Method for calculating pore pressure of stratum based on tectonic compression

Abstract

The invention provides a method for calculating pore pressure of a stratum based on tectonic compression. The calculation method for the pore pressure of the stratum based on the tectonic compression comprises the steps that S1, a density trend curve is obtained, and integration is conducted on the density trend curve to calculate the overlying stratum pressure SV; s2, based on sound waves, density, neutron logging or nuclear magnetic resonance logging, the total porosity POR of the stratum is determined; s3, analyzing features of a target interval, and determining a stratigraphic structure compression coefficient ACmC; s4, solving the pore pressure coefficient PP of the mudstone section based on the pore pressure model corrected by the tectonic compression coefficient ACmC; s5, determining the relationship between the effective stress Peff and the total porosity POR and the relationship between the effective stress coefficient alpha and the total porosity POR and the relationship between the effective stress coefficient alpha and the total porosity POR; s6, according to the relation between the effective stress Peff and the total porosity POR, the reservoir section pore pressure coefficient is reversely deduced. According to the invention, the problem of low calculation precision of a pore pressure calculation method in the prior art is solved.

Description

Technical Field

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

[0002] Formation pore pressure always runs through all important links of oil and gas field exploration and development, especially in the drilling process, fracturing construction, and oil and gas field production process. Abnormally high pressure or overpressure has always been a hot issue in oil and gas geology and exploration research due to its universal distribution in oil and gas basins, its close relationship with oil and gas reservoir formation, and its importance to drilling safety. It also has an important impact on the initial production efficiency and reservoir quality. Therefore, accurate prediction of formation pore pressure is crucial to oil and gas field exploration and development.

[0003] At present, the identification of overpressure causes and pressure calculation have always been difficult problems. Overpressures of different causes have different relationships with the formation and distribution of oil and gas reservoirs, and the methods used for pressure calculation are also different. At present, the pore pressure calculation methods are all based on the effective stress model of the middle and shallow layers, which is mainly aimed at the under-compaction causes of the formation. As for the deep structural compression causes, it can cause the compaction of rocks to be further strengthened. The overpressure generated by this mechanism will cause abnormally low porosity anomalies in the overpressure zone, making it difficult to detect overpressure. Its generation is a deviation from the compaction curve in the opposite direction of other overpressure formation mechanisms. Therefore, the overpressure caused by tectonic action cannot generally be directly calculated by density, acoustic waves or porosity, resulting in low accuracy in the calculation of pore pressure in deep oil and gas formations.

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

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

[0006] In order to achieve the above object, the present invention provides a method for calculating the pore pressure of a formation based on structural compression, comprising the following steps: Step S1: obtaining a density trend curve, and calculating the overburden formation pressure S by integrating the density trend curve. V ; Step S2: Determine the total porosity POR of the formation based on acoustic wave, density, neutron logging or nuclear magnetic resonance logging; Step S3: Analyze the characteristics of the target layer and determine the formation structural compression coefficient ACm_C; Step S4: Solve the pore pressure coefficient PP of the mudstone section based on the pore pressure model corrected by the structural compression coefficient ACm_C; Step S5: Determine the effective stress P according to the rock mechanics experimental data effand biot coefficient α and the total porosity POR respectively; Step S6: According to the effective stress P eff 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 S V satisfy:

[0008]

[0009] Where Z is the vertical depth, g is the acceleration due to gravity, and ρ is the rock density.

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

[0011]

[0012] Among them, Δt is the time difference of the sound wave.

[0013] Further, in step S3, the compression coefficient ACm_C is constructed as the average value of the stable reservoir section ACm of the target layer, and ACm satisfies:

[0014] ACm=Δt / (100-POR)*100; Formula (3)

[0015] Where Δt is the acoustic time difference and POR is the total porosity.

[0016] Further, in step S4, the pore pressure coefficient PP satisfies:

[0017]

[0018] Among them, S V is the overburden pressure, Ph is the hydrostatic pressure, Δt is the acoustic time difference, Δt ACm The normal trend equation for mudstone compaction is fitted with the acoustic time difference, where Z is the vertical depth and k is the Eaton coefficient.

[0019] Furthermore, it satisfies:

[0020] Δt ACm =ACm_C+(Δt mf -ACm_C)×e -CZ ; Formula (5)

[0021] Where ACm_C is the structural compression coefficient, Δt mf is the surface acoustic wave time difference, Z is the vertical depth, and C is a constant.

[0022] Furthermore, in step S5, the following conditions are satisfied:

[0023] Peff =-14.55*ln(POR)+6.3166; Formula (6)

[0024] Among them, P eff is the effective stress and POR is the total porosity.

