A rock specific surface evaluation method based on gas well dynamic data

Abstract

The application discloses a rock specific surface evaluation method based on gas well dynamic data, and comprises the following steps: S1, collecting and arranging gas well static data and gas well dynamic data; S2, using a Blasingame modern production harmonic decline graph board curve to extract a part meeting the Darcy seepage law, and recording a time period as [t0, t1]; S3, calculating an equivalent gas discharge radius and a gas well skin coefficient; selecting a subinterval [t'0, t'1], using an exponential decline model to carry out fitting, and calculating a decline rate; S4, establishing a rock specific surface model, and obtaining the rock specific surface by using the rock specific surface model. The application establishes a quantitative model of the rock specific surface, effectively avoids the limitation of a laboratory overburden condition; meanwhile, by means of well logging interpretation results and seepage mechanics theory, the rock specific surface calculation scale is expanded from a core scale to a large scale of a well logging interpretation series detection radius and a well control range, the rock specific surface model can reduce core analysis experiments, can reduce gas reservoir development cost from the economic aspect, and can improve gas reservoir development benefit.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development technology, and in particular to a method for evaluating rock specific surface area based on gas well dynamic data. Background Technology

[0002] Specific surface area is one of the important properties of rock physics. It not only reflects the sedimentary and diagenetic characteristics of strata, but also plays a crucial role in the formation mechanism of oil and gas reservoirs, the main occurrence mode of fluids, and the development characteristics of oil and gas wells. Therefore, how to calculate and evaluate specific surface area has become an important research topic in oil and gas reservoir development and a hot topic for experts and scholars at home and abroad. For example, oil and gas reservoir developers at home and abroad generally use experimental methods to calculate specific surface area, that is, based on the Kozeny-Carman equation, the specific surface area is calculated by measuring relevant parameters through core experiments (Qin Jishun, Li Aifen. Reservoir Physics [M]. Beijing: China University of Petroleum Press, 2006). The evaluation results are based on laboratory conditions and core scale. Zhou Hong et al. (Calculation Method of Pore Specific Surface Area under Overburden Conditions [C]; Proceedings of the 2017 National Natural Gas Academic Conference. 2017.) introduced the rock pore volume compressibility coefficient into the Kozeny-Carman equation and established a new method for calculating the specific surface area of ​​cores. The theoretical method assumes that porosity remains constant under formation conditions. The calculation results are extended from laboratory conditions to formation conditions, realizing the simulation of formation conditions in the laboratory. The calculation scale is also based on the core scale, and the laboratory conditions are required to reach the formation conditions. Yao Yabin et al. (A method for calculating the specific surface area of ​​marine shale [C]; 2020 International Conference on Oil and Gas Field Exploration and Development (IFEDC2020). 2020) established a method for obtaining the specific surface area of ​​shale based on well logging curves through multivariate linear retrospective. The calculation results are also based on experimental conditions, and the scale of the calculated specific surface area of ​​the core is the detection radius of the well logging series.

[0003] The above methods for calculating rock specific surface area have the following main problems: (1) As the burial depth of the gas reservoir increases, the rock overburden pressure gradually increases, making it more difficult to simulate high-pressure formation conditions based on experiments. The experimental equipment is difficult to meet the formation temperature and pressure conditions, making it difficult to obtain the actual rock specific surface area under formation overburden pressure conditions, resulting in inaccurate calculation results; (2) As the development of the gas reservoir deepens, the heterogeneity of the gas reservoir geological conditions becomes more prominent, and the rock specific surface area varies greatly at different scales. It is difficult to characterize the rock specific surface area of ​​the gas well, well area, or even the entire gas reservoir using traditional core size or logging series detection radius scales; (3) When the gas reservoir is developed to a deep level, the geological conditions of the gas reservoir are more complex. The rock specific surface area obtained by using local core sampling cannot truly represent the gas well discharge area, and the calculation results deviate greatly from the actual results. Therefore, a new method for evaluating rock specific surface area is urgently needed. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem that the rock specific surface area calculated using core scale in the prior art is difficult to meet the needs of gas reservoir evaluation when the gas reservoir burial depth increases or the geological conditions of the gas reservoir become complex, and the results deviate significantly from the actual situation. This invention provides a rock specific surface area evaluation method based on gas well dynamic data.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] A method for evaluating the specific surface area of ​​rocks based on dynamic data of gas wells includes the following steps:

[0007] S1. Collect and organize static and dynamic data of gas wells;

[0008] S2. Using the gas well dynamic data in step S1, extract the part of the seepage law that satisfies Darcy's law using the Blasingame modern production harmonization decline chart curve, and record the time period corresponding to the part that satisfies Darcy's law as [t0, t1].

