Method for determining formation pressure coefficient of fold area

Abstract

The invention relates to a method for determining a formation pressure coefficient of a fold area, and belongs to the technical field of oil-gas field exploration. Aiming at the defects of a common method for predicting the formation pore pressure by utilizing the seismic velocity at present in a wrinkle region, the method is partitioned according to a structural form, and the formation pressure coefficient calculated by adopting the conventional seismic velocity is corrected by taking vertical components of horizontal stress at different positions as a basis, so that the accurate formation pressure coefficient is obtained. According to the method for determining the formation pressure coefficient of the wrinkled area, the target layer of the wrinkled area is partitioned according to the structural form, and the formation pressure coefficient at each gridding point in the anticline area and the inclined area is corrected by utilizing the actual values of the formation pressure coefficients at the anticline area and the inclined area of the target layer encountered by a drilled well; the prediction accuracy of the formation pressure coefficient of the wrinkle area can be improved.

Description

Technical Field

[0001] This invention relates to a method for determining the formation pressure coefficient in folded areas, belonging to the field of oil and gas field exploration technology. Background Technology

[0002] Formation pore pressure, also known as formation pressure, refers to the pressure exerted on fluids (oil, gas, water, etc.) within the pores of rock. Formation pressure is typically characterized by a pressure coefficient, which is the ratio of the measured formation pressure to the hydrostatic pressure at the same depth. Under normal compaction conditions, the pressure acting on the pore fluid is the hydrostatic pressure. Formation pore fluid pressures deviating from the hydrostatic pressure are generally referred to as abnormal formation pressures. The existence of abnormal formation pressures presents numerous technical challenges to oil exploration, drilling, and development. The accuracy of formation pore pressure prediction affects the degree of damage to the gas reservoir during drilling. Insufficient prediction can lead to inappropriate mud density during drilling, causing wellbore collapse and blowouts; excessive prediction can result in inappropriate mud density during drilling, leading to severe leakage and hindering effective oil and gas extraction. Therefore, accurate prediction of formation pore pressure provides fundamental data for wellbore structure design, drilling fluid density determination, reservoir protection, and improving drilling success rates.

[0003] Currently, most oil and gas exploration targets in my country are continental lacustrine basins with complex structures formed by the multi-directional superposition of multiple single-type basins. These basins have undergone multiple tectonic movements since their formation, with most basins in the central and western regions experiencing more than one stage of compressional alteration. This compressional alteration often results in various types of folds, including synclines, anticlines, and combinations of synclines and anticlines. Taking the Sichuan Basin as an example, influenced by the Yanshanian and Himalayan orogenies, the northern Dabashan and Xuefengshan areas underwent folding deformation, forming northeast-trending uplifts and depressions within the basin. Different scales of stratigraphic folds have developed within each tectonic unit. In the exploration of continental tight gas and shale gas in northeastern Sichuan, significant differences in pore pressure have been found in different structural locations within the same compressional folded tectonic zone. Currently, most scholars use seismic layer velocity to predict formation pressure. Taking the exploration area in northeastern Sichuan as an example, there is a certain error between the formation pore pressure measured by actual drilling and the formation pore pressure predicted by the Eaton method based on seismic layer velocity. Often, the measured value of formation pore pressure in the anticline area is lower than the predicted value, while the measured value of formation pore pressure in the syncline area is usually higher than the predicted value.

[0004] In their articles "Prediction Model of Formation Pressure in Compression Structures" (2009, Vol. 5) and "Influence of Tectonic Compression on Abnormal Formation Pressure in the Kuqa Depression" (2004, Vol. 5), Yang Jin and Zeng Lianbo of China University of Petroleum affirmed the influence of compressional stress on pore pressure. However, they only proposed a regional macroscopic tectonic pressure factor. This regional macroscopic tectonic pressure factor is still affected by tectonic morphology and horizontal stress within different tectonic morphologies, resulting in low accuracy of the calculation results.

