Calculation method of paleopressure of clastic gas reservoir based on compressibility of rock skeleton

Abstract

The present invention provides a method for calculating the paleopressure of clastic gas reservoirs based on the rock skeleton compression coefficient. By analyzing the porosity of rock samples at normal pressure, the rock skeleton compression coefficient under different effective stresses, and the whole-rock XRD test data, combined with the definition of the rock formation compaction coefficient and the rock skeleton compression coefficient, a formula is established to characterize the change in pore volume during geological history, thereby obtaining the change in pore volume during each historical period. When the reservoir is a dry gas or wet gas reservoir, the paleopressure of each historical period is calculated based on the current measured pressure and temperature of the reservoir and the paleotemperature curve of the simulated formation thermal evolution history. To a certain extent, this method solves the problem that the previous paleopressure quantitative calculation method relied on microscopic fluid inclusion observation and testing and was difficult to continuously calculate the paleopressure of each geological historical period. It can accurately calculate the paleopressure value of gas reservoirs, has stronger applicability and practicality, and can continuously calculate the paleopressure value of each historical period, and has certain industrial application value.

Description

Technical Field

[0001] The present invention relates to the field of geological exploration, and in particular to a method for calculating paleopressure of clastic gas reservoirs based on rock skeleton compression coefficient. Background Art

[0002] Paleopressure recovery in sedimentary basins is a crucial component of basin analysis and reservoir dynamics research, playing a crucial role in oil and gas geology research and exploration. Paleopressure recovery involves calculating the pore pressure or pore pressure coefficient of a reservoir at various geological stages during its uplift, based on existing geological data, analytical laboratory data, and the sedimentary burial history of the reservoir.

[0003] A variety of methods for recovering paleopressure have been developed, which can be roughly divided into the following categories: (1) Using fluid inclusions to recover paleopressure of formations, the paleopressure at the time of fluid capture is obtained by using the equilibrium relationship between the uniform temperature and fluid composition of hydrocarbon inclusions and brine inclusions of the same period. Common methods include: calculating paleopressure of oil inclusions by PVT-sim software and calculating paleopressure by laser Raman shift of methane inclusions. These methods require a large number of hydrocarbon inclusions that can be observed and measured under a microscope, and are not applicable to reservoirs with few or small inclusions. (2) Using mudstone acoustic time difference data, based on the principle of irreversible mudstone compaction, the paleopressure at the maximum burial depth of the formation can be deduced. Common methods include the equivalent depth method, the Fillippone formula method, etc. These methods can only estimate the pore pressure of the formation except for the maximum burial depth of the formation. (3) Using PetroMod, BasinMod, etc. Basin simulation software such as [1] can be used to restore the paleopressure characteristics of single wells, profiles, and planes. This method is based on the backstripping model. In order to obtain reasonable calculation results, a large amount of evolutionary data from geological history is often required. However, these data are difficult to obtain and require a lot of debugging and testing. (4) For carbonate rock formations that lack oil inclusions and brine inclusions containing gaseous hydrocarbons, calcite twins can be used as paleopressure gauges. Combined with fracture analysis, suture roughness, and rock mechanics parameters, the evolution of paleofluid pressure can be restored by the differential paleostress method. This method can only qualitatively analyze whether there is paleooverpressure, and cannot quantitatively calculate the paleopressure values of formations in various historical periods. (5) Other methods include estimating paleopressure using mineral veins, estimating the formation pressure of clay minerals based on the formation temperature and actual curve of clay minerals, and the tectonic stress method used to study the paleopressure of formations under tectonic compression. These methods are all based on certain assumptions and can only qualitatively estimate the magnitude of paleopressure.

[0004] In summary, most of the existing reservoir paleopressure calculation methods have limitations and are only applicable to qualitative estimation or specific areas. The more reliable quantitative calculation methods, such as the laser Raman shift calculation of methane inclusions, require the observation and testing of a large number of microscopic fluid inclusions, but can only calculate the reservoir paleopressure value at the historical moment of inclusion filling. The paleopressure of other historical periods is based on the fitting and inference of test points. At present, there is still a lack of a quantitative paleopressure calculation method that is highly applicable to clastic gas reservoirs and takes into account the continuous historical time evolution. Summary of the Invention

[0005] The main technical problem solved by the present invention is to provide a quantitative calculation method for paleopressure of clastic gas reservoirs which has strong applicability and takes into account the continuous evolution of historical time.

