A method for calculating oil saturation based on four-water conductivity model

Abstract

The present application belongs to the technical field of oil and gas exploration, and is especially a method for calculating oil saturation based on a four-water conductive model. The method comprises the following steps: S1: constructing a four-water saturation equation; S2: calculating four porosity; S3: determining the resistivity parameter; S4: determining the lithology coefficient and the cementation exponent by using an optimization method; and S5: calculating the oil saturation. On the basis of the traditional three-water conductive model, the present application introduces a new conductive component, i.e. fine silt pore water, which is more in line with the conductive characteristics of a shale-developed sandstone reservoir, realizes fine characterization of the complex conductive mechanism, improves the reliability of the oil saturation calculation result, and makes the logging interpretation conclusion more reliable. Through the combination of laboratory core analysis and logging data, the parameters can be determined and rapidly calculated in different regions, and the present application has good practicability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas exploration, in particular to a method for calculating oil saturation based on a four-water conductivity model. BACKGROUND

[0002] With the deepening of the research on low porosity and low permeability reservoirs, researchers have gradually realized that there are problems such as the development of argillaceous, complex pore structure and diverse conductivity characteristics in such reservoirs. These characteristics make the logging response characteristics not conform to the ideal Archie formula, and make the traditional saturation calculation method difficult to apply. In order to more accurately characterize and evaluate the saturation characteristics of such complex reservoirs, scholars have proposed various conductivity models. The dual-water model considers that the conductive medium in argillaceous sandstone reservoirs mainly includes free water and clay bound water. However, experimental studies have shown that there is also bound water in capillary pores, and the dual-water model does not consider the conductivity contribution of this part of water. Based on this, Li Zhoubo et al. proposed a three-water conductivity model, which has achieved good application effect in the interpretation of low-resistivity oil layers in the Tarim Basin. Due to the limitation of experimental data, the three-water model is simplified in parameter setting and does not consider the lithology coefficient. After that, Zhang Lihua et al. proposed a new three-water conductivity model, which introduces the lithology coefficient on the basis of the three-water conductivity model, further improving the applicability and accuracy of the model.

[0003] However, the three-water conductivity model and the new three-water conductivity model generally only consider the bound water in the effective pore in the division of micro-pore water, and do not fully consider the conductivity contribution of the fine silt part of the pore water in the argillaceous. In fact, the fine silt particles in the argillaceous also have a certain porosity, and the water inside will affect the overall conductivity characteristics of the reservoir. In order to solve these problems, we provide a method for calculating oil saturation based on a four-water conductivity model. SUMMARY

[0004] This section is intended to summarize some aspects of the embodiments of the present application and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of the specification of the present application in order to avoid obscuring the purpose of this section, the abstract and the title, and such simplifications or omissions cannot be used to limit the scope of the present application.

[0005] To solve the above technical problems, according to one aspect of the present application, the present application provides the following technical scheme:

[0006] A method for calculating oil saturation based on a four-water conductivity model, comprising the following steps:

[0007] S1: Constructing a four-water saturation equation: establishing a saturation equation containing four types of conductive media, including free fluid water, effective pore bound water, fine silt pore water and clay bound water, and the conductivity is represented as:

[0008]

[0009]

[0010] wherein, is the rock conductivity of saturated water, is the rock resistivity of saturated water, is the rock conductivity of oil and gas bearing, is the rock resistivity of oil and gas bearing, is the free water porosity, is the bound water porosity in effective porosity, is the silt porosity, is the clay water porosity;

[0011] S2: calculating four porosities: calculating free fluid porosity, effective porosity bound water porosity, silt porosity and clay bound water porosity respectively;

[0012] S3: resistivity parameter determination: determining formation water resistivity through experiment , combining experimental data to optimize inversion of clay bound water resistivity ;

[0013] S4: optimal method to determine lithology coefficient and cementation exponent : using optimization algorithm to invert model parameters , to make the model calculated resistivity and measured resistivity best match;

[0014] S5: calculating oil saturation: substituting the fitted parameters into the four water saturation equation to obtain the water saturation of the reservoir , and further calculating the oil saturation .

