A fracturing method for reducing the impact of fracturing-induced faulting

Abstract

The application discloses a fracturing method for reducing the influence of fracturing on a fault, and comprises the following steps: according to the fault type, the fault extension, the distance between the fault and the fracturing section and the micro-fracture development degree, the maximum displacement and the maximum injection liquid volume of the first section fracturing construction are determined; supercritical carbon dioxide is used as a pre-fluid to perform the first section fracturing construction; according to the distance between the fault and the fracturing section, the microseismic event spatial distribution monitored in the first section fracturing construction and the micro-fracture development degree between the two fracturing sections and the fault, the minimum time interval of the adjacent construction section is determined; the micro-fracture development degree between the fracturing section and the fault is rechecked, the maximum displacement and the maximum injection liquid volume of the second section fracturing construction are determined; the second section fracturing construction is performed based on the minimum time interval; and the above steps are repeated until the fracturing construction of all sections is completed. The application can be directly applied to an oil and gas development site, greatly reduces the influence of fracturing on the fault, and achieves the purpose of safe fracturing.

Description

Technical Field

[0001] This invention relates to the field of unconventional oil and gas and low-permeability oil and gas reservoir stimulation technology, and in particular to a fracturing method for reducing the impact of fracturing disturbance on faults. Background Technology

[0002] Since large-scale fracturing was widely applied in oil and gas development, it has achieved significant economic and social benefits, but it has also brought a series of environmental problems. Fracturing is a technology that releases oil and gas resources by injecting high-pressure fluids into rock formations to induce fractures. This process can potentially trigger earthquakes by altering geostress, fluid pressure, or triggering slippage. In particular, the risk of fracturing-induced earthquakes increases significantly if concealed faults exist in the underground rock formations. Concealed faults are widespread in oil and gas reservoirs, posing a significant challenge to the geological safety of oil and gas development. Oil and gas resources near faults are often not exploitable for safety reasons. Therefore, minimizing the impact of fracturing on faults is crucial for maximizing the utilization of oil and gas resources.

[0003] Patent CN202310202224.X authorizes a method and system for real-time assessment of potential catastrophic risks to optimize fracturing construction parameters. This method acquires real-time seismic data and location information during shale gas extraction in the target area through near-field monitoring, obtains real-time production factor data and casing deformation data during single-well fracturing, calculates correlation and regression coefficients of each production factor data, calculates the weights of each production factor data, determines the key production factor data, determines the risk threshold, and conducts real-time assessment of potential seismic risks, thereby reducing potential seismic and casing deformation risks during shale gas extraction. Patent CN202310016875.X authorizes an evaluation method for hydraulic fracturing-induced fault-induced earthquakes. This method can quantitatively evaluate the probability of induced earthquakes at different stages of hydraulic fracturing construction, under different injection methods, and under different production conditions for each evaluation unit or single well, providing a quantitative result and data support for optimizing hydraulic fracturing construction and production conditions to reduce induced earthquake disasters. Patent CN202311352119.0 discloses a physical simulation experimental method for earthquakes induced by hydraulic fracturing in hot dry rock, comprising four steps: specimen fabrication, fault construction, fracturing experiment, and data analysis. This invention can simulate fault slippage caused by hydraulic fracturing in hot dry rock under laboratory conditions. Patent CN202311313876.7 discloses a test system for simulating fault activation and earthquake induction under hydraulic fracturing in horizontal wells, comprising a horizontal well geological model, a distributed fiber optic monitoring system, a perforation system, a fracturing system, a formation temperature simulation system, and a stress application system. It can perform real-time and continuous monitoring of formation pressure, temperature, and multi-physics fields of fault-containing geological reservoirs under the entire process and multiple steps of horizontal well hydraulic fracturing. It can be used to study the formation and propagation of rock fracture networks, fault activation, and well casing deformation and damage processes during the entire fracturing process at different stages of horizontal well fracturing. Patent CN202110227231.6 authorizes a method for assessing the seismic hazard of active faults. By considering the influence of deep stress on shallow stress, it establishes a response model of shallow stress to deep stress and analyzes the impact of stress adjustment on seismic hazard, effectively reducing the risk of underestimating seismic hazard in low-stress areas. In addition, patents CN202011231661.7, CN202310202224.X, and CN202211461347.7 disclose or authorize methods for activating or assessing the risk of fracturing-induced earthquakes. These methods mainly focus on evaluating experimental equipment, determining safe distances, seismic risk assessment, numerical simulation, and optimizing fracturing parameters. They play a positive role in evaluating and studying the risk of fracturing-induced earthquakes, but lack fracturing methods that can be directly applied in the field to reduce the impact of fracturing disturbance on hidden faults.

