Methods and applications for testing the closed-porosity of shale reservoirs relative to methane gas.

Abstract

This invention provides a method and application for testing the closed-porosity of shale reservoirs relative to methane gas, specifically relating to the field of shale gas exploration and development technology. The method for testing the closed-porosity of shale reservoirs relative to methane gas includes a undisturbed sample pretreatment module, a undisturbed sample interconnected porosity testing module, a pulverized sample total porosity testing module, and a data processing module. The undisturbed sample interconnected porosity testing module uses methane isothermal adsorption testing for calculation compensation to obtain the total absolute adsorption amount of the undisturbed sample, and obtains the interconnected porosity based on the total absolute adsorption amount. The pulverized sample total porosity testing module is used to pulverize the undisturbed sample, taking a unit mass of pulverized sample and using a testing method that does not penetrate the internal pores of the particles to determine the total volume of the pulverized sample. Then, a methane isothermal adsorption test is performed on the pulverized sample to obtain the total absolute adsorption amount of methane in the pulverized sample, and obtains the total porosity based on the total absolute adsorption amount.

Description

Technical Field

[0001] This invention relates to the field of shale gas exploration and development technology, and in particular to a method and application for testing the porosity of shale reservoirs relative to methane gas. Background Technology

[0002] Shale reservoir closed-porosity (i.e., the percentage of closed pores to total porosity) is a core parameter for evaluating shale gas occurrence capacity, calculating geological reserves, and optimizing development plans. Current closed-porosity calculations rely on the formula (total porosity - connected porosity) / total porosity, but these two types of porosity are typically obtained using independent testing methods based on different principles, media, and samples. This separate testing approach has three inherent drawbacks: (1) Medium mismatch: The diameter of helium molecules (0.26 nm) is much smaller than that of methane (0.38 nm), and they have no adsorption properties. This means that the interconnected pores that helium recognizes may actually be closed pores for methane, resulting in a systematic underestimation of the closed pore rate.

[0003] (2) Systematic error superposition: Different methods have different dimensions, temperature and pressure conditions, and calibration systems. The errors cannot be propagated and canceled, resulting in high uncertainty of the results.

[0004] (3) Heterogeneity amplification error: Parallel sample testing cannot avoid the strong heterogeneity of shale microstructure, and the measured closed-pore rate deviation can reach more than 40%.

[0005] While image-based methods have attempted to directly statistically analyze pore connectivity, limitations in resolution and the difficulty of three-dimensional connectivity identification make it challenging to quantitatively characterize effective connectivity at the methane scale. Therefore, there is an urgent need for a method to determine closed-porosity using methane as the sole medium, sequential testing of the same sample, and in-situ adsorption correction, to achieve precise quantification of the actual fluid response in formations.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a method and application for testing the porosity of shale reservoirs relative to methane gas, aiming to solve at least one of the aforementioned technical problems in the prior art.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: The first aspect of the present invention provides a method for testing the closed porosity of shale reservoir relative to methane gas, including an undisturbed sample pretreatment module, an undisturbed sample interconnected porosity testing module, a pulverized sample total porosity testing module, and a data processing module.

[0009] The undisturbed sample preprocessing module is used to obtain fresh core samples as undisturbed samples along the bedding direction of the target reservoir, and to obtain the volume V of the undisturbed samples. 柱塞 .

[0010] The undisturbed sample interconnected porosity testing module uses a dual-chamber gas intrusion method to adsorb methane into the undisturbed sample, followed by degassing and drying to obtain the mass of the undisturbed sample; it uses a methane isothermal adsorption test for calculation compensation to obtain the total absolute adsorption amount of the undisturbed sample, and obtains the interconnected porosity through the total absolute adsorption amount of the undisturbed sample.

[0011] The total porosity testing module for the pulverized sample is used to pulverize the original sample, take a unit mass of pulverized sample and use a test method that does not penetrate the internal pores of the particles to determine the total volume of the pulverized sample, and then perform a methane isothermal adsorption test on the pulverized sample to obtain the total absolute adsorption amount of methane by the pulverized sample, and obtain the total porosity based on the total absolute adsorption amount of the pulverized sample.

[0012] The data processing module is used to calculate and output the closed-pore ratio of shale reservoir relative to methane gas based on the connected porosity and the total porosity.

[0013] In some embodiments of the present invention, the undisturbed sample is subjected to methane adsorption using a dual-chamber gas intrusion method, followed by degassing and drying to obtain the mass of the undisturbed sample. This includes: using a dual-chamber gas intrusion method to allow the undisturbed sample to reach equilibrium with methane adsorption at an experimental temperature T and a reference chamber pressure P1; recording the sample chamber pressure P2; after the test, degassing and drying the undisturbed sample; and weighing and obtaining the mass m of the undisturbed sample. 柱塞 .

[0014] In some embodiments of the present invention, the total absolute adsorption capacity of the undisturbed sample is obtained by calculating compensation using a methane isothermal adsorption test, including: using a two-chamber gas intrusion method to degas and dry the undisturbed sample at an experimental temperature T and a reference chamber pressure P1, until the sample chamber pressure reaches P2, and then obtaining the total absolute adsorption capacity V per unit mass of the undisturbed sample at this point. abs柱塞 , through m 柱塞 and V abs柱塞 V was calculated 吸附柱塞 .

[0015] In some embodiments of the present invention, V 吸附柱塞 The calculation formula is: V 吸附柱塞 =m 柱塞 ×V abs柱塞 .

[0016] V 吸附柱塞 This represents the total absolute adsorption capacity of the plunger sample under the conditions of temperature T and equilibrium pressure P2, expressed in cm³. 3 m 柱塞 V represents the plunger sample mass, in grams. abs柱塞 The absolute adsorption capacity per unit mass of plunger sample, expressed in cm³. 3 / g.

[0017] In some embodiments of the present invention, the interconnected porosity is obtained by measuring the total absolute adsorption amount of the undisturbed sample, including: first calculating the skeletal volume V of the undisturbed sample based on Boyle's law. 骨架 Then according to V 骨架 V 柱塞 V 吸附柱塞 And V in the dual-chamber gas intrusion method 参比室 and V 样品室 Calculate the connectivity porosity φ 连通 .

