A well seismic dispersion correction method suitable for tight sandstone formations

Abstract

The present invention provides a well seismic dispersion correction method suitable for dense sandstone formations, and the well seismic dispersion correction method suitable for dense sandstone formations comprises: step 1, selecting a target reservoir core, and carrying out lithology, physical properties and low-frequency rock physical parameter measurements; step 2, constructing a full-band dense sandstone rock physical model; step 3, calibrating a dynamic equivalent micro-scale model according to experimental data; and step 4, performing well seismic velocity dispersion correction. The well seismic dispersion correction method suitable for dense sandstone formations verifies the rationality of the rock physical model by finely calibrating the rock physical experimental data and the rock physical model, and then based on the rock physical model, adjusts the fracture density to make it consistent with the actual logging data of the calculated logging data or less than the error, and then realizes the calculation of the P- and S-wave velocities under the seismic frequency band.

Description

Technical Field

[0001] The invention relates to the technical field of reservoir rock physical property research, and in particular to a well seismic dispersion correction method suitable for dense sandstone formations. Background Art

[0002] When seismic waves propagate in the formation, the velocities of seismic waves of different frequencies will change, and energy will attenuate in the frequency band where the velocity changes dramatically. This characteristic of velocity changing with frequency is called velocity dispersion. In actual production, due to the inconsistency of well seismic velocity data, there is always a problem of mismatching well seismic data when synthetic seismic records are made from logging data. Stretching or compression (with unclear physical meaning) is required to improve the accuracy of synthetic record production. In addition to scale problems and the poor quality of logging data caused by borehole quality problems, the difference in measurement frequency cannot be ignored. In actual engineering, the measurement frequency of acoustic logging is generally in the range of 2KHz to 20KHz, which is much higher than the frequency of seismic waves in conventional surface exploration. The significant frequency difference makes the propagation speed of logging acoustic waves and surface exploration seismic waves different in non-uniform formations containing fluids. In terms of intrinsic physical mechanism, there is a mismatch between logging synthetic records and seismic traces.

[0003] In recent years, some scholars have carried out research on well-seismic dispersion correction methods. Zhao Jianguo et al. measured the full-band P- and S-wave velocities of ancient Ordovician-Cambrian carbonate rocks using low-frequency measurement equipment, and used the seismic band velocities at different pressures to fit the relationship between formation pressure and seismic band velocity. Then, the logging band velocities at different pressures were used to fit the relationship between formation pressure and logging band velocity, and then the logging and seismic velocities were fitted. This method only considers the relationship between formation pressure and well-seismic velocity, and does not consider the influence of formation mineral composition, microscopic pores, fluid saturation and viscosity. Therefore, the prediction effect is less accurate. Deng Jixin et al. used the resonant Q model to correct well-seismic dispersion, in which the value of Q is a constant. However, experiments have shown that if there is dispersion between well-seismic, Q must not be a constant, so the accuracy of well-seismic dispersion correction is also low.

[0004] P-wave and S-wave velocity data are irreplaceable in oil and gas exploration, and play a very important role in time-depth conversion, synthetic record production, seismic data inversion, reservoir modeling, etc. However, due to the dispersion of some formations such as tight sandstone formations, it is risky to directly use the P-wave and S-wave velocities of the logging frequency band instead of the P-wave and S-wave velocities of the seismic frequency band, and caution is required.

[0005] In the Chinese patent application with application number: CN201910343232.X, a method for matching well logging and seismic velocity based on seismic rock physics experimental analysis is involved, including: step 1, establishing a velocity variation curve with frequency, that is, the velocity dispersion variation law, through seismic frequency band rock physics experimental analysis; step 2, constructing a rock physics model suitable for characterizing the dispersion characteristics of the seismic frequency band; step 3, using the rock physics model modulus calculation formula to perform point-by-point mapping dispersion correction of the acoustic wave curve; step 4, calibrating the acoustic wave curve after dispersion correction by synthetic recording, comparing and analyzing the seismic well bypass and the synthetic seismic record, and outputting the correction curve results of all depths of the entire acoustic logging curve.

