CN106940451B - Method for predicting plastic stratum deformation - Google Patents
Method for predicting plastic stratum deformation Download PDFInfo
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- CN106940451B CN106940451B CN201710316868.6A CN201710316868A CN106940451B CN 106940451 B CN106940451 B CN 106940451B CN 201710316868 A CN201710316868 A CN 201710316868A CN 106940451 B CN106940451 B CN 106940451B
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- 238000004364 calculation method Methods 0.000 claims description 8
- 230000000149 penetrating effect Effects 0.000 claims description 7
- 238000012545 processing Methods 0.000 claims description 6
- 230000010355 oscillation Effects 0.000 claims description 2
- 230000010354 integration Effects 0.000 claims 1
- 239000011435 rock Substances 0.000 abstract description 24
- 238000004088 simulation Methods 0.000 abstract description 21
- 230000008569 process Effects 0.000 abstract description 12
- 230000005856 abnormality Effects 0.000 abstract description 2
- 238000012795 verification Methods 0.000 abstract description 2
- 229910001220 stainless steel Inorganic materials 0.000 description 22
- 239000010935 stainless steel Substances 0.000 description 22
- 239000011521 glass Substances 0.000 description 14
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 12
- 239000000463 material Substances 0.000 description 9
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 6
- 238000001125 extrusion Methods 0.000 description 6
- 239000004576 sand Substances 0.000 description 5
- 238000007493 shaping process Methods 0.000 description 5
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- 238000012360 testing method Methods 0.000 description 4
- 230000008859 change Effects 0.000 description 3
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- 239000002360 explosive Substances 0.000 description 3
- 229910052742 iron Inorganic materials 0.000 description 3
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- 230000007480 spreading Effects 0.000 description 3
- 239000006004 Quartz sand Substances 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
- G01V1/28—Processing seismic data, e.g. for interpretation or for event detection
- G01V1/30—Analysis
- G01V1/306—Analysis for determining physical properties of the subsurface, e.g. impedance, porosity or attenuation profiles
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V2210/00—Details of seismic processing or analysis
- G01V2210/60—Analysis
- G01V2210/62—Physical property of subsurface
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Abstract
The invention discloses a method for predicting plastic stratum deformation, which comprises the steps of carrying out short-time window discrete Fourier transform on a three-dimensional seismic data volume in a time domain to obtain single-frequency data volume information, and obviously distinguishing the difference of plastic stratum by extracting the difference abnormality of peak amplitude and average amplitude, wherein the reliability is high, and the plastic stratum deformation trend and the deformed plane form are effectively predicted; the simulation device designed based on the simulation method simulates the actual plastic stratum and overlying and underlying surrounding rocks, performs verification and comparison with the prediction result obtained by the prediction method and the actual seismic profile, simulates and predicts the deformation trend of the plastic stratum, and further verifies the formation process and the deformation trend of the deformation form of the plastic stratum profile in the actual seismic profile.
Description
Technical Field
The invention relates to the technical field of stratum deformation trend prediction, in particular to a method for predicting plastic stratum deformation.
Background
In the existing work of predicting plastic stratum deformation, a method for extracting the attribute of a seismic data volume is adopted to predict the deformation form spread of the plastic stratum on a plane. However, this method has the following disadvantages: 1) The data body is a full-band seismic data body, after the seismic attribute is extracted, the difference is not obvious, and the form of the predicted plastic stratum distribution area is not clear; 2) The different frequencies reflect that the seismic response of the stratum with different lithology and different acoustic wave propagation speed is different, namely the plastic stratum is consistent with the seismic response corresponding to a certain frequency or a certain section of frequency because the lithology and the seismic propagation speed are different from surrounding rocks. In summary, the conventional prediction method used at present cannot extract the seismic information of such frequencies alone, so that the reliability of the prediction method is not high, and the deviation of the prediction result is large.
Disclosure of Invention
The invention aims to provide a method for predicting plastic stratum deformation trend by extracting single-frequency data volume information in seismic data.
