Stratum strain calculation method based on two-phase medium pressure balance equation

Abstract

The invention relates to a formation strain calculation method based on a two-phase medium pressure balance equation, and belongs to the field of energy exploration such as oil and gas field exploration, shale gas exploration and geothermal exploration. The method comprises the following steps of: firstly, calculating a real strain value of a target interval encountered by a drilling well by adopting a formation strain calculation method based on a two-phase medium pressure balance equation on the basis of logging data, and then calculating an apparent strain value of the target interval of a research area by adopting an apparent dip angle method on the basis of three-dimensional seismic data; and finally, establishing a fitting relational expression between the visual strain value and the real strain value, thereby obtaining a strain array of the target interval of the research area.

Description

Technical Field

[0001] The present invention relates to the technical field of resource exploration, especially in the energy exploration fields such as oil and gas field exploration, shale gas exploration, geothermal exploration, etc., and specifically relates to a method for calculating formation strain based on the pressure balance equation of a two-phase medium. Background Art

[0002] In the technical field of resource exploration, especially in the energy exploration fields such as oil and gas field exploration, shale gas exploration, geothermal exploration, etc., the accurate calculation of the strain value of the formation is of great significance for research such as reservoir prediction, fracture development analysis, in-situ stress analysis, etc. Traditional methods mostly rely on well logging data or laboratory tests, and it is difficult to achieve large-scale and high-precision prediction of strain distribution, such as the planar characteristic analysis of the strain value in the target interval. In recent years, with the wide application of three-dimensional seismic technology, calculating formation strain by combining seismic data and well logging parameters has become a research hotspot. However, existing methods still have deficiencies in formula derivation, parameter fusion, and calculation accuracy. Therefore, there is an urgent need for a method for calculating formation strain based on the pressure balance equation of a two-phase medium to achieve high-precision and high-efficiency prediction of strain distribution.

[0003] Traditional methods for calculating the formation strain value mainly rely on well logging data and laboratory tests. Well logging data can provide detailed information about the formation around the wellbore, but its coverage is limited and it is difficult to achieve large-scale prediction of formation strain. Although laboratory tests can provide accurate physical parameters, they are costly, time-consuming, and difficult to reflect the complex changes under actual formation conditions. In addition, traditional methods such as using regional empirical formulas or sensitive parameter fitting methods also have great limitations in practical applications.

[0004] In recent years, the rapid development of three-dimensional seismic technology has provided a new way for calculating the (planar, two-dimensional array) strain value of the formation. Three-dimensional seismic data can cover a large range of formations and provide rich geological information, making it possible to accurately calculate large-scale and high-precision strain values. However, how to effectively fuse seismic data and well logging parameters to achieve high-precision calculation of formation strain values is still a technical problem. Existing methods have deficiencies in formula derivation and parameter fusion, resulting in a large deviation between the calculation results and the actual situation.

[0005] To solve this problem, there is an urgent need for a method for calculating formation strain based on the pressure balance equation of a two-phase medium. The two-phase medium model can better describe the interaction between fluids and solids in the formation and is suitable for strain calculation under complex geological conditions. By combining seismic data and well logging parameters and using the pressure balance equation of a two-phase medium, high-precision and high-efficiency prediction of strain distribution can be achieved. Summary of the Invention

[0006] (I) Analysis of the advantages of the present invention compared with conventional technologies

[0007] 1. Conventional techniques usually rely on a single data source (such as seismic attribute parameters, logging data, or rock physics tests), which may lead to inaccurate calculation results. The present invention comprehensively utilizes the high-precision local information (well point location) provided by logging data and the full-field information (three-dimensional space) provided by seismic data, realizing the comprehensive application of multi-source data, significantly improving the overall accuracy of strain value calculation, especially having stronger applicability under complex geological conditions.

[0008] 2. Conventional techniques often require a large number of laboratory tests or regional empirical fitting analyses, with high costs, low accuracy, and difficulty in large-scale application. The present invention simplifies the calculation process and has high calculation accuracy by establishing a fitting relationship between logging strain and seismic strain, extending local high-precision logging data to the full regional range (the planar distribution characteristics of strain values in the target interval can be obtained). This step-by-step process and fitting method are applicable to the formation strain analysis of large-scale geological regions, with high engineering practicability and popularization value.

