A method for establishing a water-invaded gas reservoir map with heterogeneous fractures and caves

Abstract

The present invention discloses a method for establishing a water-invaded gas reservoir map with heterogeneous fracture-cavity development, comprising the following steps: S1, conducting a depletion experiment simulation development process on large-scale rock samples of pore-cavity type, fracture-cavity type and fracture-cavity type; S2, analyzing the distribution of pores, fractures and caves of the rock samples through CT scanning, calculating the proportion of pores, fractures and caves in the rock samples and the contribution rate to the permeability of the target reservoir, as well as the dimensionless heterogeneity coefficient of the volume proportion product; S3, establishing a prediction model for the amount of water and the amount of natural gas sealed by fractures, matrix and caves; S4, establishing a material balance equation for closed gas reservoirs, and establishing a water-invaded gas reservoir identification map relationship based on the material balance equation, which is used to predict the water invasion response law of the target gas reservoir. The water-invaded gas reservoir identification map established by the present invention is more in line with the actual situation, has a more accurate fitting, is easy to apply on site, and is more suitable for the recognition of water invasion in actual gas reservoirs.

Description

Technical Field

[0001] The invention relates to the technical field of natural gas reservoir development, and in particular to a method for establishing a water-invaded gas reservoir map with heterogeneous fractures and caves. Background Art

[0002] my country has rich reserves of carbonate gas reservoirs, which are often accompanied by bottom water or edge water. During the development process, water intrusion often occurs in gas reservoirs. Because the development degree of fractures and caves in carbonate gas reservoirs varies, bottom water and edge water have different effects on the recovery degree of gas reservoirs, and form different characteristics of pressure response in the production process. Many scholars at home and abroad have conducted different degrees of analysis on the water-sealed gas in heterogeneous water-invaded gas reservoirs. From the perspective of the impact of water-sealed gas on production, many researchers pointed out that when stratum water invades gas reservoirs, the gas reservoirs will experience the phenomenon of "water-sealed gas" due to the influence of abnormally high pressure, and the mining effect of the gas reservoirs will be seriously damaged, and the recovery rate and recovery degree will be seriously reduced. Most scholars calculate and judge the factors of water-sealed gas in gas reservoirs based on on-site production data combined with material balance equations. In recent years, many studies have considered dividing the high-permeability and low-permeability areas of large heterogeneous gas reservoirs, and considering the fracture density. On the basis of assuming that fractures, matrix, small pores and wellbore are evenly distributed physical models, a water-sealed gas material balance equation considering the heterogeneity coefficient is established. However, the heterogeneous gas reservoir model considered in this model is relatively idealized and theoretical, lacking consideration of the multi-morphology and intricate connectivity of fracture-cavity development in actual reservoirs, and ignoring the possibility that fracture-cavity space may also be closed by micropores and matrix. It is slightly insufficient for reference in actual gas reservoirs. Therefore, it is very necessary to study a method for establishing a water-invaded gas reservoir map with heterogeneous fracture-cavity development. Summary of the invention

[0003] The purpose of the present invention is to provide a method for establishing a water-invaded gas reservoir map with heterogeneous fractures and caves, and to establish a water-invaded gas reservoir identification map by establishing a heterogeneous coefficient and combining the material balance equation of a closed gas reservoir.

[0004] To achieve the above object, the present invention provides the following technical solution: a method for establishing a water-invaded gas reservoir map with heterogeneous fracture-cavity development, comprising the following steps:

[0005] S1. When simulating the presence of water bodies of different multiples for large-scale rock samples of hole-type, fracture-type and fracture-cavity type, the water invasion process is simulated by mining at a fixed gas production rate, and various measured parameters are recorded: bottom hole pressure, wellhead gas flow rate, and cumulative gas production;

[0006] S2. Analyze the distribution of pores, cracks and caves in rock samples through CT scanning, calculate the proportion of pores, cracks and caves in rock samples and their contribution to the permeability of target reservoirs, as well as the dimensionless heterogeneity coefficient of volume proportion product;

[0007] S3. Establish a prediction model for the amount of water and natural gas trapped in fractures, matrix and caves;

[0008] S4. Establish a material balance equation for a closed gas reservoir, and establish a water-invaded gas reservoir identification chart relationship based on the material balance equation to predict the water invasion response law of the target gas reservoir.

