Method for calculating pore pressure in a formation based on construction compression

Abstract

The application provides a calculation method of pore pressure of a tectonic compression formation. The calculation method of pore pressure of the tectonic compression formation comprises the following steps: S1, obtaining a density trend curve, and performing integral calculation on the density trend curve to obtain overburden pressure S V ; S2, determining total porosity POR of the formation based on acoustic logging, density logging, neutron logging or nuclear magnetic resonance logging; S3, analyzing characteristics of a target layer section to determine a tectonic compression coefficient ACm_C of the formation; S4, solving a pore pressure coefficient PP of a mudstone section based on a pore pressure model corrected based on the tectonic compression coefficient ACm_C; S5, determining a relationship between effective stress P eff and biot coefficient α and total porosity POR; and S6, inversely deducing a pore pressure coefficient of a reservoir section according to the relationship between the effective stress P eff and the total porosity POR. The application solves the problem of low calculation accuracy of the pore pressure calculation method in the prior art.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas exploration equipment, in particular to a method for calculating pore pressure of a formation based on structural compression. BACKGROUND

[0002] Formation pore pressure is always involved in various important links of oil and gas field exploration and development, especially in the drilling process, fracturing operation and oil and gas field production process. Abnormal high pressure or overpressure is a hot issue in oil and gas geology and exploration research due to its universality in oil and gas bearing basin, close relationship with oil and gas reservoir formation and importance to drilling safety. It also has an important influence on initial production efficiency and reservoir quality. Therefore, accurately predicting formation pore pressure is crucial to oil and gas field exploration and development.

[0003] At present, overpressure origin identification and pressure calculation are always difficult problems. Different overpressure origins have different relationships with oil and gas reservoir formation and distribution, and the methods used for pressure calculation are also different. The current pore pressure calculation method is based on the effective stress model of shallow formation, which is mainly aimed at the undercompaction origin of formation. As for the structural compression origin of deep formation, it can further strengthen the compaction of rock. The overpressure generated by this mechanism will lead to an abnormal low porosity anomaly in the overpressure zone, making it difficult to find overpressure. The deviation of this overpressure formation mechanism from the compaction curve is in the opposite direction of other overpressure formation mechanisms. Therefore, the overpressure caused by tectonic action cannot be directly calculated by density, acoustic wave or porosity, resulting in low calculation accuracy of deep formation pore pressure.

[0004] That is, the pore pressure calculation method in the prior art has the problem of low calculation accuracy. SUMMARY

[0005] The main purpose of the present application is to provide a method for calculating pore pressure of a formation based on structural compression, to solve the problem of low calculation accuracy of pore pressure calculation method in the prior art.

[0006] In order to achieve the above purpose, the present application provides a method for calculating pore pressure of a formation based on structural compression, comprising the following steps: step S1: obtaining a density trend curve, calculating the overburden pressure by integrating the density trend curve ; step S2: determining the total porosity POR of the formation based on acoustic wave, density, neutron logging or nuclear magnetic resonance logging; step S3: analyzing the characteristics of the target layer section to determine the structural compression coefficient ACm_C of the formation; step S4: solving the pore pressure coefficient of the mudstone section based on the pore pressure model corrected by the structural compression coefficient ACm_C ; step S5: determining the effective stress and biot coefficient Relationship with total porosity POR; Step S6: According to effective stress The relationship with the total porosity POR is used to infer the pore pressure coefficient of the reservoir section.

[0007] Furthermore, in step S1, the overburden pressure satisfy:

[0008] ; Formula (1);

[0009] in, is the vertical depth, is the acceleration due to gravity, is the rock density.

[0010] Furthermore, in step S1, the rock density satisfy:

[0011] ; Formula (2);

[0012] in, It is the time difference of sound waves.

[0013] Furthermore, in step S3, the compression coefficient ACm_C is constructed as the target layer stable reservoir segment The average value of satisfy:

[0014] ; Formula (3);

[0015] in, is the acoustic transit time, and POR is the total porosity.

