A method for quantitatively evaluating fault sealing property

Abstract

This application provides a quantitative evaluation method for fault sealing, relating to the field of oil and gas exploration technology. Its key technical points include the following steps: calculating the improved SGR index of the target layer according to the formula, where ∑H1 is the total thickness of the hanging wall mudstone layer in the study section, ∑H2 is the total thickness of the footwall mudstone layer connected to the study section, and D is the vertical fault displacement; and evaluating the sealing of all faults in the study area based on the improved SGR index. Verification in a new area shows that the improved SGR index is more reliable than the traditional high SGR index and can more accurately evaluate fault sealing.

Description

Technical Field

[0001] This application relates to the field of oil and gas exploration technology, and in particular to a method for quantitative evaluation of fault sealing. Background Technology

[0002] Fault sealing capacity refers to the ability of a fault to impede the migration of oil and gas (crude oil, natural gas, N2, CO2, etc.). Fault sealing capacity is divided into vertical sealing capacity and lateral sealing capacity, which represent the ability of a fault to impede the migration of oil and gas in the vertical and lateral directions, respectively.

[0003] In the theoretical research and exploration practice of hydrocarbon accumulation, the study of fault sealing has always been a difficult problem for oil and gas geologists. Existing technologies typically use sand-mud joint models, mudstone smearing potential calculation methods, mudstone smearing factor calculation methods, and cross-sectional graphical methods to evaluate fault sealing. However, existing evaluation methods neglect the proportion of sandstone and mudstone strata in the joint block, resulting in significant errors in judging fault sealing, and even misjudgments, leading to huge economic losses in the process of oil and gas exploration and development. Summary of the Invention

[0004] This application provides a quantitative evaluation method for fault closure, which improves the accuracy of fault closure assessment.

[0005] In an embodiment of this application, a method for quantitatively evaluating fault closure is provided, comprising the following steps:

[0006] The improved SGR index of the target layer is calculated according to formula (1).

[0007]

[0008] In formula (1), ∑H1 is the total thickness of the hanging mudstone layer in the study section, ∑H2 is the total thickness of the hanging mudstone layer connected to the study section, and D is the vertical fault displacement.

[0009] The closure of all faults in the study area was evaluated based on the improved SGR index.

[0010] In some embodiments of this application, the assessment of the closure of all faults in the study area based on the improved SGR index includes verifying the reliability of the improved SGR index;

[0011] The verification of the reliability of the improved SGR index includes:

[0012] The new area within the study area was surveyed, and the improved SGR index of the new area was calculated.

[0013] Determine whether there is any overlap between the improved SGR index interval corresponding to the existing Tibetan areas within the new area and the improved SGR index interval corresponding to the non-Tibetan areas within the new area;

[0014] If the improved SGR index interval corresponding to the existing Tibetan areas within the new area and the improved SGR index interval corresponding to the non-Tibetan areas within the new area do not overlap, then the improved SGR index is reliable.

[0015] In some embodiments of this application, the assessment of the closure of all faults in the study area based on the improved SGR index includes verifying the reliability of the improved SGR index;

[0016] The verification of the reliability of the improved SGR index includes:

[0017] The new area within the study area was surveyed, and the traditional SGR index of the new area was calculated according to formula (2).

[0018]

[0019] In formula (2), ∑H0 is the total thickness of the mudstone layer in the study section, and D is the vertical fault displacement.

[0020] Calculate the improved SGR index of the new area;

[0021] Determine whether there is an overlap between the traditional SGR index interval corresponding to the existing Tibetan areas within the new area and the traditional SGR index interval corresponding to the non-Tibetan areas within the new area;

[0022] Determine whether there is any overlap between the improved SGR index interval corresponding to the existing Tibetan areas within the new area and the improved SGR index interval corresponding to the non-Tibetan areas within the new area;

[0023] If the traditional SGR index interval corresponding to the existing Tibetan areas in the new area and the traditional SGR index interval corresponding to the non-Tibetan areas in the new area overlap, and the improved SGR index interval corresponding to the existing Tibetan areas in the new area and the improved SGR index interval corresponding to the non-Tibetan areas in the new area do not overlap, then the improved SGR index is reliable.

[0024] In some embodiments of this application, the improved SGR index for calculating the target layer includes:

[0025] Calculate the fault capillary force Pc of the target layer according to formula (3).

[0026] Pc=10(SGR / dc) (3),

[0027] In formula (3), d is an empirical parameter and c is a coefficient;

[0028] The improved SGR index is determined based on the capillary force Pc of the fault rock.

[0029] In some embodiments of this application, the improved SGR index for calculating the target layer includes:

[0030] The height of the hydrocarbon column Hmin in the target layer is calculated according to formula (4).

[0031]

[0032] In formula (4), ρ w ρ is the density of water. 烃 Where is the density of the oil and gas, g is the acceleration due to gravity, d is an empirical parameter, and c is a coefficient;

[0033] The improved SGR index is determined based on the hydrocarbon column height Hmin.

[0034] In some embodiments of this application, the improved SGR index for calculating the target layer includes:

[0035] The CO2 column height Hmin of the target layer is calculated according to formula (5).