[0006] According to a first aspect of the present invention, a method for calculating paleopressure of a clastic gas reservoir based on rock skeleton compressibility is provided, comprising the following steps:

[0007] Obtaining a rock sample of the clastic rock formation to be calculated;

[0008] A functional relationship between the total volume of the rock sample, the rock skeleton compressibility, the rock matrix compressibility, the confining pressure and the pore volume of the rock sample is established as a first expression:

[0009] V p =aV(C bc -C s )·P c

[0010] Where a is the integration constant, V represents the total volume of the rock sample, and C bc Indicates the rock skeleton compression coefficient, C s represents the rock matrix compressibility, P c Represents the confining pressure, V p represents the pore volume;

[0011] Based on the discrete values of the rock skeleton compression coefficient under different effective stresses and the relationship between rock effective stress, confining pressure and pore pressure, a fitting relationship between the rock skeleton compression coefficient and confining pressure and pore pressure is established, which is the second expression:

[0012]

[0013] Where k and b are the prior values obtained by fitting; σ eff is the effective stress of rock, is the confining pressure P c and pore pressure P p The difference between

[0014] Based on the ideal gas state equation, the reservoir paleopressure P at any geological time t is established. pt The expression of is the third expression:

[0015]

[0016] Where, P p0 , T0 and V p0 are the current measured formation pressure, temperature and pore volume of the reservoir, which are a priori values; T t is the ground temperature at any geological time t; V pt is the pore volume at any geological time t;

[0017] According to the first, second and third expressions, the reservoir paleopressure P at any geological history time t is calculated based on the rock skeleton compression coefficient. pt The expression of is the fourth expression:

[0018]

[0019] Obtain the rock matrix compressibility, confining pressure and ground temperature at any geological time t, and calculate the reservoir paleopressure P at any geological time t using the fourth expression based on the current measured formation pressure, temperature and pore volume of the reservoir. pt .

[0020] Furthermore, the step of establishing a functional relationship between the total volume of the rock sample, the rock skeleton compressibility, the rock matrix compressibility, the confining pressure and the pore volume of the rock sample comprises:

[0021] The functional relationship between the compaction coefficient of rock formation and pore volume, pore volume change, and confining pressure change is obtained as the fifth expression:

[0022]

[0023] Where C pc is the rock formation compaction coefficient, P -1 ;ΔP c is the change of confining pressure; V p is the pore volume; ΔV p is the change in pore volume;

[0024] The functional relationship between the rock formation compaction coefficient and the rock skeleton compression coefficient, rock matrix compression coefficient, and porosity is obtained as the sixth expression:

[0025]

[0026] Where C bc is the rock skeleton compression coefficient, P-1 ; C s is the rock matrix compressibility coefficient, P -1 ; φ is porosity;

[0027] Based on the fifth and sixth expressions, a functional relationship among the rock skeleton compressibility, rock matrix compressibility, porosity, confining pressure change, pore volume, and pore volume change is established as the seventh expression:

[0028]

[0029] According to the definition of porosity φ=V p / V, where V is the total volume of the rock sample. The functional relationship among the rock skeleton compressibility, rock matrix compressibility, total volume of the rock sample, confining pressure change, and pore volume change is obtained as the eighth expression:

[0030] V(C bc -C s )·ΔP c =-ΔV p

[0031] Integrating both sides of the eighth expression yields the functional relationship between the total volume of the rock sample, the rock skeleton compressibility, the rock matrix compressibility, the confining pressure, and the pore volume, which is the first expression:

[0032] V p =aV(C bc -C s )·P c .