[0015] As a preferred scheme of the oil saturation calculation method based on the four water conductivity model, the specific method of S2 is: S2.1 calculating shale content based on logging data: shale content :

[0016]

[0017]

[0018]

[0019] wherein, is the shale index, , is the natural potential, natural gamma curve logging value, , Natural potential and natural gamma value of pure sandstone layer, , Natural potential and natural gamma value of pure mudstone layer, Formation coefficient, new formation is 3.7, and old formation is 2;

[0020] S2.2 Calculate the clay content: clay content The quantitative conversion relationship between shale content and clay content is established through experimental data, and the calculation formula is:

[0021]

[0022] Wherein, c is the fitting coefficient;

[0023] S2.3 Calculate the effective porosity: effective porosity The calculation is obtained by logging curve:

[0024]

[0025]

[0026] Wherein, , The neutron porosity and density logging value are respectively, , The matrix neutron porosity and density logging value are respectively, , The fluid neutron porosity and density logging value are respectively, , The shale neutron porosity and density logging value are respectively;

[0027] S2.4 Determine the irreducible water saturation: irreducible water saturation It is obtained by establishing the relationship between the experimental irreducible water saturation and porosity, and the calculation formula is:

[0028]

[0029] Wherein, And are fitting coefficients, is the effective porosity measured by experiment;

[0030] S2.5 Calculate the free fluid porosity: free fluid porosity It is calculated by the relationship between effective porosity and irreducible water saturation, and the calculation formula is:

[0031] ;

[0032] S2.6 Calculate clay water porosity: clay water porosity The clay content and wet clay porosity are calculated, and the calculation formula is:

[0033]

[0034] Wherein The wet clay porosity is determined in combination with the measured data of the region and the interpretation experience;

[0035] S2.7 Determine the reference porosity of fine silt: select a pure sandstone section as the reference section, and read the porosity of the section as the reference porosity of fine silt ;

[0036] S2.8 Calculate micro-porosity: effective pore bound water porosity , fine silt porosity , micro-porosity .

[0037] As a preferred scheme of the oil saturation calculation method based on the four-water conductivity model, the specific method of S3 is: S3.1 Determine the formation water resistivity;

[0038] S3.2 Calculate clay water resistivity: clay water resistivity The calculation formula is:

[0039]

[0040] Wherein The cation exchange capacity per unit volume is calculated as follows:

[0041]

[0042] Wherein, The formation temperature is in Celsius;

[0043] The equivalent conductivity of the compensating Na+ ion in the diffusion layer is calculated as follows:

[0044]

[0045] The diffusion factor of the diffusion layer is calculated as follows:

[0046]

[0047] Wherein, The actual formation water salinity is, The clay surface diffusion layer thickness is the minimum formation water salinity, which is equivalent to the salinity of 0.35 mol / L water.

[0048] As a preferred scheme of the oil saturation calculation method based on the four-water conductivity model, in the S4, the lithology coefficient and the cementation exponent The equation group is established by experimental data, and the optimal method is combined to determine the optimal equation group as follows:

[0049]

[0050] Among them is the resistivity of the first saturated rock sample, , , The lithology coefficients corresponding to the free fluid pore, micro-pore and clay water pore are respectively , , The cementation exponents corresponding to the free fluid pore, micro-pore and clay water pore are respectively

[0051] The optimal parameter combination is obtained, and the optimization objective function is defined as:

[0052]

[0053] Among them, is the model calculation resistivity, is the measured resistivity, is the parameter combination to be optimized, ; the particle swarm algorithm constantly adjusts the parameters , so that the objective function gradually decreases, and finally the optimal parameter combination is obtained, and the parameter updating principle is:

[0054]

[0055]

[0056] Among them is the position of the particle in the first iteration in the first dimension, is the velocity of the particle in the first iteration in the first dimension, is the inertia weight, is the individual learning factor, is the social learning factor, , is a random number between 0 and 1, Optimal position for individual, Global optimal position.

