A zonal hydraulic fracturing and injection method for co2 geological sequestration

Abstract

The application discloses a kind of partition hydraulic fracturing and injection method of CO2 geological storage, it is related to carbon dioxide geological storage, underground engineering safety control technical field, and successively carries out geomechanics evaluation and parameter acquisition, wellbore operation area division and packer assembly arrangement, target modification area is tested, target modification area is implemented controlled hydraulic fracturing, constant-speed test injection and well shut-in pressure drop test, formal carbon dioxide injection, risk discrimination and linkage pressure relief and adjustment;In the application, after regional division, the target storage layer is implemented controlled hydraulic fracturing, and combined with multi-source monitoring and linkage pressure relief operation, the whole process constraint to bottom hole pressure, fracture height and abnormal channel formation is realized.

Description

Technical Field

[0001] This invention relates to the fields of carbon dioxide geological storage and underground engineering safety control technology, and in particular to a method for zoned hydraulic fracturing and injection of CO2 for geological storage. Background Technology

[0002] Carbon dioxide geological storage is a technology to reduce atmospheric CO2 concentration and mitigate climate change. In deep, low-permeability storage formations, the natural flow capacity of the reservoir is often insufficient to meet engineering requirements; reservoir stimulation methods such as hydraulic fracturing are typically used to construct flow channels, reduce flow resistance near the wellbore, and increase storage space. However, in geological storage projects, hydraulic fracturing, in addition to increasing injection capacity, may also cause safety issues such as excessive fracture propagation towards the caprock, enhanced anomalous responses in adjacent layers, and the formation of potential leakage channels.

[0003] If the sole objective is to increase the injection volume without considering constraints related to caprock integrity and pressure management, a conflict between "increased injection" and "safety" can easily arise. Furthermore, current technologies often involve direct injection of critical-state CO2 after fracturing, or relying solely on bottomhole pressure to determine whether continued operation is feasible; the lack of multi-parameter joint verification makes it difficult to quantify whether controllable CO2 injection and continuous operation are truly possible after fracturing. Summary of the Invention

[0004] The purpose of this invention is to provide a zoned hydraulic fracturing and injection method for CO2 geological storage, in order to solve the problems existing in the prior art. After the zone is divided, controlled hydraulic fracturing is carried out on the target storage layer, and combined with multi-source monitoring and coordinated pressure relief operation, the whole process of bottom hole pressure, fracture height and abnormal channel formation is constrained.