[0018] In some embodiments of the present invention, a unit mass of pulverized sample m is taken for pulverizing the original sample. 颗粒 A test method that does not penetrate the internal pores of the particles is used to determine the total volume of the pulverized sample, including: pulverizing the original sample to 40-60 mesh and drying it; weighing a unit mass of the pulverized sample; and calculating the total volume V of the unit mass of the particle sample before pulverization using the density method. 颗粒 .

[0019] In some embodiments of the present invention, the pulverized sample undergoes a methane isothermal adsorption test to obtain the total absolute adsorption capacity of the pulverized sample for methane, and the total porosity is obtained based on the total absolute adsorption capacity of the pulverized sample. This includes: using a dual-chamber gas intrusion method to allow the pulverized sample to reach methane adsorption equilibrium at an experimental temperature T and a reference chamber pressure P3, recording the sample chamber pressure P4, and obtaining the total absolute adsorption capacity V per unit mass of the pulverized sample at this time. abs颗粒 , through m 颗粒 and V abs颗粒 V was calculated 吸附颗粒 Then, according to V 颗粒 V 吸附颗粒 And V in the dual-chamber gas intrusion method 参比室’ and V 样品室’ Calculate total porosity φ 总 .

[0020] In some embodiments of the present invention, calculating and outputting the closed-porosity of the shale reservoir relative to methane gas based on the interconnected porosity and the total porosity includes: using the difference between the total porosity and the interconnected porosity as the closed-porosity, and using the proportion of the closed-porosity to the total porosity as the closed-porosity of the shale reservoir relative to methane gas.

[0021] In some embodiments of the present invention, the formula for calculating the closed-pore ratio is: η=(φ 总 -φ 连通 ) / φ 总 ×100%.

[0022] Where η is the closed-pore ratio of the undisturbed sample; φ 总 The total porosity of the pulverized sample; φ 连通 The porosity of the original sample.

[0023] The second aspect of this invention provides the application of the aforementioned porosity testing method in shale gas exploration and development.

[0024] Compared with the prior art, the present invention has at least the following beneficial effects: The testing method provided by this invention uses high-purity methane as the sole testing medium throughout the entire process. It combines a sequential process of testing interconnected porosity with a undisturbed plunger for the same sample, followed by testing total porosity by crushing particles. This eliminates three major technical bottlenecks from the source: misjudgment of porosity effectiveness caused by medium mismatch, superposition of systematic errors between methods, and interference from heterogeneity of parallel samples. It introduces a real-time correction mechanism for in-situ isothermal adsorption of methane, accurately removing the interference of adsorbed phase volume on Boyle's law calculation, and realizing adsorption compensation inversion of framework volume. Finally, it obtains physically consistent interconnected porosity and total porosity under unified temperature, pressure, and fluid scales, so that the closed-pore ratio calculation results truly reflect the pore-closing characteristics at the methane molecular scale.

[0025] This testing method can provide more accurate data on porosity that closely reflects the actual flow capacity of shale gas reservoirs, enabling detailed evaluation of shale gas reservoirs, calculation of geological reserves, and assessment of the effectiveness of development plans. It significantly improves the accuracy of geological modeling and the reliability of production prediction. Attached Figure Description

[0026] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific 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 from these drawings without creative effort.

[0027] Figure 1 This is a flowchart illustrating a method for testing the closed-porosity of shale reservoirs relative to methane gas. Figure 2 This is a flowchart illustrating another method for testing the closed-porosity of shale reservoirs relative to methane gas. Figure 3 This is a schematic diagram of a dual-chamber gas intrusion test apparatus. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0029] In the following, the terms “comprising,” “having,” and their cognates, which may be used in various embodiments of the invention, are intended only to indicate a particular feature, number, step, operation, element, component, or combination thereof, and should not be construed as excluding, firstly, the presence of one or more other features, numbers, steps, operations, elements, components, or combinations thereof, or adding the possibility of one or more features, numbers, steps, operations, elements, components, or combinations thereof.

[0030] The first aspect of this invention provides a method for testing the closed-porosity of shale reservoirs relative to methane gas, such as... Figure 1 As shown, it includes the S10 undisturbed sample pretreatment module, the S20 undisturbed sample interconnected porosity testing module, the S30 pulverized sample total porosity testing module, and the S40 data processing module.

[0031] The four modules of this invention constitute a complete shale porosity testing system: The S10 original sample pretreatment module focuses on sample fidelity, preserving the original pore structure characteristics to the maximum extent, eliminating interference from external fluids and impurities, and laying the foundation for subsequent testing.

[0032] The core of the S20 undisturbed sample connectivity porosity testing module lies in real fluid response. It does not rely on small molecule inert gases (such as helium), but directly uses methane as the test medium. Under simulated formation temperature and pressure conditions, methane molecules are allowed to actually contact and enter the rock pore system. Then, through precise adsorption measurement and volume inversion, the connectivity pore spaces that are truly open to methane and can participate in seepage transport are quantitatively characterized, thereby obtaining connectivity porosity with engineering flow significance.

[0033] The S30 pulverized sample total porosity testing module focuses on restoring the total porosity. By controllably pulverizing the same original sample, the physical barriers between the original particle boundaries and closed pores are broken, exposing all pores (including closed pores originally encased inside the particles) to the test environment. The test is then conducted under the same methane medium and similar temperature and pressure conditions, thereby measuring the total porosity covering the entire pore space. This achieves strict comparability with connected porosity in terms of fluid scale, test principle, and sample source.

[0034] As the final output stage, the S40 data processing module directly derives the key geological engineering indicator of closed porosity based on the pore parameters obtained from the first two modules, which have the same physical definition and origin. It reflects the proportion of silent pores in shale that exist but are actually inaccessible or unusable for methane due to factors such as size, connectivity, or surface effects. This truly serves the practical needs of assessing shale gas storage, predicting production capacity, and optimizing extraction plans.

