Evaluation method for estimating size of karst cave main body of karst fracture-vug type carbonate reservoir by utilizing width of fracture zone

Abstract

The invention discloses an evaluation method for estimating the size of a karst cave main body of a karst fracture-vug type carbonate reservoir by utilizing the width of a fracture zone, and relates to the technical field of oil and gas field exploration and development. According to the method, data such as outcrop in a research area is utilized, fine characterization of fracture-cavity body size research is taken as a core, an internal structure and a forming mechanism of a fracture-cavity body are dissected, then correlation between a fracture zone and a karst cave main body is established, the height of the karst cave main body is calculated, the height of the fracture-cavity body is determined, then correlation between an earthquake fracture-cavity carving body and the height of the fracture-cavity body is established, and the height of the fracture-cavity body is determined. And determining a correction coefficient or a correction formula of the seismic fracture-cavity carving body, correcting the seismic fracture-cavity carving body, and finally accurately depicting the position, the scale and the spatial distribution of the fracture-cavity body, thereby providing a geological basis for efficient exploration and development of the fracture-cavity type carbonate oil and gas reservoir.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field exploration and development, and more particularly to an evaluation method for estimating the size of the main body of a karst fissure-cave carbonate reservoir by using the width of a fracture zone. Background Art

[0002] Carbonate rock oil and gas reservoirs play an important role in the world. Their oil and gas reserves account for about 50% of the total global oil and gas reserves, and their oil and gas production reaches more than 60% of the total global oil and gas production. It is one of the most important exploration and development fields in China's energy strategic layout.

[0003] Fissure-cave carbonate rock oil and gas reservoirs are the main types of carbonate rock oil and gas reservoirs. They have large differences in pore-fissure-cave scales, complex structures, and diverse reservoir types (pore type, cave type, fracture type, fracture-pore type, fracture-vug type, and fracture-cave type). The development positions, scales, and distribution characteristics of different types of reservoirs vary greatly, the reservoir continuity is poor, the changes are rapid, and the heterogeneity is extremely strong. The seismic response characteristics of the reservoir are complex.

[0004] Among them, the caves formed by buried hill karst or interlayer karst are affected by the long-term corrosion of bright and dark river water bodies, resulting in huge cave scales, with a height that can reach more than 600m, and forming sinkholes with a length that can reach several kilometers or dozens of kilometers. When a drilling encounters such a karst fissure-cave body, serious losses or blowouts will occur, making it difficult to continue the drilling, resulting in early completion of the drilling, and unable to conduct logging. Therefore, it is very difficult to completely drill through a large buried hill karst fissure-cave body or an interlayer karst fissure-cave body through drilling to determine the scale of such fissure-cave bodies.

[0005] Through research, it is found that under the action of overlying pressure, the upper part and surrounding strata of the karst fissure-cave bodies in buried hills or interlayer karst fissure-cave bodies will form fracture zones under the action of stress. Therefore, the karst fissure-cave bodies in buried hills or interlayer karst fissure-cave bodies are divided into three zones: the main cave body, the fracture zone, and the surrounding rock. The surrounding rock is relatively dense with few developed fractures, mainly bioclastic limestone and dolomitic limestone, which are formed by corrosion and expansion on the basis of biogenic debris and dolomite crystal pores. They are mostly oval or irregularly circular in shape, with pore diameters of 2 - 10 mm and a maximum of 10 cm. They are distributed in clusters, layers, or bands on the plane. Drilling generally does not show leakage or has only a small amount of leakage, having little impact on drilling. The fracture zone is affected by multiple phases of tectonic movement and develops multiple phases of cave roof collapse fracture zones. Under the action of groundwater, small-scale corrosion holes are formed along the fractures. Drilling is prone to leakage, but generally can proceed smoothly. The main cave body is mainly semi-filled or unfilled, with a height of more than 3 m and a width of more than 6 m. When the drilling encounters the main cave body, serious leakage or blowout is likely to occur, and the drilling cannot continue and is completed in advance. Comprehensive analysis shows that when the drilling encounters the karst fissure-cave bodies in buried hills or interlayer karst fissure-cave bodies, generally the surrounding rock and fracture zone of the karst fissure-cave bodies in buried hills or interlayer karst fissure-cave bodies can be completely drilled through, but it is very difficult to completely drill through the main cave body. However, the size of the main cave body determines the scale of the available space, which is crucial for the exploration and development of oil and gas reservoirs. Through technical research, currently no estimation method for the size of the main cave body has been found.

