Method for determining width of fault-related wrinkle associated fracture zone
By obtaining the influencing factors of the associated fracture bandwidth of fault-related folds and establishing a calculation model, the problems of low accuracy, high cost and poor promotion in the existing technology are solved, and the accurate identification of the associated fracture bandwidth of fault-related folds is achieved, providing technical support for the development of oil and gas reservoirs.
Patent Information
- Application Number
- CN202411716562.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-27
- Publication Date
- 2025-04-11
AI Technical Summary
The prior art has problems of low accuracy, high cost and poor promotion when determining the width of fault-related fold associated fracture bands.
By obtaining the factors affecting the fracture bandwidth of the fault-related folds, such as fault distance, fault inclination and formation fold degree, and establishing a computational model, the associated fracture width is quantitatively evaluated using multiple linear regression analysis and normalization treatment.
The accurate quantitative identification of the bandwidth of the associated folds associated with faults is achieved, and the defects of high cost, low accuracy and poor promotion are overcome, providing technical support for the well deployment and dessert area search of oil and gas reservoirs.
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Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of fracture evaluation of fractured oil and gas reservoirs, and in particular relates to a method for determining the width of a fracture zone associated with fault-related folds. Background Art
[0002] Cracks play a vital role in fractured oil and gas reservoirs, especially in tight sandstone reservoirs. Their existence increases the matrix permeability of low-porosity and low-permeability reservoirs by 2 or 3 orders of magnitude, providing seepage channels for the migration of oil and gas. At the same time, for fractured tight sandstone reservoirs, the existence of cracks can even become the main storage space for oil and gas molecules, becoming a "sweet spot" for well deployment.
[0003] Previous research results show that the degree of fault development directly determines the degree of crack development. The stronger the fault activity, the more faults penetrate the layers, and the larger the scale of crack development. Generally speaking, as the distance from a large-scale fault gradually increases, the stress on the surrounding rock gradually decreases, the rock is less likely to break and form cracks, and the crack density becomes smaller and smaller. In the parallel knee fold structure of fault propagation folds, when the fault dip is less than 29°, folds with the same dip on both wings and inverted strata on one side will be formed; when the fault dip is greater than 29°, folds with basically the same dip on both wings will be formed, and the two wings of the fault propagation fold structure are often fracture development areas. After the formation folds are deformed, relative sliding may occur between layers, resulting in the formation of interlayer traction folds in the weak layer. The relative sliding between layers is related to the formation dip and layer thickness, and the crack density also changes with the change of the formation dip.
[0004] Fault-related fold-associated cracks are fold-associated cracks formed with fault activity. Faults and folds complement each other. Faults and folds are two basic forms of tectonic deformation of rock formations. There are two forms of the order of their development: one is that the rock bends when it is subjected to force, and when the elastic limit of the rock is exceeded, a fault occurs; the other is that after the rock is subjected to force, a fault occurs first and then a fold occurs, that is, during the development of the fault, the shear effect on the plane or section caused by the relative movement of the two plates of rock causes the formation to bend and deform, thus forming fault-related folds.
[0005] As early as 1974, foreign countries have conducted research on the fractures associated with fault-related folds. Combined with the research results of predecessors, the research on the width of the fracture zone associated with fault-related folds mainly includes the following methods: ① Field geological outcrop statistics method, through field outcrops, the density of fracture development at different distances from the fault is measured and counted to determine the width of the fracture zone associated with fault-related folds. This method is the most direct and the data obtained is the most accurate, but the distribution of underground faults cannot be judged. ② Geophysical method, one is to determine the fracture development zone through imaging logging data, so as to obtain the width of the associated fracture zone. Although the data obtained by this method is accurate, it is costly and cannot identify the width of the associated fracture zone for wells without imaging logging data; the second is to determine the width of the fracture zone associated with fault-related folds by pre-stack and post-stack fracture prediction based on seismic data. This method obtains a surface prediction result and cannot accurately obtain the distribution of the associated fracture zone. ③ The numerical simulation method of tectonic stress field, based on a full understanding of tectonic evolution, establishes a geological model and conducts numerical simulation of the stress field to obtain the width of the associated fracture zone; this method requires clear mechanical parameters of the rock. If the mechanical parameters of the rock are unclear, simulation cannot be performed, and the accuracy of the model simulated by finite elements is difficult to meet the requirements.