[0009] In some embodiments, in S2, the proportion of pores, cracks, and caves in the rock sample is:

[0010]

[0011] The contribution rate of the pores, fractures and caves in the rock sample to the permeability of the target reservoir is:

[0012]

[0013] In the formula, φ m is the pore ratio of the rock sample; φ f is the proportion of rock sample cracks; v A is the proportion of rock sample caves; m is the pore area, m 2 ; L is the length of the rock sample, m; V m is the pore volume, m 3 ; V P is the rock sample volume, m 3 ; A f is the crack area, m 2 ; V f is the crack volume, m 3 ; A v is the cave area, m 2 ; V v is the cave volume, m 3 ; is the contribution rate of rock sample porosity to the target reservoir permeability; is the contribution rate of rock sample fracture ratio to the target reservoir permeability; K is the contribution rate of the cave ratio of the rock sample to the permeability of the target reservoir; m Contribution to pore permeability, mD; K f Contribution to fracture permeability, mD; K v is the cave contribution permeability, mD; K is the rock sample permeability, mD.

[0014] In some embodiments, in S2, a dimensionless heterogeneity coefficient is established to characterize reservoir heterogeneity, and the dimensionless heterogeneity coefficient is:

[0015]

[0016] In the formula, φ mis the pore ratio of the rock sample; φ f is the proportion of rock sample cracks; v is the proportion of rock sample caves; is the contribution rate of rock sample porosity to the target reservoir permeability; is the contribution rate of rock sample fracture ratio to the target reservoir permeability; is the contribution rate of the cave ratio in the rock sample to the permeability of the target reservoir.

[0017] In some embodiments, in S3, the prediction model is:

[0018]

[0019] in,

[0020]

[0021] Where W f is the volume of water in the rock sample fractures to isolate the natural gas, m 3 ; W v is the volume of water that seals the natural gas in the rock sample cave, m 3 ; W m is the volume of water that seals the natural gas in the rock matrix, m 3 ; W e is the water intrusion, m 3 ; W P is the water production, m 3 ; B w is the formation water volume coefficient, dimensionless; φ K is the connected porosity of the rock sample, a decimal; φ is the porosity of the rock sample, a decimal; φ S is the unconnected porosity, a decimal; W B is the volume of water that seals the natural gas, m 3 .

[0022] In some embodiments, the volume of water in the rock sample fractures, matrix, and caves that seal the natural gas is:

[0023]

[0024] in,

[0025]

[0026] Where W f is the volume of water in the rock sample fractures to isolate the natural gas, m 3 ; W v is the volume of water that seals the natural gas in the rock sample cave, m 3 ; W m is the volume of water that seals the natural gas in the rock matrix, m 3 ; W eis the water intrusion, m 3 ; W P is the water production, m 3 ; B w is the formation water volume coefficient, dimensionless; q f is the flow rate in the fracture area of ​​the rock sample, m 3 / d;q m is the flow rate in the rock matrix area, m 3 / d;q v is the flow rate in the cave area of ​​the rock sample, m 3 / d;A f is the crack area, m 2 ; K f Contribution permeability to fractures, mD; μ w is the formation water viscosity, cp; ΔP is the production pressure difference, MPa; L is the length of the rock sample, m; A m is the pore area, m 2 ; K m Contribution to pore permeability, mD; A v is the cave area, m 2 ; K v Contribution to cave permeability, mD.

[0027] In some embodiments, in S4, the material balance equation of the closed gas reservoir is:

[0028]

[0029] The relationship between the water invasion gas reservoir identification chart and the water invasion gas reservoir identification chart is:

[0030]

[0031] In the formula, φ K is the connected porosity of the rock sample; A is the given heterogeneity coefficient, dimensionless; R is the recovery degree, dimensionless; B is the water invasion constant; G is the geological reserves, m 3 ; G B is the gas volume in the water-sealed gas area, m 3 ; G P is the cumulative output, m 3 ; B g is the gas volume coefficient, dimensionless; B gi is the original gas volume coefficient, dimensionless; C w is the formation water compressibility coefficient, dimensionless; S wi is the original bound water saturation, dimensionless; C f is the comprehensive compression coefficient, dimensionless; p i is the original formation pressure, MPa; p is the current formation pressure, MPa; W e is the water intrusion, m 3 ; WP is the water production, m 3 ; B w is the formation water volume coefficient, dimensionless.