[0009] S3. Using static and dynamic data of gas wells, calculate the equivalent gas leakage radius and gas well skin coefficient; using the time period [t0, t1] of step S2, select the sub-interval [t'0, t'1], and use an exponential decreasing model for fitting to obtain the decreasing rate;

[0010] S4. Combining the theoretical model of declining gas well production with the Kozeny-Carman equation, a rock specific surface area model is established. Using the equivalent venting radius, well skin coefficient, and gas well static data, the rock specific surface area is obtained from the rock specific surface area model. The calculation formula for the rock specific surface area is as follows:

[0011]

[0012] In the formula S φ Let K be the specific surface area of ​​the rock, D be the Kozeny constant, and u be the decrease rate. g (p′) represents the viscosity of natural gas under the average formation pressure p′, and c g (p′) is the volume compressibility coefficient under the mean formation pressure p′, s wi To constrain water saturation, r e r is the equivalent vent radius. w Where λ is the wellbore radius and λ is the gas well skin coefficient.

[0013] This invention aims to study the Darcy flow stage (or Darcy flow-dominant stage) of gas well production under quasi-steady-state conditions, focusing on the Darcy flow law. Based on the Darcy flow law, the Darcy flow interval is derived, and the equivalent venting radius and well skin coefficient are calculated. An exponential decline model is used to fit the model and obtain the decline rate. Then, the gas well production decline theoretical model is organically combined with the Kozeny-Carman equation to establish a well-controlled scale model for evaluating rock specific surface area under formation conditions. This invention utilizes gas well production data, gas well static data, and Blasingame dynamic diagnostic parameters to establish a new method for calculating rock specific surface area on a large scale under formation conditions, thus providing technical support for comprehensive gas reservoir research and efficient gas reservoir evaluation and development.

[0014] Furthermore, the static data of gas wells includes high-pressure physical property analysis data tables, geological description data tables, etc. The high-pressure physical property analysis data tables include deviation factors, viscosity, compressibility coefficient, etc.; the geological description data tables include basic gas reservoir data, reservoir characteristics, rock properties, etc.; the dynamic data of gas wells includes production data tables, dynamic monitoring data tables, etc.

[0015] Furthermore, the formula that satisfies Darcy's law of seepage is:

[0016]

[0017] In the formula q Dd To normalize the output, t a,Db To normalize time,

[0018] Furthermore, the specific steps of step S3 are as follows:

[0019] S31. Select the portion of the harmonic decreasing curve that satisfies Darcy's law of permeability as the gas well fitting line; arbitrarily select point M(t) on the gas well fitting line. a,Db,M ,q Dd,M) The geological reserves of the gas well are calculated using the following formula:

[0020]

[0021] In the formula, G represents the geological reserves of the gas well, and c ti t represents the overall compressibility coefficient of the formation under the initial formation conditions. a,Db,M For normalized time, q Dd,M To normalize the output, The pseudo-pressure under the initial formation pressure, The pseudo-pressure under the bottom hole flowing pressure, q sc For gas well production;

[0022] S32. Calculate the natural gas volume factor under the conditions of original formation pressure and formation temperature;

[0023] S33. Combining the interpretation of bound water saturation and porosity from gas well static data logging, the gas well seepage model is equivalent to a homogeneous circular central well model. The equivalent gas leakage radius is calculated using the volumetric method, and the gas well skin coefficient is calculated. The formula for calculating the equivalent gas leakage radius is as follows:

[0024]

[0025] In the formula B gi φ represents the natural gas volume factor under the original formation conditions, h represents the reservoir thickness, and φ represents the porosity.

[0026] S34. Using the time interval [t0, t1] from step S2, select the sub-interval [t'0, t'1], and fit it using an exponentially decreasing model to obtain the decreasing rate D.

[0027] Furthermore, the formula for calculating the natural gas volume factor is as follows:

[0028]

[0029] In the formula z i p is the deviation factor in the initial state of the formation. i denoted as , where is the initial formation pressure, and T is the formation temperature.