[0006] In summary, the current determination of the width of the fracture zone associated with fault-related folds has the disadvantages of high cost, difficulty in determining geological parameters, and poor generalizability. Therefore, the above method cannot accurately evaluate the width of the fracture zone associated with fault-related folds and quantitatively identify its width. Summary of the invention
[0007] The purpose of the present invention is to provide a method for determining the width of a fracture zone associated with a fault-related fold, so as to solve the problems of low accuracy and poor generalizability in the prior art when determining the width of a fracture zone associated with a fault-related fold.
[0008] The present invention provides a method for determining the width of a fault-related fold-associated fracture zone to solve the above technical problem, comprising the following steps: 1) Obtain the magnitude of the influencing factors of the width of the fold-associated fracture zone of the fault near the single well of the target layer in the study area, the influencing factors include fault throw, fault dip and formation fold degree; 2) Inputting each influencing factor in step 1) into the pre-constructed fold-associated fracture zone width calculation model, the fault-related fold-associated fracture zone width of the target layer in the study area is obtained; According to the existing imaging logging data in the study area, the width of the corresponding single well fault-related fold-associated fracture zone is obtained, and the corresponding influencing factors are obtained by fine structural interpretation using logging data and seismic data. A relationship model between the width of the fault-related fold-associated fracture zone and various influencing factors is established. The relationship model is the calculation model of the fold-associated fracture zone width.
[0009] Furthermore, when constructing the calculation model of the fold-associated fracture zone width, a multivariate linear regression analysis was performed on the obtained fault-related fold-associated fracture zone width and the corresponding influencing factors to establish the calculation model of the fold-associated fracture zone width: ,in, E is the width of the fold-associated crack zone, H i For the i The influencing factor of the width of the fold-associated seam zone is A i For the i The weighted coefficient of the influencing factor of the width of the fold-associated fracture zone is n is the number of factors affecting the width of the fold-associated seam zone, N is a constant.
[0010] Furthermore, when constructing the calculation model for the width of the fold-associated fracture zone, the obtained influencing factors are normalized, and based on the normalized influencing factors, a relationship model between the width of the fault-related fold-associated fracture zone and the influencing factors is established; the influencing factors of the width of the fold-associated fracture zone obtained in step 1) are normalized, and the normalized influencing factors are input into the pre-constructed calculation model for the width of the fold-associated fracture zone.
[0011] Furthermore, the formula for the normalization process is: H i = ( x i - x i,min ) / ( x i,max - x i,min ),in, x i The first fault near the single well in the target interval i The influencing factors of the width of the fold-associated crack zone are: x i,min The first i The minimum value of the influencing factor of the width of the fold-associated crack zone is x i,max The first i The maximum value of the influencing factor of the width of the fracture zone associated with each fold.
[0012] Furthermore, when constructing the calculation model for the width of the fold-associated fracture zone, the fracture density mutation point on the single well is determined based on the existing imaging logging data of each single well near the fault in the study area; the vertical distance from the mutation point to the fault is taken as the width of the fold-associated fracture zone of the single well.
[0013] Furthermore, when obtaining each influencing shadow, the target layer in the study area is finely tracked and the structure is finely interpreted to confirm the distribution characteristics of the target layer and the fault development zone, and to determine the influencing factors that characterize the width of the associated fracture zone.
[0014] Furthermore, based on the detailed tracking of the target layer in the study area, the curvature of the target layer is calculated to implement the fold amplitude of different structural parts in the study area, thereby determining the degree of stratigraphic folding.
[0015] The beneficial effects of the present invention are as follows: the present invention uses a fine stratigraphic framework as the background, clarifies the influencing factors of the width of the fault-related fold-associated fracture zone, and under the constraints of multiple influencing factors, establishes a relationship model between the width of the fault-related fold-associated fracture zone and its corresponding influencing factors, thereby achieving the purpose of quantitatively evaluating the width of the associated fracture zone, overcoming the defects of the current identification method such as high cost, low identification accuracy and poor scalability, and providing technical support for the subsequent well site deployment and search for sweet spots in oil and gas reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Figure 1 is a flow chart of a method for determining the width of a fault-related fold-associated fracture zone according to an embodiment of the present invention; Figure 2 This is a planar structural diagram of a fractured gas reservoir in my country according to an embodiment of the present invention; Figure 3 is a comprehensive histogram of imaging logging of well P1 in an embodiment of the present invention; Figure 4 is a cross-sectional view of a well trajectory through the P1 well according to an embodiment of the present invention; Figure 5 It is a correlation diagram between the actual associated seam width and the calculated associated seam width in an embodiment of the present invention. DETAILED DESCRIPTION
[0017] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings.