For this purpose, the technical scheme of the invention is as follows:
a method of predicting plastic formation deformation comprising the steps of:
s1, exciting an artificial earthquake in a working area, collecting acoustic information of the earthquake, and processing the acoustic information by a computer to obtain a three-dimensional earthquake data body in a time domain;
s2, carrying out short-time window discrete Fourier transform formula calculation on the three-dimensional seismic data body under the time domain obtained in the step S1 to obtain single-frequency seismic data bodies under a plurality of frequency domains;
s3, calculating the difference value of the peak amplitude and the average amplitude of the single-frequency data volume obtained in the step S2, determining a frequency band with an abnormal calculated difference value, and correspondingly outlining a plane coordinate position corresponding to the frequency band with the abnormal difference value on a plane spread image of a working area to obtain the range of the seismic amplitude attribute with the abnormal difference value, namely reflecting the deformation form of the plastic stratum of the area.
The artificial earthquake in the step S1 is excited to collect acoustic information of the earthquake, namely acoustic signals in the whole time domain, and the acoustic signals can be changed from the time domain to the frequency domain through Fourier transformation; however, since the acoustic signals in the full-time domain are converted, the acoustic signals corresponding to the full-frequency domain obtained by fourier transform have a "mixing effect", as shown in fig. 3, and the difference value cannot be extracted, so that the acoustic signals in the full-frequency domain can be disassembled into single-frequency seismic data volumes in a plurality of frequency domains only by further limiting the time window range calculated by fourier transform, that is, "single-frequency information" of a certain section of frequency corresponding to the plastic stratum is obtained, as shown in fig. 4.
The specific processing steps of the step S2 include:
s201, due to artificial earthquake excitation in the step S1, the phenomenon of penetrating through layers of an overlying stratum or a lower stratum can occur after the plastic layer is deformed, so that the time range of penetrating through layers of the plastic layer can be determined to be A milliseconds from an earthquake section view;
s202, equally dividing the time range of the plastic layer penetrating deformation into n parts, wherein the time interval A/n millisecond of each equal part is used as the time window range limit for carrying out Fourier transform calculation, namely, an A/n millisecond short time window; wherein n is an integer, and n is more than or equal to 1;
s203, carrying out Fourier transform on the three-dimensional seismic data volume under the time domain obtained in the step S1 according to the A/n millisecond short time window selected in the step S2, and converting the time domain seismic data volume into a seismic data volume in the frequency domain;
fourier transform formula:
where i is an imaginary unit, e -iωt Expressed as an imaginary number i rotated counter-clockwise by an angle ωt (i.e. a rotation factor), ω being the angular velocity and t being the time; specifically, the essence of the fourier transform is to multiply the function f (t) of the time domain by a twiddle factor e -iωt Then integrating over a limited time window; in this way, the acoustic wave signal is converted from the function of time t to the function of angular velocity omega through the function operation, and the corresponding converted angular velocity omega is converted into the corresponding frequency, namely the conversion from the time domain to the frequency domain is realized;
in order to further express the whole seismic data volume excited by artificial earthquake, namely the acoustic wave signal through a function, f (t) in a Fourier transform formula is further expanded by substituting into a Fourier series formula (taking a cosine formula as an example):
wherein a is k The amplitude, k is the number of oscillations, ωt is the angle, ω is the angular velocity, t is the time,is the phase; the expression of the fourier series is further converted into functions related to the 3 parameters of amplitude, speed and phase, namely three parameters consistent with the parameters contained in the acoustic wave signal obtained in the step S1; carrying out integral operation according to a selected short-time window by taking the Fourier transform formula, and finally obtaining a plurality of frequency domain seismic data volumes;
of course, since the sine wave and cosine wave differ only in phaseThe fourier series can also be expressed in the form of a more complex sine wave and be incorporated into the fourier transform formula.
