Method and device for determining saturated adsorption phase density and absolute adsorption quantity conversion

Abstract

The invention provides a method and device for determining saturated adsorption phase density and absolute adsorption quantity conversion, and the method comprises the steps: determining an excessive adsorption quantity relational expression based on a conversion relation between an absolute adsorption gas quantity and an excessive adsorption gas quantity, a single-layer saturated adsorption quantity nL relational expression, an absolute adsorption quantity nabs (p) relational expression and an adsorption phase density relational expression; and fitting an excessive adsorption quantity curve obtained by experiment or molecular simulation by using the excessive adsorption quantity relational expression to obtain the saturated adsorption phase density rhoL, thereby realizing accurate conversion from the excessive adsorption quantity to the absolute adsorption quantity. In addition, an experimental or molecular mode is further utilized, the function relation between the adsorption phase density and the pressure is fully considered, a conversion method of the absolute adsorption gas quantity and the excess adsorption gas quantity is established, the method can be used for converting an excess adsorption curve obtained through experiment or molecular simulation, and the calculation accuracy of the absolute adsorption quantity is improved.

Description

Technical Field

[0001] The present invention belongs to the field of computer technology, and in particular relates to a method and a device for determining the saturated adsorption phase density and the absolute adsorption amount conversion. Background Art

[0002] The main component of shale gas is methane, which is in a supercritical state under reservoir conditions (critical temperature -82.6℃, critical pressure 4.60MPa), and exists mainly in the form of free gas and adsorbed gas, with a small amount of shale gas dissolved in organic matter, asphalt and formation water. Among them, adsorbed gas accounts for as high as 20-85%, which exists on the surface of organic matter and clay minerals, and is of great significance to the stable production of shale gas reserves and low-pressure and small-production stages.

[0003] The laboratory commonly uses weighing method and volume method to test the adsorbed gas content. Specifically, after testing the pore volume of shale, its actual storage gas volume is tested under specific temperature and pressure conditions. The difference between the actual storage gas volume and the theoretical storage free gas volume of the pore volume is the adsorbed gas volume on the pore surface, and this result is the excess adsorption volume. The amount of gas actually adsorbed on the pore surface is the absolute adsorbed gas volume. Various isothermal adsorption models in adsorption theory, such as Langmuir, Freundlich, Sips and Toth, are all functions of absolute adsorption volume and pressure (and temperature). When gas is adsorbed in the subcritical state, the density of the bulk gas can be ignored compared to the density of the adsorbed phase, and the experimentally measured results can be approximated as the absolute adsorption volume and directly used for the evaluation of the adsorbed gas content. However, the bulk density of supercritical gas is relatively large, which cannot be ignored relative to the density of the adsorbed phase gas, and the excess adsorption volume cannot be equivalently treated as the absolute adsorption volume. The usual practice is to use theoretical methods to convert the excess adsorbed gas volume tested in the experiment into the absolute adsorption volume. At present, all conversion methods have a certain degree of applicability when the pressure is less than 10MPa, but different methods will produce contradictory results of absolute adsorption amount rising and falling under high pressure. The result of absolute adsorption amount rising is wrongly interpreted as a multilayer adsorption phenomenon, and the result of falling cannot be explained by adsorption theory. This is because the existing absolute adsorption amount conversion method ignores the relationship between the change of adsorption phase density and pressure, and there is a deviation in the density estimation of the adsorption phase. Therefore, the traditional model cannot be applied to the absolute adsorption amount conversion under reservoir pressure conditions, and a new absolute adsorption amount conversion method needs to be developed.

[0004] In the study of adsorption mechanism, the advantage of molecular simulation is that it can accurately describe the microscopic occurrence characteristics of shale gas in various pores, statistically analyze the relationship between adsorption layer thickness, density, temperature and pressure, and obtain absolute adsorption and excess adsorption, which can be used to guide the establishment of macro-absolute adsorption conversion methods. Accurate conversion of absolute adsorption will effectively improve the accuracy of shale gas reserve calculation, gas well productivity evaluation and production dynamic analysis.

[0005] In order to achieve accurate conversion, accurate characterization of the adsorption phase density is very important. However, the adsorption phase density currently used in the conversion is mostly a constant value, and the change of the adsorption phase density with pressure is not taken into account. Therefore, the obtained adsorption phase density is inaccurate, which in turn affects the calculation of the absolute adsorption amount. Summary of the invention

[0006] To solve the above problems, the present disclosure provides a method and device for determining the saturated adsorption phase density and the conversion of the absolute adsorption amount, which fully considers the conversion relationship between the absolute adsorbed gas amount and the excess adsorbed gas amount and fits the excess adsorption curve obtained by experiments or molecular simulations to obtain the saturated adsorption phase density, thereby improving the accuracy of obtaining the single-layer saturated adsorption amount, thereby improving the accuracy of the absolute adsorption amount calculation, and can realize the accurate conversion of the excess adsorption amount to the absolute adsorption amount.

