Shale reservoir formation pore pressure logging prediction method based on improved bowers equation

Abstract

The present application relates to a shale reservoir formation pore pressure logging prediction method based on improved Bowers equation, comprising: combining Bowers equation, establishing a sound wave velocity response equation considering the influence of density and organic matter content; soaking experiment is carried out on rock sample, and based on acoustic travel time, density, deep and shallow resistivity in logging data, the formation acoustic velocity and density corrected by hydration are obtained; based on the sound wave velocity and density of the original formation corrected by hydration, the Bowers equation of the research formation is obtained; the Bowers equation of the research formation is modified to obtain the improved Bowers equation of the research formation; based on the improved Bowers equation, the formation effective stress and vertical stress are calculated; based on the formation effective stress and vertical stress, the formation pore pressure of the research formation is calculated. The modified Bowers formation pore pressure prediction model established in the present application has obviously improved prediction accuracy, which is beneficial to reduce the occurrence of construction accidents and reduce the development cost.

Description

Technical Field

[0001] This invention relates to the field of pore pressure prediction technology, and in particular to a well logging prediction method for shale reservoir formations based on the improved Bowers equation. Background Technology

[0002] Continental shale oil is attracting increasing attention due to its large resource reserves. The formation pressure formation mechanism of continental shale oil reservoirs is complex, influenced by factors such as undercompaction, hydrocarbon generation expansion, and tectonic compression. Hydrocarbon generation and tectonic compression can obscure the logging responses of abnormally high-pressure formations, making it difficult for formation pressure calculation methods based on undercompaction theory to accurately predict the pore pressure of continental shale oil formations. Therefore, organic hydrocarbon generation correction is needed for predicting the pore pressure of continental shale oil formations to avoid the influence of these factors on formation pressure calculations.

[0003] Existing research indicates that formation pressure prediction methods based on effective stress are suitable for predicting pore pressure in formations with complex genesis, such as the Bowers method. However, this method does not consider the impact of organic hydrocarbon generation correction. Furthermore, during shale oil reservoir drilling, after drilling fluid penetrates the formation, a series of physicochemical interactions occur between the drilling fluid and shale, altering the physical properties of the shale formation. This leads to formation logging parameters failing to reflect the true physical properties of the original formation; for example, drilling fluid penetration causes a decrease in resistivity, P-wave velocity, and density. Therefore, when calculating formation pore pressure in shale oil reservoirs, the logging information after the shale oil formation comes into contact with the drilling fluid needs to be hydrated and corrected to obtain the original formation logging information. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a well logging prediction method for shale reservoir formation pore pressure based on an improved Bowers equation.

[0005] This invention is achieved through the following technical solution:

[0006] A well logging prediction method for shale reservoir formation pore pressure based on the improved Bowers equation includes the following steps:

[0007] Based on the Bowers equation, a sound wave velocity response equation considering the effects of density and organic matter content is established.

[0008] Immersion experiments were conducted on the collected rock samples, and the resistivity, acoustic velocity, and density of the rock samples after immersion were measured to obtain the relationship between the changes in density, longitudinal wave velocity, and resistivity after drilling fluid intrusion.

[0009] Based on the relationship between the density change, P-wave velocity change, and resistivity change after drilling fluid invasion, and using the sonic transit time, density, and shallow / deep resistivity data from the well logging data, the hydration-corrected sonic velocity and density are obtained:

[0010] Based on the acoustic velocity and density of the undisturbed formation after hydration correction, the measured acoustic velocity of the formation will be... The result of hydration correction Effective stress Maximum vertical effective stress at the start of unloading of the overlying cover Substituting Bowers' loading and unloading equations, we obtain the Bowers equations for the studied formation.

[0011] Based on the sonic wave velocity response equation that takes into account the influence of density and organic matter content, combined with density logging information and organic carbon content logging calculation results, the density and organic carbon content corresponding to the depth of the formation pressure measurement point are read, and the unloading equation of the Bowers equation of the studied formation is modified to obtain the improved Bowers equation of the studied formation.

