Method and device for determining thickness of hydration film of shale reservoir

Abstract

The invention relates to the technical field of exploration and development of unconventional oil and gas reservoirs, in particular to a method and device for determining the thickness of a hydration film of a shale reservoir. The method comprises the following steps: acquiring a core sample of a target shale, and determining an initial dissociation temperature T1 and a complete dissociation temperature T2 of a hydration membrane in the core sample through molecular dynamics simulation; based on the dissociation temperatures T1 and T2, determining the mass m of a hydration membrane in the rock core sample through a temperature-controlled drying experiment; determining the specific surface area SBET of the rock core sample by using a gas adsorption experiment; and determining the average hydration film thickness h of the shale reservoir according to the mass m of the hydration film and the specific surface area SBET of the rock core sample. According to the method, microscopic simulation and macroscopic experiments are combined, quantitative and accurate evaluation of the overall average hydration film thickness of the shale reservoir is achieved, and key parameters are provided for seepage mechanism research and development scheme formulation of unconventional oil and gas reservoirs.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of unconventional oil and gas reservoir exploration and development, and particularly relates to a method and device for determining the hydration film thickness of a shale reservoir. BACKGROUND

[0002] With the continuous development of oil fields, the productivity of conventional reservoirs with good reservoir properties gradually decreases after years of exploitation, and unconventional oil and gas resources such as shale oil are increasingly attracting attention. Although unconventional reservoirs have poor physical properties, they have huge reserves and broad development prospects. When developing sandstone reservoirs with large pore sizes, the influence of hydration film thickness on pore size is often ignored. However, during the development of shale reservoirs, the large number of nanoscale pores in the reservoirs makes the hydration film thickness affect the flowable space in the pores.

[0003] Currently, the hydration film thickness is measured by a theoretical calculation method. This method is based on the double-electric-layer theory and combines the electrical properties, ion concentration and other parameters in the clay solution to calculate the theoretical thickness of the double-electric-layer. However, this calculation method requires many related parameters such as clay particles and aqueous solutions, and the calculation process is complex. Moreover, since it is a theoretical calculation, it only has reference value for actual reservoirs.

[0004] With the continuous development of equipment, a method for measuring the hydration film thickness by means of an atomic force microscope has emerged. This method obtains the penetration and retraction curve by means of the hydration film model and the penetration test principle, and obtains the hydration film thickness by analyzing the curve. This method directly measures the hydration film thickness on the surface of the reservoir. However, due to the small size of the atomic force microscope probe, this technology is limited to analyzing the hydration film thickness of a small local part of the mineral sample, and lacks a macroscopic understanding of the whole. Therefore, it is necessary to establish a new calculation method for measuring the average hydration film thickness of shale reservoirs. SUMMARY

[0005] The present application provides a method and device for determining the hydration film thickness of a shale reservoir, to solve the problems that the existing method cannot accurately and conveniently obtain the macroscopic average hydration film thickness of shale nanometer pores, the traditional theoretical calculation is complex and has many parameters, and the atomic force microscope measurement is local and difficult to represent the whole.

[0006] According to an aspect of the present application, a method for determining the hydration film thickness of a shale reservoir is provided, comprising:

[0007] Obtaining a core sample of a target shale, determining the initial dissociation temperature T1 and the complete dissociation temperature T2 of the hydration film in the core sample by molecular dynamics simulation;

[0008] Based on the dissociation temperatures T1 and T2, determining the mass m of the hydration film in the core sample by a temperature-controlled drying experiment;

[0009] determining the specific surface area S of the core sample by gas adsorption experiment BET ;

[0010] determining the average hydration film thickness h of the shale reservoir according to the mass m of the hydration film and the specific surface area S of the core sample BET .

[0011] Preferably, the method for determining the initial dissociation temperature T1 and the complete dissociation temperature T2 of the hydration film in the core sample by molecular dynamics simulation comprises:

[0012] obtaining the mineral composition of the target shale core;

[0013] establishing a corresponding water-mineral model system for each type of mineral in the mineral composition;

[0014] determining the relative concentration curve of water molecules of each type of mineral under different temperature conditions according to the water-mineral model system;

[0015] determining the initial dissociation temperature T1 and the complete dissociation temperature T2 of each type of mineral according to the relative concentration curve of water molecules.