[0036]

[0037] In formula (5), ρ w For the density of water, Where is the density of CO2, g is the acceleration due to gravity, d is an empirical parameter, and c is a coefficient;

[0038] The improved SGR index is determined based on the CO2 column height Hmin.

[0039] In some embodiments of this application, calculating the column height Hmin includes:

[0040] Calculate the fault normal pressure P of the target layer according to formula (6). 断面 ,

[0041]

[0042] In formula (6) ρ w ρ is the density of the formation water, g is the gravitational acceleration, H is the burial depth, θ is the cross-sectional dip angle, and a and b are coefficients;

[0043] Based on the fault normal pressure P 断面 Calculate the column height Hmin.

[0044] In some embodiments of this application, calculating the column height Hmin includes:

[0045] The empirical coefficient c1 is calculated according to formula (7).

[0046] Pmin = 10 (SGR / d-c) (7),

[0047] In formula (7), Pmin is the minimum opening pressure, d is an empirical parameter, and c is a coefficient;

[0048] The column height Hmin is calculated based on the minimum opening pressure Pmin.

[0049] In some embodiments of this application, calculating the column height Hmin includes:

[0050] Compare the capillary force Pc of the fault rock and the normal force P of the fault. 断面 Size;

[0051] If Pc > P 断面 Then, the fault normal pressure P 断面 The minimum opening pressure Pmin;

[0052] If Pc≤P 断面 Then, the fault capillary force Pc is taken as the minimum opening pressure Pmin.

[0053] In some embodiments of this application, the method for quantitatively evaluating fault closure further includes the following steps:

[0054] The column height Hmin threshold is determined by the column height Hmin in the already formed oil-bearing areas and the column height Hmin in the non-oil-bearing areas within the study area;

[0055] The improved SGR threshold is determined based on the column height Hmin threshold.

[0056] The improved SGR threshold is determined by the improved SGR index of the established gas-bearing areas and the improved SGR index of the non-established gas-bearing areas within the study area;

[0057] The closure of all faults in the study area was evaluated based on the improved SGR threshold.

[0058] This application has the following beneficial effects:

[0059] The quantitative evaluation method for fault sealing provided in this application, targeting a specific fault in an oil and gas field, firstly involves fault interpretation. Through the interpretation of 3D seismic data, the fault displacement and dip angle of the fault whose sealing needs to be evaluated are obtained. Using existing drilling, logging, and well logging data of the study area, the vertical distribution data of sandstone, mudstone, and other lithologies in the target layer are acquired. Based on this, the SGR value is calculated using the classical SGR formula and the improved SGR formula. The Pc value of the target layer is then calculated using the formula for calculating fault capillary force Pc. The fault normal force (Pc) is then used... 断面 Formula for calculating P 断面 Value, through Pc value and P 断面 By comparing the values, the minimum opening pressure of the fault is obtained (the smaller of the two is the minimum opening pressure), and this pressure is then used to calculate the hydrocarbon column height H. min Finally, the SGR value and hydrocarbon column height H were calculated using existing faults in the hydrocarbon-bearing areas of the study region. min The values ​​of SGR and H of faults in non-hydrocarbon-forming areas are used to obtain the values ​​for fault sealing in research studies. min The threshold value. Once this threshold is obtained, the SGR value and H can be used to determine the threshold. min The values ​​were calculated to evaluate the sealing of all faults. Validation in the new area showed that the improved SGR index is more reliable than the traditional high SGR index and can more accurately evaluate fault sealing. Attached Figure Description

[0060] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0061] Figure 1 This is a schematic diagram illustrating the concept of mudstone smearing coefficient in existing technologies;

[0062] Figure 2 This is a schematic diagram of the SGR calculation method in the prior art;

[0063] Figure 3 This is a schematic diagram of mudstone smearing and SGR calculation in existing technology;

[0064] Figure 4 This is a flowchart illustrating the quantitative evaluation method for fault closure in the embodiments of this application;

[0065] Figure 5 This is a schematic diagram of mudstone smearing effect and SGR calculation in the embodiments of this application;

[0066] Figure 6This is a schematic diagram of the seismic profile for fault interpretation in the embodiments of this application;

[0067] Figure 7 This is a schematic diagram of the top surface structure of a target layer of a certain fault block in an embodiment of this application;

[0068] Figure 8 This is a columnar section of sand body development in a single well, as described in the embodiments of this application.

[0069] Figure 9 This is a schematic diagram illustrating the relationship between density and depth in an embodiment of this application;

[0070] Figure 10 This is a schematic diagram of a cross-section of a fault-bounded reservoir in an embodiment of this application. Detailed Implementation

[0071] The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The terminology used in the embodiments section of this application is only used to explain the specific embodiments of this application and is not intended to limit this application.