[0033] Preferably, the step of establishing a functional relationship between the total volume of the rock sample, the rock skeleton compressibility, the rock matrix compressibility, the confining pressure and the pore volume of the rock sample further includes:

[0034] Get the integral constant a; the method to get the integral constant a is:

[0035] Using the current confining pressure P c0 The rock skeleton compression coefficient C bc0 , pore volume V p0 , the total volume of the rock sample V and the rock matrix compressibility C s Substituting the discrete value into the first expression yields:

[0036] a=V p0 +V·(C bc0 -C s )·P c0 .

[0037] Furthermore, the step of establishing a functional relationship between the total volume of the rock sample, the rock skeleton compressibility, the rock matrix compressibility, the confining pressure and the pore volume of the rock sample further includes:

[0038] The rock skeleton compression coefficient, rock matrix compression coefficient, and confining pressure in the first expression are converted into values at any geological history time, that is, the paleopore volume V at any geological history time is obtained. pt The calculation formula is:

[0039] V pt =aV·(C bct -C st )·P ct

[0040] Where a is the integration constant; V pt is the pore volume at any geological time t; C bct is the rock skeleton compression coefficient at any geological time t; P ct is the confining pressure at any geological time t; C st is the rock matrix compression coefficient at any geological time t; assuming that there is only mechanical deformation and no mineral chemical reaction during the stratum uplift process, and its mineral composition does not change, then C st =C s .

[0041] Preferably, the step of obtaining the rock matrix compressibility coefficient at any geological historical time t comprises:

[0042] Obtain the volume percentage f of each mineral in the rock sample at normal pressure i ;

[0043] According to the volume percentage of each mineral in the rock sample i , the Voigt-Reuss-Hill average modulus model is used to calculate the rock matrix compressibility C of the rock sample s , C st =C s :

[0044]

[0045] Where C i is the compression coefficient of N mineral components in the rock sample, i is an integer greater than or equal to 1, C st is the rock matrix compressibility coefficient at any geological time t.

[0046] Preferably, the calculation formula for obtaining the confining pressure at any geological historical time t is as follows:

[0047] P ct =Pc0 +ρ s (H t -H0)

[0048] Where, P ct is the confining pressure at any geological time t, P c0 is the current formation confining pressure, which is a priori value; ρ s is the empirical value of shallow stratum density, which is a priori value; H t is the stratigraphic depth at any geological time t, obtained by simulating the burial history map based on the basin; H0 is the current stratigraphic depth, a priori value.

[0049] Preferably, the ground temperature at any geological historical time t is obtained by a specific method of obtaining the ground temperature based on a basin thermal history simulation temperature-geological time evolution diagram.

[0050] The technical solution provided by the present invention has the following beneficial effects:

[0051] To address the current difficulty in quantitatively calculating paleopressures in gas reservoirs, a method using the rock skeleton compressibility, a rock elastic parameter, as a key model parameter has been used to theoretically establish a quantitative relationship between pore volume changes, the rock skeleton compressibility, and the overburden load during various historical periods. Furthermore, the ideal gas equation of state is used to calculate formation paleopressures for each historical period. This novel method for calculating formation paleopressures enables continuous calculation of paleopressures for each historical period by measuring porosity at normal pressure, rock skeleton compressibility at different effective stresses, and whole-rock mineral XRD data. This method addresses the difficulty of previous quantitative paleopressure calculation methods, which relied on microscopic fluid inclusion observations and testing and struggled to continuously calculate paleopressures across geological periods. It plays an important role in basin analysis and oil and gas reservoir dynamics research, and has significant industrial application value in oil and gas exploration and evaluation. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The specific effects of the present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0053] Figure 1 This is a flow chart of a method for calculating paleopressure of a clastic gas reservoir based on rock skeleton compression coefficient according to an embodiment of the present invention;

[0054] Figure 2 is the correlation between the rock skeleton compression coefficient and the effective stress of the clastic rock sample according to the embodiment of the present invention;

[0055] Figure 3 This is a 3500m burial depth-geological time evolution diagram of a well in a tight clastic gas reservoir in a craton sedimentary basin according to an embodiment of the present invention;

[0056] Figure 4 This is a temperature-geological time evolution diagram at 3500 m in a well of a tight clastic gas reservoir in a craton sedimentary basin according to an embodiment of the present invention;