[0016] Preferably, the method for determining the initial dissociation temperature T1 and the complete dissociation temperature T2 of each type of mineral according to the relative concentration curve of water molecules comprises:

[0017] analyzing the relative concentration distribution curve of water molecules of the mineral at different temperatures, and in a temperature sequence from low to high, the temperature at which the relative concentration value of the bulk phase platform region of the concentration distribution curve first appears is greater than 0 is recorded as T start . The previous adjacent temperature of T start is determined as the initial dissociation temperature T1 of the mineral.

[0018] In a temperature sequence from low to high, the temperature at which the relative concentration value of the bulk phase platform region of the concentration distribution curve first appears is greater than a predetermined value is determined as the complete dissociation temperature T2 of the mineral.

[0019] Preferably, the method for obtaining the mineral composition of the target shale core comprises:

[0020] Selecting a plurality of shale core samples, washing the shale core samples with oil, and performing drying treatment;

[0021] After cutting a part of the core and grinding it to a particle size less than a predetermined value, performing XRD test to identify different types of minerals in the shale core sample.

[0022] Preferably, the method for determining the mass m of the hydration film in the core sample based on the dissociation temperatures T1 and T2 by temperature-controlled drying experiment comprises:

[0023] Saturating the core sample with water;

[0024] Drying the core sample saturated with water at a temperature lower than T1 to a first constant weight, and recording the mass as m1;

[0025] Drying the core sample at a temperature higher than T2 to a second constant weight, and recording the mass as m2;

[0026] The mass of the hydration film is m = m1-m2.

[0027] Preferably, the specific surface area S of the core sample is determined by using a gas adsorption experiment BET , and the method comprises:

[0028] Performing a nitrogen adsorption experiment on the shale core sample under the condition of liquid nitrogen bath temperature, and according to the adsorption data corresponding to the relative pressure of nitrogen at 0.05-0.35 during the experiment, the specific surface area of the shale is calculated according to the BET theory.

[0029] Preferably, the method for calculating the specific surface area of the shale according to the adsorption data corresponding to the relative pressure of nitrogen at 0.05-0.35 during the experiment comprises:

[0030] According to the adsorption data corresponding to the relative pressure of nitrogen at 0.05-0.35 during the experiment, the monolayer adsorption capacity V m is calculated by using formula (1).

[0031] (1) ;

[0032] In the formula, P is the equilibrium pressure, P0 is the saturated vapor pressure, V is the adsorption volume, V m is the monolayer adsorption capacity, and C is the BET constant.

[0033] According to the monolayer adsorption capacity, the specific surface area value S BET of the core sample is calculated by using formula (2).

[0034] (2) ;

[0035] In the formula, S BET is the specific surface area value of the sample, N is the Avogadro constant, A m is the cross-sectional area of a single adsorbed gas molecule, W is the mass of the sample, and V m is the monolayer adsorption capacity.

[0036] Preferably, the mass m of the hydration film and the specific surface area S BETdetermining the average hydration film thickness h of the shale reservoir, comprising:

[0037] obtaining the density of water under the temperature and pressure conditions of the formation in combination with the mass m of the hydration film, determining the volume V of the hydration film;

[0038] determining the specific surface area S of the core according to the core specific surface area S BET determining the core pore internal surface area S;

[0039] determining the average thickness h of the core hydration film according to the ratio of the volume V of the hydration film and the core pore internal surface area S.

[0040] Preferably, the volume V of the hydration film is determined by formula (3);

[0041] (3) ;

[0042] In the formula, m is the mass of the hydration film; is the density of water under the temperature and pressure conditions of the formation;

[0043] The core pore internal surface area S is determined by formula (4);

[0044] (4) ;

[0045] In the formula, m2 is the mass of the core after the hydration film is removed; S BET is the specific surface area of the core.

[0046] According to one aspect of the present application, a device for determining the thickness of the hydration film of a shale reservoir is also provided, comprising:

[0047] a temperature measuring unit for obtaining a core sample of a target shale, determining the initial dissociation temperature T1 and the complete dissociation temperature T2 of the hydration film in the core sample through molecular dynamics simulation;

[0048] a mass measuring unit for determining the mass m of the hydration film in the core sample through a temperature-controlled drying experiment based on the dissociation temperatures T1 and T2;

[0049] a specific surface area measuring unit for determining the specific surface area S of the core sample by using a gas adsorption experiment BET ;

[0050] a thickness calculating unit for determining the average hydration film thickness h of the shale reservoir according to the mass m of the hydration film and the specific surface area S of the core sample BET .