[0030] Furthermore, the formula for calculating the gas well skin coefficient is as follows:

[0031]

[0032] In the formula q sc For gas well production, u gi The initial formation viscosity. k is the pseudo-average pressure under formation pressure. g For gas permeability, C A Where A is the shape factor and A is the seepage area.

[0033] Furthermore, the formula for the exponentially decreasing model is as follows:

[0034]

[0035] In the formula, q0 represents the gas well production at time t′0.

[0036] Furthermore, in step S3, when selecting the sub-interval [t'0, t'1], the condition that needs to be met is p(t'0) - p(t'1) ≤ ε, where ε is a constant and ε ≤ 0.01.

[0037] Furthermore, the formula for the theoretical model of declining gas well production is as follows:

[0038]

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] 1. The evaluation method of this invention uses the Blasingame modern production decline model to determine the natural gas seepage law of gas wells, and uses the chart curve to extract the part of the seepage law that satisfies Darcy's law, avoiding the complexity of traditional methods of dividing the fluid seepage law intervals using hydraulic resistance coefficient and Reynolds number, and providing a new means for determining the Darcy flow interval of fluid under gas reservoir formation conditions.

[0041] 2. The evaluation method of this invention organically combines the theoretical model of declining gas well production in the Darcy flow interval under the production model of determining production first and then pressure, which is common in actual gas wells, with the Kozeny-Carman equation to establish a new quantitative model for calculating rock specific surface area. This rock specific surface area model effectively avoids the limitations of laboratory overburden pressure conditions. At the same time, by using well logging interpretation results and seepage mechanics theory, the calculation scale of rock specific surface area is extended from the core scale to a large scale of well logging interpretation series detection radius and well control range, which plays a positive role in eliminating the influence of reservoir heterogeneity. In addition, the new rock specific surface area model can reduce core analysis experiments, which can reduce gas reservoir development costs and improve gas reservoir development efficiency from an economic perspective.

[0042] 3. The rock specific surface area model proposed in this invention can quantitatively calculate the specific surface area of ​​rocks, making it possible to widely evaluate the specific surface area of ​​formation rocks. This plays an important role in the comprehensive geological research of sedimentary facies, diagenetic facies, and reservoir properties, and also plays a positive role in the analysis of the main controlling factors of gas well productivity and engineering process decision-making. Attached image description:

[0043] Figure 1 This is a flowchart illustrating a method for evaluating rock specific surface area based on gas well dynamic data.

[0044] Figure 2 A diagram showing the decline template for gas well production under Darcy flow conditions;

[0045] Figure 3 A graph showing normalized time versus normalized output calculated using the Blasingame modern declining output model;

[0046] Figure 4 A production data graph for the sub-interval [t'0, t'1];

[0047] Figure 5 A statistical chart showing the calculated specific surface area of ​​rocks in different classification zones of the Xu'er gas reservoir in the Sichuan Basin. Detailed Implementation

[0048] The present invention will be further described in detail below with reference to experimental examples and specific embodiments. However, this should not be construed as limiting the scope of the above-mentioned subject matter of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0049] Example 1

[0050] A method for evaluating the specific surface area of ​​rocks based on dynamic data of gas wells includes the following steps:

[0051] S1. Collect and organize static and dynamic data of gas wells.

[0052] A gas well data database will be established based on the collected static and dynamic data for use in subsequent evaluation processes. The static data of gas wells includes high-pressure physical property analysis data tables, geological description data tables, etc. The high-pressure physical property analysis data tables include deviation factors, viscosity, compressibility coefficient, etc.; the geological description data tables include basic gas reservoir data, reservoir characteristics, rock properties, etc.; the dynamic data of gas wells includes production data tables, dynamic monitoring data tables, etc.

[0053] S2. Using the gas well dynamic data in step S1, extract the part of the seepage law that satisfies Darcy's law using the Blasingame modern production harmonization decline chart curve, and record the time period corresponding to the part that satisfies Darcy's law as [t0, t1].

