CO2 burying safety evaluation method

Abstract

The invention discloses a CO2 burying safety evaluation method which comprises the following steps: S1, carrying out oil area overall safety evaluation, and screening burying blocks; s2, fault plugging performance, cover layer integrity and wellbore stability evaluation is carried out on the target block; the CO2 storage safety evaluation method is suitable for the technical field of CO2 storage, and a CO2 storage safety evaluation system is established. Integrally evaluating geological conditions of the oil area according to factors such as cap thickness, fault density and cap-breaking combination relation, and screening burying blocks; and geological static evaluation and stress dynamic evaluation are adopted to evaluate the fault plugging performance, the cover layer integrity and the shaft stability of the target block, and the CO2 burying limit is determined.

Description

Technical Field

[0001] The present invention belongs to the technical field of CO 2 sequestration technology, and specifically relates to a method for evaluating the safety of CO 2 sequestration. Background Art

[0002] With the development of the global economy, the consumption of fossil energy by people has increased significantly, resulting in a large amount of greenhouse gases mainly composed of carbon dioxide being emitted into the atmosphere. At present, the phenomenon of global warming is already very significant. To address this challenge, effective methods are needed to reduce the content of carbon dioxide in the atmosphere. Currently, the main emission reduction approaches include avoiding and reducing the use of fossil energy and developing and utilizing cleaner energy. However, the implementation of these approaches faces many limitations. For this reason, domestic and foreign scholars have proposed carbon capture and storage technology (Carbon Capture and Storage, abbreviated as CCS).

[0003] Carbon capture and storage technology is a practical technology achieved with the development of science and technology and extensive in-depth research at home and abroad in recent years, and has very broad prospects. At the 21st United Nations Climate Change Conference, carbon capture and storage technology was strongly advocated for application in mitigating the greenhouse effect; the assessment report of the Intergovernmental Panel on Climate Change also shows that the application of carbon capture and storage technology can significantly reduce the cost of carbon emission reduction; according to the statistics of the Global CCS Institute, as of 2016, carbon capture and storage technology has been widely developed worldwide.

[0004] Carbon capture and storage technology is one of the best solutions to alleviate the problem of global greenhouse gas emissions. However, due to the operational risks of carbon dioxide sequestration technology, there are potential safety hazards in some aspects. If not handled properly, it will lead to sequestration failure, and sequestration failure will cause carbon dioxide to leak and escape into the upper strata or the atmosphere, thereby damaging the groundwater system and the ecological system, etc. In carbon dioxide sequestration technology, the sealing ability of the carbon dioxide sequestration system is the key to the geological sequestration conditions of carbon dioxide. Currently, the evaluation methods for the sequestration capacity of mines include evaluation based on geological parameters and evaluation using numerical simulation methods, etc. However, CO 2 sequestration is a dynamic process. It is difficult to evaluate the situation after gas injection based solely on some geological parameters. Similarly, limited by computing power, it is also difficult to carry out safety evaluations at the oil field level using numerical simulation methods.

[0005] At present, there is still a lack of a systematic safety CO 2 sealing evaluation method. Therefore, it is necessary to establish a safety evaluation system to qualitatively and quantitatively analyze the impact of carbon dioxide on the integrity of the sequestration system through methods such as laboratory experiments and numerical simulations, and explore the potential leakage risks of carbon dioxide. Summary of the invention

[0006] The purpose of the present invention is to overcome the defects of the prior art and provide a CO 2 Storage safety assessment method.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A CO 2 The method for evaluating storage safety comprises the following steps:

[0009] S1 conducts overall safety assessment of the oil field and screens storage blocks;

[0010] S2 conducts fault sealing, caprock integrity, and wellbore stability evaluation for target blocks;

[0011] S3 forms CO 2 Bury safety limits.

[0012] Preferably, in step S1, the overall safety assessment of the oil field includes cap rock safety assessment, fault safety assessment and cap rock-fault combined safety assessment.

[0013] Preferably, in step S1, the cap rock safety assessment specifically includes: assessing the cap rock safety by analyzing the lithology and thickness of the cap rock.

[0014] Preferably, in step S1, the fault safety evaluation specifically includes:

[0015] According to the fault density that breaks through the top of the cover, the faults are divided into three types: Type I: no faults, safe area; Type II: low fault density, relatively safe area; Type III: high fault density, unsafe area.