[0016] Furthermore, in step S4, the pore pressure coefficient satisfy:

[0017] ; Formula (4);

[0018] in, is the overburden pressure, is the hydrostatic column pressure, is the time difference of sound waves, Fit the acoustic transit time to the normal trend equation for mudstone compaction, is the vertical depth, and k is the Eaton coefficient.

[0019] Furthermore, it satisfies:

[0020] ; Formula (5);

[0021] wherein, is the tectonic compression coefficient, is the surface acoustic time difference, is the vertical depth, and C is a constant.

[0022] Further, in step S5, the following is satisfied:

[0023] Equation (6);

[0024] wherein, is the effective stress, and POR is the total porosity.

[0025] Further, in step S5, the following is satisfied:

[0026] Equation (7);

[0027] wherein, is the biot coefficient, and POR is the total porosity.

[0028] Further, in step S6,

[0029] Equation (8); Equation (9);

[0030] wherein, is the overburden pressure, POR is the total porosity, is the vertical depth, and A is an adjustment parameter, is the biot coefficient, is the effective stress, is the pore pressure coefficient.

[0031] Further, the adjustment parameter A is adjusted so that the pore pressure coefficients calculated by Equation (8) and Equation (9) are are matched in the shale section, and a continuous pore pressure coefficient profile is finally obtained.

[0032] The technical solution of the present application is applied to the method for calculating the pore pressure of a tectonic compression stratum, which comprises the following steps: step S1: obtaining a density trend curve, and calculating the overburden pressure by integrating the density trend curve ; step S2: determining the total porosity POR of the stratum based on acoustic logging, density logging, neutron logging or nuclear magnetic resonance logging; step S3: analyzing the characteristics of the target section to determine the tectonic compression coefficient ACm_C; step S4: solving the pore pressure coefficient of the shale section based on the pore pressure model corrected by the tectonic compression coefficient ACm_C ; step S5: determining the effective stress and the biot coefficient according to the rock mechanics experimental data. Relationship with total porosity POR; Step S6: According to effective stress The relationship with the total porosity POR is used to infer the pore pressure coefficient of the reservoir section.

[0033] This application constructs the formation structural compression coefficient to obtain a normal trend equation based on the correction of the structural compression coefficient. Based on the normal trend equation corrected by the structural compression coefficient, combined with the relationship between effective stress and porosity, a continuous formation pore pressure calculation method is established, which can effectively avoid the inaccurate calculation of existing methods and the low accuracy of deep formation compaction trend equations, and provide more accurate formation pore pressure parameters for drilling and reservoir evaluation. Compared with traditional methods in the industry, the pore pressure calculated by the present invention has significantly improved calculation accuracy, and the implementation method is also more convenient. All parameters in the present invention can be obtained by calculation from other logging data without adding new costs. The calculated parameters are compared with the core experiment parameters. The absolute error of the pore pressure coefficient calculation is reduced to 0.1 MPa per 100 meters, and the accuracy can fully meet the technical requirements of shale oil and gas exploration and development. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0035] Figure 1 A flow chart showing a method for calculating pore pressure of a formation based on structural compression according to an alternative embodiment of the present invention;

[0036] Figure 2 A diagram showing the result of determining the structural compression coefficient ACm in step S2 of the method for calculating the pore pressure of a formation based on structural compression of the present invention;

[0037] Figure 3 A graph showing the relationship between effective stress and porosity in step S5 of the method for calculating pore pressure of a formation based on structural compression of the present invention;

[0038] Figure 4 A diagram showing the relationship between the biot coefficient and the porosity in step S5 of the method for calculating the pore pressure of a formation based on structural compression of the present invention;

[0039] Figure 5 Continuous pore pressure coefficient cross-sectional views are shown in step S6 of the method for calculating pore pressure of a formation based on structural compression according to the present invention. DETAILED DESCRIPTION

[0040] It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other in the case of no conflict. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0041] It should be noted that, unless otherwise specified, all technical and scientific terms used in the present application have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0042] In the present application, unless otherwise specified, the orientation words such as "upper", "lower", "top", "bottom" are generally directed to the directions shown in the drawings, or are directed to the vertical, perpendicular or gravity directions of the components themselves; similarly, for the convenience of understanding and description, "inner" and "outer" refer to the inner and outer relative to the contour of the components themselves, but the above orientation words are not used to limit the present application.