[0006] Fracture-vuggy carbonate reservoirs are prone to leakage or blowout, resulting in early completion of drilling. Without logging data, the scale of the fracture-cave bodies cannot be directly determined. There are multiple difficulties in accurately determining the scale of the fracture-cave bodies: (1) The pores, fractures, and caves in the karst fissure-cave bodies in buried hills or interlayer karst fissure-cave bodies are well-developed and the internal structure is complex; (2) Drilling is prone to leakage or blowout, resulting in early completion of drilling. Without logging data and with little characterization data of the fracture-cave bodies, the accuracy is relatively low; (3) The scale of the fracture-cave bodies is mainly determined by seismic fracture-cave body carving technology. However, affected by the quality and accuracy of seismic data, the carving results of the fracture-cave bodies are difficult to meet the requirements of exploration and development.

[0007] Currently, no estimation method has been formed to accurately determine the size of the fracture-cave bodies, especially the size of the main cave body. There is an urgent need for an evaluation method for the size of the main cave body of fracture-vuggy carbonate reservoirs to improve the characterization accuracy of the fracture-cave bodies. Summary of the Invention

[0008] In order to overcome the defects and deficiencies existing in the above-mentioned prior art, the present invention provides an evaluation method for estimating the size of the main body of a karst cave in a karst fissure-vug carbonate reservoir by using the width of the fracture zone. The object of the present invention is to provide an evaluation method for the size of the main body of a karst cave in a karst fissure-vug carbonate reservoir to improve the characterization accuracy of the fissure-vug body. Through research, it is found that for the karst caves formed by buried hill karst or interlayer karst, under the action of the overlying formation pressure, fracture zones will be formed in the upper part and around the karst caves of the formation under the action of stress, and there is a certain positive correlation between the width of the fracture zone and the scale of the main body of the karst cave. The present invention uses data such as outcrops in the study area to draw a crossplot of the width of the fracture zone and the height of the main body of the karst cave, establish a formula for the width of the fracture zone and the height of the main body of the karst cave, and through fine interpretation of logging data, can accurately determine the width of the fracture zone. Finally, using the fitting formula, the height of the main body of the karst cave is calculated to determine the size of the main body of the karst cave.

[0009] The carbonate reservoir with fissure-vug bodies is the most important type in carbonate reservoirs. The quantitative characterization of fissure-vug carbonate reservoirs is the key to the efficient exploration and development of fissure-vug carbonate oil and gas reservoirs. Among them, the determination of the size of the fissure-vug body, especially the size of the main body of the karst cave, is an important parameter for estimating the reserves of fissure-vug carbonate reservoirs and an important parameter for formulating development technical countermeasures for oil and gas reservoirs. Therefore, accurately determining the size of the fissure-vug body by this method is one of the key technologies for the efficient exploration and development of fissure-vug carbonate oil and gas reservoirs, and has a large market demand and broad application prospects.

[0010] To solve the problems existing in the above-mentioned prior art, the present invention is realized through the following technical solutions.

