A method for evaluating the vertical sealing of faults by combining static and dynamic analysis of water-bearing traps

Abstract

The present invention provides a method for evaluating the vertical sealing property of a fault combining static and dynamic characteristics of a water-bearing trap, and the method comprises: step 1, a detailed geological description of a target fault; step 2, a geological description and grade evaluation; step 3, judging the static sealing capacity of the target fault, and giving corresponding suggestions or measures; step 4, establishing a geomechanical model according to seismic structural interpretation and logging data, simulating the activation of the fault under different injection and production cycles; step 5, establishing a finite element analysis model under seepage-stress coupling, and analyzing the dynamic sealing change and mechanical stability of the fault with the injection years. The method for evaluating the vertical sealing property of a fault combining static and dynamic characteristics of a water-bearing trap finally obtains the vertical sealing property of a fault in an aquifer gas storage reservoir and the corresponding service life, and is suitable for the analysis of the vertical sealing property of a fault in various underground projects.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield development, and in particular to a method for evaluating the vertical sealing property of a fault combining static and dynamic characteristics of a water-containing trap. Background Art

[0002] The vertical closure of a fault is the ability of the fractured material to prevent the fluid from migrating vertically along the fault zone. For fault-block aquifer traps, fault closure is one of the important factors affecting reservoir construction. Previous studies have mostly been conducted from the perspective of exploration or oil and gas reservoir statics, mainly focusing on the relationship between the lithology configuration of the two sides of the fault, fluid properties, and the combination of faults and the static closure of the fault.

[0003] At present, in terms of content, most people focus on the study of fault geometry, morphology or material smear on the fault surface; some scholars also use the comparison between the fault surface pressure and the plastic deformation of mudstone to indirectly evaluate the vertical closure of faults. Abroad, the earliest fault butt closure model proposed by Allan was the Allan diagram developed by considering the relationship between the lithology thickness, stratigraphic morphology and fault throw on both sides of the fault. This method has a low success rate in evaluating the fault closure capacity; followed by the mudstone smear factor (SSF) proposed by Linday, which established the critical value of mudstone smear continuity in meter-scale faults in the field through a large amount of field data. This method only considers the relationship between mud content and closure, and has certain limitations. In China, Fu Guang (1998) evaluated the vertical sealing of faults by using the normal pressure of the fault plane, the sand-mud ratio of the fault-displacement strata, and the relative relationship between the acoustic time difference of the fault filling and the surrounding rock; Lu Yanfang et al. studied the vertical sealing capacity of faults by establishing a cross-section pressure calculation method based on the docking sealing model; Hou Yawei (2013) proposed a fault vertical sealing evaluation model and defined the fault vertical sealing index (FVSI) to characterize the vertical sealing capacity and stability of faults.

[0004] The vertical closure of faults is not only related to the normal stress of the section and the mudstone smear factor, but also closely related to the fault dip, burial depth, fault distance, mechanical factors and environment formed in the geological structure process. Since the gas storage reservoir needs to implement strong injection and strong mining operations in a short period of time, the analysis of fault closure from a static perspective is often one-sided and difficult to involve the impact of fault activation during the gas injection process of the gas storage reservoir. Therefore, it is necessary to establish a dynamic and static combined fault vertical closure evaluation method.

[0005] In the Chinese patent application with application number: CN201610183490.2, a method for quantitatively evaluating the three-dimensional closure of a fault based on geostress simulation is involved, which includes the following steps: Step 1, testing the mechanical parameters of rock strength; Step 2, testing the current magnitude and direction of geostress; Step 3, establishing a fault structural mechanical model; Step 4, calculating closure evaluation parameters; Step 5, optimizing the fault closure index; Step 6, evaluating the three-dimensional closure of the fault.

[0006] In the Chinese patent application with application number: CN201810087049.3, a method for evaluating the sealing property of a fault in the field of oil and gas field exploration technology is involved, and the steps are as follows: (1) selecting a breakpoint on a fault in a reservoir that needs to be evaluated for sealing property, determining each sand and mud stratum that slides across the breakpoint, and determining the thickness ΔZi of each sand and mud stratum; (2) sequentially obtaining the mud content Vshi of each sand and mud stratum that slides across the breakpoint; (3) sequentially obtaining the weighted coefficient Wi that slides across each sand and mud stratum; (4) calculating the weighted mudstone fault mud ratio WSGR value of the breakpoint; (5) using the weighted mudstone fault mud ratio WSGR value to evaluate the sealing property of the reservoir at the breakpoint position, when the WSGR value is greater than or equal to 0.6, it indicates that the fault sealing property at the breakpoint position is good and can form an effective plugging for oil and gas, and it is highly likely to be an oil layer or an oil-bearing water layer; otherwise, it is highly likely to be a water layer.