[0016] Preferably, in step S1, the safety assessment of the cap rock fault combination specifically includes:

[0017] According to the different relationship between the two cover layers caused by the fault, the fault is divided into cover-disappearance fault, cover-joining fault and cover-separation fault.

[0018] Among them, the cover-disappearing fault is the fault disappearing into the cover layer;

[0019] The cap-joint fault is a fault that breaks through the cap rock, but the fault throw is less than the thickness of the cap rock, and there is a transverse butt joint section of the cap rock on both sides of the fault;

[0020] A cap-break fault is a fault that breaks through the cap rock, with a fault throw greater than the thickness of the cap rock, and there is no lateral butt joint section of the cap rock between the two sides of the fault.

[0021] Preferably, the step S1 further includes:

[0022] Based on the caprock safety evaluation, fault safety evaluation, and combined caprock-fault safety evaluation, preliminarily evaluate the storage conditions of the entire oilfield. When screening storage blocks, avoid reservoirs with relatively poor overall safety for the CO2 storage project;

[0023] Among them, when the caprock thickness is greater than 50 meters and there are no faults, the overall safety is good;

[0024] The caprock thickness is 30 to 50 meters; there are caprock-consuming and caprock-connecting faults developed, and the fault density is relatively low, the overall safety is average;

[0025] The caprock thickness is 0 to 30 meters; there are caprock-connecting and caprock-separating faults developed, and the fault density is relatively high, the overall safety is relatively poor.

[0026] Preferably, in step S2, it specifically includes:

[0027] Based on the overall evaluation of the oilfield, conduct fault sealing, caprock integrity, and wellbore stability evaluations on the initially screened target blocks.

[0028] Preferably, in step S2, the evaluation adopts a combination of geological static evaluation and stress dynamic evaluation. Among them, the geological static evaluation evaluates the storage feasibility from a geological perspective by calculating the sand-sand docking rate and shale smear factor; the stress dynamic evaluation uses four-dimensional in-situ stress simulation to evaluate the safety during storage from the perspective of mechanical evolution.

[0029] Preferably, in step S2, the geological static evaluation includes fault lateral sealing evaluation, fault vertical sealing evaluation, and caprock sealing evaluation.

[0030] Preferably, in step S2, the fault lateral sealing is evaluated by the sand-sand docking rate, shale smear factor, and fault gouge ratio;

[0031] Analyze the lithologic configuration relationship of the two fault blocks through the sand-sand docking rate. The higher the sand-sand docking rate, the weaker the lateral sealing. When the SSR of the hanging wall is less than 50%, the configuration relationship is good. When the SSR of the footwall is less than that of the hanging wall, the configuration relationship is better;

[0032] Calculate the smear factor to analyze the shale smear property. The larger the smear factor, the poorer the smear property. When the smear factor is greater than 7, it is discontinuous smearing. When the smear factor is less than 7, it is continuous smearing;

[0033] Calculate the fault gouge ratio to analyze the shale smear property. The larger the fault gouge ratio, the better the smear property. When the fault gouge ratio is greater than 30%, the composite smearing effect is strong. When the fault gouge ratio is 30%, the composite smearing effect is weak;

[0034] Based on the above evaluation criteria, establish a parallel fault lateral safety qualitative evaluation system.

[0035] Preferably, in the step S2, the calculation method of the smear factor SSF is:

[0036]

[0037] Preferably, in the step S2, the calculation method of the gouge ratio SGR is

[0038]

[0039] Preferably, in the step S2, the longitudinal sealing property of the fault is analyzed through the longitudinal extension of the fault and the degree of fracture opening:

[0040] First, evaluate the relationship between the fault extension and the caprock configuration. If the longitudinal extension of the fault is long and the fault throw is large, the damage to the caprock is strong and the longitudinal sealing property is poor;

[0041] By calculating the fault tightness coefficient I FT evaluate the degree of fracture opening of the fault:

[0042]

[0043] Among them, the tightness coefficient is controlled by the in-situ stress state. The higher it is, the more closed the fracture is; I FT is greater than 1, the fracture is tight and the longitudinal sealing property is good; I FT is less than 1, the fracture is loose and the longitudinal sealing property is poor;

[0044] Based on the above evaluation criteria, a progressive evaluation system for the longitudinal sealing property of the fault is established.

[0045] Preferably, in the step S2, considering the key influencing factors of the caprock sealing ability, a static comprehensive evaluation method for the caprock sealing ability is constructed with the caprock lithology, spatial distribution, sealing ability and rock mechanics as the core.