[0007] The present disclosure provides a method for determining the density of a saturated adsorption phase based on a conversion relationship, the method comprising:

[0008] Based on the conversion relationship between absolute adsorption volume and excess adsorption volume, the single-layer saturated adsorption volume n L Relationship, absolute adsorption amount n abs (p) relationship and adsorption phase density relationship, determine the excess adsorption amount relationship;

[0009] The excess adsorption amount relationship is used to fit the excess adsorption amount curve obtained by experiment or molecular simulation to obtain the saturated adsorption phase density ρ L .

[0010] Alternatively, based on the adsorbed phase density ρ a (p) and gas density ρ b (p) to form the absolute adsorption volume n abs (p) and excess adsorption volume n exc (p), where p is pressure.

[0011] Optionally, the absolute adsorption volume n abs (p) and excess adsorption volume n exc The conversion relationship of (p) is,

[0012]

[0013] Optionally, the absolute adsorption amount n abs (p) The relationship is, n abs (p) = n L θ(ρ b ); and / or, the adsorption phase density relationship is, ρ a (p) = ρ L θ(ρ b ),in,

[0014] θ(ρ b ) is the gas phase density ρ b The coverage rate under L Saturated adsorption capacity of monolayer.

[0015] Optionally, the gas phase density ρ is determined by a monolayer adsorption model b is the coverage rate θ(ρ b ).

[0016] Optionally, the excess adsorption amount relationship is:

[0017]

[0018] Among them, ρ L is the saturated adsorption phase density, σ g is the molecular radius of the adsorbed gas, M is the molar mass, θ is the coverage, ρ b is the gas density.

[0019] Optionally, the excess adsorption amount n in the excess adsorption amount relation is exc The parameters are obtained by experimental methods or molecular simulation.

[0020] Optionally,

[0021] The molecular simulation method is to use the established pore molecular model to determine the ensemble average number <n> μ and pore volume Vp; according to the ensemble average quantity <n> μ and the pore volume Vp to calculate the excess adsorbed gas volume n exc parameter; or,

[0022] The experimental method is: conducting an adsorption gas test experiment with reference to a volume method or a weight method.

[0023] Optionally,

[0024] The pore volume Vp is:

[0025]

[0026] in,

[0027] <N He > is the ensemble average number of helium molecules in the pores; N A is Avogadro's constant; ρ He is the bulk helium density; M He is the molar mass of helium.

[0028] The present disclosure also provides a method for determining the adsorption phase density ρ a (p) The method comprises:

[0029] The saturated adsorption phase density ρ is obtained by any of the above methods. L ; Using the monolayer adsorption model to determine the coverage θ(ρ b );

[0030] Based on the saturated adsorption phase density ρ L and coverage θ(ρ b ) Determine the adsorption phase density ρ a (p).

[0031] Optionally, the saturated adsorption phase density ρ is determined based on the following formula: a

[0032] ρ a (p) = ρ L θ(ρ b ).

[0033] The present disclosure also provides a device for determining the density of a saturated adsorption phase based on a conversion relationship, the device comprising a first unit and a second unit, wherein:

[0034] The first unit is configured to convert the absolute adsorption gas volume to the excess adsorption gas volume, the single-layer saturated adsorption volume n L Relationship, absolute adsorption amount n abs (p) relationship and adsorption phase density relationship, determine the excess adsorption amount relationship;

[0035] The second unit is configured to use the excess adsorption amount relationship to fit the excess adsorption amount curve obtained by experiment or molecular simulation to obtain the saturated adsorption phase density ρ L .

[0036] The present disclosure also provides a method for determining the adsorption phase density ρ a (p) The device comprises an acquisition unit and a determination unit, wherein:

[0037] The acquisition unit is configured to acquire the saturated adsorption phase density ρ using the method described above. L ; Using the monolayer adsorption model to determine the coverage θ(ρ b );

[0038] The determination unit is configured to determine the adsorption of the saturated phase based on the saturated adsorption phase density ρ L and coverage θ(ρ b ) Determine the adsorption phase density ρ a (p).

[0039] The present disclosure also provides an electronic device, the electronic device comprising at least one processor and at least one memory, the memory being data-connected to the processor, wherein:

[0040] The memory stores instructions that can be executed by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to perform any of the above methods.

[0041] Compared with the prior art, the present invention has the following advantages:

[0042] The present invention firstly uses the theoretical relationship between absolute adsorption and excess adsorption, combined with the monolayer saturated adsorption capacity n L Relationship, absolute adsorption amount n abs The excess adsorption amount relationship is formed by using the theoretical relationship of the relationship (p) and the adsorption phase density relationship. The excess adsorption amount relationship is then used to fit the excess adsorption amount curve obtained by experiment or molecular simulation to obtain the saturated adsorption phase density. The parameters obtained in this way are more accurate.