[0035] It should be noted that the "original sample" mentioned in this invention refers to the "plunger sample".

[0036] In one embodiment of the present invention, the method for testing the closed-porosity of the shale reservoir relative to methane gas includes the following steps, such as... Figure 2 As shown: S12. The undisturbed sample pretreatment module is used to obtain fresh core samples as undisturbed samples along the bedding direction of the target reservoir, and to obtain the volume V of the undisturbed samples. 柱塞 .

[0037] In the specific implementation process, the preparation and pretreatment of undisturbed samples should strictly adhere to the principles of geological representativeness and structural fidelity: First, fresh, dense, and unweathered core samples are selected from the target reservoir along the original bedding direction. These are then processed using standard drilling equipment into cylindrical plunger samples with a diameter of 25.0 mm and a length of 45-55 mm (i.e., 50 mm ± 5 mm). Subsequently, through visual inspection using a stereomicroscope, samples with structural defects such as natural fractures, bedding stripping, edge chipping, or uneven end faces are removed, retaining only qualified plungers with intact structures and uniform surfaces. For qualified samples, the diameter and length are repeatedly measured in multiple orientations using vernier calipers, and the average value is used to accurately calculate the geometric total volume V. 柱塞 .

[0038] Pretreatment is carried out in two steps: the first step is organic matter removal, which involves continuous extraction using chloroform Soxhlet extraction for 72-120 hours to thoroughly remove residual oil and gas, asphaltene, and soluble organic matter; the second step is dehydration and drying, which is carried out differently according to the clay mineral content of the samples: for samples with high clay content, the drying process is carried out at 80℃ and a vacuum degree ≤1×10⁻⁶. -2 Drying at constant temperature for 24 hours under Pa conditions is necessary to avoid clay lattice collapse and irreversible changes in pore structure caused by high temperature. For samples with low clay content, drying at 105℃ and the same vacuum degree for 24 hours can remove free water and weakly bound water more efficiently.

[0039] After drying, the original sample must be naturally cooled to room temperature (about 25°C) in a vacuum drying oven, and then sealed for storage to prevent moisture absorption and ensure that subsequent tests reflect the intrinsic porosity characteristics of shale rather than interference from moisture or organic matter.

[0040] S22. The original sample interconnected porosity testing module uses a dual-chamber gas intrusion method to adsorb methane into the original sample, followed by degassing and drying to obtain the mass of the original sample; it uses a methane isothermal adsorption test for calculation compensation to obtain the total absolute adsorption amount of the original sample, and obtains the interconnected porosity through the total absolute adsorption amount of the original sample.

[0041] In some embodiments of the present invention, the undisturbed sample is subjected to methane adsorption using a dual-chamber gas intrusion method, followed by degassing and drying to obtain the mass of the undisturbed sample. This includes: using a dual-chamber gas intrusion method to allow the undisturbed sample to reach equilibrium with methane adsorption at an experimental temperature T and a reference chamber pressure P1; recording the sample chamber pressure P2; after the test, degassing and drying the undisturbed sample; and weighing and obtaining the mass m of the undisturbed sample. 柱塞 .

[0042] In the specific implementation process, the interconnected porosity of the plunger sample is tested using the two-chamber gas intrusion method, replacing the helium test medium with high-purity methane (purity ≥99.999%). The basic principle of the two-chamber porosity gas measurement method based on Boyle's law is as follows: Figure 3 As shown.

[0043] The first stage is constant pressure filling of the reference chamber: keep valves 2 and 3 closed, open only valve 1, and inject high-purity methane gas into the reference chamber at a preset and stable initial pressure P1; after the system pressure stabilizes (fluctuation less than 0.1 psi, lasting ≥5 min), close valve 1 to complete the initial state setting of the reference chamber.

[0044] The second stage is gas expansion and adsorption equilibrium: with valve 3 kept closed, valve 2 is opened, allowing the methane gas in the reference chamber to rapidly expand into the sample chamber loaded with the plunger sample. At this time, the gas first fills the macroscopic gaps and open channels between sample particles, and then slowly penetrates into the micro-nano pores of the shale matrix, where it undergoes physical adsorption on the solid surface. This process is significantly affected by pore structure, specific surface area, and methane-mineral interaction. Therefore, pressure equilibrium is not achieved instantaneously, but requires continuous monitoring of pressure changes in the sample chamber until the pressure fluctuation does not exceed 0.05 psi for 10 consecutive minutes, at which point the system can be considered to have reached both thermodynamic and adsorption kinetic equilibrium.

[0045] For conventional shale samples, the equilibrium time usually exceeds 2 hours, while for dense samples with low porosity, poor permeability, and high organic matter or clay content, the equilibrium time may be extended to 6 hours or even longer. The experiment maintains a constant temperature (e.g., 25℃) throughout, and after equilibrium is achieved, the experimental temperature T, the initial pressure P1 of the reference chamber, and the final equilibrium pressure P2 of the sample chamber are accurately recorded to provide reliable basic data for subsequent skeleton volume inversion based on Boyle's law and combined with adsorption correction.

[0046] Although the system reaches macroscopic pressure equilibrium (i.e., the pressure in the reference chamber and the sample chamber is stable and consistent) after valve 2 is opened, the equilibrium pressure P2 measured at this time cannot be directly used for Boyle's law calculation. The reason is that some methane gas does not exist in the pore space as a free gas phase, but is physically adsorbed on the surface of highly adsorbent components such as shale organic matter and clay minerals, forming a non-negligible adsorbed phase volume.

[0047] The adsorbed phase does not participate in the compressible free volume change during gas expansion, but it significantly occupies the true pressure response signal that should reflect the pore space. This leads to a systematic bias in the framework volume inferred from the ideal gas model—that is, traditional Boyle's law calculations misjudge the adsorbed gas as free gas occupying the pore volume, thus overestimating the framework volume and underestimating the interconnected porosity. Therefore, it is necessary to introduce an adsorption capacity measurement and volume compensation mechanism. By simultaneously conducting isothermal adsorption experiments of methane under the same temperature and pressure conditions, the absolute adsorption capacity per unit mass of sample can be accurately obtained and converted into an equivalent volume, which is then subtracted from the gas expansion model. Only in this way can the accurate inversion of the framework volume be achieved, ensuring that the physical meaning of interconnected porosity truly reflects the effective permeation channels at the methane molecular scale.