[0057] As a preferred scheme of the oil saturation calculation method based on the four-water conduction model, the specific method of S5 is: S5.1 calculating water saturation: calculating water saturation by using measured formation resistivity and theoretically calculated saturated water resistivity The calculation formula is:

[0058]

[0059] Wherein, Saturation index, determined by rock-electricity experiment, Measured result of formation resistivity logging, finally, boundary constraint is applied to the calculated water saturation result To ensure the rationality of the calculation result;

[0060] S5.2 calculating oil saturation: the calculation formula is as follows:

[0061] .

[0062] Compared with the prior art, the present application has the beneficial effects that:

[0063] 1. More complete conduction mechanism representation: based on the traditional three-water conduction model (free fluid water, micro-pore water, clay bound water), the present application introduces a new conduction component of fine silt pore water, which is more in line with the conduction characteristics of shale-developed sandstone reservoirs, and realizes fine representation of complex conduction mechanisms.

[0064] 2. Improved calculation accuracy and more accurate interpretation results: by introducing the conduction contribution of fine silt pore water, the model can more comprehensively consider the effects of various conduction media under the condition of multiple media in parallel. The reliability of the oil saturation calculation result is improved, and the logging interpretation conclusion is more reliable.

[0065] 3. Forming an analysis technology for directly calculating oil saturation based on well data: the present application constructs a complete technical process from parameter determination to model calculation. By combining laboratory core analysis and logging data, the parameters can be determined and quickly calculated in different regions, and the present application has good practicability. BRIEF DESCRIPTION OF DRAWINGS

[0066] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the present application will be described in detail below with reference to the drawings and specific embodiments. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor. Among them:

[0067] Figure 1 A flowchart of the oil saturation calculation method based on the four-water conductivity model of the present application;

[0068] Figure 2 A three-water conductivity model and a four-water conductivity model pore division comparison chart of the oil saturation calculation method based on the four-water conductivity model of the present application;

[0069] Figure 3 A relationship chart between shale content and clay content in the embodiment of the oil saturation calculation method based on the four-water conductivity model of the present application;

[0070] Figure 4 A porosity and irreducible water saturation relationship chart in the embodiment of the oil saturation calculation method based on the four-water conductivity model of the present application;

[0071] Figure 5 A certain well four-water conductivity model logging interpretation result chart in the embodiment of the oil saturation calculation method based on the four-water conductivity model of the present application;

[0072] Figure 6 A four-water conductivity model, a new three-water conductivity model, and an Archie formula oil saturation average absolute error comparison chart in the embodiment of the oil saturation calculation method based on the four-water conductivity model of the present application. DETAILED DESCRIPTION

[0073] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below with reference to the drawings.

[0074] Secondly, the present application is described in detail in combination with the schematic diagram. In the detailed description of the embodiments of the present application, the cross-sectional view of the device structure will be partially enlarged without the general proportion for the convenience of description, and the schematic diagram is only an example, which should not limit the scope of protection of the present application here. In addition, the three-dimensional spatial dimensions of length, width and depth should be included in the actual manufacture.

[0075] In order to make the purposes, technical solutions and advantages of the present application more clear, the embodiments of the present application will be further described in detail below with reference to the drawings.

[0076] The application further introduces a fine silt pore part on the basis of the new three-water conductive model, and constructs a more perfect four-water conductive model. The model further introduces the concept of fine silt pore water on the basis of the traditional three components of free fluid water, micro-pore water and clay bound water, so that the pore division is more fine and reasonable. By subdividing the micro-pore water into two conductive media of bound water in the effective pore and fine silt pore water, the application can more truly reflect the conductive mechanism and water-bearing characteristics of argillaceous sandstone reservoirs, and provide a higher-precision theoretical basis and interpretation method for oil saturation calculation of complex reservoirs, so as to more truly reflect the conductive characteristics of the reservoir and improve the accuracy of oil saturation calculation.