S204, because the stratum environments of the working areas are different, namely the propagation medium difference of the seismic waves, the time window range limitation selected for the first time in the step S202 may cause that a plurality of single frequency data bodies are decomposed into a plurality of single frequency data bodies which are possibly decomposed into thick or thin data bodies, so that the single frequency data bodies cannot be completely decomposed or the single frequency data bodies are decomposed into distortion, and therefore, whether the dismantling result of the step S203 meets the requirement of further analysis or not needs to be determined by further calculating and verifying the magnitude of abnormal difference values of the peak amplitude and the average amplitude of a plurality of vibration peaks in the single frequency data bodies, as shown in fig. 4; specifically, the amplitudes of the vibration peaks of the single-frequency data volumes of certain frequency bands in the single-frequency data volumes calculated in step S203 have obvious differences, and can be preliminarily determined as an abnormal frequency band whenWhen the difference between the peak amplitude and the average amplitude is calculated, if the abnormal difference between the peak amplitude and the average amplitude does not fall at 10 4 ～10 6 A (a is the unit of amplitude of the seismic acoustic wave) indicates that the data volume obtained in step S203 still has the mixing property; at this time, returning to step S202, increasing the value of N to n+N (N is an integer and N is more than or equal to 1), and so on; repeating steps S203 and S204 simultaneously until the difference between the peak amplitude and the average amplitude of a single frequency data volume falls to 10 4 ～10 6 And in the range A, a plurality of single-frequency data bodies are obtained through calculation of a Fourier transform formula for explaining the time short time window, and the single-frequency data bodies can be used for effectively analyzing the stratum.
Further, the value range of the short time window A/n millisecond is 6-96 ms.
By the prediction method, the deformation trend of the shaping stratum can be effectively and reasonably predicted accurately, and necessary bedding is carried out for subsequent drilling work so as to avoid the drilling area from being positioned in the deformation area of the plastic layer; in addition, the trap type related to the plastic deformation zone can be explored by researching the trap related to the deformation zone of the shaping stratum.
The invention also provides a simulation device for predicting the deformation of the plastic stratum, which not only can be used for verifying the plane spreading form and the section style of the deformation of the plastic stratum, namely the deformation trend of the plastic stratum, but also can further study and confirm the deformation mechanism of the plastic stratum.
Specifically, the simulation device for predicting plastic stratum deformation comprises a box body with an opening at the top, wherein the box body is formed by a rectangular bottom plate which is horizontally arranged and four coamings which are arranged at four edges of the upper surface of the rectangular bottom plate; the upper surface of the rectangular bottom plate is provided with two movable rails which are parallel to each other and extend to the edge of the other side along the radial direction from the middle part of the edge of one side of each group of opposite side sides; the bottom surface of each coaming is provided with a track connecting piece which is matched with two parallel movable tracks below the coaming, so that four coamings can be movably connected with the movable tracks through the track connecting pieces and can reciprocate on the rectangular bottom plate along the movable tracks; and a driving device for pushing the coamings to reciprocate is arranged on the outer side of each set of contralateral coamings.
Wherein, the box is set up to open-top's form be convenient for observe the plane of simulation stratum and spread form and follow-up form change process from the box top.
Further, each coaming comprises a main board and two auxiliary boards, wherein the main boards are arranged in a coplanar mode, the two auxiliary boards are positioned on two sides of the main board, and the height and the thickness of the auxiliary boards are consistent with those of the main board; the main board and the auxiliary boards forming the same coaming are movably connected through hinges, so that the auxiliary boards can be laterally folded relative to the outside of the box body, and the same positions of the outer side wall surfaces of the two auxiliary boards are respectively provided with a retaining ring with a radial through hole, so that the movably connected main board and the two auxiliary boards lock the relative positions of the two main boards and the two auxiliary boards through connecting rods inserted on the two retaining rings. Wherein, the mainboard width is fixed, and the accessory plate correspondingly can design a plurality of different widths to be convenient for carry out timely adjustment to the whole width of rail according to the condition of taking the simulated stratum. When the movement of the opposite side coaming is blocked due to the influence of stress on the stratum at the later stage, the original movable connection state between the main board and the auxiliary board can be recovered by removing the connecting rod after the opposite side coaming is relatively moved, so that the auxiliary board is folded after the coaming is blocked, the width of the coaming is changed, and the opposite movement is continuously carried out on the bottom board, so that the movement result after the stress is simulated.