[0051] The present application has at least the following beneficial effects:

[0052] The application provides a shale reservoir hydration film thickness determination method and device, and the average thickness of the hydration film in the nanopore is calculated by determining the dissociation temperature of the hydration film through molecular dynamics simulation, accurately separating the hydration film mass based on the temperature, and combining the core specific surface area measured by the nitrogen adsorption method. BRIEF DESCRIPTION OF DRAWINGS

[0053] The drawings incorporated in the specification and forming a part thereof illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the application.

[0054] Figure 1 A flow chart of a shale reservoir hydration film thickness determination method according to an embodiment of the application is shown;

[0055] Figure 2 A water molecule relative concentration distribution diagram of quartz according to an embodiment of the application is shown. DETAILED DESCRIPTION

[0056] Various exemplary embodiments, features and aspects of the present application will be described in detail, with reference to the drawings. The same reference numbers in different drawings denote the same or similar elements. Although various aspects of the embodiments are shown in the drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

[0057] The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any implementation described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other implementations.

[0058] The term "and / or", merely an associative relationship of the associated objects, means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the term "at least one" herein means any one of the plurality or any combination of at least two of the plurality, for example, including at least one of A, B and C, which can mean including any one or more elements selected from the set consisting of A, B and C.

[0059] In addition, in order to better illustrate the present application, numerous specific details are given in the following detailed description. Those skilled in the art should understand that the present application can be implemented without certain specific details. In some examples, methods, means, elements and circuits well known to those skilled in the art are not described in detail, in order to highlight the main idea of the present application.

[0060] Figure 1 A flow chart of a method for determining a shale reservoir hydration film thickness according to an embodiment of the present application is shown. Figure 2 A diagram of a water molecule relative concentration distribution of quartz according to an embodiment of the present application is shown. Figures 1-2 As shown, a method for determining a shale reservoir hydration film thickness includes: step S01: obtaining a core sample of a target shale, determining an initial dissociation temperature T1 and a complete dissociation temperature T2 of a hydration film in the core sample through molecular dynamics simulation; step S02: based on the dissociation temperatures T1 and T2, determining a mass m of the hydration film in the core sample through a temperature-controlled drying experiment; step S03: using a gas adsorption experiment, determining a specific surface area S BET of the core sample; and step S04: determining an average hydration film thickness h of the shale reservoir according to the mass m of the hydration film and the specific surface area S BET of the core sample.

[0061] A method for determining a shale reservoir hydration film thickness according to an embodiment of the present application specifically includes the following steps:

[0062] Step S01: obtaining a core sample of a target shale, determining an initial dissociation temperature T1 and a complete dissociation temperature T2 of a hydration film in the core sample through molecular dynamics simulation.

[0063] In the present application, the method for determining an initial dissociation temperature T1 and a complete dissociation temperature T2 of a hydration film in a core sample through molecular dynamics simulation includes: obtaining a mineral composition of the target shale core; for different mineral types in the mineral composition, respectively establishing a corresponding water-mineral model system; according to the water-mineral model system, determining a water molecule relative concentration curve of each type of mineral under different temperature conditions; and according to each water molecule relative concentration curve, determining an initial dissociation temperature T1 and a complete dissociation temperature T2 of each type of mineral.

[0064] In an embodiment of the present application, a required number of cores are selected, the core diameter is required to be 2.5 cm, the columnar core is washed with oil, a solvent and a rotation are used as physical modes, and the duration is about 25 days. The core is dried according to GB / T 29172-2012 “Core Analysis Method” for drying treatment.

[0065] Part of it is ground for XRD testing, and it is found that the main minerals are quartz, montmorillonite and calcite.

[0066] Using Materials Studio software, the water-mineral interface model of each type of mineral is constructed, and all the models consider the periodic boundary conditions, the crystal structure of different minerals is called in the MS crystal library, if the MS crystal library does not have the crystal structure of the mineral, the model needs to be established by using the Build Crystal module, and then the supercell is formed by cutting the surface and expanding the cell.

[0067] The H2O molecule model is constructed by using the Sketch Atom function of the software, and the water molecule model structure is obtained.

[0068] The solution and rock wall are assembled into a box by using the Build layers function to construct the solution-rock model.

