Reservoir medium random displacement method in carbon dioxide geological sequestration

Abstract

The invention discloses a reservoir medium random displacement method in carbon dioxide geological sequestration, which comprises the following steps of: determining a theoretical rock physical model and an earthquake forward modeling model by using actual logging data and earthquake data, and constructing a forward modeling framework; performing forward modeling according to a fluid replacement theory and a Gassmann equation; in an existing reservoir parameter seismic forward modeling process, an existing algorithm is optimized, a random process of the content and proportion of a medium participating in displacement is added, and a more complete underground model numerical simulation scheme is provided; further correcting and optimizing the fluid replacement theoretical formula; according to the method, actual physical property parameters of the underground reservoir serve as input, and finally high-reliability elastic parameter and seismic record estimation is achieved. According to the method, different conditions of medium composition proportions in different reservoir models obtained in different work areas can be better predicted, and a larger and real data set is provided for subsequent underground reservoir model seismic inversion.

Description

Technical Field

[0001] The present invention relates to the field of fire seismic exploration technology, and in particular to a random displacement method of reservoir media in geological storage of carbon dioxide. Background Art

[0002] Carbon dioxide capture and storage (CCS) is recognized worldwide as one of the fastest and most effective technologies for reducing carbon dioxide concentrations. Through detailed description of reservoirs and monitoring of carbon dioxide migration, it is ensured that the carbon dioxide storage site has stable geological conditions and suitable storage and confinement space, and that carbon dioxide is effectively sealed. The safe storage of carbon dioxide requires stable geological conditions and suitable storage and confinement space, so that carbon dioxide can be effectively sealed for a long time after being injected underground. Therefore, before carbon dioxide is stored, it is necessary to select the carbon dioxide storage site to ensure that the storage site has good storage space, suitable pressure, stable structural development, etc.

[0003] In the existing seismic forward modeling of reservoir parameters, the methods used are often based on the existing fluid replacement theory. Through some basic physical parameters obtained by field drilling in the work area, the underground reservoir model is approximated by forward numerical simulation, while the composition of the actual logging reservoir medium is ignored. In the seismic forward modeling of reservoir parameters, the actual content and proportion of the reservoir medium involved in the displacement during the carbon dioxide storage process are only roughly simulated and approximated, so that the final numerical simulation results are often far from the actual situation in the work area. In practical applications, it is often difficult to obtain a large number of real underground model parameters, and the prediction results have non-physical consistency, which limits the data-driven method from obtaining better inversion effects.

[0004] In summary, the existing research on reservoir parameter seismic forward modeling methods has the following problems: the existing research uses a large number of approximate formulas and models in the process of reservoir parameter seismic forward modeling, and the modeling process has non-physical completeness, which leads to limited accuracy in reservoir parameter prediction. At the same time, in the process of reservoir parameter seismic forward modeling, the actual content and displacement ratio of the medium involved in the carbon dioxide geological storage process are often ignored, resulting in a large deviation between the final numerical simulation results and the actual situation of the well logging. Summary of the invention

[0005] In order to overcome the shortcomings and deficiencies of the prior art, the present invention provides a random displacement method for reservoir media in geological storage of carbon dioxide.

[0006] The present invention effectively solves the problem that the content and proportion of the reservoir parameters involved in displacement in the existing method are greatly different from the content and proportion in the actual work area, so that the results obtained by the seismic forward modeling of the reservoir parameters more truly reflect the actual situation of the reservoir model in the work area, and obtain a more realistic underground model, so as to explore more complete underground reservoir conditions for the geological storage of carbon dioxide, adjust the storage plan of carbon dioxide, and provide guidance for further research on fine detection methods for carbon dioxide storage monitoring. The method includes:

[0007] Step 101: Determine specific parameters of a theoretical rock physics model and a seismic forward model using actual logging data and seismic data, and establish the most basic underground reservoir model based on fluid replacement theory and the Wood equation and Gassmann equation in rock physics;

[0008] Step 102, according to the actual reservoir medium composition inside the well logging, correct the composition of various media contents and proportions in the underground reservoir during the forward modeling of the underground reservoir model, the various media including: reservoir porosity, shale content, water saturation, oil saturation, carbon dioxide saturation;