Further, the inner diameter of the upper part of the movable rail arranged on the upper surface of the rectangular bottom plate is smaller than that of the lower part, so that the axial section of the movable rail is in an inverted T shape; the track connecting piece is arranged on the bottom surface of the main board and comprises two inverted T-shaped protruding structures which are formed by extending along the axial direction from the bottom surface of each main board and mutually matched with the inverted T-shaped movable track, so that the track connecting piece can only radially enter the movable track from one end of the movable track, and the movement of the track connecting piece in the axial direction is limited, and the track connecting piece is prevented from falling out of the movable track in the simulation process.
Further, the rectangular bottom plate is a stainless steel rectangular plate; the main board and the auxiliary board forming the coaming are both composed of an organic glass board and two stainless steel short boards arranged on the top surface and the bottom surface of the organic glass board; the organic glass plate and the two stainless steel short plates are arranged in a coplanar manner and are sequentially connected and fixed.
In the design of the coaming, a plastic glass plate is adopted and arranged in the middle part so as to be convenient for observing the deformation form change of the plastic stratum on the section in the simulation process; the upper end and the lower end of the organic glass plate are respectively spliced and fixed with a stainless steel short plate, so that additional components are conveniently arranged without damaging the structural strength of the main plate and the auxiliary plate, namely, the connecting hinge and the buckling part are arranged on the stainless steel short plate. Wherein the area of the organic glass plate occupies about 2/3 of the whole area of the main plate or the auxiliary plate.
The organic glass plate and the stainless steel short plates at the two ends can be fixedly connected in a bonding mode, and can also be movably connected in a movable connection mode between the bottom plate and the coaming, namely, a T-shaped protruding structure and an inverted T-shaped protruding structure are respectively processed on the upper end face and the lower end face of the organic glass plate, and movable rails respectively adapting to the T-shaped protruding structure and the inverted T-shaped protruding structure are arranged on the lower end face of the stainless steel short plate above and the upper end face of the stainless steel short plate below, so that the organic glass plate, the coaming and the stainless steel short plate are fixedly connected and are not easy to deviate from in the axial direction to be separated.
Further, test materials are paved in the box body to simulate a plastic stratum and an overlying or underlying surrounding rock stratum. Specifically, a mud layer simulated by hydrous yellow clay or a salt rock layer simulated by polyester silica gel, a fault simulated by iron scale, a fine sandstone surrounding layer, a coarse sandstone surrounding layer and a quartz sandstone surrounding layer simulated by beach sand, river sand or quartz sand are paved in the box body with the top opening.
In actual work, the main common plastic stratum types are mudstone and salt rock, so in order to effectively simulate the plastic stratum, a clay layer with the same density and viscosity as the actual stratum is prepared by adding water into yellow clay to simulate the actual mud stratum; simulating an actual salt rock stratum by adopting a polyester silica gel layer to simulate the salt rock; respectively simulating fine sandstone, coarse sandstone and quartz sandstone in an actual stratum by using beach sand, river sand and quartz sand according to surrounding rock conditions; and the fault under the actual stratum is simulated by inserting iron scales into corresponding test materials.
Further, for the convenience of observation, different property layers and different kinds of surrounding rocks can be dyed differently, so that the change of plane spreading morphology and section patterns in the deformation process of the simulated stratum can be distinguished in the process of simulating the stress of the stratum.
In order to prevent experimental materials from blocking the movable rail, a wax seal is arranged in the movable rail. In addition, through the processing mode that adopts whole tectorial membrane on the bounding wall inside wall face to guarantee that the junction can not spill experimental material.