[0007] In the Chinese patent application with application number: CN201811073289.4, a quantitative evaluation method for the lateral closure of a fault is involved, which belongs to the field of oil and gas exploration and includes the following steps: for each time unit from the oil and gas accumulation period to the present period, the strata of each time unit from the oil and gas accumulation period to the present period are restored by the decompaction correction method, and the ancient mudstone smear factor, ancient mudstone smear potential and ancient fault mud ratio corresponding to the single sand layer at different depths in each time unit are calculated respectively; the present mudstone smear factor, present mudstone smear potential and present fault mud ratio corresponding to the present period are calculated; when the mudstone smear factor, mudstone smear potential and fault mud ratio corresponding to the ancient period and the present period all meet the threshold requirements, the fault is laterally closed; otherwise, the fault was laterally opened.

[0008] The above existing technologies are greatly different from the present invention and fail to solve the technical problem we want to solve. Therefore, we have invented a new method for evaluating the vertical sealing property of faults by combining static and dynamic methods of water-bearing traps. Summary of the invention

[0009] The purpose of the present invention is to provide a method for evaluating the vertical sealing property of faults by combining static and dynamic methods of water-bearing traps, which is applicable to the analysis of the vertical sealing property of faults in various underground projects.

[0010] The object of the present invention can be achieved by the following technical measures: a method for evaluating the vertical sealing property of a fault combining static and dynamic characteristics of a water-bearing trap, the method comprising:

[0011] Step 1: Conduct a detailed geological description of the target fault.

[0012] Step 2, establishing a static sealing evaluation system and evaluation level of the target fault based on fault mechanics, fault environmental conditions, fault lithology and fault occurrence;

[0013] Step 3, static sealing evaluation of the target fault is performed as the basis for dynamic sealing research;

[0014] Step 4: Establish a geomechanical model based on seismic structural interpretation and logging data to simulate fault activation under different injection and production cycles;

[0015] Step 5: Establish a finite element analysis model under seepage-stress coupling to analyze the dynamic sealing changes and mechanical stability of the fault with injection years.

[0016] The purpose of the present invention can also be achieved by the following technical measures:

[0017] In step 1, a detailed geological description of the target fault is carried out by combining the existing geological data of the target fault, interpretation of seismic structural characteristics, logging data and field exploration sampling.

[0018] In step 1, the four main aspects of fault lithology, fault mechanical factors, fault environmental conditions and fault attitude are taken into consideration. Starting from the most basic geological conditions, on-site exploration is the main method for analyzing geological data, so as to obtain various level 2 indicator parameters and provide reliable prerequisites for the subsequent scoring stage.

[0019] In step 2, based on seismic interpretation and logging data, geological description and grade evaluation are performed from 14 level 2 indicators under the four level 1 indicators of fault lithology, fault environmental conditions, fault mechanical factors, and fault occurrence, and the corresponding weight values ​​of each level of indicators are calculated.

[0020] In step 2, whole-rock mineral content and clay content analysis are performed based on field exploration sampling to obtain the properties of the fault zone filling and the mud content.

[0021] In step 2, the mud smear coefficient of the fault plane is calculated based on the existing geological data and the mud smear empirical formula, that is:

[0022]

[0023] In the formula, f m is the mud smear coefficient; L is the fault throw; Hi is the thickness of the i-th mudstone layer offset by the fault; n is the number of mudstone layers offset by the fault; H is the thickness of the stratum offset by the fault; R m It is the ratio of the mudstone thickness of the stratum displaced by the fault to the stratum thickness.

[0024] In step 2, the shale content in the fault zone is estimated based on the data of fault throw, fault-displacement stratum lithology and thickness, and compared with the shale content obtained from whole-rock analysis. The estimation formula is:

[0025]

[0026] Where, L is the vertical distance; h i 、h j are the thickness of the i-th and j-th mudstone layers in the upper and lower walls of the fault, respectively; n1 and n2 are the numbers of mudstone layers displaced in the two walls of the fault, respectively; and H is the thickness of the fault-displaced stratum.