[0004] Therefore, there is an urgent need for a fracturing method that can increase the volume of fracturing and reduce the impact of fracturing on fault disturbance. Summary of the Invention

[0005] The present invention aims to provide a fracturing method that can reduce the impact of fracturing disturbance on faults by achieving fracturing disturbance control, in order to solve the problem that there is a lack of existing methods that can be directly applied to the field to reduce the impact of fracturing disturbance on faults. The present invention can be directly applied to oil and gas development sites and can significantly reduce the impact of fracturing on faults, thereby achieving the goal of safe fracturing.

[0006] To achieve the above objectives, the basic solution of the present invention is as follows: A fracturing method for reducing the influence of fracturing disturbance faults, comprising the following steps: S1: Determining the maximum displacement and maximum injection fluid volume for the first stage of fracturing operation based on the fault type, fault extension, distance between the fault and the fracturing section, and the degree of microfracture development between the fracturing section and the fault; S2: Based on the maximum displacement and maximum injection fluid volume, using supercritical carbon dioxide as a pre-fluid, performing the first stage of fracturing operation according to a predetermined fracturing pumping procedure; S3: Based on the distance between the fault and the fracturing section, and the monitoring during the first stage of fracturing operation... Based on the spatial distribution of microseismic events and the development degree of microfractures between the first and second fracturing segments and the fault, determine the minimum time interval between the completion of the first fracturing segment and the start of the second fracturing segment; S4: Analyze the newly generated fractures based on the microseismic events monitored during the first fracturing segment, re-verify the development degree of microfractures between the fracturing segment and the fault, and determine the maximum displacement and maximum injection volume for the second fracturing segment; S5: Based on the minimum time interval, perform the second fracturing segment using the method in step S2, and repeat steps S3-S5 until all segments of fracturing are completed.

[0007] Furthermore, the maximum displacement Q is:

[0008]

[0009] In the formula, This is the fault type displacement correction factor. This is the displacement correction factor for fault extension. This is the discharge correction factor for the distance between the fault and the fracturing section. This is a displacement correction factor for the degree of microfracture development between the fracturing section and the fault. This represents the average maximum construction discharge rate for a single section of a faultless well within the block.

[0010] Furthermore, the maximum injected fluid volume V is:

[0011]

[0012] In the formula, This is the fluid volume correction factor for fault type. This is the fluid volume correction factor for fault extension. This is the fluid volume correction factor for the distance between the fault and the fracturing section. This is a fluid volume correction factor for the degree of microfracture development between the fractured section and the fault. This represents the average maximum injection volume per segment for fault-free wells within the block.

[0013] Furthermore, the injection volume of supercritical carbon dioxide is no more than 30% of the total injection volume in this fracturing section, and the maximum injection displacement is no more than 25% of the maximum displacement in this fracturing section.

[0014] Furthermore, the minimum time interval T between the completion of the first stage of fracturing and the start of the second stage of fracturing is:

[0015]

[0016] In the formula, This is a correction factor for the time interval between the fault and the fracturing section. This is a correction factor for the spatial distribution time interval of microseismic events. The degree of microfracture development between the first and second fracturing sections and the fault. This is the average time interval between the completion of the upper section of the fractured well within a 3km radius of the block and the start of the second stage of fractured construction.

