Method for quantifying heterogeneous distribution of shale oil components based on multi-scale phase equilibrium

Abstract

The invention discloses a method for quantifying shale oil component heterogeneous distribution based on multi-scale phase equilibrium, and the method comprises the steps: correcting a PR-EOS state equation suitable for a fluid state in shale nanopores based on an adsorption effect in a nanometer confinement space; coupling a capillary force effect and an adsorption effect, and establishing a behavior description method of the fluid phase in the shale nanopores based on a corrected PR-EOS state equation; establishing a multi-scale phase equilibrium characterization model on the basis of considering the overall thermodynamic equilibrium of a matrix-fracture system by combining the multi-scale structural characteristics of the shale reservoir; and quantitatively describing heterogeneous distribution characteristics of shale oil components in a multi-scale space based on the multi-scale phase equilibrium characterization model.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field exploitation, and in particular to a method for quantifying heterogeneous distribution of shale oil components based on multi-scale phase equilibrium. Background Art

[0002] Behind the global economic growth is a substantial increase in energy demand. The development of conventional oil and gas resources can no longer meet the growing energy demand. Extracting oil and gas from unconventional reservoirs such as shale is an inevitable choice to ensure national energy security, and plays a vital role in alleviating the energy crisis and promoting sustainable economic development. In the development process, the accurate characterization of crude oil components and phase characteristics in the reservoir is the basis for the successful development of shale oil, and is of great significance to the evaluation of shale oil reserves and the formulation of development plans.

[0003] Compared with conventional reservoirs, the biggest feature of shale oil reservoirs is the large number of nanopores with a size of 10-100 nm, that is, nanomatrix pores are the main storage space for crude oil. How to extract the crude oil in the shale matrix pores is the key to achieving efficient development of shale oil and gas. At the nanoscale, the interface effect (the force between fluid molecules and the force between fluid and solid wall) makes the fluid in the pores show different characteristics from those in the conventional scale space. Traditional characterization methods and models are no longer applicable, which leads to unclear understanding of the occurrence characteristics and phase change laws of shale oil, affecting the formulation of production technology policies.

[0004] It is precisely because shale oil reservoirs have the characteristics of low permeability and developed nanopores that large-scale hydraulic fracturing must be adopted to achieve effective development. Fracturing makes the pore space of shale reservoirs have multi-scale characteristics, including natural fractures and hydraulic fractures with scales ranging from micrometers to centimeters, and matrix pores with radii ranging from a few nanometers to tens of nanometers. At the same time, matrix nanopores and fractures do not exist in isolation, but are interconnected to form fluid flow channels. In the matrix pore-fracture system, the phase state of the fluid in the fracture is manifested as a bulk phase, which can be described by traditional methods; however, due to the significant influence of scale effects, the phase state of the fluid in the matrix pores deviates from the classical theoretical description, and the connectivity of matrix pores and fractures will cause the two to affect each other and further affect the distribution characteristics of shale oil components. However, the component distribution and phase state of shale oil in multi-scale space are still unclear, and there is a lack of effective quantitative methods, which fundamentally restricts the accurate evaluation of shale oil reserves and production dynamic prediction.

[0005] The above contents are only used to assist in understanding the technical solution of the present invention and do not constitute an admission that the above contents are prior art. Summary of the invention

[0006] The main purpose of the present invention is to provide a method for quantifying the heterogeneous distribution of shale oil components based on multi-scale phase equilibrium, aiming to solve or partially solve the above-mentioned problems.

[0007] To achieve the above object, the present invention provides a method for quantifying the heterogeneous distribution of shale oil components based on multi-scale phase equilibrium, comprising:

[0008] Based on the adsorption effect in nano-confined space, the PR-EOS state equation suitable for the fluid state in shale nanopores is modified;

[0009] By coupling capillary force and adsorption, a method for describing the fluid phase behavior in shale nanopores based on the modified PR-EOS equation of state was established.

[0010] Combining the multi-scale structural characteristics of shale reservoirs, a multi-scale phase equilibrium characterization model is established based on the overall thermodynamic equilibrium of the matrix-fracture system.

[0011] Based on the multi-scale phase equilibrium characterization model, the heterogeneous distribution characteristics of shale oil components in the multi-scale space are quantitatively described.