[0027] In step 2, based on geological data such as earthquakes and well logging, determine the lithology of the two sides of the fault zone and the formation environment in which the fault zone is located, including: the fluid properties and temperature-pressure system of the two sides of the fault; interpret the ground stress, fault type, fault dip, fault burial depth and fault distance of the enclosed fault based on field exploration, seismic structural data and well logging data; and combine the field exploration situation to determine whether the fault has completely dislocated the caprock, so as to determine the degree of damage caused by the fault to the caprock.

[0028] In step 3, the calculation model of the entire fault is established by combining the hierarchical analysis method, and the weight value of each indicator is multiplied by the score obtained by the evaluation indicator, that is:

[0029]

[0030] In the formula, m i is the quantitative value of each evaluation index; ω i is the weight value of each evaluation index; i=1,2,…,13

[0031] Determine whether the target fault is suitable for database construction, and decide whether to continue dynamic sealing evaluation based on the static sealing results.

[0032] In step 4, a geomechanical model is established based on seismic structural interpretation and logging data, and a shear-permeability test is carried out under alternating stress conditions to test the critical value of cumulative slip to simulate the activation of faults under different injection-production cycles.

[0033] In step 5, based on geological coring, rock mechanics parameters are obtained through triaxial compression tests of rock mechanics, and a finite element analysis model under seepage-stress coupling is established. The finite element method is used for simulation analysis, and the dynamic sealing changes and mechanical stability of the fault with the injection years are analyzed based on the cumulative slip displacement, critical internal friction angle and tensile failure criterion.

[0034] In step 5, the confining pressure under the fault burial depth condition is calculated, that is:

[0035] P z =0.0226MPa / m×d

[0036] Where, d is the depth of the stratum where the core is located, unit, m;

[0037] According to the calculated confining pressure, triaxial compression mechanical tests on the core are carried out to obtain the fault rock mechanical parameters, and the finite element simulation results are used to predict the activity of the fault.

[0038] In step 5, the minimum principal compressive stress is used to define the pressure margin PMF of the fault hydraulic fracture:

[0039] P in <PMF=max(σ′1,σ′2,σ′3)

[0040] Where, are the maximum, intermediate and minimum principal stresses in the fault zone, respectively, and negative values ​​represent compression.

[0041] In step 5, the fault slip trend is predicted using the Mohr-Coulomb criterion, namely:

[0042] τ=c0+μ s σ′ n

[0043] Where τ is the critical activation shear stress of the fault plane, σ' n is the normal effective stress of the fault plane, C0 is the cohesion of the fault zone, μ s is the static friction coefficient of the fault.

[0044] In step 5, the accumulated shear deformation or fault slip is the injection pressure P in The implicit relationship between the number of alternations n and the fault alternation effect is as follows:

[0045] δ(P in ,n)<δ lim

[0046] In the formula, δ lim The allowable cumulative amount of fault displacement can be determined through alternating tests or finite element simulations under injection-production cycles.

[0047] The method for evaluating the vertical sealing property of a fault combining static and dynamic conditions of a water-bearing trap in the present invention comprehensively considers four main influencing factors, namely, fault mechanics, fault occurrence, fault formation environment and fault lithology, and uses existing empirical formulas, interpretation of seismic logging geological data, literature research and expert consultation to establish evaluation criteria for each index of the vertical sealing property of a water-bearing trap fault and evaluation levels for suitability database construction. The analytic hierarchy process is used to calculate the specific weight value of each index, and a mathematical model for comprehensive scoring of the vertical sealing property of a target fault under dynamic and static conditions is established. Finally, the comprehensive scoring result is compared with the established evaluation criteria for suitability database construction to judge the static sealing property of the target fault. Based on the evaluation result of the static sealing property, a finite element mechanical analysis model is established through geological structural characteristics, and the upper limit injection pressure of the fault is predicted according to the Mohr-Coulomb shear activation criterion and the tensile failure criterion. Combined with the shear-permeability test under alternating stress conditions, the mechanical stability and injection and production service life of the target fault are analyzed. The combined dynamic and static evaluation method for aquifer gas storage faults described in the present invention concentrates on summarizing and analyzing the understanding of fault geological conditions, theoretical analysis, establishment of evaluation criteria, finite element simulation analysis and indoor experiments, and ultimately obtains the vertical sealing conditions of aquifer gas storage faults and the corresponding service life, which is suitable for the analysis of vertical sealing properties of faults in various underground projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a flow chart of a specific embodiment of the method for evaluating the vertical sealing property of a fault combining static and dynamic water-bearing traps of the present invention;

