Multidimensional determination method for fracture activation condition of casing deformation-acoustic emission b value in combined wellbore

Abstract

The application discloses a joint wellbore casing deformation-acoustic emission b-value fracture activation condition multidimensional judgment method, which comprises the following steps: based on casing deformation analysis, preliminarily statistically controlling law of fracture own properties on fracture activation, obtaining acoustic emission b-value of experimental scale critical activation point, and constructing a fracture activation condition judgment method combining casing deformation analysis and acoustic emission b-value; the application considers the influence law of multiple properties of the fracture itself on casing deformation intensity, combines wellbore casing deformation information with acoustic emission sequence b-value of the experimental scale critical activation point, and extrapolates the experimental results to geological conditions by taking the underground statistical law as a constraint, thereby solving the problem that the laboratory test results are too idealized, simultaneously considering the multi-solution of the actual geological engineering data, and realizing quantitative characterization of the fracture activation, which greatly improves the accuracy and applicability of the activation condition prediction in theory and method, and meanwhile, the wellbore casing deformation information and fracture geometric data are easy to obtain, and the application range is wide.

Description

Technical Field

[0001] This invention relates to the field of fault activation condition determination technology, and in particular to a multidimensional determination method for fault activation conditions that combines the variable-acoustic emission b-value of the well casing. Background Technology

[0002] Fault activity modes include stable creep and unstable stick-slip. Creep is a slow, non-vibrating frictional sliding along a fault, which can lead to wellbore instability during drilling and shear damage to production wells. Stick-slip is accompanied by intermittent, sudden sliding, which not only causes the aforementioned engineering risks but can also increase the permeability of the fault zone, leading to oil and gas migration or leakage, and even inducing earthquakes. This highlights the application value of fault instability condition determination and accurate activity assessment in safe oil and gas extraction.

[0003] Fault instability behavior is extremely complex, with its main influencing factors including both internal and external factors. Internal factors include fault dip angle, lithology, cross-sectional roughness, sliding surface morphology, sliding surface contact area, pore pressure, particle size, and contact surface fluid properties. External factors include temperature and stress environment. The friction coefficient is controlled by factors such as fault dip angle, lithology, cross-sectional roughness, and contact surface fluid properties, and is often used as a quantitative parameter characterizing fault friction intensity. Determining fault activation conditions can clarify fault instability behavior from a mechanistic perspective and can be applied to multi-scale fault zone activation risk assessment, thereby enabling precise design of fracturing and production enhancement, as well as prediction and prevention of engineering disasters such as casing deformation and wellbore collapse.

[0004] Fault activation condition identification is a core component in the accurate evaluation of fracture stability and activity. Currently, domestic and international research on fault activation condition identification mainly focuses on activation identification methods based on physical simulation experiments and those based on friction coefficients. These methods generally only utilize stress drop, acoustic emission event point response, and relative slip as activation signals from physical simulation experiments, failing to recreate the activation patterns exhibited at complex geological scales. This results in overly idealized evaluation results. Furthermore, most indoor experiments primarily focus on regularity studies, making them difficult to directly apply to activation identification under actual geological conditions. Additionally, using only friction coefficients for simple mathematical statistical qualitative analysis lacks quantitative threshold definition, thus reducing the accuracy of risk prediction. Moreover, limited sampling conditions in outcrop fault zones and the difficulty in obtaining friction coefficients significantly restrict the widespread application of fault activation condition identification. Therefore, this invention proposes a multi-dimensional fault activation condition identification method combining well casing variation and acoustic emission b-value to address the problems existing in the prior art. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to propose a multi-dimensional method for determining fracture activation conditions by combining well casing variation-acoustic emission b-values. This method solves the problems of current methods for determining fault activation conditions failing to reproduce the activation patterns exhibited at complex geological scales, resulting in overly idealized evaluation results that are difficult to directly apply to activation determination under actual geological conditions. Furthermore, the lack of quantitative threshold definitions reduces the accuracy of risk prediction, and the difficulty in obtaining friction coefficients greatly limits the widespread application of fracture activation condition discrimination.

