A predictive method for the height of a fault-sealed air column using cross-sectional stress.

Abstract

This invention relates to a method for predicting the height of a fault-sealed gas column using cross-sectional stress. Based on the principle that faults, regardless of their lithology, size, or burial depth, are always subject to pressure from the overlying strata and regional stress fields—meaning cross-sectional stress is universally present—this invention establishes a relationship between the magnitude of stress on the cross-section and the height of the hydrocarbon column it can seal. This allows for the prediction of the height of the fault-sealed oil and gas column in all lithological regions, particularly in igneous, metamorphic, and carbonate rock regions. This invention has broad applicability and can solve the problem of determining the height of a fault-sealed hydrocarbon column in special lithological regions.

Description

Technical Field

[0001] This invention relates to the field of oil and gas exploration technology, and more specifically, to a method for predicting the height of a fault-sealed gas column using cross-sectional stress. Background Technology

[0002] Whether a fault is sealed or not directly affects the hydrocarbon-bearing potential of the trap (Luo Qun, 2002), controls the flow pattern of underground fluids (Hao Fang et al., 2004), and influences the effectiveness of water injection development. After conducting extensive simulation and practical research on the fault sealing problem, Watts NL (1987, 1991), Knipe RJ (1992), and Antonellini M (1995) believe that the sealing mechanism of faults mainly consists of four aspects: juxtaposition and docking, mudstone smearing, fracturing, and diagenetic cementation.

[0003] Based on this, scholars at home and abroad have proposed a series of methods for evaluating fault sealing. Bouvier et al. (1989), while conducting research in the Nun River oil field in Nigeria, proposed the clay smear potential (CSP), also known as clay smearing potential or clay staining potential, expressed by CSP. Lindsay et al. (1993), based on statistical analysis of actual data, proposed a parameter to characterize the continuity of clay smear layers—the shale smear factor (SSF). Yielding (1997) proposed the shale fault gouge ratio (SGR) algorithm. It represents the clay content in fault rocks as the ratio of the cumulative thickness of clay rock after a point passes through the fault to the fault displacement. Unlike SSF, which has silicate characteristics, it can most effectively represent the clay content in the formation. It is a quantitative evaluation method for the lateral sealing of faults in fault-sealing types, which can make up for the shortcomings of SSF in evaluating sand-sand connection windows. Domestic scholars Fu Guang et al. (1999) proposed a method (Rm) to study fault sealing performance using the mass fraction of clay in the fracture filling. Wang Ping (1994) proposed the idea of ​​evaluating fault sealing performance using cross-sectional normal stress. Underground, the stress on the fault surface is a superposition of gravitational stress, tectonic stress, and fluid pressure. Based on this, Liu Zerong et al. (1998) established a formula for evaluating fault sealing performance using cross-sectional stress:

[0004] P=H(ρ r -ρ w )gcosθ+σsinθsinβ

[0005] Where: P is the normal pressure borne by the cross-section, MPa; H is the burial depth of the cross-section, m; ρ r The average density of the overlying strata is given in g / cm³. 3 ;ρ wDensity of formation water, g / cm³ 3 g is the gravitational acceleration; σ is the horizontal ground stress, MPa; θ is the cross-sectional dip angle, (°); β is the angle between the ground stress and the fault strike, (°).

[0006] The above methods can provide good quantitative parameters for judging the opening and closing of faults, laying a solid foundation for comprehensively judging the sealing of faults. However, the ability of faults to block hydrocarbons, especially the height of the sealed hydrocarbon column, has always been a difficult problem in the study of fault-controlled hydrocarbon accumulation.

[0007] The principle for estimating hydrocarbon column height is that when the pressure difference between water and hydrocarbon phases (i.e., buoyancy) exceeds the pressure required for hydrocarbons to enter and pass through the largest pore throat in the fault zone (i.e., capillary displacement pressure), hydrocarbons will leak through the fault zone. Therefore, the smaller the pore throat size of the rock within the fault zone, the higher the estimated SGR value, the higher the capillary displacement pressure required to form a seal, and the larger the hydrocarbon column that can be supported (Peter B, 2003). The sealing capacity of a fault can be represented by the height of the hydrocarbon column it can seal. Fu Xiaofei et al. (2021) proposed a formula for estimating hydrocarbon column height using SGR values:

[0008]

[0009] In the formula: H is the height of the hydrocarbon column that the fault can seal; ρhydrocarbon is the density of underground hydrocarbons; d is a dimensionless parameter.

