose of this course work is to consolidate knowledge in the course "seismic exploration"

The objectives of this course work are:

1) consideration of the theoretical foundations of the CDP method;

2) compilation of a seismic geological model, on the basis of which the parameters of the CDP-2D observation system are calculated;

3) consideration of technology for conducting seismic exploration;

1. Theoretical foundations of the common depth point method

1.1 Theory of the CDP method

The method (method) of the common depth point (CDP) is a modification of the MDP, based on a system of multiple overlaps and characterized by the summation (accumulation) of reflections from common sections of the boundary at different locations of sources and receivers. The CDP method is based on the assumption of the correlation of waves excited by sources distant at different distances, but reflected from a common section of the boundary. Inevitable differences in the spectra of different sources and errors in time during summation require a reduction in the spectra of useful signals. The main advantage of the CDP method is the ability to amplify single reflected waves against the background of multiple and exchanged reflected waves by equalizing the times reflected from common depth points and summing them up. The specific features of the CDP method are determined by the directional properties during summation, data redundancy and statistical effect. They are most successfully implemented in digital recording and processing of primary data.

Rice. 1.1 Schematic representation of an element of the observation system and a seismogram obtained by the CDP method. A And A"-- in-phase axes of the reflected single wave, respectively, before and after the introduction of the kinematic correction; IN And IN"-- the in-phase axis of the multiple reflected wave, respectively, before and after the introduction of the kinematic correction.

Rice. 1.1 illustrates the principle of summation using CDP using the example of a five-fold overlap system. Sources of elastic waves and receivers are located on the profile symmetrically to the projection onto it of the common depth point R of the horizontal boundary. A seismogram composed of five records received at receiving points 1, 3, 5, 7, 9 (counting receiving points starts from its excitation point) when excited at points V, IV, III, II, I is shown above the CD line. It forms a CDP seismogram, and the hodographs of reflected waves correlated on it are CDP hodographs. On observation bases usually used in the CDP method, not exceeding 3 km, the CDP hodograph of a single reflected wave is approximated with sufficient accuracy by a hyperbola. In this case, the minimum of the hyperbola is close to the projection onto the observation line of the common depth point. This property of the CDP hodograph largely determines the relative simplicity and efficiency of data processing.

To convert a set of seismic records into a time section, kinematic corrections are introduced into each CDP seismogram, the values of which are determined by the velocities of the media covering the reflecting boundaries, i.e., they are calculated for single reflections. As a result of introducing corrections, the in-phase axes of single reflections are transformed into lines t 0 = const. In this case, the in-phase axes of regular interference waves (multiple, converted waves), the kinematics of which differ from the introduced kinematic corrections, are transformed into smooth curves. After introducing kinematic corrections, the traces of the corrected seismogram are simultaneously summed up. In this case, the singly reflected waves are added in phase and thus emphasized, and regular interference, and among them, first of all, the multiply reflected waves added with phase shifts, are attenuated. Knowing the kinematic features of the interference wave, it is possible to pre-calculate the parameters of the observation system using the CDP method (the length of the CDP hodograph, the number of channels on the CDP seismogram, equal to the tracking multiplicity) at which the required attenuation of the interference is ensured.

CDP seismograms are formed by selecting channels from the seismogram from each excitation point (called common excitation point seismograms - OPV) in accordance with the requirements of the system element shown in Fig. 1., which shows: the first record of the fifth excitation point, the third record of the fourth, etc. until the ninth record of the first excitation point.

This procedure of continuous sampling along the profile is possible only with multiple overlaps. It corresponds to the superposition of time sections obtained independently from each excitation point, and indicates the redundancy of information implemented in the CDP method. This redundancy is an important feature of the method and underlies the refinement (correction) of static and kinematic corrections.

The velocities required to clarify the introduced kinematic corrections are determined from the CDP hodographs. For this purpose, CDP seismograms with approximately calculated kinematic corrections are subjected to multi-time summation with additional nonlinear operations. Using CDP sum tapes, in addition to determining the effective velocities of singly reflected waves, the kinematic features of interference waves are found to calculate the parameters of the receiving system. Observations using the CDP method are carried out along longitudinal profiles.

To excite waves, explosive and shock sources are used, which require observations with a large (24-48) overlap ratio.

Processing of CDP data on a computer is divided into a number of stages, each of which ends with the output of results for decision-making by the interpreter: 1) pre-processing; 2) determination of optimal parameters and construction of the final time section; H) determination of the velocity model of the environment; 4) construction of a deep section.

Systems of multiple overlaps currently form the basis of field observations (data collection) in MOV and determine the development of the method. Summation by CDP is one of the main and effective processing procedures that can be implemented on the basis of these systems. The CDP method is the main modification of MOM in the search and exploration of oil and gas fields in almost all seismic geological conditions. However, the results of summation using CDP have some limitations. These include: a) a significant reduction in the frequency of registration; b) weakening of the locality property of the waveform due to an increase in the volume of inhomogeneous space at large distances from the source, characteristic of the CDP method and necessary for suppressing multiple waves; c) superposition of single reflections from close boundaries due to the inherent convergence of their axes of in-phase at large distances from the source; d) sensitivity to lateral waves that interfere with tracking target subhorizontal boundaries due to the location of the main maximum of the spatial characteristic of the stacking direction in a plane perpendicular to the stacking base (profile).

These limitations generally determine the tendency for the resolution of the MOV to decrease. Considering the prevalence of the CDP method, they should be taken into account in specific seismic geological conditions.

1.2 Features of the CDP hodograph

Rice. 1.2 Scheme of the CDP method for the inclined occurrence of the reflecting boundary.

1. The CDP hodograph of a single-reflected wave for a homogeneous covering medium is a hyperbola with a minimum at the symmetry point (CDP point);

2. with an increase in the angle of inclination of the interface, the steepness of the CDP hodograph and, accordingly, the time increment decrease;

3. the shape of the CDP hodograph does not depend on the sign of the angle of inclination of the interface (this feature follows from the principle of reciprocity and is one of the main properties of the symmetrical explosion-device system;

4. for a given t 0 the CDP hodograph is a function of only one parameter - v CDP, which is called fictitious speed.

These features mean that to approximate the observed CDP hodograph with a hyperbola, it is necessary to select a v CDP value that satisfies the given t 0, determined by the formula (v CDP = v/cosс). This important consequence makes it possible to easily search for the in-phase axis of the reflected wave by analyzing the CDP seismogram along a fan of hyperbolas having a common value t 0 and different v CDPs.

1.3 CDP interference system

In interference systems, the filtering procedure consists of summing seismic traces along given lines φ(x) with weights that are constant for each trace. Typically, the summation lines correspond to the shape of the useful wave travel curves. Weighted summation of oscillations of different traces y n (t) is a special case of multi-channel filtering, when the operators of individual filters h n (t) are d-functions with amplitudes equal to the weighting coefficients d n:

(1.1)

where f m - n is the difference in the summation times of oscillations on track m, to which the result obtained is attributed, and on track n.

Let us give relation (1.1) a simpler form, taking into account that the result does not depend on the position of the point m and is determined by the time shifts of the traces φ n relative to an arbitrary origin. We obtain a simple formula describing the general algorithm of interference systems,

(1.2)

Their varieties differ in the nature of changes in weight coefficients d n and time shifts φ n: both can be constant or variable in space, and the latter, in addition, can change in time.

Let a perfectly regular wave g(t,x) with arrival hodograph t(x)=t n be recorded on seismic traces:

hodograph seismological interference wave

Substituting this into (1.2), we obtain an expression describing the oscillations at the output of the interference system,

where and n =t n - f n.