[0006] In the Chinese patent application with application number: CN201911321553.6, a method for indoor measurement of wave velocity, confining pressure and dispersion correction considering formation characteristics is involved, which includes the following steps: (1) collecting geological, logging data, coring data and downhole rocks in the study area; (2) making the core samples into multiple standard rock samples, and conducting indoor acoustic wave tests to obtain indoor acoustic wave time difference values; (3) taking 25 kHz as the target frequency, correcting the indoor test acoustic wave time difference frequency, and calculating the indoor test acoustic wave time difference value; (5) establishing the relationship between the acoustic wave time difference ratio under different confining pressures and 0 confining pressure and the confining pressure, and establishing a relationship model between the acoustic wave time difference ratio and confining pressure; (4) using logging data to calculate the mud content and porosity; (5) using the established formula to establish the relationship between the corrected acoustic wave and the field acoustic wave.

[0007] In the Chinese patent application with application number: CN201810244000.4, a method, device and system for eliminating dispersion effect are involved, wherein the method includes: testing core samples to obtain logging frequency band velocities and seismic frequency band velocities under different pressures; fitting the relationship between formation pressure and logging frequency band velocity using the logging frequency band velocities under different pressures, and fitting the relationship between formation pressure and seismic frequency band velocity using the seismic frequency band velocities under different pressures; eliminating the dispersion effect of the target area using the relationship between formation pressure and logging frequency band velocity and the relationship between formation pressure and seismic frequency band velocity.

[0008] The above existing technologies are greatly different from the present invention and fail to solve the technical problem we want to solve. Therefore, we have invented a new well seismic dispersion correction method suitable for dense sandstone formations. Summary of the invention

[0009] The purpose of the present invention is to provide a method for correcting well seismic dispersion suitable for dense sandstone formations, which realizes the calculation of longitudinal and transverse wave velocities in the seismic frequency band using well logging velocity.

[0010] The purpose of the present invention can be achieved by the following technical measures: a well seismic dispersion correction method suitable for dense sandstone formations, the well seismic dispersion correction method suitable for dense sandstone formations comprises:

[0011] Step 1: Select the target reservoir core and carry out lithology, physical properties and low-frequency rock physical parameter measurements;

[0012] Step 2, constructing a full-band tight sandstone rock physics model;

[0013] Step 3, calibrating the dynamic equivalent micro-scale model according to the experimental data;

[0014] Step 4: perform well seismic velocity dispersion correction.

[0015] The purpose of the present invention can also be achieved by the following technical measures:

[0016] In step 1, a typical core of the target formation is selected to measure parameters such as porosity, permeability, density, and mineral composition, and then low-frequency rock physical parameters are measured under formation conditions. The saturation states are dry, water-saturated, and oil-saturated, and the porosity, permeability, density, and mineral composition data of the core are obtained, as well as the low-frequency longitudinal and shear wave velocity data of the core under formation conditions.

[0017] In step 1, when low-frequency rock physical parameter measurements are carried out under formation conditions, the measurement frequency is 12-200 Hz.

[0018] In step 2, the bulk modulus K of the equivalent medium of the dynamic equivalent microscale model is eff and shear modulus u eff It can be expressed as:

[0019]

[0020]

[0021] Among them, ω is the angular frequency, K is the skeleton bulk modulus, μ is the shear modulus, ε is the crack density, is the porosity, λ is the Lame coefficient, K f is the fluid bulk modulus, Kc, Kp, A, and B are all intermediate parameters without specific physical meanings, A and B are

[0022]

[0023]

[0024] in,

[0025]

[0026]

[0027] τ is the time scale, which controls the frequency band range of the dispersion characteristics. It is proportional to the viscosity η of the fluid, inversely proportional to the permeability k, and related to the microcrack radius a. Its reciprocal is called the characteristic frequency. For a smaller aspect ratio:

[0028]

[0029] is the particle size, and ν is the Poisson's ratio of the solid particle.

[0030] In step 2, the P-wave velocity V is obtained according to the formula proposed by Connell and Budiansky. P and the speed of the S wave V S They are:

[0031]

[0032]

[0033] Where Re is the real part and ρ is the density.

[0034] In step 3, firstly, the porosity, permeability, density, mineral composition, water saturation and other data obtained in step 1 are used to calculate the full-band longitudinal and transverse wave velocity data based on the dynamic equivalent microscale model, and then the fracture density is adjusted and compared with the laboratory measurement data to verify the accuracy of the model calculation.