[0054] In this invention, the Blasingame modern production decline model is used to determine whether the seepage law satisfies Darcy's law of seepage using the gas well dynamic data from step S1. This evaluation method is applicable to the stage where the gas well's constant flow pressure production satisfies Darcy's law of seepage (or the stage where Darcy flow is dominant) under quasi-steady-state conditions. If it does not, the gas well dynamic data needs to be collected again after further production. The basic principle of satisfying Darcy's law of seepage is as follows:

[0055] Let the pseudo-time function of mass equilibrium be as follows:

[0056]

[0057]

[0058]

[0059] In the formula For the proposed time; The pseudo-pressure under the initial formation pressure; The pseudo-mean pressure under formation pressure; u gi c represents the initial formation condition viscosity.ti q represents the overall compressibility coefficient of the formation under the initial formation conditions. sc For gas well production; Mean formation pressure; u g c represents the viscosity of natural gas. t The overall compressibility coefficient of the formation; Mean formation pressure The viscosity of natural gas at that time; Mean formation pressure Time-bounded overall compressibility coefficient of the strata; z i p is the deviation factor under the initial state of the formation; z is the formation deviation factor; p i denoted as ρ, where ρ is the initial formation pressure; p is the formation pressure.

[0060] The mass balance equation for a constant-volume gas reservoir is as follows:

[0061]

[0062] In the formula, G represents the geological reserves of the gas well. The average static pressure is The average natural gas deviation factor.

[0063] The formula for calculating the compressibility coefficient of natural gas is as follows:

[0064]

[0065] In the formula Average static pressure Let ρ be the compressibility coefficient of natural gas, T be the density of natural gas, R be Avogadro's constant, and M be the molar mass of natural gas. Combining equations (4) and (5), we get:

[0066]

[0067] Substituting formula (6) into formula (1), we get:

[0068]

[0069] Since gas wells are primarily driven by their own elasticity, that is:

[0070]

[0071] Combining formulas (7) and (8), and rearranging, we get:

[0072]

[0073] Combining formulas (2), (3), and (9), we get:

[0074]

[0075] (10) is deformed.

[0076]

[0077] If a gas well's production reaches the boundary region at a constant rate and Darcy's law of flow is satisfied, the pressure-production relationship satisfies the following equation:

[0078]

[0079] In the formula p is the pseudo-pressure under the bottom hole flowing pressure. wf For bottom hole flowing pressure, B gi k is the natural gas volume factor under the original formation conditions. g Where is the gas permeability, h is the reservoir thickness, λ is the gas well skin coefficient, and C A r is the shape factor. w Let A be the wellbore radius, and b be the seepage area. a,pss Let be a constant. Combining equations (11) and (12), we get:

[0080]

[0081] By rearranging and transforming formula (13), we get:

[0082]

[0083] Separately

[0084]

[0085]

[0086] Then formula (14) is transformed as follows:

[0087]

[0088] When normalized time t a,Db and normalized output q Dd When formula (17) is satisfied, the fixed production of the gas well satisfies Darcy's law of flow. Therefore, formula (17) can be used to standardize the harmonic decrease to determine whether the gas well flow satisfies Darcy's law of flow. That is, when the dimensionless production and dimensionless time satisfy formula (17), the gas well flow satisfies Darcy's law of flow or is approximately Darcy's law of flow; otherwise, it does not satisfy Darcy's law of flow.

[0089] The gas well used in this embodiment is a typical gas well from a deep tight gas reservoir in western Sichuan. Figure 2The figure shows the decline template of the Blasingame modern production decline model under the condition that the gas well production decline enters Darcy flow. As can be seen from the figure, under different geological conditions, when the gas well seepage enters Darcy flow or near Darcy flow, the normalized time and normalized production determined by equations (15) and (16) converge into a harmonic decline curve. Figure 3 The image shows the normalized time and normalized production data points calculated using the Blasingame modern production decline model after template repositioning. The image shows that the gas well production decline has entered the Darcy flow or near-Darcy flow range, with the recorded time period being [t0, t1].

[0090] S31. Select the portion of the harmonic decreasing curve that satisfies Darcy's law of permeability as the gas well fitting line; arbitrarily select point M(t) on the gas well fitting line. a,Db,M ,q Dd,M The geological reserves of the gas well are calculated using the following formula:

[0091]

[0092] Formula (18) is derived from formula (16), where

[0093]

[0094] Using c ti Based on the dynamic data of the gas well, the geological reserves of the gas well are calculated using formula (18).