[0018] The present invention is based on the fine stratigraphic framework and has discovered the following phenomena: the width of the fault-related fold-associated fracture zone is related to three parameters: fault throw, fault dip, and stratum fold degree. The fault throw reflects the development stage of the fault. Within a certain range, the width of the associated fracture zone is positively correlated with the fault throw. The fault dip can have a certain impact on the initial stress distribution characteristics of the rock mass, and indirectly affects the nature and occurrence of the fractures. The strata are bent and deformed by tectonic stress to form folds, and fold-associated fractures will develop at the turning end of the folds. The greater the degree of folding, the more obvious the bending and deformation of the strata, and the greater the degree of folding.
[0019] Based on the above findings, Figure 1As shown, the present invention obtains the width of the fold-associated fracture zone of a single well through imaging logging data, uses logging data and seismic data to carry out fine structural interpretation, determines the influencing factors corresponding to the width of the fold-associated fracture zone, establishes a relationship model between the width of the fold-associated fracture zone and each influencing factor, and quantitatively evaluates the width of the fault-related fold-associated fracture zone. The specific quantitative evaluation process is: obtaining the size of the influencing factor of the width of the fold-associated fracture zone of the fault near the single well of the target layer in the study area, and bringing the influencing factor of the width of the fold-associated fracture zone into the relationship model to obtain the width of the fault-related fold-associated fracture zone.
[0020] Specifically, the process of constructing the relationship model between the width of the fold-associated fracture zone and various influencing factors includes the following steps: 1. Based on the imaging logging data of M wells near the fault in the study area, the fracture density mutation point on a single well is determined, and the vertical distance from the mutation point to the fault is taken as the width of the fold-associated fracture zone of the well, such as Figure 3 The value of M is not limited, but the larger the value of M is, the more accurate the constructed relationship model is. In this embodiment, M=30.
[0021] 2. Carry out detailed tracking of the target layer and detailed structural interpretation in the study area, confirm the distribution characteristics of the target layer and the fault development zone, and determine the influencing factors that characterize the width of the associated fracture zone. The influencing factors include fault parameters and the degree of formation folding. Fault parameters include fault throw and fault dip. The following is a detailed explanation of the determination of each influencing factor: 2.1 Determination of fault parameters (1) Fault distance The fault throw reflects the development stage of the fault. Within a certain range, the width of the associated fracture zone is positively correlated with the fault throw. Through the detailed structural interpretation of the target layer in the study area, the location and size of the maximum and minimum fault throws of the faults in the study area are determined; Figure 2 As shown in the figure, for a fractured gas reservoir in my country, the maximum fault throw is in the middle of fault No. 1. h max The minimum fault distance is 67m, and the minimum fault distance is at the end of the fault. h min is 0m.
[0022] (2) Fault dip The inclination of the fault can have a certain impact on the initial stress distribution characteristics of the rock mass, and indirectly affect the nature and occurrence of the fracture. Through the detailed structural interpretation of the target layer in the study area, the location and size of the maximum and minimum inclination of the fault are determined, and the Figure 2 As shown in the figure, for example, the maximum fault dip is at the end of fault No. 3. t max is 54°, with the minimum dip at the end of fault No. 2.t min is 5°.
[0023] 2.2 Determination of the degree of stratum folding The strata are bent and deformed by tectonic stress to form folds, and fold-associated fractures will develop at the turning ends of the folds. The greater the degree of folding, the more obvious the bending and deformation of the strata, and the greater the degree of folding. Based on the detailed tracking of the target layer in the study area, the curvature of the target layer is calculated to determine the fold amplitude of different structural parts in the study area. Figure 2 Taking a fractured gas reservoir in my country as an example, statistical analysis shows that the fold amplitude in the study area ranges from 0 to 0.05 / km.
[0024] 3. Establishment of a calculation model for the width of fold-associated fracture zones in the study area.
[0025] Using the width of the fold-associated fracture zone of each single well and its corresponding influencing factors determined in steps 1 and 2, the relationship between the width of the fold-associated fracture zone and the corresponding influencing factors is studied and analyzed, and a calculation model for the width of the fold-associated fracture zone is established.
[0026] As a preferred implementation mode, this embodiment uses multivariate linear regression analysis to construct a relationship model between the width of the fold-associated fracture zone and the corresponding influencing factors, and the formula is as follows: (1) in, E is the width of the fold-associated crack zone, H i For the i The influencing factor of the width of the fold-associated seam zone is A i For the i The weighted coefficient of the influencing factor of the width of the fold-associated fracture zone is n is the number of factors affecting the width of the fold-associated seam zone, N is a constant.