The quantities and n determine the deviation of the wave hodograph from a given summation line. Let's find the spectrum of filtered oscillations:

If the hodograph of a regular wave coincides with the summation line (and n ? 0), then in-phase addition of oscillations occurs. For this case, denoted u=0, we have

Interference systems are built to amplify in-phase summed waves. To achieve this result it is necessary that H 0 (sch) was the maximum value of the function modulus H And(sch) Most often, single interference systems are used, having equal weights for all channels, which can be considered unit: d n ?1. In this case

In conclusion, we note that the summation of non-plane waves can be carried out using seismic sources by introducing appropriate delays at the moments of excitation of oscillations. In practice, these types of interference systems are implemented in a laboratory version, introducing the necessary shifts in the recording of oscillations from individual sources. The shifts can be selected so that the incident wave front has a shape that is optimal from the point of view of increasing the intensity of waves reflected or diffracted from local areas of the seismic geological section that are of particular interest. This technique is known as focusing the incident wave.

2. Calculation of the optimal observation system of the CDP method

2.1 Seismological model of the section and its parameters

The seismic geological model has the following parameters:

We calculate the reflection coefficients and double transmission coefficients using the formulas:

We get:

We set possible options for the passage of waves along this section:

Based on these calculations, we construct a theoretical vertical seismic profile (Fig. 2.1), which reflects the main types of waves that arise in specific seismic-geological conditions.

Rice. 2.1. Theoretical vertical seismic profile (1 - useful wave, 2.3 - multiple waves - interference, 4.5 - multiple waves that are not interference).

For the target fourth boundary we use wave number 1 - a useful wave. Waves with an arrival time of -0.01-+0.05 from the time of the “target” wave are interference waves. In this case, waves number 2 and 3. All other waves will not interfere.

Let's calculate the double travel time and the average velocity along the section for each layer using formula (3.4) and build a velocity model.

We get:

Rice. 2.2. Speed model

2.2 Calculation of the observation system of the CDP method

The amplitudes of useful reflected waves from the target boundary are calculated using the formula:

(2.5)

where A p is the reflection coefficient of the target boundary.

The amplitudes of multiple waves are calculated using the formula:

.(2.6)

In the absence of data on the absorption coefficient, we assume =1.

We calculate the amplitudes of multiple and useful waves:

Multiple wave 2 has the greatest amplitude. The obtained amplitude values of the target wave and interference make it possible to calculate the required degree of multiple wave suppression.

Because the

2.3 Calculation of hodographs of useful waves and interference waves

The calculation of multiple wave hodographs is carried out under simplifying assumptions about a horizontally layered model of the medium and flat boundaries. In this case, multiple reflections from several interfaces can be replaced by a single reflection from some fictitious interface.

The average speed of the fictitious medium is calculated along the entire vertical path of the multiple wave:

(2.7)

The time is determined by the pattern of formation of a multiple wave on a theoretical VSP or by summing the travel times in all layers.

(2.8)

We get the following values:

The multiple wave hodograph is calculated using the formula:

(2.9)

The useful wave hodograph is calculated using the formula:

(2.10)

Fig 2.3 Hodographs of useful waves and interference waves

2.4 Calculation of the delay function of interference waves

Let us introduce kinematic corrections calculated according to the formula:

?tк(x, to) = t(x) - to(2.11)

The multiple wave lag function (x) is determined by the formula:

(x) = t cr(xi) - t cr (2.12)

where tcr(xi) is the time corrected for kinematics and tcr is the time at zero distance of the receiving point from the excitation point.

Fig 2.4 Multiple wave lag function

2.5 Calculation of parameters of the optimal observing system

An optimal observation system should provide the greatest results at low material costs. The required degree of interference suppression is D=5, the lower and upper frequencies of the spectrum of the interference wave are 20 and 60 Hz, respectively.

Rice. 2.5 Characteristics of the directionality of summation according to CDP at N = 24.

According to the set of directional characteristics, the minimum multiplicity number is N=24.

(2.13)

Knowing P, we remove y min = 4 and y max = 24.5

Knowing the minimum and maximum frequencies, 20 and 60 Hz, respectively, we calculate f max.

f min *ф max =4ф max =0.2

f max *f max =24.5f max =0.408

The value of the delay function is f max =0.2, which corresponds to x max =3400 (see Fig. 2.4). After moving the first channel away from the excitation point, x m in =300, deflection arrow D = 0.05, D/f max = 0.25, which satisfies the condition. This indicates that the selected directional characteristic is satisfactory, the parameters of which are the values N = 24, f max = 0.2, x m in = 300 m and maximum distance x max = 3400 m.

Theoretical hodograph length H*= x max - x min =3100m.

The practical length of the hodograph is Н = K*?х, where K is the number of channels recording the seismic station and?х is the step between the channels.

Let's take a seismic station with 24 channels (K=24=N*24), ?x =50.

Let's recalculate the observation interval:

Let's calculate the excitation interval:

As a result, we get:

The observation system on the expanded profile is shown in Fig. 2.6

3. Field seismic technology

3.1 Requirements for the observation network in seismic exploration

Observing systems

Currently, multiple overlap systems (MSS) are mainly used, providing summation over a common depth point (CDP), and thereby a sharp increase in the signal-to-noise ratio. The use of non-longitudinal profiles reduces the cost of field work and dramatically increases the manufacturability of field work.

Currently, only complete correlation observation systems are practically used, allowing for continuous correlation of useful waves.

During reconnaissance surveys and at the stage of experimental work, seismic soundings are used for the purpose of preliminary study of the wave field in the research area. In this case, the observation system must provide information on the depths and inclination angles of the reflecting boundaries being studied, as well as determining effective velocities. There are linear, which are short sections of longitudinal profiles, and areal (cross, radial, circular) seismic soundings, when observations are made on several (two or more) intersecting longitudinal or non-longitudinal profiles.

Among linear seismic soundings, common depth point (CDP) soundings, which are elements of a multiple profiling system, are most widely used. The relative positions of the excitation points and observation sites are chosen in such a way that reflections from one total area of the studied boundary are recorded. The resulting seismograms are mounted.

The common depth point method is based on multiple profiling (overlapping) systems, which uses central systems, systems with a changing explosion point within the receiving base, flank one-sided ones without removal and with removal of the explosion point, as well as flanking double-sided (counter) systems without removal and with the removal of the explosion point.

The most convenient for production work and ensure maximum performance of the system, in the implementation of which the observation base and the excitation point are shifted after each explosion in the same direction by equal distances.

To trace and determine the elements of the spatial occurrence of steeply dipping boundaries, as well as to trace tectonic disturbances, it is advisable to use conjugate profiles. which are almost parallel, and the distance between them is chosen to ensure continuous correlation of waves, they are 100-1000 m.

When observing on one profile, the PV is placed on another, and vice versa. Such an observation system ensures continuous correlation of waves along conjugate profiles.

Repeated profiling along several (from 3 to 9) conjugate profiles forms the basis of the wide-profile method. In this case, the observation point is located on the central profile, and excitations are made sequentially from points located on parallel conjugate profiles. The frequency of tracking reflective boundaries along each of the parallel profiles can be different. The total frequency of observations is determined by the product of the multiplicity for each of the conjugate profiles and their total number. The increase in costs for conducting observations on such complex systems is justified by the possibility of obtaining information about the spatial features of reflecting boundaries.

Areal observation systems built on the basis of a cross arrangement provide areal sampling of CDP traces due to the sequential overlap of cross-shaped arrangements, sources and receivers. If the spacing of sources dy and geophones dx is the same, and the signals excited in each source are received by all geophones, then in As a result of this processing, a field of 576 midpoints is formed. If you sequentially shift the arrangement of geophones and the excitation line intersecting it along the x axis by step dx and repeat the registration, then as a result a 12-fold overlap will be achieved, the width of which is equal to half the excitation and reception base along the y axis by step dy, an additional 12-fold overlap will be achieved , and the total overlap will be 144.