[0049] Figure 2 A diagram of a static evaluation system for aquifer gas storage faults in a specific embodiment of the present invention;

[0050] Figure 3 A seismic structure interpretation diagram in a specific embodiment of the present invention;

[0051] Figure 4 A schematic diagram of a geomechanical model in a specific embodiment of the present invention;

[0052] Figure 5 It is a schematic diagram of a fault shear slip calculation method in a specific embodiment of the present invention;

[0053] Figure 6 It is a reservoir measurement line effective stress analysis diagram in a specific embodiment of the present invention;

[0054] Figure 7 Schematic diagram of the change of the Mohr circle of the F1-2 fault measuring point in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0055] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0056] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations and / or combinations thereof.

[0057] like Figure 1 As shown, Figure 1 The flowchart of the method for evaluating the vertical sealing property of a fault combining static and dynamic water-bearing traps of the present invention is as follows:

[0058] S101. Based on the existing geological data of the target fault, interpretation of seismic structural characteristics, logging data and on-site exploration sampling, a detailed geological description of the target fault is carried out.

[0059] S102. Based on seismic interpretation and logging data, 14 level 2 indicators under the four level 1 indicators of fault lithology, fault environmental conditions, fault mechanical factors, and fault attitude are described respectively. MATLAB is used to compile a calculation program to calculate the corresponding weight values ​​of each level of indicators.

[0060] S103. Combined with the analytic hierarchy process, a mathematical model for calculating the target fault is established, the appropriate value for building a fault database is calculated, the static sealing capacity of the target fault is determined by referring to the fault evaluation grade table, and corresponding suggestions or measures are given.

[0061] S104. A geomechanical model is established based on seismic structural interpretation and logging data, and a shear-permeability test is carried out under alternating stress conditions to test the critical value of cumulative slip in order to simulate the activation of faults under different injection-production cycles.

[0062] S105. Based on geological coring, rock mechanics parameters are obtained through triaxial compression tests on rock mechanics, and a finite element analysis model under seepage-stress coupling is established. The finite element method is used for simulation analysis, and the dynamic sealing changes and mechanical stability of the fault with the injection years are analyzed based on the cumulative slip displacement, critical internal friction angle and tensile failure criterion.

[0063] In a specific embodiment 1 of the present invention, the following steps are included:

[0064] S1. Combine the existing geological data of the target fault, interpretation of seismic structural characteristics, logging data and field exploration sampling, and make a detailed geological description of the target fault. Use fault mechanics, fault lithology, fault environmental conditions and fault occurrence as the first-level evaluation indicators to establish a fault static sealing evaluation system, such as Figure 2 shown.

[0065] Specifically, it focuses on four aspects: fault lithology, fault mechanical factors, fault environmental conditions and fault attitude. For actual engineering, we should start with the most basic geological conditions and focus on on-site exploration when analyzing geological data, so as to obtain various level 2 indicator parameters and provide reliable prerequisites for the subsequent scoring stage.

[0066] S2. Based on the seismic interpretation of the target fault, logging data and field exploration, the 13 level 2 indicators under the 4 level 1 indicators are described and graded.

[0067] Based on on-site exploration sampling (since fault core sampling is difficult, adjacent rocks of the same formation can be used for calibration), whole-rock mineral content and clay content analysis are carried out to obtain the properties of the fault zone filling and the mud content.

[0068] According to the existing geological data, the mud smear coefficient of the fault surface is calculated by combining the mud smear empirical formula, that is:

[0069]

[0070] In the formula, f m is the mud smear coefficient; L is the fault throw; H i is the thickness of the i-th mudstone layer offset by the fault; n is the number of mudstone layers offset by the fault; H is the thickness of the stratum offset by the fault; R m It is the ratio of the mudstone thickness of the stratum displaced by the fault to the stratum thickness.

[0071] The mud content in the fault zone is estimated based on the data of fault throw, fault-displacement stratum lithology and thickness, and compared with the mud content obtained by whole-rock analysis. The estimation formula is:

[0072]

[0073] Where, L is the vertical distance; h i 、h j are the thickness of the i-th and j-th mudstone layers in the upper and lower walls of the fault, respectively; n1 and n2 are the numbers of mudstone layers displaced in the two walls of the fault, respectively; and H is the thickness of the fault-displaced stratum.