[0027] As another implementation method, a BP neural network or the like can also be used to construct the model, with the width of the fold-associated fracture zone of each single well and its corresponding influencing factors being used as a training set and a test set, and the BP neural network model is trained using the training set, and the trained BP neural network model is verified and adjusted using the test set, and finally a calculation model for the width of the fold-associated fracture zone in the study area is obtained. The BP neural network structure can adopt an existing structure, which will not be described in detail here.
[0028] Of course, other machine learning models can also be used, which will not be explained in detail here.
[0029] As a preferred implementation mode, when using multivariate linear regression analysis to construct a relationship model between the width of the fold-associated fracture zone and the corresponding influencing factors, the influencing factors characterizing the width of the associated fracture zone of each single well are normalized, and the normalized influencing factors are used to establish a relationship model between the width of the fault-related fold-associated fracture zone and each influencing factor; correspondingly, when using the relationship model to quantitatively evaluate the width of the fault-related fold-associated fracture zone, it is also necessary to normalize the influencing factors of the fold-associated fracture zone width of each single well near the fault in the study area, and input the normalized influencing factors into the relationship model.
[0030] Preferably, the formula for normalization processing is: H i = ( x i - x i,min ) / ( x i,max - x i,min ),in, x i The first fault near the single well in the target interval i The influencing factors of the width of the fold-associated crack zone are: x i,min The first i The minimum value of the influencing factor of the width of the fold-associated crack zone is x i,max The first i The maximum value of the influencing factor of the width of the fracture zone associated with each fold.
[0031] The following is a further explanation of the method for determining the width of the fault-related fold-associated fracture zone of the present invention by taking the depth section of 3177-3283 m of the target layer in the P1 single well in the study area as an example.
[0032] First, the width of the fold-associated fracture zone is obtained. The fracture density mutation point in the target layer of Well P1 is determined by imaging logging data, such as Figure 3 As shown in Figure 2, the vertical distance between the density mutation point and the fault on the profile is 78 m. Figure 4 As shown, the width of the fold-associated fracture zone in this well is believed to be 78m.
[0033] Secondly, the three influencing factors in the depth section of the well are obtained as follows: ① Break factor H 断距 The calculation process is: H 断距 = ( h - hmin ) / ( h max - h min ), h is the fault throw of the fault near Well P1, which is 57m; h min is the minimum fault throw of the study area, which is 0m; h max is the maximum fault throw of the study area, which is 67 m; therefore, H 断距 The calculated result is 0.85.
[0034] ②Inclination factor H 倾角 The calculation process is as follows: through the detailed structural interpretation of the target layer in the study area, on the basis of clarifying the distribution of the target layer and the extension law of the fault, the inclination angle of the fault near the P1 well in the target layer is calculated. t To read, t The value is 50°, and the calculation formula of the inclination factor is: H 倾角 = ( t - t min ) / ( t max - t min ), t min is the minimum dip angle of the fault in the study area, which is 5°; t max is the maximum dip angle of the fault in the study area, which is 54°; therefore, H 倾角 The calculated result is 0.92.
[0035] ③ The calculation process of the fold degree of the formation is as follows: on the basis of fine tracking of the target layer in the study area, the curvature of the target layer is calculated, and the curvature value of the target layer of Well P1 is calculated. f is 0.041 / km, and its fold amplitude factor H 幅度 Calculated as H 幅度 = ( f - f min ) / ( f max - f min ), f min is the minimum curvature, which is 0 / km; f maxis the maximum curvature value, which is 0.05 / km; therefore, H 幅度 The calculated result is 0.82.
[0036] Furthermore, the influencing factors of the width of the fold-associated fracture zone of 30 single wells in the study area were determined according to the above-mentioned influencing factor determination method, and the corresponding relationship between the width of the fold-associated fracture zone of some single wells and their influencing factors was compiled as shown in Table 1.
[0037] Table 1 The relationship between the width of associated fractures and their influencing factors in some single wells
[0038] Using the relationship between the width of the fold-associated fracture zone of each single well and its influencing factors, a multivariate linear regression was performed on the 30 wells in the study area to establish the formula shown in formula (2): E=17.3185* H 断距 -14.8438* H 倾角 +17.2181* H 幅度 +65.6924 (2) In the formula, E is the model function of the width of the fracture zone associated with the fold in the study area; After obtaining the above model function, the remaining 25 wells with imaging logging data in the study area were used to verify the above model function, and the correlation diagram between the actual associated fracture zone width and the calculated associated fracture zone width was drawn, as shown in Figure 2. Figure 5 As shown, calculate the width of the associated seam E It has a linear correlation with the actual associated fracture width, and the correlation coefficient R is greater than 0.9.