[0057] Figure 5 This is a paleopressure-geological age relationship diagram of a well in a tight clastic gas reservoir in a craton sedimentary basin according to an embodiment of the present invention. DETAILED DESCRIPTION

[0058] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0059] refer to Figure 1 This embodiment provides a method for calculating paleopressure of clastic gas reservoirs based on rock skeleton compression coefficient, comprising the following steps:

[0060] S1: Obtain rock samples of the clastic rock formation to be calculated;

[0061] S1 specifically includes: obtaining rock samples of the clastic rock formation to be calculated (Table 1), selecting a sample with methane inclusion laser Raman shift restored paleopressure value (No.: YP02), and testing the pore volume V of the rock sample at normal pressure. p , porosity φ0 (Table 1) and rock skeleton compression coefficient C under different effective stresses bc , the volume percentage of each mineral obtained from the whole rock XRD test data i (Table 2).

[0062] Table 1 Experimental sample information and porosity test data of a well in a tight clastic gas reservoir in a craton sedimentary basin

[0063]

[0064] Table 2 Mineral content data of whole-rock XRD test of a well sample from a tight clastic gas reservoir in a craton sedimentary basin

[0065]

[0066] S2: Establish a functional relationship between the total volume of the rock sample, the rock skeleton compressibility, the rock matrix compressibility, the confining pressure and the pore volume of the rock sample, which is the first expression:

[0067] V p =aV(C bc -C s )·P c

[0068] Where a is the integration constant, V represents the total volume of the rock sample, and C bc Indicates the rock skeleton compression coefficient, C srepresents the rock matrix compressibility, P c Represents the confining pressure, V p represents the pore volume;

[0069] S2 specifically includes:

[0070] S21: Obtain the functional relationship between the rock formation compaction coefficient and the pore volume, pore volume change, and confining pressure change, which is the fifth expression:

[0071]

[0072] Where C pc is the rock formation compaction coefficient, P -1 ;ΔP c is the change of confining pressure; V p is the pore volume; ΔV p is the change in pore volume;

[0073] S22: Obtain the functional relationship between the rock formation compaction coefficient and the rock skeleton compression coefficient, rock matrix compression coefficient, and porosity, which is the sixth expression:

[0074]

[0075] Where C bc is the rock skeleton compression coefficient, P -1 ; C s is the rock matrix compressibility coefficient, P -1 ; φ is porosity;

[0076] S23: Based on the fifth expression and the sixth expression, a functional relationship among the rock skeleton compressibility, the rock matrix compressibility, the porosity, the confining pressure change, the pore volume and the pore volume change is established, which is the seventh expression:

[0077]

[0078] S24: According to the definition of porosity φ=V p / V, where V is the total volume of the rock sample. The functional relationship among the rock skeleton compressibility, rock matrix compressibility, total volume of the rock sample, confining pressure change, and pore volume change is obtained as the eighth expression:

[0079] V(C bc -C s )·ΔP c =-ΔV p

[0080] S25: Integrating both sides of the eighth expression yields the functional relationship between the total volume of the rock sample, the rock skeleton compressibility, the rock matrix compressibility, the confining pressure, and the pore volume, which is the first expression:

[0081] V p =aV(C bc -C s )·P c

[0082] S26: Convert the rock skeleton compression coefficient, rock matrix compression coefficient, and confining pressure in the first expression into values at any geological time, that is, obtain the paleopore volume V at any geological time. pt The calculation formula is:

[0083] V pt =aV·(C bct -C st )·P ct

[0084] Where a is the integration constant; V pt is the pore volume at any geological time t; C bct is the rock skeleton compression coefficient at any geological time t; P ct is the confining pressure at any geological time t; C st is the rock matrix compression coefficient at any geological time t; assuming that there is only mechanical deformation and no mineral chemical reaction during the stratum uplift process, and its mineral composition does not change, then C st =C s .

[0085] Optionally, step S2 further includes:

[0086] Get the integral constant a; the method to get the integral constant a is:

[0087] Using the current confining pressure P c0 The rock skeleton compression coefficient C bc0 , pore volume V p0 , the total volume of the rock sample V and the rock matrix compressibility C s Substituting the discrete value into the first expression yields:

[0088] a=V p0 +V·(C bc0 -C s )·P c0 .