[0048] In some embodiments of the present invention, the total absolute adsorption capacity of the undisturbed sample is obtained by calculating compensation using a methane isothermal adsorption test, including: using a two-chamber gas intrusion method to degas and dry the undisturbed sample at an experimental temperature T and a reference chamber pressure P1, until the sample chamber pressure reaches P2, and then obtaining the total absolute adsorption capacity V per unit mass of the undisturbed sample at this point. abs柱塞 , through m 柱塞 and V abs柱塞 V was calculated 吸附柱塞 .

[0049] The plunger sample was sealed and placed into the sample chamber of the high-pressure isothermal adsorption apparatus. After completing the system's airtightness and pressure holding test, the constant temperature control system was turned on to stabilize the sample chamber, reference chamber, and supporting pipelines to the set experimental temperature T throughout the process. The system was degassed under high vacuum until the vacuum level stabilized. High-purity helium was introduced to calibrate the system's free space volume. The helium was then emptied and a vacuum was evacuated again to remove residual gas. Subsequently, high-purity methane with a purity ≥99.999% was introduced into the system to the set experimental pressure P2 (the equilibrium pressure P2 in step 1). The system pressure change was continuously monitored at a constant temperature T until the pressure remained continuously stable, indicating adsorption equilibrium. Finally, based on the actual gas law, combined with the methane charge, equilibrium temperature and pressure parameters, free space volume, and methane compressibility factor under the corresponding conditions, the isothermal adsorption capacity V of the plunger sample under the conditions of temperature T and pressure P2 was calculated. abs柱塞 .

[0050] In some embodiments of the present invention, V 吸附柱塞 The calculation formula is: V 吸附柱塞 =m 柱塞 ×V abs柱塞 .

[0051] V 吸附柱塞 This represents the total absolute adsorption capacity of the plunger sample under the conditions of temperature T and equilibrium pressure P2, expressed in cm³. 3 m 柱塞 V represents the plunger sample mass, in grams.abs柱塞 The absolute adsorption capacity per unit mass of plunger sample, expressed in cm³. 3 / g.

[0052] In some embodiments of the present invention, the interconnected porosity is obtained by measuring the total absolute adsorption amount of the undisturbed sample, including: first calculating the skeletal volume V of the undisturbed sample based on Boyle's law. 骨架 Then according to V 骨架 V 柱塞 V 吸附柱塞 And V in the dual-chamber gas intrusion method 参比室 and V 样品室 Calculate the connectivity porosity φ 连通 .

[0053] In some specific embodiments of the present invention, based on Boyle's law, the following formula can be derived during the porosity test: P1×V 参比室 =P2×(V 参比室 +V 样品室 -V 骨架 ).

[0054] Where P1 is the initial pressure of the reference chamber; P2 is the pressure after expansion; V 参比室 V is the volume of the reference chamber. 样品室 V is the volume of the sample chamber. 骨架 The volume of the plunger sample's skeleton; However, in the test process using methane as the medium, the adsorption of methane on the sample must be considered. After the first stage of equilibration, methane is filled into the reference chamber under pressure P1, and its volume is V. 参比室 After the second stage of equilibration, a portion of it exists as a gaseous phase in the reference chamber and the sample chamber, with a volume of (V). 参比室 +V 样品室 -V 骨架 Another portion of the gas is adsorbed onto the solid interface surface, and its volume under pressure P2 is V. 吸附 According to Boyle's law, its volume under P1 is P2 × V. 吸附 / P1, therefore we know: P1×(V 参比室 -P2×V 吸附 / P1) = P2 × (V 参比室 +V 样品室 -V 骨架 ).

[0055] It can be further deduced that: V 骨架 =V 样品室 +V 吸附 +V 参比室 (1-P1 / P2).

[0056] According to the porosity calculation formula: φ 连通 = (V柱塞 -V 骨架 ) / V 柱塞 ×100%=[V 柱塞 -V 样品室 -V 吸附柱塞 -V 参比室 [(1-P1 / P2)] / V 柱塞 ×100%.

[0057] Among them, V 柱塞 The total volume of the plunger sample is expressed in cm³. 3 V 参比室 The volume of the reference chamber is in cm³. 3 V 样品室 This refers to the volume of the sample chamber, in cm³. 3 V 吸附柱塞 The total absolute adsorption capacity (adsorption volume) of the plunger sample under the conditions of temperature T and equilibrium pressure P2 is expressed in cm³. 3 P1 is the initial pressure in the reference chamber; P2 is the pressure after expansion; φ 连通 The porosity of the plunger sample.

[0058] S32. The total porosity test module for the pulverized sample is used to pulverize the original sample, take a unit mass of pulverized sample and use a test method that does not penetrate the internal pores of the particles to determine the total volume of the pulverized sample, and then perform a methane isothermal adsorption test on the pulverized sample to obtain the total absolute adsorption amount of methane by the pulverized sample, and obtain the total porosity based on the total absolute adsorption amount of the pulverized sample.

[0059] In some embodiments of the present invention, a unit mass of pulverized sample m is taken for pulverizing the original sample. 颗粒 The total volume of the pulverized sample is determined using a test method that does not penetrate the internal pores of the particles. This includes: pulverizing the original sample to 40-60 mesh, drying it, weighing a unit mass of the pulverized sample, and calculating the total volume V of the pulverized sample using the mercury immersion method. 颗粒 .