[0012] Preferably, in the method for quantifying the heterogeneous distribution of shale oil components based on multi-scale phase equilibrium, the PR-EOS state equation suitable for the fluid state in the nanopores of shale is corrected based on the adsorption effect in the nano-confined space, including:

[0013] According to the adsorption effect in confined space, the molar volume in the traditional PR-EOS equation of state is corrected;

[0014] According to the change of effective molar volume caused by excess adsorption, the PR-EOS equation of state suitable for describing shale nanoporous fluids is obtained.

[0015] Preferably, in the method for quantifying the heterogeneous distribution of shale oil components based on multi-scale phase equilibrium, in the correction of the molar volume in the traditional PR-EOS state equation according to the adsorption effect in the confined space, the corrected molar volume, i.e., the effective molar volume V m ’ It is expressed as:

[0016]

[0017] Among them, N A is Avogadro's constant;

[0018] V p is the pore volume, nm 3 ;

[0019] n t is the total number of fluid molecules;

[0020] n e is the number of excess adsorption molecules in the nanopores of shale;

[0021] Among them, the total number of fluid molecules can be expressed as:

[0022]

[0023] Among them, R p is the pore radius;

[0024] L is the pore length;

[0025] v b is the effective volume occupied by each molecule;

[0026] The number of excess adsorption molecules can be expressed as:

[0027]

[0028] Where σ is the size of the molecule;

[0029] v e is the volume occupied by each molecule in the excess adsorption.

[0030] Preferably, in the method for quantifying the heterogeneous distribution of shale oil components based on multi-scale phase equilibrium, the PR-EOS state equation suitable for describing shale nanoporous fluids is obtained according to the change in effective molar volume caused by excess adsorption, and the modified PR-EOS state equation is:

[0031]

[0032] Where R is the gas constant;

[0033] a and b are the virial coefficients;

[0034] T is the fluid temperature in the nanopores of shale;

[0035] P c is the critical pressure of the bulk fluid.

[0036] Preferably, in the method for quantifying the heterogeneous distribution of shale oil components based on multi-scale phase equilibrium, the parameters a and b in formula (6) are:

[0037]

[0038]

[0039] Correspondingly, the critical temperature of fluid in shale nanopores is T cm and critical pressure P cm It is expressed as:

[0040]

[0041] Ignore ρ a / ρ f and the dimensionless pore radius m, Equations (9) and (10) can be simplified to the critical temperature T of the bulk fluid c and critical pressure P c . Define the dimensionless critical temperature offset ΔT c and critical pressure offset ΔP c for:

[0042]

[0043] Preferably, in the method for quantifying the heterogeneous distribution of shale oil components based on multi-scale phase equilibrium, the coupling of capillary force and adsorption to establish a method for describing the phase behavior of fluids in shale nanopores based on the modified PR-EOS equation of state includes:

[0044] Obtain the compressibility coefficients of the liquid and gas phases based on the modified PR-EOS equation of state;

[0045] Obtain the fugacity of liquid and gas phases based on the modified PR-EOS equation of state;

[0046] The capillary force between the liquid and gas phases was obtained based on the modified PR-EOS equation of state.

[0047] Preferably, in the method for quantifying the heterogeneous distribution of shale oil components based on multi-scale phase equilibrium, in the acquisition of the compressibility coefficients of the liquid phase and the gas phase based on the modified PR-EOS state equation, the compressibility coefficients of the liquid phase and the gas phase are respectively:

[0048]

[0049] in,

[0050]

[0051] y i represents the mole fraction of component i in the vapor phase;

[0052] y j represents the mole fraction of component j in the vapor phase;

[0053] x i represents the mole fraction of component i in the liquid phase;

[0054] x j represents the mole fraction of component j in the liquid phase;

[0055] a and b are the parameters of the mixture, obtained using the van der Waals mixing rule;

[0056] Z is the compressibility coefficient of the fluid, subscripts L and V represent the liquid phase and gas phase, respectively, and subscripts i and j represent component i and component j, respectively;

[0057] k ij is the interaction coefficient between the two components.

[0058] Preferably, in the method for quantifying heterogeneous distribution of shale oil components based on multi-scale phase equilibrium, the fugacity of the liquid phase and the gas phase in the step of obtaining the fugacity of the liquid phase and the gas phase based on the modified PR-EOS state equation are:

[0059]

[0060] in, and are the fugacity of the liquid phase and the fugacity of the gas phase in the system, respectively.