[0012] Based on the improved Bowers equation, the sonic velocity before formation hydration is calculated by back-calculating the measured sonic velocity data obtained from the well logging data, and the effective stress of the formation is calculated; the formation density before formation hydration is calculated by back-calculating the density data from the well logging data, and the vertical stress is calculated.

[0013] Based on the effective stress and vertical stress of the formation, the formation pore pressure of the studied formation was calculated.

[0014] The loading and unloading equations for Bowers are as follows:

[0015] Loading curve:

[0016] Unloading curve:

[0017] In the above formula, The velocity of sound is m / s; This represents the effective stress of the formation. is the maximum vertical effective stress at the start of unloading, MPa; U is the elastic-plastic coefficient of the formation mudstone and shale, dimensionless; A and B are coefficients in the formula, dimensionless.

[0018] The acoustic wave velocity response equation considering the effects of density and organic matter content is as follows:

[0019]

[0020] In the above formula, The velocity of sound is m / s; For density, ; Organic carbon content, % is the maximum vertical effective stress at the start of unloading, MPa; U is the elastic-plastic coefficient of the formation mudstone and shale, dimensionless; A, B, C, and D are coefficients in the formula, dimensionless.

[0021] Furthermore, the relationship between the magnitude of the density change, the magnitude of the longitudinal wave velocity change, and the magnitude of the resistivity change is as follows:

[0022]

[0023]

[0024]

[0025] In the above formula, The range of rock sample density variation, The amplitude of the longitudinal wave velocity variation. The magnitude of resistivity change This is the conversion factor between the indoor resistivity of the rock sample and the resistivity of the well logging. The value represents the deep lateral resistivity in Ω·m. The value represents the shallow lateral resistivity in Ω·m.

[0026] Furthermore, the formulas for calculating the hydration-corrected longitudinal wave velocity and density are as follows:

[0027]

[0028]

[0029] In the above formula, The P-wave velocity of the formation after hydration correction, in m / s; This is the formation density after hydration correction. ; The P-wave velocity of the formation in well logging data, in m / s; For formation density in well logging data, .

[0030] Furthermore, the Bowers equation for the studied strata is as follows:

[0031]

[0032] In the above formula, The P-wave velocity of the formation after hydration correction, in m / s; This represents the effective stress of the formation. The maximum effective vertical stress at the start of unloading is expressed in MPa.

[0033] Furthermore, the improved Bowers equation for the studied strata is as follows:

[0034]

[0035] In the above formula, This represents the effective stress of the formation. The P-wave velocity of the formation after hydration correction, in m / s; This is the formation density after hydration correction. ; Organic carbon content, % The maximum effective vertical stress at the start of unloading is expressed in MPa.

[0036] Furthermore, the effective stress of the formation is calculated using the following formula:

[0037]

[0038] In the above formula, The effective stress of the formation is expressed in MPa. The P-wave velocity of the formation after hydration correction, in m / s; This is the formation density after hydration correction. ; Organic carbon content, % The maximum effective vertical stress at the start of unloading is expressed in MPa.

[0039] Furthermore, the vertical stress is calculated using the following formula:

[0040]

[0041] In the above formula, ρ is the vertical stress, MPa; ρ is the density logging value. g is the acceleration due to gravity, with a value of 9.8. ; d represents the integral algorithm; h represents the depth corresponding to the density logging value, in meters.

[0042] Furthermore, the formation pore pressure of the studied strata is calculated using the following formula:

[0043]

[0044] In the above formula, Formation pore pressure, MPa; The effective stress of the formation is expressed in MPa. For vertical stress, MPa.

[0045] Compared with the prior art, this application has at least the following beneficial effects:

[0046] This application establishes a hydration correction equation and a method for recovering real formation data. Based on experimental data analysis and the analysis results of the formation pore pressure formation mechanism of the studied formation, a modified Bowers formation pore pressure prediction model based on formation density and formation organic carbon content is established. The modified model significantly improves the prediction accuracy. This modified model can provide accurate formation pore pressure data for drilling engineering, fracturing optimization, wellbore trajectory optimization, etc., reducing the occurrence of construction accidents and reducing development costs. Attached Figure Description

[0047] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a diagram showing the relationship between effective stress and longitudinal wave velocity during the loading and unloading processes in the embodiment.