[0005] Chinese patent document CN114742666A discloses a method for predicting pressure in compressional formations. This method includes the following steps: determining the starting depth Hs for compressional formation pressure correction; calculating the equivalent density Gcor of the compressional formation pressure correction term below the starting depth Hs; calculating the equivalent density Gp of the conventional model term for compressional formation pressure; and fusing the equivalent density Gcor and Gp of the conventional model term to estimate the equivalent density G of the compressional formation pressure. While this patent document provides a method for predicting compressional formation pressure and proposes correction methods for compressional formation pressure under different depth conditions, this method is still affected by horizontal stress and formation morphology. That is, the same magnitude of horizontal stress can have significantly different effects on vertical pressure depending on the structural location and formation morphology, resulting in large errors in the predicted formation pore pressure. Summary of the Invention

[0006] The purpose of this invention is to provide a method for determining the formation pressure coefficient in folded areas, which can solve the problem of large errors in the current prediction of formation pressure coefficient in folded areas.

[0007] To achieve the above objectives, the technical solution adopted in the method for determining the formation pressure coefficient in folded areas of the present invention is as follows:

[0008] A method for determining the formation pressure coefficient in a folded zone includes the following steps:

[0009] (1) Based on the structural map of the top surface of the target layer in the study area, the target layer is divided into a gentle area, anticline area and syncline area, and then gridded.

[0010] (2) Determine the formation pressure ratio of the target layer encountered by the drilled well based on the ratio of the vertical component of the compressive stress to the hydrostatic pressure of the target layer in the anticline and syncline regions.

[0011] (3) Based on the formation pressure coefficient of the target layer encountered in the drilled well, the formation pressure coefficient calculated by the Eaton method, and the formation pressure ratio obtained in step (2), calculate the formation pressure coefficient correction coefficient of the target layer in the anticline and syncline areas.

[0012] (4) Repeat step (2) to determine the formation pressure ratio of the target layer at each grid coordinate point in the anticline and syncline areas; calculate the product of the formation pressure ratio of the target layer at each grid coordinate point and the formation pressure coefficient correction coefficient obtained in step (3) to obtain the formation pressure coefficient correction amount, and determine the formation pressure coefficient of the target layer at each grid coordinate point in the anticline and syncline areas.

[0013] The method for determining the formation pressure coefficient in folded regions according to the present invention divides the target layer in the folded region into zones based on its structural morphology. Then, it corrects the formation pressure coefficient at each grid point within the anticline and syncline zones using the actual values ​​of the formation pressure coefficient encountered in drilled wells and the vertical component of the compressive stress. This improves the accuracy of predicting the formation pressure coefficient in folded regions. Experimental results show that the method of the present invention has a smaller error when predicting the formation pressure coefficient in folded regions compared to the traditional Eaton method.

[0014] Preferably, in step (3), the calculation method for the formation pressure coefficient correction coefficient is as follows:

[0015] k=(P 实 -P 预 ) / C p

[0016] Where k is the formation pressure coefficient correction factor, P 实 P represents the actual value of the formation pressure coefficient. 预 C represents the formation pressure coefficient calculated based on the Eaton method. p This represents the formation pressure ratio.

[0017] Preferably, in step (4), after obtaining the formation pressure coefficient correction amount, the formation pressure coefficient and formation pressure coefficient correction amount of the target layer at each grid coordinate point in the anticline and syncline regions calculated based on the Eaton method are summed to obtain the formation pressure coefficient.

[0018] Preferably, in step (2), the vertical component of the compressive stress of the drilled target layer is calculated using the stress analysis results of the drilled wells located in the anticline and syncline regions. The formula for calculating the vertical component of the compressive stress is as follows:

[0019] P dv =P×cos(α-β)×sinγ

[0020] Among them, P dvLet α be the vertical component of the compressive stress, P be the transverse compressive stress, α be the strike of the formation, β be the stress azimuth angle, and γ be the dip angle of the formation.

[0021] Preferably, the transverse compressive stress, formation strike, and stress azimuth are determined based on the horizontal stress distribution map of the study area.