[0011] The present invention provides an evaluation method for estimating the size of the main body of a karst cave in a karst fissure-vug carbonate reservoir by using the width of the fracture zone. The method includes the following steps: S1. Field fissure-vug body description step: Search for outcrops of fissure-vug bodies formed under the same conditions as in the study area for field reconnaissance; measure the size of the main body of the karst cave in the fissure-vug body and measure the width of the fracture zone of the fissure-vug body. S2. Fitting the calculation formula for the main body of the karst cave step: Using the size of the main body of the karst cave and the width of the fracture zone of the fissure-vug body measured in step S1, establish a crossplot of the size of the main body of the karst cave and the width of the fracture zone, and fit to determine the calculation formula for the height of the main body of the karst cave and the width of the fracture zone. S3. Determining the width of the fracture zone of the fissure-vug body in the study area step: Using the logging data in the study area, statistically analyze the top and bottom depths of abnormal drilling in the fracture zone during the drilling process; then use the measurement data in the study area to finely interpret the top and bottom depths of the fracture zone to determine the position and width of the fracture zone within a single fissure-vug body. S4. Steps for estimating the main height of solution cavities in the study area's fracture-vug bodies: Use the calculation formula for the main height of solution cavities and the width of the fracture zone determined by fitting in step S2, and the width of the fracture zone within a single fracture-vug body determined in step S3 to calculate the main height of solution cavities in a single fracture-vug body; S5. Steps for extracting the height of solution cavities of a single fracture-vug body by seismic means: Use the quantitative carving technology for seismic fracture-vug bodies to carve the spatial distribution of fracture-vug bodies and extract the height of a single fracture-vug body; S6. Steps for fitting the correction coefficient of seismic fracture-vug bodies: Use the height of a single fracture-vug body extracted in step S5 and the main height of solution cavities in a single fracture-vug body calculated in step S4 to establish a crossplot and fit to determine the correction coefficient of the seismic fracture-vug carved body; S7. Steps for determining the size of solution cavities in fracture-vug bodies: Use the correction coefficient of the seismic fracture-vug carved body obtained in step S6 to correct the seismic fracture-vug carved body, obtain the accurate size of the fracture-vug body, and thus finely depict the scale of the fracture-vug body.

[0012] Further preferably, it also includes steps for establishing a database of the main sizes of solution cavities in various types of fracture-vug bodies. Classify and process the main sizes of solution cavities and the widths of fracture zones of fracture-vug bodies measured during field reconnaissance according to different karst types, and establish a database of the main sizes of solution cavities in fracture-vug bodies of each karst type.

[0013] Even more preferably, in step S2, according to the main sizes of solution cavities and the corresponding widths of fracture zones of fracture-vug bodies of various karst types in the database of the main sizes of solution cavities in fracture-vug bodies of each karst type, establish a crossplot of the main sizes of solution cavities and the widths of fracture zones of fracture-vug bodies of various karst types, and fit to determine the calculation formula for the main height of solution cavities and the width of the fracture zone of fracture-vug bodies of various karst types.

[0014] Further preferably, in step S5, use the quantitative carving technology for seismic fracture-vug bodies to carve the spatial distribution of fracture-vug bodies to form a seismic fracture-vug carved body, extract the main height of solution cavities of each individual fracture-vug body from the seismic fracture-vug carved body, and establish a database of the main heights of solution cavities in seismic fracture-vug bodies.

[0015] Even more preferably, in step S6, use the main height of solution cavities of each individual fracture-vug body in the database of the main heights of solution cavities of seismic fracture-vug bodies and the main height of solution cavities of the corresponding individual fracture-vug body calculated in step S4 to establish a crossplot and fit to obtain the correction coefficient of the seismic fracture-vug carved body.

[0016] Further preferably, in step S4, it also includes steps for correcting the estimated main height of solution cavities in a single fracture-vug body. Specifically, use well test data to interpret the radii of the inner and outer zones of the fracture-vug body, compare and analyze the outer zone radius with the fracture zone, and compare and analyze the inner zone radius with the estimated main size of solution cavities in a single fracture-vug body to correct the estimated main height of solution cavities.

[0017] Further preferably, the types of fracture-vug bodies include buried-hill karst fracture-vug bodies and interlayer karst fracture-vug bodies.

[0018] Further preferably, the size of the main cave body includes the length, width and height of the main cave body.

[0019] Further preferably, in step S3, the drilling anomalies include any one of loss, gas invasion, gas kick and overflow.

[0020] Further preferably, in step S2, the calculation formula for fitting and determining the height of the main cave body and the width of the fracture zone is expressed as y = a * x + b, where y represents the estimated height of the main cave body of a single fracture-vug body, x represents the proportion of the fracture zone, and a and b represent coefficients.

[0021] Further preferably, in step S6, the correction coefficient of the seismic fracture-vug carved body is determined by fitting, expressed as z = c * y, where c represents the correction coefficient, z represents the height of the main cave body of the seismic fracture-vug carved body, and y represents the estimated height of the main cave body of a single fracture-vug body.