[0043] In the present disclosure, the excess adsorption in the excess adsorption relationship is obtained by experimental methods or molecular simulation, so that the absolute adsorption curve can be obtained without conducting an adsorption test. In addition, the effect of pressure on the density of the adsorbed phase is taken into account during this experiment or molecular simulation process, which can further improve the model conversion and prediction accuracy, and provide a more accurate absolute adsorption curve for shale gas reserve calculation, gas well productivity evaluation and production dynamic analysis.

[0044] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0046] Figure 1 A flowchart of determining the saturated adsorption phase density based on the conversion relationship according to an embodiment of the present disclosure is shown;

[0047] Figure 2 A GCMC simulation gas adsorption flow chart in pores according to an embodiment of the present disclosure is shown;

[0048] Figure 3 A schematic diagram of an organic slit pore model according to an embodiment of the present disclosure is shown;

[0049] FIG. 4( a ) and FIG. 4( b ) respectively show the relationship curve between the excess adsorption amount and pressure, and the relationship between the excess adsorption amount and density of 348.15K methane in a 4nm organic slit pore according to an embodiment of the present disclosure;

[0050] Figure 5 A diagram showing the fitting results of excess adsorption of methane in organic matter slit pores at 348.15K according to an embodiment of the present disclosure is shown;

[0051] Figure 6 A comparison chart of the predicted results of the absolute adsorption of methane in organic slit pores at 348.15K according to an embodiment of the present disclosure and the GCMC results is shown;

[0052] Figure 7 A comparison diagram of the predicted results of the adsorption phase density of methane in organic matter slit pores at 348.15K according to an embodiment of the present disclosure and the GCMC results is shown;

[0053] Figure 8 The absolute adsorption amount conversion result diagram of methane in organic matter slit pores at 348.15K according to an embodiment of the present disclosure is shown;

[0054] Fig. 9 A computer system according to an embodiment of the present disclosure is shown;

[0055] Fig.10 A structural diagram of a device for determining the density of a saturated adsorption phase based on a conversion relationship according to an embodiment of the present disclosure is shown;

[0056] Fig.11 A schematic diagram of the structure of a device for determining the density of an adsorbed phase according to an embodiment of the present disclosure is shown;

[0057] Fig.12 A schematic structural diagram of a conversion device according to an embodiment of the present disclosure is shown;

[0058] Fig.13 A schematic diagram of the structure of an electronic device according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0060] The density of the adsorption phase is strongly correlated with the density of the saturated adsorption phase. Obtaining the density of the saturated adsorption phase plays an important role in accurately calculating the absolute adsorption amount. Therefore, a method is needed to determine the density of the saturated adsorption phase and realize the conversion between the absolute adsorption amount and the excess adsorption amount.

[0061] like Figure 1 The flowchart of the method for determining the saturated adsorption phase density based on the conversion relationship of the embodiment of the present disclosure is shown. The method includes: based on the conversion relationship between the absolute adsorbed gas amount and the excess adsorbed gas amount, the single-layer saturated adsorption amount n L Relationship, absolute adsorption amount n abs (p) relationship and adsorption phase density relationship, determine the excess adsorption relationship; use the excess adsorption relationship to fit the excess adsorption curve obtained by experiment or molecular simulation to obtain the saturated adsorption phase density ρ L .

[0062] In order to further illustrate the embodiments of the present disclosure, the following is an introduction and explanation starting from the establishment of a pore model.

[0063] 1) Establish pore model

[0064] First, in the embodiment of the present disclosure, a corresponding pore model can be established according to the pore type of the porous medium, wherein the porous medium can be a pore molecular model that can represent the adsorbate, such as organic pores, illite pores or montmorillonite pores.

[0065] 2) Set the simulation force field, ensemble, temperature, pressure and other conditions to perform GCMC (Grand Canonical Monte Carlo) molecular simulation

[0066] According to the required adsorption environment, the adsorption simulation conditions of the pore model are set, including force field, ensemble, temperature and pressure, etc. Methane is loaded into the constructed pore model, and adsorption simulation is performed (under the same temperature conditions, the pressure point setting can be no less than 10), and the ensemble average number of adsorbate molecules in the adsorbent under the corresponding temperature and pressure conditions is obtained. <n> μ .

[0067] 3) Obtaining excess adsorption curve from molecular simulation

[0068] The simulation result in step 2) can be processed into excess adsorption through the following formula (1).