[0022] Preferably, the dip angle of the formation is determined based on the dip angle distribution map of the target layer.

[0023] Preferably, in step (2), the static water column pressure is determined based on the static water column pressure distribution map of the study area. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating the method for determining the formation pressure coefficient in a folded region according to an embodiment of the present invention.

[0025] Figure 2 This is a schematic diagram showing the result of dividing the target layer into a flat region, an anticline region, and a syncline region in an embodiment of the present invention;

[0026] Figure 3 This is a distribution map of the calculated formation pressure coefficient of the target layer in an embodiment of the present invention;

[0027] Figure 4 This is a schematic diagram showing the decomposition of the transverse compressive stress at point y in the dip direction of the formation in an embodiment of the present invention;

[0028] Figure 5 This is a schematic diagram showing the decomposition of the compressive stress at points x and y in an embodiment of the present invention;

[0029] Figure 6 This is a distribution map of the formation pressure coefficient correction in the anticline region in an embodiment of the present invention;

[0030] Figure 7 This is a distribution map of the correction amount of the formation pressure coefficient in the syncline region in an embodiment of the present invention;

[0031] Figure 8 This is a distribution map of the formation pressure coefficient of the target layer in an embodiment of the present invention. Detailed Implementation

[0032] The method for determining the formation pressure coefficient in folded areas according to this invention is an improved invention. This invention addresses the shortcomings of currently commonly used methods for predicting formation pore pressure in folded areas using seismic velocity. It fully considers the influence of horizontal stress and formation morphology on the formation pressure coefficient, divides the area into zones according to structural morphology, and corrects the formation pressure coefficient calculated based on conventional seismic velocity by using the vertical component of horizontal stress and the actual values ​​of formation pressure coefficients from drilled wells, thus obtaining an accurate formation pressure coefficient.

[0033] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0034] Example

[0035] The method for determining the formation pressure coefficient in the folded area in this embodiment takes the southern part of the PG folded work area as the study area and the second member of the Xujiahe Formation as the target layer. Figure 1 As shown, the specific steps include:

[0036] (1) Collect well data, seismic data and regional geological data of the study area, including: horizontal stress distribution map and hydrostatic pressure distribution map of the study area, top surface structure map of the target layer, dip angle distribution map of the strata, and seismic velocity field.

[0037] (2) Based on the collected top surface structural map of the target layer, the target layer is divided into gentle slope region, anticline region and syncline region according to the structural morphology, and then gridded. The result is as follows: Figure 2 As shown.

[0038] (3) Obtain the measured formation pressure of the target layer encountered in the drilled wells in the anticline and syncline areas, and convert the measured formation pressure into the formation pressure coefficient P. 实 In this embodiment, the following is selected: Figure 2 The images show well M1, located in the anticline zone, and well PL7, located in the syncline zone. The measured formation pressure and formation pressure coefficient P encountered by well M1 in the target formation are also shown. 实 The measured formation pressure and formation pressure coefficient P of the target layer encountered during drilling in well PL7 were 22 MPa and 0.95, respectively. 实 The values ​​are 48.1 MPa and 1.30 MPa, respectively.

[0039] Using the seismic velocity field of the study area collected in step (1), the Eaton method was used to calculate the formation pressure coefficient P of the target layer encountered by well M1 in the anticline zone and well PL7 in the syncline zone. 预 Among them, the formation pressure coefficient of the target layer encountered by well M1 was 1.09, and the formation pressure coefficient of the target layer encountered by well PL7 was 1.24.

[0040] The formation pressure coefficient P of the target layer at each grid coordinate point in the anticline, gentle, and syncline regions was calculated using the method described above. 预i , drawing as Figure 3 The formation pressure coefficient P of the target layer is shown. 预 Contour distribution map.