[0022] Compared with the prior art, the beneficial technical effects brought by the present invention are as follows: 1. The present invention forms an evaluation method for estimating the size of the main cave body of karst fracture-vug type carbonate reservoirs by using the width of the fracture zone, guiding the evaluation of the size of fracture-vug bodies in karst fracture-vug type carbonate reservoirs in the Sichuan Basin, Tarim Basin, Ordos Basin and the right bank of the Amu Darya. From the analysis of the application effect, the accuracy of the size of the fracture-vug type carbonate reservoirs estimated by this technology is increased by more than 70% compared with the original carved volume of the seismic fracture-vug bodies, and the accuracy of the size of the fracture-vug bodies reaches more than 85%, playing an important role in the exploration and development process of fracture-vug type carbonate oil and gas reservoirs.

[0023] 2. This method is applicable to the characterization of fracture-vug bodies in karst fracture-vug type carbonate reservoirs. By using this method, based on the formation mechanism of fracture-vug bodies and the internal structure of fracture-vug bodies, the correlation between the fracture zone and the formation of the main cave body is found, the relevant formula between the fracture zone and the main cave body is fitted, and the size of the main cave body is estimated, so as to evaluate the size of fracture-vug bodies. The size of the fracture-vug bodies calculated by this method is an important parameter for estimating the reserves of karst fracture-vug type carbonate reservoirs and an important parameter for formulating technical countermeasures for oil and gas reservoir development, and has a large market demand and broad application prospects in the exploration and development of karst fracture-vug type carbonate reservoirs.

[0024] 3. The core of the present invention is to conduct a detailed characterization of the size of fracture-vug bodies, anatomize the internal structure and formation mechanism of fracture-vug bodies, then establish the correlation between the fracture zone and the main body of the karst cave, calculate the height of the main body of the karst cave, thereby determine the height of the fracture-vug body, and then establish the correlation between the seismic fracture-vug carving body and the height of the fracture-vug body, determine the correction coefficient or correction formula for the seismic fracture-vug carving body, correct the seismic fracture-vug carving body, and finally accurately depict the position, scale and spatial distribution of the fracture-vug body, providing a geological basis for the efficient exploration and development of fracture-vug type carbonate rock oil and gas reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a flow chart of the method of the present invention; Figure 2 is a structural diagram of the internal part of a karst fracture-vug body; Figure 3 is a crossplot of the proportion of the fracture zone width of a karst fracture-vug body and the height of the main body of the karst cave; Figure 4 is a crossplot of the height of the seismic fracture-vug carving body and the height of the fracture-vug body calculated from well logging. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The following are exemplary embodiments in conjunction with the drawings to help comprehensively understand the present invention defined by the claims and their equivalents, where the specific details will only be regarded as exemplary and will not limit the scope of the present invention. Therefore, those of ordinary skill in the art can make various changes and modifications to the embodiments without departing from the scope and spirit of the present invention.

[0027] Embodiment 1 At present, the Sinian Dengying Formation fracture-vug type carbonate rock gas reservoir in the Sichuan Basin in China has a reservoir scale of more than 2 trillion cubic meters and is the main gas reservoir for exploration and development in the southwest oil and gas region; the Ordovician fracture-vug type carbonate rock oil and gas reservoir in the Tarim Basin is the main oil and gas reservoir being developed by the Northwest Bureau of Zhongshi and Tarim Oilfield; the Cambrian fracture-vug type carbonate rock gas reservoir in the Ordos Basin is the main replacement gas reservoir in the next step. The fracture-vug type carbonate rock oil and gas reservoirs in China are large in scale and have great potential for exploration and development. However, affected by strong heterogeneity, there is a lack of a method for accurately calculating the size of fracture-vug bodies. Therefore, the evaluation method for estimating the size of the main body of karst caves in karst fracture-vug type carbonate rock reservoirs using the width of the fracture zone is of great significance for the efficient exploration and development of fracture-vug type carbonate rock oil and gas reservoirs and has a large market demand and broad application prospects.

[0028] The geological characteristics of fracture-cavity carbonate reservoirs are complex, and there are various technical problems. Competitors will face similar technical difficulties when efficiently exploring and developing fracture-cavity carbonate reservoirs, and it is difficult to bypass this method, making it difficult to avoid technology. This method involves estimating the size of fracture-cavity bodies in fracture-cavity carbonate reservoirs, improving the accuracy of the predicted results of the size of fracture-cavity bodies, and it is easy to discover or prove the infringement of others. This method has a certain technical difficulty for professionals, but it is also easy to imitate. Without patent protection, competitors can also apply this technology to compete with the company.