[0060] In a specific embodiment of the present invention, the same plunger sample that has undergone the interconnected porosity test is sieved to 40-60 mesh particles, and then subjected to a test at 80-105°C and a vacuum degree ≤1×10⁻⁶. -2 Vacuum drying under Pa conditions for 24 hours to remove free water from the sample (samples with high clay mineral content were dried at 80℃ to avoid damaging the clay structure); after cooling to room temperature in a vacuum drying oven, approximately 20g of the sample was accurately weighed using a 0.01 g electronic balance and the mass m was recorded. 颗粒 (g).

[0061] Based on the mass and total volume of the plunger sample in S22, calculate the sample density. Then, based on the mass of the weighed particle sample, calculate the true total volume V of the particle sample before crushing. 颗粒 .

[0062] In some embodiments of the present invention, the pulverized sample undergoes a methane isothermal adsorption test to obtain the total absolute adsorption capacity of the pulverized sample for methane, and the total porosity is obtained based on the total absolute adsorption capacity of the pulverized sample, including: obtaining the total absolute adsorption capacity V through an isothermal adsorption experiment. abs颗粒 , through m 颗粒 and V abs颗粒 V was calculated 吸附颗粒 Then, according to V 颗粒 V 吸附颗粒 And V in the dual-chamber gas intrusion method 参比室’ and V 样品室’ Calculate total porosity φ 总 .

[0063] The specific process for methane isothermal adsorption testing of the pulverized sample is as follows: Under temperature-controlled conditions (same as the plunger sample test temperature), the interconnected porosity of the plunger sample is tested using the dual-chamber gas intrusion method. The test steps are as follows: Stage 1: Open valve 1 to introduce the gas medium into the reference chamber at a predetermined pressure, close valve 1, and read the pressure value P3 after the pressure stabilizes; Stage 2: Open valve 2 to allow the gas in the reference chamber to expand and enter the sample chamber containing the pulverized sample, and read the pressure P4 after pressure equilibrium is reached. (Valve 3 is closed in both stages above.) The equilibrium time for shale samples is generally >2 hours. Record the two equilibrium pressures P3 and P4 under the experimental temperature T.

[0064] After degassing and drying the pulverized sample, a static volumetric method was used to conduct a methane isothermal adsorption experiment on the pulverized sample to test the isothermal adsorption capacity at an experimental temperature T and a pressure P4. The specific procedure was as follows: The pulverized sample was sealed and placed into the sample chamber of the high-pressure isothermal adsorption instrument. After completing the system's airtightness and pressure holding test, the constant temperature control system was activated to stabilize the sample chamber, reference chamber, and associated pipelines at the set experimental temperature T throughout the process. The system was degassed under high vacuum until the vacuum level stabilized. High-purity helium was introduced to calibrate the system's free space volume. The helium was then emptied, and a vacuum was evacuated again to remove residual gas. Subsequently, high-purity methane with a purity ≥99.999% was introduced into the system to the set experimental pressure P4 (the equilibrium pressure P4 in step 1). The system pressure change was continuously monitored at a constant temperature T until the pressure remained continuously stable, indicating adsorption equilibrium. Finally, based on the actual gas state equation, combined with the methane charge amount, equilibrium temperature and pressure parameters, free space volume, and the methane compressibility factor under the corresponding conditions, the isothermal adsorption capacity V of the pulverized sample at temperature T and pressure P4 was calculated. abs颗粒 .

[0065] Based on the sample mass, the total absolute adsorption capacity of the sample under the experimental temperature T and equilibrium pressure P4 can be calculated: V 吸附颗粒 =m 颗粒 ×V abs颗粒 Among them, V 吸附颗粒 This represents the total absolute adsorption capacity (adsorption volume) of the pulverized sample under the conditions of temperature T and equilibrium pressure P4, in cm³. 3 m 颗粒 Mass of the pulverized sample, in g, V abs颗粒 Absolute adsorption capacity per unit mass, expressed in grams per cubic centimeter (cm³). 3 / g).

[0066] According to the porosity calculation formula: φ 总 =[V 颗粒 -V 样品室’ -V 吸附颗粒 -V 参比室’ (1-P3 / P4)] / V 颗粒 ×100%; where V 颗粒 This represents the total volume of the pulverized sample, in cm³. 3 V 参比室’ The volume of the reference chamber is in cm³. 3 V 样品室’ This refers to the volume of the sample chamber, in cm³. 3 V 吸附颗粒 The total absolute adsorption capacity (adsorption volume) of the plunger sample under the conditions of temperature T and equilibrium pressure P4 is expressed in cm³. 3 P3 is the initial pressure in the reference chamber; P4 is the pressure after expansion; φ 总 The total porosity of the pulverized sample.

[0067] It should be noted that the volumes of the reference chamber and sample chamber of the equipment need to be recalibrated before each experiment; therefore, the V values ​​measured between two consecutive experiments will differ. 参比室’ V 样品室’ They may be different.

[0068] S32. The data processing module is used to calculate and output the closed-pore ratio of shale reservoir relative to methane gas based on the connected porosity and the total porosity.

[0069] In some embodiments of the present invention, calculating and outputting the closed-porosity of the shale reservoir relative to methane gas based on the interconnected porosity and the total porosity includes: using the difference between the total porosity and the interconnected porosity as the closed-porosity, and using the proportion of the closed-porosity to the total porosity as the closed-porosity of the shale reservoir relative to methane gas.

[0070] In some embodiments of the present invention, the formula for calculating the closed-pore ratio is: η=(φ 总 -φ 连通 ) / φ总 ×100%.

[0071] Where η is the closed-pore ratio of the undisturbed sample; φ 总 The total porosity of the pulverized sample; φ 连通 The porosity of the original sample.

[0072] The second aspect of this invention provides the application of the aforementioned porosity testing method in shale gas exploration and development.

[0073] The testing method provided by this invention uses high-purity methane as the sole testing medium throughout the entire process. It combines a sequential process of testing interconnected porosity with a undisturbed plunger for the same sample, followed by testing total porosity by crushing particles. This eliminates three major technical bottlenecks from the source: misjudgment of porosity effectiveness caused by medium mismatch, superposition of systematic errors between methods, and interference from heterogeneity of parallel samples. It introduces a real-time correction mechanism for in-situ isothermal adsorption of methane, accurately removing the interference of adsorbed phase volume on Boyle's law calculation, and realizing adsorption compensation inversion of framework volume. Finally, it obtains physically consistent interconnected porosity and total porosity under unified temperature, pressure, and fluid scales, so that the closed-pore ratio calculation results truly reflect the pore-closing characteristics at the methane molecular scale.