In practice, more economical and technologically advanced systems are used, for example 16-fold. To implement it, 240 recording channels and 32 excitation points are used. The fixed distribution of sources and receivers shown in Fig. 6 is called a block. After receiving oscillations from all 32 sources, the block is shifted by step dx, the reception from all 32 sources is repeated again, etc. Thus, the entire strip is worked along the x-axis from the beginning to the end of the research area. The next strip of five receiving lines is placed parallel to the previous one so that the distance between the adjacent (closest) receiving lines of the first and second strips is equal to the distance between the receiving lines in the block. In this case, the source lines of the first and second bands overlap by half the excitation base, etc. Thus, in this version of the system, the receiving lines are not duplicated, and at each source point the signals are excited twice.

Network profiling

For each exploration area, there is a limit on the number of observations, below which it is impossible to construct structural maps and diagrams, as well as an upper limit, above which the accuracy of the constructions does not increase. The choice of a rational observation network is influenced by the following factors: the shape of the boundaries, the range of changes in burial depths, measurement errors at observation points, sections of seismic maps, and others. Exact mathematical dependencies have not yet been found, and therefore approximate expressions are used.

There are three stages of seismic exploration: regional, prospecting and detailed. At the stage of regional work, the profiles tend to be directed to cross the strike of the structures after 10-20 km. This rule is deviated from when carrying out connecting profiles and linking to wells.

During prospecting work, the distance between adjacent profiles should not exceed half the expected length of the major axis of the structure under study; usually it is no more than 4 km. In detailed studies, the density of the network of profiles in different parts of the structure is different and usually does not exceed 4 km. In detailed studies, the density of the profile network in different parts of the profiles is different and usually does not exceed 2 km. The network of profiles is concentrated in the most interesting places of the structure (arch, fault lines, pinching zones, etc.). The maximum distance between connecting profiles does not exceed twice the distance between exploration profiles. If there are discontinuities in the study area, a network of profiles is complicated in each of the large blocks to create closed polygons. If the size of the blocks is small, then only connecting profiles are carried out. Salt domes are explored along a radial network of profiles with their intersection above the dome arch, connecting profiles pass along the periphery of the dome, connecting profiles pass along the periphery of the dome.

When conducting seismic surveys in an area where seismic surveys were previously carried out, the network of new profiles should partially repeat the old profiles to compare the quality of old and new materials. If there are deep drilling wells in the study area, they should be linked in the general network of seismic observations, and the explosion points and receptions should be located near wells.

Profiles should be as straight as possible, taking into account minimal agricultural damage. When working on CDP, restrictions on the profile bend angle must be set out, since the angle of inclination and the direction of fall of the boundaries can only be approximately estimated before the start of field work, and taking into account and correlating these values in the summation process poses significant difficulties. If we take into account only the distortion of wave kinematics, then the permissible bend angle can be estimated from the relation

b=2arcsin(vav?t0/xmaxtgf),

where?t=2?H/vр - time increment normal to the boundary; xmax - maximum hodograph length; f is the angle of incidence of the boundary. The dependence of the value of b as a function of the generalized argument vсрt0/tgf for different xmax (from 0.5 to 5 km) is shown in (Fig. 4), which can be used as a palette for assessing the permissible values of the profile bend angle under specific assumptions about the structure of the medium. Having specified the permissible value of the dephasing of the pulse terms (for example, И period T), it is possible to calculate the value of the argument for the maximum possible angle of incidence of the boundary and the minimum possible average speed of wave propagation. The ordinate of a straight line with xmax at this argument value will indicate the value of the maximum permissible bend angle of the profile.

To establish the exact location of the profiles, the first reconnaissance is carried out even during the design of the work. Detailed reconnaissance is carried out during field work.

3.2 Conditions for excitation of elastic waves

Excitation of oscillations is carried out using explosions (explosive charges or DSh lines) or non-explosive sources.

Methods for exciting vibrations are selected in accordance with the conditions, tasks and methods of conducting field work.

The optimal excitation option is selected based on the practice of previous work and is refined by studying the wave field in the process of experimental work.

Excitation by explosive sources

Explosions are carried out in boreholes, pits, in cracks, on the surface of the earth, in the air. Only the electric blasting method is used.

During explosions in wells, the greatest seismic effect is achieved when the charge is immersed below the low-velocity zone, during an explosion in plastic and water-logged rocks, when charges are sealed in wells with water, drilling fluid or soil.

The selection of optimal explosion depths is carried out based on MSC observations and the results of experimental work

During field observations on a profile, one should strive to maintain constancy (optimality) of excitation conditions.

In order to obtain an authorized record, the mass of a single charge is chosen to be minimal, but sufficient (taking into account the possible grouping of explosions) to ensure the required depth of research. Grouping of explosions should be used when single charges are insufficiently effective. The correctness of the choice of charge mass is periodically monitored.

The explosive charge must be lowered to a depth that differs from the specified depth by no more than 1 m.

Preparation, immersion and explosion of the charge are carried out after the relevant instructions of the operator. The blaster must immediately inform the operator of a failure or incomplete explosion.

Upon completion of blasting work, the remaining wells, pits and pits after the explosion must be liquidated in accordance with the "Instructions for eliminating the consequences of an explosion during seismic exploration work"

When working with detonating cord lines (DFL), it is advisable to place the source along the profile. The parameters of such a source - the length and number of lines - are selected based on the conditions for ensuring sufficient intensity of the target waves and acceptable distortions in the shape of their records (the length of the source should not exceed half the minimum apparent wavelength of the useful signal). In a number of problems, the parameters of the LDS are selected in order to ensure the desired directionality of the source.

To weaken the sound wave, it is recommended to deepen the lines of the detonating cord; in winter - sprinkle with snow.

When carrying out blasting operations, the requirements stipulated by the “Unified Safety Rules for Blasting Operations” must be observed.

To excite vibrations in reservoirs, only non-explosive sources are used (gas detonation installations, pneumatic sources, etc.).

For non-explosive excitation, linear or area groups of synchronously operating sources are used. Group parameters - number of sources, base, movement step, number of influences (at a point) - depend on surface conditions, wave field of interference, required depth of research and are selected in the process of experimental work

When carrying out work with non-explosive sources, it is necessary to ensure that the basic parameters of the mode of each of the sources working in the group are identical.

The synchronization accuracy must correspond to the sampling step during registration, but be no worse than 0.002 s.

Excitation of oscillations by pulsed sources is carried out, if possible, on dense compacted soils with a preliminary compaction blow.

The depth of the “stamp” from impacts of the plate during operating excitation of the sources should not exceed 20 cm.

When carrying out work with non-explosive sources, the safety and work rules provided for by the relevant instructions for the safe conduct of work with non-explosive sources and technical operating instructions must be strictly observed.

Excitation of transverse waves is carried out using horizontally or obliquely directed shock-mechanical, explosive or vibration effects

To implement the selection of waves by polarization at the source, effects are produced at each point that differ in direction by 180 degrees.

The marking of the moment of explosion or impact, as well as vertical time, must be clear and stable, ensuring the determination of the moment with an error of no more than a sampling step.

If work at one site is carried out with different sources of excitation (explosions, vibrators, etc.), duplication of physical observations must be ensured, with recordings from each of them being obtained at places where the sources change.

Excitation by pulsed sources

Numerous experience in working with surface pulse emitters shows that the required seismic effect and acceptable signal/interference ratios are achieved with the accumulation of 16-32 impacts. This number of accumulations is equivalent to explosions of TNT charges weighing only 150-300 g. The high seismic efficiency of the emitters is explained by the high efficiency of weak sources, which makes their use in seismic exploration promising, especially in the CDP method, when N-fold stacking occurs at the processing stage, providing additional increase in signal-to-noise ratio.