[0046] Preferably, in the step S2, the static comprehensive evaluation of the caprock sealing ability includes four parts: caprock rock lithology, caprock spatial distribution, caprock breakthrough pressure and rock brittle-plasticity. A static comprehensive evaluation model of the caprock sealing ability is established. The evaluation model uses the analytic hierarchy process, and through the multi-factor comprehensive evaluation method, a comprehensive evaluation calculation model of the caprock sealing ability is constructed:

[0047]

[0048] In the formula: Y is the total score of the evaluation; Ci is the score of a single index, and wi is the weight of a single index.

[0049] Preferably, in the step S2, the dynamic stress evaluation includes establishing a full-stratum geomechanical model of the caprock-reservoir-fault-wellbore, simulating the distribution of the initial in-situ stress field, and then carrying out the CO 2 sequestration four-dimensional dynamic simulation of the in-situ stress field to evaluate the CO2 Storage safety.

[0050] Preferably, in the step S2, the establishment of the full-stratum geomechanical model of the caprock-reservoir-fault-wellbore includes:

[0051] Simulating the distribution of the initial in-situ stress field includes using the block structure and seismic interpretation data to establish a three-dimensional geological model of multiple formations in the target block. Based on the single-well logging data in the work area, using the single-well rock mechanics parameter logging interpretation model, analyzing the changes in basic rock mechanics parameters such as the elastic modulus and Poisson's ratio of single wells in the block;

[0052] Then analyze and process the logging basic data of all wells in the block, obtain the changes in rock mechanics parameters such as the elastic modulus and Poisson's ratio of the wells in the block, provide basic data for the in-situ stress field analysis, adopt the co-Kriging interpolation method, and combine the lithofacies characteristics of the block to obtain the distribution laws of rock mechanics parameters such as Poisson's ratio and elastic modulus in the block, and obtain the initial stress distribution in the block;

[0053] Obtain the mechanical boundaries of the near-well model from the three-dimensional geomechanical simulation, and establish the geomechanical model of the fault-caprock-reservoir-wellbore to lay the foundation for the in-situ stress field simulation.

[0054] Preferably, in the step S2, the development of the four-dimensional in-situ stress field dynamic simulation of CO 2 storage includes:

[0055] Track the positions of the CO 2 plume front, the pressure change front, and the stress front, consider the coupling response of in-situ stress-fluid pressure, and simulate the dynamic changes of the formation pressure and in-situ stress field during the CO 2 injection process, analyze the changes in the sealing properties of the caprock and faults, including the influence of the stress field changes on the sealing properties of the caprock and faults, judge the positions where the caprock fractures are likely to reopen and the faults are likely to slip within the stress change influence range, and identify the high-risk areas;

[0056] Track the migration of the CO 2 plume, simulate whether the CO 2 plume will reach the high-risk areas, and through means such as injection-production parameter adjustment, well pattern adjustment, and stress modification, avoid the CO 2 plume from reaching the damaged caprock and fault areas, and reduce the impact of gas injection on the high-risk areas.

[0057] Preferably, in the step S3, the formation of the CO 2 storage safety limit specifically includes:

[0058] Calculate the change of the stress Mohr circle in the high-risk area during the gas injection process, judge the fault slip, caprock failure and wellbore damage according to the Mohr-Coulomb criterion, and determine the critical value of CO 2 leakage based on the stress and strain conditions of the caprock and faults, form a safety limit, and design the injection-production plan with this limit as a constraint.

[0059] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows:

[0060] In the present invention, a safety evaluation system for CO 2 sequestration is established. According to factors such as caprock thickness, fault density and fault-caprock combination relationship, the geological conditions of the oil area are evaluated as a whole to screen the storage blocks; the fault sealing, caprock integrity and wellbore stability of the target blocks are evaluated by geological static evaluation and stress dynamic evaluation, and the CO 2 storage limit is clarified. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 is a flow chart of the present invention;

[0062] Figure 2 is a schematic diagram for explaining the mechanical parameters of a single well in an embodiment of the present invention;

[0063] Figure 3 is a distribution diagram of mechanical parameters of a block in an embodiment of the present invention;

[0064] Figure 4 is a four-dimensional geomechanical simulation diagram in an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0065] The following further describes the specific implementation manners of a CO2 storage safety evaluation method of the present invention in conjunction with the attached Figures 1-4 , and the specific implementation manners of a CO2 storage safety evaluation method of the present invention are not limited to the descriptions of the following embodiments.