[0072] To facilitate understanding of the technical solution of this application, the existing technology will be further described below: In the theoretical research and exploration practice of hydrocarbon accumulation, the study of fault sealing has always been a difficult problem for oil and gas geologists. As early as the 1960s, people began to try to evaluate fault sealing. Smith DA (1966) first proposed the sand-sludge docking model for judging fault sealing. Following Engelder JT (1974)'s study on the relationship between fracturing and fault gouge formation ( Figure 1 Weber KJ (1978) and others confirmed the existence and distribution of fault gouge using annular shear tests. Smith DA (1980) proved through field geological observation and sample testing that mudstone smears have strong sealing capabilities. Based on this, Bouvier JA (1989) and others proposed the concept of mudstone smear potential (CSP) and its calculation method, and Lindsay AG (1993) and others proposed the concept of mudstone smear factor (SSF) and its calculation method. During this period, Allan US (1989) proposed a conceptual model for studying the sand-mud joint connection state of two fault blocks using the cross-sectional diagram method, based on the theory of mudstone joint sealing.

[0073] From Smith DA's first research paper on fault sealing in 1966 to Lü Yanfang's "Quantitative Study on Fault Sealing" published in the *Acta Petrolei Sinica* in 1996, the main research achievements over the past 30 years are: (1) clarifying that the essential factor of fault sealing is differential displacement pressure; (2) pointing out that fault sealing has a bidirectional nature, both lateral and vertical; (3) confirming that sand-mud joints and mudstone smears can cause faults to form lateral sealing; and (4) proposing geological factors affecting the distribution of sand-mud joints and mudstone smears, and using these as a method for qualitatively judging fault sealing. However, the above-mentioned methods for evaluating fault sealing are all qualitative, using "sealed" and "unsealed" to describe the sealing capacity of faults. The evaluation methods themselves are not "direct," but rather indirectly infer fault sealing through the analysis of factors affecting fault sealing.

[0074] The proposal and application of quantitative evaluation methods for fault closure began in 1996. In 1997, Yielding G et al. proposed a method for evaluating fault closure by quantitatively calculating SGR. Since then, there have been more and more articles on the quantitative evaluation of fault closure and detailed descriptions of its related parameters. Knipe RJ (1997) proposed the Knipe graphical method for quantitative analysis of fault sealing based on the principle of docking sealing; Tong Hengmao (1998) proposed the concept of fault sealing coefficient and a method for quantitatively evaluating fault sealing by establishing a model of the relationship between fault normal pressure and fault-displaced strata fluid pressure; Lü Yanfang et al. (2001) studied the distribution law and influencing factors of mudstone smears through physical simulation experiments; Koledoye AK et al. (2003) studied the distribution of mudstone smears using seismic slicing technology; Bretan J et al. (2003) proposed a method for estimating the maximum hydrocarbon column height that a fault can support by using SGR based on a large amount of fault data from around the world; since then, foreign scholars have mostly focused on studying the characteristics of the fault itself, and there are few articles on methods for quantitatively evaluating fault sealing. Childs C et al. (2009) simulated the sealing of faults by studying the migration of hydrocarbons; based on statistical analysis of actual data, a model of fault displacement, fault zone width, and fault rock thickness was established.

[0075]

[0076] SSF is the displacement and tilt displacement (W) of the fault along a cross section. L The thickness of the mudstone and shale near the cross-section that has undergone significant displacement (S) L The ratio of () Figure 1 ).

[0077] In the 21st century, the most significant domestic research achievements have come from experts such as Fu Xiaofei and Lü Yanfang of Northeast Petroleum University. Lü Yanfang et al. (2005) demonstrated, through physical simulation experiments, the quantitative relationship between oil and gas migration velocity along faults and fault dip angle and fracture infill particle size, and derived the lower limit values ​​of clay content in different particle size infill materials required for fault sealing. Fu Xiaofei et al. (2005) described the differences in internal structure between brittle and ductile fault zones through field geological investigations. Fu Guang et al. (2006) utilized SiO2 and... Studies on CaCO3 precipitation and cementation environments have led to the development of a method for evaluating the vertical sealing of fault fractures. Based on the characteristics of oil and gas migration along faults, Lü Yanfang et al. (2007) proposed that the lateral sealing of faults should be studied within reservoir sections, and the vertical sealing of faults should be studied within caprock sections, and proposed a quantitative method for studying vertical sealing. Zhang Likuan et al. (2007) proposed a method for quantitatively evaluating fault sealing using a probability-based approach. Lü Yanfang et al. (2009) proposed a method for quantitatively calculating the lateral sealing of faults using the pressure difference between faults and reservoirs. Fu Guang et al. (2012) further introduced the time factor to more accurately and quantitatively evaluate fault sealing.

[0078] With the further improvement and promotion of modeling and numerical simulation technology, various mathematical methods based on geological models have emerged for fault sealing studies. For example, Lü Yanfang et al. (2021) conducted a study on the quantitative evaluation of the lateral sealing of extensional faults based on integral mathematics-geological models, and proposed a fault lateral sealing evaluation method that considers the fault-reservoir displacement pressure difference method based on diagenesis time. In recent years, fault sealing studies based on sandbox physical simulations have also emerged. For example, Xie Xiaoning et al. (2020) and Jing Ziyan et al. (2022) conducted studies on the effectiveness evaluation of fault sealing based on sandbox physical simulations, and proposed a new fault sealing evaluation parameter based on a discontinuous proportional model—the minimum thickness of continuous mudstone smearing.