[0009] Step 103, by modifying the medium content and proportion in the underground reservoir, optimizing the process of calculating the reservoir elastic parameters in the Gassmann equation, modifying the algorithms of the seismic longitudinal wave velocity, seismic shear wave velocity, and reservoir saturated rock density in the underground reservoir during the forward modeling process, and using the idea of ​​random displacement, the optimized Gassmann equation can more truly reflect the actual composition of the underground reservoir under actual engineering conditions;

[0010] Step 104: forward modeling the reservoir medium random displacement method in carbon dioxide geological storage (forward modeling is the process of obtaining seismic response from known underground parameters), and compare the elastic parameters and physical property parameters of the underground reservoir model obtained with those of the actual work area, analyze the differences, and further optimize the random displacement algorithm so that the final result is highly consistent with the underground reservoir result of the actual work area;

[0011] Step 105: After the random displacement algorithm is optimized, further numerical simulation is performed to obtain seismic records using the elastic parameters obtained by the random displacement algorithm, the AVO forward modeling theory, and the Zoeppritz equation. The seismic records obtained by forward modeling using the elastic parameters obtained by the random displacement algorithm reflect the actual seismic records of the underground reservoir.

[0012] Furthermore, the theoretical rock physics model is established by the fluid substitution theory of the Gassmann equation and the Zeoppritz equation; the seismic forward model parameters include: seismic P-wave velocity Vp, seismic S-wave velocity Vs, reservoir rock density Rho, and seismic records;

[0013] Establishing a rock physics model includes: taking known physical parameters of the reservoir, namely porosity, shale content, water saturation, oil saturation, and carbon dioxide saturation, and adjusting the corresponding contents and proportions of the above physical parameters using a random displacement algorithm, obtaining elastic parameters through the fluid substitution theory of the Gassmann equation, namely seismic longitudinal wave velocity Vp, seismic shear wave velocity Vs, and reservoir rock density Rho, and using the Zeoppritz equation to obtain seismic records to complete the forward modeling process.

[0014] Furthermore, the random displacement algorithm includes the following expressions:

[0015] ρ fl =S oil ρ oil +S H2O *[1-{min+β%(max-min+1)}]ρ H2O +S co2 ρ co2 (1)

[0016] In the formula, ρ fl It represents the density of the fluid medium in the underground reservoir after the reservoir is displaced by carbon dioxide, S oil and ρ oil represent the saturation and density of oil in the underground reservoir after carbon dioxide displacement, S co2 and ρ oil represent the saturation and density of carbon dioxide in the underground reservoir after carbon dioxide displacement, S H2O and ρ H2O They represent the saturation and density of water in the underground reservoir after carbon dioxide displacement, β represents a random number, which is related to the content of various media in the reservoir of the actual work area, and max and min are the upper and lower limits of the specific parameter random process used to limit the media involved in the displacement in the reservoir in the random displacement algorithm;

[0017]

[0018] In the formula, ρ roc represents the density of saturated rock in the reservoir after CO2 flooding, represents the porosity of the reservoir, ρ sub Represents the average density of the rock matrix.

[0019] Furthermore, through (1) and (2), the density of saturated rock in the reservoir after carbon dioxide displacement is obtained using the random displacement algorithm as one of the elastic parameters that need to be output in the end, and then the following formula is derived:

[0020]

[0021] Where V s represents the velocity of seismic shear waves in the underground reservoir after carbon dioxide displacement, μ satur represents the shear modulus of saturated rock in the underground reservoir. The velocity of seismic shear waves in the reservoir after carbon dioxide displacement is obtained by using formula (3) and random displacement algorithm, which is used as one of the elastic parameters that need to be output in the end.

[0022]

[0023] In the formula, K fl , K oil , K H2O , K CO2 Respectively represent the bulk modulus of the fluid, oil, water, and carbon dioxide in the reservoir after carbon dioxide displacement. The S involved in formula (4) ool , S H2O , S co2 , are the corresponding saturations obtained after the random displacement algorithm of formula (1);

[0024]

[0025] In the formula, K satur represents the bulk modulus of the saturated rock after CO2 displacement, K dry represents the bulk modulus of dry rock, K sub represents the elastic modulus of the rock matrix. The bulk modulus of the fluid in the reservoir obtained by formula (4) is substituted into formula (5) to obtain the bulk modulus of the saturated rock after carbon dioxide displacement using the random displacement algorithm;

[0026]