[0032] In some embodiments, the calculation expression of the gas volume in the water-sealed gas area is:

[0033]

[0034] Where W B is the volume of water that seals the natural gas, m 3 ; φ m is the pore ratio of the rock sample; φ f is the proportion of rock sample cracks; v B is the proportion of rock sample caves; gi is the original gas volume coefficient, dimensionless.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention establishes a heterogeneity coefficient and combines it with the material balance equation of a closed gas reservoir to establish a water-invaded gas reservoir identification chart that is more in line with the actual situation, has a more accurate fit, is easy to apply on site, and is more suitable for the recognition of water intrusion in actual gas reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic diagram of the structure of an experimental device according to an embodiment of the present invention;

[0038] Figure 2 This is a schematic diagram of a large-scale core CT scan according to an embodiment of the present invention;

[0039] Figure 3 This is a schematic diagram of a crack-hole type water intrusion indication curve according to an embodiment of the present invention;

[0040] Figure 4 Schematic diagram of water invasion diagram of an embodiment of the present invention; wherein, in Figure (a), the heterogeneity coefficient A = 0.2, the water invasion constant B = 1; in Figure (b), the heterogeneity coefficient A = 0.5, the water invasion constant B = 1; in Figure (c), the heterogeneity coefficient A = 0.8, the water invasion constant B = 1; in Figure (d), the heterogeneity coefficient A = 0.2, the rock sample connected porosity φ K = 0.5; in Figure (e), the heterogeneity coefficient A = 0.5, the rock sample connected porosity φ K = 0.5; in Figure (f), the heterogeneity coefficient A = 0.5, the rock sample connected porosity φ k =0.5.

[0041] As shown in the figure:

[0042] 1. Large-scale core holder, 2. Gas intermediate container, 3. Water intermediate container, 4. Constant temperature oven, 5. Confining pressure pump, 6. Displacement pump, 7. Back pressure pump, 8. Gas flow meter, 9. Gas-water separator, 10. Computer, 11. Three-way valve, 12. Pressure sensor, 13. Back pressure valve, 14. Electronic balance. DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0044] See also Figure 1 - Figure 4 A method for establishing a water-invaded gas reservoir map with heterogeneous fractures and caves includes the following steps:

[0045] S1. Conduct depletion experiments on large-scale rock samples of pore, fracture and fracture-cavity types to simulate the development process;

[0046] like Figure 1 As shown, the experimental device includes a large-scale core holder 1, the bottom of which is connected to an intermediate gas container 2 and an intermediate water container 3 via a three-way valve 11, and the other ends of the intermediate gas container 2 and the intermediate water container 3 are connected to a displacement pump 6.

[0047] The large-scale core holder 1, the gas intermediate container 2 and the water intermediate container 3 are all arranged in a constant temperature oven to simulate the real temperature of the reservoir.

[0048] One end of the large-scale core holder 1 is connected to a confining pressure pump 5, and the other end is connected to a gas-water separator 9 through a back pressure valve 13, and a back pressure pump is also connected to the back pressure valve 13. The gas-water separator 9 is arranged on an electronic balance 14, and a gas flow meter 8 is arranged at the outlet end of the gas-water separator.

[0049] The electronic balance 14 is connected to a computer 10. The computer 10 is connected to the pipeline between the large-scale core holder 1 and the back pressure valve 13, and the pipeline between the large-scale core holder 1 and the three-way valve 11 through two pressure sensors 12, respectively.

[0050] The exhaustion experiment simulation development process includes the following steps:

[0051] The experiment used large-scale rock samples of 30cm×30cm×20cm hole-type, fracture-type and fracture-cave type to simulate the development process of bottom water gas reservoirs. An intermediate container with 2, 4, 6 and 8 times of water was connected to the bottom of the large-scale core holder 1 to simulate bottom water. After the large-scale rock sample was inserted into the water saturation monitoring probe, it was loaded into the rubber sleeve in the large-scale core holder and pressurized with water from the bottom of the rock sample. After saturated water, high-purity nitrogen was slowly driven from the top of the rock sample to the bound water state at a low flow rate. The rock sample was saturated with nitrogen to 20MPa, and dimethyl silicone oil was pressurized and injected around the rubber sleeve wrapped around the rock sample as a confining pressure of 30MPa. A perforated high-pressure pipe with a length of 5cm and an inner diameter of 0.3cm was lowered to the top of the rock sample as a wellbore. After the pressure difference was established at the upper and lower ends of the rock sample, the bottom water was connected to simulate bottom water invasion, and the depletion experiment was carried out in a constant flow mining mode of 200mL / min.