[0069] A 100Å vacuum layer is added above the aqueous solution by using the Build Vacuum slab function to avoid the influence of the periodic structure condition, and the water-mineral model system is constructed.

[0070] By using the constructed molecular simulation system, the water molecule relative concentration distribution curves of each mineral under different temperature conditions are calculated and analyzed by molecular dynamics simulation.

[0071] Based on this, the upper limit T1 of the temperature at which the overall hydration film of shale has not yet dissociated is determined. At the same time, the complete dissociation temperature of the overall hydration film of shale is determined as T2.

[0072] In the present application, the method for determining the initial dissociation temperature T1 and the complete dissociation temperature T2 of each type of mineral according to the water molecule relative concentration curves comprises: analyzing the water molecule relative concentration distribution curves of minerals at different temperatures, and in the temperature sequence from low to high, the temperature at which the relative concentration value of the bulk phase platform region of the concentration distribution curve is greater than 0 for the first time is recorded as T start , the previous adjacent temperature of T start is determined as the initial dissociation temperature T1 of the mineral; in the temperature sequence from low to high, the temperature at which the relative concentration value of the bulk phase platform region of the concentration distribution curve is greater than a predetermined value for the first time is determined as the complete dissociation temperature T2 of the mineral.

[0073] In the embodiment of the present application, taking quartz as an example, the simulation data of quartz is analyzed. The temperature sequence is set to 24.85 (298K), 124.85℃ (398K), 224.85℃ (498K), 324.85℃ (598K) and 424.85℃ (598K).

[0074] The concentration curve of quartz is analyzed. It is found that when the temperature is lower than 124.85℃, the first peak close to the surface is obvious, and the bulk phase platform region (the platform region after the peak) concentration value is 0. When the temperature rises to 224.85℃, the bulk phase platform region concentration value starts to be greater than 0 (about 0.05), so the T 1i = 124.85℃.

[0075] When the temperature rises to 324.85℃, the bulk phase platform region concentration value is greater than the predetermined value (about 1.5) for the first time, so the T 2i = 325℃.

[0076] In the present application, the method for obtaining the mineral composition of the target shale core comprises: selecting a plurality of shale core samples, washing the shale core samples with oil, and performing drying treatment; grinding a part of the core to a particle size less than a predetermined value, and then performing XRD testing to determine different mineral types in the shale core sample.

[0077] In the embodiment of the present application, a part of the selected core is ground to a particle size less than 40µm or no obvious particle feeling when pinched by hand, and then XRD testing is performed. The testing is performed according to SY / T 5163-2018 "X-ray Diffraction Analysis Method for Clay Minerals and Common Non-clay Minerals in Sedimentary Rocks". In this way, different mineral types in the shale are determined.

[0078] The principle of X-ray is that the inner layer electrons in atoms jump under the bombardment of high-speed moving electrons to produce light radiation, mainly continuous X-ray and characteristic X-ray. Crystals can be used as X-ray gratings. The coherent scattering of a large number of particles will interfere with each other, so that the intensity of scattered X-rays is enhanced or weakened. Due to the superposition of a large number of particle scattering waves, the light beam with maximum intensity produced by mutual interference is called X-ray diffraction line. The diffraction condition can be applied to Bragg formula:

[0079] 2dsinθ=nλ;

[0080] In the formula, θ is the included angle between incident X-ray and crystal plane, d is the interplanar spacing, n is the diffraction order, and λ is the wavelength of incident X-ray.

[0081] Step S02: Based on the dissociation temperatures T1 and T2, the mass m of the hydration film in the core sample is determined by temperature control drying experiment.

[0082] In this invention, the method for determining the mass m of the hydration film in the core sample by a temperature-controlled drying experiment based on the dissociation temperatures T1 and T2 includes: saturating the core sample with water; drying the water-saturated core sample at a temperature below T1 to a first constant weight and recording the mass as m1; drying the core sample at a temperature above T2 to a second constant weight and recording the mass as m2; the mass of the hydration film m = m1 - m2.

[0083] In this embodiment of the invention, the shale core is saturated with water. The saturated shale core is placed in a sealed container, and a vacuum pump is used to evacuate the container. After 24 hours, the core is removed and weighed. The evacuation is then continued for another 6 hours, and the core is removed and weighed again until the mass remains constant. At this point, the saturation process is complete.

