Method for comprehensively identifying cause of crack

Abstract

The invention relates to the technical field of oil and gas geological exploration, in particular to a method for comprehensively identifying fracture causes, which comprises the following steps: S1, imaging logging; s2, collecting a sample; s3, sample analysis; and S4, crack cause classification. According to the method for comprehensively judging the cause of the crack, on the basis of determining different crack development time, crack trend and inclination angle characteristics are combined, the cause of the crack is judged under ancient stress field evolution, various factors are integrated, the cause and the formation time of the crack in a complex area can be accurately analyzed and determined, and the method is suitable for popularization and application. After matching with the oil and gas reservoir forming time, the method can preferably select the fractures beneficial to oil and gas reservoir forming, is of great significance to analysis and prediction, determination of oil and gas enriched high-yield areas and guidance of oil and gas development, meanwhile, combines the physical characteristics and activity time of the fractures, improves the accuracy of fracture cause classification, and improves the accuracy of oil and gas reservoir formation classification. And an accurate data basis is provided for research on the influence of subsequent crack activity on oil and gas accumulation, and the method has relatively good generalization performance.

Description

Technical Field

[0001] This invention relates to the field of oil and gas geological exploration technology, and in particular to a method for comprehensively identifying the causes of fractures. Background Technology

[0002] In recent years, the exploration strategy for tight sandstone gas reservoirs has shifted from the traditional reservoir "sweet spot" target to transport conductors. Faults and fractures, as the main components of transport conductors, are of great significance for oil and gas exploration, and can be used to guide the efficient exploration and development of related oil and gas resources.

[0003] Chinese invention patent application CN202211114301.8 describes a method for determining fracture-induced fracture zones in different periods of a multi-stage active fault. The method includes: classifying the development stages of fractures in the fault-induced fracture zones; determining the development time of different fractures; classifying fractures developed in different periods; measuring fractures developed in different periods; and performing quantitative characterization and modeling of fracture zones in different periods. This method distinguishes the fracture zones formed by the fault in different geological periods and quantifies the development characteristics of the fracture zones, including their size and density.

[0004] However, most of my country's tight sandstone gas reservoirs have complex tectonic settings and are affected by multiple phases of tectonic stress. The activity of fractures is complex and diverse. For fractures of different origins such as faults, folds, regional stress, and diagenesis, it is not possible to comprehensively and effectively determine the activity time, cause and classification of fractures, which is not conducive to the development of oil and gas exploration and exploitation. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies that cannot comprehensively and effectively determine the activity time, causes and classification of fractures, which affects oil and gas exploration and exploitation, and to provide a comprehensive method for identifying the causes of fractures.

[0006] This invention provides a method for comprehensively identifying the cause of cracks, including: S1. Imaging logging: Conduct imaging logging tests to obtain characteristic information of fractures; S2. Sample collection: Collect secondary mineral samples that fill the cracks with different characteristic information; S3. Sample Analysis: Based on the homogenization temperature and salinity data of inclusions in secondary mineral samples, determine the stages of fracture activity and their formation time. S4. Classification of crack formation: Based on the characteristic information of cracks, crack formation time and paleostress field evolution, the classification of crack formation is determined.

[0007] Preferably, in S1, imaging logging tests are performed on the wellbore after the production well is completed to accurately obtain the basic characteristics of the fractures.

[0008] Preferably, in S1, the crack feature information includes the crack dip angle feature and the crack orientation feature.

[0009] Preferably, in S2, the secondary mineral sample is prepared into a double-sided polished sheet structure after collection.

[0010] Preferably, in S3, the diagenetic process of the double-sided polished sheet structure is observed under a microscope, and the homogenization temperature and salinity of the inclusions are tested to obtain inclusion homogenization temperature data and salinity data.

[0011] Preferably, in S3, the homogenization temperature data and salinity data of inclusions in secondary mineral samples are analyzed based on the diagenetic sequence.

[0012] Preferably, in S3, the homogenization temperature data and salinity data of the inclusions are projected onto the burial history-thermal history map for analysis to obtain the number of crack activity periods and formation time.