[0027] Substituting the bulk modulus of the saturated rock after carbon dioxide displacement calculated by equation (5) into equation (6), we can obtain the elastic modulus M of the saturated rock after carbon dioxide displacement: satur ;

[0028] Furthermore, the random displacement algorithm, the expression also includes:

[0029]

[0030] Where V pIt represents the velocity of seismic longitudinal waves in the underground reservoir after carbon dioxide displacement. The synchronous formulas (1)-(7) obtain the required elastic parameters obtained by forward modeling of physical parameters, and all the elastic parameters obtained utilize the medium random displacement method in carbon dioxide geological storage. Then, the obtained elastic parameters are repeatedly randomly displaced until the elastic parameter results that tend to be stable and meet the actual working area conditions are obtained.

[0031] Furthermore, the AVO forward modeling theory is used with the help of the Zoeppritz equation to further perform numerical simulation to obtain seismic records. The AVO forward modeling theory refers to the phenomenon that the amplitude of seismic waves changes with the offset distance. This phenomenon is mainly caused by the inhomogeneity of the underground medium. The existence of the AVO effect causes the displacement and amplitude of seismic waves in the underground reservoir to change, so this should be considered when using the Zoeppritz equation to construct the underground seismic waveform curve. The following is an introduction to the process of obtaining seismic records through forward modeling of the Zoeppritz equation:

[0032]

[0033] The above formula is the Zoeppritz equation, where δ1, δ2, ε1, and ε2 represent the incident angle and transmission angle of the longitudinal wave, and the reflection angle and transmission angle of the transverse wave, respectively. p1 , v s1 , Rho1 and v p2 , v s2 , Rho2 represent the elastic parameters (longitudinal wave velocity, shear wave velocity, density) of medium 1 and medium 2 respectively. pp , R ps , T pp , T ps represent reflection and transmission coefficients respectively, and t represents time.

[0034] Based on the elastic parameters (Vp, Vs, Rho) obtained from the forward modeling of physical parameters, the corresponding parameters are corrected using the above formula combined with the AVO forward modeling theory to obtain the final seismic record.

[0035] Beneficial effects:

[0036] The present invention provides a method for random displacement of reservoir media in geological storage of carbon dioxide. The method optimizes the traditional seismic simulation of underground reservoir parameters, avoids the approximate treatment of the reservoir media involved in the displacement by the traditional method, can greatly improve the accuracy of numerical simulation, reduce the error in the simulation process, and obtain a more accurate underground model. The present method further corrects the fluid replacement theory used in existing research, and performs random simulation on the proportion of reservoir media involved in the displacement, so that the numerical simulation results based on the original fluid replacement theory are more consistent with the actual situation of the reservoir in the survey area. Through the medium random displacement method of the present invention, the different situations of the medium composition ratios in different reservoir models obtained in different working areas can be better predicted, and a larger and more realistic data set can be provided for the subsequent forward modeling process of obtaining seismic records by elastic parameter forward modeling and the seismic inversion of underground reservoir models. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the invention in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0038] Figure 1 is a flow chart of the method of the present invention;

[0039] Figure 2 is a diagram showing the difference in elastic parameters before and after displacement of an underground reservoir according to the method of the present invention;

[0040] Figure 3 is a schematic diagram of elastic parameters obtained by numerical simulation according to the method of the present invention;

[0041] Figure 4 It is a schematic diagram of the forward modeling result of the optimal elastic parameters obtained by continuously repeating the random displacement process of the optimization method of the present invention;

[0042] Figure 5 It is a difference diagram between the reservoir seismic record obtained by the method of the present invention and the original seismic record result. DETAILED DESCRIPTION

[0043] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other. The present application is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0044] In view of the above-mentioned problems existing in the conventional seismic forward modeling method of underground reservoir elastic parameters, such as the approximate fuzzy processing of the content and proportion of the reservoir medium involved in the displacement, the certain error between the theoretical formula of fluid replacement used and the actual result, and the large error between the underground reservoir model in the actual work area, the purpose of the present invention is to provide a medium random displacement method in carbon dioxide geological storage to achieve high-precision prediction of elastic parameters. The present invention is proposed on the basis of studying the following problems: 1. Existing studies have used a large number of approximate formulas and models in the process of reservoir parameter seismic forward modeling, and the modeling process has non-physical completeness, resulting in limited prediction accuracy of reservoir parameters; 2. In the process of reservoir parameter seismic forward modeling, the actual content and displacement ratio of the medium involved in the displacement process of carbon dioxide geological storage are ignored, resulting in a large deviation between the final numerical simulation results and the actual situation of well logging. 3. There is a certain error between the theoretical formula of fluid replacement used and the actual result. The present invention determines the theoretical rock physics model and the seismic forward model based on the actual well logging data and seismic data, generates a forward modeling data set, statistically calculates the distribution law of the corresponding elastic parameters and physical property parameters of the rock based on the well data, takes the actual well logging parameters as input, and finally realizes high-reliability elastic parameter and seismic data estimation.