[0079] Current methods for studying fault sealing have their own limitations. These studies rely on the assumption of a relatively precise stratigraphic framework, but the heterogeneity of subsurface strata makes accurately understanding this framework difficult. Displacement pressures vary at different locations along a fault, thus affecting its sealing properties.

[0080] like Figure 2 and Figure 3 As shown, the SGR method based on the mudstone content of the sandstone-mudstone fault (Yielding et al., 1997) is one of the most commonly used methods for evaluating lateral sealing performance at present. SGR represents the mudstone ratio of the fault (also known as the mudstone mass fraction of the fault). The larger the value, the better the sealing performance of the fault. The SGR value is the ratio of the total thickness of the mudstone layer (∑H0) in the study segment to the vertical fault displacement (D). Figure 2However, this method mainly considers the thickness of the mudstone layer on one side of the fault, without considering the thickness of the mudstone layer on the adjacent side. Figure 1 In this study, only the sand body thickness and fault displacement of the strata to the right of BB' were considered, but the sand body thickness of the strata to the left of BB' was not taken into account. If the percentage of sandstone on the left side of the fault does not affect the SGR value, then the existing SGR method does not consider the connection relationship between the two sides of the fault.

[0081] Current research both domestically and internationally indicates that fault sealing studies are relatively mature, with various methods and techniques developed. Among the various methods based on mudstone smearing, two main factors are utilized: the mudstone content of the target layer and the fault displacement (vertical displacement D). Extensive research both domestically and internationally has demonstrated the practicality of these methods. However, analysis of the mudstone smearing process reveals that after point A is displaced by the fault, the hanging wall moves from point A to A'. The sealing property of the fault at point A' is related not only to the mudstone content of point A' itself but also to the mudstone content of the AA' strata in the footwall where the displacement occurred. However, calculation formulas for SGR and SSF show that the sealing property of the fault corresponding to BB' within the fault displacement range is only related to the fault displacement D and the lithology within the hanging wall strata of BB'. Figure 2 SGR, SSF, and CSP all neglected the influence of their corresponding lithology on fault smearing.

[0082] For fault types where the sandstone content of the two sides of a fault differs significantly, existing mudstone smearing methods ignore the proportion of sandstone and mudstone in the strata of the connecting side. As a result, the results calculated by existing methods have a large error in judging the sealing of the fault, and may even lead to misjudgment, resulting in huge economic losses in the process of oil and gas exploration and development.

[0083] To address the aforementioned technical problems in the prior art and improve the accuracy of fault closure assessment, in the embodiments of this application, such as... Figure 4 As shown, a method for quantitatively evaluating fault closure is provided, comprising the following steps:

[0084] The improved SGR index of the target layer is calculated according to formula (1).

[0085]

[0086] In formula (1), ∑H1 is the total thickness of the hanging mudstone layer in the study section, ∑H2 is the total thickness of the hanging mudstone layer connected to the study section, and D is the vertical fault displacement.

[0087] The closure of all faults in the study area was evaluated based on the improved SGR index.

[0088] After verification in the new area, the improved SGR index is more reliable than the traditional high SGR index and can more accurately evaluate the fault closure.

[0089] In some embodiments of this example, the evaluation of the closure of all faults in the study area based on the improved SGR index includes verifying the reliability of the improved SGR index.

[0090] The verification of the reliability of the improved SGR index includes:

[0091] The new area within the study area was surveyed, and the improved SGR index of the new area was calculated.

[0092] Determine whether there is any overlap between the improved SGR index interval corresponding to the existing Tibetan areas within the new area and the improved SGR index interval corresponding to the non-Tibetan areas within the new area;

[0093] If the improved SGR index interval corresponding to the existing Tibetan areas within the new area and the improved SGR index interval corresponding to the non-Tibetan areas within the new area do not overlap, then the improved SGR index is reliable.

[0094] If the improved SGR index is reliable, then the improved SGR index is used to evaluate the closure of all faults in the study area.

[0095] In some embodiments of this example, the evaluation of the closure of all faults in the study area based on the improved SGR index includes verifying the reliability of the improved SGR index.

[0096] The verification of the reliability of the improved SGR index includes:

[0097] The new area within the study area was surveyed, and the traditional SGR index of the new area was calculated according to formula (2).

[0098]

[0099] In formula (2), ∑H0 is the total thickness of the mudstone layer in the study section, and D is the vertical fault displacement.

[0100] Calculate the improved SGR index of the new area;

[0101] Determine whether there is an overlap between the traditional SGR index interval corresponding to the existing Tibetan areas within the new area and the traditional SGR index interval corresponding to the non-Tibetan areas within the new area;

[0102] Determine whether there is any overlap between the improved SGR index interval corresponding to the existing Tibetan areas within the new area and the improved SGR index interval corresponding to the non-Tibetan areas within the new area;

[0103] If the traditional SGR index interval corresponding to the established Tibetan areas in the new area and the traditional SGR index interval corresponding to the non-established Tibetan areas in the new area overlap, and the improved SGR index interval corresponding to the established Tibetan areas in the new area and the improved SGR index interval corresponding to the non-established Tibetan areas in the new area do not overlap, then the improved SGR index is reliable.