[0095] S32. Calculate the natural gas volume factor under the original formation pressure and formation temperature conditions. The formula for calculating the natural gas volume factor is as follows:

[0096]

[0097] S33. Combining the bound water saturation and porosity interpreted from the gas well static data, the gas well seepage model is equivalent to a homogeneous circular central well model. The equivalent gas leakage radius is calculated using the volumetric method. The formula for calculating the equivalent gas leakage radius is as follows:

[0098]

[0099] In the formula r e Where φ is the equivalent vent radius, φ is the porosity, and s is the vent radius. wi To constrain water saturation, the gas well discharge is equivalent to a circular central well model, that is, let the formula (12) be... C A =π, and the skin coefficient λ of the gas well is obtained by combining (19). The formula for calculating λ is obtained by transforming formula (12):

[0100]

[0101] from Figure 3 Within the time period [t0, t1], a point M is selected for calculation. The calculated skin coefficient of the well is λ = -1.95, and the equivalent gas leakage radius is r = 750m.

[0102] S34. Using the time interval [t0, t1] from step S2, select the sub-interval [t'0, t'1], and fit it using an exponentially decreasing model to obtain the decreasing rate D.

[0103] Based on the binomial equation for gas well productivity, the gas well seepage is equivalent to a circular central well model. When the formation conditions and gas well operating regime comprehensively satisfy the Darcy flow seepage law and reach a quasi-steady state, the following formula is satisfied:

[0104]

[0105]

[0106] After the gas well reaches a pseudo-steady state, constant flow and pressure production is adopted (actual gas reservoirs generally have a production model of first setting production and then setting pressure). Combining formulas (4), (21), (23), and (24), we get:

[0107]

[0108] In the formula, q0 represents the gas well production at time t′0. The time period [t′0, t′1] is selected to be as small as possible, which requires p(t′0) - p(t′1) ≤ ε, where ε is determined according to the fitting process. In this embodiment, it is taken as 0.01. When the time period [t′0, t′1] is sufficiently small, It can be approximated as a constant, and then we get:

[0109]

[0110] The formula for the exponentially decreasing model is then obtained as follows:

[0111]

[0112] Figure 4 In order to be in Figure 3 The production data selected from the sub-intervals of the typical well production range [t0, t1] shows that the gas well production decline follows an exponential decline pattern, and D = 0.03 / mon can be obtained from the fitted exponential model.

[0113] S4. Combining the gas well production decline theoretical model with the Kozeny-Carman equation, a rock specific surface area model is established. By combining the equivalent gas leakage radius, gas well skin coefficient and well logging interpretation results in gas well static data, the rock specific surface area is obtained using the rock specific surface area model.

[0114] During the time period [t'0, t'1], the decline in gas well production follows an exponential decline model, based on which the following is obtained:

[0115]

[0116] According to the Kozeny-Carman equation

[0117]

[0118] In the formula, K represents the Kozeny constant, which is typically taken as 4.9, and S... φ The specific surface area of ​​the rock.

[0119] Combining formulas (28) and (29), the formula for calculating the specific surface area of ​​rocks is as follows:

[0120]

[0121] In the formula u g (p′), c g (p′) represents the natural gas viscosity and volume compressibility coefficient under the average formation pressure p′ condition within the approximately exponentially decreasing production data range.

[0122] comprehensive Figure 3 , Figure 4 Based on the obtained parameters, combined with the high-pressure physical property data of the gas reservoir and the well logging interpretation results, the specific surface area of ​​the rock in this well was calculated to be 8.19 × 10⁻⁶. 6 m 3 / m 3 .

[0123] Figure 5 The graph shows the rock surface area of ​​gas wells in different classification zones of the Xu'er gas reservoir in the Sichuan Basin, calculated using this invention (where gas well productivity in Class I zone > gas well productivity in Class II zone > gas well productivity in Class III zone). The graph reveals significant differences in average rock surface area among gas wells in different reservoir evaluation zones, providing a new evaluation factor for comprehensive reservoir evaluation. Furthermore, the average order of magnitude of rock surface area within the well-controlled area exceeds 10. 7According to reservoir formation theory, a larger specific surface area results in greater bound water saturation, greater fluid flow resistance, and lower gas well productivity. Therefore, effective reservoir stimulation is crucial for efficient gas reservoir development, providing a basis for adopting large-scale volumetric pressure engineering technology in this area. Applying this method to the comprehensive study of the Xujiahe Formation's Xu-2 gas reservoir in western Sichuan effectively supported the deployment and optimization of a 300 million cubic meter production capacity pilot project for the difficult-to-access reserves in the Xu-2 section of the Xujiahe Formation. Currently, all three production capacity construction wells have passed the efficiency threshold, and the stage well compliance rate has reached 100%.

