A method for identifying and evaluating cap natural gas capillary sealing mechanism

Abstract

The present application belongs to the technical field of oil and gas exploration and development, and discloses a kind of cap rock natural gas capillary sealing mechanism identification and evaluation method, including the judgment of cap rock natural gas capillary sealing mechanism based on multidimensional data;Cap rock natural gas capillary sealing mechanism evaluation model is constructed;Through density logging, neutron logging and acoustic logging data, gas-bearing layer is identified, and the gas saturation of gas-bearing layer is calculated through density logging and neutron logging data;The breakthrough pressure of sandstone and mudstone is calculated;Based on the number of layers of gas-bearing layer, gas saturation, sandstone breakthrough pressure and mudstone breakthrough pressure, cap rock natural gas capillary sealing mechanism evaluation model is substituted to obtain cap rock natural gas capillary sealing mechanism evaluation parameter.The present application can identify and evaluate the area that part of cap rock sealing capacity is less affected by physical property, overpressure and hydrocarbon concentration and mainly controlled by natural gas capillary sealing mechanism.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas exploration and development technology, and specifically relates to a method for identifying and evaluating the capillary closure mechanism of caprock natural gas. Background Technology

[0002] Caprocks are a key element in the formation of oil and gas reservoirs. Identifying and evaluating caprock sealing mechanisms is central to studying reservoir preservation, and favorable conditions for reservoir preservation are fundamental to the continued existence of deep oil and gas reservoirs. Currently, there are three main methods for evaluating caprock sealing capacity both domestically and internationally: caprock physical property sealing evaluation, caprock overpressure sealing evaluation, and caprock hydrocarbon concentration sealing evaluation. However, these methods are primarily applicable to areas with stable caprock distribution, large thickness, and predominantly physical property sealing, but not to caprocks with unstable distribution and small thickness; they are suitable for areas with strong caprock overpressure development and significantly greater overpressure than the reservoir overpressure, but not for areas with moderate caprock overpressure development and no significant difference in overpressure continuity between the reservoir and caprock; and they are suitable for areas with strong caprock hydrocarbon generation capacity, but not for areas with low organic matter abundance and weak hydrocarbon generation capacity in the caprock.

[0003] The capillary sealing mechanism of natural gas is a new sealing mechanism that is completely different from physical property sealing, overpressure sealing, and hydrocarbon concentration sealing. The existing three types of caprock sealing capacity evaluation methods are difficult to evaluate this mechanism. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention discloses a method for identifying and evaluating the capillary closure mechanism of caprock natural gas.

[0005] This invention is achieved through the following technical solution:

[0006] In a first aspect, a method for identifying and evaluating the capillary closure mechanism of caprock natural gas is characterized by comprising:

[0007] Natural gas capillary closure was identified based on multi-dimensional data;

[0008] Construct an evaluation model for the capillary closure mechanism of capillary natural gas;

[0009] Gas-bearing layers are identified using density logging, neutron logging, and sonic logging data, and the gas saturation of the gas-bearing layers is calculated using density logging and neutron logging data.

[0010] Calculate the breakthrough pressure of sandstone and mudstone;

[0011] The evaluation parameters for the capillary closure mechanism of natural gas in the caprock are obtained by substituting the number of gas-bearing layers, gas saturation, sandstone breakthrough pressure, and mudstone breakthrough pressure into the caprock natural gas capillary closure mechanism evaluation model.

[0012] In some embodiments, the multidimensional data includes lithological assemblage, source rock evolution, pressure system, and natural gas charging conditions.

[0013] In some embodiments, the lithological assemblage is the ratio of mudstone to stratum thickness in the caprock.

[0014] In some embodiments, the source rock evolution refers to the stages of source rock evolution in the study area.

[0015] In some embodiments, the pressure system is a developmental pressure storage box for the pressure system of the analysis study area.

[0016] In some embodiments, the natural gas charging situation is a comparison of the change in the caprock sealing capacity before and after natural gas charging.

[0017] In some embodiments, the formula for the capillary closure mechanism evaluation model of the caprock natural gas is:

[0018]

[0019] Where C represents the cumulative breakthrough pressure characterizing the sealing capacity of the caprock, in MPa; i represents the i-th gas layer; n represents the total number of gas layers; Pi mud Pi represents the breakthrough pressure of the i-th layer of mudstone; sand Indicates the breakthrough pressure of the i-th sandstone layer; Si g This represents the gas saturation of the i-th gas-bearing layer.