[0069]

[0070] Where: n exc is the excess adsorption per unit surface area, the physical quantity is mol / m 2 ; <n> μ is the ensemble average number of adsorbate molecules in the adsorbent under GCMC, and the physical quantity is square meters; A is the wall surface area, the total surface area of ​​the slit hole is 2xy, and the cylindrical hole is πdl / 4, and the physical quantity is square meters. 2 , x, y, are the length and width of the slit hole wall, the physical quantity is m (meter), l, d are the length and diameter of the circular hole respectively; V p is the pore volume, the physical quantity is ml; ρ b is the gas density of methane, the physical quantity is g / ml; M is the molar mass, the physical quantity is g / mol, and the molar mass of methane is 16g / mol.

[0071] 4) Calculate the pore volume

[0072] In order to obtain the pore volume Vp in formula (1), the present disclosure can be implemented by loading helium into the pore model. Helium is loaded into the constructed pore model, and the pore volume is calculated using the following formula (2). The simulation details of helium in the pores are the same as step 2) of the methane adsorption simulation, and will not be repeated here.

[0073]

[0074] Where: <N He > is the ensemble average number of helium molecules in the pores, the physical quantity is pieces; N A is Avogadro's constant, which is 6.022×10 23 mol -1 ρ He is the bulk helium density, the physical quantity is g / ml; M He is the molar mass of helium, and its physical quantity is g / mol.

[0075] 5) Absolute adsorption amount conversion

[0076] Substitute the pore volume obtained in step 4) into formula (1), and then substitute the simulation results at different temperatures and pressures respectively, to obtain the methane excess adsorption curve at different temperatures.

[0077] The excess adsorption amount obtained above is converted into an absolute adsorption amount according to the following formula (3).

[0078]

[0079] Where: n abs is the absolute adsorption per unit surface area, the physical quantity is mol / m 2 ; V a is the volume of the adsorbed phase, the physical quantity is ml.

[0080] Assume that the density of the adsorbed phase is ρ a , then the absolute adsorption amount can also be expressed as formula (4).

[0081]

[0082] Combining equations (3) and (4) yields equation (5) for the relationship between the absolute adsorption amount and the excess adsorption amount.

[0083]

[0084] In the embodiment of the present disclosure, the pressure factor is taken into account through molecular simulation, so that the adsorption phase density is a function of the pressure p. Therefore, the adsorption phase density in the above formula (5) can be replaced with a function of the pressure to obtain the conversion relationship between the absolute adsorption amount and the excess adsorption amount, as shown in the following formula (6).

[0085]

[0086] In the embodiments of the present disclosure, experiments or molecular simulation methods are used to take into account the influence of pressure when determining the adsorption phase density, that is, the adsorption phase density is used as a function of pressure, thereby overcoming the inaccuracy problem in the prior art of using the adsorption phase density as a constant to achieve the conversion between absolute adsorption amount and excess adsorption amount.

[0087] The molecular simulation results show that methane exhibits the characteristics of single-layer adsorption under low pressure, while it exhibits the characteristics of three-layer adsorption when the pressure is greater than 5MPa (supercritical methane). The density of the second and third adsorption layers of supercritical methane is close to the bulk density. The concept of quasi-monolayer adsorption is defined, and the excess adsorption of the second and third layers is included in the first adsorption layer. The quasi-monolayer adsorption hypothesis still conforms to the characteristics of the Lagmuir adsorption model. At saturated adsorption, the monolayer saturated adsorption (n L ) and saturated adsorption phase density (ρ L ) has the following relation (7).

[0088] n L =2ρ L σ g / M (7)

[0089] Where: n L is the monolayer saturated adsorption capacity, the physical quantity is mol / m 2 ρ L is the saturated adsorption phase density, the physical quantity is g / ml; σ g is the radius of the adsorbed gas molecule, the physical quantity is nm, where for methane, σ g =0.373nm.

[0090] The absolute adsorption amount and the adsorption phase density are expressed as functions of the adsorbent surface coverage, respectively. In the embodiments of the present disclosure, the absolute adsorption amount n is determined by the following equations (8) and (9): abs and the adsorbed phase density ρ a .

[0091] n abs (p) = n L θ(ρ b ) (8)

[0092] ρ a (p) = ρ L θ(ρ b ) (9)

[0093] In the embodiment of the present disclosure, (6) to (9) are integrated to obtain the following excess adsorption amount expression (10).

[0094]

[0095] Wherein, θ is the coverage, and any single-layer adsorption model can be used for calculation in the embodiments of the present disclosure. The single-layer adsorption model can adopt the well-known Langmuir model, Sips model and Toth model, etc. It should be noted that in the implementation of the present disclosure, these three models are used as examples for exemplary description, but are not limited to these three exemplary models. As long as the coverage can be obtained, any model that can achieve the calculation / determination of the coverage can be used.