Under the influence of multiple impulse loads with an optimal number of impacts at one point, the elastic properties of the soil are stabilized and the amplitudes of the excited vibrations remain practically unchanged. However, with further application of loads, the soil structure is destroyed and the amplitudes decrease. The greater the pressure on the ground d, the greater the number of impacts Nk the amplitude of oscillations reaches a maximum and the smaller the flat portion of the curve A =? (n). The number of impacts Nk, at which the amplitude of excited oscillations begins to decrease, depends on the structure, material composition and moisture content of the rocks and for most real soils does not exceed 5-8. Under pulsed loads developed by gas-dynamic sources, the difference in the amplitudes of oscillations excited by the first (A1) and second (A2) impacts is especially large, the ratio A2/A1 of which can reach values of 1.4-1.6. Differences between values A2 and A3, A3 and A4, etc. significantly less. Therefore, when using ground sources, the first impact at a given point is not summed up with the others and serves only to preliminary compact the soil.

Before production work using non-explosive sources, a cycle of work is carried out on each new area to select optimal conditions for the excitation and recording of seismic wave fields.

3.3 Conditions for receiving elastic waves

With pulsed excitation, one always strives to create a sharp and short-term pulse in the source, sufficient for the formation of intense waves reflected from the horizons under study. We do not have strong means of influencing the shape and duration of these impulses in explosive and impact sources. We also do not have highly effective means of influencing the reflective, refractive and absorbing properties of rocks. However, seismic exploration has a whole arsenal of methodological techniques and technical means that allow, during the process of excitation and especially recording of elastic waves, as well as in the process of processing the resulting records, to most clearly highlight useful waves and suppress interference waves that interfere with their isolation. For this purpose, differences are used in the direction of arrival of waves of different types to the earth's surface, in the direction of displacement of particles of the medium behind the fronts of incoming waves, in the frequency spectra of elastic waves, in the shapes of their hodographs, etc.

Elastic waves are recorded by a set of rather complex equipment mounted in special bodies installed on high-traffic vehicles - seismic stations.

A set of instruments that record soil vibrations caused by the arrival of elastic waves at a particular point on the earth’s surface is called a seismic recording (seismic) channel. Depending on the number of points on the earth's surface at which the arrival of elastic waves is simultaneously recorded, 24-, 48-channel or more seismic stations are distinguished.

The initial link of the seismic recording channel is a seismic receiver, which senses soil vibrations caused by the arrival of elastic waves and converts them into electrical voltages. Since the ground vibrations are very small, the electrical voltages arising at the geophone output are amplified before recording. Using pairs of wires, voltages from the output of seismic receivers are supplied to the input of amplifiers mounted in the seismic station. To connect geophones to amplifiers, a special multi-core seismic cable is used, which is usually called a seismic streamer.

A seismic amplifier is an electronic circuit that amplifies the voltages applied to its input by tens of thousands of times. It can, using special circuits of semi-automatic or automatic gain or amplitude regulators (PRU, PRA, AGC, ARA), amplify signals. Amplifiers include special circuits (filters) that allow the necessary frequency components of signals to be amplified to the maximum, and others - minimally, i.e., to carry out their frequency filtering.

The voltages from the output of the amplifier are supplied to the recorder. Several methods of recording seismic waves are used. Previously, the most widely used optical method was to record waves on photographic paper. Currently, elastic waves are recorded on magnetic film. In both methods, before recording begins, photographic paper or magnetic film is set in motion using tape drive mechanisms. With the optical recording method, the voltage from the output of the amplifier is supplied to the mirror galvanometer, and with the magnetic method - to the magnetic head. When continuous recording is made on photographic paper or magnetic film, the wave process recording method is called analog. Currently, the most widely used method is a discrete (intermittent) recording method, which is usually called digital. In this method, instantaneous values of voltage amplitudes at the output of the amplifier are recorded in a binary digital code, varying from 0.001 to 0.004 s at equal time intervals?t. This operation is called time quantization, and the adopted value?t is called the quantization step. Discrete digital recording in binary code makes it possible to use general-purpose computers for processing seismic materials. Analogue recordings can be processed on a computer after they have been converted into discrete digital form.

A record of ground vibrations at one point on the earth's surface is usually called a seismic trace or track. The set of seismic traces obtained at a number of adjacent points of the earth's surface (or well) on photographic paper constitutes a seismogram in a visual analog form, and on magnetic film - a magnetogram. During the recording process, time stamps are applied to seismograms and magnetograms every 0.01 s, and the moment of excitation of elastic waves is noted.

Any seismic recording equipment introduces some distortion into the recorded oscillatory process. To isolate and identify waves of the same type on adjacent paths, it is necessary that the distortions introduced into them on all paths be the same. To do this, all elements of the recording channels must be identical to each other, and the distortions they introduce into the oscillatory process must be minimal.

Magnetic seismic stations are equipped with equipment that allows the recording to be reproduced in a form suitable for visual inspection. This is necessary for visual monitoring of recording quality. Magnetograms are reproduced on a photo, plain or electrostatic paper using an oscilloscope, pen writer or matrix recorder.

In addition to the described components, seismic stations are equipped with power sources, wired or radio communication with excitation points, and various control panels. Digital stations have analog-to-code and code-to-analog converters for converting analog recording into digital and vice versa, and circuits (logic) that control their operation. To work with vibrators, the station has a correlator. The bodies of digital stations are made dust-proof and equipped with air conditioning equipment, which is especially important for the high-quality operation of magnetic stations.

3.4 Selection of hardware and special equipment

Analysis of data processing algorithms for the CDP method determines the basic requirements for equipment. Processing, which involves channel sampling (formation of CDP seismograms), AGC, introduction of static and kinematic corrections, can be performed on specialized analog machines. When processing, which includes operations of determining optimal static and kinematic corrections, recording normalization (linear AGC), various filtering modifications with calculating filter parameters from the original recording, constructing a velocity model of the environment and converting a time section into a depth one, the equipment must have ample capabilities that ensure systematic reconfiguration algorithms. The complexity of the listed algorithms and, most importantly, their continuous modification depending on the seismic-geological characteristics of the object under study determined the choice of universal electronic computers as the most effective tool for processing data from the CDP method.

Processing data from the CDP method on a computer allows you to quickly implement a full set of algorithms that optimize the process of identifying useful waves and converting them into a section. The wide capabilities of computers have largely determined the use of digital recording of seismic data directly in the process of field work.

At the same time, a significant part of seismic information is currently recorded by analog seismic stations. The complexity of seismic geological conditions and the associated nature of the recording, as well as the type of equipment used to record data in the field, determine the processing process and the type of processing equipment. In the case of analog recording, processing can be performed on analog and digital machines; in digital recording, processing can be performed on digital machines.

The digital processing system includes a mainframe computer and a number of specialized external devices. The latter are intended for input and output of seismic information, performing individual continuously repeated computational operations (convolution, Fourier integral) at a speed significantly exceeding the speed of the main computer, specialized plotters and viewing devices. In some cases, the entire processing process is implemented by two systems using a middle-class computer (preprocessor) and a high-class computer (main processor) as the main computers. The system, based on a middle-class computer, is used to enter field information, convert formats, record and place it in a standard form on a magnetic tape drive (NML) of a computer, reproduce all information in order to control field recording and input quality and a number of standard algorithmic operations, mandatory for processing in any seismic-geological conditions. As a result of data processing at the output of the preprocessor in binary code in the format of the main processor, the initial seismic vibrations can be recorded in the sequence of channels of the OPV seismogram and the CDP seismogram, seismic vibrations corrected for the value of a priori static and kinematic corrections. Reproduction of the transformed recording, in addition to analyzing the input results, allows you to select subsequent processing algorithms implemented on the main processor, as well as determine some processing parameters (filter bandwidth, AGC mode, etc.). The main processor, with a preprocessor, is designed to perform the main algorithmic operations (determining corrected static and kinematic corrections, calculating effective and reservoir velocities, filtering in various modifications, converting a time section to a depth one). Therefore, computers with high speed (10 6 operations in 1 s), operational (32-64 thousand words) and intermediate (disks with a capacity of 10 7 - 10 8 words) memory are used as the main processor. The use of a preprocessor makes it possible to increase the profitability of processing by performing a number of standard operations on a computer, the cost of operation of which is significantly lower.