[0104] If the improved SGR index is reliable, then the improved SGR index is used to evaluate the closure of all faults in the study area.

[0105] In some embodiments of this example, the improved SGR index for calculating the target layer includes:

[0106] Calculate the fault capillary force Pc of the target layer according to formula (3).

[0107] Pc = 10 (SGR / d-c) (3),

[0108] In formula (3), d is an empirical parameter and c is a coefficient;

[0109] The improved SGR index is determined based on the capillary force Pc of the fault rock.

[0110] In some embodiments of this example, the improved SGR index for calculating the target layer includes:

[0111] The height of the hydrocarbon column Hmin in the target layer is calculated according to formula (4).

[0112]

[0113] In formula (4), ρ w ρ is the density of water. 烃 Where is the density of the oil and gas, g is the acceleration due to gravity, d is an empirical parameter, and c is a coefficient;

[0114] The improved SGR index is determined based on the hydrocarbon column height Hmin.

[0115] In some embodiments of this example, the improved SGR index for calculating the target layer includes:

[0116] The CO2 column height Hmin of the target layer is calculated according to formula (5).

[0117]

[0118] In formula (5), ρ w For the density of water, Where is the density of CO2, g is the acceleration due to gravity, d is an empirical parameter, and c is a coefficient;

[0119] The improved SGR index is determined based on the CO2 column height Hmin.

[0120] In some embodiments of this example, calculating the column height Hmin includes:

[0121] Calculate the fault normal pressure P of the target layer according to formula (6). 断面 ,

[0122]

[0123] In formula (6) ρ w ρ is the density of the formation water, g is the gravitational acceleration, H is the burial depth, θ is the cross-sectional dip angle, and a and b are coefficients;

[0124] Based on the fault normal pressure P 断面 Calculate the column height Hmin.

[0125] In some embodiments of this example, calculating the column height Hmin includes:

[0126] The empirical coefficient c1 is calculated according to formula (7).

[0127] Pmin = 10 (SGR / d-c) (7),

[0128] In formula (7), Pmin is the minimum opening pressure, d is an empirical parameter, and c is a coefficient;

[0129] The column height Hmin is calculated based on the minimum opening pressure Pmin.

[0130] In some embodiments of this example, calculating the column height Hmin includes:

[0131] Compare the capillary force Pc of the fault rock and the normal force P of the fault. 断面 Size;

[0132] If Pc > P 断面 Then, the fault normal pressure P 断面 The minimum opening pressure Pmin;

[0133] If Pc≤P 断面 Then, the fault capillary force Pc is taken as the minimum opening pressure Pmin.

[0134] In some embodiments of this example, the method for quantitatively evaluating fault closure further includes the following steps:

[0135] The column height Hmin threshold is determined by the column height Hmin in the already formed oil-bearing areas and the column height Hmin in the non-oil-bearing areas within the study area;

[0136] The improved SGR threshold is determined based on the column height Hmin threshold.

[0137] The improved SGR threshold is determined by the improved SGR index of the established gas-bearing areas and the improved SGR index of the non-established gas-bearing areas within the study area;

[0138] The closure of all faults in the study area was evaluated based on the improved SGR threshold.

[0139] To facilitate understanding of the technical solution of this application, the following is combined with Figures 5 to 10 The technical solution of this application will be described in further detail below, with the specific steps as follows:

[0140] Step 1: Obtaining SGR exponent calculation parameters

[0141] The mudstone smearing theory was proposed in the 1970s. Although the calculation methods for mudstone smearing have been modified by many scholars, the basic theoretical basis has not changed significantly. The SGR method (Yielding et al., 1997) is one of the most commonly used methods for evaluating lateral sealing capacity at present. Its basic assumption is that the fault rock is composed of a mixture of mudstone fragments and sandstone fragments with different mud content, and its sealing capacity mainly depends on the mud content of the fault rock. The formula is:

[0142]

[0143] In the formula: ∑H0 is the total thickness of the mudstone layer in the studied section, and D is the vertical fault displacement (see appendix). Figure 5 ).

[0144] Therefore, the first step is to obtain the total mudstone thickness and vertical displacement involved in the SGR method. Vertical displacement is mainly obtained through two methods. The first is by analyzing faults shown in well data during drilling, determining the displacement through the missing strata. However, this method has high requirements for wells, and in most areas with limited drilling, it is difficult to calculate displacement from well data. Furthermore, obtaining the fault dip angle from well data is even more challenging. The second method is to obtain displacement through seismic data. Through structural interpretation, fault displacement and dip angle can be obtained. This method is the most commonly used for obtaining displacement and dip angle. Through detailed seismic tectonic interpretation of the study area, fault displacement and dip angle can be obtained very intuitively using fault-crossing seismic profiles (see appendix). Figure 6 Furthermore, through a comprehensive interpretation of the 3D seismic data, a top structural map of the target layer in the study area can be obtained (see attached map). Figure 7 This provides a basis for evaluating fault sealing and hydrocarbon traps.