[0005] To achieve the above objectives, the present invention provides the following solution: The present invention provides a method for zoned hydraulic fracturing and injection for CO2 geological storage, comprising the following steps: S1. Obtain the geomechanical parameters of the target sealing layer, adjacent layers, and caprock, determine the caprock tension failure control pressure, caprock or weak surface shear instability control pressure, and wellbore integrity control pressure, and calculate the bottom hole pressure upper limit for the entire fracturing process and the entire injection process according to formulas (1) and (2): (1) (2) in, This represents the upper limit of the bottom hole pressure throughout the entire fracturing process; To control the pressure for tension failure of the cap layer; The pressure is used to control shear instability in the cap layer or weak surface. Pressure is controlled to ensure wellbore integrity. For safety redundancy; This refers to the upper limit of the bottom hole pressure throughout the entire injection process; The pressure required to reopen cracks in the target containment layer; Safety redundancy is set to prevent cracks from reopening during the injection process; S2. The wellbore's working area is divided into a target modification zone, a pressure buffer zone, and a monitoring and protection zone, distributed sequentially from bottom to top. The target modification zone is used for perforation, fracturing, and injection. The pressure buffer zone is used to provide pressure transition space and does not allow fracture penetration. The monitoring and protection zone is used to detect abnormal pressure or abnormal response in the overlying direction of the target sealing layer. S3. Conduct test fracturing on the target modified zone. Obtain the engineering identification value of the fracturing initiation pressure of the target modified zone from the linear fitting curve of pressure-rate. The engineering identification value is used for the initial screening of the current section and the current fracturing design parameters, and after correction, the fracturing initiation pressure value of the target modified zone is obtained. S4. When the engineering identification value satisfies formula (3), hydraulic fracturing is carried out on the target modification area. The construction pressure shall not exceed the upper limit of the bottom hole pressure of the entire fracturing process. The fracture height is constrained by stopping the pump / reducing the pressure in combination with the response of the monitoring protection area. Formula (3) is as follows: (3) In the formula, For engineering identification values, This represents the upper limit of the bottom hole pressure throughout the entire fracturing process; S5. After fracturing, constant rate injection and shut-in pressure drop tests are performed; the injection index, response characteristics of the monitoring protection zone and the response characteristics of the wellbore annulus are determined according to formulas (4), (5) and (6), and it is determined whether there are any abnormalities in the pressure of the monitoring protection zone and the wellbore annulus, and the post-fracturing state detection is completed; formulas (4), (5) and (6) are as follows: (4) (5) (6) in, For the injection index; This refers to the injection rate during the trial injection phase. This represents the near-steady-state bottom hole pressure at the end of the test injection phase. This refers to the reservoir static pressure or the formation pressure derived from the pressure drop. To monitor the normalized response coefficient of the protected area; To monitor the pressure increment of the protected area relative to the baseline; The normalized response coefficient of the wellbore annulus; This represents the pressure increment in the wellbore annulus relative to the baseline. S6. When at least the following conditions are met simultaneously: the bottom hole pressure during the constant rate injection period does not exceed the upper limit of the bottom hole pressure during the entire injection process; no obvious signs of fracture reopening appear during the constant rate injection period; the coefficient of variation of the injection index is not greater than 15%; the normalized response coefficient of the monitoring protection zone is not greater than 0.20; and the normalized response coefficient of the wellbore annulus is not greater than 0.10, formal carbon dioxide injection shall be carried out. S7. Based on the degree to which the bottom hole pressure approaches the upper limit of operation, the degree to which the fracture height approaches the upper limit of allowable pressure, the degree of pressure anomaly in the monitoring protection zone, the degree of annular pressure anomaly, and the degree of anomaly in auxiliary monitoring, continuously perform cross-layer risk assessment; when determined to be in a normal state, maintain the established parameters unchanged; when determined to be in a slightly risky state, reduce the injection rate or switch to pulse injection; when determined to be in a moderately risky state, reduce the injection rate and cut the segment, and slightly relieve pressure; when determined to be in a highly risky state, stop the current segment injection and perform at least one of the following coordinated pressure relief measures: open the return well / adjacent pumping well, reduce the continuous injection rate and switch to intermittent injection, or block the abnormal segment and switch to another segment; after completing the coordinated pressure relief and adjustment, repeat the steps after S5.

[0006] Optionally, in step S2, multiple fracturing tubing strings are installed in the wellbore, and a segmented isolation assembly is set between two adjacent fracturing tubing strings. The wellbore operation area is divided into a target modification area, a pressure buffer zone, and a monitoring protection zone by the segmented isolation assembly.

[0007] Optionally, in step S3, after the well is shut in until the bottom pressure reaches the reservoir static pressure, the injection rate is increased in a stepwise manner to conduct a fracturing test on the target modified area.

[0008] Optionally, in step S3, the target modification zone is subjected to trial cracking at a stepwise increase of 10%, 30%, 50%, 75%, and 100% of the designed maximum injection rate.

[0009] Optionally, in step S3, when the pressure in the linear fitting curve of pressure-rate shows a significant nonlinear deviation of 5-10% from the baseline for the first time, the pressure value is used as the engineering identification value of the crack initiation pressure of the target modified zone.

[0010] Optionally, in step S3, the initiation pressure value of the target modified zone is obtained by combining the interpretation results of diagnostic fracturing injection test or small fracturing test.

[0011] Optionally, in step S4, hydraulic fracturing is performed on the target modification area under four constraints: pressure restriction, flow restriction, time restriction, and height restriction.

[0012] Optionally, in step S4, when the engineering identification value does not meet the formula (3), at least the design displacement, single section length, perforation method, and target section shall be adjusted.