[0077] Specifically, refer to Figure 1 , the application provides an oil saturation calculation method based on a four-water conductive model, comprising the following steps:

[0078] S1: constructing a four-water saturation equation: based on the multi-medium parallel conductive theory, a saturation equation containing four types of conductive media of free fluid water, effective pore bound water, fine silt pore water and clay bound water is established, which provides a theoretical basis for subsequent calculation;

[0079] S1.1 analyzing the conductive contribution of different components in the complex reservoir: the four-water conductive model is consistent in form with the new three-water conductive model, but is further refined in physical connotation. The three-water conductive model divides the pore system into three conductive media of free fluid water, micro-pore water and clay bound water. The four-water model of the application further subdivides the micro-pore water into two parts: one part is the bound water in the effective pore, and the porosity is denoted as , and the other part is the fine silt pore water in the argillaceous, and the porosity is denoted as . Therefore, the micro-porosity is the sum of the two . As shown in Figure 2 , (a) three-water conductive model; (b) four-water conductive model proposed by the application.

[0080] S1.2 constructing the four-water conductive model: the conductivity expression of the new three-water conductive model under the conditions of saturated water and oil-gas containing is respectively:

[0081] (1)

[0082] (2)

[0083] wherein, is the rock conductivity of saturated water, is the rock resistivity of saturated water, is the rock conductivity of oil-gas containing, is the rock resistivity of oil-gas containing.

[0084] In the four water conduction model, the micro-pore is further divided into two types of effective pore and bound water pore and fine silt pore, but they still share the same conduction parameter, and the conductivity can be expressed as:

[0085] (3)

[0086] (4)

[0087] S2: Calculate the four porosity: according to the neutron, density and other logging data, respectively calculate the free fluid porosity, effective pore bound water porosity, fine silt porosity and clay bound water porosity, realize the fine division of reservoir pore system.

[0088] S2.1 Calculate the shale content based on logging data: shale content , can be calculated by natural gamma or natural potential logging curve:

[0089] (5)

[0090] (6)

[0091] (7)

[0092] Wherein, is the shale index. , is the natural potential, natural gamma curve logging value. , is the natural potential and natural gamma value of pure sandstone layer. , is the natural potential and natural gamma value of pure mudstone layer. is the formation coefficient, the new formation is 3.7, and the old formation is 2.

[0093] S2.2 Calculate the clay content: clay content , the quantitative conversion relationship between shale content and clay content can be established by experimental data, and the calculation formula is:

[0094] (8)

[0095] Wherein, c is the fitting coefficient. According to formula (8), the shale content calculated by formula (7) can be converted into the corresponding clay content.

[0096] S2.3 Calculate the effective porosity: effective porosity , which is calculated by logging curve, such as by neutron, density curve:

[0097] (9)

[0098] (10)

[0099] where, , are the neutron porosity and density log values, respectively. , are the matrix neutron porosity and density log values, respectively. , are the fluid neutron porosity and density log values, respectively. , are the shale neutron porosity and density log values, respectively. is the shale content calculated from equation (7).

[0100] S2.4 Determine the irreducible water saturation: Irreducible water saturation is obtained by establishing a relationship between the experimental irreducible water saturation and porosity, and the calculation formula is:

[0101] (11)

[0102] where, and are the fitting coefficients. is the effective porosity measured experimentally.

[0103] S2.5 Calculate the free fluid porosity: Free fluid porosity is calculated by the relationship between the effective porosity and the irreducible water saturation, and the calculation formula is:

[0104] (12)

[0105] where, is the effective porosity calculated from equation (9) or (10) according to the logging curve, is the irreducible water saturation calculated by bringing the effective porosity calculated from the logging curve into equation (11).