[0020] In some embodiments, a formula for identifying the gas-bearing layer is constructed:

[0021] A = Ф DEN +Ф AC -2Ф CN ;

[0022] B = (Ф DEN ×Ф AC ) / (Ф CN ×Ф CN );

[0023] Where A>0 and B>1, it represents a gas-bearing layer; Ф DEN Ф represents the porosity value calculated from density logging. AC Ф represents the porosity value calculated by acoustic logging. CN This represents the porosity value calculated using neutron logging.

[0024] In some embodiments, a formula for calculating the gas-bearing layer saturation is constructed:

[0025] S g =0.001×(Ф DEN -Ф CN)2+1.178×(Ф DEN -Ф CN +67.63;

[0026] Among them, S g This indicates the gas saturation of the gas-bearing layer, in %; Ф DEN This represents the porosity value calculated from density logging, in %; Ф CN This represents the porosity value calculated by neutron logging, in percentages (%).

[0027] In some embodiments, calculating the breakthrough pressure of the sandstone includes:

[0028] Establish the relationship between breakthrough pressure and porosity in sandstone:

[0029] P sand =24.80×Ф AC 0.82 ;

[0030] Among them, P sand Indicates the breakthrough pressure of sandstone, in MPa; Ф AC This indicates the porosity calculated from acoustic logging, expressed as a percentage (%).

[0031] Establish the relationship between mudstone permeability, porosity, and clay mineral content:

[0032]

[0033] Where K represents the mudstone permeability, in μm 2 , The value represents the porosity of mudstone, in %; CF represents the clay mineral content of mudstone, in %;

[0034] Establish the relationship between mudstone breakthrough pressure and mudstone permeability:

[0035] P mud =0.0903×K -0.638 ;

[0036] Among them, P mud K represents the mudstone breakthrough pressure, in MPa; K represents the mudstone permeability, in μm. 2 .

[0037] Compared with the prior art, the present invention has the following advantages:

[0038] 1. Improved the standards for identifying and evaluating the capillary sealing mechanism of capillary natural gas, and improved the method for quantitatively evaluating the capillary sealing capacity of natural gas;

[0039] 2. Through accurate closure capability assessment, risks during exploration and development can be reduced, economic losses can be minimized, and the return on investment can be increased;

[0040] 3. By establishing a systematic capillary closure evaluation model for caprock natural gas, which comprehensively considers multiple influencing factors such as the number of natural gas layers, gas saturation, and breakthrough pressure of mudstone and sandstone, the accuracy of closure capacity assessment has been significantly improved.

[0041] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing this information. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 This is a schematic diagram of a method for identifying and evaluating the capillary closure mechanism of caprock natural gas in this embodiment.

[0044] Figure 2 This is a numerical diagram of the mudstone ratio of the caprock strata around the western depression of Well 1 in the Junggar Basin in this embodiment.

[0045] Figure 3 This embodiment describes the hydrocarbon generation evolution stage and gas generation potential of the source rocks in the western depression of Well 1 in the Junggar Basin.

[0046] Figure 4 This is a profile of the pressure coefficient of key wells in the western depression of the Junggar Basin Basin 1 well in this embodiment.

[0047] Figure 5 This is a schematic diagram of the hydrocarbon content of different phases in the caprock of the West Depression of Well 1 in the Junggar Basin in this embodiment.

[0048] Figure 6 This is a schematic diagram of the capillary closure mechanism of natural gas in the caprock in this embodiment.

[0049] Figure 7 This is the gas-bearing layer identified by key wells in the western depression of the Junggar Basin Basin 1 well in this embodiment.

[0050] Figure 8 This is the gas saturation predicted by key wells in the western depression of the Junggar Basin Basin 1 well in this embodiment.

[0051] Figure 9This refers to the sandstone breakthrough pressure predicted by key wells in the western depression of the Junggar Basin Basin 1 well in this embodiment.

[0052] Figure 10 This is the mudstone breakthrough pressure calculated from key wells in the western depression of the Junggar Basin Basin 1 well in this embodiment.