The driving device for pushing the coaming to reciprocate is a manual dynamometer or a stepping motor, so that the relative movement mode of the coaming arranged in four directions can be set into an electric mode or a manual mode. After the coaming moves, observing the experimental materials to deform through the organic glass coaming, and enabling the plastic layer to pierce the overlying surrounding rock and the underlying surrounding rock; the deformation form of the plastic layer in the section is not uniform with different fault positions. The formation process of the plastic layer deformation form in the actual seismic section can be verified through the simulated plastic layer deformation section.
Specifically, when the driving device is a stepping motor, an electromagnet is arranged on a stainless steel short plate at the lower side of a main plate of each coaming, and each coaming at the opposite side is controlled by one stepping motor; when the coamings on two sides are required to move oppositely, the external coils of the electromagnets on the coamings on two sides can be electrified with reverse direct current by controlling the stepping motor, so that two groups of opposite electromagnets generate attractive force; when the two sides are required to move reversely, the external coils of the coaming plates at the two sides can be electrified with direct current in the same direction, so that the two groups of opposite electromagnets generate repulsive force. When the driving device is a manual dynamometer, the four coamings can be externally connected with the spring dynamometer respectively, and then the coamings are extruded or stretched according to the set stress requirement to simulate the process of the stressed movement.
Compared with the prior art, the method for predicting the plastic stratum deformation obtains single-frequency data body information by carrying out short-time window discrete Fourier transform on the three-dimensional seismic data body in a time domain, and obviously distinguishes the difference of the plastic stratum by extracting the difference abnormality of the peak amplitude and the average amplitude, thereby having high reliability and effectively predicting the plastic stratum deformation trend and the deformed form; in addition, the simulation device is used for simulating the actual plastic stratum and the overlying and underlying surrounding rock, verification and comparison are carried out according to the actual test result and the actual seismic section, and the formation process and the deformation trend of the plastic layer deformation form in the actual seismic section are verified.
Drawings
FIG. 1 is a flow chart of a method of predicting plastic formation deformation in accordance with the present invention;
FIG. 2 is a schematic diagram of a simulation apparatus for predicting plastic deformation of a formation according to the present invention;
FIG. 3 is a flow chart of a conventional full frequency domain seismic data volume obtained via Fourier transform;
FIG. 4 is a flow chart of obtaining a single frequency seismic data volume by the method of predicting plastic formation deformation of the present invention;
FIG. 5 is a longitudinal cross-sectional view of an simulated formation in an apparatus for simulating an embodiment of the invention.
Detailed Description
The invention will now be further described with reference to the accompanying drawings and specific examples, which are in no way limiting.
According to the requirement of the seismic exploration work, firstly, acquiring artificial seismic data of a certain working area, and acquiring a three-dimensional seismic data volume under the time domain of the working area by adopting a seismic data processing algorithm. The specific prediction process is shown in fig. 1.
Step one, acquiring a three-dimensional seismic data volume under the time domain of the working area:
1) Performing geodetic measurement on a designated working area, measuring longitude and latitude of the working area, and converting the longitude and latitude of the spherical surface into plane coordinates (x, y) according to a conversion formula, wherein each position in the working area can be represented by the plane coordinates;
2) Exciting an artificial earthquake; specifically, in a working area, holes are sequentially drilled in the ground surface according to an arrangement rule that the row spacing is 200m and the column spacing is 400m, and explosives are buried and used as an excitation end of artificial earthquakes; meanwhile, a detector is arranged at the position of the embedded explosive point and is used as a receiving end of the artificial earthquake; when the two works are completed, explosive is detonated, and acoustic information is received by the detector because acoustic waves generated by explosion are reflected and refracted at interfaces of different stratum lithology according to the acoustic wave transmission principle; integrating acoustic information of each position with plane coordinates of the corresponding position through operation of a computer to obtain a three-dimensional seismic data body in a time domain, wherein the three-dimensional seismic data body comprises the position information and the acoustic information in the position;
step two, carrying out data processing on the seismic data volume in the time domain:
1) Determining that the time range of the plastic layer in the region to generate the penetrating deformation is 360 milliseconds on the seismic profile;