[0106] S2.6 Calculate the clay water porosity: Clay water porosity is calculated from the clay content and the wet clay porosity, and the calculation formula is:

[0107] (13)

[0108] where the clay content is calculated from equation (8), is the wet clay porosity, whose value is determined in combination with the measured data in the region and interpretation experience.

[0109] S2.7 Determine the fine silt reference porosity: select a pure sandstone section as the reference section, and read the porosity of this section as the fine silt reference porosity .

[0110] S2.8 Calculate the micro-porosity: the effective porosity calculated by formula (9) or (10) and the irreducible water saturation calculated by formula (11) effective porosity irreducible water porosity :

[0111] (14)

[0112] The difference between the shale content calculated by formula (7) and the clay content calculated by formula (8) and the fine silt reference porosity in Step 7 of Step 2 Calculate the fine silt porosity :

[0113] (15)

[0114] The effective porosity irreducible water porosity calculated by formula (14) and the fine silt porosity calculated by formula (15) The micro-porosity is calculated by adding :

[0115] (16)

[0116] S3: Resistivity parameter determination: determine the formation water resistivity through experiments , and optimize the inversion of clay irreducible water resistivity combined with experimental data .

[0117] S3.1 Determine the formation water resistivity: the formation water resistivity can be determined according to the analysis results of formation water salinity, and combined with the formation water resistivity-temperature relationship chart.

[0118] S3.2 Calculate the clay water resistivity: the clay water resistivity The calculation formula is:

[0119] (17)

[0120] Where is the cation exchange capacity per unit volume, and the calculation formula is as follows:

[0121] (18)

[0122] wherein, T is the formation temperature, in degrees Celsius.

[0123] is the equivalent conductivity of Na+ ions compensated in the diffusion layer, and the calculation formula is as follows:

[0124] (19)

[0125] is the diffusion factor of the diffusion layer, and the calculation formula is as follows:

[0126] (20)

[0127] wherein, is the actual formation water salinity, is the formation water salinity when the thickness of the diffusion layer on the surface of the clay is the smallest, which is equivalent to the salinity of 0.35 mol / L water.

[0128] S4: Optimal method for determining lithology coefficient and cementation exponent : An optimal algorithm is used to perform inversion on model parameters , , etc., so that the model calculation resistivity is best matched with the measured resistivity.

[0129] Lithology coefficient and cementation exponent are determined by establishing an equation group through experimental data and combining an optimal method. The optimal equation group is shown as follows:

[0130] (21)

[0131] wherein is the resistivity of the nth saturated rock sample. , , , are the lithology coefficients corresponding to the free fluid pore, the micro-pore, and the clay water pore, respectively. , , are the cementation exponents corresponding to the free fluid pore, the micro-pore, and the clay water pore, respectively.

[0132] In order to obtain an optimal parameter combination, so that the error between the calculation result and the measured resistivity or conductivity is minimized, an optimal algorithm can be used. The present application uses a particle swarm optimization algorithm. The particle swarm optimization algorithm has the following significant advantages: few parameters, easy to implement, strong global search capability, fast convergence speed, high precision, and the like. The particle swarm optimization algorithm can effectively improve the stability and reliability of the model inversion result.

[0133] The optimization objective function is defined as:

[0134] (22)

[0135] where, is the model calculated resistivity, is the measured resistivity, is the parameter combination to be optimized, .

[0136] The particle swarm algorithm continuously adjusts the parameters so that the objective function gradually decreases, and finally the optimal parameter combination is obtained.

[0137] The parameter update principle is:

[0138] (23)

[0139] (24)

[0140] where is the position of the particle in the first iteration in the first dimension, is the velocity of the particle in the first iteration in the first dimension, is the inertia weight, is the individual learning factor, is the social learning factor, , is a random number between 0 and 1, is the individual optimal position, is the global optimal position.