[0066] Embodiment 1:

[0067] A CO2 storage safety evaluation method, as Figure 1 shown, includes the following steps:

[0068] S1 Conduct an overall safety evaluation of the oil area to screen the storage blocks;

[0069] S2 Conduct evaluations on the fault sealing, caprock integrity and wellbore stability of the target blocks;

[0070] S3 Form a safety limit for CO 2 sequestration.

[0071] Further, in step S2, it specifically includes:

[0072] On the basis of the overall evaluation of the oil area, carry out the evaluation of fault sealing, caprock integrity and wellbore stability for the initially screened target blocks.

[0073] Further, in step S3, the formation of CO 2 The safety boundaries for storage specifically include:

[0074] Calculate the change of the stress Mohr circle in the high-risk area during the gas injection process, judge the fault slip, caprock failure and wellbore damage according to the Mohr-Coulomb criterion, and determine the CO 2 The critical value of leakage, form a safety boundary, and design the injection-production plan with this boundary as a constraint.

[0075] Example 2:

[0076] A method for evaluating the safety of CO2 storage, other steps are similar to those in Example 1. Further, in step S1, the overall safety evaluation of the oil area includes caprock safety evaluation, fault safety evaluation and caprock-fault combination safety evaluation.

[0077] Further, in step S1, the caprock safety evaluation specifically includes: evaluating the caprock safety by analyzing the lithology and thickness of the caprock.

[0078] Further, in step S1, the fault safety evaluation specifically includes:

[0079] Divide the faults into 3 types of areas according to the fault density of the faults cutting through the top of the caprock: Type I: no faults, safe area; Type II: low fault density, relatively safe area; Type III: high fault density, non-safe area.

[0080] Further, in step S1, the caprock-fault combination safety evaluation specifically includes:

[0081] Divide the faults into caprock-eliminating faults, caprock-connecting faults and caprock-separating faults according to the different combined relationships of the caprock on both sides of the faults;

[0082] Among them, the caprock-eliminating fault is the fault that disappears in the caprock;

[0083] The caprock-connecting fault is the fault that cuts through the caprock, but the fault throw is less than the thickness of the caprock, and there is a lateral docking section of the caprock on both sides of the fault;

[0084] The caprock-separating fault is the fault that cuts through the caprock, the fault throw is greater than the thickness of the caprock, and there is no definition of a lateral docking section of the caprock on both sides of the fault.

[0085] Further, in step S2, the evaluation adopts a combination of geological static evaluation and stress dynamic evaluation. Among them, the geological static evaluation evaluates the feasibility of storage from a geological perspective by calculating the sand-sand docking rate and shale smearability; the stress dynamic evaluation uses four-dimensional in-situ stress simulation to evaluate the safety during storage from the perspective of mechanical evolution.

[0086] Example 3:

[0087] A method for evaluating the safety of CO2 storage, other steps are similar to those in Example 2. Further, in step S1, it further includes:

[0088] Based on the evaluation of caprock safety, fault safety, and the safety of the caprock-fault combination, preliminarily evaluate the storage conditions of the entire oil area. When screening storage blocks, avoid reservoirs with relatively poor overall safety to carry out the CO2 storage project;

[0089] Among them, when the caprock thickness is greater than 50 meters and there are no faults, the overall safety is good;

[0090] The caprock thickness is 30 to 50 meters; there are caprock-dissolving and caprock-connecting faults, and the fault density is relatively low, and the overall safety is average;

[0091] The caprock thickness is 0 to 30 meters; there are caprock-connecting and caprock-separating faults, and the fault density is relatively high, and the overall safety is relatively poor.

[0092] Further, in step S2, the geological static evaluation includes the evaluation of fault lateral sealing, fault vertical sealing, and caprock sealing.

[0093] Further, in step S2, evaluate the fault lateral sealing through the sand-sand docking rate, shale smear factor, and fault gouge ratio;

[0094] Analyze the lithology configuration relationship of the two fault blocks through the sand-sand docking rate. The higher the sand-sand docking rate, the weaker the lateral sealing. When the SSR of the hanging wall is less than 50%, the configuration relationship is good. When the SSR of the footwall is less than the SSR of the hanging wall, the configuration relationship is better;

[0095] Calculate the smear factor to analyze the shale smearability. The larger the smear factor, the worse the smearability. When the smear factor is greater than 7, it is discontinuous smearing. When the smear factor is less than 7, it is continuous smearing;

[0096] Calculate the fault gouge ratio to analyze the shale smearability. The larger the fault gouge ratio, the better the smearability. When the fault gouge ratio is greater than 30%, the composite smearing effect is strong. When the fault gouge ratio is 30%, the composite smearing effect is weak;

[0097] Based on the above evaluation criteria, establish a parallel qualitative evaluation system for fault lateral safety (as shown in Table 1).