[0145] The thickness of mudstone is mainly obtained through well logging and well logging data, as well as well logging interpretation results. A single-well sand body development columnar section is obtained by analyzing the sand body development of each well (see attached). Figure 8 The cumulative sand body thickness N was obtained, and the cumulative mudstone stratum thickness H was obtained by subtracting the sand body thickness N from the stratum thickness D. That is:

[0146] H = DN

[0147] Taking the Fu 148 fault block as an example, the fault displacement, fault dip angle and mudstone thickness were obtained through the above method. The SGR index value can then be calculated using the SGR formula. The SGR index of different strata in the study area can be obtained through this method (Table 1).

[0148]

[0149] Table 1 (SGR index of different strata in the Fu 148 fault block)

[0150] Step 2: Improved SGR Index Calculation Method and Process

[0151] The SGR method proposed by previous researchers utilizes two main factors: the mudstone content and fault displacement (vertical fault displacement) of the target surface layer. Numerous studies both domestically and internationally have demonstrated the method's practicality. However, analysis of the mudstone smearing process reveals that point A, after fault displacement, moves the hanging wall from point A to A'. The sealing effect of the fault on the hanging wall at A' depends not only on the mudstone content of point A' itself but also on the mudstone content of the AA' strata in the footwall where the displacement occurred. However, calculation formulas for SGR and SSF show that the sealing effect of the fault corresponding to BB' within the fault displacement range is only related to the fault displacement D and the lithology within the hanging wall strata of BB'. SGR, SSF, and CSP all neglect the influence of the corresponding hanging wall lithology on fault smearing (see appendix). Figure 5 To address this shortcoming of existing SGR methods, an improved SGR index calculation method is proposed based on research of the study area. The formula is as follows:

[0152]

[0153] In the formula: ∑H1: total thickness of mudstone layer in the hanging wall of the studied section; ∑H2: total thickness of mudstone layer in the footwall connected to the H1 stratum; D: vertical displacement of the fault (apparent displacement).

[0154] The improved SGR index replaces the total mudstone thickness of a single mudstone layer with the total mudstone thickness of the adjacent strata of the upper and lower blocks, thus effectively overcoming the aforementioned problems. The relevant parameters are obtained in the first step. The total mudstone thickness of the adjacent block can be obtained from drilling data of wells near the fault. If drilling data for the adjacent block is unavailable, drilling data from the target block can also be used. Using the improved SGR index calculation formula, the improved SGR index of the target fault can be calculated. Calculations for the study area show that because the mudstone content of the adjacent block is higher than that of the target block, the calculated improved SGR value is larger than the standard SGR value. Furthermore, the SGR value of the Dai-2 section is only 37, while the improved SGR value is 60, showing a significant difference (Table 2).

[0155]

[0156] Table 2 (SGR index and improved SGR index of different strata in the Fu 148 fault block)

[0157] Step 3: Calculation of fault capillary force Pc and hydrocarbon column height Hmin.

[0158] The capillary pressure is still derived from the SGR method by referencing the calculation method for mudstone capillary pressure. The relationship between mudstone content and capillary pressure is as follows:

[0159] P c =10 (SGR / d-c)

[0160] In the formula: P c denoted as capillary pressure (MPa); c is a coefficient, dimensionless (c = 0.5 when the fracture depth is less than 3.0 km; c = 0.25 when the fracture depth is 3.0–3.5 km; c = 0 when the fracture depth is greater than 3.5 km). d is a parameter to be calibrated based on the oil column height of the fault reservoirs discovered in the study area, with a value ranging from 0 to 200. Based on the analysis of multiple oilfields in the current technology, the empirical value is taken as 27.

[0161] Foreign experts used this relationship to study the hydrocarbon column height H of their respective research areas. min The values ​​were estimated and compared, and the height H of the hydrocarbon column that SGR and fault rocks can seal was established. min The statistical relationship formula yields relatively ideal results.

[0162] H min The formula for calculating the value is:

[0163]

[0164] In the formula: ρ w , ρ 烃ρ represents the density of water and oil / gas, respectively; g represents the acceleration due to gravity; d represents the parameter to be calibrated based on the height of the oil column in the fault reservoirs discovered in the study area, with a value ranging from 0 to 200. In the existing technology, through the analysis of multiple oil fields, the empirical coefficient c1 is set to 27.

[0165] By analyzing the study area P c and H min The value can be calculated by replacing the crude oil density ρ with the density of CO2 in the formation. 烃 The height H of the O2 column can then be obtained. min The calculation results are shown in Table 3. It can be seen that H calculated using the SGR value and the improved SGR value... min The values ​​also vary considerably.

[0166]

[0167] Table 3 (P of different strata in the Fu 148 fault block) c and H min value)

[0168] Step 4: Fault normal pressure (P) 断面 Value calculation

[0169] The overlying pressure and the dip angle of the fault plane determine the magnitude of the vertical pressure on the fault surface. This pressure, together with the mud-soil ratio of the fault-crossing strata, determines the vertical sealing of the fault, as shown in the following formula:

[0170] P 断面 =(P H -ρ W *gH)×cosθ

[0171]

[0172] In the formula: P 断面 ρ is the vertical pressure (normal pressure) on the cross section, MPa; PH is the pressure of the overlying strata, MPa; ρ w Density of formation water, g / cm³ 3 g is the acceleration due to gravity, in m / s². 2 H is the burial depth, m; θ is the cross-sectional inclination angle, (°); a and b are the coefficients in the relationship between density and burial depth.