[0045] like Figure 1 As shown, a random displacement method of reservoir medium in geological storage of carbon dioxide specifically includes:

[0046] Step 101: Determine specific parameters of a theoretical rock physics model and a seismic forward model based on actual logging data and seismic data, and establish the most basic underground reservoir model according to fluid replacement theory and the Wood equation and Gassmann equation in rock physics.

[0047] Step 102: Based on the actual reservoir medium composition inside the well logging, the composition of the content and proportion of various media in the underground reservoir during the forward modeling of the underground reservoir model is corrected.

[0048] Step 103: Based on the correction of the medium content and proportion in the underground reservoir, the process of calculating the reservoir elastic parameters in the Gassmann equation is optimized, and the algorithms of the seismic longitudinal wave velocity, seismic shear wave velocity, and reservoir saturated rock density in the underground reservoir during the forward modeling process are corrected. By using the idea of ​​random displacement, the optimized Gassmann equation can more truly reflect the actual composition of the underground reservoir under actual engineering conditions.

[0049] Step 104: Compare and study the elastic parameters and physical property parameters of the underground reservoir model obtained by forward simulation using the random displacement method of the carbon dioxide geological sealing storage layer with the underground model of the actual work area, analyze the differences, and further optimize the random displacement algorithm so that the final result is highly consistent with the underground reservoir result of the actual work area.

[0050] Step 105: After the random displacement algorithm is optimized, further numerical simulation is performed to obtain seismic records using the elastic parameters obtained by the random displacement algorithm, the AVO forward modeling theory, and the Zoeppritz equation. At this time, the seismic records obtained by forward modeling using the elastic parameters obtained by the random displacement algorithm can more realistically reflect the actual seismic records of the underground reservoir.

[0051] The present invention specifically adopts the following working steps to realize the above invention: determine the specific parameters of the theoretical rock physics model and the seismic forward model based on the actual well logging data and seismic data, establish a basic underground reservoir model according to the fluid replacement theory and rock physics equations, and correct the composition of various media contents and proportions in the underground reservoir during the forward modeling process of the underground reservoir model based on the actual reservoir medium composition inside the well logging. Optimize the process of calculating the reservoir elastic parameters in the Gassmann equation, and correct the algorithms for the seismic longitudinal wave velocity, seismic shear wave velocity, and reservoir saturated rock density in the underground reservoir during the forward modeling process, so that the optimized Gassmann equation can more truly reflect the actual composition of the underground reservoir under actual engineering conditions. Compare the elastic parameters and physical property parameters of the underground reservoir model obtained with those of the underground model of the actual work area, analyze the differences, and further optimize the random displacement algorithm. With the elastic parameters obtained by the random displacement algorithm, using the AVO forward modeling theory, with the help of the Zoeppritz equation, further numerical simulation is performed to obtain seismic records, and the final processing results, including reservoir elastic parameters, reservoir physical property parameters, and seismic records, are output. The invention and working steps are described in detail as follows:

[0052] The present invention determines the specific parameters of the theoretical rock physics model and the seismic forward model based on actual logging data and seismic data, establishes a seismic forward model with a theoretical rock physics analytical solution, analyzes the error distribution law between the modeling results based on the theoretical physics model and the measured data, and establishes the most basic underground reservoir model according to the fluid replacement theory and the Wood equation and the Gassmann equation in rock physics.

[0053] Relevant data were investigated, and based on the composition of the reservoir medium inside the well logging, combined with the actual geological environment of the work area and the physical and chemical properties of the geological body, the composition of the content and proportion of various media in the underground reservoir during the forward modeling of the underground reservoir model was corrected, so as to further clarify the upper and lower limits of the random displacement algorithm for the displacement range of the reservoir medium parameters.