2) Dividing the time range of the plastic layer penetrating deformation into 6 parts and 7 parts of … … parts in sequence, namely gradually decreasing the time interval of each part from 60ms to 6ms in sequence, and taking the time interval as the time window range limit for carrying out Fourier transform calculation;
3) The following formula is followed in order with a short time window gradually decreasing from 60ms to 6 ms:
performing Fourier transform calculation, and introducing the seismic data volume under the time domain obtained in the step one to obtain three-dimensional seismic data volumes under a plurality of frequency domains;
4) Calculating peak amplitude and average amplitude in each data volume, and when the short time window is reduced to 6ms, obtaining peak amplitude and average amplitude differences of a plurality of single-frequency data volumes which are all 10 4 ～10 6 A (seismic acoustic wave amplitude unit) range, which shows that the obtained data volume in a plurality of frequency domains is a plurality of single-frequency data volumes capable of effectively analyzing the stratum;
step three, calculating the difference value of the peak amplitude and the average amplitude of the single-frequency data volume obtained in the step S2, determining the frequency band with the abnormal calculated amplitude difference value, and correspondingly outlining the plane coordinate position corresponding to the frequency band with the abnormal difference value on the plane construction image of the working area so as to reflect the deformation form of the plastic stratum in the area.
Specifically, it can be seen from the range diagram of the seismic amplitude attribute that the outlined difference is abnormal: the plane of the working area plastic layer outlined along the distribution range of the abnormal data value is in an irregular broken block shape after deformation; the deformation and fracture strength of the center is obviously stronger than that of a surrounding area, the area can be determined to be a plastic deformation center area, the surrounding area is called a deformation epitaxial area, and the outermost area is an undeformed area; the corresponding seismic profile is analyzed on the profile and is influenced by plastic deformation, so that an overlying stratum is pierced, the plastic layer is spread in a flower shape on the profile, the deformation and distortion of a flower core part are serious, the deformation of a petal part is slightly light, and the outermost stratum is not obviously deformed;
the deformation form of the plastic stratum obtained by the prediction method is further verified by the simulation device, so that the reliability of the result is further confirmed. The specific idea is as follows: and according to the seismic data section of the actual working area, rock and mineral identification is carried out on the drilling rock core in the working area, and the lithology of the plastic layer and the lithology of surrounding rocks in the working area range of the area are accurately judged, so that the simulation laying of the lithology of the plastic layer and the lithology of the surrounding rocks is carried out in a simulation device.
As shown in fig. 2, the simulation device for predicting plastic stratum deformation comprises a box body with an opening at the top, wherein the box body is formed by a rectangular bottom plate 1 which is horizontally arranged and four coamings which are arranged at four edges of the upper surface of the stainless steel rectangular bottom plate 1. Wherein, the upper surface of the stainless steel bottom plate 1 is provided with two movable rails which are parallel to each other and extend to the edge of the other side along the radial direction from the middle part of the edge of one side of each group of opposite side sides. Each coaming comprises a main board and two auxiliary boards, wherein the main boards are arranged in a coplanar manner, the two auxiliary boards are positioned on two sides of the main board, and the heights and the thicknesses of the main board and the auxiliary boards are consistent; the main board and the auxiliary board forming the coaming comprise a first stainless steel short board 3, an organic glass 2 and a second stainless steel short board 3 which are arranged in a coplanar manner and are sequentially connected and fixed from top to bottom; the size of the organic glass 2 accounts for 2/3 of the total area of the main board or the auxiliary board; the main board and the auxiliary boards forming the same coaming are movably connected through hinges 5 respectively arranged on the first stainless steel short board 3 and the second stainless steel short board 3, and a retaining ring 4 with a radial through hole is respectively arranged at the same position of the first stainless steel short board 3 of the two auxiliary boards, so that the movably connected main board and the two auxiliary boards lock the relative positions of the movably connected main board and the auxiliary boards through connecting rods inserted on the two retaining rings 4. The vertical section of each movable rail arranged on the upper surface of the stainless steel bottom plate 1 is in an inverted T shape, correspondingly, the rail connecting piece is arranged on the bottom surface of the main plate and comprises two inverted T-shaped protruding structures which are formed by extending along the axial direction from the bottom surface of each main plate and mutually matched with the inverted T-shaped movable rails, so that four coamings can reciprocate on the stainless steel bottom plate 1 through the movable rails. A stepping motor for pushing the coaming to reciprocate is arranged on the outer side wall surface of one coaming in each pair of side coapers.