[0039] At present, three new wells (PL1, B1, and B2) have been drilled in the study area. The imaging logging data show that the width of the fold-associated fracture zone in the PL1 well is 58 m, the width of the fold-associated fracture zone in the B1 well is 36 m, and the width of the fold-associated fracture zone in the B2 well is 42 m. Based on the above formula (2), the width of the fold-associated fracture zone of the newly drilled wells is calculated, and the error analysis table of the predicted results and the actual results of the actual drilling is compiled as shown in Table 2.
[0040] Table 2. Error analysis of actual drilling prediction results
[0041] It can be seen that the error between the predicted results and the actual results is within 10%, which verifies the feasibility of this method.
[0042] Under the premise of finely tracking the strata, the present invention achieves the purpose of quantitatively evaluating the width of the fault-related fold-associated fracture zone through the common constraints of various influencing factors, overcomes the defects of the current identification method such as high cost, low identification accuracy and poor scalability, and provides technical support for the subsequent development of oil and gas reservoirs.
Claims
1. A method for determining the width of a fracture zone associated with a fault-related fold, characterized in that: The method comprises the following steps: 1) Obtain the magnitude of the influencing factors of the width of the fold-associated fracture zone of the fault near the single well of the target layer in the study area, the influencing factors include fault throw, fault dip and formation fold degree; 2) Inputting each influencing factor in step 1) into the pre-constructed fold-associated fracture zone width calculation model, the fault-related fold-associated fracture zone width of the target layer in the study area is obtained; According to the existing imaging logging data in the study area, the width of the corresponding single well fault-related fold-associated fracture zone is obtained, and the corresponding influencing factors are obtained by fine structural interpretation using logging data and seismic data. A relationship model between the width of the fault-related fold-associated fracture zone and various influencing factors is established. The relationship model is the calculation model of the fold-associated fracture zone width.
2. The method for determining the width of the fault-related fold-associated fracture zone according to claim 1, characterized in that: When constructing the calculation model of fold-associated fracture zone width, multiple linear regression analysis was performed on the obtained fault-related fold-associated fracture zone width and the corresponding influencing factors to establish the calculation model of fold-associated fracture zone width: ,in, E is the width of the fold-associated crack zone, H i For the i The influencing factor of the width of the fold-associated seam zone is: A i For the i The weighted coefficient of the influencing factor of the width of the fold-associated fracture zone is n is the number of factors affecting the width of the fold-associated seam zone, N is a constant.
3. The method for determining the width of the fault-related fold-associated fracture zone according to claim 2, characterized in that: When constructing the calculation model of the fold-associated fracture zone width, the obtained influencing factors are normalized, and based on the normalized influencing factors, a relationship model between the fault-related fold-associated fracture zone width and the influencing factors is established; the influencing factors of the fold-associated fracture zone width obtained in step 1) are normalized, and the normalized influencing factors are input into the pre-constructed calculation model of the fold-associated fracture zone width.
4. The method for determining the width of the fault-related fold-associated fracture zone according to claim 3, characterized in that: The formula for the normalization process is: H i = ( x i - x i,min ) / ( x i,max - x i,min ), in, x i The first fault near the single well in the target interval i The influencing factor of the width of the fold-associated crack zone is x i,min The faults in the study area i The minimum value of the influencing factor of the width of the fold-associated crack zone is x i,max The faults in the study area i The maximum value of the influencing factor of the width of the fracture zone associated with each fold.
5. The method for determining the width of the fault-related fold-associated fracture zone according to claim 1, characterized in that: When constructing the calculation model for the width of the fold-associated fracture zone, the fracture density mutation point on the single well is determined based on the existing imaging logging data of each single well near the fault in the study area; the vertical distance from the mutation point to the fault is taken as the width of the fold-associated fracture zone of the single well.
6. The method for determining the width of the fracture zone associated with fault-related folds according to claim 1, characterized in that: When obtaining each influencing shadow, carry out detailed tracking of the target layer and detailed structural interpretation in the study area, confirm the distribution characteristics of the target layer and the fault development zone, and determine the influencing factors that characterize the width of the associated fracture zone.
7. The method for determining the width of the fracture zone associated with fault-related folds according to claim 6, characterized in that: Based on the detailed tracking of the target layer in the study area, the curvature of the target layer is calculated to determine the fold amplitude of different structural parts in the study area, thereby determining the degree of folding of the formation.