[0089] S3: A series of discrete values of rock skeleton compression coefficient and effective stress obtained by the test (such as Figure 1As shown in Figure 2, taking into account the fitting relationship and the complexity of subsequent calculations, the relationship between the rock skeleton compression coefficient and the effective stress under high effective stress is obtained by fitting. Then, based on the relationship between the rock effective stress, confining pressure and pore pressure, the fitting relationship between the rock skeleton compression coefficient and the confining pressure and pore pressure is established, which is the second expression:

[0090]

[0091] Where k and b are Figure 1 The prior value obtained by fitting; σ eff is the effective stress of rock, is the confining pressure P c and pore pressure P p The difference between

[0092] The above expression can be extended to calculate the rock skeleton compression coefficient at any geological history time t:

[0093]

[0094] S4: Based on the ideal gas state equation, establish the reservoir paleopressure P at any geological time t pt The calculation expression of is the third expression:

[0095]

[0096] Where, P p0 , T0 and V p0 are the current measured formation pressure, temperature and pore volume of the reservoir, which are a priori values; T t is the ground temperature at any geological time t; V pt is the pore volume at any geological time t;

[0097] S5: According to the first expression, the second expression and the third expression, the reservoir paleopressure P at any geological history time t is calculated based on the rock skeleton compression coefficient. pt The expression of is the fourth expression:

[0098]

[0099] S6: Obtain the rock matrix compressibility, confining pressure and ground temperature at any geological time t, and calculate the reservoir paleopressure P at any geological time t using the fourth expression based on the current measured formation pressure, temperature and pore volume of the reservoir. pt .

[0100] S6 specifically includes:

[0101] S61: Obtain the rock matrix compressibility coefficient at any geological history time t, including:

[0102] S61 further includes:

[0103] S611: Obtain the volume percentage f of each mineral in the rock sample at normal pressure i ;

[0104] S612: According to the volume percentage of each mineral in the rock sample f i , the Voigt-Reuss-Hill average modulus model is used to calculate the rock matrix compressibility C of the rock sample s , C st =C s :

[0105]

[0106] Where C i is the compression coefficient of N mineral components in rock samples, the laboratory test empirical value of the compression coefficient of mineral components in rock samples (Table 3), is a priori value, i is an integer greater than or equal to 1, C st is the rock matrix compressibility coefficient at any geological time t.

[0107] Table 3 Empirical values of compression coefficient of each mineral component

[0108]

[0109] S62: Obtain the confining pressure at any geological historical time t. The calculation formula is as follows:

[0110] P ct =P c0 +ρ s (H t -H0)

[0111] Where, P ct is the confining pressure at any geological time t, P c0 is the current formation confining pressure, which is a priori value; ρ s is the empirical value of shallow stratum density, which is a priori value and is taken as 2.65g / cm 3 ;H t is the stratigraphic depth at any geological time t, and is simulated according to the basin burial history map ( Figure 3 ) is obtained, for example, the sample numbered YP02 is currently buried at a depth of 3500m, and at t = 100Ma, the burial depth is H t is 4200m, H0 is the present stratum depth, a priori value.

[0112] S63: Obtain the ground temperature at any geological time t. The specific acquisition method is: simulate the temperature-geological time evolution diagram based on the basin thermal history ( Figure 4 ) to obtain.

[0113] S64: Based on the rock matrix compressibility, confining pressure and ground temperature at any geological time t calculated in S61-S63, and based on the current measured formation pressure, temperature and pore volume of the reservoir, the reservoir paleopressure P at any geological time t is calculated using the fourth expression pt .

[0114] Using the above method of the embodiment of the present invention, the calculated results are as follows Figure 5 As shown in Figure 5, the paleopressure value (line in Figure 5) is consistent with the paleopressure value restored by laser Raman shift of methane inclusions ( Figure 5 This method can accurately calculate the paleopressure value of gas reservoirs, has stronger applicability and practicality than previous methods, and can continuously calculate the paleopressure values of various historical periods, which has certain industrial application value.