[0053] Figure 11 This embodiment verifies the method for evaluating the natural gas breakthrough pressure in the caprock of the western depression surrounding Well 1 in the Junggar Basin. Detailed Implementation

[0054] The accompanying drawings are for illustrative purposes only and should not be construed as limiting this patent. To better illustrate this embodiment, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings. The positional relationships described in the drawings are for illustrative purposes only and should not be construed as limiting this patent.

[0055] like Figure 1 The method for identifying and evaluating the capillary closure mechanism of caprock natural gas, as shown, includes the following steps:

[0056] S1. Natural gas capillary closure is identified based on multi-dimensional data.

[0057] Specifically, the multi-dimensional data includes lithological assemblage, source rock evolution, pressure system, and natural gas charging conditions.

[0058] Furthermore, the lithological assemblage is an analysis of the lithological assemblage characteristics of sandstone and mudstone in the caprock strata. By statistically analyzing the ratio of mudstone to stratum thickness in the caprock strata, i.e. mudstone-to-land ratio, if the mudstone-to-land ratio is in the range of 0.3 to 0.7, it conforms to the characteristics of sandstone-mudstone interbedded layers. Therefore, the caprock sealing mechanism may be natural gas capillary sealing.

[0059] Furthermore, the source rock evolution is the stage of source rock evolution in the study area. If the source rock has entered the stage of large-scale gas generation, it meets the characteristics of relatively closed fluid, further confirming that the caprock sealing mechanism may be natural gas capillary sealing.

[0060] Furthermore, the pressure system described is the pressure system of the analysis and research area. If a pressure storage tank is developed, it conforms to the characteristics of relatively closed fluid, further increasing the possibility that the capillary sealing mechanism is natural gas capillary sealing.

[0061] Furthermore, the natural gas charging situation is determined by comparing the changes in the sealing capacity of the caprock before and after natural gas charging. If the sealing capacity of the caprock is significantly improved after natural gas charging, and considering the interlayering of sand and mud in the caprock, natural gas charging, and the relatively closed pressure system, combined with the significant improvement in the sealing mechanism of the caprock after natural gas charging, the sealing mechanism of the caprock can be identified as natural gas capillary sealing.

[0062] S2. Construct an evaluation model for the capillary closure mechanism of capillary natural gas in the caprock.

[0063] Specifically, a formula for evaluating the capillary closure of natural gas in the caprock is constructed:

[0064]

[0065] Where C represents the cumulative breakthrough pressure characterizing the sealing capacity of the caprock, in MPa; i represents the i-th gas layer; n represents the total number of gas layers; Pi mud Pi represents the breakthrough pressure of the i-th layer of mudstone; sand Indicates the breakthrough pressure of the i-th sandstone layer; Si g This represents the gas saturation of the i-th gas-bearing layer.

[0066] S3. Identify gas-bearing layers using density logging, neutron logging, and sonic logging data, and calculate the gas saturation of the gas-bearing layers using density logging and neutron logging data.

[0067] Specifically, a formula for identifying gas-bearing layers is constructed:

[0068] A = Ф DEN +Ф AC -2Ф CN (2)

[0069] B = (Ф DEN ×Ф AC ) / (Ф CN ×Ф CN (3)

[0070] Where A>0 and B>1, it represents a gas-bearing layer; Ф DEN Ф represents the porosity value calculated from density logging. AC Ф represents the porosity value calculated by acoustic logging. CN This represents the porosity value calculated using neutron logging. Gas-bearing layers are identified using the above formula, and the number of gas-bearing layers, i, is determined.

[0071] Furthermore, the formula for calculating gas saturation is as follows:

[0072] S g =0.001×(Ф DEN -Ф CN )2+1.178×(Ф DEN -ФCN )+67.63; (4)

[0073] Among them, S g This indicates the gas saturation of the gas-bearing layer, in %; Ф DEN This represents the porosity value calculated from density logging, in %; Ф CN This represents the porosity value calculated by neutron logging, in percentages (%).

[0074] S4. Calculate the breakthrough pressure of sandstone and mudstone.

[0075] Specifically, the relationship between sandstone breakthrough pressure and porosity is established:

[0076] (5)

[0077] Among them, P sand Indicates the breakthrough pressure of sandstone, in MPa; Ф AC This represents the porosity calculated using acoustic logging, expressed as a percentage.