[0035] In step 4, firstly, the lithologic component data are obtained through the logging interpretation data, and then the skeleton modulus K and μ are calculated based on the Voigt-Reuss-Hill model. Then, the porosity data are obtained through the logging interpretation data. Assuming that the porosity is entirely composed of hard pores, the elastic modulus of dry rock is calculated based on the Berrymann model. Then, the fluid component data and permeability data are obtained through the logging interpretation data, and the P-wave velocity in the logging frequency band is calculated based on the dynamic equivalent microscale model.

[0036] In step 4, if the difference between the calculated P-wave velocity and the measured P-wave velocity is less than the error, then the P- and S-wave velocities in the seismic frequency band can be directly calculated. If the difference between the calculated P-wave velocity and the measured P-wave velocity is greater than the error, then the fracture density is added and the calculation is performed again according to the above process, and the cycle is repeated until the difference between the calculated P-wave velocity and the measured P-wave velocity is less than the error.

[0037] Step 4 includes:

[0038] 4a, calculate the skeleton modulus;

[0039] 4b, calculate the elastic modulus of dry rock;

[0040] 4c, calculate the full-band P- and S-wave velocities of fluid-containing rocks.

[0041] In step 4a, when the relative content and elastic modulus of each phase constituting the rock medium are known, the upper and lower limits of the effective elastic modulus of the rock medium are calculated using the Voigt and Reuss formulas (Formula 4-17); the upper limit Voigt formula represents the ratio of the stress to the strain of the rock medium under the same strain state and the same strain for each phase constituting the rock medium; the lower limit Reuss represents the ratio of the stress to the strain of the rock medium under the same stress state and the same stress for each phase constituting the rock medium; the Hill formula is the arithmetic average result of the Voigt upper limit and the Reuss lower limit;

[0042]

[0043] Where M V 、M R 、M VRH Represents the values ​​of bulk modulus K, shear modulus μ, and Young's modulus E calculated using Voigt-Reuss-Hill; fi is the volume content of the ith component constituting the rock medium; Mi is the elastic modulus of the ith component.

[0044] In step 4b, Berryman gives the general form of the self-consistency approximation for N-phase composites:

[0045]

[0046]

[0047] In the ith material, x i is its volume fraction, P and Q represent geometric factors, and the superscript i on P and Q indicates that these factors are in the self-compatible effective modulus and The background medium contains material i; Ki and μi are the bulk modulus and shear modulus of the i-th mineral, respectively, and the sum represents the consideration of all phases, including minerals and pores; dry pores are simulated by setting the inclusion modulus to zero; fluid-saturated pores are simulated by setting the inclusion shear modulus to zero; these equations are coupled and solved by simultaneous iteration.

[0048] In step 4c, after the dry rock elastic modulus is calculated, the full-band P- and S-wave velocities can be calculated based on the dynamic equivalent micro-scale model in combination with the logging interpretation data such as porosity, permeability, and fluid saturation.

[0049] The method for correction of well seismic dispersion suitable for dense sandstone formations in the present invention starts with conducting rock physics experiments, verifies the rationality of the rock physics model by finely calibrating the rock physics experimental data and the rock physics model, and then adjusts the fracture density based on the rock physics model to make it consistent with the actual logging data of the calculated logging data or less than the error, and then realizes the calculation of the P- and S-wave velocities in the seismic frequency band. The method for correction of well seismic dispersion suitable for dense sandstone formations has advantages that other technologies do not have, and its specific advantages and characteristics are manifested in the following aspects:

[0050] First, the constructed dynamic equivalent microscale model was calibrated through experimental data to verify the practicability of the model for tight sandstone formations.