[0098] Table 1 Qualitative Evaluation System for the Lateral Safety of Faults in Parallel Type

[0099]

[0100] Furthermore, in step S2, the calculation method of the smear factor SSF is as follows:

[0101]

[0102] Furthermore, in step S2, the calculation method of the gouge ratio SGR is

[0103]

[0104] Furthermore, in step S2, analyze the longitudinal sealing property of the fault through the longitudinal extension of the fault and the degree of crack opening:

[0105] First, evaluate the relationship between the fault extension and the caprock configuration. If the longitudinal extension of the fault is long and the fault throw is large, the damage to the caprock is strong and the longitudinal sealing property is poor;

[0106] By calculating the fault tightness coefficient I FT evaluate the degree of crack opening of the fault:

[0107]

[0108] Among them, the tightness coefficient is controlled by the in-situ stress state. The higher it is, the more closed the crack is; I FT is greater than 1, the crack is tight and the longitudinal sealing property is good; I FT is less than 1, the crack is relaxed and the longitudinal sealing property is poor;

[0109] Based on the above evaluation criteria, a progressive evaluation system for the longitudinal sealing property of faults is established (as shown in Table 2).

[0110] Table 2 Progressive Evaluation System for the Longitudinal Sealing Property of Faults

[0111]

[0112] Furthermore, in step S2, considering the key influencing factors of the caprock sealing ability, a static comprehensive evaluation method for the caprock sealing ability is constructed with the caprock lithology, spatial distribution, sealing ability and rock mechanics as the core.

[0113] Furthermore, in step S2, the static comprehensive evaluation of the caprock sealing ability includes four parts: caprock lithology, caprock spatial distribution, caprock breakthrough pressure and rock brittle-plasticity. A static comprehensive evaluation model of the caprock sealing ability is established. The evaluation model uses the analytic hierarchy process, and through the multi-factor comprehensive evaluation method, a comprehensive evaluation calculation model of the caprock sealing ability is constructed:

[0114]

[0115] In the formula: Y is the total score of the evaluation; Ci is the score of a single index, and wi is the weight of a single index.

[0116] Example 4:

[0117] A method for evaluating the safety of CO2 storage, other steps are similar to those in Example 3. Further, in step S2, the stress dynamic evaluation includes establishing a full-stratum geomechanical model of the caprock-reservoir-fault-wellbore, simulating the distribution of the initial in-situ stress field, and then carrying out the four-dimensional dynamic simulation of the in-situ stress field during CO 2 storage to evaluate the safety of CO 2 storage.

[0118] Further, in step S2, establishing a full-stratum geomechanical model of the caprock-reservoir-fault-wellbore includes:

[0119] Simulating the distribution of the initial in-situ stress field includes using the block structure and seismic interpretation data to establish a three-dimensional geological model of multiple formations in the target block. Based on the single-well logging data in the work area, using the single-well rock mechanics parameter logging interpretation model, analyzing the changes in basic rock mechanics parameters such as the elastic modulus and Poisson's ratio of single wells in the block;

[0120] Then analyzing and processing the logging basic data of all wells in the block, obtaining the changes in rock mechanics parameters such as the elastic modulus and Poisson's ratio of the wells in the block, providing basic data for carrying out the in-situ stress field analysis, using the co-Kriging interpolation method, combining the lithofacies characteristics of the block, obtaining the distribution laws of rock mechanics parameters such as Poisson's ratio and elastic modulus in the block, and obtaining the initial stress distribution of the block;

[0121] Obtaining the mechanical boundaries of the near-well model from the three-dimensional geomechanical simulation, and establishing a geomechanical model of the fault-caprock-reservoir-wellbore to lay the foundation for the in-situ stress field simulation.