[0078] Furthermore, the relationship between mudstone permeability and porosity and clay mineral content was established:

[0079]

[0080] Where K represents the mudstone permeability, in μm 2 , represents mudstone porosity, in %; CF represents mudstone clay mineral content, in %.

[0081] Then establish the relationship between mudstone breakthrough pressure and mudstone permeability:

[0082] P mud =0.0903×K -0.638 (7)

[0083] Among them, P mud K represents the mudstone breakthrough pressure, in MPa; K represents the mudstone permeability, in μm. 2 .

[0084] S5. Based on the number of gas-bearing layers, gas saturation, sandstone breakthrough pressure, and mudstone breakthrough pressure, the capillary closure mechanism evaluation model of caprock natural gas is substituted to obtain the caprock natural gas capillary closure mechanism evaluation parameters.

[0085] Specifically, the sealing units are divided according to the distribution of gas-bearing layers and the changes in gas saturation. If the sealing strength is negatively correlated with the fluorescence parameters of caprock particles, i.e. the hydrocarbon content in the caprock, it indicates that the stronger the sealing capacity of the caprock, the lower the hydrocarbon content in the caprock, thus evaluating the capillary sealing capacity of natural gas.

[0086] In a specific embodiment, taking the Carboniferous and Permian strata surrounding the western depression of Well 1 in the Junggar Basin as an example, the above method is applied to identify and evaluate the capillary sealing capacity of natural gas. The specific steps are as follows:

[0087] S1. Determine the capillary closure mechanism of natural gas in the caprock based on multi-dimensional data.

[0088] The statistical results of the Permian caprock mud-soil ratio in the western depression of Well 1 in the Junggar Basin are as follows: Figure 2 As shown, the mud-to-soil ratio ranges from 0.1 to 0.8, with the main distribution range being 0.3 to 0.7. Therefore, the mud-to-soil ratio values ​​conform to the lithological combination characteristics of interbedded sand and mud, laying the lithological combination foundation for the formation of the capillary sealing mechanism of natural gas in the caprock.

[0089] Furthermore, the evolution stages of source rocks in the study area were analyzed, and the current R of the Permian Fengcheng Formation source rocks in the western depression of Well 1 in the Junggar Basin were analyzed. o A value greater than 2.0% indicates an overripe stage, such as... Figure 3 As shown, the Permian Fengcheng Formation source rocks have entered a large-scale gas generation stage since the Jurassic period, with a high natural gas charging intensity, which laid the natural gas foundation for the formation of the capillary closure mechanism of natural gas in the caprock. Therefore, the caprock mechanism may be natural gas capillary closure.

[0090] Further analysis of the pressure system in the study area reveals that the western depression of Well 1 in the Junggar Basin mainly develops two pressure systems. The system below approximately 4500m is a normal pressure system, with the pressure coefficient gradually increasing, reaching its maximum at a depth of 5000m, at approximately 2.2. Figure 3 As shown, the development of pressure storage tanks in the study area conforms to the characteristics of relatively closed fluids, laying the foundation for the formation of capillary closure mechanism of natural gas in the caprock. Therefore, the caprock closure mechanism may be natural gas capillary closure.

[0091] Furthermore, comparing the changes in caprock sealing capacity before and after natural gas injection, such as... Figure 5 The hydrocarbons in the caprock are mainly medium and light oils, with almost no condensate oil. This indicates that a large amount of moisture during the condensate oil formation period may have entered the caprock, forming a caprock natural gas capillary closure. That is, the caprock closure mechanism is significantly enhanced after natural gas injection. Therefore, considering the interbedded sand and mud layers in the caprock, natural gas injection, and the relatively closed pressure system, combined with the significant enhancement of the caprock closure mechanism after natural gas injection, the caprock closure mechanism is identified as natural gas capillary closure.

[0092] S2. Construct an evaluation model for the capillary closure mechanism of capillary natural gas in the caprock.

[0093] The capillary closure of caprock natural gas is caused by the sealing mechanism resulting from the superposition effect of capillary forces induced by natural gas filling the caprock. Figure 6As shown, the capillary sealing capacity of caprock natural gas is positively correlated with the number of natural gas layers and the gas saturation; the more natural gas layers and the higher the gas saturation, the stronger the sealing capacity. Furthermore, the sealing capacity is also positively correlated with the difference between the breakthrough pressure of mudstone and the breakthrough pressure of sandstone; the larger the difference, the stronger the sealing capacity. Considering all the influencing factors of natural gas capillary sealing, the evaluation model for the caprock natural gas capillary sealing mechanism is defined as follows:

[0094]

[0095] Where C represents the cumulative breakthrough pressure characterizing the sealing capacity of the caprock, in MPa; i represents the i-th gas layer; n represents the total number of gas layers; Pi mud Pi represents the breakthrough pressure of the i-th layer of mudstone; sand This represents the breakthrough pressure of the i-th layer of sandstone.