When processing analog seismic information on a computer, the processing system is equipped with specialized input equipment, the main element of which is a unit for converting continuous recording into binary code. Further processing of the digital record thus obtained is completely equivalent to the processing of digital recording data in the field. The use of digital stations for registration, the recording format of which coincides with the NML format of the computer, eliminates the need for a specialized input device. In fact, the data entry process comes down to installing a field tape on the NML computer. Otherwise, the computer is equipped with a buffer tape recorder with a format equivalent to the format of a digital seismic station.

Specialized devices of the digital processing complex.

Before moving on to a direct description of external devices, we will consider the issues of placing seismic information on a computer (digital station tape recorder). In the process of converting a continuous signal, the amplitudes of the sample values taken at a constant interval dt are assigned a binary code that determines its numerical value and sign. It is obvious that the number of sample values c on a given t trace with a useful recording duration t is equal to c = t/dt+1, and the total number c" of sample values on an m-channel seismogram c" = cm. In particular, at t = 5 s, dt = 0.002 s and m = 2, c = 2501, and c" = 60024 numbers written in binary code.

In the practice of digital processing, each numerical value that is the equivalent of a given amplitude is usually called a seismic word. The number of binary digits of a seismic word, called its length, is determined by the number of digits of the analogue-digital seismic station code converter (input device for encoding analog magnetic recording). The fixed number of binary bits that a digital machine operates when performing arithmetic operations is usually called a machine word. The length of the machine word is determined by the design of the computer and can coincide with the length of the seismic word or exceed it. In the latter case, when seismic information is entered into a computer, several seismic words are entered into each memory cell with a capacity of one computer word. This operation is called packaging. The order of placing information (seismic words) on the magnetic tape of a computer storage device or magnetic tape of a digital station is determined by their design and the requirements of the processing algorithms.

The process of recording digital information onto a computer tape recorder is preceded by the stage of marking it into zones. A zone is understood as a certain section of the tape, designed for the subsequent recording of k words, where k = 2, and degree n = O, 1, 2, 3. . ., and 2 should not exceed the capacity of the RAM. When marking the magnetic tape tracks, a code indicating the zone number is written, and a sequence of clock pulses separates each word.

In the process of recording useful information, each seismic word (binary code of the reference value) is recorded on a section of magnetic tape separated by a series of clock pulses within a given zone. Depending on the design of tape recorders, recording with parallel code, parallel-serial and sequential code is used. With a parallel code, a number that is equivalent to a given sampling amplitude is written in a line across the magnetic tape. For this, a multi-track block of magnetic heads is used, the number of which is equal to the number of bits in a word. Writing with a parallel-serial code involves placing all the information about a given word within several lines, arranged sequentially one after the other. Finally, with a sequential code, information about a given word is recorded by one magnetic head along the magnetic tape.

The number of machine words K 0 within the computer tape recorder area intended for storing seismic information is determined by the time t of the useful recording on a given trace, the quantization step dt and the number of seismic words r packed into one machine word.

Thus, the first stage of computer processing of seismic information recorded by a digital station in multiplex form involves its demultiplexing, i.e., sampling of reference values corresponding to their sequential placement on a given seismogram trace along the t axis and their recording in the NML zone, the number of which assigned to this channel programmatically. Input of analog seismic information into a computer, depending on the design of a specialized input device, can be performed both in channel mode and in multiplex mode. In the latter case, the machine, according to a given program, performs demultiplexing and writes information in a sequence of reading values on a given path to the corresponding NML zone.

A device for inputting analog information into a computer.

The main element of the analog seismic recording input device into a computer is an analog-to-digital converter (ADC), which performs operations of converting a continuous signal into a digital code. Currently, several ADC systems are known. To encode seismic signals, in most cases, bit-weighted converters with feedback are used. The principle of operation of such a converter is based on comparing the input voltage (reading amplitude) with the compensating one. The compensation voltage Uk changes bit by bit depending on whether the sum of the voltages exceeds the input value U x . One of the main components of the ADC is a digital-to-analog converter (DAC), controlled by a specific program by a null organ that compares the converted voltage with the output voltage of the DAC. At the first clock pulse, a voltage U K equal to 1/2Ue appears at the DAC output. If it exceeds the total voltage U x , then the high-order trigger will be in the zero position. Otherwise (U x >U Kl), the high-order trigger will be in position one. Let the inequality U x be satisfied in the first step< 1/2Uэ и в первом разряде выходного регистра записан нуль. Тогда во втором такте U x сравнивается с эталонным напряжением 1/4Uэ, соответствующим единице следующего разряда. Если U x >Ue, then a unit will be written in the second bit of the output register, and in the third comparison cycle U x will be compared with the reference voltage 1/4Ue + 1/8Ue, corresponding to one in the next bit. In each next i-th comparison cycle, if a unit was written in the previous one, the voltage Uki-1 increases by the amount Ue /2 until U x is less than Uki. In this case, the output voltage U x is compared with Uki+1 = Ue/2 Ue/2, etc. As a result of comparing U x with the bit-by-bit variable U K, the triggers of those bits, the inclusion of which caused overcompensation, will be in the “zero” position, and in position "one" - triggers the discharges that provide the best approximation to the measured voltage. In this case, a number equivalent to the input voltage will be written in the output register,

Ux = ?aiUе/2

From the output register, through the input device interface unit, upon a computer command, the digital code is sent to the computer for further program processing. Knowing the operating principle of an analog-to-digital converter, it is not difficult to understand the purpose and operating principle of the main blocks of the device for inputting analog information into a computer.

Story

Born in the early 60s of the last century, it became the main method of seismic exploration for many decades. Rapidly developing both quantitatively and qualitatively, it completely replaced the simple method of reflected waves (REM). On the one hand, this is due to the equally rapid development of machine (first analog and then digital) processing methods, on the other hand, the possibility of increasing the productivity of field work by using large reception bases, which are impossible in the MOV method. Not the least role was played here by the rise in cost of work, that is, the increase in the profitability of seismic exploration. To justify the increased cost of work, many books and articles were written about the harmfulness of multiple waves, which have since become the basis for justifying the use of the common depth point method.

However, this transition from an oscilloscope MOV to a machine CDP was not so cloudless. The MOV method was based on linking hodographs at mutual points. This linking reliably ensured the identification of hodographs belonging to the same reflecting boundary. The method did not require any corrections to ensure phase correlation - neither kinematic nor static (dynamic and static corrections). Changes in the shape of the correlated phase were directly related to changes in the properties of the reflecting horizon, and only with them. The correlation was not affected by either inaccurate knowledge of the velocities of the reflected waves or inaccurate static corrections.

Linking at mutual points is impossible at large distances of receivers from the excitation point, since the hodographs are intersected by trains of low-speed interference waves. Therefore, CDP processors abandoned the visual linking of mutual points, replacing them with obtaining a fairly stable signal shape for each result point by obtaining this shape by summing approximately homogeneous components. The exact quantitative linking of times is replaced by a qualitative assessment of the shape of the resulting total phase.

The process of recording an explosion or any other excitation source other than a vibroseis is similar to taking a photograph. The flash illuminates the environment and the response of this environment is recorded. However, the response to an explosion is much more complex than a photograph. The main difference is that a photograph captures the response of a single, albeit arbitrarily complex, surface, while an explosion evokes the response of many surfaces, one under or inside another. Moreover, each overlying surface leaves its mark on the image of the underlying ones. This effect can be seen if you look at the side of a spoon dipped in tea. It seems broken, while we know for sure that there is no break. The surfaces themselves (the boundaries of the geological section) are never flat and horizontal, which is manifested in their responses - hodographs.