[0029] As a preferred embodiment of the present invention, referring to the attached Figure 1 illustrated in the specification, this embodiment discloses an evaluation method for estimating the size of the main body of karst fracture-cavity carbonate reservoirs using the width of the fracture zone, and this method includes the following steps: S1. Field fracture-cavity body description step: Search for the outcrops of fracture-cavity bodies formed under the same conditions as the study area in the field and conduct field surveys; measure the size of the main body of the karst cave of the fracture-cavity body, and measure the width of the fracture zone of the fracture-cavity body. S2. Fitting the calculation formula for the main body of the karst cave step: Using the size of the main body of the karst cave of the fracture-cavity body and the width of the fracture zone of the fracture-cavity body measured in step S1, establish a crossplot of the size of the main body of the karst cave and the width of the fracture zone, and fit to determine the calculation formula for the height of the main body of the karst cave and the width of the fracture zone. S3. Determining the width of the fracture zone of the fracture-cavity body in the study area step: Using the logging data of the study area, statistically analyze the top and bottom depths of abnormal drilling in the fracture zone during the drilling process; then use the measurement data of the study area to finely interpret the top and bottom depths of the fracture zone to determine the position and width of the fracture zone within a single fracture-cavity body. S4. Estimating the height of the main body of the karst cave of the fracture-cavity body in the study area step: Using the calculation formula for the height of the main body of the karst cave and the width of the fracture zone determined by fitting in step S2, and the width of the fracture zone within a single fracture-cavity body determined in step S3, calculate the height of the main body of the karst cave of a single fracture-cavity body. S5. Step of extracting the height of the karst cave of a single fracture-cavity body by seismic means: Using the seismic fracture-cavity body quantitative carving technology, carve the spatial distribution of the fracture-cavity body and extract the height of a single fracture-cavity body. S6. Fitting the correction coefficient of the seismic fracture-cavity body step: Using the height of a single fracture-cavity body extracted in step S5 and the height of the main body of the karst cave of a single fracture-cavity body calculated in step S4, establish a crossplot and fit to determine the correction coefficient of the seismic fracture-cavity carved body. S7. Determining the size of the karst cave of the fracture-cavity body step: Using the correction coefficient of the seismic fracture-cavity carved body obtained in step S6, correct the seismic fracture-cavity carved body to obtain the accurate size of the fracture-cavity body, so as to finely depict the scale of the fracture-cavity body.

[0030] Embodiment 2 As another preferred embodiment of the present invention, this embodiment further elaborates and supplements the technical solution of the present invention on the basis of the above-mentioned Embodiment 1. In this embodiment, an evaluation method for estimating the size of the main body of a karst cave in a karst fracture-vug carbonate reservoir by using the width of the fracture zone specifically includes the following 9 steps: S1. Field description of fracture-vug bodies; S2. Establish a database of the sizes of various types of fracture-vug bodies; S3. Fit the calculation formula for the main body of the karst cave; S4. Determine the width of the fracture zone; S5. Estimate the height of the main body of the karst cave; S6. Correct the estimated height of the main body of the karst cave, and interpret the inner and outer zone radii through well testing; S7. Extract the height of a single fracture-vug body from seismic data; S8. Fit the correction coefficient or correction formula for seismic fracture-vug bodies; S9. Determine the size of the fracture-vug body.

[0031] The specific steps are described in detail as follows: S1. Field description of fracture-vug bodies; Search for outcrops of buried-hill karst fracture-vug bodies or interlayer karst fracture-vug bodies formed under the same conditions in the study area, conduct field reconnaissance, accurately measure the length, width, and height of the buried-hill karst fracture-vug bodies or interlayer karst fracture-vug bodies, and accurately measure the length, width, and height of the fracture zone and the main body of the karst cave of the buried-hill karst fracture-vug bodies or interlayer karst fracture-vug bodies.

[0032] S2. Establish a database of the sizes of various types of fracture-vug bodies; Classify and process the length, width, and height of the buried-hill karst fracture-vug bodies or interlayer karst fracture-vug bodies accurately measured during field reconnaissance according to different karst types, and establish a database of the sizes of fracture-vug bodies of each karst type.