[0173] A study on the relationship between density and depth of people living in poverty (see appendix) Figure 9 ), a=0.00031, b=1.9391; ρ w =1.02, the dip angle θ of the true fault ② in the 148 fault block is 48°-54°, ​​the vertical depth of the carbon dioxide reservoir is 1800-2100m, and the vertical depth of the oil reservoir is 2400-2600m. The P values ​​at different depths in the study area can be calculated using the above formula. 断面 Value. It can be seen that P断面 The value increases with increasing depth.

[0174]

[0175] Table 4 (P at different depths in the Fu 148 fault block) 断面 value)

[0176] Step 5, SGR and H min Threshold calculation

[0177] Analysis of the discovered oil and CO2 gas reservoirs in the study area reveals that a CO2 gas reservoir has formed in the first segment of the 148 fault block, while oil reservoirs have formed in the second and first segments of the Dai section. However, no reservoirs have formed in the second segment of the 148 fault block. (See appendix) Figure 10 ), and through the SGR and improved SGR values ​​of multiple reservoirs in the Fumin area, as well as H min Value calculations confirm that the improved SGR value for hydrocarbon accumulation in the Fumin area is >45, and the H... min Value >15m. The SGR threshold for hydrocarbon accumulation in the study area shows that the Dai 2 member of the rich 148 fault block is 37 according to the traditional SGR value (Table 1). Judging from the traditional SGR value, the fault of the Dai 2 member of the rich 148 fault block is open and hydrocarbon accumulation is not possible. This also illustrates the problem of the traditional SGR method.

[0178] Step 6: Verification of the method in the new area

[0179] Using the above methods, a study was conducted on the Fu 43 fault block in the Fumin area. The main controlling fault, Fu 43, has a short distance of 260m. The Duo 2 Member, Dai 2 Member, E2s16, and E2s17 sand bodies are thick, but the sandstone content in the upper part of the Duo 1 Member is less than 50%. However, hydrocarbon accumulation only occurs in the Dai 1 Member. Improved SGR calculations show that only the Dai 1 Member has a content greater than 45%, which is consistent with the fact that hydrocarbon accumulation in the Fu 43 fault block is only in the Dai 1 Member. However, it can be seen that in traditional SGR calculations, the upper Duo 1 Member, the lower Dai 2 Member, and the Dai 1 Member are all greater than 45%, but no hydrocarbon accumulation occurs in the upper Duo 1 Member and the lower Dai 2 Member. The fault in this section of the strata does not seal for oil and gas, indicating that the improved SGR method can better determine the sealing properties of the fault.

[0180]

[0181]

[0182] Table 5 (SGR index and improved SGR index of different strata in the Fu 43 fault block)

[0183] In summary, this application focuses on a specific fault in an oil and gas field. First, fault interpretation is conducted. Through the interpretation of 3D seismic data, the fault displacement and dip angle of the fault whose sealing performance needs to be evaluated are obtained. Using existing drilling, logging, and well logging data of the study area, the vertical distribution data of sandstone, mudstone, and other lithologies in the target layer are acquired. Based on this, the SGR value is calculated using the classical SGR formula and the improved SGR formula. The Pc value of the target layer is calculated using the formula for calculating fault capillary force Pc. The fault normal force (Pc) is then used. 断面 Formula for calculating P 断面 Value, through Pc value and P 断面 By comparing the values, the minimum opening pressure of the fault is obtained (the smaller of the two is the minimum opening pressure), and this pressure is then used to calculate the hydrocarbon column height H. min Finally, the SGR value and hydrocarbon column height H were calculated using existing faults in the hydrocarbon-bearing areas of the study region. min The values ​​of SGR and H of faults in non-hydrocarbon-forming areas are used to obtain the values ​​for fault sealing in research studies. min The threshold value. Once this threshold is obtained, the SGR value and H can be used to determine the threshold. min The values ​​are calculated to evaluate the closure of all faults.

[0184] The working principle of this application is to use the improved SGR formula, along with existing formulas for calculating fault capillary force Pc and fault normal pressure (P-section), to calculate the improved SGR value and hydrocarbon column height Hmin value of the study area. Furthermore, by using SGR and Hmin values ​​calculated from faults in hydrocarbon-rich areas and faults in non-hydrocarbon-rich areas, threshold values ​​for SGR and Hmin values ​​for determining fault sealing are obtained. Thus, fault parameters in unknown areas are calculated using the improved SGR formula, thereby determining fault sealing.