[0122] Further, in step S2, carrying out the four-dimensional dynamic simulation of the in-situ stress field during CO 2 storage includes:

[0123] Tracking the positions of the CO 2 plume front, the pressure change front, and the stress front. Generally, the stress front is greater than the pressure front, and the pressure front is greater than the CO 2 plume front. Considering the coupling response of in-situ stress-fluid pressure, simulating the dynamic changes of the formation pressure and in-situ stress field during the CO 2 injection process, analyzing the changes in the sealing properties of the caprock and faults, including the influence of the stress field changes on the sealing properties of the caprock and faults, judging the positions where the caprock fractures are likely to reopen and the faults are likely to slip within the stress change influence range, and clarifying the high-risk areas;

[0124] Tracking the CO 2Plume migration situation, simulating CO 2 Whether the plume will reach the high-risk area, and by means of adjusting injection-production parameters, well pattern adjustment, stress transformation, etc., avoid CO 2 The plume reaches the damaged caprock and fault zones that have already occurred, reducing the impact of gas injection on the high-risk area.

[0125] Example 5: Static safety evaluation of fault-caprock in a certain area

[0126] The structural step zone in this area is high in the southeast and low in the northwest, and faults are developed; the longitudinal extension of the faults varies greatly, 2 faults penetrate the Guantao Formation, 12 faults penetrate the lower part of the third member of the Shahejie Formation, and 23 faults disappear in the oil shale of the lower part of the third member of the Shahejie Formation; the caprock is thick and has good properties, and the safety of CO 2 is mainly controlled by faults.

[0127] Table 3

[0128]

[0129] Table 4

[0130]

[0131] Using the static safety evaluation technology of fault-caprock to evaluate the storage safety of this area as shown in Table 3 and Table 4, it can be seen that the lateral sealing property of the faults is relatively strong, and the sealing ability of the hanging wall of large-scale faults is strong. The longitudinal sealing property of the faults is relatively strong, and the possibility of CO 2 leaking out of the reservoir is small, and the possibility of leaking to the ground is even smaller. The lithology of the caprock is mudstone, brittle-plastic, with a thickness greater than 200 meters, a breakthrough pressure of 18.6 MPa, excellent sealing performance, and the possibility of CO 2 leakage caused by capillary breakthrough or layer rupture is small.

[0132] Example 6: Dynamic safety evaluation of a certain block

[0133] Taking a certain block as an example, first analyze the mechanical parameters of 17 wells based on the logging data of 17 wells in the work area, taking one of the wells as an example (such as Figure 2 shown);

[0134] Using the co-kriging interpolation method combined with the lithofacies characteristics of the block, obtain the distribution laws of rock mechanical parameters such as Poisson's ratio and elastic modulus of the high block as Figure 3 shown;

[0135] Injecting CO at 40 t / d 2 , the formation pressure gradually increases, forming a local high-pressure fluid area, which in turn leads to dynamic changes in the regional pressure field. The change in formation pressure causes changes in the stress field as Figure 4 shown. The local stress field of the fault changes greatly, and it is easy to form a leakage channel, affecting CO 2Sequestration effect. According to the stress and strain conditions of the caprock and faults, formulate the safety boundaries for injection and production measures.

[0136] Example 7:

[0137] A method for evaluating the safety of CO 2 sequestration, comprising the following steps:

[0138] 1. Conduct a primary overall evaluation of the entire oilfield based on the physical properties of the caprock and faults, preliminarily judge the overall safety of the oilfield, and screen out areas with high safety.

[0139] 2. Conduct a static safety evaluation of the areas screened in step 1, and evaluate the safety of the caprock and faults by calculating parameters such as the sand-sand docking rate and smear factor.

[0140] 3. Further conduct four-dimensional in-situ stress simulation, study the changes in the pressure field and stress field of the reservoir-caprock-fault combination during the sequestration process, and determine the safety boundaries of the caprock and faults according to the stress and strain of the caprock and faults.

[0141] The above content is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions or substitutions can be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for evaluating the safety of CO 2 sequestration It is characterized in that it includes the following steps: S1 Conduct an overall safety assessment of the oil area and screen the storage blocks; S2 Conduct an assessment of fault sealing, caprock integrity, and wellbore stability for the target blocks; S3 forms CO 2 Sequestration safety limit.

2. A method for evaluating the safety of CO 2 storage as described in claim 1 It is characterized in that in the step S1, the overall safety assessment of the oil area includes caprock safety assessment, fault safety assessment, and caprock-fault combination safety assessment.

3. The method for evaluating the safety of geological storage of a CO 2 as described in claim 2 It is characterized in that in the step S1, the caprock safety assessment specifically includes: evaluating the caprock safety by analyzing the lithology and thickness of the caprock.

