A formation strain calculation method based on the pressure balance equation of two-phase medium

Abstract

The present invention relates to a formation strain calculation method based on a two-phase medium pressure balance equation, which belongs to the fields of energy exploration such as oil and gas field exploration, shale gas exploration, and geothermal exploration. The method first calculates the true strain value of the target layer section encountered by drilling based on well logging data using a formation strain calculation method based on the two-phase medium pressure balance equation, then calculates the apparent strain value of the target layer section in the study area using an apparent dip angle method based on three-dimensional seismic data, and finally establishes a fitting relationship between the apparent strain value and the true strain value, thereby obtaining a strain array of the target layer section in the study area.

Description

Technical Field

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

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

[0003] Traditional methods for calculating formation strain rely primarily on well logging data and laboratory testing. While well logging data can provide detailed information about the formation surrounding the wellbore, its limited coverage makes it difficult to predict formation strain over a wide range. While laboratory testing can provide accurate physical parameters, it is costly, time-consuming, and difficult to reflect the complex variations in actual formation conditions. Furthermore, traditional methods such as using regional empirical formulas or sensitive parameter fitting methods also have significant limitations in practical applications.

[0004] In recent years, the rapid development of three-dimensional seismic technology has provided a new approach for calculating strain values ​​in strata (planar, two-dimensional arrays). Three-dimensional seismic data can cover a wide range of strata and provide a wealth of geological information, enabling accurate and high-precision strain calculations over a wide range. However, effectively integrating seismic data with well logging parameters to achieve high-precision formation strain calculations remains a technical challenge. Existing methods have shortcomings in formula derivation and parameter fusion, resulting in significant deviations between calculated results and actual conditions.

[0005] To address this problem, a method for calculating formation strain based on the two-phase medium pressure balance equation is urgently needed. 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 utilizing the two-phase medium pressure balance equation, high-precision and efficient strain distribution prediction can be achieved. Summary of the Invention

[0006] (1) Analysis of the advantages of the present invention over conventional technologies

[0007] Conventional techniques typically rely on a single data source (such as seismic attribute parameters, well logging data, or rock physics testing), which can lead to inaccurate calculation results. This invention utilizes the high-precision local information (well point location) provided by well logging data and the global information (three-dimensional space) provided by seismic data, achieving the integrated application of multi-source data and significantly improving the overall accuracy of strain calculations. This makes it particularly suitable for applications under complex geological conditions.

[0008] 2. Conventional techniques often require extensive laboratory testing or regional empirical fitting analysis, which is costly, inaccurate, and difficult to apply on a large scale. This invention establishes a fitting relationship between well logging strain and seismic strain, extending local high-precision logging data to the entire region (capturing the planar distribution of strain values ​​in the target layer). This step-by-step process and fitting method simplifies the calculation process and achieves high accuracy. It is applicable to formation strain analysis across a wide range of geological areas, possessing high engineering practicality and potential for widespread adoption.

[0009] (2) Core content of the present invention

[0010] This invention focuses on calculating formation strain in two-phase media. By combining the pressure balance principle of two-phase media, Hooke's law, and rock physics elastic parameter relationships, and through a series of theoretical derivations, a method for calculating formation strain based on the two-phase medium pressure balance equation has been developed. This method comprehensively considers the interaction between pore fluid pressure and rock skeleton stress, overcoming the limitation of traditional methods that ignore the influence of pore fluids and improving the calculation accuracy of strain values. Its core advantage lies in the introduction of two-phase medium theory, which effectively resolves the errors caused by the traditional method's failure to consider pore fluid pressure. This method achieves strain calculations that are more accurate than actual conditions, providing 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 two-phase medium pressure balance equation is as follows:

[0012] According to the pressure balance equation of two-phase medium,

[0013] (1)

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

[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 rock skeleton of the formation, Indicates strain.

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

[0019] (3)

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

[0021] (4)

[0022] , (5)

[0023] In formula (5), V p 、V s are the longitudinal and shear wave velocities, and is the Lamé constant.

[0024] Substituting 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 completed well data in the study area often contain the logging parameters in formula (7), such as velocity, porosity, density and other parameters. That is, formula (7) can be used to calculate the true strain value of the target layer section encountered by the completed well.

[0030] The technical steps of the present invention are as follows: first, the true strain value of the target layer segment is calculated based on the well logging parameters using formula (7); then, the apparent strain value of the target layer segment in the study area is calculated using the apparent dip angle method based on the three-dimensional seismic data; finally, the relationship between the apparent strain value and the true strain value is established, thereby obtaining the strain array of the target layer segment in the study area. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0032] Figure 2 This is the strain plane diagram of the buried mountain top interface in a certain study area in Bohai Sea. DETAILED DESCRIPTION

[0033] Example 1

[0034] A formation strain calculation method based on a two-phase medium pressure balance equation comprises the following steps:

[0035] 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 the coordinates, and calculate the partial derivative in the z direction of 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 recorded as the apparent strain array calculated based on three-dimensional seismic data;

[0038] Step 2: Input the depth data of the target layer in the study area, recorded as array Dep(x,y). Dep(x,y) 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);

[0039] Step 3: Input the coordinates of n typical wells that encountered the target layer in the study area and the logging parameters corresponding to the depth of the target layer, the longitudinal 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 ,

[0040] (2)

[0041] Assign the calculated strain values ​​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;

[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), 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 3D seismic data, E_s(2) represents the apparent strain value of the second typical well calculated based on 3D seismic data, and so on;

[0043] 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 3D seismic data in step 4, the least squares fitting method is used to obtain the fitting relationship between the two.

[0044] (3)

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

[0046] Step 6: Calculate the strain array E(x, y) of the target layer segment 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;

[0047] (4)

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

[0049] Example 2

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

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A formation strain calculation method based on a two-phase medium pressure balance equation, characterized in that: The specific steps include: 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 the coordinates, and calculate the partial derivative in the z direction of the array A(x, y, z). 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 3D seismic data. Step 2: Input the depth data of the target layer in the study area, recorded as array Dep(x,y). Dep(x,y) 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 that encountered the target layer in the study area and the logging parameters corresponding to the depth of the target layer, the longitudinal wave velocity V p , shear wave velocity V s , density ρ, porosity Overlying formation pressure P ov , pore pressure P f , where n≥5, the strain value ε of the target layer is calculated using logging parameters, 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 3D seismic data, E_s(2) represents the apparent strain value of the second typical well calculated based on 3D 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 3D seismic data in step 4, a least squares fitting method is used to obtain a fitting relationship between the two. E_w=aE_s 2 + bE_s+c (3) In formula (3), a, b, and c represent fitting coefficients; Step 6: Calculate the strain array E(x, y) of the target layer segment 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; E(x,y)=aE_s(x,y) 2 + bE_s(x,y)+c (4) Step 7: Output the strain array E(x,y) of the target layer segment in the study area.

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