[0041] (4) Based on the lateral compressive stress, formation strike, stress azimuth, and formation dip of the target layer encountered in the drilled wells located in the anticline and syncline regions, draw a stress analysis diagram and calculate the vertical component P of the compressive stress of the target layer encountered in the drilled wells. dvLet point x be the target layer encountered by well M1 in the anticline zone, and point y be the target layer encountered by well PL7 in the syncline zone. The schematic diagram of the decomposition of lateral compressive stress at point y along the dip direction of the formation is shown below. Figure 4 As shown, Figure 4 In the diagram, P represents the transverse compressive stress at point y. s P represents the component of the transverse compressive stress in the bearing direction. d This represents the component of the transverse compressive stress in the dip direction. The decomposition diagrams of the compressive stress at points x and y are shown below. Figure 5 As shown in a and 5b, Figure 5 In the middle, P d P is the component of the transverse compressive stress in the dip direction. dv P is the vertical component of the compressive stress. dh This represents the horizontal component of the compressive stress. The specific steps for calculating the vertical component of the compressive stress encountered in the drilled well are as follows:

[0042] According to the horizontal stress distribution map collected in step (1), the transverse compressive stress P at point x is 11.1 MPa, the stress azimuth angle is 90° (with true north as 0°), the strike of the stratum is 135.2°, and the component of the transverse compressive stress at point x in the dip direction of the stratum is P. d = P × cos(α - β), where α is the strike of the strata at point x, and β is the stress azimuth at point x. The calculation yields P. d =11.1MPa×cos(135.2°-90°), equals 7.82MPa, meaning the component of the horizontal stress at point x in the dip direction of the stratum is 7.82MPa. According to the dip angle distribution map of the target stratum collected in step (1), the dip angle of the stratum at point x is 30°, and the vertical component of the compressive stress at point x, P... dv =P d ×sinγ, where γ is the dip angle of the formation at point x, can be calculated to obtain the vertical component P of the compressive stress at point x. dv =7.82MPa×sin(30°), equals 3.91MPa.

[0043] According to the horizontal stress distribution map collected in step (1), the transverse compressive stress P at point y is 14.6 MPa, the stress azimuth angle is 90° (with true north as 0°), the strike of the stratum is 138.2°, and the component of the transverse compressive stress at point y in the dip direction of the stratum is P. d = P × cos(α - β), where α is the strike of the strata at point y, and β is the stress azimuth at point y. The calculation yields P. d =11.1MPa×cos(138.2°-90°), equals 9.73MPa. According to the dip angle distribution map of the target layer collected in step (1), the dip angle of the stratum at point y is 20°, and the vertical component of the compressive stress at point y is P. dv=P d ×sinγ, where γ is the dip angle of the formation at point y, the vertical component P of the compressive stress at point y can be calculated. dv =9.73MPa×sin(20°), which equals 3.33MPa.

[0044] (5) Based on step (4), the vertical component P of the compressive stress of the drilled target layer in the anticline and syncline regions. dv The ratio of the static water column pressure to the formation pressure ratio Cp of the target layer encountered in the drilled well is used to determine the formation pressure ratio Cp.

[0045] In this embodiment, according to the hydrostatic pressure distribution diagram in step (1), the hydrostatic pressure at point x is 23 MPa, and the vertical component of the compressive stress at point x is 3.91 MPa. Therefore, the ratio of the vertical component of the compressive stress at point x to the hydrostatic pressure is 3.91 / 23, which is equal to 0.17. That is, the formation pressure ratio Cp at point x is 0.17. Since the vertical component of the compressive stress in the anticline area is opposite to the direction of gravity, compared with the structurally gentle area, this part of the stress offsets part of the overlying formation pressure. Therefore, this invention considers the influence of compressive stress on the formation pressure coefficient in the anticline area, which can improve the prediction accuracy of the formation pressure coefficient.