[0010] This formula was applied to the Beier Depression in the Hailar Basin with good results.

[0011] This calculation method is effective in predicting the height of hydrocarbon columns capped by faults in clastic rocks with interbedded sand and mudstone. However, it cannot calculate the hydrocarbon column growth rate (SGR) in carbonate rocks, metamorphic rocks, and sedimentary rocks, rendering the method unusable. There is currently a lack of effective evaluation methods for the height of hydrocarbon columns capped by faults in igneous, metamorphic, and carbonate rocks.

[0012] The information disclosed in this background section is only intended to enhance the understanding of the background technology of this application, and therefore may include prior art that is not known to those skilled in the art. Summary of the Invention

[0013] This invention provides a method for predicting the height of a fault-sealed gas column using cross-sectional stress, in order to solve the technical problem that the height of a hydrocarbon column cannot be predicted when the SGR (Self-Growth Restriction) cannot be calculated.

[0014] To achieve the above objectives, the present invention adopts the following technical solution:

[0015] A method for predicting the height of a fault-sealed gas column using cross-sectional stress, the method comprising:

[0016] Determine the burial depth H (m) of the calculation point section and the average density ρ of the overlying strata. r (g / cm 3 ), Calculate the formation fluid density ρ at the point of origin n (g / cm 3 Formation pressure coefficient R, maximum horizontal principal stress σ A (MPa), minimum horizontal principal stress σ B (MPa), cross-sectional dip angle θ (°), and the angle β (°) between the maximum horizontal principal stress and the fault strike;

[0017] Predict the hydrocarbon column height h = a[H(ρ)] r –Rρ n )gcosθ+(σ A -σ B [sinθsinβ]–b;

[0018] Where g is the gravitational acceleration, and the coefficients a and b are determined in advance based on the relationship between the cross-sectional stress value calculated according to the normal stress on the cross-section of the hydrocarbon-bearing layer at different depths and the actual measured height of the hydrocarbon column at the corresponding depth.

[0019] As described above, the prediction method for predicting the height of a fault-sealed gas column using cross-sectional stress has the following relationship between the cross-sectional stress value P and the hydrocarbon column height h: h = aP – b.

[0020] The method for predicting the height of a fault-sealed gas column using cross-sectional stress as described above, wherein the cross-sectional stress value P = H(ρ) r –Rρ n )gcosθ+(σ A -σ B )sinθsinβ.

[0021] The method described above for predicting the height of the fault-sealed air column using cross-sectional stress determines the fault strike, dip, dip angle, displacement, and cutting depth using seismic data.

[0022] As described above, the method for predicting the height of the fault-sealed gas column using cross-sectional stress establishes a depth profile of the lithological connection between the two sides of the fault based on drilling data.

[0023] As described above, the prediction method for the height of the fault-sealed gas column using cross-sectional stress collects or simulates the tectonic stress field of the study area to obtain the horizontal maximum principal stress σ. A Horizontal minimum principal stress σ B Size and direction.

[0024] In the method described above for predicting the height of a fault-sealed gas column using cross-sectional stress, the formation pressure coefficient R is taken as 1 under normal pressure and as the pressure coefficient at that depth point under overpressure.

[0025] The technical solution of this invention has the following technical advantages over the prior art: This invention is based on the principle that faults, regardless of their lithology, size, or burial depth, are always subject to the pressure of the overlying strata and the regional stress field. In other words, the stress on the fault surface is universally present. By finding the relationship between the magnitude of the stress on the fault surface and the height of the hydrocarbon column it can seal, this invention can predict the height of the oil and gas column sealed by faults in all lithological development areas, especially in igneous, metamorphic, and carbonate rock development areas. This invention has wide applicability and can solve the problem of sealing the height of hydrocarbon columns by faults in special lithological areas. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a cross-sectional view of the fault depth in a specific embodiment of the present invention.