[0051] Second, the microscopic pore structure of the rock is fully considered, and the logging velocity is used as a constraint loop iteration to make the calculated seismic frequency velocity more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a schematic diagram of actual rock pores in a specific embodiment of the present invention;

[0053] Figure 2 This is a schematic diagram of rock equivalent pores in a specific embodiment of the present invention;

[0054] Figure 3 It is a schematic diagram of the comparison between the 9# core P-wave velocity measurement data and the model in a specific embodiment of the present invention;

[0055] Figure 4 It is a schematic diagram of the comparison between the 9# core shear wave velocity measurement data and the model in a specific embodiment of the present invention;

[0056] Figure 5 It is a schematic diagram of the comparison between the 1# core P-wave velocity measurement data and the model in a specific embodiment of the present invention;

[0057] Figure 6 It is a schematic diagram of the comparison between the 1# core shear wave velocity measurement data and the model in a specific embodiment of the present invention;

[0058] Figure 7 It is a flow chart of a specific embodiment of the method for correcting well seismic dispersion suitable for tight sandstone formations of the present invention;

[0059] Figure 8 This is a diagram showing the effect of frequency dispersion correction of Well XX in a specific embodiment of the present invention;

[0060] Fig. 9 This is a diagram showing the effect of frequency dispersion correction of Well XX in a specific embodiment of the present invention;

[0061] Fig.10This is a diagram showing the effect of frequency dispersion correction of Well XX in a specific embodiment of the present invention;

[0062] Fig.11 It is a schematic diagram of the comparison of synthetic records before and after dispersion correction of Well XX in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0063] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0064] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations and / or combinations thereof.

[0065] like Figure 7 As shown, Figure 7 The flowchart of the well seismic dispersion correction method suitable for dense sandstone formations of the present invention includes the following steps:

[0066] (1) Select target reservoir cores to measure lithology, physical properties and low-frequency rock physical parameters

[0067] Select typical core blocks of the target formation to measure parameters such as porosity, permeability, density, and mineral composition, and then carry out low-frequency rock physical parameter measurements under formation conditions, with a measurement frequency of 12-200Hz, and saturation states of dry, saturated with water, and saturated with oil. Finally, the porosity, permeability, density, and mineral composition data of the core, as well as the low-frequency longitudinal and transverse wave velocity data of the core under formation conditions, are obtained to provide data support for subsequent rock physical model verification.

[0068] (2) Construction of a full-band tight sandstone rock physics model

[0069] Tight sandstone generally has the geological characteristics of low porosity, low permeability and micro-fracture development, and shows strong heterogeneity. Compared with conventional sandstone reservoirs, tight sandstone reservoirs have obvious differences in rock physical properties and seepage mechanical properties. The internal heterogeneity of tight sandstone has a significant impact on elastic wave dispersion and attenuation. When the elastic properties of pore fluids are slightly different, the heterogeneity of pore structure dominates elastic wave dispersion and attenuation.

[0070] In order to describe the seismic response law of fractured media in the full frequency band, it is necessary to Figure 1)Assume that ( Figure 2 ) dual pores, one is circular pores and the other is flat pores, where circular pores have stronger rigidity and flat pores (microcracks) have weaker rigidity. Based on this dual porosity hypothesis, a dynamic equivalent microscale model is proposed to describe the flow of fluids between pores and microcracks, and between microcracks in different directions in rocks containing microcracks and pores. The process of deriving the model formula is complicated, so only the results are given here.

[0071] Bulk modulus K of the equivalent medium in the dynamic equivalent microscale model eff and shear modulus u eff It can be expressed as:

[0072]

[0073]

[0074] Among them, ω is the angular frequency, K is the skeleton bulk modulus, μ is the shear modulus, ε is the crack density, is the porosity, λ is the Lame coefficient, A and B are

[0075]

[0076]

[0077] in,

[0078]

[0079]

[0080] τ is the time scale, which controls the frequency band range where the dispersion characteristics appear. It is proportional to the viscosity η of the fluid, inversely proportional to the permeability k, and related to the microcrack radius a. Its reciprocal is called the characteristic frequency. For smaller aspect ratios:

[0081]

[0082] is the particle size, ν is the Poisson's ratio of the solid particle. According to the formula proposed by Connell and Budiansky, the P-wave velocity V is obtained P and the speed of the S wave V S They are:

[0083]

[0084]

[0085] (3) Experimental data calibration of dynamic equivalent microscale model

[0086] Two cores 9# and 1# were selected for verification. From the mineral composition analysis data, it can be seen that the quartz content of core 9# is 77%, the clay content is 23%, and the cracks are relatively developed, but it cannot be quantitatively evaluated. From the physical property measurement, it can be seen that the density of core 9# is 2.41g / cm3, the porosity is 0.1059, and the permeability is 14.7mD. It is also known that the quartz content of core 1# is 85%, the clay content is 15%, the cracks are not developed, the porosity is 0.1454, the permeability is 58.95mD, and the density is 2.41g / cm3. The test state of core 9# is saturated with water, and the test state of core 1# is saturated with oil. The viscosity of water is 1cP, and the viscosity of oil is 2.2cP. In order to compare the joint logging data, the 20Mpa experimental measurement results and model simulation results are displayed.