[0013] Preferably, in S4, the classification of fracture genesis includes a classification scheme that divides fractures into longitudinal tension fractures, shear fractures, and bedding fractures, with longitudinal tension fractures corresponding to fold genesis, shear fractures corresponding to fault genesis, and bedding fractures corresponding to sedimentary genesis.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention provides a comprehensive method for identifying the causes of fractures. Based on determining the development time of different fractures, and combining the characteristics of fracture direction and dip angle, the method identifies the causes of fractures under the evolution of paleostress field. It integrates multiple factors and can accurately analyze and determine the causes and formation time of fractures in complex areas. After matching with the time of hydrocarbon accumulation, it can select fractures that are conducive to hydrocarbon accumulation. This method is of great significance for analyzing and predicting, identifying high-yield hydrocarbon areas, and guiding hydrocarbon development. 2. The present invention provides a comprehensive method for identifying the origin of fractures, which combines the physical characteristics and activity time of fractures, improves the accuracy of fracture origin classification, provides an accurate data basis for subsequent research on the impact of fracture activity on hydrocarbon accumulation, and has good applicability. Attached Figure Description Figure 1 This is a flowchart illustrating a method for comprehensively identifying the cause of cracks in Example 1; Figure 2 This is a microscopic feature of the fracture filling material in a fault zone in western Sichuan, as shown in Example 1. Figure 3 This is the second feature of the fracture filling material in the fault zone of a certain area in western Sichuan under a microscope in Example 1; Figure 4 This is a cross-plot of the homogenization temperature and salinity of the fracture filling material in a fault zone in western Sichuan, as shown in Example 1. Figure 5 This is a typical well burial history-thermal history curve from a certain area in western Sichuan, as shown in Example 1. Figure 6 This is a diagram showing the evolution of the paleostress field in a certain area of ​​western Sichuan in Example 1; Figure 7 Analysis of the tectonic stress field for crack formation in Example 1 Figure 1 ; Figure 8 Analysis of the tectonic stress field for crack formation in Example 1 Figure 2 ; Figure 9 This is a schematic diagram of imaging logging data from well A1 in a certain area of ​​western Sichuan in Example 1; Figure 10 This is a schematic diagram of the genetic classification of well A1 in Example 1 as bedding fractures; Figure 11 This is a schematic diagram illustrating the genetic classification of well A1 as a shear fracture in Example 1; Figure 12 This is a schematic diagram of the formation of well A1 in Example 1, which is classified as a longitudinal tension fracture. Detailed Implementation

[0015] The present invention will now be described in further detail with reference to specific embodiments. However, this should not be construed as limiting the scope of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0016] Example 1 A comprehensive method for identifying the causes of cracks includes: S1. Imaging Logging: Conduct imaging logging tests to obtain characteristic information about fractures.

[0017] Specifically, imaging logging tests can be performed on the wellbore after the production well is completed to obtain the dip angle and dip data of the fractures around the well. The dip data can be converted into strike data.

[0018] S2. Sample collection: Collect secondary mineral samples that fill the cracks with different characteristic information.

[0019] Specifically, for cracks with different dip angles and orientations in S1, secondary mineral samples filling the cracks were selected, and the collected secondary mineral samples were prepared into double-sided polished sheet structures.

[0020] S3. Sample Analysis: Based on the homogenization temperature and salinity data of inclusions in secondary mineral samples, determine the stages of fracture activity and their formation time.

[0021] Specifically, the diagenetic process of the double-sided polished sheet structure prepared by S2 was observed under a microscope, and the homogenization temperature and salinity of the inclusions were tested to obtain homogenization temperature and salinity data of the inclusions. Based on the diagenetic sequence, the homogenization temperature and salinity data of the inclusions of the secondary mineral samples were analyzed.

[0022] Furthermore, the homogenization temperature and salinity data of the inclusions were plotted onto the burial history-thermal history map for analysis to obtain the periods of crack activity and formation time.