[0074] This testing method can provide more accurate data on porosity that closely reflects the actual flow capacity of shale gas reservoirs, enabling detailed evaluation of shale gas reservoirs, calculation of geological reserves, and assessment of the effectiveness of development plans. It significantly improves the accuracy of geological modeling and the reliability of production prediction.

[0075] The present invention is further illustrated below with specific embodiments and comparative examples. However, it should be understood that these embodiments are merely for illustrative purposes and should not be construed as limiting the invention in any way. Unless otherwise specified, the raw materials used in the embodiments and comparative examples of the present invention were carried out under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0076] Application examples and verification examples This application example uses the Cambrian Niutitang Formation shale in western Hubei Province as the test object. The method of this invention is used to test the relative methane gas porosity, and the results are compared with those of the traditional method using helium as the medium. The specific implementation process and test results are as follows: 1. Plunger Sample Preparation and Pretreatment Fresh, full-diameter core samples from the target stratum were selected, and two standard plunger samples were drilled along the bedding direction. After examination with a stereomicroscope, the samples showed no natural cracks, no bedding stripping, no spalling, and smooth end faces, meeting the testing requirements. The average diameter and length of each sample were calculated using multi-point measurements with vernier calipers, and the total geometric volume of the samples was calculated (Table 1).

[0077] The sample was subjected to a 96-hour oil washing treatment using chloroform Soxhlet extraction to thoroughly remove residual oil vapors and asphaltenes. After washing, the sample was stored at 105℃ under a vacuum of ≤1×10⁻⁶. -2 Vacuum dried under Pa conditions for 24 hours, cooled to 25°C in a vacuum drying oven, and then the dry weight of the plunger sample was weighed and sealed for later use.

[0078] 2. Helium plunger sample interconnection porosity test The test medium was high-purity helium gas with a purity ≥99.999%. The experimental temperature was constant at 25℃, with temperature fluctuations ≤±0.1℃. The test method followed the dual-chamber gas intrusion method of GB / T29172-2012 "Core Analysis Methods". The test results are shown in Table 1.

[0079] Table 1. Results of Helium Diffusion Porosity Measurement of Samples

[0080] 3. Testing the interconnected porosity of high-purity methane media plunger samples After the plunger samples underwent helium porosity testing, they were left to stand in a dry environment for 24 hours before undergoing porosity testing using methane as the medium. The test medium was high-purity methane with a purity ≥99.999%. The experimental temperature was constant at 25℃, with temperature fluctuations ≤±0.1℃. The test method followed the dual-chamber gas intrusion method of GB / T29172-2012 "Core Analysis Methods". The test results are shown in Table 2.

[0081] (1) System calibration: Before the experiment, the porosity meter was calibrated using a standard gauge block that had been calibrated by metrology to obtain the volume V of the reference chamber. 参比室 =9.875cm 3 Sample chamber volume V 样品室= 24.921cm 3 The airtightness test was completed, and the system pressure drop was ≤0.1psi for 24 hours at 200psi pressure, which meets the test requirements.

[0082] (2) Reference chamber filling: Fix the plunger sample in the sample chamber, close valves 2 and 3, open valve 1 to introduce high-purity methane into the reference chamber to the initial pressure, close valve 1, and record P1 after the pressure stabilizes.

[0083] (3) Gas expansion and equilibrium: Open valve 2 to allow methane in the reference chamber to expand into the sample chamber. Continuously monitor the system pressure change. After 8 hours, if the pressure fluctuates continuously for 10 minutes with a value ≤0.05 psi, it is determined to be in pressure equilibrium. Record the second equilibrium pressure P2. The experimental temperature is 25℃.

[0084] Table 2 Porosity data of methane plunger samples (without isothermal adsorption correction)

[0085] 4. Calibration of methane isothermal adsorption capacity under corresponding temperature and pressure conditions for plunger samples For the plunger samples that have completed the interconnected porosity test, a methane isothermal adsorption experiment was conducted under isothermal conditions of 25℃ and P2 pressure using the static volumetric method, as detailed below: (1) Isothermal adsorption test: The plunger sample was sealed and placed into the sample chamber of the high-pressure isothermal adsorption instrument. After the airtightness test was completed, the temperature was kept constant at 25℃ throughout the process. The system was degassed under high vacuum until the vacuum degree was ≤1×10 -3 The free space volume was calibrated by introducing high-purity helium gas, and then the helium was purged before evacuating the vacuum again. High-purity methane was then introduced until the equilibrium pressure P2 was reached. The isothermal adsorption apparatus has a pressure control accuracy of 0.1 MPa (approximately 1.45 psi). The P2 values ​​for the three samples ranged from 83.67 to 92.69 psi. Therefore, the experimental pressure was uniformly set at 0.6 MPa (approximately 87 psi) during the isothermal adsorption experiment, and the pressure was continuously monitored until adsorption equilibrium was reached.

[0086] (2) Adsorption capacity calculation: Based on the actual gas law, the absolute adsorption capacity V per unit mass of sample under the conditions of 25 degrees Celsius and P2 pressure is calculated. abs柱塞 After converting to gas phase volume under 25℃ and P2 conditions, the total absolute adsorption volume of the sample is calculated: V 吸附柱塞 =m 柱塞 ×V abs柱塞 .

[0087] The experimental results are shown in Table 3.

[0088] Table 3. Results of methane isothermal adsorption (25℃, 0.6 MPa)

[0089] 5. Calculation of the interconnected porosity of the plunger sample after adsorption correction To address the interference from the adsorbed phase in methane media testing, a corrected formula for calculating the framework volume and interconnected porosity is derived based on Boyle's law, eliminating systematic errors caused by adsorbed gas. The details are as follows: According to the porosity calculation formula: φ 连通 = [V 柱塞 -V 样品室 -V 吸附柱塞 -V 参比室 [(1-P1 / P2)] / V 柱塞 ×100%.