[0054] Based on the correction of the medium content and proportion in the underground reservoir, the process of calculating the reservoir elastic parameters in the Gassmann equation is optimized. The idea of ​​random displacement is used to correct the algorithms of seismic longitudinal wave velocity, seismic shear wave velocity, and reservoir saturated rock density in the underground reservoir during the forward modeling process. The optimized Gassmann equation can more realistically reflect the actual composition of the underground reservoir under actual engineering conditions. In order to characterize the process of random displacement of reservoir media in carbon dioxide geological storage, the random displacement algorithm is designed as follows:

[0055] ρ fI =S oil ρ oil +S H2O *[1-{min+β%(max-min+1)}]ρ H2O +S co2 ρ co2 (1)

[0056] In the formula, ρ fl It represents the density of the fluid medium in the underground reservoir after the reservoir is displaced by carbon dioxide, S oil and ρ oil represent the saturation and density of oil in the underground reservoir after carbon dioxide displacement, S co2 and ρ oil represent the saturation and density of carbon dioxide in the underground reservoir after carbon dioxide displacement, S H2O and ρ H2O Respectively represent the saturation and density of water in the underground reservoir after carbon dioxide displacement, β represents a random number, which is related to the content of various media in the reservoir of the actual work area. max and min are the upper and lower limits of the specific parameter random process used to limit the media involved in the displacement in the reservoir in the random displacement algorithm. It should be noted that, in the formula, S co2 , S oil , S H2O The sum of the three is always 100% during the displacement process, that is, it is actually considered that the media involved in the carbon dioxide displacement in the reservoir during the whole process are only oil and water. Therefore, it is only necessary to use a random displacement algorithm for the water or oil in the reservoir to obtain the saturation of the other two media through the quantitative relationship of the three.

[0057]

[0058] In the formula, ρ roc represents the density of saturated rock in the reservoir after CO2 flooding, represents the porosity of the reservoir, ρ sub Represents the average density of the rock matrix.

[0059] Through (1) and (2), the density of saturated rock in the reservoir after carbon dioxide displacement can be obtained using the random displacement algorithm as one of the elastic parameters that need to be output in the end. From this, the following formula can be derived:

[0060]

[0061] Where V s represents the velocity of seismic shear waves in the underground reservoir after carbon dioxide displacement, μ satur It represents the shear modulus of saturated rock in the underground reservoir. Through formula (3), the velocity of seismic shear waves in the reservoir after carbon dioxide displacement can be obtained by random displacement algorithm, which is one of the elastic parameters that need to be output in the end.

[0062]

[0063] In the formula, K fl , K oil , K H2O , K CO2 Respectively represent the bulk modulus of fluid, oil, water, and carbon dioxide in the reservoir after carbon dioxide displacement. It should be noted that the S involved in the formula oil , S H2O , S co2 , are the corresponding saturations obtained after the random displacement algorithm of formula (1).

[0064]

[0065] In the formula, K satur represents the bulk modulus of the saturated rock after CO2 displacement, K dry represents the bulk modulus of dry rock, K sub represents the elastic modulus of the rock matrix. Substituting the bulk modulus of the fluid in the reservoir obtained by equation (4) into equation (5), we can obtain the bulk modulus of the saturated rock after carbon dioxide displacement using the random displacement algorithm.

[0066]

[0067] Then, the bulk modulus of the saturated rock after carbon dioxide displacement calculated by formula (5) is substituted into formula (6) to obtain the elastic modulus M of the saturated rock after carbon dioxide displacement: satur .

[0068]

[0069] Where V p Represents the velocity of seismic P-waves in underground reservoirs after CO2 flooding.

[0070] like Figure 2 As shown in the figure, the elastic parameters of the underground reservoir changed accordingly before and after the carbon dioxide displacement, which is reflected in the curve graph that the seismic longitudinal wave velocity curve, seismic shear wave velocity curve and reservoir rock density curve before and after the displacement do not overlap.

[0071] like Figure 3 As shown in the figure, the content and proportion of each reservoir medium involved in the displacement are repeatedly corrected by using the random displacement algorithm, and then the elastic parameter curve closest to the actual situation can be obtained. At this point, the required elastic parameters obtained by forward modeling of physical parameters are obtained, and all the elastic parameters obtained use the random displacement method of the medium in carbon dioxide geological storage. After that, the elastic parameters obtained can be further repeatedly randomly displaced until the elastic parameter results that tend to be stable and meet the actual work area conditions are obtained.