[0013] Optionally, in step S5, after fracturing is completed, a constant injection rate of 50%-70% of the designed formal injection rate is performed for 24-72 hours, and a shut-in pressure drop test is performed for no less than 24 hours.

[0014] Optionally, in step S7, the degree to which the bottom hole pressure approaches the upper limit of operation, the degree to which the fracture height approaches the upper limit of allowable operation, the degree of pressure anomaly in the monitoring protection zone, the degree of annular pressure anomaly, and the degree of auxiliary monitoring anomaly are first subjected to dimensionless normalization processing, and the results of this processing are comprehensively calculated according to formula (7) to obtain the quantitative value of the risk index: (7) In the formula, Risk index; These are the weighting coefficients for the degree to which bottomhole pressure approaches the operating upper limit, the degree to which fracture height approaches the allowable upper limit, the degree of pressure anomaly in the monitoring protection zone, the degree of annular pressure anomaly, and the degree of anomaly in auxiliary monitoring. , , , , ; These are the dimensionless normalized results of the degree to which the bottom hole pressure approaches the upper limit of operation, the degree to which the fracture height approaches the upper limit of allowable operation, the degree of pressure anomaly in the monitoring protection zone, the degree of anomaly in the annulus pressure, and the degree of anomaly in auxiliary monitoring. when When this occurs, it is considered a normal state; when At that time, it was determined to be a state of mild risk; when At that time, it was determined to be a medium-risk situation; when At that time, it was determined to be a high-risk situation.

[0015] The present invention achieves the following technical effects compared to the prior art: This invention discloses a zoned hydraulic fracturing and injection method for CO2 geological storage. First, during the constant-rate injection test phase, five types of data are collected in real time: bottomhole pressure, fracture response, injection index fluctuation, pressure response of the monitoring protection zone, and annular pressure response. Only when all five types of data simultaneously meet their respective pre-set numerical indicators is the formal injection phase permitted. This eliminates reliance on experience for injection permission, instead relying on clearly defined numerical standards. Second, after formal injection begins, cross-layer risk is assessed based on the real-time deviation of the five monitoring indicators. Corresponding measures are then implemented at different levels. This integrates previously independent multi-source monitoring information into a directly referenced comprehensive numerical value, providing a basis for risk identification and intervention. Furthermore, when risk assessment triggers a shutdown of injection, the system is not permanently shut down but rather pressure is released in a coordinated manner, and process control is reinstated. This ensures that the entire storage process can resume orderly operation even after a risk warning. This changes the existing reliance on manual experience for hydraulic fracturing and injection processes in CO2 geological storage, allowing for quantitative control based on real-time monitoring data. After the area is divided, controlled hydraulic fracturing is carried out on the target storage layer, and multi-source monitoring and coordinated pressure relief operations are combined to achieve full-process constraints on bottom hole pressure, fracture height and abnormal channel formation. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments 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.

[0017] Figure 1 This is an overall flowchart disclosed in an embodiment of the present invention; Figure 2 This is a schematic diagram of region division according to an embodiment of the present invention; Figure 3 This is a logic diagram of a fracturing-injection method disclosed in an embodiment of the present invention; Figure 4 This is a risk assessment logic diagram disclosed in an embodiment of the present invention; Among them, 1-target sealing layer, 2-adjacent layer, 3-caprock base, 4-target modification zone, 5-pressure buffer zone, 6-monitoring protection zone, 7-segmented isolation assembly, 8-fracturing tubing string, 9-wellbore. Detailed Implementation

[0018] 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.

[0019] The purpose of this invention is to provide a zoned hydraulic fracturing and injection method for CO2 geological storage, in order to solve the problems existing in the prior art. After the zone is divided, controlled hydraulic fracturing is carried out on the target storage layer, and combined with multi-source monitoring and coordinated pressure relief operation, the whole process of bottom hole pressure, fracture height and abnormal channel formation is constrained.