[0090] Table 4. Corrected Piston Connectivity Porosity Results

[0091] 6. Granulation treatment of the same sample and total porosity test of helium gas This step uses the same plunger sample that underwent the connectivity porosity test as described above for processing, completely eliminating parallel sample testing errors caused by shale heterogeneity. The specific operation is as follows: (1) Sample crushing and sieving: The plunger sample was crushed using an agate mortar and sieved to 40-60 mesh using a standard test sieve. Preliminary experiments have verified that this particle size can completely open the original closed pores of the sample without the formation of artificial pores due to excessive crushing.

[0092] (2) Drying and weighing: The sieved pulverized sample was placed in a vacuum drying oven at 80℃ and a vacuum degree ≤1×10 - 2 After vacuum drying for 24 hours under Pa conditions and cooling to 25°C, the matrix porosity (total porosity) of the particle samples was tested using a vacuum density meter with helium as the medium. The experimental method was in accordance with GB / T 29172-2012 Core Analysis Methods. The total porosity of the two particle samples was obtained: NTT-1 had a total porosity of 4.20% and NTT-2 had a total porosity of 4.50%.

[0093] 7. High-purity methane media pulverized sample skeleton volume test (1) Take another pretreated particle sample and weigh it accurately using an electronic balance with an accuracy of 0.01g to obtain the sample mass m. 颗粒 .

[0094] (2) Calculate the density of the sample based on the mass and total volume of the plunger sample, and then calculate the true total volume V of the particle sample before crushing based on the mass of the particle sample weighed. 颗粒 The test results are shown in Table 5.

[0095] Table 5 Basic data of particle samples

[0096] (3) The total porosity of the particulate sample was tested using high-purity methane with a purity ≥ 99.999% as the medium. The temperature was kept constant at 25℃ throughout the test, with temperature fluctuations ≤ ±0.1℃. The test method was the two-chamber gas intrusion method based on Boyle's law for ideal gases. The specific steps are as follows: ①System calibration and airtightness test: Before the experiment, the porosity meter was recalibrated using standard gauge blocks to obtain the reference chamber volume V. 参比室’ =9.872cm 3 Because the sample volume in the sample chamber has decreased, resulting in an excessively large dead volume, it is necessary to add a standard block to the sample chamber. After adding the standard block, the sample chamber volume V will be increased. 样品室’ =7.933cm 3 The airtightness test was completed, and the system pressure drop was ≤0.5psi for 24 hours at 200psi pressure, which meets the test requirements.

[0097] ② Pressurize the reference chamber: Evenly load the weighed pulverized sample into the sample chamber, close valves 2 and 3, open valve 1 to introduce high-purity methane into the reference chamber until the initial pressure P3 is about 200 psi, close valve 1, and record P3 after the pressure stabilizes.

[0098] ③ Gas expansion and equilibrium: Open valve 2 to allow the methane gas in the reference chamber to expand into the sample chamber. Continuously monitor the system pressure change. After 4 hours, if the pressure fluctuation is ≤0.05psi for 10 minutes, the pressure is considered to be in equilibrium. Record the equilibrium pressure P4 and the experimental temperature 25℃. Calculate the particle sample skeleton volume and porosity. The results are shown in Table 6.

[0099] Table 6. Porosity data of methane particulate samples (without isothermal adsorption correction)

[0100] 8. Correction of methane isothermal adsorption capacity in particulate samples For the pulverized sample that has completed the skeleton volume test, a methane isothermal adsorption experiment was conducted at 25℃ and P4 conditions using the static volumetric method. The absolute adsorption capacity under the test conditions was directly output, ignoring the influence of the gas compressibility factor. The specific steps are as follows: (1) Remove the pulverized sample from the porosimeter and test it again at 105℃ and a vacuum degree ≤1×10 -2 Vacuum dried under Pa conditions for 12 hours, cooled to 25°C and the quality was checked again to confirm that there was no loss of sample quality.

[0101] (2) Isothermal adsorption test: The pulverized sample was sealed and placed into the sample chamber of the high-pressure isothermal adsorption instrument. After the airtightness test was completed, the temperature was kept constant at 25℃ throughout the process. The system was degassed under high vacuum until the vacuum degree was ≤1×10. -3 Pa, high-purity helium was introduced to calibrate the free space volume, and after the helium was purged, a vacuum was drawn again; then high-purity methane was introduced to the equilibrium pressure of 0.8 MPa (about 116 psi), and the pressure was continuously monitored until adsorption equilibrium was reached.

[0102] (3) Adsorption capacity calculation: Based on the ideal gas law, by substituting the test parameters of 25℃ and P4, the absolute adsorption capacity V per unit mass of pulverized sample under the test conditions is directly calculated. abs颗粒 Total absolute adsorption volume V 吸附颗粒 The results are shown in Table 7.

[0103] Table 7. Isothermal adsorption results of methane in particulate samples (25℃, 0.8MPa)

[0104] 9. Calculation of total porosity of the pulverized sample after adsorption correction Based on the correction formula for Boyle's law for ideal gases, the total porosity of the pulverized sample is calculated using the following formula: φ总 =[V 颗粒 -V 样品室 -V 吸附颗粒 -V 参比室 (1-P3 / P4)] / V 颗粒 ×100%; values ​​and calculation results are shown in Table 8.

[0105] Table 8. Results of Corrected Piston Connectivity Porosity

[0106] 10. Calculation of relative methane closed-porosity in shale reservoirs and comparison with traditional methods Based on the total porosity and connected porosity obtained from sequential testing of the same sample, the closed-porosity of the sample relative to methane and the closed-porosity tested using helium as the medium are calculated using the core formula for closed-porosity: η=(φ 总 -φ 连通 ) / φ 总 ×100%. The results are shown in Table 9.