[0115] This example derives and establishes a theoretical formula for characterizing pore volume changes over geological history by analyzing the porosity of sandstone samples at normal pressure, the rock skeleton compression coefficient under different effective stresses, and whole-rock XRD test data in the test area, combined with the definitions of the rock formation compaction coefficient and the rock skeleton compression coefficient. The changes in pore volume over each historical period are then obtained. When the reservoir is a dry gas or wet gas reservoir (the reservoir temperature is always higher than the fluid phase envelope, and there is no phase change process), based on the ideal gas state equation, with the current measured reservoir pressure and temperature as the starting point, combined with the simulated paleotemperature curve of the formation thermal evolution history, the reservoir paleopressure values over each historical period are calculated.

[0116] This example addresses the current difficulties in universal applicability and continuous quantitative paleopressure calculation for clastic gas reservoirs. A method for calculating paleopressure in gas reservoirs based on the rock skeleton compressibility coefficient is proposed. This method addresses, to a certain extent, the difficulty of previous quantitative paleopressure calculation methods, which relied on microscopic fluid inclusion observations and testing and struggled to consistently calculate paleopressure across geological periods. By comparing the calculated paleopressure values with those recovered from laser Raman shifts of methane inclusions, it is clear that this method can accurately calculate paleopressure values for gas reservoirs, offering greater applicability and practicality than previous methods. Furthermore, it can continuously calculate paleopressure values across historical periods, demonstrating significant industrial application value.

[0117] It should be noted that, in this document, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or system comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or system. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or system comprising the element.

[0118] The serial numbers of the embodiments of the present invention are for descriptive purposes only and do not represent superiority or inferiority of the embodiments. In a unit claim that lists several means, several of these means may be embodied by the same item of hardware. The use of the terms first, second, and third, etc., does not denote any order and should be construed as identifiers.

[0119] The above are only preferred embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for calculating paleopressure of clastic gas reservoirs based on rock skeleton compression coefficient, characterized in that: The following steps are involved: Obtaining a rock sample of the clastic rock formation to be calculated; A functional relationship between the total volume of the rock sample, the rock skeleton compressibility, the rock matrix compressibility, the confining pressure and the pore volume of the rock sample is established as a first expression: In p =aV(C bc -C s )·P c Where a is the integration constant, V represents the total volume of the rock sample, and C bc Indicates the rock skeleton compression coefficient, C s represents the rock matrix compressibility, P c Represents the confining pressure, V p represents the pore volume; Based on the discrete values of the rock skeleton compression coefficient under different effective stresses and the relationship between rock effective stress, confining pressure and pore pressure, a fitting relationship between the rock skeleton compression coefficient and confining pressure and pore pressure is established, which is the second expression: Where k and b are the prior values obtained by fitting; σ eff is the effective stress of rock, is the confining pressure P c and pore pressure P p The difference between Based on the ideal gas state equation, the reservoir paleopressure P at any geological time t is established. pt The calculation expression of is the third expression: Where, P p0 , T0 and V p0 are the current measured formation pressure, temperature and pore volume of the reservoir, which are a priori values; T t is the ground temperature at any geological time t; V pt is the pore volume at any geological time t; According to the first, second and third expressions, the reservoir paleopressure P at any geological history time t is calculated based on the rock skeleton compression coefficient. pt The expression of is the fourth expression: Obtain the rock matrix compressibility, confining pressure and ground temperature at any geological time t, and calculate the reservoir paleopressure P at any geological time t using the fourth expression based on the current measured formation pressure, temperature and pore volume of the reservoir. pt .