[0084] Place the shale core in a constant temperature chamber and set the temperature of the chamber to be lower than T1. Dry the core until the mass is constant. Then raise the temperature of the chamber so that it is still lower than T1. Continue drying until the mass is constant until the core mass no longer changes with the temperature. Record the final mass m1.

[0085] Place the shale core in a constant temperature chamber and set the temperature of the chamber to be greater than T2. ​​Dry it until the mass is constant. Then raise the temperature of the constant temperature chamber and continue drying until the mass is constant. Continue drying until the mass of the core does not change with the increase of temperature. Record the final mass m2. The mass of the hydration film in the shale core is m = m1 - m2.

[0086] Step S03: Measure the specific surface area S of the core sample using a gas adsorption experiment. BET .

[0087] In this invention, the specific surface area S of the core sample is determined using a gas adsorption experiment. BET The method includes: conducting nitrogen adsorption experiments on shale core samples under liquid nitrogen bath temperature conditions, and calculating the specific surface area of ​​mudstone and shale based on the adsorption data corresponding to the nitrogen relative pressure of 0.05~0.35 during the experiment, according to BET theory.

[0088] In this invention, the method for calculating the specific surface area of ​​shale based on the adsorption data corresponding to the nitrogen relative pressure of 0.05~0.35 during the experiment, according to BET theory, includes: calculating the monolayer adsorption capacity V using equation (1) based on the adsorption data corresponding to the nitrogen relative pressure of 0.05~0.35 during the experiment. m ;

[0089] (1);

[0090] In the formula: P is the equilibrium pressure, P0 is the saturated vapor pressure, V is the adsorption volume, and V0 is the volume of adsorption.m Where C is the monolayer adsorption capacity and C is the BET constant.

[0091] Based on the monolayer adsorption capacity, the specific surface area S of the core sample is calculated using equation (2). BET ;

[0092] (2);

[0093] In the formula: S BET Here, N is the sample specific surface area, and A is Avogadro's constant. m Let W be the cross-sectional area of ​​a single adsorbed gas molecule, and W be the sample mass.

[0094] In this embodiment of the invention, a gas adsorption experiment (nitrogen adsorption method) was used to determine the specific surface area, pore volume, and pore size distribution of the porous media in the core. The low-temperature nitrogen adsorption experiment was conducted using a specific surface area and porosity analyzer, with high-purity nitrogen gas (purity greater than 99.999%) as the adsorbate. The specific surface area was determined according to the national standard GB / T 19587-2017 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method", and the SBET was calculated using the BET equation within the relative pressure range of 0.05–0.35.

[0095] Gas adsorption experiments mainly utilize the properties of nitrogen adsorption and capillary condensation in porous media. Nitrogen adsorption experiments were conducted on shale samples (shale cores) under liquid nitrogen bath temperature conditions. When the relative pressure of nitrogen was between 0.05 and 0.35, adsorption occurred on the pore surface of the shale. At this relative pressure, the adsorption conforms to the pressure range of monolayer adsorption according to the BET equation. Therefore, the adsorption data within this pressure range of 0.05 to 0.35 can be used to fit equation (1) to obtain V. m .

[0096] The pressure required for liquid to condense in a tiny capillary is relatively low. Therefore, as the pressure increases, the gas first condenses in the small pores and then in the large pores, resulting in V... m The specific surface area of ​​the sample can be obtained by equation (2).

[0097] Step S04: Based on the mass m of the hydration film and the specific surface area S of the core sample... BET The average hydration film thickness h of the shale reservoir is determined.

[0098] In this invention, the mass m of the hydration film and the specific surface area S of the core sample are used as the basis for determining the hydration film composition. BET A method for determining the average hydration film thickness h of the shale reservoir includes: obtaining the density of water under formation temperature and pressure conditions. , in combination with the mass m of the hydration film, to determine the volume V of the hydration film; according to the specific surface area S of the core BET , to determine the core pore internal surface area S; according to the ratio of the volume V of the hydration film to the core pore internal surface area S, to determine the average thickness h of the core hydration film.

[0099] In the present application, the volume V of the hydration film is determined by formula (3);

[0100] (3) ;

[0101] In the formula, m is the mass of the hydration film; is the density of water under the formation temperature and pressure conditions;

[0102] The core pore internal surface area S is determined by formula (4);

[0103] (4) ;

[0104] In the formula, m2 is the mass of the core after the hydration film is removed; S BET is the specific surface area of the core.