[0020] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] like Figures 1 to 4 As shown, this invention provides a method for zoned hydraulic fracturing and injection of CO2 in geological storage, comprising the following steps: S1. Obtain the geomechanical parameters of the target sealing layer 1, adjacent layer 2 and caprock, determine the caprock tension failure control pressure, caprock or weak surface shear instability control pressure, and wellbore integrity control pressure, and calculate the bottom hole pressure upper limit for the entire fracturing process and the entire injection process according to formula (1) and formula (2): (1) (2) in, This represents the upper limit of the bottom hole pressure throughout the entire fracturing process; To control the pressure for tension failure of the cap layer; The pressure is used to control shear instability in the cap layer or weak surface. Pressure is controlled to ensure the integrity of wellbore 9; For safety redundancy; This refers to the upper limit of the bottom hole pressure throughout the entire injection process; The pressure required to reopen the crack in the target containment layer 1; Safety redundancy is set to prevent cracks from reopening during the injection process; It should be noted that, , , , , , , and The units are all MPa.

[0022] And in some examples, Take a pressure of 2.0-5.0 MPa; Take 0.5-2.0 MPa.

[0023] S2. The working area of ​​the wellbore 9 is divided into a target modification zone 4, a pressure buffer zone 5, and a monitoring and protection zone 6, which are distributed from bottom to top. The target modification zone 4 is used for perforation, fracturing, and injection. The pressure buffer zone 5 is used to provide pressure transition space and does not allow fracture penetration. The monitoring and protection zone 6 is used to detect abnormal pressure or abnormal response in the overlying direction of the target sealing layer 1. In some examples, the height of the target modification zone 4 is 20-80m; the height of the pressure buffer zone 5 is 10-50m; and the monitoring and protection zone 6 is located in the adjacent layer 2, 5-30m below the caprock base 3.

[0024] In one embodiment, multiple fracturing tubing strings 8 are installed inside the wellbore 9, and a segmented isolation assembly 7 is provided between two adjacent fracturing tubing strings 8. The segmented isolation assembly 7 divides the working area of ​​the wellbore 9 into a target modification area 4, a pressure buffer zone 5, and a monitoring and protection zone 6.

[0025] S3. Perform test fracturing on target modification zone 4. Obtain the engineering identification value of fracturing initiation pressure of target modification zone 4 from the linear fitting curve of pressure-rate. The engineering identification value is used for the initial screening of the current section and the current fracturing design parameters, and after correction, the fracturing initiation pressure value of target modification zone 4 is obtained. In one embodiment, after the well is shut in until the bottomhole pressure reaches the reservoir static pressure, the injection rate is increased in steps to conduct fracturing tests on the target stimulation zone 4. For example, the target stimulation zone 4 is subjected to fracturing tests in steps of 10%, 30%, 50%, 75%, and 100% of the designed maximum injection rate.

[0026] In one embodiment, when the pressure deviates significantly from the baseline by 5-10% for the first time in the linear fitting curve of pressure-rate, the pressure value is used as the engineering identification value of the crack initiation pressure in the target modification zone 4.

[0027] In one embodiment, the initiation pressure value of the target modified zone 4 is obtained by correcting the results of the diagnostic fracturing injection test (DFIT) or mini-frac test.

[0028] S4. When the engineering identification value satisfies formula (3), hydraulic fracturing is carried out on the target modification area 4. The construction pressure does not exceed the upper limit of the bottom hole pressure of the entire fracturing process. The fracture height is constrained by stopping the pump / reducing the pressure in combination with the response of the monitoring protection area 6. Formula (3) is as follows: (3) In the formula, For engineering identification values, This represents the upper limit of the bottom hole pressure throughout the entire fracturing process; The goal is to construct near-wellbore diversion channels rather than to maximize the volume of the fracturing process, so as to constrain the single-stage discharge rate and the maximum fracturing duration to avoid excessive expansion of the fractures toward the caprock.

[0029] In one embodiment, hydraulic fracturing is performed on the target modification area 4 under four constraints: pressure restriction, flow restriction, time restriction, and height restriction.

[0030] In one embodiment, when the engineering identification value does not meet the formula (3), at least the design displacement, single section length, perforation method, and target section are adjusted.