[0043] In order to solve the problem of low calculation accuracy of the pore pressure calculation method in the prior art, the present application provides a pore pressure calculation method based on tectonic compression strata.

[0044] As shown in Figures 1 to 5 , the pore pressure calculation method based on tectonic compression strata comprises the following steps:

[0045] Step S1: Obtain a density trend curve, and calculate the overburden pressure by integrating the density trend curve .

[0046] Step S2: Determine the total porosity POR of the strata based on acoustic logging, density logging, neutron logging or nuclear magnetic resonance logging

[0047] Step S3: Analyze the characteristics of the target layer section, and determine the tectonic compression coefficient ACm_C

[0048] Step S4: Correct the pore pressure model based on the tectonic compression coefficient ACm_C to solve the pore pressure coefficient of the mudstone section .

[0049] Step S5: Determine the relationship between the effective stress and biot coefficient and the total porosity POR according to the rock mechanics experimental data

[0050] Step S6: According to the relationship between the effective stress and the total porosity POR, the pore pressure coefficient of the reservoir section is inversely deduced.

[0051] The present application obtains a normal trend equation corrected based on a structure compression coefficient by constructing the structure compression coefficient. The normal trend equation corrected based on the structure compression coefficient, in combination with the relationship between the effective stress and the porosity, establishes a calculation method of continuous formation pore pressure, which can effectively avoid the problems of inaccurate calculation and low precision of deep formation compaction trend equation of the existing method, and provides more accurate formation pore pressure parameters for drilling and reservoir evaluation. The calculated pore pressure of the present application has significantly improved calculation precision compared with the traditional method in the industry, and the implementation method is also more convenient. All parameters in the present application can be calculated from other logging data, without increasing new cost. The absolute error of the pore pressure coefficient calculation is reduced to 0.1 MPa per 100 m by comparing the calculation parameters with the core experiment parameters, and the precision can fully meet the technical requirements of shale oil and gas exploration and development.

[0052] Specifically, in step S1, a density trend line is constructed based on a continuous measurement precision density curve, and the overburden pressure is calculated by using a density integration method The overburden pressure (unit: MPa) satisfies:

[0053] ; formula (1);

[0054] wherein, is the vertical depth (unit: m), is the gravity acceleration (unit: m / s 2 ), is the rock density (unit: g / cm 3 ).

[0055] satisfies:

[0056] ; formula (2);

[0057] wherein, is the acoustic travel time (unit: us / ft).

[0058] In summary, in step S1, the synthetic density is calculated by using the Gardner formula based on the acoustic travel time curve, referring to formula (2), the density trend curve from zero depth to the bottom of the well is constructed by combining the logging density curve and the synthetic density curve, the density trend curve is adjusted to make the wellhead and bottom nodes consistent with the logging density curve as much as possible, and the continuous density trend curve from the wellhead to the bottom of the well is integrated, referring to formula (1), to obtain the overburden pressure

[0059] In step S2, the total porosity POR of the formation is determined based on density, acoustic, neutron or nuclear magnetic resonance logging data. The total porosity POR of the formation can be directly obtained by nuclear magnetic resonance logging, and for no nuclear magnetic resonance logging, the total porosity POR of the formation can be calculated according to a volume model by conventional density, acoustic, neutron logging.

[0060] Specifically, in step S3, the lithologically stable reservoir section is selected to determine the structural compression coefficient ACm, see formula (3), indicating the degree of structural compression of the formation, and the average value of the ACm continuously calculated in this section of the lithologically stable reservoir section is taken as the final structural compression coefficient ACm_C. That is, the structural compression coefficient ACm_C is the average value of the stable reservoir section of the target layer , satisfies:

[0061] ; formula (3);

[0062] wherein, is the acoustic travel time, and POR is the total porosity of the formation (unit: %).