[0017] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: By determining the fault type, fault extension, distance between the fault and the fracturing section, and the degree of microfracture development between the fracturing section and the fault, the maximum displacement and maximum injection volume of the first stage of fracturing construction are determined, so as to achieve precise control of the displacement and injection volume during fracturing and reduce the disturbance effect of fracturing on the fault; Based on the maximum fluid volume and maximum injection volume, using supercritical carbon dioxide as the pre-fluid, the first stage of fracturing construction is carried out according to the predetermined fracturing pumping procedure, which can generate more secondary small fractures, thereby reducing the disturbance to the fault; According to the distance between the fault and the fracturing section, the spatial distribution of microseismic events monitored during the first stage of fracturing construction, and the micro-fracture development between the first and second fracturing sections and the fault, the present invention can achieve precise control of the displacement and injection volume during fracturing and reduce the disturbance effect of fracturing on the fault; Based on ... The degree of fracture development is used to determine the minimum time interval between the completion of the first stage of fracturing and the start of the second stage, enabling reasonable control of the time interval, effectively mitigating stress concentration caused by the previous stage of fracturing, and reducing stress concentration disturbance to the fault. Based on the microseismic events monitored during the first stage of fracturing, the newly generated fracture situation is analyzed, and the degree of microfracture development between the fracturing stage and the fault is re-verified. The maximum displacement and maximum injection volume for the second stage of fracturing are determined, and the second stage of fracturing is carried out based on the minimum time interval. The above steps are repeated until all stages of fracturing are completed. This method can be directly applied to oil and gas development sites, significantly reducing the disturbance impact of fracturing on the fault and achieving the goal of safe fracturing, so as to maximize the utilization of oil and gas resources. Attached Figure Description

[0018] Figure 1 This is a schematic flowchart of a fracturing method for reducing the impact of fracturing disturbance faults in one embodiment;

[0019] Figure 2 This is a schematic diagram of the seismic interpretation results of microfractures in a certain block in one embodiment. Detailed Implementation

[0020] To make the present invention clearer, 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.

[0021] like Figure 1 As shown, a fracturing method for reducing the influence of fracturing disturbance faults is provided, comprising the following steps:

[0022] Step S1: Determine the maximum displacement and maximum injection volume of the first stage of fracturing operation based on the fault type, fault extension, distance between the fault and the fracturing section, and the degree of microfracture development between the fracturing section and the fault.

[0023] Specifically, based on the fault type, fault extension, distance between the fault and the fracturing section, and the degree of microfracture development between the fracturing section and the fault, the maximum displacement and maximum injection volume of a fracturing operation are determined. By precisely controlling the maximum displacement of the fracturing operation, the width and extension length of the fracturing fractures can be effectively controlled, effectively preventing fault penetration or reducing the impact disturbance of penetrating faults. At the same time, precise control of the fracturing fluid volume can be achieved, effectively controlling the amount of fracturing fractures generated or reducing the lubrication effect of penetrating faults, thus weakening the impact of fracturing on the fault cohesion or the surrounding rock, and thereby reducing the disturbance impact on the fault.

[0024] The maximum displacement Q is:

[0025]

[0026] In the formula, This is the fault type displacement correction factor. This is the displacement correction factor for fault extension. This is the discharge correction factor for the distance between the fault and the fracturing section. This is a displacement correction factor for the degree of microfracture development between the fracturing section and the fault. This represents the average maximum construction discharge rate for a single section of a faultless well within the block.

[0027] Specifically, the degree of microfracture development between the fracturing section and the fault is described by fracture intensity, which is a dimensionless value obtained using the three-dimensional seismic ant body tracking interpretation method. The values ​​of each correction coefficient are determined by Table 1 below.

[0028] Table 1

[0029]

[0030] The maximum injection volume V is:

[0031]

[0032] In the formula, This is the fluid volume correction factor for fault type. This is the fluid volume correction factor for fault extension. This is the fluid volume correction factor for the distance between the fault and the fracturing section. This is a fluid volume correction factor for the degree of microfracture development between the fractured section and the fault. This represents the average maximum injection volume per segment for fault-free wells within the block.