[0052] Record the pressure and cumulative gas production respectively, and obtain the pseudo pressure by calculation The relationship curve with the recovery degree R, that is, the water invasion curve;

[0053]

[0054] Where p is the current formation pressure, MPa; Z is the gas compression factor under the current formation pressure, dimensionless; p i is the original formation pressure, MPa; Z i is the gas compression factor at the original formation pressure, dimensionless; B gi is the original gas volume coefficient, dimensionless; B g is the gas compressibility coefficient at the current formation pressure, dimensionless.

[0055] S2. Analyze the distribution of pores, cracks and caves in rock samples through CT scanning, calculate the proportion of pores, cracks and caves in rock samples and their contribution to the permeability of target reservoirs, as well as the dimensionless heterogeneity coefficient of volume proportion product;

[0056] like Figure 2 As shown in Table 1, CT scanning is used to analyze the pore and cave structure of the digital rock sample, and the relevant parameters in the digital rock sample are obtained.

[0057] Table 1 Rock sample medium parameters

[0058]

[0059] Considering that bottom water gas reservoirs are replenished with bottom water energy during gas production, bottom water rocks with good connectivity may penetrate into the pores during pressure drop, forming water-locked gas. Based on the material balance model considering water-locked gas, the mass conservation principle of the proportion of pores, fractures and vugs and the proportion of connected pores is characterized respectively, and the material balance equation of water-locked gas considering the proportion of pores, fractures and vugs and the proportion of connected pores is established.

[0060] The proportion of pores, cracks and caves in rock samples is defined as:

[0061]

[0062]

[0063] The contribution rate of the pores, fractures and caves in the rock sample to the permeability of the target reservoir is:

[0064]

[0065] In the formula, φ m is the pore ratio of the rock sample; φ f is the proportion of rock sample cracks; v A is the proportion of rock sample caves; m is the pore area, m 2 ; L is the length of the rock sample, m; V m is the pore volume, m 3 ; V P is the rock sample volume, m 3 ; A f is the crack area, m 2 ; V f is the crack volume, m 3 ; A v is the cave area, m 2 ; V v is the cave volume, m 3 ; is the contribution rate of rock sample porosity to the target reservoir permeability; is the contribution rate of rock sample fracture ratio to the target reservoir permeability; K is the contribution rate of the cave ratio of the rock sample to the permeability of the target reservoir; m Contribution to pore permeability, mD; K f Contribution to fracture permeability, mD; K v is the cave contribution permeability, mD; K is the rock sample permeability, mD.

[0066] S3. Establish a prediction model for the amount of water and natural gas trapped in fractures, matrix and caves;

[0067] The flow equation for the intrusion into the fracture, matrix, and cave areas of the rock sample is:

[0068]

[0069] In the formula, q f is the flow rate in the fracture area of ​​the rock sample, m 3 / d;q m is the flow rate in the rock matrix area, m 3 / d;qv is the flow rate in the cave area of ​​the rock sample, m 3 / d;A f is the crack area, m 2 ; K f Contribution permeability to fractures, mD; μ w is the formation water viscosity, cp; ΔP is the production pressure difference, MPa; L is the length of the rock sample, m; A m is the pore area, m 2 ; K m Contribution to pore permeability, mD; A v is the cave area, m 2 ; K v Contribution to cave permeability, mD.

[0070] Then, the amount of water in the rock sample fractures, matrix, and caves that seal the natural gas is obtained as:

[0071]

[0072] Where W e is the water intrusion, m 3 ; W P is the water production, m 3 ; B w is the formation water volume coefficient, dimensionless.