[0031] S5. After fracturing, constant rate injection and shut-in pressure drop tests are performed; the injection index, response characteristics of monitoring protection zone 6 and response characteristics of wellbore annulus 9 are determined according to formulas (4), (5) and (6), and it is determined whether there are any abnormalities in the pressure of monitoring protection zone 6 and wellbore annulus 9, and the post-fracturing state detection is completed; formulas (4), (5) and (6) are as follows: (4) (5) (6) in, For the injection index; This refers to the injection rate during the trial injection phase. This represents the near-steady-state bottom hole pressure at the end of the test injection phase. This refers to the reservoir static pressure or the formation pressure derived from the pressure drop. To monitor the normalized response coefficient of protected area 6; To monitor the pressure increment relative to the baseline in protected area 6; The normalized response coefficient of the annulus in wellbore 9; This represents the pressure increment in the annulus of wellbore 9 relative to the baseline. Understandable, Used to characterize the near-wellbore injection capacity of the target sealing layer 1 after fracturing; The unit is m 3 / d; The unit is MPa; The unit is MPa; Used to characterize the relative response intensity of 6 pairs of target modification zones 4 pressure drives in the monitoring protected area; The unit is MPa; The response intensity is used to characterize the abnormal pressure in the annulus of wellbore 9; MPa.

[0032] In one embodiment, after fracturing is completed, a constant injection rate of 50%-70% of the designed formal injection rate is performed for 24-72 hours, followed by a shut-in pressure drop test for no less than 24 hours.

[0033] S6. When at least the following conditions are met simultaneously: the bottom hole pressure during the constant rate injection period does not exceed the upper limit of the bottom hole pressure during the entire injection process; no obvious signs of fracture reopening appear during the constant rate injection period; the coefficient of variation of the injection index is not greater than 15%; the normalized response coefficient of the monitoring protection zone 6 is not greater than 0.20; and the normalized response coefficient of the wellbore annulus is not greater than 0.10, formal carbon dioxide injection shall be carried out. S7. Based on the degree to which the bottomhole pressure approaches the upper limit of operation, the degree to which the fracture height approaches the upper limit of allowable operation, the degree of pressure anomaly in monitoring protection zone 6, the degree of annular pressure anomaly, and the degree of anomaly in auxiliary monitoring, continuous cross-layer risk assessment is conducted. It can be understood that the comprehensive decision made based on these five indicators is used to continuously assess cross-layer risk. When the condition is determined to be normal, the established parameters are maintained unchanged. When the condition is determined to be slightly risky, the injection rate is reduced or pulse injection is switched. When the condition is determined to be moderately risky, the injection rate is reduced and the injection is cut off, and slight pressure relief is applied. When the condition is determined to be highly risky, the current injection section is stopped and at least one of the following coordinated pressure relief measures is implemented: opening a return well / adjacent pumping well, reducing the continuous injection rate and switching to intermittent injection, or sealing the abnormal section and switching to another section. After completing the coordinated pressure relief and adjustment, the steps after S5 are repeated.

[0034] In one embodiment, the degree to which the bottom hole pressure approaches the upper limit of operation, the degree to which the fracture height approaches the upper limit of allowable operation, the degree of pressure anomaly in the monitoring protection zone 6, the degree of annular pressure anomaly, and the degree of auxiliary monitoring anomaly are first subjected to dimensionless normalization processing, and the results of this processing are comprehensively calculated according to formula (7) to obtain a quantitative value of the risk index: (7) In the formula, Risk index; The weighting coefficients are as follows: the degree to which the bottom hole pressure approaches the upper limit of operation; the degree to which the fracture height approaches the upper limit of allowable operation; the degree of pressure anomaly in the monitoring protection zone 6; the degree of anomaly in the annulus pressure; and the degree of anomaly in auxiliary monitoring. , , , , ; The results are dimensionless normalized values ​​for the degree to which the bottom hole pressure approaches the upper limit of operation, the degree to which the fracture height approaches the upper limit of allowable operation, the degree of pressure anomaly in monitoring protection zone 6, the degree of annular pressure anomaly, and the degree of anomaly in auxiliary monitoring. when When this occurs, it is considered a normal state; when At that time, it was determined to be a state of mild risk; when At that time, it was determined to be a medium-risk situation; when At that time, it was determined to be a high-risk situation.