2. The method for calculating paleopressure of clastic gas reservoirs based on rock skeleton compressibility according to claim 1, wherein: The step of establishing a functional relationship between the total volume of the rock sample, the rock skeleton compressibility, the rock matrix compressibility, the confining pressure and the pore volume of the rock sample comprises: The functional relationship between the compaction coefficient of rock formation and pore volume, pore volume change, and confining pressure change is obtained as the fifth expression: Where C pc is the rock formation compaction coefficient, P -1 ;ΔP c is the change of confining pressure; V p is the pore volume; ΔV p is the change in pore volume; The functional relationship between the rock formation compaction coefficient and the rock skeleton compression coefficient, rock matrix compression coefficient, and porosity is obtained as the sixth expression: Where C bc is the rock skeleton compression coefficient, P -1 ; C s is the rock matrix compressibility coefficient, P -1 ; φ is porosity; Based on the fifth and sixth expressions, a functional relationship among the rock skeleton compressibility, rock matrix compressibility, porosity, confining pressure change, pore volume, and pore volume change is established as the seventh expression: According to the definition of porosity φ=V p / V, where V is the total volume of the rock sample. The functional relationship among the rock skeleton compressibility, rock matrix compressibility, total volume of the rock sample, confining pressure change, and pore volume change is obtained as the eighth expression: V(C bc -C s )·ΔP c =-ΔV p Integrating both sides of the eighth expression yields the functional relationship between the total volume of the rock sample, the rock skeleton compressibility, the rock matrix compressibility, the confining pressure, and the pore volume, which is the first expression: In p =aV(C bc -C s )·P c 。 3. The method for calculating paleopressure of clastic gas reservoirs based on rock skeleton compressibility according to claim 2, wherein: The step of establishing a functional relationship between the total volume of the rock sample, the rock skeleton compressibility, the rock matrix compressibility, the confining pressure and the pore volume of the rock sample further includes: Get the integral constant a; the method to get the integral constant a is: Using the current confining pressure P c0 The rock skeleton compression coefficient C bc0 , pore volume V p0 , the total volume of the rock sample V and the rock matrix compressibility C s Substituting the discrete value into the first expression yields: a=V p0 +V·(C bc0 -C s )·P c0 。 4. The method for calculating paleopressure of clastic gas reservoirs based on rock skeleton compressibility according to claim 2, wherein: The step of establishing a functional relationship between the total volume of the rock sample, the rock skeleton compressibility, the rock matrix compressibility, the confining pressure and the pore volume of the rock sample further includes: The rock skeleton compression coefficient, rock matrix compression coefficient, and confining pressure in the first expression are converted into values at any geological time, that is, the paleopore volume V at any geological time is obtained. pt The calculation formula is: In pt =aV·(C bct -C st )·P ct Where a is the integration constant; V pt is the pore volume at any geological time t; C bct is the rock skeleton compression coefficient at any geological time t; P ct is the confining pressure at any geological time t; C st is the rock matrix compression coefficient at any geological time t; assuming that there is only mechanical deformation and no mineral chemical reaction during the stratum uplift process, and its mineral composition does not change, then C st =C s .

5. The method for calculating paleopressure of clastic gas reservoirs based on rock skeleton compressibility according to claim 1, wherein: The step of obtaining the rock matrix compressibility coefficient at any geological historical time t includes: Obtain the volume percentage f of each mineral in the rock sample at normal pressure i ; According to the volume percentage of each mineral in the rock sample i , the Voigt-Reuss-Hill average modulus model is used to calculate the rock matrix compressibility C of the rock sample s , C st =C s : Where C i is the compression coefficient of N mineral components in the rock sample, is a priori value, i is an integer greater than or equal to 1, C st is the rock matrix compressibility coefficient at any geological time t.

6. The method for calculating paleopressure of clastic gas reservoirs based on rock skeleton compressibility according to claim 1, wherein: The calculation formula for obtaining the confining pressure at any geological historical time t is as follows: P ct =P c0 +ρ s (H t -H0) Where, P ct is the confining pressure at any geological time t, P c0 is the current formation confining pressure, which is a priori value; ρ s is the empirical value of shallow stratum density, which is a priori value; H t is the stratigraphic depth at any geological time t, obtained by simulating the burial history map based on the basin; H0 is the current stratigraphic depth, a priori value.

7. The method for calculating paleopressure of clastic gas reservoirs based on rock skeleton compressibility according to claim 1, wherein: The ground temperature at any geological history time t is obtained by a specific method: obtaining it according to a basin thermal history simulation temperature-geological time evolution diagram.

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