[0028] Figure 2 This is a diagram showing the relationship between cross-sectional profitability and the height of the closed hydrocarbon column in a specific embodiment of the present invention. Detailed Implementation

[0029] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0030] In the description of this application, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0031] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0032] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0033] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0034] The following disclosure provides many different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0035] Modern oil and gas exploration has entered a stage of refined exploration. The evaluation of fault sealing performance, which is currently limited to simply indicating good or poor sealing, is insufficient for refined exploration needs. There is a need to evaluate the ability of faults to seal oil and gas, specifically the height of the sealed hydrocarbon column. The method of using SGR (Sequencing Restriction Gravity) to calculate the height of a sealed hydrocarbon column is only applicable to the sealing strength of faults in clastic rock areas with interbedded sandstone and mudstone. It cannot predict the height of sealed hydrocarbon columns from faults in igneous, metamorphic, and carbonate rock areas. However, regardless of the lithology, size, or depth of a fault, it is always subject to the pressure of the overlying strata and the regional stress field. In other words, fault stress is ubiquitous. If the relationship between the magnitude of the stress on the fault surface and the height of the sealed hydrocarbon column can be found, it would be possible to predict the height of the sealed oil and gas column in all lithological areas, especially in igneous, metamorphic, and carbonate rock areas. This method has broad applicability and solves the problem of determining the height of sealed hydrocarbon columns from faults in special lithological areas.

[0036] This embodiment is applicable to faults developed in all lithological regions, and can calculate and predict the height of the fault cap hydrocarbon column. Therefore, this embodiment has universality.

[0037] 1) Interpretation of seismic data to determine the fault strike, dip, dip angle, fault displacement, and cutting depth, and to clarify the fault scale and nature.

[0038] 2) Based on drilling data, clarify the lithological characteristics of the study area and establish a depth profile of the lithological connection between the two sides of the fault, such as... Figure 1 As shown.

[0039] 3) Collect, or simulate the tectonic stress field of the study area using the finite element (or discrete element) method, to obtain the horizontal maximum principal stress (σ). A ), Horizontal minimum principal stress (σ B Size and direction.

[0040] 4) Using the improved formula (1) for normal stress at different depths of the cross section, calculate the normal stress along the cross section at different depths of the fractured rock strata:

[0041] P=H(ρ r –Rρ n )gcosθ+(σ A -σ B )sinθsinβ(1).

[0042] At present, oil and gas basins are basically covered by seismic data, with numerous wells drilled, and most of them have undergone digital simulation of tectonic stress field. The parameters required for the formula (1) for calculating the normal stress of the cross section are easy to meet.

[0043] In equation (1): P is the normal pressure borne by the cross-section, MPa; H is the burial depth of the cross-section at the calculation point, m; ρ r The average density of the overlying strata is given in g / cm³.3 ;ρ n To calculate the density of formation fluids (water, oil, or gas) in g / cm³ 3 R is the formation pressure coefficient, which is taken as 1 under normal pressure and as the pressure coefficient at that depth under overpressure; g is the acceleration due to gravity; σ A Horizontal maximum principal stress, σ B θ is the minimum horizontal principal stress, MPa; θ is the cross-sectional dip angle, (°); β is the angle between the maximum horizontal principal stress and the fault strike, (°). Specific calculation parameters are as follows: Figure 1 As shown.

[0044] If stress data is unavailable, the magnitude and direction of the horizontal principal stress (σ) can be simulated using the finite element method or discrete element method. A , σ B Then, based on the fault strike obtained from seismic interpretation, the angle (β) between the maximum horizontal principal stress and the fault strike can be calculated. The fault dip angle (θ) can be obtained from the seismic profile, the calculation point depth (H) can be obtained from well layer data, and the average density of the overlying strata (ρ) can be calculated. r The commonly used value is 2.7 g / cm³. 3 Formation fluid density (ρ) n If it is water, take the value as 1g / cm³. 3 If the substance is oil or gas, its average density is used. The formation pressure coefficient (R) can be calculated based on the bottom hole pressure or the mud mix density.

[0045] 5) The normal stress on the cross section of the hydrocarbon-bearing strata at different depths sealed by the fault in the study area was calculated to obtain a series of cross section stress values. At the same time, based on the drilling, logging, oil testing and gas testing data, the corresponding actual measured hydrocarbon column height was obtained, and a rectangular coordinate system was established, where the vertical axis is the height of the sealed hydrocarbon column and the horizontal axis is the cross section stress value. The relationship between the height of the sealed hydrocarbon column and the cross section stress value was obtained (2):

[0046] h = aP – b(2).