[0072] like Figure 4 As shown, in Figure 3 On this basis, the optimal elastic parameter result diagram under numerical simulation was obtained, and the elastic parameters of the forward model obtained by using the random displacement algorithm were output, and compared with the elastic parameters of the underground model of the actual work area. The differences were analyzed and the random displacement algorithm was further optimized, so that the final results were highly consistent with the underground reservoir results of the actual work area.

[0073] like Figure 5 As shown, Figure 5 (a) is the original seismic record obtained by further forward modeling the elastic parameters before carbon dioxide displacement using the Zoeppritz equation. Figure 5 (b) is the seismic record after carbon dioxide displacement obtained by forward modeling using the optimal elastic parameters after carbon dioxide displacement based on the random displacement algorithm. According to the elastic parameters obtained by the continuously optimized random displacement algorithm, the AVO forward modeling theory and the Zoeppritz equation are used to further perform numerical simulation to obtain the seismic record. Finally, a more realistic underground reservoir seismic record is obtained.

[0074] The final results are output, including the original physical parameters of the reservoir, the elastic parameters obtained according to the random displacement algorithm of the reservoir parameters, and the seismic records obtained based on the elastic parameters obtained by the optimized random displacement algorithm.

[0075] The present invention has the following advantages: 1. The present invention optimizes the traditional seismic simulation of underground reservoir parameters, avoiding the traditional method of approximate processing of the reservoir medium involved in the displacement, which can greatly improve the accuracy of the numerical simulation, reduce the error in the simulation process, and obtain a more accurate underground model. 2. This technology has made further corrections to the fluid replacement theory used in existing research, and has made a random simulation of the proportion of reservoir media involved in the displacement, so that the numerical simulation results based on the original fluid replacement theory are more consistent with the actual situation of the reservoir in the survey area. 3. The medium ratio random displacement method based on this technology can better predict the different situations of the medium composition ratio in different reservoir models obtained in different work areas, and provide a larger and more realistic data set for further seismic inversion of underground reservoir models.

[0076] Those skilled in the art should understand that the purpose of the above description of the embodiments of the present invention is only to exemplarily illustrate the beneficial effects of the embodiments of the present invention, and is not intended to limit the embodiments of the present invention to any given examples.

[0077] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

[0078] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various equivalent changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for random displacement of reservoir medium in geological storage of carbon dioxide, characterized in that , the method comprises: Step 101: Determine the parameters of the theoretical rock physics model and the seismic forward model using actual logging data and seismic data, and establish an underground reservoir model based on the fluid replacement theory and the Wood equation and Gassmann equation in rock physics; Step 102, according to the actual reservoir medium composition inside the well logging, correct the composition of various medium contents and proportions in the underground reservoir during the forward modeling of the underground reservoir model; Step 103, by modifying the medium content and proportion in the underground reservoir, optimizing the calculation process of the reservoir elastic parameters in the Gassmann equation, modifying the algorithms of the seismic longitudinal wave velocity, seismic shear wave velocity, and reservoir saturated rock density in the underground reservoir during the forward modeling process, and using the idea of ​​random displacement, making the optimized Gassmann equation reflect the real composition of the underground reservoir under actual engineering conditions; Step 104: Compare and study the elastic parameters and physical property parameters of the underground reservoir model obtained by forward modeling using the random displacement method of reservoir media in carbon dioxide geological storage with those of the underground model of the actual work area, analyze the differences, and further optimize the random displacement algorithm so that the final result is consistent with the underground reservoir result of the actual work area; Step 105: After optimizing the random displacement algorithm, further numerical simulation is performed to obtain seismic records using the elastic parameters obtained by the random displacement algorithm, the AVO forward modeling theory, and the Zoeppritz equation. The seismic records obtained by forward modeling using the elastic parameters obtained by the random displacement algorithm reflect the actual seismic records of the underground reservoir.