[0141] Through multiple iterations of updates, the particle swarm continuously searches and approaches the global optimal solution in the parameter space, thereby achieving efficient optimization of the model parameters.

[0142] S5: Calculate oil saturation: Substitute the fitted parameters into the four-water saturation equation to calculate the water saturation of the reservoir , and then calculate the oil saturation , thereby realizing quantitative interpretation of the reservoir fluid.

[0143] S5.1 Calculate water saturation: Calculate the water saturation using the measured formation resistivity and the theoretically calculated water-saturated resistivity , and the calculation formula is:

[0144] (25)

[0145] wherein, is the saturation exponent, determined from rock electrical experiments. is the formation water saturation calculated by formula (3) with the parameters determined in the above steps. is the formation resistivity measured by resistivity logging. Finally, the boundary constraint is imposed on the calculated water saturation to ensure the rationality of the calculation results.

[0146] S5.2 Calculate oil saturation: calculate the oil saturation using the water saturation calculated by formula (25) .

[0147] (26)

[0148] Embodiment

[0149] Taking a well as an example, the specific implementation process of the method of the present application is shown.

[0150] S1: Construct four water saturation equations: based on the multi-medium parallel conduction theory, establish saturation equations containing four types of conductive media of free fluid water, effective pore bound water, fine silt pore water and clay bound water, which provide a theoretical basis for subsequent calculation. See formulas (3) and (4) for details.

[0151] S2: Calculate four porosities: according to neutron, density and other logging data, calculate the free fluid porosity, effective pore bound water porosity, fine silt porosity and clay bound water porosity respectively, and realize the fine division of the reservoir pore system.

[0152] S2.1 Calculate shale content based on logging data: use formulas (6) and (7) to calculate the shale content based on the natural gamma curve.

[0153] S2.2 Calculate clay content: according to the relationship between clay content and shale content (such as Figure 3 ), the calculation formula is:

[0154] (27)

[0155] S2.3 Calculate effective porosity: use the density logging curve data to calculate the effective porosity according to formula (10).

[0156] S2.4 Determine the bound water saturation: according to the relationship between the bound water saturation and the porosity (such as Figure 4 ), the calculation formula is as follows:

[0157] (28)

[0158] The effective porosity is brought into equation (28) to calculate the irreducible water saturation .

[0159] S2.5 Calculate the free fluid porosity: Calculate the free fluid porosity according to equation (12) .

[0160] S2.6 Calculate the clay water porosity: Calculate the clay water porosity according to equation (13) , wherein The value is 0.2 combined with the relevant data in this area.

[0161] S2.7 Determine the fine silt reference porosity: Read the porosity of the pure sandstone layer of the well as the fine silt reference porosity = 0.15.

[0162] S2.8 Calculate the micro-porosity: Calculate the effective pore irreducible water porosity according to equation (14) , calculate the fine silt porosity according to equation (15) , and calculate the micro-porosity by adding the two according to equation (16) .

[0163] S3: Resistivity parameter determination:

[0164] S3.1 Determine the formation water resistivity: Determine the formation water resistivity according to the experimental data = 0.06.

[0165] S3.2 Calculate the clay water resistivity: Calculate the clay water resistivity according to equation (17) = 0.045.

[0166] S4: Optimal method to determine lithology coefficient and cementation exponent :

[0167] According to the equation group of equation (21), the particle swarm optimization algorithm is used to solve the lithology coefficient and cementation exponent , and the following parameter results are obtained: = 0.9596, = 3.9628, = 1.5746, = 2.1798, = 2.1858, = 1.7893.

[0168] S5: Oil saturation calculation:

[0169] S5.1 Calculate water saturation: Calculate water saturation according to formula (25), wherein the saturation index = 1.983, which is determined by rock-electricity experiment.