[0035] This invention discloses a zoned hydraulic fracturing and injection method for CO2 geological storage. First, during the constant-rate injection test phase, five types of data are collected in real time: bottomhole pressure, fracture response, injection index fluctuation, pressure response in the monitoring protection zone, and annular pressure response. Only when all five types of data simultaneously meet their respective pre-set numerical indicators is the formal injection phase permitted. This ensures that injection is no longer based on empirical judgment but on a judgment with clear numerical standards. Second, after formal injection begins, cross-layer risk is assessed based on the real-time deviation of the five monitoring indicators. Corresponding measures are then implemented at different levels. This integrates the previously independent multi-source monitoring information into a directly referenced comprehensive value, providing a basis for risk identification and intervention. Furthermore, when risk assessment triggers a stop injection, the system is not permanently shut down but rather pressure is released in a coordinated manner, and process control is reinstated. This ensures that the entire storage process can resume operation in an orderly manner even after a risk warning. This changes the existing technology that relies on human experience for hydraulic fracturing and injection processes in carbon dioxide geological storage, allowing for quantitative control based on real-time monitoring data. After regional division, controlled hydraulic fracturing is implemented on the target storage layer 1, and combined with multi-source monitoring and coordinated pressure relief operations, the entire process of bottom hole pressure, fracture height, and abnormal channel formation is constrained.

[0036] Furthermore, the present invention also provides a specific example, as follows: Taking a deep reservoir as an example, the target reservoir is buried at a depth of 1730m. Based on the geomechanical evaluation and wellbore integrity check, it is known that the caprock tension failure control pressure is... MPa, control pressure for shear instability in the caprock or weak surface MPa, wellbore integrity control pressure MPa, reservoir static pressure MPa, the pressure required for the reopening of the crack in the target containment layer 1. MPa.

[0037] Take safety redundancy MPa, safety redundancy set during injection to prevent crack reopening. MPa, calculated as follows: MPa MPa.

[0038] A three-stage packer was deployed in the target well, comprising three sections: a target modification zone 4 at a height of 40m, a pressure buffer zone 5 at a height of 20m, and a monitoring and protection zone 6 at a height of 15m, located 10m below the caprock basement 3. The maximum designed injection rate for the fracturing test stage was 3.0m / s². 3 / min, according to 0.3, 0.9, 1.5, 2.25 and 3.0m 3 Injection was performed in stages at a rate of / min; the injection rate was monitored to be 2.25m during this period. 3 At a rate of / min, a significant nonlinear deviation of more than 5% from the baseline was observed for the first time. Further analysis of the DFIT results yielded the engineering identification values ​​for the four initiation pressures in the target modified zone. MPa.

[0039] Calculations show that The target area 4 met the fracturing criteria, meaning controlled hydraulic fracturing was carried out. After fracturing, a constant-rate injection test was conducted for 48 hours at 60% of the designed injection rate. m 3 / d; Near-steady-state bottom hole pressure at the end of the test injection phase MPa, followed by a 24-hour shut-in pressure drop test; the injection index was calculated. m 3 / (d·MPa).

[0040] Actual measurement: Monitoring the pressure increment in the protected area 6 MPa, annular pressure increment in wellbore 9 MPa; the normalized response coefficient of the monitored protected area 6 was calculated. Normalized response coefficient of wellbore 9 annulus It meets the eligibility criteria for formal carbon dioxide injection.

[0041] At a certain point during the formal injection phase, the normalized result of the bottom hole pressure approaching the upper limit of operation was observed. Normalized results for crack height approaching the upper limit of allowable values Normalized results of the pressure anomaly degree in the monitoring protected area 6 Normalized results of the degree of anomalous ring space Normalized results for assisting in monitoring the degree of abnormality Take the weighting coefficients of each indicator. , , , , .

[0042] Calculate the risk index The risk index can be determined. The situation was determined to be of mild risk, and emission reduction operations were implemented.

[0043] Any adaptive changes made according to actual needs are within the scope of protection of this invention.