[0105] In the embodiment of the present application, the density of water under the formation temperature and pressure conditions is obtained through data investigation , and the volume V of the hydration film can be calculated by formula (3) in combination with the mass m of the hydration film obtained by the above experiment.

[0106] The specific surface area S of the core is obtained by core specific surface testing BET , and the core pore internal surface area S is calculated by formula (4).

[0107] According to the ratio of the volume V of the hydration film to the core pore internal surface area S , the average thickness h of the core hydration film is determined.

[0108] In the embodiment of the present application, the present application will be further described in combination with specific examples as follows:

[0109] 1. Core preparation

[0110] Select a number of cores as required, and the core diameter is required to be 2.5 cm. The cores are dried according to GB / T 29172-2012 “Core Analysis Method”.

[0111] 2. XRD testing

[0112] The selected core is cut and ground to a size of less than 40 microns or a size that can be felt by hand without obvious particles, and XRD testing is performed. The test is performed according to SY / T 5163-2018 "X-ray Diffraction Analysis Method for Clay Minerals and Common Non-clay Minerals in Sedimentary Rocks". Different mineral types in the shale are determined. Through the test, it is found that the brittle mineral composition of the shale is mainly quartz and calcite, and the clay mineral composition is mainly montmorillonite and kaolinite.

[0113] 3. Hydration film dissociation temperature determination

[0114] A water-mineral model system is constructed using Materials Studio software.

[0115] Using the constructed molecular simulation system, the relative concentration curves of water molecules of various minerals under different temperature conditions are calculated and analyzed. Based on this, the upper limit of the temperature at which the overall hydration film of the shale has not yet dissociated is determined as T1=124.85℃. At the same time, the complete dissociation temperature of the overall hydration film of the shale is determined as T2=324.85℃.

[0116] Specifically, taking quartz as an example, it can be clearly seen from the attached Figure 2 that when the temperature reaches 124.85℃ (red line), the hydration film has not yet dissociated, at 224.85℃ (green line), the hydration film begins to dissociate, and free water is produced, and at 324.85℃, the hydration film is completely dissociated.

[0117] 4. Core hydration film mass determination

[0118] After the shale core is saturated with water, it is placed in an oven, the oven temperature is set to a temperature lower than T1, and dried until the mass is constant. Then increase the oven temperature, continue to dry until the mass is constant, and record the final mass m1=76.9441g.

[0119] Place the shale core in an oven, set the oven temperature to a temperature greater than T2, and dry until the mass is constant. Then increase the oven temperature, continue to dry until the mass is constant, and record the final mass m2=76.5382g. Thus, the mass of the hydration film in the shale core is m=m1-m2=0.4059g.

[0120] 5. Core specific surface area determination

[0121] Nitrogen adsorption experiments on mud shale samples under liquid nitrogen bath temperature conditions, using adsorption data at a relative pressure of nitrogen of 0.05-0.35, combined with formula (1), the V m .

[0122] According to the V m In combination with the size of nitrogen molecules, the specific surface area S can be calculated by formula (2) BET = 11.049 m 3 / g.

[0123] 6. Experimental data and processing

[0124] Through data investigation, the density under the formation temperature and pressure condition is 1.6 g / cm 3 In combination with the mass m of the hydration film obtained by the above experiment, the volume V of the hydration film can be obtained by formula (3).

[0125] The specific surface area S of the core obtained by the core specific surface test BET The core pore inner surface area S is calculated by formula (4).

[0126] In combination with the volume of the hydration film, the average thickness h of the core hydration film can be obtained, and the results are shown in Table 1.

[0127] Table 1: Calculation results of the average thickness of the core hydration film

[0128]

[0129] It can be understood that the above-mentioned various method embodiments of the present application can be combined with each other to form combined embodiments without violating the principle logic. Due to the limited space, the present application will not be described again.

[0130] The execution subject of the shale reservoir hydration film thickness determination method can be a shale reservoir hydration film thickness determination device. For example, the shale reservoir hydration film thickness determination method can be executed by a terminal device or a server or other processing device. The terminal device can be a user equipment (User Equipment, UE), a mobile device, a user terminal, a terminal, a cellular phone, a cordless phone, a personal digital assistant (Personal Digital Assistant, PDA), a handheld device, a computing device, a vehicle-mounted device, a wearable device, etc. In some possible implementation manners, the shale reservoir hydration film thickness determination method can be realized by a processor calling computer readable instructions stored in a memory.