Treatment

The essence of processing CDP materials is that each result trace is obtained by summing the original channels in such a way that the sum includes signals reflected from the same point in the deep horizon. Before summation, it was necessary to introduce corrections to the recording times in order to transform the recording of each individual trace, bring it to a form similar to the trace at the explosion point, that is, convert it to the t0 form. This was the primary idea of the authors of the method. Of course, it is impossible to select the necessary channels for summation without knowing the structure of the medium, and the authors set the condition for using the method to have a horizontally layered section with inclination angles no higher than 3 degrees. In this case, the coordinate of the reflecting point is quite accurately equal to half the sum of the coordinates of the receiver and source.

However, practice has shown that if this condition is violated, nothing terrible happens; effective cuts have a familiar appearance. The fact that this violates the theoretical justification of the method, that reflections are no longer summed up from one point, but from an area, the greater the greater the angle of inclination of the horizon, did not worry anyone, because the assessment of the quality and reliability of the section was no longer accurate, quantitative, but approximate, qualitative. This results in a continuous in-phase axis, which means everything is in order.

Since each result trace is the sum of a certain set of channels, and the quality of the result is assessed by the stability of the phase shape, it is enough to have a stable set of the strongest components of this sum, regardless of the nature of these components. So, summing up the low-speed interference alone, we get a quite decent section, approximately horizontally layered, rich in dynamics. Of course, it will have nothing to do with the real geological section, but it will fully meet the requirements for the result - the stability and extent of the phases of co-phase. In practical work, a certain amount of such interference always ends up in the sum, and, as a rule, the amplitude of this interference is much greater than the amplitude of the reflected waves.

Let's return to the analogy between seismic exploration and photography. Let's imagine that on a dark street we meet a man with a lantern, which he shines into our eyes. How can we look at it? Apparently, we will try to cover our eyes with our hands, shield them from the lantern, then it will be possible to see the person. Thus, we divide the total lighting into components, remove what is unnecessary, and focus on what is needed.

When processing MOGT materials, we do exactly the opposite - we summarize, combine the necessary and the unnecessary, hoping that the necessary will push its way forward. Moreover. From photography we know that the smaller the image element (the grain of the photographic material), the better, more detailed the picture. You can often see in television documentaries, when you need to hide or distort an image, it is presented with large elements, behind which you can see some object, see its movements, but it is simply impossible to see such an object in detail. This is exactly what happens when summing channels during processing of CDP materials.

In order to obtain in-phase addition of signals even with a perfectly flat and horizontal reflecting boundary, it is necessary to introduce corrections that ideally compensate for the inhomogeneities of the relief and the upper part of the section. It is also ideal to compensate for the curvature of the hodograph in order to move the reflection phases obtained at distances from the excitation point by times corresponding to the time of passage of the seismic beam to the reflecting surface and back along the normal to the surface. Both are impossible without detailed knowledge of the structure of the upper part of the section and the shape of the reflecting horizon, which is impossible to provide. Therefore, during processing, point, fragmentary information about the low-velocity zone and approximation of reflecting horizons by a horizontal plane are used. The consequences of this and methods for extracting maximum information from the rich material provided by CDP are discussed in the description of “Dominant processing (Baibekov Method)”.

Keywords

SEISMIC PROSPECTING / DIRECT SEARCH FOR HYDROCARBONS DEPOSITS / INDUCED GEODYNAMIC NOISE / EXPLORATION DRILLING SUCCESS RATE/ CDPM SEISMIC / DIRECT HYDROCARBON EXPLORATION/INDUCED GEODYNAMIC NOISE/ PROSPECTING AND EXPLORATORY DRILLING SUCCESS RATIO

annotation scientific article on Earth sciences and related environmental sciences, author of the scientific work - Maksimov L.A., Vedernikov G.V., Yashkov G.N.

Information is provided on the technology of passive-active seismic exploration using the common depth point method (CDMP), which solves the problem direct search for hydrocarbon deposits according to the dynamic parameters emitted by these deposits induced geodynamic noise. It has been shown that the use of this technology can prevent the drilling of unproductive wells. Materials and methods The proposed PAS CDP technology combines the registration and interpretation of waves emitted by hydrocarbon deposits and waves reflected from seismic boundaries. This ensures high efficiency in studying the geometry of reflecting boundaries and recording hydrocarbons emitted by deposits induced geodynamic noise. Results The PAS CDP technology has been tested at dozens of hydrocarbon fields in Western and Eastern Siberia and has shown its effectiveness: all fields are marked by anomalies in the intensity of geodynamic noise and the absence of such anomalies outside the fields. Conclusions The above-mentioned capabilities of the PAS COGT technology are very relevant at the present time, when the economic crisis continues to intensify. This technology will allow oil workers to drill hydrocarbon traps rather than structures, which will increase the efficiency of geological exploration work (manifold) when searching for oil and gas.

Text of scientific work on the topic "Geodynamic noise of hydrocarbon deposits and passive-active seismic exploration of CDP"

GEOPHYSICS

Geodynamic noise of hydrocarbon deposits and passive-active seismic exploration of CDP

L.A. Maksimov

Ph.D., Art. teacher1 [email protected]

G.V. Vedernikov

Doctor of Geology and Mineralogy, Deputy Director of Science2 [email protected]

G.N. Yashkov

Ch. geophysicist2 [email protected]

Novosibirsk State University, Novosibirsk, Russia 2NMT-Seis LLC, Novosibirsk, Russia

Information is provided on the technology of passive-active seismic exploration using the common depth point method (CDC), which solves the problem of direct search for hydrocarbon deposits based on the dynamic parameters emitted by these deposits of induced geodynamic noise. It has been shown that the use of this technology can prevent the drilling of unproductive wells.

Materials and methods

The proposed PAS CDP technology combines the registration and interpretation of induced geodynamic noise emitted by hydrocarbon deposits and waves reflected from seismic boundaries. This ensures high efficiency in studying the geometry of reflecting boundaries and recording induced geodynamic noise emitted by hydrocarbon deposits.

Keywords

CDP seismic survey, direct search for hydrocarbon deposits, induced geodynamic noise, success rate of exploratory drilling

The main task of currently used seismic methods is to study the spatial distribution of physical parameters and indicators of spontaneous seismic activity.

Seismic exploration today is the main method of preparing objects for prospecting and exploration drilling. It reveals with a sufficient degree of reliability structures that, under certain favorable conditions, may or may not contain oil deposits. Only a well will confirm this uncertainty, but at what cost?

The success of searching for oil and gas deposits was within 10...30% in the past (in the USSR and the USA), and remains within these limits today (Fig. 1). And it will continue to do so tomorrow and the day after tomorrow, and until the oil workers move from searching for structures to searching for oil-containing traps. The point of increasing the efficiency of prospecting and exploration works comes down to the obvious task - to divide the structures identified by seismic exploration into productive and unproductive oil and gas traps. If this problem is solved, then huge amounts of money are saved, which are spent on prospecting and exploration drilling on obviously unproductive structures.

It is known that oil and gas reservoirs, being unstable thermodynamic systems, emit an increased level of spontaneous and induced geodynamic noise. To analyze such noise for the purpose of direct search for hydrocarbon (HC) deposits, the innovative technology of passive-active seismic exploration using the common depth point method (PAS CDP), developed at NMT-Seis LLC (analogous to the active version of the ANCHAR technology), can be used.

Modern standard CDP seismic exploration is essentially passive-active. Indeed, on the seismic route in the area before the first arrivals of regular waves, microseisms and geodynamic noise are recorded - a passive component of the record. On the rest of the record, together with microseisms and geodynamic noise, oscillations of regular waves are recorded - the active component of the record, containing information about the geometry of seismic boundaries in the earth's strata. The passive component contains information about the presence (absence) of hydrocarbon deposits emitting geodynamic noise.