[0061] Preferably, in the method for quantifying heterogeneous distribution of shale oil components based on multi-scale phase equilibrium, in the step of obtaining the capillary force between the liquid phase and the gas phase based on the modified PR-EOS state equation, the capillary pressure is:

[0062]

[0063] Where θ is the contact angle, which is generally assumed to be 0°;

[0064] γ is the interfacial tension. γ is determined by the Parachor model and the calculation formula is as follows:

[0065]

[0066] Among them, p i is the Parachor of component i;

[0067] ρ L and ρ V are the densities of the liquid and gas phases, respectively.

[0068] Preferably, in the method for quantifying the heterogeneous distribution of shale oil components based on multi-scale phase equilibrium, in the step of establishing a multi-scale phase equilibrium characterization model based on the multi-scale structural characteristics of the shale reservoir and considering the overall thermodynamic equilibrium of the matrix-fracture system, the multi-scale system needs to achieve thermodynamic equilibrium with the fugacity of each component in the matrix nanopores being equal to the fugacity in the fractures, that is:

[0069]

[0070] Where f is the fugacity, superscript i is component i, and subscripts F and M represent fractures and matrix nanopores, respectively;

[0071] The conversion format of formula (31) is:

[0072]

[0073] Equation (32) is the multi-scale phase equilibrium characterization model.

[0074] The present invention has at least the following beneficial effects:

[0075] The present invention modifies the PR-EOS state equation suitable for the fluid state in shale nanopores based on the adsorption effect in nano-confined space; couples the capillary force and the adsorption effect to establish a method for describing the phase behavior of the fluid in the shale nanopores based on the modified PR-EOS state equation; combines the multi-scale structural characteristics of the shale reservoir, and establishes a multi-scale phase equilibrium characterization model on the basis of considering the overall thermodynamic equilibrium of the matrix-fracture system; based on the multi-scale phase equilibrium characterization model, quantitatively describes the heterogeneous distribution characteristics of shale oil components in the multi-scale space, thereby providing an effective quantitative means for the component distribution and phase state of shale oil in the multi-scale space, and fundamentally solving or partially solving the accurate evaluation of shale oil reserves and production dynamic prediction.

[0076] Furthermore, on the basis of the traditional PR-EOS state equation, the adsorption effect in nano-confined space is considered to establish a modified PR-EOS equation suitable for describing the fluid state in shale nanopores; combined with the multi-scale structural characteristics of shale reservoirs, a multi-scale phase equilibrium characterization model is established on the basis of the overall thermodynamic equilibrium of the matrix-fracture system to quantitatively describe the heterogeneous distribution characteristics of shale oil components in multi-scale space. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Figure 1 A schematic diagram of a method for quantifying heterogeneous distribution of shale oil components based on multi-scale phase equilibrium provided by the present invention;

[0078] Figure 2 is the dimensionless critical temperature offset ΔT c Double natural logarithm plot with dimensionless pore radius;

[0079] Figure 3 Schematic diagram of the shale matrix pore-fracture multi-scale phase equilibrium model in an embodiment of the present invention;

[0080] Figure 4 This is a flow chart of determining the distribution of components in a nanopore based on a multi-scale phase equilibrium model obtained in an embodiment of the present invention;

[0081] Figure 5 This is a comparison chart of the crude oil component ratios in nanopores of different sizes and the crude oil components in fractures obtained in an embodiment of the present invention.

[0082] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0083] In the embodiments of the present invention, the term "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent three situations: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0084] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0085] In the embodiments of the present invention, the term "plurality" refers to two or more than two, and other quantifiers are similar.

[0086] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings. However, it can be understood by those skilled in the art that in the embodiments of the present invention, many technical details are proposed in order to enable the reader to better understand the present invention. However, even without these technical details and various changes and modifications based on the following embodiments, the technical scheme claimed in the present invention can also be implemented. The division of the following embodiments is for the convenience of description and should not constitute any limitation on the specific implementation of the present invention. The various embodiments can be combined and referenced with each other under the premise of no contradiction.

[0087] The present invention provides a method for quantifying the heterogeneous distribution of shale oil components based on multi-scale phase equilibrium. Figure 1 A schematic diagram of the method for quantifying the heterogeneous distribution of shale oil components based on multi-scale phase equilibrium provided by the present invention is illustrated.

[0088] In step S100, the adsorption effect in the nano-confined space modifies the PR-EOS state equation suitable for the fluid state in the nano-pores of shale.

[0089] Step S100 includes step S110 and step S120.