[0131] Those skilled in the art can understand that in the above method of the specific embodiment, the writing order of each step does not mean a strict execution order and does not constitute any limitation on the implementation process. The specific execution order of each step should be determined by its function and possible internal logic.

[0132] In the present application, a device for determining the thickness of a hydration film in a shale reservoir is also provided, comprising: a temperature determination unit for obtaining a core sample of a target shale, determining an initial dissociation temperature T1 and a complete dissociation temperature T2 of a hydration film in the core sample through molecular dynamics simulation; a mass determination unit for determining the mass m of the hydration film in the core sample through a temperature-controlled drying experiment based on the dissociation temperatures T1 and T2; a specific surface area determination unit for determining the specific surface area S of the core sample by using a gas adsorption experiment BET ; and a thickness calculation unit for determining the average hydration film thickness h of the shale reservoir according to the mass m of the hydration film and the specific surface area S of the core sample BET .

[0133] In some embodiments, the device provided by the embodiments of the present application has functions or includes modules and units that can be used to execute the methods described in the above method embodiments, and specific implementations can be referred to the descriptions of the above method embodiments, which will not be described here in detail for the sake of brevity.

[0134] The present application establishes a method for obtaining the dissociation temperature of a hydration film based on molecular dynamics simulation, and then measuring the specific surface area of a core pore and the mass change in a water-containing state, and calculating the average hydration film thickness in a rock nanometer pore. The method combines molecular dynamics simulation and core experiment, obtains parameter information from two scales of micro and macro, so as to realize quantitative calculation of the hydration film thickness in a nanometer pore.

[0135] The present application first uses molecular dynamics simulation to determine the dissociation temperature of a hydration film instability; then saturates the core with water, measures the mass of the core at different temperatures to obtain the mass change of the core in different water-containing states, and then accurately measures the specific surface area of the pore by using a specific surface area instrument; finally, the hydration film thickness of the core is calculated by combining the two.

[0136] The present application uses molecular dynamics simulation to reveal the dual advantages of micro critical state and core experiment to obtain macro average data, so as to realize quantitative calculation of the hydration film thickness in a nanometer pore. By combining the dissociation temperature with the core experiment data, not only the complex operation is avoided, but also the average hydration film thickness of the core is obtained. Therefore, the method has broad development prospects.

[0137] The above has described the embodiments of the present application, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments. The selection of the terms used herein is intended to best explain the principles, practical applications or technical improvements in the market of the embodiments, or to enable other ordinary skilled persons in the art to understand the embodiments disclosed herein.

Claims

1. A method for determining the thickness of a hydration film in a shale reservoir, characterized in that, include: Core samples of the target shale were obtained, and the initial dissociation temperature T1 and the complete dissociation temperature T2 of the hydration film in the core samples were determined by molecular dynamics simulation. Based on the dissociation temperatures T1 and T2, the mass m of the hydration film in the core sample was determined by a temperature-controlled drying experiment. The specific surface area S of the core sample was determined using a gas adsorption experiment. BET ; Based on the mass m of the hydration film and the specific surface area S of the core sample BET The average hydration film thickness h of the shale reservoir is determined.

2. The method for determining the thickness of the hydration film in a shale reservoir according to claim 1, characterized in that, The method for determining the initial dissociation temperature T1 and the complete dissociation temperature T2 of the hydration film in a core sample through molecular dynamics simulation includes: Obtain the mineral composition of the target shale core; For different mineral types in the aforementioned mineral composition, corresponding water mineral model systems are established respectively; Based on the aforementioned water mineral model system, the relative concentration curves of water molecules for each type of mineral under different temperature conditions were determined; Based on the relative concentration curves of water molecules described above, the initial dissociation temperature T1 and the complete dissociation temperature T2 of each type of mineral are determined.

3. The method for determining the thickness of the hydration film in a shale reservoir according to claim 2, characterized in that, The method for determining the initial dissociation temperature T1 and the complete dissociation temperature T2 of each type of mineral based on the relative concentration curves of each water molecule includes: Analyzing the relative concentration distribution curves of water molecules in minerals at different temperatures, the temperature at which the first bulk plateau region with a relative concentration value greater than 0 appears in the temperature sequence from low to high is denoted as T. start , will T start The preceding adjacent temperature is determined as the initial liberation temperature T1 of the mineral; In the temperature sequence from low to high temperature, the temperature at which the relative concentration value of the first bulk plateau region where the concentration distribution curve appears is greater than the predetermined value is determined as the complete dissociation temperature T2 of the mineral.