Specifically, according to the stratum condition to be simulated, an auxiliary plate with a proper size is selected to be connected with a main plate to form two coamings with the size of 80cm multiplied by 50cm and two coamings with the size of 35cm multiplied by 50cm, and the four coamings are clamped into an inverted T-shaped sliding rail on the upper surface of the stainless steel bottom plate 1 through an inverted T-shaped rail connecting piece, as shown in fig. 2, so that the coamings stably slide on the stainless steel bottom plate 1 in a reciprocating manner, and a box body with the size of 80cm multiplied by 36cm multiplied by 50cm and with an opening at the top is assembled.
Then, according to the actual plastic stratum condition of the working area, experimental materials are paved in the box body of the simulation device. Specifically, as shown in fig. 5, experimental materials laid in the box body are correspondingly simulated into an upper mud surrounding rock layer, a plastic mud rock layer and a lower mud surrounding rock layer, namely, the plastic mud rock in the region is simulated as a plastic deformation process, and surrounding rocks are brittle deformation. The simulated test material of the plastic mud stratum has the density of 1.42g/cm 3 The viscosity is 109Pa.S, and the compressive strength is 22g/cm 2 Black colored hydrous yellow clay of 3cm in thickness; the simulated material of the surrounding stratum on the mud is selected to have the density of 2.5g/cm 3 Internal frictionQuartz sand with an angle of 16 degrees simulates quartz sandstone in an actual stratum, and is dyed green with the thickness of 4cm; the surrounding rock under mud is simulated by colored glass beads with the diameter of 8mm, a relatively hard ground stratum under mud is simulated, and the surrounding rock under mud is tiled on a stainless steel table top at the bottom of the device, and the thickness is 1.6cm. According to the earthquake section, three iron sheet simulated faults with the length multiplied by the width multiplied by the thickness of 27 multiplied by 62 multiplied by 0.09cm are inserted into a plastic mud stratum of a simulator, the three faults incline in the same direction, the fault inclination angles are 37 degrees, 39 degrees and 37 degrees in sequence, the faults can be approximately regarded as the same group of faults, and the geological stress environment is single, so that a unidirectional stress field acts on the stratum.
According to the actual seismic section, the original stratum length without extrusion can be determined through recovering the fault interval, and the distance shortened by the extrusion influence on the stratum plane is 18-40 km from the current actual length after extrusion; the actual seismic section observation shows that the extrusion time is 5.2-5.8 Ma (1 Ma is 100 vans); from these two values, an extrusion rate of 3.5 to 6.9mm/year can be calculated.
For the convenience of observation, the extrusion per unit time is simulated as one year, and the average speed of the coaming sliding along the sliding rail is 5.3mm/year; the distance between the coamings on two sides of the simulation device and the horizontal length of the actual seismic section are unified in proportion, and in order to facilitate equal proportion calculation of the compression length, the length proportion of the distance between the coamings of the simulation device and the actual seismic section is set to be 1:500 ten thousand, namely 1cm in the simulation device represents 2km in the actual work area.
The specific simulation experiment process comprises the following steps: starting a stepping motor, and extruding the single-side coaming along the long axis direction of the die device for 6 times by controlling an electromagnet arranged on the coaming on the opposite side, namely moving 2.6cm each time along the setting direction of three faults, wherein each time the interval is 2 hours, so that the plastic mudstone, the overlying and underlying surrounding rocks are fully deformed.