[0033] Specifically, the values ​​of each liquid volume correction coefficient are determined by Table 2 below.

[0034] Table 2

[0035]

[0036] Step S2: Based on the maximum displacement and maximum injection volume, supercritical carbon dioxide is used as the pre-fluid, and the first stage of fracturing is carried out according to the predetermined fracturing pump injection procedure.

[0037] Specifically, based on the maximum displacement and maximum injection volume, supercritical carbon dioxide is used as the pre-fluid, and the first stage of fracturing is carried out according to the predetermined fracturing pump injection procedure. This fully utilizes the dissolution and superior diffusion characteristics of supercritical carbon dioxide to reduce the impact of fracturing on the fault, thereby reducing the risk of fracturing-induced earthquakes.

[0038] The injection volume of supercritical carbon dioxide shall not exceed 30% of the total injection volume in this fracturing section, and the maximum injection displacement shall not exceed 25% of the maximum displacement in this fracturing section.

[0039] Specifically, the volume of supercritical carbon dioxide injected should not exceed 30% of the total volume injected in this fracturing stage, and the maximum injection rate should not exceed 25% of the maximum injection rate in this fracturing stage. A low injection rate is used initially, and the maximum injection rate is used in the later stages until all supercritical carbon dioxide is injected. After complete supercritical carbon dioxide injection, a well shut-in interval of at least 30 minutes is maintained before continuing injection of subsequent fracturing fluids according to the predetermined pumping procedure.

[0040] By rationally controlling the injection and discharge rates of supercritical carbon dioxide, more secondary small fractures can be triggered, thereby reducing the generation of more large or penetrating fractures under the same fracturing scale. This reduces the amount and risk of fracturing fluid flowing into the fault, and thus reduces the disturbance to the fault.

[0041] Step S3: Based on the distance between the fault and the fracturing segment, the spatial distribution of microseismic events monitored during the first fracturing operation, and the degree of microfracture development between the first and second fracturing segments and the fault, determine the minimum time interval between the completion of the first fracturing operation and the start of the second fracturing operation.

[0042] Specifically, based on the distance between the fault and the fracturing segment, the spatial distribution of microseismic events monitored during the first fracturing operation, and the degree of microfracture development between the first and second fracturing segments and the fault, the minimum time interval between the completion of the first fracturing operation and the start of the second fracturing operation is determined. This allows for a reasonable determination of the fracturing time interval between two adjacent fracturing operations, which can adequately and appropriately alleviate the stress concentration caused by the previous fracturing operation, thereby reducing the disturbance of the fault caused by the high stress concentration.

[0043] The minimum time interval T between the completion of the first stage of fracturing and the start of the second stage of fracturing is:

[0044]

[0045] In the formula,

[0046] This is a correction factor for the time interval between the fault and the fracturing section.

[0047] This is a correction factor for the spatial distribution time interval of microseismic events.

[0048] The degree of microfracture development between the first and second fracturing sections and the fault.

[0049] This is the average time interval between the completion of the upper section of the fractured well within a 3km radius of the block and the start of the second stage of fractured construction.

[0050] Specifically, the values ​​of the correction coefficients for each time interval are determined by Table 3 below.

[0051] Table 3

[0052]

[0053] Step S4: Analyze the newly generated fractures based on the microseismic events monitored during the first stage of fracturing, re-verify the degree of microfracture development between the fracturing section and the fault, and determine the maximum discharge rate and maximum injection rate for the second stage of fracturing.

[0054] Specifically, after the first stage of fracturing is completed, the newly generated fractures are analyzed based on the microseismic events monitored during the process, and the degree of microfracture development between the fracturing stage and the fault is re-checked. Using the same method as in step S1, the maximum discharge rate and maximum injection rate of the second stage of fracturing are determined to achieve precise control over the maximum discharge rate and maximum injection rate of the second stage of fracturing, effectively reducing the disturbance impact of fracturing on the fault.

[0055] Step S5: Based on the minimum time interval, perform the second stage of fracturing using the method in step S2. Repeat steps S3-S5 until all stages of fracturing are completed.