[0023] S4. Classification of crack formation: Based on the characteristic information of cracks, crack formation time and paleostress field evolution, the classification of crack formation is determined.

[0024] Specifically, the classification of fracture genesis includes a classification scheme that divides fractures into longitudinal tension fractures, shear fractures, and bedding fractures. Longitudinal tension fractures correspond to folding genesis, are usually perpendicular to the strata, and are characterized by a large dip angle and a strike consistent with the direction of the regional principal stress. Shear fractures correspond to faulting genesis, are a set of conjugate shear fractures associated with faults, intersect the strata at a certain angle, and are characterized by a large dip angle and two sets of strikes. Bedding fractures correspond to sedimentary genesis, are nearly parallel to the strata, and are characterized by a small dip angle and different strikes.

[0025] This embodiment presents a comprehensive method for identifying fracture origins. Based on determining the development time of different fractures, it combines fracture orientation and dip characteristics to identify fracture origins under paleostress field evolution. By integrating multiple factors, it can accurately analyze and determine the origins and formation times of fractures in complex areas. After matching these with hydrocarbon accumulation times, it can select fractures that are conducive to hydrocarbon accumulation. This is of great significance for analyzing and predicting, identifying high-yield hydrocarbon areas, and guiding hydrocarbon development. At the same time, by combining the physical characteristics and activity time of fractures, it improves the accuracy of fracture origin classification and provides an accurate data foundation for subsequent research on the impact of fracture activity on hydrocarbon accumulation. It has good applicability.

[0026] Taking a certain area in western Sichuan as an example, this area is affected by multiple phases of tectonic stress, resulting in complex fracture activity phases and diverse orientations. The distinction between fractures of different origins, such as faults, folds, regional stress, and diagenesis, has remained inconclusive. Therefore, this embodiment proposes a comprehensive method for identifying the origin of fractures. Figure 1 As shown, it specifically includes: Step 1: Imaging Logging: After drilling of well A1, imaging logging tests are performed on the wellbore to obtain the dip angle and dip direction data of the surrounding fractures. The dip direction data is then converted into strike data to obtain... Figure 9 The dip angle and strike data shown in the diagram indicate that there is no obvious pattern in the dip angle and strike of the cracks.

[0027] Step 2, Sample Collection: Collect secondary minerals filling the cracks near the fault and prepare double-sided polished thin sections for observation and testing under a microscope.

[0028] Step 3, Sample Analysis: The double-sided polished thin sections obtained in Step 2 were observed under a microscope to observe the diagenesis, homogenization temperature of inclusions, and salinity. The characteristics of different types of fracture filling materials under a microscope were obtained and presented in single-polarized light photographs.

[0029] Specifically, temperature and salt content measurement, laser Raman spectroscopy, and microfluorescence were performed on double-sided polished thin films to obtain: like Figure 2 As shown, the cracks are filled with calcite, and the hydrocarbon-containing brine inclusions are distributed in transparent, colorless bands with a homogenization temperature of 97℃.

[0030] like Figure 3 As shown, the cracks are filled with quartz, and the hydrocarbon brine inclusions are distributed in transparent, colorless bands with a homogenization temperature of 179℃.

[0031] Further sorting yielded the following results: Figure 4 As shown, this is a cross-plot of the homogenization temperature and salinity of the inclusions in the crack filling material.

[0032] Combination such as Figure 5 The typical well burial history-thermal history curves for this region are shown. The homogenization temperature and salinity data of inclusions are projected onto the burial history-thermal history curves for analysis to obtain the fracture activity periods and formation times. It is determined that the fracture activity can be divided into three periods: the first period is the early Yanshanian period, the second period is the middle and late Yanshanian period, and the third period is the Himalayan period.

[0033] Step 4: Classification of Crack Causes: Combining with, for example... Figure 6 The paleostress field evolution in this region is generally accepted by scholars, and as shown in the figure... Figures 7-8 The analysis of the tectonic stress field of the cracks shown allows for the classification of the causes of cracks at different stages.