[0087] Figure 3 , Figure 4 The comparison results of the P-wave and S-wave velocities of the 9# core and the rock physics model simulation are shown. Figure 5 , Figure 6 The comparison results of the P-wave and S-wave velocities of the 1# core and the rock physics model simulation are shown. Since the fracture density is a microscopic parameter and is not easy to obtain, and the fracture density parameter in the rock physics model is a parameter that must be input, the fracture density parameter can be adjusted to make the calculated P-wave and S-wave velocities in the well logging frequency band match the P-wave and S-wave velocities in the well logging. At this time, the calculated low-frequency P-wave and S-wave velocity data is the data to be simulated. Figure 3 , Figure 4 It can be seen that the P-wave and S-wave velocities measured in the low-frequency band of core 9# are in good agreement with those calculated by the rock physics model, with the P-wave velocity agreement exceeding 85% and the S-wave velocity agreement exceeding 80%. Figure 5 , Figure 6 It can be seen that the low-frequency P- and S-wave velocity measurement data of core 1# also agree well with the model, with an agreement of more than 80%. The experimental data of the two cores agree well with the rock physics model simulation results, which verifies the practicability of the model for tight sandstone.

[0088] (4) Well seismic velocity dispersion correction

[0089] First, the lithologic component data are obtained through the logging interpretation data, and then the skeleton modulus K and μ are calculated based on the Voigt-Reuss-Hill model. Then, the porosity data are obtained through the logging interpretation data. Assuming that the porosity is entirely composed of hard pores, the elastic modulus of dry rock is calculated based on the Berrymann model. Then, the fluid component data and permeability data are obtained through the logging interpretation data. The P-wave velocity in the logging frequency band is calculated based on the dynamic equivalent microscale model. If the difference between the calculated P-wave velocity and the measured P-wave velocity is less than the error, then the P-wave and S-wave velocities in the seismic frequency band can be directly calculated. If the difference between the calculated P-wave velocity and the measured P-wave velocity is greater than the error, then the fracture density is added and the calculation is performed again according to the above process, and the cycle is repeated until the difference between the calculated P-wave velocity and the measured P-wave velocity is less than the error.

[0090] ① Calculation of skeleton modulus—Voigt-Reuss-Hill average theory

[0091] When the relative content and elastic modulus of each phase of the rock medium are known, the upper and lower limits of the effective elastic modulus of the rock medium can be calculated using the Voigt and Reuss formula (Mavko and Mukerji et al., 1998) (Formula 1-7). The upper limit of the Voigt formula represents the ratio of the stress to the strain of the rock medium under the same strain state and the same strain of each phase of the rock medium; the lower limit of the Reuss formula represents the ratio of the stress to the strain of the rock medium under the same stress state and the same stress of each phase of the rock medium. The Hill formula is the arithmetic average of the Voigt upper limit and the Reuss lower limit.

[0092] Wherein MV, MR, MVRH represent the values ​​of bulk modulus K, shear modulus μ, and Young's modulus Ε calculated by Voigt-Reuss-Hill; fi is the volume content of the i-th component constituting the rock medium; Mi is the elastic modulus of the i-th component.

[0093] ② Calculation of elastic modulus of dry rock

[0094] Berryman (1980b, 1995) gave the general form of the self-consistency approximation for N-phase composites:

[0095]

[0096]

[0097] In the ith material, x iis its volume fraction, P and Q represent geometric factors, and the superscript i on P and Q indicates that these factors are in the self-compatible effective modulus and The background medium contains material i. The summation takes into account all phases, including minerals and pores. Dry pores can be simulated by setting the inclusion modulus to zero. Fluid-saturated pores can be simulated by setting the inclusion shear modulus to zero. It is important to note that these equations are coupled and must be solved by simultaneous iterations.