[0006] To achieve the objectives of this invention, the invention is implemented through the following technical solution: a multi-dimensional determination method for fracture activation conditions combining well casing variable-acoustic emission b-value, comprising the following steps:

[0007] Step 1: First, identify the casing deformation depth and deformation degree information corresponding to each single well casing deformation point in the work area. Then, obtain the plane distribution of the fracture in the work area, project the casing deformation points onto the fracture plane distribution map, and screen out the casing deformation points caused by fracture slip. Next, perform correlation statistical analysis on the deformation degree of the casing deformation points near each fracture with the fracture's own properties and the petrological characteristics of the two sides of the fracture. Summarize the geological factors with the strongest correlation with the fracture activation conditions, and preliminarily clarify the control law of the fracture's own properties on fracture activation from the perspective of casing deformation analysis.

[0008] Step 2: Using the lithological composition and structure of the stratigraphic layer in the work area as the experimental model, and the geological factors most strongly correlated with the fault activation conditions as the experimental variables, conduct physical simulation experiments on rock masses with non-penetrating fractures under compression-shear loading conditions. Select the biaxial stress difference coefficient of the field slip fracture as the similarity index, calibrate the experimental scale matching segment corresponding to the fault-induced sleeve deformation in the work area, verify the critical slip initiation point of the scale matching segment, and calculate its corresponding acoustic emission b value.

[0009] Step 3: Fit the acoustic emission b-value to the acoustic emission b-value variation curve under specific experimental variables, and combine it with the deformation intensity variation curve obtained by the analysis of the deformation under the same variables. Continuously optimize and adjust the experimental scale-field scale matching results under different variables to obtain the activation threshold of different variables. Combine the different activation thresholds until the optimal fracture activation threshold suitable for the research area is obtained, and perform multi-dimensional determination of fracture activation conditions.

[0010] Further improvements are made in the following ways: In step one, the information on the casing deformation depth and deformation degree corresponding to each single well casing deformation point in the work area is obtained by identifying the obstruction encountered during well drilling and the logging data of the multi-arm well diameter during the fracturing operation. The distribution of the fracture plane in the work area is obtained by seismic data interpretation technology, and a fracture plane distribution map is obtained at the same time.

[0011] A further improvement is made in the following: In step one, the formula for calculating the degree of deformation is:

[0012] I = (Ap - Bp) / Ap * 100%

[0013] Where I represents the degree of deformation, Ap represents the inner diameter of the casing, and Bp represents the inner diameter of the well.

[0014] A further improvement is that, in step one, the fracture's intrinsic properties include the fracture orientation, fracture dip angle, and planar extension length.

[0015] A further improvement is made in step two, where the stress-strain and acoustic emission energy evolution curves of the entire loading process are obtained from physical simulation experiments, and different extended evolution stages are divided according to the change law.

[0016] A further improvement is made in the following: In step two, the field slip fracture is a fracture that induces sheath deformation. After calibrating the experimental scale matching segment corresponding to the fracture-induced sheath deformation in the work area, the critical slip initiation point of the experimental scale matching segment is determined by stress drop and acoustic emission energy signals.

[0017] A further improvement is made in step two, where the formula for calculating the acoustic emission b-value is:

[0018] A = 20log 10 V max -A pre

[0019] log 10 N = ab(A / 20)

[0020] Where N is the number of events with amplitude greater than A, b is the distribution of acoustic emission event magnitudes, A is the acoustic emission amplitude, and V max For peak voltage, A pre Let 'a' be the threshold value and 'a' be logarithm. 10 The intercept of the N-A / 20 fitted curve.

[0021] A further improvement is made in step two, where the acoustic emission b-value reflects the activation risk of the fractured rock mass; the larger the b-value, the stronger the stability, and the smaller the b-value, the weaker the stability.