[0073] According to the pore volume ratio of pores, fractures and caves, the amount of water that isolates natural gas is the water volume that invades the connected fracture-cave space (φ K ) The water volume of the reservoir is calculated as:

[0074]

[0075] Among them, φ K is the porosity ratio of the connected fracture-hole space:

[0076]

[0077] Substituting formulas (11), (12), and (13) into formula (14), we have:

[0078]

[0079] From the large-scale fixed water body depletion production water invasion experiment, it is found that the water intrusion and the formation of water-locked gas are not only related to the heterogeneity of the core and reservoir, but also the main seepage channel is the well-connected fracture-cavity space in the core (φ K ), that is, the more connected fractures and pores there are in the reservoir, the stronger the water-sealed gas in the matrix pores will be.

[0080] The volume of water that seals the natural gas is W B for:

[0081]

[0082] Gas volume G in water-sealed gas area B The volume of water W that isolates the natural gas B The relationship between the high permeability crack space and the low permeability small hole space is established as follows:

[0083]

[0084] In the formula, B gi is the original gas volume coefficient, dimensionless.

[0085] Substituting formula (17) into formula (18), the gas volume G in the water-sealed gas area is B The volume of water W that isolates the natural gas B The relationship is:

[0086]

[0087] A dimensionless heterogeneity coefficient is established to characterize the reservoir heterogeneity by considering the contribution rate and volume ratio of pores, fractures and caves to the permeability of the target reservoir:

[0088]

[0089] S4. Establish a material balance equation for a closed gas reservoir, and establish a water-invaded gas reservoir identification chart relationship based on the material balance equation to predict the water invasion response law of the target gas reservoir.

[0090] The material balance equation of the closed gas reservoir is:

[0091]

[0092] The relationship established by converting the material balance equation into the water invasion gas reservoir identification chart is:

[0093]

[0094] In the formula, φ K is the connected porosity of the rock sample; A is the given heterogeneity coefficient, dimensionless; R is the recovery degree, dimensionless; B is the water invasion constant; G is the geological reserves, m 3 ; G B is the gas volume in the water-sealed gas area, m 3 ; G P is the cumulative output, m 3 ; B g is the gas volume coefficient, dimensionless; B gi is the original gas volume coefficient, dimensionless; C w is the formation water compressibility coefficient, dimensionless; Swi is the original bound water saturation, dimensionless; C f is the comprehensive compression coefficient, dimensionless; p i is the original formation pressure, MPa; p is the current formation pressure, MPa; W e is the water intrusion, m 3 ; W P is the water production, m 3 ; B w is the formation water volume coefficient, dimensionless.

[0095] The heterogeneity coefficient of the target core is obtained by using the heterogeneity coefficient calculation formula, as shown in Table 2. The water invasion curve of the corresponding core is obtained by combining the material balance equation, and the experimental results are fitted with the material balance calculation results. The fitting results are relatively matched and can reflect the real water invasion response chart of the large-scale core. It verifies that the established heterogeneity coefficient calculation method and water invasion chart can accurately predict the water invasion response law of the gas reservoir.

[0096] Table 2 Heterogeneity parameters of rock samples

[0097]

[0098] When the heterogeneity coefficient A and the connected porosity φ are given K , water invasion constant B, we can create the corresponding chart, such as Figure 3 - Figure 4 By obtaining the heterogeneity, connectivity and water energy of the corresponding gas reservoir, the water invasion characteristics and ultimate recovery rate of different types of heterogeneous gas reservoirs can be better predicted through the chart.