[0047] The relationship between the normal stress of the cross section and the height of the closed hydrocarbon column is statistically analyzed to determine the values ​​of a and b in formula (2).

[0048] In equation (2): h is the predicted height at which the fault can seal the hydrocarbon column, in meters; P is the normal pressure borne by the fault section, in MPa; a is the gradient of stress on the fault section with depth, which is the slope of the statistical trend line, in meters per MPa; b is a constant, which is the intercept of the statistical trend line on the vertical axis, in meters. Specific calculation parameters are as follows: Figure 2 As shown.

[0049] 6) Substituting formula (1) into formula (2), we obtain formula (3) which uses the magnitude of the normal stress on the cross section and the height of the hydrocarbon column that can be sealed:

[0050] h=a[H(ρ r –Rρ n )gcosθ+(σ A -σ B )sinθsinβ]–b(3).

[0051] Therefore, when predicting the height of a hydrocarbon column at a certain location, it is only necessary to determine the burial depth H (m) of the calculation point section and the average density ρ of the overlying strata. r (g / cm 3 ), Calculate the formation fluid density ρ at the point of origin n (g / cm 3 Formation pressure coefficient R, maximum horizontal principal stress σ A (MPa), minimum horizontal principal stress σ B (MPa), cross-sectional dip angle θ (°), angle β (°) between the maximum horizontal principal stress and the fault strike, and coefficients a and b, can be calculated according to formula (3). The parameters involved above are also data that are easy to obtain in oil and gas field production.

[0052] By statistically analyzing the relationship between the magnitude of the cross-sectional normal stress and the height of the closed hydrocarbon column in more than 60 hydrocarbon-bearing strata in the Qiongdongnan Basin, the values ​​of a and b in this relationship were determined to be 48.875 and 416.67, respectively.

[0053] After substituting the parameter into formula (3), the hydrocarbon height of pre-drilled well locations YC13-A, LS29-B and other locations was estimated, and the error between the hydrocarbon column height and the actual measured height after drilling was within 15% (Table 1).

[0054] Table 1 Comparison of Application Effects

[0055]

[0056]

[0057] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A prediction method for predicting a fault seal gas column height using cross-sectional stress, characterized by, The method is: determining the calculated point section burial depth H (m), the overlying strata average density p r (g / cm 3 ), the calculated point strata fluid density p n (g / cm 3 ), the strata pressure coefficient R, the horizontal maximum principal stress s A (MPa), the horizontal minimum principal stress s B (MPa), the section dip angle Q (°), the angle between the horizontal maximum principal stress and the fault strike angle b (°); Predicted hydrocarbon column height h = a[H(ρ r - Rρ n )g cos θ + (σ A - σ B ) sin θ sin β] - b; Wherein, g is the acceleration of gravity, the coefficient a, b is the corresponding relationship between the cross section stress value and the actual measured hydrocarbon column height at the corresponding depth, which is determined in advance according to the normal stress of the cross section of different depth hydrocarbon bearing intervals.

2. The prediction method of predicting a fault seal gas column height using a fault stress according to claim 1, characterized by, The corresponding relationship between the cross section stress value P and the hydrocarbon column height h is: h=aP-b.

3. The prediction method for predicting a fault seal gas column height using a fault stress according to claim 1, characterized by, The cross-sectional stress value P = H(ρ) r –Rρ n )gcosθ+(σ A -σ B )sinθsinβ.

4. The prediction method for predicting a fault seal gas column height using a fault stress according to claim 1, characterized by, Determine the fault strike, tendency, dip angle, fault throw and cutting depth through seismic data.

5. The prediction method for predicting a fault seal gas column height using a fault stress according to claim 1, characterized by, Establish the lithology butt joint depth profile of the two plates of the fault according to the drilling data.

6. The prediction method for predicting a fault seal gas column height using a fault stress according to claim 1, characterized by, The magnitude and direction of the horizontal maximum principal stress σ A , and the horizontal minimum principal stress σ B are obtained by collecting or simulating the tectonic stress field of the study area.

7. The prediction method for predicting a fault seal gas column height using a fault stress according to claim 2, characterized by, The formation pressure coefficient R takes the value of 1 when the pressure is normal, and takes the pressure coefficient of the depth point when the pressure is overpressure.

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