[0034] Among them, the evolution of paleostress field is mainly used to reconstruct the tectonic stress situation of the region in different geological periods, while the tectonic stress field is used to understand the information on the direction of the principal stress of the region. Combined with the dip angle and direction information of the cracks actually formed in that period, the actual tectonic cause of the cracks can be understood, and then the classification of crack formation can be determined.

[0035] Specifically, the homogenization temperature of the minerals filling the fractures ranges from 90 to 110 ℃, and the salinity ranges from 0 to 10 wt% NaCl, indicating that the fractures formed during the early Yanshanian period. The principal stress of the regional tectonic stress is SN-oriented. The fractures formed during this period have a dip angle range of 60-90° and a strike direction of EW. Combined with the tectonic stress analysis, the fractures are longitudinal tension fractures.

[0036] Specifically, the homogenization temperature range of the minerals filling the fractures is 110-230℃, and the salinity range is 10-20 wt% NaCl, indicating that the fractures formed during the middle and late Yanshanian period. During this period, the principal stress direction of the regional tectonic structure was NW-SE. The fractures formed during this stage are characterized by a strike of NE-SW and a dip angle range of 30-60°. The fractures were formed by fault-associated shear fractures.

[0037] Specifically, the homogenization temperature range of the minerals filling the fractures is 110-230℃, and the salinity range is 0-10 wt% NaCl, indicating that the fractures formed during the Himalayan period. During this period, the principal stress direction of the regional tectonic structure was EW. The fractures formed during this stage are characterized by a strike of SN and a dip angle range of 30-60°. The fractures were formed by fault-associated shear fractures.

[0038] Specifically, there is another type of crack with diverse and irregular orientations and a dip angle range of 0-30°. These cracks are formed during three phases of activity and are low-angle bedding fractures.

[0039] Combining the analysis results of steps one, three, and four—namely, the fracture orientation, dip angle characteristics, and fracture formation time determined by experimental analysis—the genetic classification of complex, multi-stage fractures in a single well was completed within the context of paleostress evolution and geological background, yielding results such as... Figure 10 The diagram shown is a classification of crack formation based on bedding joints, as follows: Figure 11 The diagram showing the classification of crack formation based on shear cracks and as shown below. Figure 12 The diagram shown is a classification of crack formation based on longitudinal tension joints.

[0040] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of integrated fracture origin discrimination, characterized by, The method comprises the following steps: S1, imaging logging: performing imaging logging test to obtain characteristic information of the fractures; S2, sample collection: collecting secondary mineral samples filled between the fractures with different characteristic information; S3, sample analysis: determining fracture activity period and formation time based on homogenization temperature data and salinity data of the secondary mineral samples; S4, fracture genetic classification: determining fracture genetic classification by comprehensively considering the characteristic information of the fractures, the formation time of the fractures and the evolution of the paleostress field.

2. The method of claim 1, wherein, In S1, the imaging logging test is performed on the wellbore after the production well is completed.

3. The method of claim 1, wherein, In S1, the characteristic information of the fractures includes the dip angle characteristics and the strike characteristics of the fractures.

4. The method of claim 1, wherein, In S2, the secondary mineral samples are prepared into a double-side polished section structure after being collected.

5. The method of claim 4, wherein, In S3, diagenesis observation, homogenization temperature and salinity test are performed on the double-side polished section structure under a microscope to obtain the homogenization temperature data and the salinity data.

6. The method of claim 5, wherein, In S3, the homogenization temperature data and the salinity data of the secondary mineral samples are analyzed based on diagenetic sequence.

7. The method of claim 6, wherein, In S3, the homogenization temperature data and the salinity data are projected onto a burial history-thermal history diagram for analysis to obtain the fracture activity period and the formation time.

8. The method of claim 1, wherein, In S4, the fracture genetic classification includes a classification scheme of classifying the fractures into longitudinal tension fractures, shear fractures and bedding fractures, the longitudinal tension fractures correspond to fold genesis, the shear fractures correspond to fault genesis, and the bedding fractures correspond to sedimentary genesis.

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