[0185] In the description of the embodiments of this application, it should be noted that the terms "the above embodiments," "some embodiments," "the above implementation methods," "some implementation methods," "possible embodiments," or "possible implementation methods," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the embodiments of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0186] The above embodiments are merely explanations of this application and are not intended to limit it. After reading this specification, those skilled in the art can make modifications to the implementation methods of this application without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for quantitatively evaluating fault sealing, characterized in that, Includes the following steps: The improved SGR index of the target layer is calculated according to formula (1). （1）， In formula (1), ∑H1 is the total thickness of the hanging mudstone layer in the study section, ∑H2 is the total thickness of the hanging mudstone layer connected to the study section, and D is the vertical fault displacement. The sealing performance of all faults in the study area was evaluated based on the improved SGR index. The improved SGR index replaces the total thickness of mudstone layers in the opposing strata of the upper and lower blocks with the total thickness of mudstone layers in one block. The total thickness of mudstone layers in the opposing strata can be obtained from drilling data of wells near the faults of the opposing strata. In the case of a lack of drilling data in the opposing strata, drilling data of the target strata can also be used to obtain the total thickness of mudstone layers in the opposing strata. The improved SGR index for the target layer includes: Calculate the fault capillary force Pc of the target layer according to formula (3). （3）， In formula (3), d is an empirical parameter and c is a coefficient; The improved SGR index is determined based on the fault capillary force Pc. The improved SGR index for the target layer includes: The hydrocarbon column height Hmin of the target layer is calculated according to formula (4). （4）， In formula (4), For the density of water, For oil and gas density, It is the acceleration due to gravity. Here, c is an empirical parameter, and c is a coefficient. The improved SGR index is determined based on the hydrocarbon column height Hmin; The improved SGR index for the target layer includes: The CO2 column height Hmin of the target layer is calculated according to formula (5). （5）， In formula (5), For the density of water, CO2 density It is the acceleration due to gravity. Here, c is an empirical parameter, and c is a coefficient. The improved SGR index is determined based on the CO2 column height Hmin.

2. The method for quantitative evaluation of fault sealing according to claim 1, characterized in that, The assessment of the closure of all faults in the study area based on the improved SGR index includes verifying the reliability of the improved SGR index. The verification of the reliability of the improved SGR index includes: The new area within the study area was surveyed, and the improved SGR index of the new area was calculated. Determine whether there is any overlap between the improved SGR index interval corresponding to the existing Tibetan areas within the new area and the improved SGR index interval corresponding to the non-Tibetan areas within the new area; If the improved SGR index interval corresponding to the existing Tibetan areas within the new area and the improved SGR index interval corresponding to the non-Tibetan areas within the new area do not overlap, then the improved SGR index is reliable.

3. The method for quantitative evaluation of fault sealing according to claim 1, characterized in that, The assessment of the closure of all faults in the study area based on the improved SGR index includes verifying the reliability of the improved SGR index. The verification of the reliability of the improved SGR index includes: The new area within the study area was surveyed, and the traditional SGR index of the new area was calculated according to formula (2). （2）， In formula (2), ∑H0 is the total thickness of the mudstone layer in the study section, and D is the vertical fault displacement. Calculate the improved SGR index of the new area; Determine whether there is an overlap between the traditional SGR index interval corresponding to the existing Tibetan areas within the new area and the traditional SGR index interval corresponding to the non-Tibetan areas within the new area; Determine whether there is any overlap between the improved SGR index interval corresponding to the existing Tibetan areas within the new area and the improved SGR index interval corresponding to the non-Tibetan areas within the new area; If the traditional SGR index interval corresponding to the existing Tibetan areas in the new area and the traditional SGR index interval corresponding to the non-Tibetan areas in the new area overlap, and the improved SGR index interval corresponding to the existing Tibetan areas in the new area and the improved SGR index interval corresponding to the non-Tibetan areas in the new area do not overlap, then the improved SGR index is reliable.

4. The method for quantitative evaluation of fault sealing according to claim 1, characterized in that, Calculating the column height Hmin includes: Calculate the fault normal pressure P of the target layer according to formula (6). 断面 , （6）， In formula (6) ρ w ρ is the density of the formation water, g is the gravitational acceleration, H is the burial depth, θ is the cross-sectional dip angle, and a and b are coefficients; Based on the fault normal pressure P 断面 Calculate the column height Hmin.

5. The method for quantitative evaluation of fault sealing according to claim 4, characterized in that, Calculating the column height Hmin includes: The empirical coefficient c1 is calculated according to formula (7). （7）， In formula (7), Pmin is the minimum opening pressure, c1 is an empirical coefficient, and c2 is a coefficient. The column height Hmin is calculated based on the minimum opening pressure Pmin.

6. The method for quantitative evaluation of fault sealing according to claim 5, characterized in that, Calculating the column height Hmin includes: Compare the capillary force Pc of the fault rock and the normal force P of the fault. 断面 Size; If Pc > P 断面 Then, the fault normal pressure P 断面 The minimum opening pressure Pmin; If Pc≤P 断面 Then, the fault capillary force Pc is taken as the minimum opening pressure Pmin.

7. The method for quantitative evaluation of fault sealing according to claim 6, characterized in that, The quantitative evaluation method for fault sealing also includes the following steps: The column height Hmin threshold is determined by the column height Hmin in the already formed oil-bearing areas and the column height Hmin in the non-oil-bearing areas within the study area; The improved SGR threshold is determined based on the column height Hmin threshold. The improved SGR threshold is determined by the improved SGR index of the established gas-bearing areas and the improved SGR index of the non-established gas-bearing areas within the study area; The closure of all faults in the study area was evaluated based on the improved SGR threshold.

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