[0096] S3. Identify gas-bearing layers using density logging, neutron logging, and sonic logging data, and calculate the gas saturation of the gas-bearing layers using density logging and neutron logging data.

[0097] Constructing a formula for identifying gas-bearing layers:

[0098] A = Ф DEN +Ф AC -2Ф CN (2)

[0099] B = (Ф DEN ×Ф AC ) / (Ф CN ×Ф CN (3)

[0100] Where A>0 and B>1, it represents a gas-bearing layer; Ф DEN Ф represents the porosity value calculated from density logging. AC Ф represents the porosity value calculated by acoustic logging. CN This represents the porosity value calculated by neutron logging. Based on the above formula, gas-bearing layers are identified, and the number of gas-bearing layers i is determined.

[0101] Key wells were selected around the western depression of Well 1 in the Junggar Basin to identify gas-bearing strata. Gas-bearing strata were identified according to formulas (2) and (3), determining that the number of gas-bearing strata in T1b was 10 and the number of gas-bearing strata in P3w was 3. Figure 7 As shown.

[0102] Furthermore, the formula for calculating gas saturation is as follows:

[0103] S g =0.001×(Ф DEN -Ф CN )2+1.178×(Ф DEN -ФCN )+67.63; (4)

[0104] Among them, S g This indicates the gas saturation of the gas-bearing layer, in %; Ф DEN This represents the porosity value calculated from density logging, in %; Ф CN This represents the porosity value calculated by neutron logging, in percentages (%).

[0105] Key wells were selected in the western depression of the Junggar Basin (Ben 1 Well) to identify gas-bearing strata. Gas saturation was calculated using formula (4). Most strata in this well had gas saturation below 30%, some strata had saturation between 30% and 70%, and very few strata had saturation above 70%. Figure 8 As shown.

[0106] S4. Calculate the breakthrough pressure of sandstone and mudstone.

[0107] Establish the relationship between breakthrough pressure and porosity in sandstone:

[0108] P sand =24.80×Ф AC 0.82 (5)

[0109] Among them, P sand Indicates the breakthrough pressure of sandstone, in MPa; Ф AC This represents the porosity calculated using acoustic logging, expressed as a percentage.

[0110] Key wells were selected in the western depression surrounding Well 1 in the Junggar Basin to calculate the sandstone breakthrough pressure, which ranged from 3 to 6 MPa. Figure 9 As shown.

[0111] Furthermore, the relationship between mudstone permeability and porosity and clay mineral content was established:

[0112]

[0113] Where K represents the mudstone permeability, in μm 2 , represents mudstone porosity, in %; CF represents mudstone clay mineral content, in %.

[0114] Then establish the relationship between mudstone breakthrough pressure and mudstone permeability:

[0115] P mud =0.0903×K -0.638 (7)

[0116] Among them, P mud K represents the mudstone breakthrough pressure, in MPa; K represents the mudstone permeability, in μm.2 .

[0117] Selecting key wells in the western depression of the Junggar Basin (Ben 1 well), the mudstone breakthrough pressure was calculated, ranging from 2 to 8 MPa. Figure 10 As shown.

[0118] S5. Based on the number of gas-bearing layers, gas saturation, sandstone breakthrough pressure, and mudstone breakthrough pressure, the capillary closure mechanism evaluation model of caprock natural gas is substituted to obtain the caprock natural gas capillary closure mechanism evaluation parameters.

[0119] Substituting the parameters obtained from formulas (2), (3), (4), (5), and (7) into formula (1), we obtain the capillary sealing capacity evaluation parameter C for the caprock natural gas. Based on the gas layer distribution and changes in gas saturation, sealing units are divided. The sealing strength is significantly negatively correlated with the caprock particle fluorescence parameter, which characterizes the hydrocarbon content in the caprock. Figure 11 As shown, the stronger the capillary sealing ability, the lower the hydrocarbon content in the capillary, thus evaluating the capillary sealing ability of natural gas.