4. The method for determining the thickness of the hydration film in a shale reservoir according to claim 2, characterized in that, The method for obtaining the mineral composition of the target shale core includes: Several shale core samples were selected, and the shale core samples were washed with oil and then dried. A portion of the core was cut off and ground until all the particles were smaller than the predetermined value. Then, XRD tests were performed to identify the different mineral types in the shale core sample.

5. The method for determining the thickness of the hydration film in a shale reservoir according to claim 1, characterized in that, The method for determining the mass m of the hydration film in the core sample through a temperature-controlled drying experiment based on the dissociation temperatures T1 and T2 includes: Saturate the core sample with water; The core sample after being saturated with water was dried to the first constant weight at a temperature below T1, and the mass was recorded as m1. The core sample was dried to a second constant weight at a temperature higher than T2, and the mass was recorded as m2; The mass of the hydration membrane is m = m1 - m2.

6. The method for determining the thickness of the hydration film in a shale reservoir according to claim 1, characterized in that, The specific surface area S of the core sample was determined using a gas adsorption experiment. BET The methods include: Nitrogen adsorption experiments were conducted on shale core samples under liquid nitrogen bath temperature conditions. Based on the adsorption data corresponding to nitrogen relative pressures of 0.05 to 0.35 during the experiment, the specific surface area of ​​the mudstone and shale was calculated according to BET theory.

7. The method for determining the thickness of the hydration film in a shale reservoir according to claim 6, characterized in that, The method for calculating the specific surface area of ​​shale based on the adsorption data corresponding to nitrogen relative pressures of 0.05~0.35 during the experiment, according to BET theory, includes: Based on the adsorption data corresponding to nitrogen relative pressures of 0.05–0.35 during the experiment, the monolayer adsorption capacity V was calculated using equation (1). m ; （1）； In the formula: P is the equilibrium pressure, P0 is the saturated vapor pressure, V is the adsorption volume, and V0 is the volume of adsorption. m Where C is the monolayer adsorption capacity and C is the BET constant. Based on the monolayer adsorption capacity, the specific surface area S of the core sample is calculated using equation (2). BET ; （2）； In the formula: S BET Here, N is the sample specific surface area, and A is Avogadro's constant. m V is the cross-sectional area of ​​a single adsorbed gas molecule, W is the sample mass, and V is the cross-sectional area of ​​a single adsorbed gas molecule. m This represents the adsorption capacity of a single layer.

8. The method for determining the thickness of the hydration film in a shale reservoir according to any one of claims 1-7, characterized in that, Based on the mass m of the hydration film and the specific surface area S of the core sample BET A method for determining the average hydration film thickness h of the shale reservoir includes: Obtain the density of water under formation temperature and pressure conditions. Based on the mass m of the hydration membrane, the volume V of the hydration membrane is determined. Based on the specific surface area S of the core BET Determine the internal surface area S of the core pores; The average thickness h of the hydration film in the core is determined based on the ratio of the volume V of the hydration film to the surface area S inside the pores of the core.

9. The method for determining the thickness of the hydration film in a shale reservoir according to claim 8, characterized in that: The volume V of the hydration film is determined using equation (3); （3）； In the formula: m is the mass of the hydration film; The density of water under the given temperature and pressure conditions of the formation; The inner surface area S of the core pores is determined using equation (4); （4）； In the formula: m2 is the mass of the core after dehydration and film removal; S BET is the specific surface area of ​​the core.

10. A device for determining the thickness of a hydration film in a shale reservoir, characterized in that, include: The temperature measurement unit is used to obtain core samples of the target shale and determine the initial dissociation temperature T1 and the complete dissociation temperature T2 of the hydration film in the core sample through molecular dynamics simulation. The mass measurement unit is used to determine the mass m of the hydration film in the core sample by a temperature-controlled drying experiment based on the dissociation temperatures T1 and T2. The specific surface area measurement unit is used to determine the specific surface area S of the core sample using a gas adsorption experiment. BET ; The thickness calculation unit is used to calculate the thickness based on the mass m of the hydration film and the specific surface area S of the core sample. BET The average hydration film thickness h of the shale reservoir is determined.

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