Tensile-tensional-torsional basin bed rock fracture safety evaluation method related to CO2 sequestration

Abstract

The invention relates to the field of related theoretical research and application of CO2 storage in a tensional basin and even a tensional basin, and particularly discloses a CO2 storage related tensional-tensional basin bed rock fracture safety evaluation method. On the basis of processing bedrock three-dimensional seismic data interference waves and signal-to-noise ratios, the corresponding relation between the fault scale and the fault activity intensity in bedrock is determined, the main bedrock fracture in a research area is utilized, the corresponding relation between the bedrock and the tectonic stress is quantified, and based on the porosity and permeability relation of samples, the fluid storage space distribution rule of different fracture causes is established, and the fracture formation is determined. Through a CO2 filling pressure test, breakthrough pressure distribution of different structural units of the fault under the constraint of the CO2 filling pressure is determined, a safety evaluation boundary during CO2 storage during bed rock fracture is finally established, and a new research technical means is provided for CO2 safety storage in the tensional-tensional basin.

Description

Technical Field

[0001] The present invention relates to the related theoretical research and application fields of CO2 storage in extensional basins and even extensional-torsional basins. Specifically, it is a method for safety evaluation of the relevant boundary bedrock fractures of CO2 storage and the activity of the internal bedrock fractures based on geological geophysical data, geochemical data and related mathematical methods. Background Art

[0002] In extensional and extension-torsion oil and gas basins, the developed faults play an extremely important role in the formation and evolution of the basins, especially the boundary bedrock faults in the multi-stage superimposed basins control the scale of the basins, affect the distribution of various traps in the basins, and restrict the distribution of formation pressure. The epigenetic faults increase the complexity of the distribution of fluids in the basins. Therefore, both inherited bedrock faults and epigenetic bedrock faults are the research focus of early oil and gas exploration, and are also the key evaluation content for large-scale CO2 storage in basins in the later period. However, the main difficulty in the evaluation of such bedrock faults lies in their variability in seismic reflection, the difficulty in fault distribution and prediction, and the poor results of fluid evaluation, which greatly restricts the evaluation of fluids in the basins.

[0003] The evaluation of fractures in tensile and tension-torsion oil and gas basins can be carried out by improving the seismic resolution to characterize the spatial distribution of fractures; the corresponding characteristics of rock porosity based on conventional logging data, combined with the distribution law of fractures in the fractures, are used to summarize the indirect characterization of the fault zone structure based on the identification of fractures based on conventional logging (Chen Wei et al., 2010); it is also possible to use imaging logging to extend the characterization length of fractures based on the identification of fracture structures in a large number of cores of mature oil and gas basins dominated by clastic rocks (a quantitative identification method for fracture zone structural units in faulted basins, Lao Haigang et al., 2022), and combine the response of fractures on conventional logging to achieve the desired effect. Quantitative characterization of structural units of fault zones, although different types of conventional logging have different focuses on the indirect expression of fractures. However, when CO2 is stored in existing oil and gas basins, the most common method is to increase the recovery rate by displacing carbon dioxide to achieve CO2 storage, but the amount of CO2 stored in this part is relatively small and the scope of use is limited to oil and gas reservoirs with relatively low permeability. How to use abandoned oil fields in tensional-tensional oil and gas basins in eastern China for long-term storage of carbon dioxide is a very desirable and cost-effective method. When storing large-scale CO2, the safety evaluation of bedrock fractures requires an evaluation method that is completely different from that of oil and gas transport and closure.

[0004] Inspired by the conventional evaluation of fault sealing and the application of capillary pressure, a test was conducted on the bedrock fracture with complete core sampling to evaluate the CO2 storage differences caused by geological differences in different structural parts, and a reliable evaluation method with key factors involved and CO2 filling pressure as the detection standard was established, achieving the purpose of classifying and evaluating different structural units of the fault and establishing the safety evaluation boundary as a whole. Overcoming the research defects of the conventional fault sealing line zone, a scale for CO2 safety evaluation of bedrock fractures of different scales and activity intensities in oil and gas basins can be realized. Summary of the invention

[0005] The present invention provides a method for evaluating the safety of bedrock fractures in a tension-tension-torsion basin related to CO2 storage, and the purpose of the invention is achieved in the following ways:

[0006] S1. Determine the relationship between bedrock fracture scale and activity intensity

[0007] Based on the interference wave and signal-to-noise ratio processing of bedrock three-dimensional seismic data, the seismic attributes that can better display invisible faults in bedrock strata are used to constrain the distribution of faults in the bedrock and clarify the corresponding relationship between the scale of faults in the bedrock and the activity intensity of faults.