[0049] Figure 2 This is a graph showing the relationship between rock acoustic velocity and organic carbon content in the examples;

[0050] Figure 3 This is a graph showing the relationship between the acoustic velocity and density of rock in the embodiment;

[0051] Figure 4 This example compares the acoustic velocity calculation results between the improved Bowers equation and the original Bowers equation.

[0052] Figure 5 This is a correlation diagram showing the relationship between the magnitude of rock density variation and the magnitude of resistivity variation in the example.

[0053] Figure 6 This is a correlation diagram showing the relationship between the variation amplitude of rock P-wave velocity and the variation amplitude of resistivity in the example.

[0054] Figure 7 Analysis diagram for studying the formation mechanism of pore pressure in strata

[0055] Figure 8 The example shows the fitting results of Bowers' loading equation;

[0056] Figure 9 The following is the fitting result of Bowers' unloading equation in the example;

[0057] Figure 10 shows the calculation results of formation pore pressure in the embodiment;

[0058] Figure 11 is a cross-sectional view of the formation pore pressure prediction in the embodiment. Detailed Implementation

[0059] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0060] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other. It should also be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments; similar or identical parts between embodiments can be referred to interchangeably.

[0061] The shale reservoir formation pore pressure prediction method based on the improved Bowers equation disclosed in this embodiment includes the following steps:

[0062] Step 1: Prepare experimental core data, geological data, drilling fluid for field drilling, logging data, and drilling and completion reports for the study area; describe the core samples obtained from the downhole experiments in the study area, and obtain the porosity and permeability, mineral composition, total organic carbon (TOC) content, density, resistivity, and acoustic velocity of the original rock samples.

[0063] Specifically, 20-30 standard rock samples are drilled. After drying the experimental samples, the core is first described, mainly including the apparent and lithological characteristics of the core. Then, the dried rock samples are tested for porosity, permeability, mineral composition, organic carbon content, density, resistivity, and acoustic velocity to obtain the porosity and permeability, mineral composition, total organic carbon (TOC), density, resistivity, and acoustic velocity of the original rock samples.

[0064] Step 2: Based on the organic carbon content test results of the rock samples, rock samples with different organic carbon content distribution ranges were selected. The formation loading process was simulated by increasing confining pressure and maintaining constant pore pressure, and the formation unloading process was simulated by maintaining constant confining pressure and increasing pore pressure. At each pressure point, the pressure was first maintained for 4 hours before acoustic wave testing was conducted to obtain the acoustic wave velocity at different pressure points. The test results are as follows: Figure 1 As shown. From Figure 1As can be seen, the rock acoustic velocity increases with increasing effective stress during both loading and unloading processes. Combining the test results from step 1, the correlation between rock acoustic velocity and parameters such as rock porosity, permeability, density, organic carbon content, quartz content, feldspar content, carbonate rock content, and clay mineral content at the same pressure point during loading and unloading was further analyzed. It was found that rock organic matter content and density exhibit a high correlation with rock acoustic velocity. Figure 2 , Figure 3 As shown.

[0065] Step 3: Based on Step 2, and in conjunction with the Bowers equation (as shown in Equation (1)), establish the acoustic wave velocity response equation based on the influence of density and organic matter content, that is, the improved Bowers equation considering organic matter content and rock density, as shown in Equation (2):

[0066] (1)

[0067] (2)

[0068] In the above formula, The velocity of sound is m / s; For density, ; Organic carbon content, % is the maximum vertical effective stress at the start of unloading, MPa; U is the elastic-plastic coefficient of the formation mudstone and shale, dimensionless; A, B, C, and D are coefficients in the formula, dimensionless.

[0069] Based on the experimental data, the fitted coefficients are shown in Table 1, and the calculated sound wave velocity is as follows: Figure 4 As shown in the figure, the improved Bowers equation calculates a smaller difference in rock acoustic wave velocity, resulting in more accurate predictions.