Claims

1. A method for establishing a water-invaded gas reservoir map with heterogeneous fractures and caves, characterized in that: The following steps are involved: S1. Conduct depletion experiments on large-scale rock samples of hole-type, fracture-type and fracture-cavity type to simulate the development process; S2. Analyze the distribution of pores, cracks and caves in the rock sample through CT scanning, calculate the proportion of pores, cracks and caves in the rock sample and their contribution to the permeability of the target reservoir, as well as the dimensionless heterogeneity coefficient of the volume proportion product; the dimensionless heterogeneity coefficient is: In the formula, φ m is the pore ratio of the rock sample; φ f is the proportion of rock sample cracks; v is the proportion of rock sample caves; is the contribution rate of rock sample porosity to the target reservoir permeability; is the contribution rate of rock sample fracture ratio to the target reservoir permeability; is the contribution rate of the cave ratio of the rock sample to the permeability of the target reservoir; S3. Establish a prediction model for the amount of water and natural gas trapped in fractures, matrix and caves: in, Where W f is the volume of water in the rock sample fractures to isolate the natural gas, m 3 ; W v is the volume of water that seals the natural gas in the rock sample cave, m 3 ; W m is the volume of water that seals the natural gas in the rock matrix, m 3 ; W e is the water intrusion, m 3 ; W P is the water production, m 3 ; B w is the formation water volume coefficient, dimensionless; φ K is the connected porosity of the rock sample, a decimal; φ is the porosity of the rock sample, a decimal; φ S is the unconnected porosity, a decimal; W B is the volume of water that seals the natural gas, m 3 ; S4. Establish a material balance equation for a closed gas reservoir, and establish a water invasion gas reservoir identification chart relationship based on the material balance equation to predict the water invasion response law of the target gas reservoir; the material balance equation for the closed gas reservoir is: The relationship between the water invasion gas reservoir identification chart and the water invasion gas reservoir identification chart is: In the formula, φ K is the connected porosity of the rock sample; A is the given heterogeneity coefficient, dimensionless; R is the recovery degree, dimensionless; B is the water invasion constant; G is the geological reserves, m 3 ; G B is the gas volume in the water-sealed gas area, m 3 ; G P is the cumulative output, m 3 ; B g is the gas volume coefficient, dimensionless; B gi is the original gas volume coefficient, dimensionless; C w is the formation water compressibility coefficient, dimensionless; S wi is the original bound water saturation, dimensionless; C f is the comprehensive compression coefficient, dimensionless; p i is the original formation pressure, MPa; p is the current formation pressure, MPa; W e is the water intrusion, m 3 ; W P is the water production, m 3 ; B w is the formation water volume coefficient, dimensionless.

2. The method for establishing a water-invaded gas reservoir map with heterogeneous fractures and caves according to claim 1 is characterized in that: In S2, the proportion of pores, cracks and caves in the rock sample is: The contribution rate of the pores, fractures and caves in the rock sample to the permeability of the target reservoir is: In the formula, φ m is the pore ratio of the rock sample; φ f is the proportion of rock sample cracks; v A is the proportion of rock sample caves; m is the pore area, m 2 ; L is the length of the rock sample, m; V m is the pore volume, m 3 ; V P is the rock sample volume, m 3 ; A f is the crack area, m 2 ; V f is the crack volume, m 3 ; A v is the cave area, m 2 ; V v is the cave volume, m 3 ; is the contribution rate of rock sample porosity to the target reservoir permeability; is the contribution rate of rock sample fracture ratio to the target reservoir permeability; K is the contribution rate of the cave ratio of the rock sample to the permeability of the target reservoir; m Contribution to pore permeability, mD; K f Contribution to fracture permeability, mD; K v is the cave contribution permeability, mD; K is the rock sample permeability, mD.

3. The method for establishing a water-invaded gas reservoir map with heterogeneous fractures and caves according to claim 1 is characterized in that: The volume of water in the rock sample fractures, matrix, and caves that seal the natural gas is: in, Where W f is the volume of water in the rock sample fractures to isolate the natural gas, m 3 ; W v is the volume of water that seals the natural gas in the rock sample cave, m 3 ; W m is the volume of water that seals the natural gas in the rock matrix, m 3 ; W e is the water intrusion, m 3 ; W P is the water production, m 3 ; B w is the formation water volume coefficient, dimensionless; q f is the flow rate in the fracture area of ​​the rock sample, m 3 / d;q m is the flow rate in the rock matrix area, m 3 / d;q v is the flow rate in the cave area of ​​the rock sample, m 3 / d;A f is the crack area, m 2 ; K f Contribution permeability to fractures, mD; μ w is the formation water viscosity, cp; ΔP is the production pressure difference, MPa; L is the length of the rock sample, m; A m is the pore area, m 2 ; K m Contribution to pore permeability, mD; A v is the cave area, m 2 ; K v Contribution to cave permeability, mD.

4. The method for establishing a water-invaded gas reservoir map with heterogeneous fractures and caves according to claim 1 is characterized in that: The calculation expression of the gas volume in the water-sealed gas area is: Where W B is the volume of water that seals the natural gas, m 3 ; φ m is the pore ratio of the rock sample; φ f is the proportion of rock sample cracks; v B is the proportion of rock sample caves; gi is the original gas volume coefficient, dimensionless.

Images