[0008] S2. Quantifying the correspondence between bedrock and tectonic stress

[0009] S21. For coring wells that continuously coring and cross faults, identify the distribution characteristics of the dissolution pores and holes in the rock under a microscope according to the differences in lithology; count the nature of the fracture development, the type of filling material and the degree of fracture development in different bedrock types, and identify single-stage fractures and multi-stage combined fractures;

[0010] S22. Identify the mineral combination types corresponding to the lithology of different bedrocks, clarify the types of light-colored minerals and dark-colored minerals, and establish the relationship between minerals, mineral combinations and rock types based on the color ratio of the minerals.

[0011] S23. Establish the corresponding relationship between minerals, mineral assemblages and rock types and rock sensitivity trace elements, determine the corresponding relationship between the degree of fracture development and sensitive trace elements, and fit the corresponding relationship between the two;

[0012] S24. Based on triaxial stress tests, the similar brittleness indexes of different rocks are clarified and a rock type sequence is established based on the difficulty of fracture development.

[0013] S3. Clarify the law of vertical reservoir space variation of bedrock fractures

[0014] Use cores to test the apparent porosity of different structural parts of the fault, constrain the apparent porosity results calculated based on the aperture of pores and fractures in FMI, and find out the distribution of porosity close to the real fault in space. Use the porosity-permeability relationship to establish the fluid reservoir space law of different genetic elements of the fault;

[0015] S4. Clarify the pressure breakthrough of bedrock fractures under CO2 injection

[0016] For different structural parts of the fault and rocks with different mineral combinations, tests were carried out under CO2 filling pressure. According to the intensity of the injected gas, the filling pressure drop curves under single-stage and multi-stage combined fractures, opening sizes, and porosity and permeability differences were analyzed to clarify the breakthrough pressure distribution of different structural units of the fault under the constraint of CO2 filling pressure.

[0017] S5. Establish safety assessment boundary for CO2 storage in bedrock fractures

[0018] Establish the response relationship between fault activity intensity, bedrock characteristics, tectonic stress characteristics, and reservoir space characteristics related to porosity and permeability to CO2 injection pressure, and establish the safety assessment boundary for CO2 storage in different bedrock faults.

[0019] Effects of the invention:

[0020] The good effect of the present invention is that a clear corresponding relationship is established between the geological attribute characteristics of different structural units of the bedrock fault and the filling pressure during CO2 storage, and a fault safety evaluation method for detecting bedrock faults under changes in filling pressure during CO2 storage is proposed, which provides a new research technical means for the safe storage of CO2 in tensional-tensional-torsional basins. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 .Flowchart for safety assessment of bedrock fractures related to CO2 storage in extensional-tensional-torsional basins;

[0022] Figure 2 .Statistics and sorting template of key elements of bedrock fractures in X structural drape belt;

[0023] Figure 3 .Comparison of the differences in the occurrence of cracks and faults between two groups of different fillings;

[0024] Figure 4 .Bedrock density log and pore volume cross plot;

[0025] Figure 5 .X structural covering zone bedrock fracture with a fault throw of 240 meters and the results of CO2 storage safety assessment. DETAILED DESCRIPTION

[0026] The effect of the present invention is further illustrated below by taking the safety evaluation of bedrock fractures during CO2 storage in an X-tectonic drape belt controlled by developed bedrock fractures as an example. The specific implementation steps of the safety evaluation of CO2 sealing in bedrock fractures are as follows: Figure 1 ):

[0027] S1. Determine the relationship between bedrock fracture scale and activity intensity

[0028] Based on the interference wave and signal-to-noise ratio processing of the bedrock three-dimensional seismic data body, two parameters, instantaneous frequency and phase, which can clearly show the properties of bedrock fractures, are selected to explain the spatial distribution of bedrock fractures and their invisible fractures; the fracture breakpoint position is determined according to the benchmark standard surface, and on this basis, the relationship between the intensity of fracture activity and the spatial distribution of bedrock fractures is fitted.

[0029] By statistically analyzing the width and fault distance of the main fault in the study area, the fitting relationship between the two in the study area is y=46.607In(x)-147.48, where y is the width of the fault and x is the fault distance.

[0030] Table 1. Width and fault distance of the fault in the study area

[0031]

[0032]

[0033] S2. Quantifying the correspondence between bedrock and tectonic stress

[0034] For the main bedrock fractures in the study area, we selected fractures with continuous coring and a recovery rate of more than 95%, and adopted the sampling requirement of 25 cm interval (the depth of the sampling point is required to be consistent with the logging measurement depth), and characterized and tested the relationship between core structural fractures, mineral assemblage trace elements and triaxial stress ( Figure 2 );

[0035] (1) Perform microscopic identification on the samples and count the number of dissolution holes, caves and structural fractures ( Figure 1 210, 220); clarify the type of fracture filling and its filling degree, and for large fractures or dissolution caves, determine the mineral composition of their fillings. Combine the description of directional core and the fracture interpretation of imaging logging, and determine the fracture stage and its relationship with bedrock fractures based on the fracture cutting relationship and filling method.