[0063] It should be noted here that POR=( ) / ( ft- ), is the acoustic, density or neutron logging value, is the skeleton value of the acoustic, density or neutron of the formation, ft is the fluid value of the acoustic, density or neutron of the formation.

[0064] Specifically, in step S4, the core parameter of the existing Eaton model is the trend line of the mudstone section, which cannot reflect the difference in the strength of structural compression of the formation, and will lead to a smaller calculated pore pressure. The present application introduces the structural compression coefficient to correct the trend line to the reservoir section, and constructs a normal trend equation based on the structural compression coefficient correction. The difference in the structural compression coefficient of the formation caused by the difference in the strength of structural compression of the deep formation, and the difference between the acoustic travel time of the reservoir and non-reservoir section and the trend line corrected by the structural compression can reflect the difference in the pore pressure. The pore pressure coefficient of the mudstone section of the formation can be calculated according to the Eaton model corrected by the structural compression coefficient, as shown in formula (4). The pore pressure coefficient (unit: MPa / 100m) satisfies:

[0065] ; formula (4);

[0066] wherein, is the overburden pressure, is the hydrostatic pressure (unit: MPa), is the acoustic travel time (unit: us / ft), is the acoustic travel time (unit: us / ft) fitted by the normal trend equation of shale compaction, is the vertical depth, and k is the Eaton coefficient.

[0067] Also meet:

[0068] Formula (5);

[0069] wherein, is the formation tectonic compression coefficient, is the surface acoustic travel time, is the vertical depth, and C is a constant.

[0070] In summary, the main parameters include the overburden pressure , formula 1, 2 can be obtained according to the density integral method, hydrostatic pressure is the depth Z divided by 100, the surface acoustic travel time is generally taken as 185, the constant C is 0.00137, the Eaton coefficient k is 3, and the tectonic compression coefficient ACm_C is constructed by determining the core parameters. The pore pressure coefficient of the shale section is calculated according to formula (4).

[0071] In step S5, formula (6) and formula (7) are met:

[0072] Formula (6);

[0073] wherein, is the effective stress (unit: Mpa), and POR is the total porosity of the formation.

[0074] Formula (7);

[0075] wherein, is the biot coefficient, and POR is the total porosity of the formation.

[0076] In step S6, the pore pressure coefficient of the reservoir section is inversely deduced according to the relationship between the effective stress and the porosity. According to the effective stress model, the effective stress, the overburden stress and the pore pressure meet the following relationship, see formula (8). Combined with formula (6) and formula (7), the relationship between the pore pressure and the porosity can be established, see formula (9). This relationship mainly meets in the reservoir section, and is affected by the lithology and physical properties of the reservoir section. It needs to be corrected by the pore pressure coefficient of the shale section according to formula (4). The method is: adjusting the adjustment parameter A, so that the pore pressure coefficients calculated by formula (4) and formula (8) are In the shale section, the continuous pore pressure coefficient profile is finally obtained.

[0077] ; Formula (8);

[0078] ; Formula (9);

[0079] in, is the overburden pressure, POR is the total porosity of the formation, is the vertical depth, A is the adjustment parameter, is the biot coefficient, is the effective stress, is the pore pressure coefficient.

[0080] The following describes the method for calculating pore pressure of a formation based on structural compression of the present invention in conjunction with specific embodiments. The method for calculating pore pressure of a formation based on structural compression of the present invention is illustrated by taking a deep reservoir of a well as an example.

[0081] Through step S1, based on the continuous logging density curve, the density integration method is used to calculate the overburden pressure , according to formula (1) and formula (2), the overburden pressure is calculated using conventional logging acoustic wave time difference and density curve .

[0082] In step S2, the total formation porosity (POR) is determined based on density, acoustic, neutron or nuclear magnetic resonance logging data. The total formation porosity (POR) is obtained using nuclear magnetic resonance logging. If nuclear magnetic resonance logging is not available, the total formation porosity (POR) is calculated using conventional density, acoustic or neutron logging based on a volume model.