[0025] Furthermore, in step S5, the following conditions are satisfied:

[0026] α=1.154*POR+0.717; Formula (7)

[0027] Among them, α is the biot coefficient and POR is the total porosity.

[0028] Further, in step S6,

[0029] P eff =S V -α*PP; Formula (8)

[0030] PP=(((S V +14.55*log(POR)-6.3166) / Z·100)+A) / α; Formula (9)

[0031] Among them, S V is the overburden pressure, POR is the total porosity, Z is the vertical depth, A is the adjustment parameter, α is the biot coefficient, P eff is the effective stress and PP is the pore pressure coefficient.

[0032] Furthermore, the adjustment parameter A is adjusted to make the pore pressure coefficient PP calculated by formula (4) and formula (8) stable in the mudstone section, and finally a continuous pore pressure coefficient profile is obtained.

[0033] The method for calculating the pore pressure of a stratum based on structural compression by applying the technical solution of the present invention comprises the following steps: Step S1: obtaining a density trend curve, and calculating the overburden stratum pressure S by integrating the density trend curve. V ; Step S2: Determine the total porosity POR of the formation based on acoustic wave, density, neutron logging or nuclear magnetic resonance logging; Step S3: Analyze the characteristics of the target layer and determine the structural compression coefficient ACm_C; Step S4: Solve the pore pressure coefficient PP of the mudstone section based on the pore pressure model corrected by the structural compression coefficient ACm_C; Step S5: Determine the effective stress P according to the rock mechanics experimental data eff and biot coefficient α and the total porosity POR respectively; Step S6: According to the effective stress P eff The relationship with the total porosity POR is used to infer the pore pressure coefficient of the reservoir section.

[0034] This application obtains a normal trend equation based on the correction of the structural compression coefficient by constructing the formation structure 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 calculated 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

[0035] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0036] 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;

[0037] Figure 2 A diagram showing the determination result of 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;

[0038] 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;

[0039] Figure 4 A graph 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;

[0040] Figure 5 The continuous pore pressure coefficient cross-section diagram of step S6 of the method for calculating the pore pressure of a formation based on structural compression of the present invention is shown. DETAILED DESCRIPTION

[0041] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0042] It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meanings as commonly understood by ordinary technicians in the technical field to which this application belongs.

[0043] In the present invention, unless otherwise specified, the directional words used, such as "up, down, top, bottom", usually refer to the directions shown in the drawings, or to the components themselves in the vertical, perpendicular or gravity directions; similarly, for ease of understanding and description, "inside and outside" refer to the inside and outside relative to the outline of each component itself, but the above-mentioned directional words are not used to limit the present invention.

[0044] In order to solve the problem of low calculation accuracy in the prior art pore pressure calculation method, the present invention provides a calculation method for pore pressure of a formation based on structural compression.

[0045] like Figures 1 to 5 As shown, the method for calculating the pore pressure of the formation based on structural compression includes the following steps:

[0046] Step S1: Obtain the density trend curve and calculate the overburden pressure S by integrating the density trend curve. V ;

[0047] Step S2: Determine the total formation porosity POR based on acoustic wave, density, neutron logging or nuclear magnetic resonance logging;

[0048] Step S3: Analyze the characteristics of the target layer segment and determine the structural compression coefficient ACm_C;

[0049] Step S4: solving the pore pressure coefficient PP of the mudstone section based on the pore pressure model corrected by the structural compressibility coefficient ACm_C;

[0050] Step S5: Determine the effective stress P according to the rock mechanics experimental data eff and biot coefficient α and the total porosity POR, respectively;

[0051] Step S6: According to the effective stress P eff The relationship with the total porosity POR is used to infer the pore pressure coefficient of the reservoir section.

[0052] This application obtains a normal trend equation based on the correction of the structural compression coefficient by constructing the formation structure 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 calculated 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.

[0053] Specifically, in step S1, based on the continuous measurement precision curve, a density trend line is constructed, and the overburden pressure S is calculated using the density integration method. V , overburden pressure S V (Unit: MPa) meets:

[0054]

[0055] Where Z is the vertical depth (unit: m), g is the gravitational acceleration (unit: m / s 2 ), ρ is the rock density (unit: g / cm 3 ).

[0056] ρ satisfies:

[0057]

[0058] Among them, Δt is the sound wave time difference (unit: us / ft).

[0059] In summary, in step S1, the synthetic density is calculated based on the acoustic time difference curve using the Gardner formula, see formula (2), and the well logging density curve and the synthetic density curve are combined to construct a density trend curve from zero depth to the bottom of the well. The density trend curve is adjusted to make the top and bottom nodes of the well as consistent as possible with the well logging density curve. The continuous density trend curve is integrated from the wellhead to the bottom of the well, see formula (1), and the overburden pressure S is obtained. V .