[0056] Specifically, based on the obtained minimum time interval, the second stage of fracturing is carried out using the method in step S2, with supercritical carbon dioxide as the pre-fluid, according to the predetermined fracturing pump injection procedure. After the second stage of fracturing is completed, the minimum time interval between it and the third stage of fracturing is determined using the method in step S3. The degree of microfracture development between the fracturing stage and the fault is rechecked using the method in step S4, and the maximum displacement and maximum injection volume of the third stage of fracturing are determined. Based on the minimum time interval, the third stage of fracturing is carried out using the method in step S2. The above steps are repeated to complete the fracturing of all stages.

[0057] In this embodiment, the maximum displacement and injection volume of the first stage of fracturing are determined by the fault type, fault extension, distance between the fault and the fracturing segment, and the degree of microfracture development between the fracturing segment and the fault. This allows for precise control of the displacement and injection volume during fracturing, reducing the disturbance to the fault. Based on the maximum fluid volume and injection volume, supercritical carbon dioxide is used as the pre-fluid, and the first stage of fracturing is carried out according to a predetermined fracturing pumping procedure. This can generate more secondary small fractures, further reducing disturbance to the fault. The maximum displacement and injection volume are determined by the distance between the fault and the fracturing segment, the spatial distribution of microseismic events monitored during the first stage of fracturing, and the degree of microfracture development between the first and second fracturing segments and the fault. The minimum time interval between the completion of the first fracturing stage and the start of the second fracturing stage is determined to achieve reasonable control of the time interval, effectively mitigate the stress concentration caused by the first fracturing stage, and reduce the disturbance of the fault caused by stress concentration. Based on the microseismic events monitored during the first fracturing stage, the newly generated fractures are analyzed, and the development degree of microfractures between the fracturing stage and the fault is re-verified. The maximum displacement and maximum injection volume of the second fracturing stage are determined, and the second fracturing stage is carried out based on the minimum time interval. The above steps are repeated until all fracturing stages are completed. This method can be directly applied to oil and gas development sites, significantly reducing the disturbance impact of fracturing on the fault and achieving the goal of safe fracturing, so as to maximize the utilization of oil and gas resources.

[0058] In one embodiment, such as Figure 2 As shown in the figure, 1 represents a fractured well, 2 represents a fracture development cloud map, and 3 represents a fault. In a certain block, the horizontal section of the fractured well is 2000m long and 4100m deep, with each fractured section being 80m long, for a total of 25 sections. The first fractured well is 2.1km from the nearest fault, and the last section is 3.91km from the nearest fault. The fault type is a normal fault, and the fault extension is intra-layer extension. Using 3D seismic ant body tracking interpretation, the microfracture development intensity (before fracturing) between the first fractured section and the fault is 30. The average maximum construction flow rate of a single section of a faultless well in the block is 21.5 cubic meters per minute. The average maximum injection volume of a single section of an adjacent faultless well in the block is 2250 cubic meters. The average time interval between the completion of the upper section of a fractured well within 3km of a fault in the block and the start of the second section of fracturing is 18 hours.

[0059] The calculated correction coefficients for each displacement rate and the maximum displacement rate for fracturing operations are shown in Table 4.

[0060] Table 4. Correction coefficients and calculation results of maximum displacement during fracturing operations in the examples.

[0061]

[0062] The calculated correction coefficients for each injection volume and the maximum injection volume for fracturing operations are shown in Table 5.

[0063] Table 5 Correction coefficient and calculation results of maximum injection volume for fracturing operations in the example.

[0064]

[0065] Supercritical carbon dioxide was used as the pre-fluid. The volume of supercritical carbon dioxide in the first stage was no more than 30% of the total volume injected in this fracturing stage, and the maximum injection rate was no more than 25% of the maximum injection rate in this fracturing stage. In the initial stage of supercritical carbon dioxide injection, a flow rate of no more than 2 cubic meters per minute was used, and the initial maximum injection volume was no more than 35% of the maximum volume. The maximum flow rate was used in the middle and later stages of injection until all supercritical carbon dioxide was injected. After complete supercritical carbon dioxide injection, the well shut-in interval was greater than 30 minutes. The calculation results for the maximum flow rate and maximum volume of supercritical carbon dioxide injection are shown in Table 6.