[0096] Molecular simulation results show that the real gas coverage is better correlated with the bulk gas density than the ideal gas adsorption coverage with pressure. The surface coverage of the real gas θ is expressed as the bulk gas density ρ b The function of

[0097]

[0098] where ρ L It is the bulk gas density when the saturated adsorption capacity reaches 50%.

[0099] In order to simplify the calculation, the ideal gas adsorption model can also be used to calculate the coverage, such as the Langmuir, Sips and Toth models.

[0100] The Langmuir model assumes that: a) gas molecules form a monolayer adsorption on the solid surface; b) the surface is uniform, the adsorption capacity at each point is the same, and the adsorption heat does not change with the coverage; c) intermolecular forces are ignored; d) the adsorption rate is equal to the desorption rate at dynamic adsorption equilibrium. θ is the surface coverage, which is the adsorption amount q and the saturated adsorption amount q S The surface coverage θ is expressed as a function of pressure p,

[0101]

[0102] where p L It is the pressure when the saturated adsorption capacity reaches 50%.

[0103] The Sips model is derived from Langmuir and Freundlich, so it is also called the Langmuir-Freundlich model. This model can better predict heterogeneous adsorption systems at any temperature and overcome the problem that the Freundlich model cannot describe saturated adsorption. Under low pressure, it exhibits the characteristics of the Freundlich model; under high pressure conditions, it exhibits the monolayer adsorption characteristics described by the Langmuir model. Generally speaking, the equation parameters mainly depend on the experimental conditions, such as changes in pH, temperature, concentration or pressure.

[0104]

[0105] Where: b and η are functions of temperature.

[0106]

[0107]

[0108] Where: b0 is the affinity constant at the reference temperature T0, η0 is the parameter η constant at the reference temperature, α is a constant, R is the ideal gas constant, and Q is the adsorption heat.

[0109] The coverage expression of the Toth model is:

[0110]

[0111] n=A t +B t T (16)

[0112] n is the non-uniformity value of the adsorbent surface, and n is calculated by fitting the linear relationship between the parameters A1, B1 and the adsorption temperature T. When n=1, the equation is the same as the expression of the Langmuir model and also satisfies the Vant Hoff equation. In the embodiments of the present disclosure, the fitting parameters are not specifically limited, and in practice, those skilled in the art can set and adjust them according to actual conditions.

[0113] In the embodiment of the present disclosure, the excess adsorption curve obtained by GCMC in step 3) is fitted using formula (10) to obtain ρ L .

[0114] In the embodiment of the present disclosure, the n obtained by the above fitting is L Substituting into formula (8), we can get the absolute adsorption amount curve, that is, the relationship curve between the absolute adsorption amount and the pressure; L Substituting into formula (9), we can obtain the adsorption phase density (ρ a ) curve, that is, the relationship curve between the adsorption phase density and pressure is obtained; a Substituting into formula (6), we can obtain the conversion relationship between absolute adsorption amount and excess adsorption amount.

[0115] Optionally, the embodiment of the present disclosure may be based on the obtained n abs Convert to adsorption per unit mass:

[0116] The above-mentioned abs The adsorption amount per unit area can be converted into the adsorption amount per unit mass using the following formula (17).

[0117] V abs (p) = 10 3 Svn abs (p) (17)

[0118] Where: V abs is the adsorption per unit mass, and the physical quantity is m 3 / t; S is the specific surface area of ​​shale tested by low-pressure gas (nitrogen, carbon dioxide, argon, etc.), physical quantity m 2 / g; v is the molar volume, which is 22.4L / mol.

[0119] In the embodiments of the present disclosure, the adsorption of methane by highly mature to over-mature organic-rich shale is used as an example to explain the analysis process of the present disclosure. GCMC simulation technology is widely used in the study of microscopic adsorption characteristics of various porous media. In the embodiments of the present disclosure, the following can be used: Figure 2 The GCMC simulation flow chart of gas adsorption in pores is shown for GCMC ensemble simulation.

[0120] 1) Establish pore model

[0121] The pores of highly to over-mature organic-rich shale are mainly organic pores, and the surface of organic pores is mainly composed of C elements. Figure 3 A schematic diagram of an organic slit pore model according to an embodiment of the present disclosure is shown. In order to simplify the surface structure, three layers (the upper three layers and the lower three layers marked with black dots in the figure) of graphene sheets are used to represent the shale organic pore wall surface, and the pore diameter ( Figure 3 The organic slit hole is 4 nm, and the distance between the three layers is (angstrom).