2. A method for random displacement of reservoir medium in geological storage of carbon dioxide according to claim 1, characterized in that: The theoretical rock physics model is established by the fluid substitution theory of the Gassmann equation and the Zeoppritz equation; The parameters of the seismic forward model include: seismic P-wave velocity Vp, seismic S-wave velocity Vs, reservoir rock density Rho, and seismic records; Establishing a rock physics model includes: taking known physical parameters of the reservoir, namely porosity, shale content, water saturation, oil saturation, and carbon dioxide saturation, and adjusting the corresponding contents and proportions of the above physical parameters using a random displacement algorithm, obtaining elastic parameters through the fluid substitution theory of the Gassmann equation, namely seismic longitudinal wave velocity Vp, seismic shear wave velocity Vs, and reservoir rock density Rho, and using the Zeoppritz equation to obtain seismic records to complete the forward modeling process.

3. The method for random displacement of reservoir medium in geological storage of carbon dioxide according to claim 1, characterized in that: The random displacement algorithm, the expression includes: r fl =S oil r oil +S H2O *[1-{min+β%(max-min+1)}]ρ H2O +S co2 r co2 (1) In the formula, ρ fl It represents the density of the fluid medium in the underground reservoir after the reservoir is displaced by carbon dioxide, S oil and ρ oil represent the saturation and density of oil in the underground reservoir after carbon dioxide displacement, S co2 and ρ oil represent the saturation and density of carbon dioxide in the underground reservoir after carbon dioxide displacement, S H2O and ρ H2O They represent the saturation and density of water in the underground reservoir after carbon dioxide displacement, β represents a random number, which is related to the content of various media in the reservoir of the actual work area, and max and min are the upper and lower limits of the specific parameter random process used to limit the media involved in the displacement in the reservoir in the random displacement algorithm; In the formula, ρ roc represents the density of saturated rock in the reservoir after CO2 flooding, represents the porosity of the reservoir, ρ sub Represents the average density of the rock matrix.

4. A method for random displacement of reservoir medium in geological storage of carbon dioxide according to claim 3, characterized in that: Through (1) and (2), the density of saturated rock in the reservoir after carbon dioxide displacement is obtained using the random displacement algorithm as one of the elastic parameters that need to be output in the end, and then the following formula is derived: Where V s represents the velocity of seismic shear waves in the underground reservoir after carbon dioxide displacement, μ satur represents the shear modulus of saturated rock in the underground reservoir. The velocity of seismic shear waves in the reservoir after carbon dioxide displacement is obtained by using formula (3) and random displacement algorithm, which is used as one of the elastic parameters that need to be output in the end. In the formula, K fl , K oil , K H2O , K CO2 Respectively represent the bulk modulus of the fluid, oil, water, and carbon dioxide in the reservoir after carbon dioxide displacement. The S involved in formula (4) oil , S H2O , S co2 , are the corresponding saturations obtained after the random displacement algorithm of formula (1); In the formula, K satur represents the bulk modulus of the saturated rock after CO2 displacement, K dry represents the bulk modulus of dry rock, K sub represents the elastic modulus of the rock matrix. The bulk modulus of the fluid in the reservoir obtained by formula (4) is substituted into formula (5) to obtain the bulk modulus of the saturated rock after carbon dioxide displacement using the random displacement algorithm; Substituting the bulk modulus of the saturated rock after carbon dioxide displacement calculated by equation (5) into equation (6), we can obtain the elastic modulus M of the saturated rock after carbon dioxide displacement: satur .

5. A method for random displacement of reservoir medium in geological storage of carbon dioxide according to claim 4, characterized in that: The random displacement algorithm is expressed as: Where V p It represents the velocity of seismic P-waves in the underground reservoir after carbon dioxide displacement. The synchronous formulas (1)-(7) are used to obtain the required elastic parameters obtained by forward modeling of physical parameters, and all the obtained elastic parameters are subjected to the random displacement method of the medium in carbon dioxide geological storage. The obtained elastic parameters are then subjected to repeated random displacement until the elastic parameter results that are stable and meet the actual working area conditions are obtained.

6. The method for random displacement of reservoir medium in geological storage of carbon dioxide according to claim 1, characterized in that: The Zoeppritz equation is expressed as: Among them, δ1, δ2, ε1, ε2 represent the incident angle and transmission angle of longitudinal wave, the reflection angle and transmission angle of shear wave, respectively, v p1 , v s1 , Rho1 and v p2 , v s2 , Rho2 represent the elastic parameters of medium 1 and medium 2 respectively, R pp , R ps , T pp , T ps represent reflection and transmission coefficients respectively, and t represents time.

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