[0009] (II) Core content of the present invention

[0010] The present invention focuses on the calculation of formation strain in a biphasic medium. By combining the pressure balance principle of the biphasic medium, Hooke's law, and the elastic parameter relationship in rock physics, through a series of theoretical derivations, a formation strain calculation method based on the pressure balance equation of the biphasic medium is invented. This method comprehensively considers the interaction between pore fluid pressure and rock skeleton stress, overcomes the limitation of ignoring the influence of pore fluid in traditional methods, improves the calculation accuracy of strain values, and its core advantage lies in introducing the biphasic medium theory, effectively solving the error problem caused by not considering pore fluid pressure in traditional methods, realizing a more realistic strain calculation, and providing an important theoretical basis and technical support for engineering practice under complex geological conditions.

[0011] The derivation process of the core formula of a formation strain calculation method based on the pressure balance equation of the biphasic medium is as follows:

[0012] According to the pressure balance equation of the biphasic medium,

[0013] (1)

[0014] In formula (1), P ov represents the overburden pressure, represents the formation porosity, P f represents the formation fluid pore pressure, represents the effective stress of the formation rock skeleton.

[0015] Based on Hooke's law and the definition of Young's modulus (the ratio of stress to strain),

[0016] (2)

[0017] In formula (2), E represents Young's modulus, represents the effective stress of the formation rock skeleton, represents strain.

[0018] Substitute formula (2) into formula (1),

[0019] (3)

[0020] Based on the relationship between elastic parameters in rock physics,

[0021] (4)

[0022] , (5)

[0023] In formula (5), V p , V s are the longitudinal wave velocity and the transverse wave velocity, and are the Lame constants.

[0024] Substitute formulas (4) and (5) into formula (3),

[0025] (6)

[0026] Based on formula (6),

[0027] (7)

[0028] Formula (7) is the core calculation formula of the formation strain calculation method based on the two-phase medium pressure balance equation derived in the present invention.

[0029] The well-completed drilling data in the study area often contains logging parameters in formula (7), such as parameters like velocity, porosity, density, etc. That is, the true strain value of the target interval drilled by the well-completed drilling can be calculated using formula (7).

[0030] The technical steps of the present invention: First, calculate the true strain value of the target interval based on logging parameters using formula (7), then calculate the apparent strain value of the target interval in the study area using the apparent dip angle method based on 3D seismic data, and finally establish the relationship between the apparent strain value and the true strain value, so as to obtain the strain array of the target interval in the study area. Brief Description of the Drawings

[0031] Figure 1 is the flow chart of the present invention;

[0032] Figure 2 It is the strain plan view of the buried hill top interface in a certain research area in the Bohai Sea. Specific implementation manner

[0033] Example 1

[0034] A formation strain calculation method based on the pressure balance equation of biphasic media, the steps include:

[0035] Step 1, input the three-dimensional seismic data volume in the depth domain of the research area, denoted as the numerical value A(x, y, z), where x, y, z represent coordinates, and calculate the partial derivative in the z direction for the array A(x, y, z).

[0036] (1)

[0037] In formula (1), r(x, y, z) represents the apparent dip angle. The principle of calculating strain using the apparent dip angle is adopted, and ES(x, y, z) is denoted as the apparent strain array calculated based on three-dimensional seismic data.

[0038] Step 2, input the depth data of the target layer section in the research area, denoted as the array Dep(x, y). Dep(x, y) records the depth values corresponding to coordinates x and y. Based on the coordinates and depth values of the target layer section, extract the apparent strain array E_s(x, y) of the target layer section from the array ES(x, y, z).