[0070] Table 1: Correction Factors

[0071]

[0072] Step 4: Immersion experiments were conducted on the collected rock samples using drilling fluid from the field. During the immersion process, the rock samples and drilling fluid underwent hydration, thereby altering the physical properties of the rock. The resistivity, acoustic velocity, and density of the rock samples were measured after immersion. The results showed that the density, resistivity, and acoustic velocity of the rock samples decreased after immersion. Using the magnitude of resistivity change as the independent variable and the magnitudes of density and P-wave velocity change as dependent variables, statistical analysis revealed a good relationship between the magnitudes of density and P-wave velocity changes and the magnitudes of resistivity changes after hydration caused by drilling fluid intrusion. Figure 5 , Figure 6 As shown:

[0073] (3)

[0074] (4)

[0075] (5)

[0076] (6)

[0077] (7)

[0078] In the above formula, The P-wave velocity of the formation in well logging data, in m / s; The P-wave velocity of the formation after hydration correction, in m / s; For formation density in well logging data, ; This is the formation density after hydration correction. ; ρ represents the resistivity of the dried rock sample, in Ω·m; The resistivity of the rock sample after hydration is expressed in Ω·m. This represents the range of density change in the rock sample after hydration. The amplitude of the change in longitudinal wave velocity after hydration. This represents the magnitude of the resistivity change after hydration. It can be calculated using formula (8).

[0079] Step 5: During drilling, drilling fluid invades the formation, altering its rock physical properties. Dual-lateral resistivity logging can reflect the difference in resistivity between the intruded zone and the original formation, particularly in deep dual-lateral resistivity logging. Reflects the original formation resistivity, shallow bilateral resistivity Reflecting the formation resistivity of the intruded zone, the magnitude of the change in formation resistivity after drilling fluid intrusion can be obtained:

[0080] (8)

[0081] In the above formula, This represents the change in formation resistivity after drilling fluid intrusion. This is the conversion coefficient between the indoor resistivity of the rock sample and the resistivity of the well logging; The value represents the deep lateral resistivity, in Ω·m. The value represents the shallow lateral resistivity in Ω·m.

[0082] Step 6: Based on the information such as sonic transit time, density, and shallow and deep resistivity in the well logging data, and according to the inverse operation of (Formula 3) and (Formula 4), the formation P-wave velocity and density after hydration correction can be obtained as follows:

[0083] (9)

[0084] (10)

[0085] In the above formula, The P-wave velocity of the formation in well logging data, in m / s; The P-wave velocity of the formation after hydration correction, in m / s; For formation density in well logging data, ; This is the formation density after hydration correction. .

[0086] Step 7: Based on the geological and well logging data collected in Step 1, conduct an analysis of the formation anomaly pressure formation mechanism. Collect measured formation pore pressure data and depths from the geological data, and combine this with well logging data to obtain data such as acoustic velocity and compensated density corresponding to the measured formation pore pressure depth points. Based on this data, plot an acoustic velocity-density cross-plot, such as... Figure 7 As shown, from Figure 7 As can be seen from the data, the formation pore pressure of the studied strata is mainly caused by three mechanisms: tectonic compression, hydrocarbon generation-induced pressure, and undercompaction.

[0087] Step 8: Based on the hydration-corrected acoustic velocity and density data, draw a diagram analyzing the formation pressure mechanism, as shown below. Figure 7 As shown, if the formation is under normal pressure, the data points should be concentrated around the black fitted line. However, the data points of the target formation, the Lucaogou Formation, are relatively dispersed, with some data points far from the standard fitted line. Combined with research on the causes of abnormal pressure loading and unloading in formations, it can be analyzed that the target formation is affected by tectonic compression, hydrocarbon generation, and undercompaction, resulting in abnormally high pressure. Therefore, the Bowers method, suitable for formations with abnormal pressure, is used for prediction. Based on the measured pressure data of the formation, and according to Bowers' loading and unloading equations, the measured formation acoustic velocity is used... The result of hydration correction Effective stress Maximum vertical effective stress at the start of unloading of the overlying cover Substituting the Bowers loading and unloading equations into formula (1), the coefficients A, B, and U in the Bowers equations are obtained respectively: A = 274.52, B = 0.6478, and U = 1.2. Figure 8and Figure 9 As shown.