[0090] In step S110 , the molar volume in the conventional PR-EOS state equation is corrected by taking into account the adsorption effect in the confined space.

[0091] In conventional reservoirs, fluid molecules are evenly distributed in the pore space, and the fluid molar volume in the traditional PR-EOS state equation is expressed as:

[0092]

[0093] Among them, N A is Avogadro's constant;

[0094] V p is the pore volume, nm 3 ;

[0095] n t is the total number of molecules in the fluid.

[0096] In shale nanopores, the interaction between molecules and pore walls causes part of the fluid to adsorb on the pore walls. Compared with the uniform distribution state, the excess adsorption at the pore walls (the difference between the number of adsorbed molecules and the number of molecules in the traditional uniform distribution state) will cause the effective molar volume of molecules in the entire space to change. After considering the adsorption effect, the effective molar volume V in shale nanopores m ’ (i.e. the corrected fluid molar volume) can be expressed as:

[0097]

[0098] Among them, N A is Avogadro's constant;

[0099] V p is the pore volume, nm 3 ;

[0100] n t is the total number of fluid molecules;

[0101] n e is the number of excess adsorption molecules in the nanopores of shale.

[0102] The total number of fluid molecules can be expressed as:

[0103]

[0104] Among them, R p is the pore radius;

[0105] L is the pore length;

[0106] v b is the effective volume occupied by each molecule.

[0107] Usually, the adsorption thickness of shale oil is generally 2 molecular layers, so the number of excess adsorption molecules can be expressed as:

[0108]

[0109] Where σ is the size of the molecule;

[0110] v eis the volume occupied by each molecule in the excess adsorption.

[0111] Combining equations (1) to (3), equation (1) can be expressed as:

[0112]

[0113] Since the volume ratio is inversely proportional to the density ratio, equation (4) can be further expressed as:

[0114]

[0115] Among them, ρ a is the density of the adsorbed phase;

[0116] ρ b is the bulk density;

[0117] ρ e is the excess adsorption phase density;

[0118] The parameter m is the dimensionless pore radius.

[0119] In step S120, the effective molar volume change caused by excess adsorption is taken into account to obtain the PR-EOS state equation (Peng-Robinson state equation) suitable for describing the shale nanoporous fluid.

[0120] Considering the change of effective molar volume caused by excess adsorption, the traditional PR-EOS state equation is modified, that is, according to the effective molar volume V m ’ , the PR-EOS state equation is corrected to:

[0121]

[0122] in,

[0123] P is pressure;

[0124] R is the gas constant;

[0125] a and b are the virial coefficients;

[0126] T is the fluid temperature in the nanopores of shale;

[0127] P c is the critical pressure of the bulk fluid.

[0128] For the state equation, there is an inflection point at the critical point. The first-order derivative and second-order derivative of pressure P with respect to volume are equal to zero at the critical point. Based on this, the parameters a and b in the modified PR-EOS state equation can be obtained as follows:

[0129]

[0130] in,

[0131] Correspondingly, the critical temperature of fluid in shale nanopores is T cm and critical pressure P cm It is expressed as:

[0132]

[0133] Among them, T r is the relative temperature.

[0134] Ignore ρ a / ρ b and the dimensionless pore radius m, Equations (9) and (10) can be simplified to the critical temperature T of the bulk fluid c and critical pressure P c . Define the dimensionless critical temperature offset ΔT c and critical pressure offset ΔP c for:

[0135]

[0136] According to the deviation of critical temperature of different fluids in pores of different sizes, the dimensionless critical temperature deviation ΔT can be obtained. c The general relationship between and the dimensionless pore radius m.

[0137] Figure 2 is the dimensionless critical temperature offset ΔT c And the dimensionless pore radius double natural logarithm diagram. It should be noted that Figure 2 The right side in the middle shows the literature of the relevant persons for the data point selection.

[0138] like Figure 2 As shown, on the double natural logarithmic graph, the dimensionless critical temperature offset ΔT c It shows a good linear relationship with the dimensionless pore radius m, and its mathematical form is:

[0139] ln(ΔT c )=-1.3659ln(m)+0.2256; (13)

[0140] Where, the dimensionless critical temperature offset ΔT c and critical pressure offset ΔP c Can be expressed as:

[0141] ΔT c =1.253m -1.3659 ; (14)

[0142] ΔPc =2.506m-1.57m -2.7318 ; (15)

[0143] Combining equation (14) and equation (11), we can get the adsorption phase density ρ a and bulk density ρ f The ratio can be expressed as:

[0144]

[0145] In step S200, the capillary force and the adsorption are coupled to establish a method for describing the fluid phase behavior in shale nanopores.