[0122] 2) Set simulation force field, ensemble, temperature, and pressure conditions

[0123] (i) Force field

[0124] The adsorption behavior is determined by the gas-gas potential and the gas-solid potential. The potential in the model includes van der Waals interaction and Coulomb interaction. The Lennard-Jones 12-6 potential model is used to describe the intermolecular van der Waals interaction, with a cutoff radius of 5σ, and the Lorentz-Berthelot mixing rule is used for different types of intermolecular forces. The Coulomb interaction potential between two charged particles is inversely proportional to the distance, and the Ewarld superposition method is used to describe the Coulomb interaction.

[0125] The TraPPE-UA model is used to describe methane, and the graphene force field is used to describe organic matter.

[0126] (ii) GCMC ensemble simulation

[0127] A 4 nm organic slit hole was established, and the dimensions of the simulation box x, y, and z were 4.92, 4.26, and 4+4*0.335+4 nm, respectively. The simulation box used periodic boundaries in the x, y, and z directions, and a 2 nm vacuum layer was added to the outside of the pore wall. The model parameters are shown in Table 1.

[0128] Table 1 Pore model parameters

[0129]

[0130] Two types of motion are considered in the GCMC simulation: the first is insertion and deletion, which are attempted with a probability of 40%, and the second is movement, which is attempted with a probability of 60%.

[0131] System balancing process settings 10 5 Step 10: Collect data 6 Step 2. Collect data from the second phase of the run (including molecular number and gas density distribution, etc.). Divide the output phase data into five blocks and analyze the deviations from the ensemble average calculation results.

[0132] (iii) Temperature and pressure

[0133] Assuming the reservoir is buried at a depth of 3000m, the pressure coefficient is 1.7, and the temperature gradient is 2.5K / 100m. The simulation conditions are selected as 348.15K, 1-50MPa. The GCMC method is used to simulate the He gas test pore volume experimental process, and the simulation conditions are selected as 293K (20℃), 1MPa.

[0134] 3) Calculate the pore volume

[0135] Helium was loaded into the constructed 4 nm organic slit pore model. The GCMC simulation details of helium in the pores were the same as those of methane, and the pore volume was calculated using formula (1). The simulation details of helium in the pores were the same as those of methane.

[0136]

[0137] 4) Obtaining excess adsorption curve from molecular simulation

[0138] The GCMC simulation results are converted into excess adsorption through equation (2), as shown in Fig. 4(a) and Fig. 4(b), which are the relationship curves of excess adsorption of methane at 348.15K in a 4nm organic slit pore and pressure, and the relationship of excess adsorption of methane at 348.15K in a 4nm organic slit pore and density, respectively. As shown in the figure, the gray box is the simulation result, and the curve line is the guide line.

[0139] The discrete excess adsorption curve represented by squares obtained by GCMC is fitted using formula (10), as shown in Figure 5 The figure shows the fitting result of excess adsorption of methane in organic slit pores at 348.15K. The fitting result is: ρ L =0.384, n L =0.0251, correlation coefficient R 2 =0.989. It can be seen from the correlation coefficient that it is close to 1, which shows that the fitting degree of the embodiment of the present disclosure is very good.

[0140] 5) Absolute adsorption amount conversion

[0141] The n obtained by the above fitting L Substituting into formula (8), we can get the absolute adsorption curve, as Figure 6 As shown in the figure, the results show that when the pressure is greater than 2MPa, the relative error between the absolute adsorption amount predicted by the model of the embodiment of the present disclosure and the GCMC simulation is less than 5%. The abandoned pressure of the gas reservoir is usually greater than 2MPa, so the model of the embodiment of the present disclosure can be used to convert the excess adsorption amount under shale gas reservoir conditions into absolute adsorption amount. L Substituting into formula (9) we can get the adsorption phase density: Figure 7 shown.

[0142] 6) Conversion formula between absolute adsorption amount and excess adsorption amount

[0143] ρ L Substituting into formula (9), we can get the relationship between the density of the adsorption phase and the pressure. Then substituting formula (9) back into formula (6), we can get the conversion relationship between the absolute adsorption amount and the excess adsorption amount, which can be used to convert the excess adsorption amount obtained in the experiment.

[0144] 7) Convert to adsorption per unit mass

[0145] The experimentally measured specific surface area of ​​shale samples is 15m 2 / g, and the adsorption per unit area is converted into the adsorption per unit mass using formula (17), as follows: Figure 8 shown.

[0146] Based on the above method, the present disclosure also provides a computer system, such as Fig. 9 As shown, the computer system may include multiple processors, input and output interfaces (I / O interfaces), memory (such as ROM, RAM, flash memory, etc.), network interfaces and device interfaces, and each device unit may be connected to each other through a data line (such as CAN bus). Multiple processors read computer program instructions from the memory through the I / O interface and store the processing results in the memory; the computer system is connected to the external network through the network interface to transmit data to the external network or receive data from the external network; the computer system is connected to the external interface of the computer system through the device interface to transmit data to the external device or receive data from the external device.