[0170] S5.2 Calculate oil saturation: Calculate oil saturation according to formula (26), and convert the result into percentage form to compare with core data.

[0171] The final calculation result is shown in Figure 5 . The first track is a lithology logging curve (including natural gamma, natural potential and caliper curve), the second track is a depth track, the third track is a resistivity logging curve, the fourth track is a porosity logging curve (including neutron, density and acoustic time difference curve), the fifth track is a porosity analysis, which shows the comparison of the effective porosity calculated by the present application and the core measured porosity, the sixth track is the comparison of the oil saturation calculated by the four water conductivity model and the core measured oil saturation, the seventh track is the comparison of the oil saturation calculated by the new three water conductivity model and the core measured oil saturation, the eighth track is the comparison of the oil saturation calculated by the Archie formula and the core measured oil saturation, the ninth track is the four porosity analysis results of the four water conductivity model, and the tenth track is the volume distribution of formation sand, clay, fine silt and pore. It can be seen that the oil saturation calculated by the four water conductivity model is most consistent with the core measured oil saturation, indicating that the model can more accurately reflect the true oil-bearing characteristics of the reservoir.

[0172] The Archie formula is a commonly used saturation calculation method for sandstone reservoirs, and the specific form is as follows:

[0173] (29)

[0174] wherein, is the formation water resistivity, is the formation resistivity, is the porosity.

[0175] In order to verify the calculation effect of the model of the present application, the error analysis of the oil saturation results obtained by the three methods and the core measured oil saturation is shown in Figure 6 . From the results, it can be seen that the results obtained by the four water conductivity model proposed by the present application are closest to the measured values, and the average absolute error is significantly lower than that of the other two comparison models, proving that the model proposed by the present application can more truly reflect the conductivity characteristics of complex formations, thereby improving the accuracy of oil saturation calculation.

[0176] Although the present application has been described with reference to the embodiments above, various changes and modifications can be suggested to one skilled in the art, and it is intended that the present application encompass such changes and modifications as fall within the scope of the appended claims. Particularly, each feature disclosed in the description and / or the claims can be used in the combination with each of the features disclosed in the description and / or the claims, unless specifically stated otherwise. Therefore, the present application is not intended to be limited to the particular embodiments disclosed in the description and / or the claims.

Claims

1. A method for calculating oil saturation based on a four-water conductivity model, characterized in that, Includes the following steps: S1: Constructing a Four-Water Saturation Equation: Establishing saturation equations for four types of conductive media, including free-flowing water, effectively pore-bound water, fine silt pore water, and clay-bound water. The conductivity is expressed as: ； ； in, The electrical conductivity of rocks saturated with water, The resistivity of rocks saturated with water, Electrical conductivity of oil and gas-bearing rocks, The resistivity of oil and gas-bearing rocks, For free water pores, For bound water pores in the effective pores, It consists of fine sand pores. Clay water pores; S2: Calculate the four porosities: calculate the free fluid porosity, effective pore bound water porosity, fine silt porosity, and clay bound water porosity respectively. S3: Determination of resistivity parameters: Determining the resistivity of formation water through experiments. The resistivity of clay-bound water was optimized by combining experimental data. ; S4: Determining Lithology Coefficients Using Optimization Methods and cementation index : An optimization algorithm is used to optimize the model parameters. , Inversion is performed to achieve the best match between the model-calculated resistivity and the measured resistivity; S5: Calculate oil saturation: Substitute the fitted parameters into the four-water saturation equation to obtain the water saturation of the reservoir. Then calculate the oil saturation. .