[0146] In step S210, the compressibility coefficients of the liquid phase and the gas phase based on the modified PR-EOS state equation are obtained.

[0147] One of the keys to describing fluid phase behavior is to obtain the compressibility coefficient. Based on the PR-EOS state equation taking into account the adsorption effect, the compressibility coefficients of the liquid phase and the gas phase are obtained as follows:

[0148]

[0149] in,

[0150]

[0151] y i represents the mole fraction of component i in the vapor phase;

[0152] y j represents the mole fraction of component j in the vapor phase;

[0153] x i represents the mole fraction of component i in the liquid phase;

[0154] x j represents the mole fraction of component j in the liquid phase;

[0155] a and b are the parameters of the mixture, obtained using the van der Waals mixing rule, Z is the compressibility of the fluid, subscripts L and V represent the liquid phase and gas phase, respectively, and subscripts i and j represent component i and component j, respectively; k ij is the interaction coefficient between the two components.

[0156] In step S220, the fugacity of the liquid phase and the gas phase based on the modified PR-EOS state equation is obtained.

[0157] Another key parameter to describe the behavior of the fluid phase is to obtain the fugacity. Based on the PR-EOS state equation considering the adsorption effect, the fugacity of the liquid phase and the gas phase are obtained as follows:

[0158]

[0159] in, and are the fugacity of the liquid phase and the fugacity of the gas phase in the system respectively;

[0160] a and b are the parameters of the mixture, obtained using the van der Waals mixing rule, Z is the compressibility of the fluid, subscripts L and V represent the liquid phase and gas phase, respectively, and subscripts i and j represent component i and component j, respectively;

[0161] P L and P V The pressures of the liquid and gas phases respectively.

[0162] In step S230, the capillary force between the liquid phase and the gas phase is calculated. The capillary force effect needs to be considered in the PR-EOS state equation.

[0163] In addition to the adsorption effect, the capillary pressure P between the liquid and gas phases c It also needs to be coupled to the calculation of phase behavior in the nanopore. Usually the liquid phase is the wetting phase, the gas phase is the non-wetting phase, and the capillary pressure is:

[0164]

[0165] Where θ is the contact angle, which is generally assumed to be 0°;

[0166] γ is the interfacial tension. γ is determined by the Parachor model and the calculation formula is as follows:

[0167]

[0168] Among them, p i is the Parachor of component i;

[0169] ρ L and ρ V are the densities of the liquid and gas phases, respectively.

[0170] In step S300, a multi-scale phase equilibrium characterization model is established.

[0171] Shale reservoirs have multi-scale pore structure characteristics, including natural fractures and hydraulic fractures with widths ranging from micrometers to centimeters, and matrix pores with a main radius ranging from a few nanometers to tens of nanometers. At the same time, matrix nanopores and fractures do not exist in isolation, but are interconnected to form fluid flow channels. Based on this feature, a multi-scale nanopore system is constructed, such as Figure 3 As shown in Figure 1, a multi-scale phase equilibrium characterization model for shale oil reservoirs is established. Several key conditions followed in the model are as follows:

[0172] (1) The temperature of the matrix and cracks in the overall system remains constant;

[0173] (2) The phase behavior of the fluid in the fracture follows the traditional PR-EOS model, while the phase behavior of the fluid in the nanopore follows the PR-EOS model modified by considering the adsorption effect and capillary force effect.

[0174] (3) Generally speaking, the components obtained through laboratory measurements are the components of the fluid in the fracture, that is, these are known parameters, and the distribution of the fluid components in the unknown nanopores is determined by these parameters.

[0175] Among them, the thermodynamic equilibrium of the multiscale system requires that the fugacity of each component in the matrix nanopores is equal to the fugacity in the cracks, that is:

[0176]

[0177] Here, f is the fugacity, superscript i is component i, and subscripts F and M represent cracks and matrix nanopores, respectively.

[0178] The conversion format of formula (31) is:

[0179]

[0180] Formula (32) includes a series of nonlinear equations that cannot be solved by analytical methods. In this embodiment, the Newton-Raphson (NR) method is used. For calculation, it is necessary to supplement the material balance equation in the shale nanopores and fractures, as follows:

[0181]

[0182]

[0183] The flow chart of determining the component distribution in nanopores based on the multiscale phase equilibrium model is as follows Figure 4 shown.