4. A method for evaluating the safety of CO 2 burial storage as claimed in claim 2 It is characterized in that in the step S1, the fault safety assessment specifically includes: dividing faults into 3 types of areas according to the fault density of the faults breaking through the top of the caprock: Type I: no faults, safe area; Type II: low fault density, relatively safe area; Type III: high fault density, non-safe area.

5. A method for evaluating the safety of CO 2 sequestration as claimed in claim 2 It is characterized in that in the step S1, the caprock-fault combination safety assessment specifically includes: dividing faults into caprock-consuming faults, caprock-connecting faults, and caprock-separating faults according to the different combination relationships of the caprocks on both sides of the faults; wherein, the caprock-consuming fault is the fault disappearing within the caprock; the caprock-connecting fault is the fault breaking through the caprock, but the fault throw is less than the thickness of the caprock, and there is a lateral docking section of the caprock on both sides of the fault; the caprock-separating fault is defined as the fault breaking through the caprock, the fault throw is greater than the thickness of the caprock, and there is no lateral docking section of the caprock on both sides of the fault.

6. The method for evaluating the storage safety of a CO 2 as described in claim 2 It is characterized in that in the step S1, it further includes: on the basis of the caprock safety assessment, fault safety assessment, and caprock-fault combination safety assessment, preliminarily evaluate the storage conditions of the entire oil area, and when screening the storage blocks, avoid carrying out the CO2 storage project in the reservoirs with relatively poor overall safety; wherein, when the caprock thickness is greater than 50 meters and there are no faults, the overall safety is good; the caprock thickness is 30 to 50 meters; caprock-consuming and caprock-connecting faults develop, and the fault density is relatively low, the overall safety is average; the caprock thickness is 0 to 30 meters; caprock-connecting and caprock-separating faults develop, and the fault density is relatively high, the overall safety is relatively poor.

7. A method for evaluating the safety of CO 2 burial as described in claim 1 It is characterized in that in the step S2, it specifically includes: on the basis of the overall assessment of the oil area, conduct an assessment of fault sealing, caprock integrity, and wellbore stability for the initially screened target blocks.

8. A method for evaluating the safety of CO 2 storage as claimed in claim 7 It is characterized in that in the step S2, the assessment adopts a combination of geological static assessment and stress dynamic assessment. Among them, the geological static assessment evaluates the storage feasibility from a geological perspective by calculating the sand-sand docking rate and mudstone smearability; the stress dynamic assessment uses four-dimensional in-situ stress simulation to evaluate the safety during storage from the perspective of mechanical evolution.

9. A method for evaluating the safety of CO 2 burial as described in claim 8 It is characterized in that in the step S2, the geological static assessment includes fault lateral sealing assessment, fault vertical sealing assessment, and caprock sealing assessment.

10. A method for evaluating the storage safety of CO as described in claim 9 2 ​ It is characterized in that in the step S2, evaluate the fault lateral sealing by the sand-sand docking rate, mudstone smear factor, and fault gouge ratio; analyze the lithology configuration relationship on both sides of the fault by the sand-sand docking rate. The higher the sand-sand docking rate, the weaker the lateral sealing. When the SSR of the hanging wall is less than 50%, the configuration relationship is good. When the SSR of the footwall is less than the SSR of the hanging wall, the configuration relationship is better; Calculate the smear factor to analyze the smearing property of mudstone. The larger the smear factor, the poorer the smearing property. When the smear factor is greater than 7, it is discontinuous smearing; when the smear factor is less than 7, it is continuous smearing. Calculate the gouge ratio to analyze the smearing property of mudstone. The larger the gouge ratio, the better the smearing property. When the gouge ratio is greater than 30%, the composite smearing effect is strong; when the gouge ratio is 30%, the composite smearing effect is weak. Based on the above evaluation criteria, a parallel qualitative evaluation system for the lateral safety of faults is established.

11. A method for evaluating the safety of CO 2 sequestration as claimed in claim 10 It is characterized in that In step S2, the calculation method of the smear factor SSF is:

12. A method for evaluating the safety of CO 2 storage as claimed in claim 10 It is characterized in that In step S2, the calculation method of the gouge ratio SGR is 13. A method for evaluating the safety of CO 2 burial as claimed in claim 9, It is characterized in that In step S2, analyze the longitudinal sealing property of the fault through the longitudinal extension of the fault and the degree of crack opening: First, evaluate the relationship between the fault extension and the caprock configuration. If the longitudinal extension of the fault is long and the fault throw is large, the damage to the caprock is strong and the longitudinal sealing property is poor. Evaluating the degree of fault fracture opening by calculating the tomography tightness coefficient I FT Evaluating the degree of fault fracture opening: Among them, the tightness coefficient is controlled by the in-situ stress state. The higher it is, the more closed the fracture is; I FT Greater than 1, the fracture is tightly closed and has good longitudinal sealing performance; I FT Less than 1, the fracture is loose and has poor longitudinal sealing performance; Based on the above evaluation criteria, a progressive evaluation system for the longitudinal sealing property of faults is established.