[0044] It should be noted that, for those skilled in the art, it is obvious that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0045] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for zoned hydraulic fracturing and injection for CO2 geological storage, characterized in that, Includes the following steps: S1. Obtain the geomechanical parameters of the target sealing layer, adjacent layers, and caprock, determine the caprock tension failure control pressure, caprock or weak surface shear instability control pressure, and wellbore integrity control pressure, and calculate the bottom hole pressure upper limit for the entire fracturing process and the entire injection process according to formulas (1) and (2): （1） （2） in, This represents the upper limit of the bottom hole pressure during the entire fracturing process, expressed in MPa. The tensile failure control pressure of the caprock is expressed in MPa. The control pressure for shear instability of the cap layer or weak surface, expressed in MPa; The wellbore integrity control pressure, in MPa; This is a safety redundancy measure, expressed in MPa. The maximum bottom hole pressure for the entire injection process, expressed in MPa. The pressure required to reopen cracks in the target containment layer, expressed in MPa. The safety redundancy set to prevent cracks from reopening during the injection process, in MPa; S2. The wellbore operating area is divided into a target modification zone, a pressure buffer zone, and a monitoring and protection zone, distributed from bottom to top. The target modification zone is used for perforation, fracturing, and injection. The pressure buffer zone is used to provide pressure transition space and does not allow fracture penetration. The monitoring and protection zone is used to detect abnormal pressure or abnormal response in the overlying direction of the target sealing layer. S3. Conduct test fracturing on the target modified area. Obtain the engineering identification value of the fracturing initiation pressure of the target modified area from the linear fitting curve of pressure-rate. The engineering identification value is used for the initial screening of the current section and the current fracturing design parameters, and after correction, the fracturing initiation pressure value of the target modified area is obtained. S4. When the engineering identification value satisfies formula (3), hydraulic fracturing is carried out on the target modification area. The construction pressure shall not exceed the upper limit of the bottom hole pressure of the entire fracturing process. The fracture height shall be constrained by stopping the pump / reducing the pressure in combination with the response of the monitoring protection area. Formula (3) is as follows: （3） In the formula, These are engineering identification values, in MPa. This represents the upper limit of the bottom hole pressure during the entire fracturing process, expressed in MPa. S5. After fracturing, constant rate injection and shut-in pressure drop tests are performed; the injection index, response characteristics of the monitoring protection zone and the response characteristics of the wellbore annulus are determined according to formulas (4), (5) and (6), and it is determined whether there are any abnormalities in the pressure of the monitoring protection zone and the wellbore annulus, and the post-fracturing state detection is completed; formulas (4), (5) and (6) are as follows: （4） （5） （6） in, The injection index is in m. 3 / (d·MPa); This refers to the injection rate during the trial injection phase, expressed in meters per second (m). 3 / d; This represents the near-steady-state bottom hole pressure at the end of the test injection phase, expressed in MPa. This refers to the reservoir static pressure or the formation pressure derived from the pressure drop, expressed in MPa. To monitor the normalized response coefficient of the protected area; The pressure increment relative to the baseline in the protected area is measured in MPa. The normalized response coefficient of the wellbore annulus; This represents the pressure increment in the wellbore annulus relative to the baseline, in MPa. S6. When at least the following conditions are met simultaneously: the bottom hole pressure during the constant rate injection period does not exceed the upper limit of the bottom hole pressure of the entire injection process, no obvious signs of fracture reopening appear during the constant rate injection period, the coefficient of variation of the injection index is not greater than 15%, the normalized response coefficient of the monitoring protection zone is not greater than 0.20, and the normalized response coefficient of the wellbore annulus is not greater than 0.10, formal carbon dioxide injection shall be carried out. S7. Based on the degree to which the bottomhole pressure approaches the upper limit of operation, the degree to which the fracture height approaches the upper limit of allowable pressure, the degree of pressure anomaly in the monitoring protection zone, the degree of annular pressure anomaly, and the degree of anomaly in auxiliary monitoring, continuously perform cross-layer risk assessment; when determined to be in a normal state, maintain the established parameters unchanged; when determined to be in a slightly risky state, reduce the injection rate or switch to pulse injection; when determined to be in a moderately risky state, reduce the injection rate and cut the segment, and slightly relieve pressure; when determined to be in a highly risky state, stop the current segment injection and perform at least one of the following coordinated pressure relief measures: open the return well / adjacent pumping well, reduce the continuous injection rate and switch to intermittent injection, or block the abnormal segment and switch to another segment; after completing the coordinated pressure relief and adjustment, repeat the steps after S5; In step S7, the degree to which the bottom hole pressure approaches the upper limit of operation, the degree to which the fracture height approaches the upper limit of allowable operation, the degree of pressure anomaly in the monitoring protection zone, the degree of annular pressure anomaly, and the degree of auxiliary monitoring anomaly are first subjected to dimensionless normalization processing, and the results of this processing are comprehensively calculated according to formula (7) to obtain the quantitative value of the risk index: （7） In the formula, Risk index; These are the weighting coefficients for the degree to which bottomhole pressure approaches the operating upper limit, the degree to which fracture height approaches the allowable upper limit, the degree of pressure anomaly in the monitoring protection zone, the degree of annular pressure anomaly, and the degree of anomaly in auxiliary monitoring. , , , , ; These are the dimensionless normalized results of the degree to which the bottom hole pressure approaches the upper limit of operation, the degree to which the fracture height approaches the upper limit of allowable operation, the degree of pressure anomaly in the monitoring protection zone, the degree of anomaly in the annulus pressure, and the degree of anomaly in auxiliary monitoring. when When this occurs, it is considered a normal state; when At that time, it was determined to be a state of mild risk; when At that time, it was determined to be a medium-risk situation; when At that time, it was determined to be a high-risk situation.