[0039] Step 3, input the coordinates of n typical wells in the research area that drill through the target layer section and the logging parameters corresponding to the depth of the target layer section, the longitudinal wave velocity V p , the shear wave velocity V s , the density , the porosity , the overburden pressure P ov , the pore pressure P f , where n ≥ 5, calculate the strain value of the target layer section using the logging parameters ,

[0040] (2)

[0041] Assign the calculated strain value to the strain array E_w(i), i = 1, …, n, where E_w(1) represents the strain value calculated based on logging parameters of the first typical well, E_w(2) represents the strain value calculated based on logging parameters of the second typical well, and so on.

[0042] Step 4: Using the x and y coordinates of the n typical wells in Step 3, extract the apparent strain values of the array E_s(x, y), denoted as the array E_s(i), where i = 1, …, n. Here, E_s(1) represents the apparent strain value calculated based on 3D seismic data for the 1st typical well, E_s(2) represents the apparent strain value calculated based on 3D seismic data for the 2nd typical well, and so on;

[0043] Step 5: Based on the strain array E_w(i) calculated from well logging parameters in Step 3 and the apparent strain array E_s(i) calculated from 3D seismic data in Step 4, use the least squares fitting method to obtain the fitting relationship between the two.

[0044] (3)

[0045] In formula (3), a, b, and c represent fitting coefficients;

[0046] Step 6: Using the apparent strain array E_s(x, y) of the target interval in Step 2 and the fitting coefficients a, b, and c in Step 5, calculate the strain array E(x, y) of the target interval;

[0047] (4)

[0048] Step 7: Output the strain array E(x, y) of the target interval in the study area.

[0049] Example 2

[0050] Figure 2 It is the strain plan view of the top interface of the buried hill (Carboniferous strata) in a certain study area in the Bohai Sea. It can be seen from this that after applying the present invention, the strain attribute plan view of the top interface of the buried hill is accurately obtained, and it has a positive correlation matching relationship with the faults or fracture zones in the study area, laying a foundation for subsequent prediction of high-angle fractures in the inner zone.

[0051] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A formation strain calculation method based on a two-phase medium pressure balance equation includes the following specific steps: Step 1: Input the depth domain 3D seismic data volume of the study area, recorded as the value A(x, y, z), where x, y, z represent coordinates, and calculate the partial derivative in the z direction of the array A(x, y, z). (1) In formula (1), r(x, y, z) represents the apparent dip angle. The principle of calculating strain using the apparent dip angle is adopted, and ES(x, y, z) is recorded as the apparent strain array calculated based on three-dimensional seismic data; Step 2: Input the depth data of the target layer in the study area, recorded as array Dep(x,y), which records the depth values ​​corresponding to the coordinates x and y. Based on the coordinates and depth values ​​of the target layer, extract the apparent strain array E_s(x,y) of the target layer from the array ES(x,y,z); Step 3: Input the coordinates of n typical wells in the study area that encounter the target layer and the logging parameters corresponding to the depth of the target layer, the P-wave velocity V p , shear wave velocity V s ,density , porosity , overlying formation pressure P ov , pore pressure P f , where n≥5, the strain value of the target layer is calculated using the logging parameters , (2) The calculated strain values ​​are assigned to the strain array E_w(i), i=1,…,n, where E_w(1) represents the strain value calculated based on the logging parameters of the first typical well, E_w(2) represents the strain value calculated based on the logging parameters of the second typical well, and so on; Step 4, using the x and y coordinates of the n typical wells in step 3, extract the apparent strain values ​​of the array E_s(x, y), recorded as array E_s(i), i=1,…,n, where E_s(1) represents the apparent strain value of the first typical well calculated based on the three-dimensional seismic data, E_s(2) represents the apparent strain value of the second typical well calculated based on the three-dimensional seismic data, and so on; Step 5, based on the strain array E_w(i) calculated based on the well logging parameters in step 3 and the apparent strain array E_s(i) calculated based on the three-dimensional seismic data in step 4, a least squares fitting method is used to obtain a fitting relationship between the two; (3) In formula (3), a, b, and c represent fitting coefficients; Step 6, using the apparent strain array E_s(x, y) of the target layer segment in step 2 and the fitting coefficients a, b, c in step 5, calculate the strain array E(x, y) of the target layer segment; (4) Step 7: Output the strain array E(x,y) of the target layer segment in the study area.

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