[0036] Through downhole identification, the types of fracture fillings are calcareous and siliceous; the filling degree is 63-79%; the main filling minerals of large fractures or dissolution caves are calcite; there are two obvious stages of fractures, and the direction of the Yanshanian fractures is basically consistent with that of the bedrock faults.

[0037] Figure 3As shown in Figure 2, the occurrence relationship of filled and unfilled fractures in the same fault with a fault throw of 240 meters, the number of filled fractures is 3.3 times that of unfilled fractures.

[0038] (2) Determine the mineral assemblage type of the sample, clarify the types of light-colored minerals and dark-colored minerals and their proportions in the sample; on this basis, first determine the hue ratio of the light-colored mineral according to the ratio of quartz to feldspar, and then determine the hue ratio corresponding to the mineral assemblage type controlled by both light-colored and dark-colored minerals, and then further expand to the hue ratio of the corresponding rock type ( Figure 1 230);

[0039] The types of light-colored minerals and dark-colored minerals include quartz and feldspar, among which feldspar includes plagioclase and potassium feldspar, which account for 15-90% and 0-85% in the sample respectively. The corresponding light-colored minerals have a hue rate of 15-90%, and the dark-colored minerals have a hue rate of 0-85%. The hue of the corresponding rock type is determined by a hue greater than 50%.

[0040] (3) Establish the corresponding relationship between rock types under the constraints of light-colored and dark-colored minerals and their corresponding sensitive trace elements. First, use the major and trace elements of the measured core to correct the data obtained from special logging and establish a major and trace element data table for the well section. Second, fit the corresponding relationship between the degree of fracture development and sensitive trace elements. The selected two major elements, calcium oxide and silicon dioxide, and the four trace elements, iron, magnesium, calcium and aluminum, have a high degree of fit with the fracture density, thus establishing the corresponding relationship between major elements, trace elements and fractures.

[0041] According to the trace element data table of the study area, the main element silica in the study area is reduced, calcium oxide is increased, and the trace element aluminum content is high, and the iron and magnesium content is high, indicating the dominant development section of the cracks.

[0042] (4) Based on the triaxial stress test, the brittleness index of different rock types is calculated for samples of different rock types, and a rock type sequence (240) based on the difficulty of fracture development is established based on the brittleness index, so as to determine the influence of fracture stage, fracture development degree and fracture filling mineral type on the brittleness index of rock types with different chromaticity rates.

[0043] The brittleness index of the rock types in the study area (B it ) is in the range of 0.73 to 0.99. When there are two-stage cracks in the study area, the degree of crack development is greater than 3 / dm, and the fracture filling mineral type is siliceous filling, the brittleness index of the high-tone rate rock type increases significantly.

[0044] S3. Clarify the law of vertical reservoir space variation of bedrock fractures

[0045] The apparent porosity of the core samples is calculated point by point, and the apparent porosity results calculated based on the aperture of pores and fractures in FMI are constrained to establish a spatial distribution of porosity close to the real fracture. Based on the porosity-permeability relationship of the samples, the spatial distribution law of fluid reservoirs of different origins in the fracture is established;

[0046] The relationship between fault throw and reservoir development is y = -460In(x) + 830, where y is the fault throw and x is the reservoir-to-land ratio. The dominant interval of structural fractures and karst caves is located in the area with pore volume ≤ 5400 mm3 and rock density ≤ 2.6 g / cm3 ( Figure 4 ).

[0047] S4. Clarify the pressure breakthrough of bedrock fractures under CO2 injection

[0048] For the samples obtained, tests were carried out under CO2 filling pressure according to the different structural parts of the fault and different mineral combinations; according to the intensity difference of the injected CO2 gas, the injection fluid pressure drop curves under single-stage and multi-stage fracture combinations, opening sizes, and porosity and permeability differences were analyzed to clarify the breakthrough pressure distribution of different structural units of the fault under the constraint of CO2 filling pressure.

[0049] The breakthrough pressure of the fault core under the constraint of CO2 filling pressure in the study area ranges from 0.49 to 5.37 MPa, and the breakthrough pressure of the broken zone ranges from 1.82 to 17.35 MPa. The breakthrough pressure of the upper plate broken zone is significantly smaller than that of the lower plate broken zone.