[0074] Based on geological data such as earthquakes and well logging, the lithology of the two sides of the fault zone and the formation environment of the fault zone are determined, including: the fluid properties and temperature and pressure system of the two sides of the fault.

[0075] Based on field exploration, seismic structural data and logging data, the geostress, fault type, fault dip, fault depth and fault distance of the trapped fault are interpreted.

[0076] Combined with the on-site exploration situation, it is determined whether the fault has completely dislocated the caprock to determine the extent of damage caused by the fault to the caprock.

[0077] S3. Based on literature research and expert consultation, establish evaluation index standards for influencing factors, and assign points based on the index data at all levels obtained in S2, as shown in Table 1.

[0078] Table 1 Evaluation criteria for comprehensive indicators of vertical closure of faults

[0079]

[0080]

[0081] S4. Combined with the index weight values ​​calculated by the MATLAB program, a calculation model for the entire fault is established (which can be directly applied later). The weight value of each index is multiplied by the score obtained by the evaluation index, that is:

[0082]

[0083] In the formula, m i is the quantitative value of each evaluation index; ω i is the weight value of each evaluation index; i=1,2,3…,13.

[0084] As shown in Table 2, the suitability of the target fault for database construction is judged according to the fault static sealing evaluation grade table, and whether to continue the dynamic sealing evaluation is determined according to the static sealing results.

[0085] Table 2 Comprehensive evaluation table of vertical sealing of faults

[0086]

[0087] S5. Based on the static sealing results, triaxial compression tests were carried out through core sampling to obtain rock mechanical parameters, and a finite element analysis model under seepage-stress coupling was established. The dynamic sealing and mechanical stability of the fault were determined according to the cumulative slip critical value, Mohr-Coulomb shear slip criterion, and Mohr-Coulomb hydraulic fracturing failure criterion.

[0088] Combined with core sampling of adjacent strata, the product of the stratum depth where the core is located and the pressure gradient is used as the highest effective overburden pressure.

[0089] According to the standard SY / T5815-2016, the pressure gradient is selected as 0.0226MPa / m (1psi / ft), and the confining pressure under the fault burial depth condition is calculated, that is:

[0090] P z =0.0226MPa / m×d

[0091] Where d is the depth of the stratum where the core is located, unit, m.

[0092] According to the calculated confining pressure, triaxial compression mechanical tests on the core are carried out to obtain the fault rock mechanical parameters, and the finite element simulation results are used to predict the activity of the fault.

[0093] The Mohr-Coulomb fracture criterion predicts fault hydraulic fractures. Assuming that the tensile strength of the fault zone is zero, according to this criterion, hydraulic (tensile) fractures will occur once the fluid pressure exceeds the minimum principal compressive stress. Therefore, the pressure margin (PMF) of fault hydraulic fractures is defined using the minimum principal compressive stress:

[0094] P in <PMF=max(σ′1,σ′2,σ′3)

[0095] Where σ′1, σ′2, σ′3 are the maximum, intermediate and minimum principal stresses in the fault zone, respectively, and negative values ​​represent compression.

[0096] The fault slip trend was predicted using the Mohr-Coulomb criterion, namely:

[0097] τ=c0+μ s σ′ n

[0098] Where τ is the critical activation shear stress of the fault plane, σ' n is the normal effective stress of the fault plane, C0 is the cohesion of the fault zone, μ s is the static friction coefficient of the fault.

[0099] The accumulated shear deformation or fault slip is the injection pressure P in The implicit relationship between the number of alternations n and the fault alternation effect is as follows:

[0100] δ(P in ,n)<δ lim

[0101] In the formula, δ 1im The allowable cumulative amount of fault displacement can be determined through alternating tests or finite element simulations under injection-production cycles.

[0102] S6. Based on the results of indoor tests and numerical simulations, the mechanical stability of the fault under injection-production conditions is analyzed, and the injection-production upper limit pressure and service life of the target fault are predicted.