[0120] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions 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. A method for identifying and evaluating the capillary closure mechanism of caprock natural gas, characterized in that, include: Natural gas capillary closure was identified based on multi-dimensional data; Construct an evaluation model for the capillary closure mechanism of capillary natural gas; Gas-bearing layers are identified using density logging, neutron logging, and sonic logging data, and the gas saturation of the gas-bearing layers is calculated using density logging and neutron logging data. Calculate the breakthrough pressure of sandstone and mudstone; The evaluation parameters for the capillary closure mechanism of natural gas in the caprock are obtained by substituting the number of gas-bearing layers, gas saturation, sandstone breakthrough pressure, and mudstone breakthrough pressure into the caprock natural gas capillary closure mechanism evaluation model.

2. The method for identifying and evaluating the capillary closure mechanism of caprock natural gas according to claim 1, characterized in that: The multidimensional data includes lithological assemblage, source rock evolution, pressure system, and natural gas injection status.

3. The method for identifying and evaluating the capillary closure mechanism of caprock natural gas according to claim 2, characterized in that: The lithological assemblage is the ratio of mudstone to stratum thickness in the caprock.

4. The method for identifying and evaluating the capillary closure mechanism of caprock natural gas according to claim 2, characterized in that: The evolution of the source rocks described refers to the stages of source rock evolution in the study area.

5. The method for identifying and evaluating the capillary closure mechanism of caprock natural gas according to claim 2, characterized in that: The pressure system is a pressure storage box for analyzing the development of the pressure system in the study area.

6. The method for identifying and evaluating the capillary closure mechanism of caprock natural gas according to claim 2, characterized in that: The natural gas filling situation refers to the comparison of the changes in the sealing capacity of the caprock before and after natural gas filling.

7. The method for identifying and evaluating the capillary closure mechanism of caprock natural gas according to claim 1, characterized in that: The formula for the evaluation model of the capillary closure mechanism of caprock natural gas is: Where C represents the cumulative breakthrough pressure characterizing the sealing capacity of the caprock, in MPa; i represents the i-th gas layer; n represents the total number of gas layers; Pi mud Pi represents the breakthrough pressure of the i-th layer of mudstone; sand Indicates the breakthrough pressure of the i-th sandstone layer; Si g This represents the gas saturation of the i-th gas-bearing layer.

8. The method for identifying and evaluating the capillary closure mechanism of caprock natural gas according to claim 1, characterized in that: Construct the identification formula for the gas-bearing layer: A=φ DEN +φ AC -2f CN ; B=(φx EN ×φ AC ) / (φ CN ×φ CN ); Where A>0 and B>1, it represents a gas-bearing layer; Ф DEN Ф represents the porosity value calculated from density logging. AC Ф represents the porosity value calculated by acoustic logging. CN This represents the porosity value calculated using neutron logging.

9. The method for identifying and evaluating the capillary closure mechanism of caprock natural gas according to claim 1, characterized in that: Construct the formula for calculating the gas saturation of the gas-bearing layer: S g =0.001×(φ DEN -f CN )2+1.178×(φ DEN -f CN )+67.63; Among them, S g This indicates the gas saturation of the gas-bearing layer, in %; Ф DEN This represents the porosity value calculated from density logging, in %; Ф CN This represents the porosity value calculated by neutron logging, in percentages (%).

10. The method for identifying and evaluating the capillary closure mechanism of caprock natural gas according to claim 1, characterized in that, The calculation of the breakthrough pressure of the sandstone includes: Establish the relationship between breakthrough pressure and porosity in sandstone: P sand =24.80×φ AC 0.82 ; Among them, P sand Indicates the breakthrough pressure of sandstone, in MPa; Ф AC This indicates the porosity calculated from acoustic logging, expressed as a percentage (%). Establish the relationship between mudstone permeability, porosity, and clay mineral content: Where K represents the mudstone permeability, in μm 2 , The value represents the porosity of mudstone, in %; CF represents the clay mineral content of mudstone, in %; Establish the relationship between mudstone breakthrough pressure and mudstone permeability: P mud =0.0903×K -0.638 ; Among them, P mud K represents the mudstone breakthrough pressure, in MPa; K represents the mudstone permeability, in μm. 2 .

Images