2. The method for zoned hydraulic fracturing and injection of CO2 for geological sequestration according to claim 1, characterized in that, In step S2, multiple fracturing tubing strings are inserted into the wellbore, and segmented isolation components are set between adjacent fracturing tubing strings. The wellbore operation area is divided into a target modification area, a pressure buffer zone, and a monitoring and protection zone by the segmented isolation components.

3. The method for zoned hydraulic fracturing and injection of CO2 for geological sequestration according to claim 1, characterized in that, In step S3, after the well is shut in until the bottom pressure reaches the reservoir static pressure, the injection rate increases in a stepwise manner to conduct fracturing tests on the target modified area.

4. The method for zoned hydraulic fracturing and injection of CO2 for geological sequestration according to claim 3, characterized in that, In step S3, the target modification zone is subjected to trial cracking at a stepwise increase of 10%, 30%, 50%, 75%, and 100% of the designed maximum injection rate.

5. The method for zoned hydraulic fracturing and injection of CO2 for geological sequestration according to claim 1, characterized in that, In step S3, when the pressure in the linear fitting curve of pressure-rate shows a significant nonlinear deviation of 5-10% from the baseline for the first time, the pressure value is used as the engineering identification value of the crack initiation pressure of the target modification zone.

6. The method for zoned hydraulic fracturing and injection of CO2 for geological sequestration according to claim 1, characterized in that, In step S3, the initiation pressure value of the target modified zone is obtained by combining the interpretation results of diagnostic fracturing injection test or small fracturing test.

7. The method for zoned hydraulic fracturing and injection of CO2 for geological sequestration according to claim 1, characterized in that, In step S4, hydraulic fracturing is performed on the target modification area under four constraints: pressure restriction, flow restriction, time restriction, and height restriction.

8. The method for zoned hydraulic fracturing and injection of CO2 for geological sequestration according to claim 1, characterized in that, In step S4, when the engineering identification value does not meet the formula (3), at least the design displacement, single section length, perforation method, and target section shall be adjusted.

9. The method for zoned hydraulic fracturing and injection of CO2 for geological storage according to claim 1, characterized in that, In step S5, after fracturing is completed, a constant injection rate of 50%-70% of the designed formal injection rate is carried out for 24-72 hours, and a shut-in pressure drop test is carried out for no less than 24 hours.

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