[0046] According to the hydrostatic pressure distribution diagram in step (1), the hydrostatic pressure at point y is 37 MPa, and the vertical component of the compressive stress at point y is 3.33 MPa. Therefore, the ratio of the vertical component of the compressive stress to the hydrostatic pressure at point y is 3.33 / 37, which is equal to 0.09. That is, the formation pressure ratio Cp at point y is 0.09. Since the vertical component of the compressive stress in the synclinal area is in the same direction as gravity, this part of the stress enhances the pressure of the overlying strata compared to the structurally gentle area. Therefore, this invention considers the influence of compressive stress on the formation pressure coefficient in the synclinal area, which can improve the prediction accuracy of the formation pressure coefficient.

[0047] (6) Based on the formation pressure coefficient P of the target layer encountered in the drilled wells in the anticline and syncline regions obtained in step (3), 实 Formation pressure coefficient P 预 Using the formation pressure ratio Cp obtained in step (5), calculate the formation pressure coefficient correction factor k for the target layer in the anticline and syncline regions. The calculation method for the formation pressure coefficient correction factor is as follows:

[0048] k=(P 实 -P 预 ) / C p

[0049] Where k is the formation pressure coefficient correction factor, P 实 P represents the actual value of the formation pressure coefficient. 预C is the formation pressure coefficient calculated using the Eaton method. p This represents the formation pressure ratio.

[0050] In this embodiment, well M1 is located in an anticline region and well PL7 is located in a syncline region. Therefore, the formation pressure coefficients P at point x where well M1 encounters the target layer and point y where well PL7 encounters the target layer can be utilized. 实 Formation pressure coefficient P 预 The formation pressure ratio Cp is used to calculate the formation pressure coefficient correction coefficients for the target strata in the anticline and syncline regions, respectively. The specific calculation process is as follows: the formation pressure ratio Cp at point x is 0.17, and the formation pressure coefficient P at point x... 实 and formation pressure coefficient P 预 The values ​​are 0.95 and 1.09 respectively. Therefore, the formation pressure coefficient correction factor k for the target layer in the anticline area can be calculated as k = (0.95 - 1.09) / 0.17 = -0.82; the formation pressure ratio Cp at point y is 0.09, and the formation pressure coefficient P at point y is... 实 and formation pressure coefficient P 预 The values ​​are 1.3 and 1.24 respectively. Therefore, the formation pressure coefficient correction coefficient k of the target layer in the anticline area can be calculated as k = (1.3-1.24) / 0.09 = 0.67.

[0051] The formation pressure coefficient correction factor k of the target layer at each grid coordinate point in the anticline and syncline regions is calculated using the method described above. i , drawing as Figure 6 The distribution map of formation pressure coefficient correction in the anticline region shown below and as follows Figure 7 The diagram shows the distribution of corrections for formation pressure coefficients in synclinal areas. Calculations show that the pressure coefficient in anticline areas requires a maximum correction of -0.14, while the pressure coefficient in synclinal areas requires a maximum correction of 0.08.

[0052] (7) Based on the formation pressure coefficient correction coefficient k of the target layer at each grid coordinate point in the anticline and syncline regions obtained in step (6). i The formation pressure coefficient correction amount of the target layer at each grid coordinate point is determined by multiplying the formation pressure ratio Cp obtained in step (6).

[0053] (8) Based on the formation pressure coefficient correction amount of the target layer at each grid coordinate point in the anticline and syncline regions obtained in step (7), adjust the formation pressure coefficient P of the target layer at each grid coordinate point in the anticline and syncline regions calculated based on the Eaton method in step (3). 预i The correction is performed by adjusting the formation pressure coefficient P. 预iThe formation pressure coefficient correction is added together to obtain the formation pressure coefficient of the target layer at each grid coordinate point in the anticline and syncline regions. The formation pressure coefficient of the target layer at each grid coordinate point in the anticline region, the formation pressure coefficient of the target layer at each grid coordinate point in the syncline region, and the formation pressure coefficient P of the target layer at each grid coordinate point in the gentle area calculated based on the Eaton method in step (3) are then combined. 预i By merging, we can obtain, as follows Figure 8 The distribution map of formation pressure coefficients of the target layer is shown.