[0184] In step S400, based on the multi-scale phase equilibrium characterization model, the heterogeneous distribution characteristics of shale oil components in the multi-scale space are quantitatively described.

[0185] Based on the multi-scale phase equilibrium model proposed in step S300, combined with specific shale oil components, a quantitative description of the heterogeneous characteristics of shale oil components in multi-scale space is carried out. Based on the multi-scale phase equilibrium model, the component ratios of crude oil in different pores are calculated and compared with the component ratios in fractures.

[0186] Specific applications

[0187] Table 1 shows the measured components of a shale oil sample and the relevant parameters of each component required for calculation. It should be noted that the fluid here is the fluid in the fracture.

[0188] Table 1 Proportions of shale oil components in fractures and related key parameters

[0189] Components x <![CDATA[P cb ]]> <![CDATA[T cb ]]> ω <![CDATA[M w ]]> parachor σ <![CDATA[C1]]> 0.5816 4.60 190.56 0.01 16.04 74.05 0.38 <![CDATA[C2-C3-CO2]]> 0.1393 5.10 324.44 0.14 36.59 120.07 0.45 <![CDATA[C4-C6]]> 0.0528 3.55 452.79 0.22 67.49 218.99 0.57 <![CDATA[C 7+ ]]> 0.2263 2.230 678.129 0.515 178.040 582.359 0.764

[0190] Based on the multi-scale phase equilibrium model, the component ratios of crude oil in different pores are calculated and compared with the component ratios in fractures.

[0191] Among them, x in Table 1 represents the mole fraction of each component in the crack;

[0192] P cb Critical pressure under bulk conditions, MPa;

[0193] T cb Critical temperature in bulk state, K;

[0194] ω is the centrifugal factor, a dimensionless quantity;

[0195] M w Molecular molar mass, g / mol;

[0196] σ is the size of the molecule, nm.

[0197] In this embodiment, the specific analysis results show that:

[0198] like Figure 5 As shown in the figure, when the radius of the nanopore is less than 30 nm, the component distribution of the fracture and the nanopore is very different, and as the pore size decreases, the heterogeneity increases, the content of heavy hydrocarbons in the nanopores is higher, and the content of light hydrocarbons in the fractures is higher. 7+ The molar fraction of C1 is particularly sensitive to changes in pore radius. When the pore radius is 3 nm, the molar fraction of C1 drops significantly to 0.27, which is 54.08% less than that in the cracks. 7+ The mole fraction of increased sharply to 0.61, an increase of 169.35% compared with the content in the fractures. In this way, the quantitative evaluation of the heterogeneous distribution of components in shale oil reservoirs was achieved.

[0199] Obviously, the embodiments described above are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, ordinary technicians in this field can make other different forms of changes or modifications without creative work, which should fall within the scope of protection of the present invention.

Claims

1. A method for quantifying the heterogeneous distribution of shale oil components based on multi-scale phase equilibrium, characterized in that: include: Based on the adsorption effect in nano-confined space, the PR-EOS state equation suitable for the fluid state in shale nanopores is modified; By coupling capillary force and adsorption, a method for describing the fluid phase behavior in shale nanopores based on the modified PR-EOS equation of state was established. Combining the multi-scale structural characteristics of shale reservoirs, a multi-scale phase equilibrium characterization model is established based on the overall thermodynamic equilibrium of the matrix-fracture system. Based on the multi-scale phase equilibrium characterization model, the heterogeneous distribution characteristics of shale oil components in the multi-scale space are quantitatively described.

2. The method for quantifying the heterogeneous distribution of shale oil components based on multi-scale phase equilibrium according to claim 1, characterized in that: The PR-EOS state equation suitable for the fluid state in the nanopores of shale is modified based on the adsorption effect in the nano-confined space, including: According to the adsorption effect in confined space, the molar volume in the traditional PR-EOS equation of state is corrected; According to the change of effective molar volume caused by excess adsorption, the PR-EOS equation of state suitable for describing shale nanoporous fluids is obtained.