[0088] The Bowers equation for the studied strata is then obtained, as shown in equation (11):

[0089] (11)

[0090] In the above formula, The P-wave velocity of the formation after hydration correction, in m / s; This represents the effective stress of the formation. The maximum effective vertical stress at the start of unloading is expressed in MPa.

[0091] Formula (11) can be used to calculate the pore pressure of the formation. The calculation results are as follows: Figure 10 As shown, from Figure 10 It can be seen that the relative error of the formation pore pressure prediction results based on the Bowers equation is 85.68%.

[0092] Step 9: Based on the improved Bowers equation form constructed in Step 3 (as shown in Equation (2)), combined with density logging information and organic carbon content logging calculation results, read the density and organic carbon content corresponding to the depth of the measured pore pressure point in the formation. Considering the influence of density and organic carbon content, the Bowers unloading equation shown in Equation (11) is modified to obtain the improved Bowers equation for the studied formation, as shown in Equation (12):

[0093] (12)

[0094] In the above formula, This represents the effective stress of the formation. The P-wave velocity of the formation after hydration correction, in m / s; This is the formation density after hydration correction. ; Organic carbon content, % The maximum effective vertical stress at the start of unloading is expressed in MPa.

[0095] Step 10: Based on the Bowers correction model established in Step 9, the effective stress of the formation is calculated by using the measured sonic velocity logging data of the formation obtained from the logging data. The calculation formula is shown in Equation (13). At the same time, based on the density logging data in the logging data, the vertical stress, i.e. the overlying formation pressure, is calculated using Equation (13).

[0096] (13)

[0097] (14)

[0098] In the above formula, The effective stress of the formation is expressed in MPa. The P-wave velocity of the formation after hydration correction, in m / s; This is the formation density after hydration correction. ; Organic carbon content, % The maximum effective vertical stress at the start of unloading, in MPa; ρ is the vertical stress, MPa; ρ is the density logging value. g is the acceleration due to gravity, with a value of 9.8. h represents the depth measured by density logging, in meters; d represents the integral algorithm.

[0099] Step 11: Based on the vertical stress and effective formation stress obtained in step 10, the formation pore pressure of the studied formation can be obtained by using equation (15).

[0100] (15)

[0101] In the above formula, Formation pore pressure, MPa; The effective stress of the formation is expressed in MPa. The vertical stress is measured in MPa.

[0102] The formation pore pressure calculated using formula (15) is as follows: Figure 10 As shown in the figure, the relative error of the formation pore pressure prediction results based on the improved Bowers equation is 92.13%, and the prediction accuracy is improved by 6.45%. The well logging prediction profile is shown below. Figure 11 As shown, the formation pore pressure prediction results based on the improved Bowers equation are in better agreement with the measured results.

[0103] It should be noted that when hydration occurs in shale formations, it is not necessary to perform hydration correction on well logging information such as formation density and P-wave velocity.

[0104] This invention establishes a hydration correction equation and a method for recovering real formation data. Based on experimental data analysis and the analysis results of the formation pore pressure formation mechanism, a modified Bowers formation pore pressure prediction model based on formation density and formation organic carbon content is established. The modified model significantly improves prediction accuracy. This modified model can provide accurate formation pore pressure data for drilling engineering, fracturing optimization, and wellbore trajectory optimization, reducing the occurrence of construction accidents and lowering development costs.