2. The method for calculating oil saturation based on a four-water conductivity model according to claim 1, characterized in that, The specific method of S2 is as follows: S2.1 Calculate the clay content based on well logging data: clay content : ； ； ； in, The mud quality index, , These are the logging values ​​for spontaneous potential and natural gamma curve. , The spontaneous potential and spontaneous gamma value of pure sandstone layers. , The spontaneous potential and spontaneous gamma value of pure mudstone layer. The stratigraphic coefficient is 3.7 for new strata and 2 for old strata. S2.2 Calculation of clay content: Clay content A quantitative conversion relationship between mud content and clay content was established using experimental data. The calculation formula is as follows: ； Where c is the fitting coefficient; S2.3 Calculation of effective porosity: Effective porosity Calculated from well logging curves: ； ； in, , These are the neutron porosity and density logging values, respectively. , These are the matrix neutron porosity and density logging values, respectively. , These are the logging values ​​for fluid neutron porosity and density, respectively. , These are the logging values ​​for neutron porosity and density in shale; S2.4 Determine the bound water saturation: Bound water saturation The relationship between experimentally determined bound water saturation and porosity is established, and the calculation formula is as follows: ； in, and These are the fitting coefficients. The effective porosity measured experimentally; S2.5 Calculation of Free Fluid Porosity: Free Fluid Porosity The formula for calculating the relationship between effective porosity and bound water saturation is as follows: ； S2.6 Calculation of water porosity in clay: Water porosity in clay It is calculated from the clay content and the porosity of wet clay, and the calculation formula is: ； in The porosity of wet clay is determined by combining regional measured data and interpretation experience. S2.7 Determining the reference porosity of fine silt: Select a pure sandstone section as the reference section, and read the porosity of this section as the reference porosity of fine silt. ; S2.8 Calculation of microporosity: Effective pore bound water porosity Porosity of fine sand microporosity .

3. The method for calculating oil saturation based on a four-water conductivity model according to claim 1, characterized in that, The specific method of S3 is as follows: S3.1 Determine the formation water resistivity; S3.2 Calculation of clay water resistivity: Clay water resistivity The calculation formula is: ； in The cation exchange capacity per unit volume is calculated using the following formula: ； in, The temperature of the formation is in degrees Celsius. The formula for calculating the equivalent conductivity of Na+ ions in the diffusion layer is as follows: ； The diffusion factor of the diffusion layer is calculated using the following formula: ； in, This represents the actual formation water salinity. This represents the formation water salinity at the minimum thickness of the clay surface diffusion layer, equivalent to the salinity of 0.35 mol / L water.

4. The method for calculating oil saturation based on a four-water conductivity model according to claim 1, characterized in that, In S4, the lithology coefficient and cementation index A system of equations was established based on experimental data and then determined using optimization methods. The optimal system of equations is shown below: ； in For the first resistivity of a saturated rock sample , , These are the lithology coefficients corresponding to free fluid porosity, micropores, and clay water porosity, respectively. , , These are the cementation indices corresponding to free fluid pores, micropores, and clay water pores, respectively. The objective function for obtaining the optimal parameter combination is defined as follows: ； in, Calculate the resistivity for the model. For measured resistivity, For the parameter combination to be optimized, Particle swarm optimization continuously adjusts parameters. , so that the objective function By gradually decreasing the parameter count, the optimal parameter combination is eventually obtained. The parameter update principle is as follows: ； ； in For particles In the During the nth iteration, at the... Position in each dimension For particles In the During the nth iteration, at the... Speed ​​in each dimension For inertial weights, For individual learning factors, As a social learning factor, , A random number between 0 and 1. For the individual's optimal position, This is the globally optimal position.

5. The method for calculating oil saturation based on a four-water conductivity model according to claim 1, characterized in that, The specific method of S5 is as follows: S5.1 Calculate water saturation: Calculate water saturation using measured formation resistivity and theoretically calculated saturated water resistivity. The calculation formula is as follows: ； in, The saturation index is determined by rock electrical experiments. Based on the formation resistivity logging results, boundary constraints were finally applied to the calculated water saturation results. This is to ensure the reasonableness of the calculation results; S5.2 Calculation of oil saturation: The calculation formula is as follows: 。

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