[0022] A further improvement is made in the following: In step three, the acoustic emission b-value variation curve is obtained using the curve fitting method in Origin software. A multidimensional fracture activation condition determination method based on acoustic emission b-value and overlay variation data is constructed according to the optimal fracture activation threshold and applied to the fracture activation condition determination in cases where overlay variation data is limited.

[0023] The beneficial effects of this invention are as follows: This invention considers the influence of various properties of the fracture itself on the strength of the casing deformation, and combines the casing deformation information of the wellbore with the b-value of the acoustic emission sequence of the critical activation point on the experimental scale to construct a multi-dimensional determination method for fracture activation conditions. The experimental results are extrapolated to geological conditions with downhole statistical laws as constraints, which solves the problem of overly idealized indoor experimental results. At the same time, it considers the pluralism of actual geological engineering data, and can realize the quantitative characterization of fracture activation. Theoretically and methodologically, it greatly improves the accuracy and applicability of activation condition prediction. In addition, the casing deformation information and fracture geometry data in this invention are relatively easy to obtain, and the application range is wide. It has theoretical and practical significance for the precise design of fracturing and production enhancement, as well as the prediction and prevention of engineering disasters such as casing deformation and casing damage, and wellbore collapse. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the multi-dimensional determination method for fracture activation conditions of combined well casing variable-acoustic emission b-value according to Embodiment 1 of the present invention;

[0026] Figure 2 This is a graph showing the relationship between the deformation strength at the sleeve point and the extension length of the fracture plane in Embodiment 2 of the present invention.

[0027] Figure 3 This is a correlation diagram between the deformation strength at the sleeve deformation point and the fracture-maximum principal stress angle in Embodiment 2 of the present invention;

[0028] Figure 4 This is a graph showing the relationship between the deformation strength at the sleeve deformation point and the longitudinal extension length of the fracture in Embodiment 2 of the present invention.

[0029] Figure 5 This is a correlation diagram between the deformation strength and fracture inclination angle at the sleeve deformation point in Embodiment 2 of the present invention;

[0030] Figure 6 This is a schematic diagram of the shear stress, acoustic emission event points, and their cumulative energy evolution curves during the entire stress loading process of Embodiment 2 of the present invention.

[0031] Figure 7 This relates to the experimental scale fault-horizontal maximum principal stress angle and acoustic emission b-value in Embodiment 2 of the present invention.

[0032] Figure 8 This is a correlation diagram between the experimental scale of the fault and the acoustic emission b-value in Embodiment 2 of the present invention;

[0033] Figure 9 This is a coupled diagram of the experimental-engineering scale evolution under different fracture and stress angle conditions in Embodiment 2 of the present invention;

[0034] Figure 10 This is a coupled diagram of the experimental-engineering scale evolution under different planar extension lengths in Embodiment 2 of the present invention. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Example 1

[0037] See Figure 1 This embodiment provides a multi-dimensional determination method for fracture activation conditions based on the combined well casing variable-acoustic emission b-value, including the following steps:

[0038] Step 1: Based on the analysis of the fracture structure, conduct preliminary statistical analysis of the control law of the fracture's own properties on fracture activation.

[0039] First, by analyzing the wellbore obstruction encountered during fracturing operations and using logging data from multi-arm wellbore calipers, the corresponding casing deformation depth and degree of deformation information for each single well casing deformation point in the work area are identified. The formula for calculating the degree of deformation is as follows:

[0040] I = (Ap - Bp) / Ap * 100%

[0041] Where I represents the degree of deformation, Ap represents the inner diameter of the casing, and Bp represents the inner diameter of the well. The plane distribution of fractures in the work area is obtained through seismic data interpretation technology. At the same time, a plane distribution map of fractures is obtained. The casing deformation points are projected onto the plane distribution map of fractures and the casing deformation points caused by fracture slip are screened out. Then, the degree of deformation of the casing deformation points near each fracture is correlated with the fracture's own properties and the petrological characteristics of the two sides of the fracture. The geological factors with the strongest correlation with the fracture activation conditions are summarized. From the perspective of casing deformation analysis, the control law of the fracture's own properties on fracture activation in the work area is preliminarily clarified. The fracture's own properties include information such as fracture strike, fracture dip angle, and plane extension length.