[0033] S3. Fit the calculation formula for the main body of the karst cave; Use the length, width, and height of the fracture zone and the main body of the karst cave of the buried-hill karst fracture-vug bodies or interlayer karst fracture-vug bodies measured from outcrops to establish a crossplot of the height of the main body of the karst cave and the width of the fracture zone for various types of karst fracture-vug bodies, and fit and determine the calculation formula for the height of the main body of the karst cave and the width of the fracture zone (abbreviation: Formula 1, and each study area needs to refit this calculation formula according to the measured data).

[0034] S4. Determine the width of the fracture zone; Use logging data to statistically analyze the top and bottom depths of abnormal drilling (leakage, gas invasion, gas gush, overflow, etc.) in the fracture zone during the drilling process, use well logging data to finely interpret the top and bottom depths of the fracture zone, and accurately determine the position and width of the fracture zone within a single fracture-vug body.

[0035] S5. Estimate the height of the main body of the karst cave; Use Formula 1 to calculate the height of the main body of the karst cave of a single fracture-vug body.

[0036] S6. Estimate the correction of the main height of the karst cave; using well test data, interpret the radii of the inner and outer regions of the fracture-cave body, compare the outer region radius with the width of the fractured zone, and compare the inner region radius with the estimated size of the main karst cave, then correct the estimated size of the main karst cave and the fracture-cave body.

[0037] S7. Extract the height of a single fracture-cave body from seismic data; using the quantitative carving technology for seismic fracture-cave bodies, carve the spatial distribution of the fracture-cave bodies (abbreviation: seismic fracture-cave carved body), extract the height of each single fracture-cave body, and establish a database of the heights of seismic fracture-cave bodies.

[0038] S8. Fit the correction coefficient or correction formula for the seismic fracture-cave body; using the height of each single fracture-cave body extracted from the quantitative carving body of the seismic fracture-cave and the height of the same single fracture-cave body calculated previously, establish a crossplot, and fit to determine the correction coefficient or correction formula for the carved body of the seismic fracture-cave body (abbreviation: Formula 2, and each research area needs to re-fit this calculation formula according to the measured data).

[0039] S9. Determine the size of the fracture-cave body; using the correction coefficient or correction formula for the carved body of the seismic fracture-cave, correct the carved body of the seismic fracture-cave to obtain the accurate size of the fracture-cave body, so as to finely depict the scale of the fracture-cave body.

[0040] Example 3 As another preferred embodiment of the present invention, in this method embodiment, a certain gas field in Xinjiang is selected. When drilling encounters buried hill karst fracture-cave bodies or interlayer karst fracture-cave bodies, serious lost circulation or blowout will occur, making it difficult to maintain drilling, resulting in early completion of drilling, and logging cannot be carried out. Therefore, it is very difficult to completely drill through large buried hill karst fracture-cave bodies or interlayer karst fracture-cave bodies through drilling to determine the scale of such fracture-cave bodies.

[0041] After research, under the action of the overlying pressure, the upper part and the surrounding strata of the karst cave in the buried hill karst fracture-cave body or the interlayer karst fracture-cave body will form a fractured zone under the action of stress. We divide the buried hill karst fracture-cave body or the interlayer karst fracture-cave body into three zones: the main karst cave, the fractured zone, and the surrounding rock (as Figure 2 shown).

[0042] Through field exploration in this area, accurately measure the length, width, and height of the buried hill karst fracture-cave body or the interlayer karst fracture-cave body, and accurately measure the length, width, and height of the fractured zone and the main karst cave of the buried hill karst fracture-cave body or the interlayer karst fracture-cave body. Classify and process the length, width, and height of the buried hill karst fracture-cave body or the interlayer karst fracture-cave body accurately measured through field exploration according to different karst types, and establish a database of the sizes of fracture-cave bodies of each karst type.