[0054] Will Figure 8 and Figure 2 The comparison shows that the top of the target layer anticline in the study area is a low-pressure area with a pressure coefficient of less than 1, while there is a local high-pressure area with a pressure coefficient of 1.3 in the syncline area.

[0055] Application examples

[0056] In this embodiment, two exploratory wells, M2 and PL701, were deployed in the target layer of the study area. Well M2 is located in an anticline region, and well PL701 is located in a syncline region. Using the Eaton method, the formation pressure coefficient of the target layer encountered by well M2 was calculated to be 1.08, and that of well PL701 was 1.22. Using the method of this embodiment, the formation pressure coefficient of the target layer encountered by well M2 was calculated to be 0.98, and that of well PL701 was 1.27. However, actual test results show that the formation pressure coefficient of the target layer encountered by well M2 was 0.99, and that of well PL701 was 1.26. Therefore, the comparison shows that the absolute and relative errors of the pressure coefficients predicted by this invention are both smaller than those of the Eaton method.

Claims

1. A method for determining the formation pressure coefficient in a folded region, characterized in that, Includes the following steps: (1) Based on the structural map of the top surface of the target layer in the study area, the target layer is divided into a gentle area, anticline area and syncline area, and then gridded. (2) Determine the formation pressure ratio of the target layer encountered by the drilled well based on the ratio of the vertical component of the compressive stress to the hydrostatic pressure of the target layer in the anticline and syncline regions. (3) Based on the formation pressure coefficient of the target layer encountered in the drilled well, the formation pressure coefficient calculated by the Eaton method, and the formation pressure ratio obtained in step (2), calculate the formation pressure coefficient correction coefficient of the target layer in the anticline and syncline areas. (4) Repeat step (2) to determine the formation pressure ratio of the target layer at each grid coordinate point in the anticline and syncline areas; calculate the product of the formation pressure ratio of the target layer at each grid coordinate point and the formation pressure coefficient correction coefficient obtained in step (3) to obtain the formation pressure coefficient correction amount, and determine the formation pressure coefficient of the target layer at each grid coordinate point in the anticline and syncline areas.

2. The method for determining the formation pressure coefficient in folded areas as described in claim 1, characterized in that, In step (3), the calculation method for the formation pressure coefficient correction coefficient is as follows: k=(P 实 -P 预 ) / C p Where k is the formation pressure coefficient correction factor, P 实 P represents the actual value of the formation pressure coefficient. 预 C represents the formation pressure coefficient calculated based on the Eaton method. p This represents the formation pressure ratio.

3. The method for determining the formation pressure coefficient in folded areas as described in claim 1, characterized in that, In step (4), after obtaining the formation pressure coefficient correction amount, the formation pressure coefficient and formation pressure coefficient correction amount of the target layer at each grid coordinate point in the anticline and syncline areas calculated based on the Eaton method are summed to obtain the formation pressure coefficient.

4. The method for determining the formation pressure coefficient in a folded area as described in any one of claims 1-3, characterized in that, In step (2), using the stress analysis results of the drilled wells that have encountered the target layer in the anticline and syncline regions, the vertical component of the compressive stress of the drilled wells that have encountered the target layer is calculated. The formula for calculating the vertical component of the compressive stress is as follows: P dv =P×cos(α-β)×sinγ Among them, P dv Let α be the vertical component of the compressive stress, P be the transverse compressive stress, α be the strike of the formation, β be the stress azimuth angle, and γ be the dip angle of the formation.

5. The method for determining the formation pressure coefficient in a folded area as described in claim 4, characterized in that, The transverse compressive stress, formation strike, and stress azimuth are determined based on the horizontal stress distribution map of the study area.

6. The method for determining the formation pressure coefficient in a folded area as described in claim 4, characterized in that, The dip angle of the strata is determined based on the dip angle distribution map of the target stratum.

7. The method for determining the formation pressure coefficient in a folded area as described in any one of claims 1-3, characterized in that, In step (2), the static pressure is determined based on the static pressure distribution map of the study area.

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