[0060] In step S2, the total formation porosity POR is determined based on density, acoustic wave, neutron or nuclear magnetic resonance logging data. Nuclear magnetic resonance logging can directly obtain the total formation porosity POR. If there is no nuclear magnetic resonance logging, conventional density, acoustic wave, and neutron logging can calculate the total formation porosity POR based on the volume model.

[0061] Specifically, in step S3, a lithologically stable reservoir section is selected to determine the structural compression coefficient ACm, referring to formula (3), indicating the degree of stratum structural compression, and the average value of ACm continuously calculated in the lithologically stable reservoir section is taken as the final structural compression coefficient ACm_C. In other words, the structural compression coefficient ACm_C is the average value of ACm in the target layer stable reservoir section, and ACm satisfies:

[0062] ACm=Δt / (100-POR)*100; Formula (3)

[0063] Wherein, Δt is the acoustic time difference, and POR is the total porosity of the formation (unit: %).

[0064] It should be noted here that POR = (ΔX-ΔXma) / (ΔXft-ΔXma), ΔX is the acoustic wave, density or neutron logging value, ΔXma is the skeleton value of the formation acoustic wave, density or neutron, and ΔXft is the fluid value of the formation acoustic wave, density or neutron.

[0065] Specifically, in step S4, the core parameter of the Eaton model in the prior art is the trend line of the mudstone section, which cannot reflect the difference in the strength of structural compression of the formation, and will cause the calculated pore pressure to be too small. The present application introduces a 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 strength of deep formation structural compression leads to the difference in the formation structural compression coefficient, and the difference between the trend lines of the acoustic time difference between the reservoir and non-reservoir sections relative to the structural compression correction can reflect the difference in pore pressure. The pore pressure coefficient of the mudstone section of the formation can be calculated based on the Eaton model corrected by the structural compression coefficient, refer to formula (4). The pore pressure coefficient PP (unit: MPa / 100m) satisfies:

[0066]

[0067] Among them, S V is the overburden pressure, P h is the hydrostatic column pressure (unit: MPa), Δt is the acoustic time difference (unit: us / ft), Δt ACm The normal trend equation for mudstone compaction is fitted with the acoustic time difference (unit: us / ft), Z is the vertical depth, and k is the Eaton coefficient.

[0068] Also meets:

[0069] Δt ACm =ACm_C+(Δt mf -ACm_C)×e -CZ ; Formula (5)

[0070] Among them, ACm_C is the stratum structural compression coefficient, Δtmf is the surface acoustic wave time difference, Z is the vertical depth, and C is a constant.

[0071] In summary, the main parameters include the overburden pressure S V , formula (1) and (2) can be obtained according to the density integration method, the static liquid column pressure P h The depth Z is divided by 100, and the surface acoustic wave time difference Δt mf Generally, it is taken as 185, the constant C is 0.00137, the Eaton coefficient k is 3, and the compression coefficient ACm_C is determined by determining the core parameter structure. The pore pressure coefficient of the mudstone section is calculated according to formula (4).

[0072] In step S5, formula (6) and formula (7) are satisfied:

[0073] P eff =-14.55*ln(POR)+6.3166; Formula (6)

[0074] Among them, P eff is the effective stress (unit: MPa), and POR is the total porosity of the formation.

[0075] α=1.154*POR+0.717; Formula (7)

[0076] Among them, α is the biot coefficient and POR is the total porosity of the formation.

[0077] In step S6, the pore pressure coefficient of the reservoir section is inferred based on the relationship between effective stress and porosity. Specifically, according to the effective stress model, the effective stress, the overlying formation stress and the pore pressure satisfy the following relationship, see formula (8). Combining formula (6) and formula (7), the relationship between pore pressure and porosity can be established, see formula (9). This relationship is mainly satisfied in the reservoir section. Affected by the lithology and physical properties of the reservoir section, it is necessary to correct it by combining the pore pressure coefficient of the mudstone section in formula (4). The method is as follows: adjust the adjustment parameter A so that the pore pressure coefficient PP calculated by formula (4) and formula (8) is stable in the mudstone section, and finally obtain a continuous pore pressure coefficient profile.

[0078] P eff =S V -α*PP; Formula (8)

[0079] PP=(((S V +14.55*log(POR)-6.3166) / Z·100)+A) / α; Formula (9)

[0080] Among them, S V is the overburden pressure, POR is the total porosity of the formation, Z is the vertical depth, A is the adjustment parameter, α is the biot coefficient, Peff is the effective stress and PP is the pore pressure coefficient.