[0103] In the second embodiment of the present invention, the Yong'an oil and gas field where the Yong 21 block is located is located in the south of Yong'an Town, Kenli County, Dongying City, Shandong Province. The structural position is in the northeast of Dongying Depression, in the eastern section of Tuo-Sheng-Yong Fault Zone. The gas reservoir type is high porosity and high permeability, structural gas reservoir; the gas-bearing area is large, about 0.52km 2 , geological reserves of 3.68×10 8 m 3 In April 1966, drilling of Yong 21, Yong 21-1 and Yong 211 wells began. They were put into production in 1967, 1978 and 1990 respectively. The cumulative production of Yong 21 block is 2.63×10 8 m 3 The recovery rate is 71.5%, which is a water-flooded gas reservoir.

[0104] The Yong 21 fault is a blocking fault block structure. There is a fault F1-2 in the trap, and there is a blocking fault on each side to block it. The closure height of the trap is 80m, and the structural change amplitude is small. Existing studies have shown that the upper limit pressure of the gas reservoir is 18.9MPa and the lower limit is 13MPa; the original gas-water interface is near the depth of 1870m, the water body is widely distributed, and the edge and bottom water are active;

[0105] According to the on-site earthquake structural analysis ( Figure 3 As shown in the figure, the two plates of the target fault F1-2 are sand-mud butted, with good sealing performance. The burial depth is about 1850-2160m, the fault dip angle in the study area is about 30°-57°, and the fault throw is 4-76m; the structure gradually rises from west to east, and is a local small anticline structure; F1-1 and F1-3 are boundary faults, and the fault activity is relatively low.

[0106] Evaluation of vertical static sealing of faults

[0107] Since there are few fault-related data and well logging interpretations in this block, the static sealing performance is scored under the condition of little data according to the evaluation indicators described in Table 1. The indicator parameters required for the static sealing evaluation of aquifer gas storage faults are sorted and screened, and the weights of indicators at all levels are redistributed using MATLAB. The specific evaluation indicator values ​​are shown in Table 3.

[0108] According to the analysis of Table 2, the static sealing property of the target fault is good at 7.6396, which is a suitable reservoir site, indicating that the site is suitable for the construction of an aquifer gas storage reservoir.

[0109] Table 3 The vertical influencing factor scores of the F1-2 fault of the Yong 21 trap

[0110]

[0111] Fault dynamic stability analysis

[0112] 3.1 Establishing the geomechanical model

[0113] According to the on-site geological exploration and well logging, the Figure 4 The geomechanical model shown.

[0114] 3.2 Rock mechanical properties

[0115] Well logging interpretation was performed on Yong 21 Well, Yong 21-1 Well and Yong 211 Well. The rock mechanics interpretation results of the caprock section are shown in Table 4. The fault parameters were calibrated with reference to existing literature and the mechanical parameters of the adjacent rock formations.

[0116] Table 4 Caprock rock mechanics logging interpretation results

[0117]

[0118]

[0119] (1) Fault F1-2 shear slip

[0120] like Figure 5 As shown in the figure, F1-2c represents a partial fault in the reservoir, F1-2g represents a partial fault in the cap rock, and F1-2s represents a fault in the upper part of the cap rock. A method for calculating the fault slip during injection and production is established to calculate the shear slip generated by faults at different positions during pressure injection, i.e., U C =1.391mm, U g =0.154mm, U s =0.878mm.

[0121] (2) Hydraulic fracturing damage

[0122] like Figure 6 As shown in the figure, with the increase of injection distance, the effective stress on the left side of the reservoir shows a decreasing trend, and on the right side it gradually increases. However, the effective stress at fault F1-2 does not show a positive value, that is, no tensile stress appears, and no tensile failure occurs. On the right side of the reservoir, the right side of fault F1-3 is a rock mass with extremely low permeability, which leads to stress concentration. The stress on the right side of F1-3 is relatively small, indicating that during the injection process, more attention should be paid to faults with large permeability changes.

[0123] (3) Stability prediction of fault F1-2

[0124] According to the geological profile of Yong-21, the critical internal friction angle and Mohr circle of fault F1-2 under three different permeability zones are considered. Figure 7It can be seen that the Mohr circle of F1-2c with greater permeability changes greatly, and the critical internal friction angle increases to 35°, while the critical internal friction angles of F1-2g and F1-2s with smaller permeabilities are smaller. Due to the continuous increase in pore pressure, the excess pore pressure is difficult to diffuse in the reservoir, which in turn produces a squeeze phenomenon on the cap rock and F1-2c, thereby enhancing the shear effect of F1-2c. According to the CFF Coulomb rupture criterion, the fault stability parameter is calculated, that is,

[0125] CFF=τ-μσ' n

[0126] Where μ is the friction coefficient of the fault surface, which is generally 0.6 to 1.0; σ' n is the effective normal stress, MPa; τ is the shear stress, MPa.