[0147] One of the plurality of processors reads the conversion relationship between the absolute adsorbed gas volume and the excess adsorbed gas volume, the single-layer saturated adsorption volume n and the L Relationship, absolute adsorption amount n abs (p) relationship and adsorption phase density relationship, and execute computer program instructions in the memory to calculate the above data to determine the excess adsorption amount relationship.

[0148] The processor or another processor executes the computer program instructions in the memory to fit the excess adsorption amount curve obtained by GCMC using the excess adsorption amount relationship to obtain the saturated adsorption phase density ρ L .

[0149] One of the plurality of processors may obtain the adsorption phase density ρ from a memory. a (p) and gas density ρ b (p) and other data, and based on the acquired data, the computer program instructions in the memory are executed to calculate the above data to form the absolute adsorption gas volume n abs (p) and excess adsorption volume n exc conversion relationship.

[0150] One of the plurality of processors may execute computer program instructions to implement the molecular simulation process as described above.

[0151] One of the plurality of processors may execute computer program instructions to generate a saturated adsorption phase density based on the saturated adsorption phase density p. L and coverage θ(ρ b ) determines the density of the adsorbed phase.

[0152] It should be noted that the present disclosure does not limit the method for obtaining the above data, that is, it is not limited to obtaining from the memory of the computer system, and can be obtained from the external network through a network interface, or from an external device through a device interface.

[0153] Based on the above disclosed content, the present disclosure also provides a device for determining the density of the saturated adsorption phase based on the conversion relationship. Fig.10 The device comprises a first unit, a second unit and a third unit, wherein the first unit is configured to convert the absolute adsorbed gas volume to the excess adsorbed gas volume, the single-layer saturated adsorption volume n L Relationship, absolute adsorption amount n abs (p) relationship and adsorption phase density relationship, determine the excess adsorption relationship; the second unit is configured to use the excess adsorption relationship to fit the excess adsorption curve obtained by GCMC to obtain the saturated adsorption phase density ρ L The third unit is configured to obtain the excess adsorption amount n in the excess adsorption amount relationship by molecular simulation. exc parameter.

[0154] Based on the above disclosure, the present disclosure also provides a method for determining the adsorption phase density ρ a (p) devices, such as Fig.11 The device shown in the figure includes an acquisition unit and a determination unit, wherein the acquisition unit uses the method as described above to obtain the saturated adsorption phase density ρ L ; Using the monolayer adsorption model to determine the coverage θ(ρ b ); the determination unit is based on the saturated adsorption phase density ρ L and coverage θ(ρ b ) Determine the adsorption phase density ρ a (p).

[0155] Based on the above disclosed content, the present disclosure also provides a method for converting the absolute adsorption amount n abs (p) is converted to excess adsorption amount n exc Devices such as Fig.12 The device shown in the figure comprises an interface unit and a conversion unit, wherein the interface unit is used to obtain the adsorption phase density ρ a (p) and gas density ρ b (p) parameter, the conversion unit connected to the interface unit is configured to utilize the obtained adsorption phase density ρ a (p) and gas density ρ b The (p) parameter converts the excess adsorption amount into the absolute adsorption amount.

[0156] Based on the above disclosed content, the present disclosure also provides an electronic device, such as Fig.13 As shown, the electronic device includes at least one processor and at least one memory, the memory is electrically connected to the processor, wherein the memory stores instructions that can be executed by at least one processor, and the instructions are executed by at least one processor so that the at least one processor can execute the above method.

[0157] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.< / n> < / n> < / n> < / n>

Claims

1. A method for determining the density of a saturated adsorption phase based on a conversion relationship, characterized in that: The method comprises, Based on the conversion relationship between absolute adsorption volume and excess adsorption volume, the single-layer saturated adsorption volume n L Relationship, absolute adsorption amount n abs (p) relationship and adsorption phase density relationship, determine the excess adsorption amount relationship; The excess adsorption amount relationship is used to fit the excess adsorption amount curve obtained by experiment or molecular simulation to obtain the saturated adsorption phase density ρ L .

2. The method according to claim 1, characterized in that Based on the adsorption phase density ρ a (p) and gas density ρ b (p) to form the absolute adsorption volume n abs (p) and excess adsorption volume n exc (p), where p is pressure.

3. The method according to claim 1 or 2, characterized in that: The absolute adsorption volume n abs (p) and excess adsorption volume n exc The conversion relationship of (p) is, 4. The method according to claim 1, characterized in that The absolute adsorption amount n abs (p) The relationship is, n abs (p) = n L θ(ρ b ); and / or, The adsorption phase density relationship is: a (p) = ρ L θ(ρ b ),in, θ(ρ b ) is the gas phase density ρ b is the coverage rate below; n L is the saturated adsorption capacity of the monolayer.