[0098] ③ Calculation of full-band longitudinal and transverse wave velocities of fluid-containing rocks

[0099] After calculating the elastic modulus of dry rock, the full-band P- and S-wave velocities can be calculated based on the dynamic equivalent microscale model in combination with the porosity, permeability, fluid saturation and other parameters of the logging interpretation data.

[0100] In a specific embodiment 1 of the present invention, taking Well X as an example, the correction effect is analyzed in detail. Figure 8 This is the correction effect diagram of Well XX. The first track is the permeability curve, the second track is the shale content curve, the third track is the porosity curve, the fourth track Vp is the measured P-wave velocity (well logging), Vp1 is the P-wave velocity of the seismic frequency band (40Hz) after correction, the fifth track is the calculated S-wave velocity of the seismic frequency band, the sixth track is the density, and the seventh track is the water saturation. Figure 8 It can be seen that the mud content of the 3820m-3840m formation in Well XX is low, the porosity is generally more than 10%, and the permeability is approximately 50-70mD. The comprehensive interpretation is that oil and water are in the same layer. The characteristic frequency is calculated to be between the wellbore and seismic waves. The fourth track shows that the longitudinal wave velocity of the wellbore and seismic waves in this section is significantly different, with a maximum of 80m / s and a dispersion amplitude of about 3%. Fig.11 The synthetic records made by using the well curves of Well X before and after dispersion correction are compared. From the ellipse in the figure, it can be seen that the synthetic record made by the well curve after correction matches the seismic record waveform energy better.

[0101] Embodiment 2:

[0102] In the specific embodiment 2 of the present invention, the correction effect is analyzed in detail by taking the XX well as an example. Fig. 9This is the dispersion correction effect diagram of Well XX. The first track is the mud content, the second track is the measured P-wave velocity of Vp, Vp1 is the corrected P-wave velocity, and the third track is the calculated S-wave velocity. From the figure, we can see that the well is in mudstone formation at 2580-2660m. The porosity and permeability of mudstone formations are generally small (except for shallow layers). Although there is water in mudstone formations, it is all structural water. When seismic waves pass through, structural water is not easy to flow as part of clay, and there is no condition for generating jet flow. Therefore, the mudstone section is similar to the dry layer. From the second track, we can see that the P-wave velocities of this section of well seismic coincide with each other, and there is no dispersion. Therefore, there is no need to recalibrate the synthetic record in the mudstone section.

[0103] Embodiment 3:

[0104] In specific embodiment 3 of the present invention, taking XXX well as an example, the correction effect is analyzed in detail. Fig.10 This is the dispersion correction effect diagram of Well XX. The first track is the permeability curve, the second track is the shale content, the third track is the porosity, the fourth track Vp is the measured P-wave velocity, Vp1 is the corrected P-wave velocity, and the fifth track is the calculated S-wave velocity. It can be seen from the figure that the shale content of the two sections of 2793-2803m and 2807-2817m in the well is low, both are sandstone reservoirs, the porosity is close to 20%, and the permeability is higher than 150mD. The comprehensive interpretation is that the oil and water are in the same layer. After calculation by the dispersion correction program, the characteristic frequency is greater than the logging frequency band. Therefore, the fourth track shows that there is no difference between the logging P-wave velocity and the seismic frequency band P-wave velocity. Therefore, there is no need to re-calibrate the synthetic record at the permeability exceeding 100 Hao Darcy.

[0105] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions recorded in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0106] Except for the technical features described in the specification, all other technical features are known technologies to those skilled in the art.

Claims

1. A method for correcting well seismic dispersion suitable for dense sandstone formations, characterized in that: The well seismic dispersion correction method suitable for tight sandstone formations includes: Step 1: Select the target reservoir core and carry out lithology, physical properties and low-frequency rock physical parameter measurements; Step 2, constructing a full-band tight sandstone rock physics model, wherein the rock physics model is a dynamic equivalent micro-scale model; Step 3, calibrating the dynamic equivalent micro-scale model according to the experimental data; Step 4, performing well seismic velocity dispersion correction; In step 2, the bulk modulus K of the equivalent medium of the dynamic equivalent microscale model is eff and shear modulus u eff It can be expressed as: Among them, ω is the angular frequency, K is the skeleton bulk modulus, μ is the shear modulus, ε is the crack density, is the porosity, λ is the Lame coefficient, K f is the fluid bulk modulus, Kc, Kp, A, and B are all intermediate parameters without specific physical meanings, A and B are in, τ is the time scale, which controls the frequency band range of the dispersion characteristics. It is proportional to the viscosity η of the fluid, inversely proportional to the permeability k, and related to the microcrack radius a. Its reciprocal is called the characteristic frequency. For a smaller aspect ratio: is the particle size, and ν is the Poisson's ratio of the solid particle.