[0081] The following describes the method for calculating pore pressure of a formation based on structural compression of the present application in conjunction with specific embodiments. The method for calculating pore pressure of a formation based on structural compression of the present invention is described by taking a deep reservoir of a well as an example.

[0082] Through step S1, based on the continuous logging density curve, the overburden pressure S is calculated by density integration method. V According to formula (1) and formula (2), the overburden pressure S is calculated using conventional logging acoustic wave time difference and density curve. V .

[0083] Through step S2, the total formation porosity POR is determined based on density, acoustic wave, neutron or nuclear magnetic resonance logging data. The total formation porosity POR is obtained by nuclear magnetic resonance logging. If there is no nuclear magnetic resonance logging, the total formation porosity POR is calculated by conventional density, acoustic wave, and neutron logging based on the volume model.

[0084] 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, and the structural compression coefficient ACm_C value indicates the degree of formation structural compression by selecting the average value of the lithologically stable reservoir section: Figure 2 As shown, according to the calculated ACm curve, the stable reservoir section of 4820-5400m was selected, and the average value was taken to determine the structural compression coefficient ACm_C value.

[0085] 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.

[0086] Through step S5, according to the experimental data, the relationship between the effective stress and the biot coefficient and the porosity is determined. According to the rock mechanics experimental data, the relationship between the effective stress and the biot coefficient and the porosity is determined as follows: Figure 3 and Figure 4 , and calculate the biot coefficient according to formula (6) and formula (7).

[0087] In step S6, according to formula (8) and formula (9), the pore pressure coefficient of the reservoir section is calculated, and the pore pressure coefficient of the mudstone section is corrected by combining formula (4) as follows: Figure 5 As mentioned above, the adjustment parameter A is adjusted to make the pore pressure coefficient PP calculated by formula (4) and formula (8) stable 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 calculated results of this achievement is greatly improved in line with the tested pore pressure.

[0088] Obviously, the above-described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0089] 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, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0090] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope 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 S by integrating the density trend curve. V ; Step S2: Determine the total formation porosity POR based on acoustic wave, density, neutron logging or nuclear magnetic resonance logging; Step S3: Analyze the characteristics of the target layer segment and determine the formation structure compression coefficient ACm_C; Step S4: solving the pore pressure coefficient PP of the mudstone section based on the pore pressure model corrected by the structural compressibility coefficient ACm_C; Step S5: Determine the effective stress P according to the rock mechanics experimental data eff and biot coefficient α are respectively related to the total porosity POR; Step S6: According to the effective stress P eff The relationship between the total porosity POR and the reservoir section pore pressure coefficient is inferred.

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 S V satisfy: Where Z is the vertical depth, g is the acceleration due to gravity, and ρ 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 ρ satisfies: Among them, Δt is the time difference of the sound wave.

4. The method for calculating pore pressure of a formation based on structural compression according to claim 1, characterized in that: In step S3, the structural compression coefficient ACm_C is the average value of the stable reservoir section ACm of the target layer, and ACm satisfies: ACm=Δt / (100-POR)*100; Formula (3) Where Δt is the acoustic time difference 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 S4, the pore pressure coefficient PP satisfies: Among them, S V is the overburden pressure, P h is the hydrostatic column pressure, Δt is the acoustic time difference, Δt ACm The normal trend equation for mudstone compaction is fitted with the acoustic time difference, where Z is the vertical depth and k is the Eaton coefficient.

6. The method for calculating pore pressure of a formation based on structural compression according to claim 5, characterized in that: satisfy: Δt ACm =ACm_C+(Δt mf -ACm_C)×e -CZ ; Formula (5) Where ACm_C is the structural compression coefficient, Δt mf is the surface acoustic wave time difference, Z is the vertical depth, and C is a constant.

7. 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: P eff =-14.55*ln(POR)+6.3166; Formula (6) Among them, P eff is the effective stress and POR is the total porosity.

8. 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: α=1.154*POR+0.717; Formula (7) Among them, α is the biot coefficient and POR is the total porosity.

9. The method for calculating pore pressure of a formation based on structural compression according to claim 5, characterized in that: In step S6, P eff =S V -α*PP; Formula (8) PP = (((S V + 14.55 * log(POR) - 6.3166) / Z · 100) + A) / α; Equation (9) Among them, S V is the overburden pressure, POR is the total porosity, Z is the vertical depth, A is the adjustment parameter, α is the biot coefficient, P eff is the effective stress and PP is the pore pressure coefficient.

10. The method for calculating pore pressure of a formation based on structural compression according to claim 9, characterized in that: The adjustment parameter A is adjusted so that the pore pressure coefficient PP calculated by the formula (4) and the formula (8) is stable in the mudstone section, and finally a continuous pore pressure coefficient profile is obtained.

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