[0066] Table 6 Calculation results of maximum displacement and maximum liquid volume of supercritical carbon dioxide injection in the examples

[0067]

[0068] The minimum time interval for each fracturing operation was calculated and is shown in Table 7.

[0069] Table 7. Calculation results of the minimum time interval for fracturing operations between different segments in the examples.

[0070]

[0071] Repeat the above steps to carry out the fracturing construction of the second and remaining sections. The construction parameters for each section are shown in Table 4-7. Finally, the fracturing construction is completed.

[0072] By taking the above steps, we can both increase the volume of fracturing and reduce the disturbance of the fault by fracturing, so as to maximize the use of all oil and gas resources.

[0073] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0074] The above descriptions are merely embodiments of the present invention. Commonly known structures and characteristics are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can, under the guidance of this application, improve and implement this solution in combination with their own capabilities. Some typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A fracturing method for reducing the influence of fracturing disturbance faults, characterized in that, Includes the following steps: S1: Determine the maximum displacement and maximum injection volume of the first stage of fracturing based on the fault type, fault extension, distance between the fault and the fracturing section, and the degree of microfracture development between the fracturing section and the fault. S2: Based on the maximum displacement and maximum injection volume, supercritical carbon dioxide is used as the pre-fracturing liquid, and the first stage of fracturing is carried out according to the predetermined fracturing pump injection procedure. S3: Determine the minimum time interval between the completion of the first stage of fracturing and the start of the second stage of fracturing based on the distance between the fault and the fracturing section, the spatial distribution of microseismic events monitored during the first stage of fracturing, and the degree of microfracture development between the first and second fracturing sections and the fault. S4: Analyze the newly generated fractures by monitoring the microseismic events in the first stage of fracturing, re-verify the degree of microfracture development between the fracturing section and the fault, and determine the maximum displacement and maximum injection volume for the second stage of fracturing. S5: Based on the minimum time interval, perform the second stage of fracturing using the method in step S2, and repeat steps S3-S5 until all stages of fracturing are completed.

2. The fracturing method for reducing the influence of fracturing disturbance faults according to claim 1, characterized in that, The maximum displacement Q is: In the formula, This is the fault type displacement correction factor. This is the displacement correction factor for fault extension. This is the discharge correction factor for the distance between the fault and the fracturing section. This is a displacement correction factor for the degree of microfracture development between the fracturing section and the fault. This represents the average maximum construction discharge rate for a single section of a faultless well within the block.

3. The fracturing method for reducing the influence of fracturing disturbance faults according to claim 1, characterized in that, The maximum injected fluid volume V is: In the formula, This is the fluid volume correction factor for fault type. This is the fluid volume correction factor for fault extension. This is the fluid volume correction factor for the distance between the fault and the fracturing section. This is a fluid volume correction factor for the degree of microfracture development between the fractured section and the fault. This represents the average maximum injection volume per segment for fault-free wells within the block.

4. The fracturing method for reducing the influence of fracturing disturbance faults according to claim 1, characterized in that, The injection volume of supercritical carbon dioxide shall not exceed 30% of the total injection volume in this fracturing section, and the maximum injection displacement shall not exceed 25% of the maximum displacement in this fracturing section.

5. The fracturing method for reducing the influence of fracturing disturbance faults according to claim 1, characterized in that, The minimum time interval T between the completion of the first stage of fracturing and the start of the second stage of fracturing is: In the formula, This is a correction factor for the time interval between the fault and the fracturing section. This is a correction factor for the spatial distribution time interval of microseismic events. The degree of microfracture development between the first and second fracturing sections and the fault. This is the average time interval between the completion of the upper section of the fractured well within a 3km radius of the block and the start of the second stage of fractured construction.

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