14. A method for evaluating the safety of CO 2 burial as described in claim 9 It is characterized in that In step S2, considering the key influencing factors of the caprock sealing ability, a static comprehensive evaluation method for the caprock sealing ability is constructed with the caprock lithology, spatial distribution, sealing ability, and rock mechanics as the core.

15. A method for evaluating the safety of CO 2 sequestration as described in claim 14, It is characterized in that In step S2, the static comprehensive evaluation of the caprock sealing ability includes four parts: the lithology of the caprock rock, the spatial distribution of the caprock, the breakthrough pressure of the caprock, and the rock brittle-plasticity. A static comprehensive evaluation model of the caprock sealing ability is established. The evaluation model uses the analytic hierarchy process, and through the multi-factor comprehensive evaluation method, a comprehensive evaluation calculation model of the caprock sealing ability is constructed: In the formula: Y is the total score of the evaluation; Ci is the score of a single index, and wi is the weight of a single index.

16. A method for evaluating the safety of CO 2 sequestration as claimed in claim 8, It is characterized in that In the step S2, the stress dynamic evaluation includes establishing a full-stratum geomechanical model of the caprock-reservoir-fault-wellbore, simulating the distribution of the initial in-situ stress field, and then conducting a four-dimensional dynamic simulation of the in-situ stress field during CO 2 storage to evaluate the safety of CO 2 storage.

17. A method for evaluating the safety of CO 2 burial as described in claim 16 It is characterized in that In step S2, the establishment of the full-stratum geomechanical model of the caprock-reservoir-fault-wellbore includes: Simulating the distribution of the initial in-situ stress field includes using the block structure and seismic interpretation data to establish a three-dimensional geological model of multiple formations in the target block. Based on the single-well logging data in the work area, using the single-well rock mechanics parameter logging interpretation model, analyze the changes in basic rock mechanics parameters such as the elastic modulus and Poisson's ratio of single wells in the block. Then analyze and process the logging basic data of all wells in the block to obtain the changes in rock mechanics parameters such as the elastic modulus and Poisson's ratio of the wells in the block, providing basic data for the in-situ stress field analysis. Using the co-Kriging interpolation method, combined with the lithofacies characteristics of the block, obtain the distribution laws of rock mechanics parameters such as Poisson's ratio and elastic modulus in the block, and obtain the initial stress distribution in the block. Obtain the mechanical boundary of the near-well model from the three-dimensional geomechanical simulation, and establish a geomechanical model of the fault-caprock-reservoir-wellbore, laying a foundation for the in-situ stress field simulation.

18. A method for evaluating the safety of CO 2 sequestration as claimed in claim 16, It is characterized in that In the step S2, the dynamic simulation of the four-dimensional in-situ stress field for CO 2 sequestration is carried out, including: Tracking CO 2 The leading edge positions of the plume, pressure change, and stress, considering the coupled response of in-situ stress and fluid pressure, simulate the injection of CO 2 The dynamic changes of formation pressure and in-situ stress field during the process, analyze the changes in caprock and fault sealing properties, including the influence of stress field changes on caprock and fault sealing properties, determine the positions where caprock fractures are likely to reopen and faults are likely to slip within the stress change influence range, and identify high-risk areas; Tracking CO 2 plume migration situation, simulating CO 2 whether the plume will reach high-risk areas, and by means of adjusting injection-production parameters, well pattern adjustment and stress transformation, etc., to avoid CO 2 the plume reaching the already damaged caprock and fault areas, reducing the impact of gas injection on high-risk areas.

19. A method for evaluating the safety of CO 2 burial as described in claim 1 It is characterized in that In the step S3, the formation of CO 2 sequestration safety limit, specifically including: Calculate the change of the stress Mohr circle in the high-risk area during the gas injection process, judge the fault slip, caprock failure and wellbore damage according to the Mohr-Coulomb criterion, and determine the critical value of CO 2 leakage based on the stress and strain conditions of the caprock and faults, form a safety limit, and design the injection and production plan with this limit as a constraint.

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