[0083] In step S3, according to formula (3), the structural compression curve ACm is calculated using the conventional logging acoustic time difference curve and the total porosity POR. The structural compression coefficient ACm_C is determined by taking the average value of the lithologic stable reservoir section to indicate the degree of structural compression of the formation: Figure 2 As shown in the figure, the stable reservoir section of 4820-5400m was selected according to the calculated ACm curve, and the average value was taken to determine the structural compression coefficient ACm_C value.

[0084] In step S4, the compressibility-corrected Eaton model is constructed according to formula (4) and formula (5) to calculate the pore pressure coefficient of the mudstone section of the formation.

[0085] In step S5, the relationship between effective stress and biot coefficient and porosity is determined according to the experimental data. According to the rock mechanics experimental data, the relationship between effective stress and biot coefficient and porosity is determined as follows: Figure 3 and Figure 4 , and calculate the biot coefficient according to formula (6) and formula (7).

[0086] In step S6, the pore pressure coefficient of the reservoir section is calculated according to formula (8) and formula (9), and the pore pressure coefficient of the mudstone section is corrected by combining formula (4) as follows: Figure 5 As mentioned above, the parameter A is adjusted to make the pore pressure coefficient PP calculated by formula (8) and formula (9) coincide in the mudstone section of 4570-4630m, and finally a continuous pore pressure coefficient profile is obtained. Figure 5 ,It can be seen from the figure that the accuracy of the results calculated by this achievement is greatly improved in line with the test pore pressure.

[0087] Obviously, the embodiments described above are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0088] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, tasks, devices, components and / or combinations thereof.

[0089] It should be noted that the terms "first," "second," and the like in the specification and claims of this application and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein.

[0090] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for calculating pore pressure of a formation based on structural compression, characterized in that: The steps include: Step S1: Obtain a density trend curve and calculate the overburden pressure by integrating the density trend curve. ; Step S2: determining the total formation porosity POR based on acoustic, density, neutron logging or nuclear magnetic resonance logging; Step S3: Analyze the characteristics of the target layer segment and determine the formation structural compression coefficient ACm_C; the structural compression coefficient ACm_C is the target layer stable reservoir segment The average value of satisfy: ; Formula (3); where, is the acoustic transit time, POR is the total porosity; Step S4: Solve the pore pressure coefficient of the mudstone section based on the pore pressure model corrected by the structural compressibility coefficient ACm_C ; The pore pressure coefficient satisfy: ; Formula (4); where, is the overburden pressure, is the hydrostatic column pressure, is the time difference of sound waves, Fit the acoustic transit time to the normal trend equation for mudstone compaction, is the vertical depth, k is the Eaton coefficient; ; Formula (5); where, To construct the compression coefficient, is the surface acoustic time difference, is the vertical depth, C is a constant; Step S5: Determine the effective stress based on rock mechanics experimental data and biot coefficient Relationship with the total porosity POR respectively; Step S6: According to the effective stress The relationship between the total porosity POR and the reservoir section pore pressure coefficient is inversely calculated; ; Formula (8); ; Formula (9); where, is the overburden pressure, POR is the total porosity, is the vertical depth, A is the adjustment parameter, is the biot coefficient, is the effective stress, is the pore pressure coefficient; adjust the adjustment parameter A so that the pore pressure coefficient calculated by formula (8) and formula (9) The results are consistent in the mudstone section, and finally a continuous pore pressure coefficient profile is obtained.

2. The method for calculating pore pressure of a formation based on structural compression according to claim 1, characterized in that: In step S1, the overburden pressure satisfy: Formula (1) in, is the vertical depth, is the acceleration due to gravity, is the rock density.

3. The method for calculating pore pressure of a formation based on structural compression according to claim 2, characterized in that: In step S1, the rock density satisfy: Formula (2) in, It is the time difference of sound waves.

4. The method for calculating pore pressure of a formation based on structural compression according to claim 1, characterized in that: In step S5, the following conditions are met: Formula (6) in, is the effective stress and POR is the total porosity.

5. The method for calculating pore pressure of a formation based on structural compression according to claim 1, characterized in that: In step S5, the following conditions are met: Formula (7) in, is the biot coefficient, and POR is the total porosity.

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