[0127] According to the above formula, the stability of F1-2 fault is calculated, that is,

[0128]

[0129] According to the Coulomb failure criterion, under the current injection and production pressure, some faults of F1-2s and F1-2g are in a stable state and have not been activated; however, due to the diffusion of pore pressure, some faults of the F1-2c reservoir suffer shear failure in the reservoir and reservoir section, resulting in local instability without affecting the overall stability.

[0130] The method for evaluating the vertical closure of faults combining static and dynamic methods for water-bearing closures described in the present invention summarizes and organizes the data related to the evaluation indicators at each level under the static evaluation system through geological data, on-site exploration and geological sampling analysis, and calculates the score of each level of indicators according to the evaluation criteria and weight values; combined with the triaxial compression experiment of rock mechanics and finite element simulation analysis, it comprehensively judges whether the target fault is suitable for reservoir construction. The method for evaluating the vertical closure of faults in aquifer gas storage reservoirs described in the present invention combines dynamic and static methods, which focuses on summarizing and analyzing the understanding of fault geological conditions, theoretical analysis, establishment of evaluation criteria, finite element simulation analysis and indoor tests, and finally obtains the vertical closure of faults in aquifer gas storage reservoirs and the corresponding service life, which is suitable for the analysis of the vertical closure of faults in various underground projects.

[0131] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions recorded in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0132] Except for the technical features described in the specification, all other technical features are known technologies to those skilled in the art.

Claims

1. A method for evaluating the vertical sealing property of faults by combining static and dynamic methods of water-bearing traps, characterized in that: The method for evaluating the vertical sealing property of the fault combining static and dynamic characteristics of the water-bearing trap includes: Step 1: Conduct a detailed geological description of the target fault. Step 2: Establish a static sealing evaluation system and evaluation level for the target fault based on four aspects: fault mechanics, fault environmental conditions, fault lithology, and fault occurrence; Step 3, static sealing evaluation of the target fault is performed as the basis for dynamic sealing research; Step 4: Establish a geomechanical model based on seismic structural interpretation and logging data to simulate fault activation under different injection and production cycles; Step 5, establish a finite element analysis model under seepage-stress coupling to analyze the dynamic sealing change and mechanical stability of the fault with injection years; In step 2, based on seismic interpretation and logging data, geological description and grade evaluation are performed from the second-level indicators under the four first-level indicators, namely, fault lithology, fault environmental conditions, fault mechanical factors, and fault occurrence. The corresponding weight values ​​of each level of indicators are calculated, and the evaluation index standard for judging influencing factors is established based on literature research and expert consultation, and the points are assigned in combination with the obtained data of indicators at all levels. In step 3, combined with the hierarchical analysis method, a mathematical model for calculating the target fault is established, the fault database suitability value is calculated, and the static sealing capacity of the target fault is judged by referring to the fault evaluation grade table to determine whether the target fault is suitable for database construction. Based on the static sealing results, it is decided whether to continue the dynamic sealing evaluation.

2. The method for evaluating the vertical sealing property of faults by combining static and dynamic methods of water-bearing traps according to claim 1, characterized in that: In step 1, a detailed geological description of the target fault is carried out by combining the existing geological data of the target fault, interpretation of seismic structural characteristics, logging data and field exploration sampling.

3. The method for evaluating the vertical sealing property of faults by combining static and dynamic methods of water-bearing traps according to claim 2 is characterized in that: In step 1, the four main aspects of fault lithology, fault mechanical factors, fault environmental conditions and fault attitude are taken into consideration. Starting from the most basic geological conditions, on-site exploration is the main method for analyzing geological data, so as to obtain various level 2 indicator parameters and provide reliable prerequisites for the subsequent scoring stage.

4. The method for evaluating the vertical sealing property of faults by combining static and dynamic methods of water-bearing traps according to claim 1, characterized in that: In step 2, whole-rock mineral content and clay content analysis are performed based on field exploration sampling to obtain the properties of the fault zone filling and the mud content.