2. The method for correcting well seismic dispersion in dense sandstone formations according to claim 1, characterized in that: In step 1, a typical core of the target formation is selected to measure parameters such as porosity, permeability, density, and mineral composition, and then low-frequency rock physical parameters are measured under formation conditions. The saturation states are dry, saturated with water, and saturated with oil, and the porosity, permeability, density, and mineral composition data of the core are obtained, as well as the low-frequency longitudinal and shear wave velocity data of the core under formation conditions.

3. The method for correcting well seismic dispersion suitable for dense sandstone formations according to claim 2, characterized in that: In step 1, when low-frequency rock physical parameter measurements are carried out under formation conditions, the measurement frequency is 12-200 Hz.

4. The method for correcting well seismic dispersion suitable for dense sandstone formations according to claim 1, characterized in that: In step 2, the P-wave velocity V is obtained according to the formula proposed by Connell and Budiansky. P and the speed of the S wave V S They are: Where Re is the real part and ρ is the density.

5. The method for correcting well seismic dispersion suitable for dense sandstone formations according to claim 2, characterized in that: In step 3, firstly, the porosity, permeability, density, mineral composition, and water saturation data obtained in step 1 are used to calculate the full-band longitudinal and transverse wave velocity data based on the dynamic equivalent microscale model, and then the fracture density is adjusted and compared with the laboratory measurement data to verify the accuracy of the model calculation.

6. The method for correcting well seismic dispersion suitable for dense sandstone formations according to claim 1, characterized in that: Step 4 includes: 4a, calculate the skeleton modulus; 4b, calculate the elastic modulus of dry rock; 4c, calculate the full-band P- and S-wave velocities of fluid-containing rocks.

7. The method for correcting well seismic dispersion suitable for dense sandstone formations according to claim 6, characterized in that: In step 4a, when the relative content and elastic modulus of each phase constituting the rock medium are known, the upper and lower limits of the effective elastic modulus of the rock medium are calculated using the Voigt and Reuss formulas, i.e., formula 4-17; wherein the upper limit Voigt formula represents the ratio of the stress to the strain of the rock medium under the same strain state and the same strain of each phase constituting the rock medium; The Reuss lower limit represents the ratio of stress to strain of the rock medium under the same stress state, when all phases constituting the rock medium are under the same stress; The Hill formula is the arithmetic average of the Voigt upper bound and the Reuss lower bound; Where M V 、M R 、M VRH Represents the values ​​of bulk modulus K, shear modulus μ, and Young's modulus E calculated using Voigt-Reuss-Hill; fi is the volume content of the ith component constituting the rock medium; Mi is the elastic modulus of the ith component.

8. The method for correcting well seismic dispersion in dense sandstone formations according to claim 6, characterized in that: In step 4b, the elastic modulus of dry rock is calculated based on the Berrymann model. Berrymann gave the general form of the self-consistency approximation for N-phase composite materials: In the ith material, x i is its volume fraction, P and Q represent geometric factors, and the superscript i on P and Q indicates that these factors are in the self-compatible effective modulus and The background medium contains material i; Ki, μi are the bulk modulus and shear modulus of the i-th mineral, respectively, and the sum represents the consideration of all phases, including minerals and pores; dry pores are simulated by setting the inclusion modulus to zero; fluid-saturated pores are simulated by setting the inclusion shear modulus to zero; These equations are coupled and solved by simultaneous iterations.

9. The method for correcting well seismic dispersion suitable for dense sandstone formations according to claim 6, characterized in that: In step 4c, after the dry rock elastic modulus is calculated, the full-band P- and S-wave velocities are calculated based on the dynamic equivalent microscale model in combination with the logging interpretation data of porosity, permeability, and fluid saturation.

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