[0124] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for evaluating the specific surface area of ​​rocks based on dynamic data of gas wells, characterized in that, Includes the following steps: S1. Collect and organize static and dynamic data of gas wells; S2. Using the gas well dynamic data in step S1, extract the part of the seepage law that satisfies Darcy's law using the Blasingame modern production harmonization decline chart curve, and record the time period corresponding to the part that satisfies Darcy's law as [t0, t1]. S3. Using static and dynamic data of the gas well, calculate the equivalent leakage radius and the gas well skin coefficient; using the time interval [t0, t1] from step S2, select a sub-interval [t'0, t'1], and use an exponential decline model for fitting to obtain the decline rate D. The formula for the exponential decline model is as follows: In the formula Let t'0 be the gas well production. Let t be the gas well production rate corresponding to time t. For a given time in the interval [t'0, t'1]; S4. Combining the theoretical model of declining gas well production with the Kozeny-Carman equation, a rock specific surface area model is established. The formula for the theoretical model of declining gas well production is as follows: In the formula Porosity Gas permeability; Combining the equivalent venting radius, well skin coefficient, and gas well static data, the rock specific surface area is obtained using a rock specific surface area model. The calculation formula for the rock specific surface area is as follows: In the formula Let K be the specific surface area of ​​the rock, and K be the Kozeny constant. The rate of decline, Mean formation pressure Natural gas viscosity under certain conditions Mean formation pressure Under certain conditions, the volume compressibility coefficient, To restrict water saturation, For the equivalent vent radius, Where is the wellbore radius. This is the skin coefficient of the gas well.

2. The method for evaluating rock specific surface area based on gas well dynamic data according to claim 1, characterized in that, Gas well static data includes high-pressure physical property analysis data tables and geological description data tables; gas well dynamic data includes production data tables and dynamic monitoring data tables.

3. The method for evaluating rock specific surface area based on gas well dynamic data according to claim 1, characterized in that, The formula that satisfies Darcy's law of seepage is: In the formula To normalize the output, ; To normalize time, , For gas well production, The pseudo-pressure under the initial formation pressure, The pseudo-pressure under the bottom hole flowing pressure, It is a constant. For gas well geological reserves, The overall compressibility coefficient of the formation under the initial formation conditions. This is a tentative timeframe.

4. The method for evaluating rock specific surface area based on gas well dynamic data according to claim 1, characterized in that, The specific steps of step S3 are as follows: S31. Select the portion of the harmonic decreasing curve that satisfies Darcy's law of permeability as the gas well fitting line; arbitrarily select points on the gas well fitting line. The geological reserves of the gas well are calculated using the following formula: In the formula For gas well geological reserves, The overall compressibility coefficient of the formation under the initial formation conditions. The normalized time corresponding to point M. The normalized output corresponding to point M. The pseudo-pressure under the initial formation pressure, The pseudo-pressure under the bottom hole flowing pressure, For gas well production, The pseudo-time used for point M. The normalized output corresponding to point M; S32. Calculate the natural gas volume factor under the conditions of original formation pressure and formation temperature; S33. Combining the interpretation of bound water saturation and porosity from gas well static data logging, the gas well seepage model is equivalent to a homogeneous circular central well model. The equivalent gas leakage radius is calculated using the volumetric method, and the gas well skin coefficient is calculated. The formula for calculating the equivalent gas leakage radius is as follows: In the formula This represents the natural gas volume factor under the original formation conditions. For reservoir thickness, Porosity; S34. Using the time interval [t0, t1] from step S2, select a sub-interval [t'0, t'1], fit it using an exponentially decreasing model, and calculate the decreasing rate. .

5. The method for evaluating rock specific surface area based on gas well dynamic data according to claim 4, characterized in that, The formula for calculating the volume factor of natural gas is as follows: In the formula This is the deviation factor under the initial state of the formation. This represents the initial formation pressure. This refers to the formation temperature.

6. The method for evaluating rock specific surface area based on gas well dynamic data according to claim 4, characterized in that, The formula for calculating the skin factor of a gas well is as follows: In the formula For gas well production, The initial formation viscosity. The pseudo-mean pressure under formation pressure. For gas permeability, For shape factor, The seepage area is denoted as .

7. The method for evaluating rock specific surface area based on gas well dynamic data according to any one of claims 1-6, characterized in that, In step S3, when selecting the sub-interval [t'0, t'1], the following condition must be met: , It is a constant. .

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