5. The method according to claim 4, characterized in that The gas phase density ρ is determined by the monolayer adsorption model b The coverage rate θ(ρ b ).

6. The method according to claim 1, characterized in that The excess adsorption capacity relationship is: Among them, ρ L is the saturated adsorption phase density, σ g is the molecular radius of the adsorbed gas, M is the molar mass, θ is the coverage, ρ b is the gas density.

7. The method according to claim 6, characterized in that The excess adsorption amount n in the excess adsorption amount relation is exc The parameters are obtained by experimental methods or molecular simulation.

8. The method according to claim 7, characterized in that The molecular simulation method is to use the established pore molecular model to determine the ensemble average number <n> μ and pore volume Vp; according to the ensemble average quantity <n> μ and the pore volume Vp to calculate the excess adsorbed gas volume n exc parameter; or,< / n> < / n> The experimental method is: conducting an adsorption gas test experiment with reference to a volume method or a weight method.

9. The method according to claim 7 or 8, characterized in that: The pore volume Vp is: in, <N He > is the ensemble average number of helium molecules in the pores; N A is Avogadro's constant; ρ He is the bulk helium density; M He is the molar mass of helium.

10. A method for determining the density ρ of the adsorbed phase a (p) The method is characterized in that The method comprises, The saturated adsorption phase density ρ is obtained by using the method according to any one of claims 1 to 9. L ; Using the monolayer adsorption model to determine the coverage θ(ρ b ); Based on the saturated adsorption phase density ρ L and coverage θ(ρ b ) Determine the adsorption phase density ρ a (p).

11. The method according to claim 10, characterized in that The adsorption phase density ρ is determined based on the following formula a (p): r a (p)=ρ L θ(ρ b )。 12. A method to convert the absolute adsorption amount n abs (p) is converted to excess adsorption amount n exc The method is characterized in that The method comprises, Using the adsorption phase density p obtained as claimed in claim 10 or 11 a (p) and gas density ρ b The (p) parameter converts the excess adsorption amount into the absolute adsorption amount.

13. The method according to claim 12, characterized in that The excess adsorption amount was converted to the absolute adsorption amount based on the following formula:

14. A device for determining the density of a saturated adsorption phase based on a conversion relationship, the device comprising a first unit and a second unit, characterized in that: The first unit is configured to convert the absolute adsorption gas volume to the excess adsorption gas volume, the single-layer saturated adsorption volume n L Relationship, absolute adsorption amount n abs (p) relationship and adsorption phase density relationship, determine the excess adsorption amount relationship; The second unit is configured to use the excess adsorption amount relationship to fit the excess adsorption amount curve obtained by experiment or molecular simulation to obtain the saturated adsorption phase density ρ L .

15. The device according to claim 14, characterized in that The absolute adsorption volume n abs (p) and excess adsorption volume n exc The conversion relationship of (p) is, Among them, ρ a (p) is the density of the adsorbed phase, ρ b (p) is the gas density and p is the pressure.

16. The device according to claim 14, characterized in that The excess adsorption capacity relationship is: Among them, ρ L is the saturated adsorption phase density, σ g is the molecular radius of the adsorbed gas, M is the molar mass, θ is the coverage, ρ b is the gas density.

17. The device according to any one of claims 14 to 16, further comprising a third unit, characterized in that: The third unit is configured to obtain the excess adsorption gas amount n in the excess adsorption amount relationship by experimental method or molecular simulation. exc parameter.

18. A method for determining the density ρ of the adsorbed phase a (p) The device comprises an acquisition unit and a determination unit, characterized in that: The acquisition unit is configured to acquire the saturated adsorption phase density ρ using the method according to any one of claims 1 to 9. L ; Using the monolayer adsorption model to determine the coverage θ(ρ b ); The determination unit is configured to determine the adsorption of the saturated phase based on the saturated adsorption phase density ρ L and coverage θ(ρ b ) Determine the adsorption phase density ρ a (p).

19. The device according to claim 18, characterized in that The saturated adsorption phase density ρ is determined based on the following formula a (p), r a (p)=ρ L θ(ρ b )。 20. A method of converting the absolute adsorption amount n abs (p) is converted to excess adsorption amount n exc The device comprises a conversion unit, characterized in that The conversion unit is configured to utilize the adsorption phase density p obtained as claimed in claim 10, 11, 18 or 19 a (p) and gas density ρ b The (p) parameter converts the excess adsorption amount into the absolute adsorption amount.

21. The device according to claim 20, characterized in that The excess adsorption amount was converted to the absolute adsorption amount based on the following formula:

22. An electronic device, comprising at least one processor and at least one memory, wherein the memory is data-connected to the processor, wherein: The memory stores instructions that can be executed by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to perform the method according to any one of claims 1 to 13.

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