[0042] Step 2: Obtain the acoustic emission b-value at the critical activation point of the experimental scale.

[0043] Using the lithological composition and structure of the study area as an experimental model, and the geological factors most strongly correlated with fracture activation conditions as experimental variables, physical simulation experiments were conducted on rock masses containing non-penetrating fractures under compression-shear loading conditions. Stress-strain and acoustic emission energy evolution curves were obtained throughout the loading process, and different extension evolution stages were defined based on these changes. The biaxial stress difference coefficient of field slip fractures (fractures inducing nesting deformation) was selected as a similarity index to calibrate the experimental-scale matching segments corresponding to fracture-induced nesting deformation in the study area. The critical initiation point of the experimental-scale matching segments was determined using stress drop and acoustic emission energy signals, and the acoustic emission b-value corresponding to the critical initiation point was calculated. The acoustic emission b-value reflects the activation risk of the fractured rock mass; a larger b-value indicates stronger stability, and a smaller b-value indicates weaker stability (more prone to activation and instability). The formula for calculating the acoustic emission b-value is:

[0044] A = 20log 10 V max -A pre

[0045] log 10 N = ab(A / 20)

[0046] Where N is the number of events (n) with amplitude greater than A, b is the size distribution of acoustic emission events (dimensionless), A is the acoustic emission amplitude (dB), and V max For peak voltage, A pre Let 'a' be the threshold value (dB) and 'a' be logarithm. 10 The intercept of the fitted curve N with respect to A / 20;

[0047] Step 3: Constructing a fracture activation condition determination method based on the analytical-acoustic emission b-value of the fusion-structured variable.

[0048] The acoustic emission b-value was fitted to a curve of acoustic emission b-value variation under specific experimental variables using the curve fitting method in Origin software. This curve was then combined with the curve of strain intensity variation obtained from the analysis of the strain under the same variables. The experimental scale-field scale matching results under different variables were continuously optimized and adjusted to obtain activation thresholds for different variables. The different activation thresholds were combined until the optimal fracture activation threshold applicable to the study area was obtained. In this way, a multidimensional fracture activation condition determination method based on acoustic emission b-value and strain data was constructed and applied to the fracture activation condition determination in cases where strain data is limited.

[0049] This embodiment combines analytical statistical results of the alternating geological structure with experimental simulation results. While considering complex geological conditions, it is also constrained by theoretical instability models, making the evaluation results of specific research areas more representative and targeted.

[0050] Example 2

[0051] See Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 , Figure 9 , Figure 10 This embodiment determines the activation conditions of the Wufeng Formation-Longmaxi Formation fault in the Luzhou work area, specifically including the following steps:

[0052] Step 1: Analysis of the Main Controlling Factors of Fracture Activation Based on Analytical Analysis

[0053] Based on wellbore tool conditions and multi-arm logging data, 410 casing deformation points were identified during fracturing operations in the Wufeng-Longmaxi Formation shale reservoir in the Luzhou work area. Combining this with fracture plane distribution, 120 casing deformation points with fracture slip origin were selected. Furthermore, the deformation intensity information of single-well casing deformation points was converted into current activity intensity information for individual fractures. The casing deformation intensity near the fracture and the fracture plane extension length (e.g., ...) were statistically analyzed. Figure 2 (as shown), fracture-horizontal maximum principal stress angle (as shown) Figure 3 As shown), longitudinal extension length (as shown) Figure 4 (as shown), fracture dip angle (as shown) Figure 5 The correlation analysis of attributes such as (as shown) revealed that the fault slip in the study area is mainly controlled by the plane extension length and the angle between the fault and the maximum horizontal stress, while the correlation with the fault dip angle and longitudinal extension length is relatively weak.