[0043] Using the length, width, and height of the fractured zone and the main karst cave of the buried hill karst fracture-cave body or the interlayer karst fracture-cave body measured from the field outcrop, establish a crossplot of the height of the main karst cave and the width of the fractured zone of various karst fracture-cave bodies (as Figure 3As shown in the figure, the calculation formula for fitting and determining the height of the main body of the karst cave and the width of the fractured zone is: height of the main body of the karst cave = -0.6629 * proportion of the fractured zone + 79.01 (Formula 1). Then, using the logging data of this gas field, the top and bottom depths of drilling anomalies (such as lost circulation, gas invasion, gas kick, overflow, etc.) in the fractured zone during the drilling process are statistically analyzed. The top and bottom depths of the fractured zone are finely interpreted using logging data to accurately determine the position and width of the fractured zone within a single fracture-cavity body. Using Formula 1, the height of the main body of the karst cave in a single fracture-cavity body is calculated (Table 1).

[0044] Table 1 Estimation data table of the height of fracture-cavity bodies encountered in a single well of a certain oil and gas field Using the seismic fracture-cavity body quantitative carving technology, the spatial distribution of fracture-cavity bodies (abbreviation: seismic fracture-cavity carving body) is carved, the height of each individual fracture-cavity body is extracted, and a seismic fracture-cavity body height database is established.

[0045] Using the height of each individual fracture-cavity body extracted from the seismic fracture-cavity quantitative carving body and the height of the same individual fracture-cavity body calculated previously, a crossplot is established to fit and determine the correction coefficient or correction formula for the seismic fracture-cavity carving body (abbreviation: Formula 2, for reference, see Figure 4 )

[0046] Height of the seismic fracture-cavity carving body = 0.4962 * height of the fracture-cavity body calculated from logging and surveying (Formula 2) Using the correction formula for the seismic fracture-cavity carving body, the seismic fracture-cavity carving body is corrected to obtain the accurate size of the fracture-cavity body (Table 2). The volume of the corrected fracture-cavity body is more consistent with the actual situation, thereby finely depicting the scale of the fracture-cavity body.

[0047] Table 2 Estimation data table of the height of fracture-cavity bodies encountered in a single well of a certain oil and gas field .

[0048] Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An evaluation method for estimating the size of the main body of solution caves in karst fractured-vuggy carbonate reservoirs using the width of the fracture zone, which is characterized in that: This method includes the following steps, S1. Field description step of fractured-vuggy bodies: Search for the outcrops of fractured-vuggy bodies formed under the same conditions as the study area and conduct field reconnaissance; measure the size of the main body of the solution cave in the fractured-vuggy body and measure the width of the fracture zone of the fractured-vuggy body; S2. Step of fitting the calculation formula for the main body of the solution cave: Using the size of the main body of the solution cave in the fractured-vuggy body and the width of the fracture zone of the fractured-vuggy body measured in step S1, establish a crossplot of the size of the main body of the solution cave and the width of the fracture zone, and fit to determine the calculation formula for the height of the main body of the solution cave and the width of the fracture zone; S3. Step of determining the width of the fracture zone of the fractured-vuggy body in the study area: Use the logging data of the study area to statistically analyze the top and bottom depths of abnormal drilling in the fracture zone during the drilling process; then use the survey data of the study area to finely interpret the top and bottom depths of the fracture zone to determine the position and width of the fracture zone within a single fractured-vuggy body; S4. Step of estimating the height of the main body of the solution cave of the fractured-vuggy body in the study area: Using the calculation formula for the height of the main body of the solution cave and the width of the fracture zone determined by fitting in step S2, and the width of the fracture zone within a single fractured-vuggy body determined in step S3, calculate the height of the main body of the solution cave of a single fractured-vuggy body; S5. Step of extracting the height of the solution cave of a single fractured-vuggy body from seismic data: Use the seismic quantitative carving technology for fractured-vuggy bodies to carve the spatial distribution of fractured-vuggy bodies and extract the height of a single fractured-vuggy body; S6. Step of fitting the correction coefficient of the seismic fractured-vuggy body: Using the height of a single fractured-vuggy body extracted in step S5 and the height of the main body of the solution cave of a single fractured-vuggy body calculated in step S4, establish a crossplot and fit to determine the correction coefficient of the seismic fractured-vuggy carved body; S7. Step of determining the size of the solution cave of the fractured-vuggy body: Use the correction coefficient of the seismic fractured-vuggy carved body obtained in step S6 to correct the seismic fractured-vuggy carved body to obtain the accurate size of the fractured-vuggy body, thereby finely depicting the scale of the fractured-vuggy body.