[0105] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A well logging prediction method for shale reservoir formation pore pressure based on an improved Bowers equation, characterized in that, Includes the following steps: Based on the Bowers equation, a sound wave velocity response equation considering the effects of density and organic matter content is established. Immersion experiments were conducted on the collected rock samples, and the resistivity, acoustic velocity, and density of the rock samples after immersion were measured to obtain the relationship between the density change, longitudinal wave velocity change, and resistivity change after drilling fluid intrusion and hydration. Based on the relationship between the density change, P-wave velocity change, and resistivity change after drilling fluid intrusion and hydration, and using the sonic velocity, density, and depth-level resistivity from well logging data, the hydration-corrected sonic velocity and density are obtained: Based on the acoustic velocity and density of the undisturbed formation after hydration correction, the measured acoustic velocity of the formation will be... The result of hydration correction Effective stress Maximum vertical effective stress at the start of unloading of the overlying cover Substituting Bowers' loading and unloading equations, we obtain the Bowers equations for the studied formation. Based on the sonic wave velocity response equation that takes into account the influence of density and organic matter content, combined with density logging information and organic carbon content logging calculation results, the density and organic carbon content corresponding to the depth of the formation pressure measurement point are read, and the unloading equation of the Bowers equation of the studied formation is modified to obtain the improved Bowers equation of the studied formation. Based on the improved Bowers equation, the sonic velocity before formation hydration is calculated by back-calculating the measured sonic velocity data obtained from the well logging data, and the effective stress of the formation is calculated; the formation density before formation hydration is calculated by back-calculating the density data from the well logging data, and the vertical stress is calculated. Based on the effective stress and vertical stress of the formation, the formation pore pressure of the studied formation was calculated. The acoustic wave velocity response equation considering the effects of density and organic matter content is as follows: ， In the above formula, The velocity of sound is m / s; For density, ; Organic carbon content, % The maximum effective vertical stress at the start of unloading is MPa; U is the elastic-plastic coefficient of the formation mudstone and shale, dimensionless; A, B, C, and D are coefficients in the formula, dimensionless. The relationship between the magnitude of density change, the magnitude of longitudinal wave velocity change, and the magnitude of resistivity change is as follows: ， ， ， In the above formula, ρ represents the resistivity of the dried rock sample, in Ω·m; The resistivity of the rock sample after hydration is expressed in Ω·m. This represents the range of density change in the rock sample after hydration. The amplitude of the change in longitudinal wave velocity after hydration. The magnitude of the resistivity change after hydration; The formulas for calculating the hydration-corrected sound wave velocity and density are as follows: ， ， In the above formula, The P-wave velocity of the formation after hydration correction, in m / s; This is the formation density after hydration correction. ; The P-wave velocity of the formation in well logging data, in m / s; For formation density in well logging data, ; The range of rock sample density variation, The amplitude of the longitudinal wave velocity variation; The improved Bowers equation for the studied strata is: ， In the above formula, The P-wave velocity of the formation after hydration correction, in m / s; This represents the effective stress of the formation. This is the formation density after hydration correction. ; Organic carbon content, % The maximum effective vertical stress at the start of unloading is expressed in MPa.

2. The method for predicting formation pore pressure in shale reservoirs based on the improved Bowers equation according to claim 1, characterized in that, The loading and unloading equations for Bowers are as follows: Loading curve: , Unloading curve: , In the above formula, The velocity of sound is m / s; This represents the effective stress of the formation. is the maximum vertical effective stress at the start of unloading, MPa; U is the elastic-plastic coefficient of the formation mudstone and shale, dimensionless; A and B are coefficients in the formula, dimensionless.

3. The method for predicting formation pore pressure in shale reservoirs based on the improved Bowers equation according to claim 1, characterized in that, The Bowers equation for the studied strata is: ， In the above formula, The P-wave velocity of the formation after hydration correction, in m / s; This represents the effective stress of the formation. The maximum effective vertical stress at the start of unloading is expressed in MPa.

4. The method for predicting formation pore pressure in shale reservoirs based on the improved Bowers equation according to claim 1, characterized in that, The effective stress of the formation is calculated using the following formula: ， In the above formula, The effective stress of the formation is expressed in MPa. The P-wave velocity of the formation after hydration correction, in m / s; This is the formation density after hydration correction. ; Organic carbon content, % The maximum effective vertical stress at the start of unloading is expressed in MPa.

5. The method for predicting formation pore pressure in shale reservoirs based on the improved Bowers equation according to claim 1, characterized in that, The vertical stress is calculated using the following formula: ， In the above formula, The vertical stress is measured in MPa. ρ is the density logging value. g is the acceleration due to gravity, with a value of 9.

8. h represents the depth corresponding to the density logging value, in meters.

6. The method for predicting formation pore pressure in shale reservoirs based on the improved Bowers equation as described in claim 1, characterized in that, The formation pore pressure of the studied strata is calculated using the following formula: ， In the above formula, Formation pore pressure, MPa; The effective stress of the formation is expressed in MPa. For vertical stress, MPa.

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