The proposed PAS MOGT technology integrates registration and

Rice. 1 - Dynamics of changes in the success rate (in%) when drilling prospecting and exploration wells in the USA

Rice. 2 - Seismic time section (A), amplitude-frequency spectrum of microseisms (B) and spectrum intensity graphs in frequency bands (C)

interpretation of artificially induced geodynamic noise emitted by hydrocarbon deposits and waves reflected from seismic boundaries. This ensures both high efficiency in studying the geometry of reflecting boundaries and the velocities between them due to repeated tracking of waves reflected from these boundaries, and high efficiency in searching for hydrocarbon deposits due to repeated exposure to seismic waves and registration of induced geodynamic noise emitted by them. An important advantage of the method is the possibility of independent parallel extraction of information from wave fields that have a fundamentally different nature and are recorded almost simultaneously in one place. In principle, the PAS CDP technology is one of the modifications of multi-wave seismic exploration, in a broader sense of the term “multi-wave seismic exploration” - that is, not only waves of different polarization. Thus, having carried out a joint interpretation of reflected waves and noise, we will have information about the geometry of boundaries in the medium and the presence of shock waves in the medium, i.e., we will be able to solve the problem of direct searches for shock wave traps, and not structures, as is done today. And this point is very important, since it becomes possible to solve the main problem in exploratory drilling. At the same time, the success of drilling increases sharply (by several times).

The PAS CDP technology has been tested at dozens of hydrocarbon fields in Western and Eastern Siberia and has shown its effectiveness: all fields are marked by anomalies

intensity of geodynamic noise (Fig. 2) and the absence of such anomalies outside the fields (Fig. 3).

Over the past 7 years, work has been carried out under State contracts jointly with the Federal State Unitary Enterprise SNIIGGiMS to forecast oil and gas accumulation zones in Western and Eastern Siberia in a volume of over 13 thousand linear meters. km of profiles and shows the effectiveness of using the PAS CDP technology at all stages of geological exploration:

During regional work - identification of promising areas for prospecting and exploration work;

At the pre-exploration stage - preparation of information packages for licensing subsoil areas;

During prospecting and exploration work

Identification and ranking of promising objects, especially non-anticlinal types;

When planning drilling operations

The fundamental feature of PAS CDP technologies is the excitation of vibrations and registration of microseisms and regular waves using the multiple overlap technique. The consequence of this is the following unique advantages of these technologies compared to the ANCHAR technology: 1. Multiple (rather than single) pulse-wave (rather than monoharmonic) long-term external

impact on hydrocarbon deposits by waves created by a man-made source. The multiplicity of such an impact is equal to the multiplicity of the CDP observation system. The duration of exposure with an average time interval for excitation of oscillations from PV to PV, equal to 2-3 minutes, is 60-180 minutes (1-3 hours). As a result, hydrocarbon deposits are exposed to a continuous train of seismic waves for 1-3 hours with an increase in their intensity periodically repeated every 2-3 minutes. This provides a higher, in a frequency band of up to 40 Hz, intensity of induced geodynamic noise from hydrocarbon deposits, which can be recorded using standard seismic equipment.

2. Microseisms are registered by a multi-channel CDP observation system, which ensures a high density of PPs on the profile with a registration duration of microseisms at each PP of about 2-6 hours. This

increases the amount of information received about geodynamic noise by an order of magnitude or more and increases the reliability and accuracy of their identification without additional costs for such work.

3. This technology can also be implemented based on the results of previously carried out CDP work, using stock materials. This allowed from 2006 to 2014. without the cost of special field work, process CDP data in the amount of about 13,000 linear meters using this technology. km obtained in many areas

Rice. 3 - Time seismic section (A) and characteristics of microseisms (B, C) in the area of unproductive wells

Rice. 5 - Location of geodynamic noise zones 1-5 and structural plan of the B10 formation at the Alenkinsky license area

Rice. 4 - A typical example of the location of a hydrocarbon deposit on the wings of a fold. South of the West Siberian Lowland

Rice. 6 - Time section (A) and noise spectrum (B) in the transition zone from oil to gas deposits

Western and Eastern Siberia, including the areas of more than 30 known fields with the presence of more than 200 productive and “empty” wells. It was found that by the location of sections (on the profile) and zones (on the area) of geodynamic noise, it is possible to determine the contours of hydrocarbon deposits (Fig. 2) and the type of traps (anticlinal, non-anticlinal) (Fig. 4, 5). Based on such features of the noise spectrum as their overall intensity, predominant frequency and modality, it is possible to predict the relative volume of hydrocarbon reserves in an object and a forecast about the presence of the type of fluid (oil, gas, condensate) in the object (Fig. 6).

The above-mentioned capabilities of PAS COGT technology are very relevant at the present time, when the crisis in the economy continues to intensify. The use of this technology will allow oil workers to drill hydrocarbon traps rather than structures, which will increase the efficiency of geological exploration work (manifold) when searching for oil and gas.

In Russia, 6,500 exploration wells were drilled in 2013, and 5,850 wells in 2014. The cost of drilling one exploratory well in the Russian Federation ranges from

100 to 500 million rubles. depending on the geographic location of the well, design, existing infrastructure, etc.; average cost is about 300 million rubles. With a drilling success rate of 10..30% in 2013, out of 6,500 wells drilled, 3,900 wells turned out to be unproductive; about 1.2 trillion rubles were spent on their drilling.

The PAS CDP technology has been tested at dozens of hydrocarbon fields in Western and Eastern Siberia and has shown its effectiveness: all fields are marked by anomalies in the intensity of geodynamic noise and the absence of such anomalies outside the fields.

The above-mentioned capabilities of PAS COGT technology are very relevant at the present time, when the crisis in the economy continues to intensify. This technology will allow oil workers to drill hydrocarbon traps rather than structures, which will increase the efficiency of geological exploration work (manifold) when searching for oil and gas.

Bibliography

1. Puzyrev N.N. Methods and objects

seismic research. Introduction to general seismology. Novosibirsk: SO

RAS; NIC OIGGM, 1997. 301 p.

2. Timurziev A.I. The current state of practice and methodology of oil exploration - from the misconceptions of stagnation to a new worldview of progress // Geology, geophysics and development of oil and gas fields. 2010. No. 11.

3. Grafov B.M., Arutyunov S.A., Kazarinov

B.E., Kuznetsov O.L., Sirotinsky Yu.V., Suntsov A.E. Analysis of geoacoustic radiation of oil and gas deposits using ANCHAR technology // Geophysics. 1998. No. 5. pp. 24-28.

4. Patent No. 2 263 932 C1 in 01 U/00 Russian Federation. Seismic exploration method. Application 07/30/2004.

5. Vedernikov G.V. Methods of passive seismic exploration // Instruments and systems of exploration geophysics. 2013. No. 2.

6. Vedernikov G.V., Maksimov L.A., Chernyshova T.I., Chusov M.V. Innovative technologies. What does the experience of seismic exploration work on the Shushukskaya area say? //Geology and mineral resources of Siberia. 2015. No. 2 (22). pp. 48-56.

Geodynamic noise of hydrocarbon pools and passive and active seismic CDPM

Leonid A. Maksimov - Ph. D., lecturer1; [email protected] Gennadiy V. Vedernikov - Sc. D., deputy of science work2; [email protected] Georgiy N. Yashkov - chief geoscientist2; [email protected]

Novosibirsk State University, Novosibirsk, Russian Federation 2"NMT-Seis" LLC, Novosibirsk, Russian Federation

The information on the technology of passive and active seismic using the common-depth-point method (hereinafter "the PAS CDPM"), solving the problem of direct exploration of hydrocarbon accumulations using the amplitude information of induced geodynamic noise emitted by these accumulations is containing .

It is shown that the use of this technology can prevent drilling of nonproductive wells.

Materials and methods

The proposed PAS CDPM technology complexes registration and interpretation of induced

geodynamic noises emitted by hydrocarbon accumulations, and waves reflected from the seismic horizons. This provides high efficiency of studying of reflectors geometry and registration of induced geodynamic noises emitted by hydrocarbon accumulations.

The PAS CDPM technology tested in dozens of hydrocarbon accumulations of Western and Eastern Siberia has proven its efficiency, namely all accumulations have displayed intensity anomalies of geodynamic noises, and no such anomalies have been observed outside accumulations.