5. The method for evaluating the vertical sealing property of faults by combining static and dynamic methods of water-bearing traps according to claim 1, characterized in that: In step 2, the mud smear coefficient of the fault plane is calculated based on the existing geological data and the mud smear empirical formula, that is: In the formula, f m is the mud smear coefficient; L is the fault throw; H i is the thickness of the i-th mudstone layer offset by the fault; n is the number of mudstone layers offset by the fault; H is the thickness of the stratum offset by the fault; R m It is the ratio of the mudstone thickness of the stratum displaced by the fault to the stratum thickness.

6. The method for evaluating the vertical sealing property of faults by combining static and dynamic methods of water-bearing traps according to claim 1, characterized in that: In step 2, the shale content in the fault zone is estimated based on the data of fault throw, fault-displacement stratum lithology and thickness, and compared with the shale content obtained from whole-rock analysis. The estimation formula is: Where, L is the vertical distance; h i 、h j are the thickness of the i-th and j-th mudstone layers in the upper and lower walls of the fault, respectively; n1 and n2 are the numbers of mudstone layers displaced in the two walls of the fault, respectively; and H is the thickness of the fault-displaced stratum.

7. The method for evaluating the vertical sealing property of faults by combining static and dynamic methods of water-bearing traps according to claim 1, characterized in that: In step 2, based on geological data such as earthquakes and well logging, determine the lithology of the two sides of the fault zone and the formation environment in which the fault zone is located, including: the fluid properties and temperature-pressure system of the two sides of the fault; interpret the ground stress, fault type, fault dip, fault burial depth and fault distance of the enclosed fault based on field exploration, seismic structural data and well logging data; and combine the field exploration situation to determine whether the fault has completely dislocated the caprock, so as to determine the degree of damage caused by the fault to the caprock.

8. The method for evaluating the vertical sealing property of faults by combining static and dynamic methods of water-bearing traps according to claim 1, characterized in that: In step 4, a geomechanical model is established based on seismic structural interpretation and logging data, and a shear-permeability test is carried out under alternating stress conditions to test the critical value of cumulative slip to simulate the activation of faults under different injection-production cycles.

9. The method for evaluating the vertical sealing property of faults by combining static and dynamic methods of water-bearing traps according to claim 1, characterized in that: In step 5, based on geological coring, rock mechanics parameters are obtained through triaxial compression tests of rock mechanics, and a finite element analysis model under seepage-stress coupling is established. The finite element method is used for simulation analysis, and the dynamic sealing changes and mechanical stability of the fault with the injection years are analyzed based on the cumulative slip displacement, critical internal friction angle and tensile failure criterion.

10. The method for evaluating the vertical sealing property of faults by combining static and dynamic methods of water-bearing traps according to claim 9, characterized in that: In step 5, the confining pressure under the fault burial depth condition is calculated, that is: P z =0.0226MPa / m×d Where, d is the depth of the stratum where the core is located, unit, m; According to the calculated confining pressure, triaxial compression mechanical tests on the core are carried out to obtain the fault rock mechanical parameters, and the finite element simulation results are used to predict the activity of the fault.

11. The method for evaluating the vertical sealing property of faults by combining static and dynamic methods of water-bearing traps according to claim 9, characterized in that: In step 5, the minimum principal compressive stress is used to define the pressure margin PMF of the fault hydraulic fracture: P in <PMF=max(σ1′,σ2′,σ3′) Where σ1′, σ2′, σ3′ are the maximum, intermediate and minimum principal stresses in the fault zone, respectively, and negative values ​​represent compression.

12. The method for evaluating the vertical sealing property of faults by combining static and dynamic methods of water-bearing traps according to claim 9, characterized in that: In step 5, the fault slip trend is predicted using the Mohr-Coulomb criterion, namely: τ=c0+μ s s n ′ Where τ is the critical activation shear stress of the fault plane, σ n ′ is the normal effective stress of the fault plane, C0 is the cohesion of the fault zone, μ s is the static friction coefficient of the fault.

13. The method for evaluating the vertical sealing property of faults by combining static and dynamic methods of water-bearing traps according to claim 9, characterized in that: In step 5, the accumulated shear deformation or fault slip is the injection pressure P in The implicit relationship between the number of alternations n and the fault alternation effect is as follows: δ(P in ,n)<δ lim In the formula, δ 1im The allowable cumulative amount of fault displacement can be determined through alternating tests or finite element simulations under injection-production cycles.

Images