3. The method for quantifying the heterogeneous distribution of shale oil components based on multi-scale phase equilibrium according to claim 2, characterized in that: In the modification of the molar volume in the conventional PR-EOS state equation according to the adsorption effect in the confined space, the modified molar volume, i.e., the effective molar volume V m ’ It is expressed as: Among them, N A is Avogadro's constant; V p is the pore volume, nm 3 ; n t is the total number of fluid molecules; n e is the number of excess adsorption molecules in the nanopores of shale; Among them, the total number of fluid molecules can be expressed as: Among them, R p is the pore radius; L is the pore length; v b is the effective volume occupied by each molecule; The number of excess adsorption molecules can be expressed as: Where σ is the size of the molecule; v e is the volume occupied by each molecule in the excess adsorption.

4. The method for quantifying heterogeneous distribution of shale oil components based on multi-scale phase equilibrium according to claim 3, characterized in that: According to the change in effective molar volume caused by excess adsorption, the PR-EOS state equation suitable for describing shale nanoporous fluid is obtained. The modified PR-EOS state equation is: Where R is the gas constant; a and b are the virial coefficients; T is the fluid temperature in the nanopores of shale; P c is the critical pressure of the bulk fluid.

5. The method for quantifying heterogeneous distribution of shale oil components based on multi-scale phase equilibrium according to claim 4, characterized in that: The parameters a and b in formula (6) are: Correspondingly, the critical temperature of fluid in shale nanopores is T cm and critical pressure P cm It is expressed as: Ignore ρ a / ρ b and the dimensionless pore radius m, Equations (9) and (10) can be simplified to the critical temperature T of the bulk fluid c and critical pressure P c , define the dimensionless critical temperature offset ΔT c and critical pressure offset ΔP c for:

6. The method for quantifying heterogeneous distribution of shale oil components based on multi-scale phase equilibrium according to claim 1, characterized in that: The coupling of capillary force and adsorption to establish a method for describing the phase behavior of fluid in shale nanopores based on the modified PR-EOS equation of state includes: Obtain the compressibility of the liquid and gas phases based on the modified PR-EOS equation of state; Obtain the fugacity of liquid and gas phases based on the modified PR-EOS equation of state; The capillary force between the liquid and gas phases was obtained based on the modified PR-EOS equation of state.

7. The method for quantifying heterogeneous distribution of shale oil components based on multi-scale phase equilibrium according to claim 6, characterized in that: In the acquisition of the compressibility coefficients of the liquid phase and the gas phase based on the modified PR-EOS state equation, the compressibility coefficients of the liquid phase and the gas phase are respectively: (22) in, y i represents the mole fraction of component i in the vapor phase; y j represents the mole fraction of component j in the vapor phase; x i represents the mole fraction of component i in the liquid phase; x j represents the mole fraction of component j in the liquid phase; a and b are the parameters of the mixture, obtained using the van der Waals mixing rule, Z is the compressibility of the fluid, subscripts L and V represent the liquid phase and gas phase, respectively, and subscripts i and j represent component i and component j, respectively; k ij is the interaction coefficient between the two components.

8. The method for quantifying heterogeneous distribution of shale oil components based on multi-scale phase equilibrium according to claim 7, characterized in that: In the step of obtaining the fugacity of the liquid phase and the gas phase based on the modified PR-EOS state equation, the fugacity of the liquid phase and the gas phase are respectively: in, and are the fugacity of the liquid phase and the fugacity of the gas phase in the system, respectively.

9. The method for quantifying the heterogeneous distribution of shale oil components based on multi-scale phase equilibrium according to claim 8, characterized in that: In the step of obtaining the capillary force between the liquid phase and the gas phase based on the modified PR-EOS state equation, the capillary pressure is: Where θ is the contact angle, which is generally assumed to be 0°; γ is the interfacial tension, which is determined by the Parachor model and is calculated as follows: Among them, p i is the Parachor of component i; ρ L and ρ V are the densities of the liquid and gas phases, respectively.

10. The method for quantifying heterogeneous distribution of shale oil components based on multi-scale phase equilibrium according to claim 1, characterized in that: In the step of establishing a multi-scale phase equilibrium characterization model based on the multi-scale structural characteristics of the shale reservoir and considering the overall thermodynamic equilibrium of the matrix-fracture system, the thermodynamic equilibrium of the multi-scale system requires that the fugacity of each component in the matrix nanopores is equal to the fugacity in the fractures, that is: Where f is the fugacity, superscript i is component i, and subscripts F and M represent fractures and matrix nanopores, respectively; The conversion format of formula (31) is: Equation (32) is the multi-scale phase equilibrium characterization model.

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