[0107] Table 9: Calculation Results of Relative Methane and Helium Pore Closure Rates in Shale Reservoirs

[0108] Comparative experimental results show that when methane is used directly as a medium to test the porosity of plungers or particulate samples, the test results deviate far from the true values ​​due to the influence of methane adsorption.

[0109] After correction using the methane isothermal adsorption experiment, the porosity was smaller than that measured by helium under the same experimental conditions, which is consistent with the understanding that methane molecules have a large diameter and can penetrate a smaller proportion of the pores than helium.

[0110] The closed-pore ratio of shale gas measured by methane is larger than that measured by helium, proving that more pores are closed pores for methane. This key factor should be considered when using the volumetric method to calculate shale gas resources to avoid overestimating the resource amount.

[0111] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, 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, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for testing the relative shut-in rate of a shale reservoir to methane gas, characterized by, The original sample pretreatment module, the original sample connected porosity testing module, the crushed sample total porosity testing module, and the data processing module are included. The in-situ sample pretreatment module is configured to obtain a fresh core as an in-situ sample along a bedding direction of a target reservoir, and obtain a volume V of the in-situ sample 柱塞 ; The original sample connected porosity testing module uses a double-chamber gas intrusion method to make the original sample adsorb methane, and then degas and dry to obtain the mass of the original sample; a methane isothermal adsorption test is used for calculation compensation to obtain the total absolute adsorption amount of the original sample, and the connected porosity is obtained through the total absolute adsorption amount of the original sample; The crushed sample total porosity testing module is used for crushing the original sample, taking a unit mass of the crushed sample, using a test method that does not intrude into the internal pores of the particles, measuring the total volume of the crushed sample, then performing a methane isothermal adsorption test on the crushed sample to obtain the total absolute adsorption amount of the crushed sample to the methane, and obtaining the total porosity according to the total absolute adsorption amount of the crushed sample; The data processing module is used for calculating and outputting the closed porosity rate of the shale reservoir relative to the methane gas based on the connected porosity and the total porosity.

2. The closed cell fraction test method of claim 1, wherein, The original sample connected porosity testing module uses a double-chamber gas intrusion method to make the original sample adsorb methane, and then degas and dry to obtain the mass of the original sample; a methane isothermal adsorption test is used for calculation compensation to obtain the total absolute adsorption amount of the original sample, and the connected porosity is obtained through the total absolute adsorption amount of the original sample; The original sample is made to adsorb methane to reach equilibrium at experimental temperature T and reference chamber pressure P1 by using double-chamber gas invasion method, and sample chamber pressure P2 is recorded. After the test is completed, the original sample is dehydrated and dried, and the mass m of the original sample is weighed and obtained 柱塞 .

3. The closed cell fraction test method of claim 1, wherein, The crushed sample total porosity testing module is used for crushing the original sample, taking a unit mass of the crushed sample, using a test method that does not intrude into the internal pores of the particles, measuring the total volume of the crushed sample, then performing a methane isothermal adsorption test on the crushed sample to obtain the total absolute adsorption amount of the crushed sample to the methane, and obtaining the total porosity according to the total absolute adsorption amount of the crushed sample; The total absolute adsorption amount V of the undisturbed sample per unit mass of the sample is obtained when the sample chamber pressure is P2 at the experimental temperature T and the reference chamber pressure P1 by using the double-chamber gas intrusion method after degassing and drying the undisturbed sample abs柱塞 , V is calculated by m 柱塞 and V abs柱塞 . 吸附柱塞 .

4. The closed cell fraction test method of claim 3, wherein, V 吸附柱塞 The calculation formula is: V 吸附柱塞 = m 柱塞 × V abs柱塞 ; V 吸附柱塞 Q is the total absolute adsorbed amount of the sample at temperature T, equilibrium pressure P2, in cm3 / g 3 ; m 柱塞 m is the mass of the sample in g; V abs柱塞 The absolute adsorption amount is the amount of adsorbed gas per unit mass of the sample, and is expressed in cm3 / g. 3 / g.

5. The closed cell fraction test method of claim 1, wherein, The data processing module is used for calculating and outputting the closed porosity rate of the shale reservoir relative to the methane gas based on the connected porosity and the total porosity. Based on Boyle's law, the original sample skeleton volume V is calculated first 骨架 Then, according to V 骨架 , V 柱塞 , V 吸附柱塞 and V 参比室 and V 样品室 , the connected porosity φ 连通 is calculated.

6. The closed cell fraction test method of claim 1, wherein, The raw sample is crushed, and a unit mass of the crushed sample m is taken 颗粒 The total volume of the crushed sample is measured using a method that does not invade the pores inside the particles, including: The as-received sample is crushed to 40-60 mesh and a unit mass of the crushed sample is dried and used to calculate the total volume V of the crushed sample using the mercury intrusion method 颗粒 .

7. The closed cell fraction test method of claim 1, wherein, The difference between the total porosity and the connected porosity is the closed porosity, and the proportion of the closed porosity in the total porosity is taken as the closed porosity rate of the shale reservoir relative to the methane gas. The double-chamber gas invasion method is used to make the crushed sample adsorb methane to reach equilibrium at the experimental temperature T and the reference chamber pressure P3, and the sample chamber pressure P4 is recorded to obtain the total absolute adsorption amount V of the unit mass sample of the crushed sample at this time abs颗粒 , V 颗粒 is calculated by m abs颗粒 and V 吸附颗粒 ; Next, the total porosity φ 颗粒 is calculated from V 吸附颗粒 and V 参比室’ and V 样品室’ in the double-chamber gas intrusion method. 总 ​ 8. The closed cell fraction test method of claim 1, wherein, The formula for calculating the closed porosity rate is:

10. The closed porosity test method according to any one of claims 1-9 is applied in shale gas exploration and development.

9. The closed cell fraction test method of claim 8, wherein, ​ η = (φ 总 - φ 连通 ) / φ 总 x 100%; wherein η is the closed porosity of the as-received sample; φ 总 is the total porosity of the crushed sample; φ 连通 is the connected porosity of the as-received sample. ​

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