[0054] The influence of the fracture properties on the deformation is as follows: as the length of the fracture plane increases, the deformation strength at the deformation point increases accordingly; when the angle between the fracture and the maximum principal stress approaches 30°, the fracture slip strength is the greatest.

[0055] Step 2: Obtain the acoustic emission b-value under different fracture-maximum principal stress angles and planar extension lengths experimental conditions.

[0056] Based on the above analysis of the main controlling factors of fracture activation in the Luzhou work area, a physical simulation experiment of rock mass instability with non-penetrating fractures was designed under different fracture-horizontal maximum principal stress angles and planar extension lengths. This clarified that the entire stress loading process underwent a fracture compaction stage (e.g., Figure 6 The OA segment shown), the linear elastic stage (such as...) Figure 6 (as shown in segment AB), rapid crack propagation stage (such as...) Figure 6 The BC segment shown), macroscopic rupture stage (such as...) Figure 6 The CD segment shown), macroscopic friction stage (such as...) Figure 6 The stress difference coefficient of the typical slip fracture in the Luzhou work area (shown as segment DE) is calculated to be 0.15–0.16. Furthermore, based on the second similarity theorem, the experimental results are extrapolated to geological conditions, and the experimental matching segment at the actual instability of the work area is calibrated as follows: Figure 6The OD segment shown is characterized by a sharp increase in the first stress drop and acoustic emission energy. Different experimental samples were identified in the experimental agreement segment (e.g.,...) Figure 6 The critical starting point of the OD segment shown (e.g.) Figure 6 Point C (as shown in the example) is further calculated using the acoustic emission b-value calculation formula in the embodiment. A nonlinear curve fitting method is then used to obtain the curve showing the relationship between the fault-maximum principal stress angle and the acoustic emission b-value (e.g., point C). Figure 7 As shown in the figure, with the increase of the fault-maximum principal stress angle, the acoustic emission b-value shows a trend of first decreasing and then increasing. Linear regression was used to fit the curves of the change in fault length and acoustic emission b-value. With the increase of fault scale, the b-value shows a gradually decreasing trend (e.g., ...). Figure 8 (as shown);

[0057] Step 3: Calibration of Fault Activation Conditions in the Work Area

[0058] Box plots were used to statistically analyze the strain strength and fracture-maximum principal stress angle for different fracture types. Coupled with the variation curves of fracture-maximum principal stress angle and acoustic emission b-value under the aforementioned experimental scale, the threshold for easy fracture activation in the Luzhou work area was determined to be b < 1.80, with the fracture-stress angle between 0 and 75° (e.g., ...). Figure 9 (As shown), box plots were then used to statistically analyze the strain strength and fracture scale of different fractures. Coupled with the variation curves of fracture scale and acoustic emission b-value under the experimental scale, the threshold for easy activation of fractures in the Luzhou work area was determined to be b < 1.85 and fracture scale < 1 km. Finally, the activation thresholds under the two variables were combined, and the optimal threshold was obtained by using downhole statistical laws as constraints, namely b < 1.85, fracture and stress angle between 0 and 60°, and fracture scale < 1 km. Figure 10 This is a coupled diagram of the experimental-engineering scale evolution under different planar extension lengths.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A multidimensional determination method for fracture activation conditions of combined well casing variable-acoustic emission b-value, characterized in that, Includes the following steps: Step 1: First, identify the casing deformation depth and deformation degree information corresponding to each single well casing deformation point in the work area. Then, obtain the plane distribution of the fracture in the work area, project the casing deformation points onto the fracture plane distribution map, and screen out the casing deformation points caused by fracture slip. Next, perform correlation statistical analysis on the deformation degree of the casing deformation points near each fracture with the fracture's own properties and the petrological characteristics of the two sides of the fracture. Summarize the geological factors with the strongest correlation with the fracture activation conditions, and preliminarily clarify the control law of the fracture's own properties on fracture activation from the perspective of casing deformation analysis. Step 2: Using the lithological composition and structure of the stratigraphic layer in the work area as the experimental model, and the geological factors most strongly correlated with the fracture activation conditions as the experimental variables, conduct physical simulation experiments on rock masses with non-penetrating fractures under compression-shear loading conditions. Select the biaxial stress difference coefficient of the field slip fracture as the similarity index, calibrate the experimental scale matching segment corresponding to the fracture-induced sleeve deformation in the work area, clarify the critical slip initiation point of the experimental scale matching segment, and calculate its corresponding acoustic emission b value. Step 3: Fit the acoustic emission b-value to the acoustic emission b-value variation curve under specific experimental variables, and combine it with the deformation intensity variation curve obtained by the analysis of the deformation under the same variables. Continuously optimize and adjust the experimental scale-field scale matching results under different variables to obtain the activation threshold of different variables. Combine the different activation thresholds until the optimal fracture activation threshold suitable for the research area is obtained, and perform multi-dimensional determination of fracture activation conditions.