The above mentioned PAS CDPM technology capability is relevant nowadays, when the economic crisis is gathering pace. The defined technology will make it possible for petroleum experts to drill traps instead of drilling structures that will increase severalfold efficiency of oil and gas geological exploration.

CDPM seismic, direct hydrocarbon exploration, induced geodynamic noise, prospecting and exploratory drilling success ratio

1. Puzyrev N.N. Metody i ob"ekty seysmicheskikh issledovaniy. Vvedenie v obshchuyu seysmologiyu. Novosibirsk: SO RAN; NITs OIGGM, 1997, 301 p.

2. Timurziev A.I. Sovremennoe sostoyanie praktiki i metodologii poiskov nefti

Otzabluzhdeniyzastoya k novomu mirovozzreniyu progressa. Geology,

geofizika i razrabotka neftyanykh i gazovykh mestorozhdeniy, 2010, issue 11, pp. 20-31.

3. Grafov B.M., Arutyunov S.A., Kazarinov V.E., Kuznetsov O.L., Sirotinskiy Yu.V., Suntsov A.E. Analiz geoakusticheskogo izlucheniya neftegazovoyzalezhi pri ispol "zovanii tekhnologiiANChAR. Geofizika, 1998, issue 5, pp. 24-28.

4. Patent Russian Federation No. 2 263 932 CI G 01 V/00 Sposob seysmicheskoy razvedki. Declared 07/30/2004.

5. Vedernikov G.V. Metody passive ceysmorazvedki. Pribory i systemy razvedochnoygeofiziki, 2013, issue 2, pp. 30-36.

6. Vedernikov G.V., Maksimov L.A., Chernyshova T.I., Chusov M.V. Innovatsionnye tekhnologii. O chem govorit opytseysmorazvedochnykh rabot na Shushukskoy ploshchadi. Geologiya i mineral"no-syr"evye resursy Sibiri, 2015, issue 2 (22), pp. 48-56.

Methodology and technology of seismic exploration can. Common depth point method 2D seismic survey CDP method

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Introduction

1. Theoretical foundations of the common depth point method

1.1 Theory of the CDP method

To excite waves, explosive and shock sources are used, which require observations with a large (24-48) overlap ratio.

These limitations generally determine the tendency for the resolution of the MOV to decrease. Considering the prevalence of the CDP method, they should be taken into account in specific seismic geological conditions.

1.2 Features of the CDP hodograph

Rice. 1.2 Scheme of the CDP method for the inclined occurrence of the reflecting boundary.

1.3 CDP interference system

(1.1)

where f m - n is the difference in the summation times of oscillations on track m, to which the result obtained is attributed, and on track n.

Let us give relation (1.1) a simpler form, taking into account that the result does not depend on the position of the point m and is determined by the time shifts of the traces φ n relative to an arbitrary origin. We obtain a simple formula describing the general algorithm of interference systems,

(1.2)

Their varieties differ in the nature of changes in weight coefficients d n and time shifts φ n: both can be constant or variable in space, and the latter, in addition, can change in time.

Let a perfectly regular wave g(t,x) with arrival hodograph t(x)=t n be recorded on seismic traces:

hodograph seismological interference wave

Substituting this into (1.2), we obtain an expression describing the oscillations at the output of the interference system,

where and n =t n - f n.

The quantities and n determine the deviation of the wave hodograph from a given summation line. Let's find the spectrum of filtered oscillations:

If the hodograph of a regular wave coincides with the summation line (and n ? 0), then in-phase addition of oscillations occurs. For this case, denoted u=0, we have

2.2 Calculation of the observation system of the CDP method

The amplitudes of useful reflected waves from the target boundary are calculated using the formula:

(2.5)

where A p is the reflection coefficient of the target boundary.

The amplitudes of multiple waves are calculated using the formula:

.(2.6)

In the absence of data on the absorption coefficient, we assume =1.

We calculate the amplitudes of multiple and useful waves:

Multiple wave 2 has the greatest amplitude. The obtained amplitude values ​​of the target wave and interference make it possible to calculate the required degree of multiple wave suppression.

Because the

2.3 Calculation of hodographs of useful waves and interference waves

The calculation of multiple wave hodographs is carried out under simplifying assumptions about a horizontally layered model of the medium and flat boundaries. In this case, multiple reflections from several interfaces can be replaced by a single reflection from some fictitious interface.

The average speed of the fictitious medium is calculated along the entire vertical path of the multiple wave:

(2.7)

The time is determined by the pattern of formation of a multiple wave on a theoretical VSP or by summing the travel times in all layers.

(2.8)

We get the following values:

The multiple wave hodograph is calculated using the formula:

(2.9)

The useful wave hodograph is calculated using the formula:

(2.10)

Fig 2.3 Hodographs of useful waves and interference waves

2.4 Calculation of the delay function of interference waves

Let us introduce kinematic corrections calculated according to the formula:

?tк(x, to) = t(x) - to(2.11)

The multiple wave lag function (x) is determined by the formula:

(x) = t cr(xi) - t cr (2.12)

where tcr(xi) is the time corrected for kinematics and tcr is the time at zero distance of the receiving point from the excitation point.

Fig 2.4 Multiple wave lag function

2.5 Calculation of parameters of the optimal observing system

An optimal observation system should provide the greatest results at low material costs. The required degree of interference suppression is D=5, the lower and upper frequencies of the spectrum of the interference wave are 20 and 60 Hz, respectively.

Rice. 2.5 Characteristics of the directionality of summation according to CDP at N = 24.

According to the set of directional characteristics, the minimum multiplicity number is N=24.

(2.13)

Knowing P, we remove y min = 4 and y max = 24.5

Knowing the minimum and maximum frequencies, 20 and 60 Hz, respectively, we calculate f max.

f min *ф max =4ф max =0.2

f max *f max =24.5f max =0.408

Theoretical hodograph length H*= x max - x min =3100m.

3. Field seismic technology

3.1 Requirements for the observation network in seismic exploration

Observing systems

Currently, only complete correlation observation systems are practically used, allowing for continuous correlation of useful waves.

The most convenient for production work and ensure maximum performance of the system, in the implementation of which the observation base and the excitation point are shifted after each explosion in the same direction by equal distances.

When observing on one profile, the PV is placed on another, and vice versa. Such an observation system ensures continuous correlation of waves along conjugate profiles.

Network profiling

There are three stages of seismic exploration: regional, prospecting and detailed. At the stage of regional work, the profiles tend to be directed to cross the strike of the structures after 10-20 km. This rule is deviated from when carrying out connecting profiles and linking to wells.

b=2arcsin(vav?t0/xmaxtgf),

To establish the exact location of the profiles, the first reconnaissance is carried out even during the design of the work. Detailed reconnaissance is carried out during field work.

3.2 Conditions for excitation of elastic waves

Excitation of oscillations is carried out using explosions (explosive charges or DSh lines) or non-explosive sources.

Methods for exciting vibrations are selected in accordance with the conditions, tasks and methods of conducting field work.

The optimal excitation option is selected based on the practice of previous work and is refined by studying the wave field in the process of experimental work.

Excitation by explosive sources

Explosions are carried out in boreholes, pits, in cracks, on the surface of the earth, in the air. Only the electric blasting method is used.

During explosions in wells, the greatest seismic effect is achieved when the charge is immersed below the low-velocity zone, during an explosion in plastic and water-logged rocks, when charges are sealed in wells with water, drilling fluid or soil.

The selection of optimal explosion depths is carried out based on MSC observations and the results of experimental work

During field observations on a profile, one should strive to maintain constancy (optimality) of excitation conditions.

The explosive charge must be lowered to a depth that differs from the specified depth by no more than 1 m.

Multiple wave 2 has the greatest amplitude. The obtained amplitude values of the target wave and interference make it possible to calculate the required degree of multiple wave suppression.