2. The evaluation method for estimating the size of the main body of solution caves in karst fractured-vuggy carbonate reservoirs using the width of the fracture zone as described in claim 1, which is characterized in that: It further includes the step of establishing a database for the size of the main body of solution caves of various types of fractured-vuggy bodies. Classify and process the size of the main body of the solution cave and the width of the fracture zone of the fractured-vuggy bodies measured during field reconnaissance according to different karst types, and establish a database for the size of the main body of the solution cave of the fractured-vuggy bodies of each karst type.

3. The evaluation method for estimating the size of the main body of solution caves in karst fractured-vuggy carbonate reservoirs using the width of the fracture zone as described in claim 2, which is characterized in that: In step S2, according to the size of the main body of the solution cave of the fractured-vuggy bodies of each karst type and the corresponding width of the fracture zone in the database for the size of the main body of the solution cave of the fractured-vuggy bodies of each karst type, establish a crossplot of the size of the main body of the solution cave and the width of the fracture zone of the fractured-vuggy bodies of each karst type, and fit to determine the calculation formula for the height of the main body of the solution cave and the width of the fracture zone of the fractured-vuggy bodies of each karst type.

4. The evaluation method for estimating the size of the main body of solution caves in karst fractured-vuggy carbonate reservoirs using the width of the fracture zone as described in any one of claims 1 - 3, which is characterized in that: In step S5, using the seismic fracture-vug body quantitative carving technology, the spatial distribution of the fracture-vug body is carved to form a seismic fracture-vug carved body, and the karst cave main body height of each individual fracture-vug body is extracted from the seismic fracture-vug carved body to establish a database of the karst cave main body height of the seismic fracture-vug body.

5. The evaluation method for estimating the karst cave main body size of a karst fracture-vug type carbonate reservoir using the fracture zone width as claimed in claim 4, characterized in that: In step S6, using the karst cave main body height of each individual fracture-vug body in the karst cave main body height database of the seismic fracture-vug body and the karst cave main body height of the corresponding individual fracture-vug body calculated in step S4, a cross plot is established, and a correction coefficient of the seismic fracture-vug carved body is obtained by fitting.

6. The evaluation method for estimating the karst cave main body size of a karst fracture-vug type carbonate reservoir using the fracture zone width as claimed in any one of claims 1-3, characterized in that: In step S4, it further includes a step of correcting the estimated karst cave main body height of an individual fracture-vug body. Specifically, using well test data, the radii of the inner and outer regions of the fracture-vug body are interpreted, the outer region radius is compared and analyzed with the fracture zone, and the inner region radius is compared and analyzed with the estimated karst cave main body size of the individual fracture-vug body to correct the estimated karst cave main body height.

7. The evaluation method for estimating the karst cave main body size of a karst fracture-vug type carbonate reservoir using the fracture zone width as claimed in any one of claims 1-3, characterized in that: The types of fracture-vug bodies include buried hill karst fracture-vug bodies and interlayer karst fracture-vug bodies.

8. The evaluation method for estimating the karst cave main body size of a karst fracture-vug type carbonate reservoir using the fracture zone width as claimed in any one of claims 1-3, characterized in that: The karst cave main body size includes the length, width and height of the karst cave main body.

9. The evaluation method for estimating the karst cave main body size of a karst fracture-vug type carbonate reservoir using the fracture zone width as claimed in any one of claims 1-3, characterized in that: In step S3, the drilling anomalies include any one of loss of circulation, gas invasion, gas kick and overflow.

10. The evaluation method for estimating the karst cave main body size of a karst fracture-vug type carbonate reservoir using the fracture zone width as claimed in any one of claims 1-3, characterized in that: In step S2, the calculation formula for fitting and determining the karst cave main body height and the fracture zone width is expressed as y = a * x + b, where y represents the estimated karst cave main body height of an individual fracture-vug body, x represents the proportion of the fracture zone, and a and b represent coefficients.

11. The evaluation method for estimating the karst cave main body size of a karst fracture-vug type carbonate reservoir using the fracture zone width as claimed in any one of claims 1-3, characterized in that: In step S6, the correction coefficient of the seismic fracture-vug carved body obtained by fitting and determination is expressed as z = c * y, where c represents the correction coefficient, z represents the karst cave main body height of the seismic fracture-vug carved body, and y represents the estimated karst cave main body height of an individual fracture-vug body.

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