2. The multidimensional determination method for fracture activation conditions of combined well casing variable-acoustic emission b-value according to claim 1, characterized in that: In step one, the information on the casing deformation depth and deformation degree corresponding to each single well casing deformation point in the work area is obtained by identifying the well obstruction situation during the fracturing operation and the logging data of the multi-arm well diameter. The fracture plane distribution in the work area is obtained by seismic data interpretation technology, and a fracture plane distribution map is obtained at the same time.

3. The multidimensional determination method for fracture activation conditions of combined well casing variable-acoustic emission b-value according to claim 1, characterized in that: In step one, the formula for calculating the degree of deformation is: ; Where I represents the degree of deformation, Ap represents the inner diameter of the casing, and Bp represents the inner diameter of the well.

4. The multidimensional determination method for fracture activation conditions of combined well casing variable-acoustic emission b-value according to claim 1, characterized in that: In step one, the fracture properties include fracture orientation, fracture dip angle, and planar extension length.

5. The multidimensional determination method for fracture activation conditions of combined well casing variable-acoustic emission b-value according to claim 1, characterized in that: In step two, stress-strain and acoustic emission energy evolution curves of the entire loading process are obtained based on physical simulation experiments, and different extended evolution stages are divided according to the change law.

6. The multidimensional determination method for fracture activation conditions of combined well casing variable-acoustic emission b-value according to claim 1, characterized in that: In step two, the field slip fracture is a fracture that induces sheath deformation. After calibrating the experimental scale matching segment corresponding to the fracture-induced sheath deformation in the work area, the critical slip initiation point of the experimental scale matching segment is determined by stress drop and acoustic emission energy signals.

7. The multidimensional determination method for fracture activation conditions of combined well casing variable-acoustic emission b-value according to claim 1, characterized in that: In step two, the formula for calculating the acoustic emission b-value is: ; ； where N is the number of events with amplitude greater than A, b is the acoustic emission event size distribution, A is the acoustic emission amplitude, V max is the peak voltage, A pre is the threshold value, a is the log 10 N and the intercept of the curve fit of N vs. A / 20.

8. The multidimensional determination method for fracture activation conditions of combined well casing variable-acoustic emission b-value according to claim 1, characterized in that: In step two, the acoustic emission b-value reflects the activation risk of the fractured rock mass. The larger the b-value, the stronger the stability, and the smaller the b-value, the weaker the stability.

9. The multidimensional determination method for fracture activation conditions of combined well casing variable-acoustic emission b-value according to claim 1, characterized in that: In step three, the acoustic emission b-value variation curve is obtained using the curve fitting method in Origin software. A multidimensional fracture activation condition determination method based on acoustic emission b-value and overlay data is constructed according to the optimal fracture activation threshold and applied to the fracture activation condition determination in cases where overlay data is limited.

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