[0050] S5. Establish safety assessment boundary for CO2 storage in bedrock fractures

[0051] Establish the response relationship between fault-related structural fractures and dissolution caves, bedrock characteristics, structural stress characteristics, and reservoir space characteristics related to porosity and permeability to CO2 injection pressure, and establish the safety assessment boundary for CO2 storage in bedrock fractures with different activity intensities;

[0052] like Figure 5 As shown in the figure, the correspondence between the characteristics of the fracture development section inside the broken zone of the fault and the rock tone rate, combined with the breakthrough pressure obtained by the injection of CO2 gas, determines that the CO2 safety storage level of the fracture depth section that solves the fault core is low, and the CO2 safety storage level of the fracture depth section far away from the fault core is high. The fracture development section within the broken zone of the fault 80m above and below is the safety boundary for CO2 storage in bedrock fractures.

Claims

1. A method for evaluating the safety of bedrock fractures in a tensile-tensional basin related to CO2 storage, characterized in that: The evaluation method comprises the following steps: S1. Determine the relationship between bedrock fracture scale and activity intensity Based on the interference wave and signal-to-noise ratio processing of bedrock 3D seismic data, two parameters, instantaneous frequency and phase, which can clearly show the properties of bedrock fractures, are selected to explain the spatial distribution of bedrock fractures and their invisible fractures; the fracture breakpoint position is determined according to the datum standard surface, and on this basis, the relationship between the intensity of fracture activity and the spatial distribution of bedrock fractures is fitted; S2. Quantifying the correspondence between bedrock and tectonic stress For the main bedrock fractures in the study area, we selected fractures with continuous coring and took samples at intervals of 25 cm to characterize and test the relationship between core structural fractures and cavities, mineral assemblage trace elements and triaxial stress; S3. Clarify the law of vertical reservoir space variation of bedrock fractures The apparent porosity of the core samples is calculated point by point, and the apparent porosity results calculated based on the aperture of pores and fractures in FMI are constrained to establish the spatial distribution of porosity close to the real fracture. Based on the porosity-permeability relationship of the samples, the spatial distribution law of fluid reservoirs of different origins in the fracture is established. S4. Clarify the pressure breakthrough of bedrock fractures under CO2 injection For the samples obtained, the CO2 filling pressure was tested according to the different structural parts and mineral combinations of the faults. According to the intensity difference of the injected CO2 gas, the pressure drop curve of the filling fluid under the combination of single-stage and multi-stage fractures, the size of the opening, and the porosity and permeability difference were analyzed to clarify the breakthrough pressure distribution of different structural units of the fault under the constraint of CO2 filling pressure. S5. Establish safety assessment boundaries for CO2 storage in bedrock fractures Establish the response relationship between fault-related structural cracks and dissolution caves, bedrock characteristics, structural stress characteristics, and porosity-permeability-related reservoir space characteristics to CO2 injection pressure, and establish the safety evaluation boundary for CO2 storage in different bedrock faults.

2. A method for safety assessment of bedrock fractures in a tensile-tensional-torsional basin related to CO2 storage according to claim 1, characterized in that: In the step S2, the recovery rate of the continuous coring fractures should reach more than 95%.

3. A method for safety assessment of bedrock fractures in a tensile-tensional-torsional basin related to CO2 storage according to claim 1, characterized in that: The specific method of step S2 is: S21. Conduct microscopic identification on the samples, count the dissolved holes, caves and structural fractures, clarify the type of fracture fillings and their filling degree. For large fractures or dissolved caves, it is necessary to determine the mineral composition of their fillings. Combine the description of directional core and the fracture interpretation of imaging logging, and determine the fracture stage and its relationship with bedrock fractures based on the fracture cutting relationship and filling method. S22. Determine the mineral assemblage type of the sample, clarify the types of light-colored minerals and dark-colored minerals and their proportions in the sample; on this basis, first determine the hue ratio of the light-colored minerals according to the ratio of quartz to feldspar, and then determine the hue ratio corresponding to the mineral assemblage type jointly controlled by the light-colored and dark-colored minerals, and then further expand to the hue ratio of the corresponding rock type; S23. Establish the corresponding relationship between the rock types under the constraints of light-colored and dark-colored minerals and their corresponding sensitive trace elements. First, use the major and trace elements of the measured core to correct the data obtained by special logging, and establish the major and trace element data table of the well section. Secondly, fit the corresponding relationship between the degree of fracture development and sensitive trace elements. The selected two major elements of calcium oxide and silicon dioxide and the four trace elements of iron, magnesium, calcium and aluminum have a high degree of fit with the fracture density, so as to establish the corresponding relationship between major elements, trace elements and fractures. S24. Based on the triaxial stress test, the brittleness index of different rock types is calculated for samples of different rock types. Based on the brittleness index, a rock type sequence based on the difficulty of crack development is established to determine the influence of the crack stage, crack development degree and crack filling mineral type on the brittleness index of rock types with different tone rates.

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