Experimental results: and finally, the coaming plate moves by 31.2cm, and the actual stratum is simulated to be shortened by 31.2km. Observing the plane spreading form of the simulated stratum and the section form of the organic glass part passing through the coaming from the upper part of the box body respectively; by observing, the deformation of the final plastic stratum is consistent with the deformation theory and the actual seismic profile predicted by the prediction method: the plane is in an irregular broken block shape; the deformation and fracture strength of the center is obviously stronger than that of a surrounding area, the area can be determined to be a plastic deformation center area, the surrounding area is called a deformation epitaxial area, and the outermost area is an undeformed area; the corresponding seismic profile is analyzed from the profile, is influenced by plastic deformation, so that the overlying stratum is pierced, the plastic layer is spread in a flower shape in the profile, the deformation of the flower core part is serious, the deformation of the petal part is slightly light, and the outermost stratum is not obviously deformed.
In summary, the plastic layer deformation form distribution pattern outlined by the method for predicting the deformation of the shaping stratum is consistent with the simulation result of the plane form of the shaping stratum actually simulated by the simulation device, the section deformation form obtained by the simulation experiment is consistent with the section deformation form shown by the actual seismic section through observation of surrounding plates, and the deformation trend and the stress deformation mechanism of the shaping stratum can be effectively and accurately predicted.
Claims (3)
1. A method of predicting plastic deformation of a subterranean formation, comprising the steps of:
s1, exciting an artificial earthquake in a working area, collecting acoustic information of the earthquake, and obtaining a three-dimensional earthquake data body in a time domain through computer processing;
s2, carrying out short-time window discrete Fourier transform formula calculation on the time domain three-dimensional seismic data body obtained in the step S1 to obtain a plurality of single-frequency seismic data bodies in a frequency domain;
s3, calculating the difference value of the peak amplitude and the average amplitude of the single-frequency data volume obtained in the step S2, determining a frequency band with an abnormal calculated difference value, and correspondingly outlining a plane coordinate position corresponding to the frequency band with the abnormal difference value on a plane spread image of a working area to obtain the range of the seismic amplitude attribute with the abnormal difference value, namely reflecting the deformation form of the plastic stratum of the area.
2. The method of predicting plastic deformation of a subterranean formation according to claim 1, wherein the specific step of step S2 comprises:
s201, determining that the time range of the plastic layer to generate the penetrating deformation is A milliseconds on the seismic profile;
s202, equally dividing the time range of the plastic layer penetrating deformation into n parts, wherein the time interval A/n millisecond of each equal part is used as the time window range limit for carrying out Fourier transform calculation, namely, an A/n millisecond short time window; wherein n is an integer, and n is more than or equal to 1;
s203, carrying out a Fourier transform formula on the three-dimensional seismic data volume under the time domain obtained in the step S1:
calculating; where i is an imaginary unit, e -iωt Expressed as an imaginary number i rotated counter-clockwise by an angle ωt (i.e. a rotation factor), ω being the angular velocity and t being the time; the time integration range is the short time window selected in the step S202; f (t) is substituted into a Fourier series formula:
wherein a is k The amplitude, k is the number of oscillations, ωt is the angle, ω is the angular velocity, t is the time,is the phase;
s204, calculating peak amplitude and average amplitude of the single-frequency data volume, and comparing the difference value of the peak amplitude and the average amplitude: when the abnormal difference value does not fall at 10 4 ～10 6 Returning to the step S202 when the range of A (the seismic sound wave amplitude unit) is within, increasing the value of N to n+N (N is an integer and N is more than or equal to 1); repeating steps S203 and S204 until the calculated abnormal difference between the peak amplitude and the average amplitude of a single frequency data volume is 10 4 ～10 6 And in the range A, a plurality of single-frequency data volumes which can effectively analyze the stratum are obtained.
3. The method of predicting plastic deformation of a subterranean formation of claim 2, wherein the short time window a/n ms in step S202 is in the range of 6-96 ms.
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