Method and device for determining saturation of low-porosity and low-permeability argillaceous sandstone reservoir

Abstract

The invention relates to the technical field of oil reservoir development, in particular to a low-porosity and low-permeability argillaceous sandstone reservoir saturation determination method and device. A logging curve of the research area is obtained, the shale content and the total porosity of the target interval are determined according to the logging curve, the clay content is determined according to the shale content, and the bound water porosity is determined according to the shale content and the total porosity; determining the clay water porosity according to the clay content; according to the bound water porosity and the clay water porosity, the microcapillary water porosity is determined; determining free water porosity according to the total porosity and bound water porosity; and determining the water saturation of the target layer according to the free water porosity, the microcapillary water porosity, the clay water porosity and the resistivity logging curve. The problem that the saturation precision of the obtained low-porosity and low-permeability argillaceous sandstone reservoir is low due to the fact that the relation between the rock resistivity increase index and the water saturation cannot be explained in the prior art is solved.

Description

Technical Field

[0001] This invention relates to the field of oil reservoir development technology, and in particular to a method and apparatus for determining the saturation of low-porosity, low-permeability argillaceous sandstone reservoirs. Background Technology

[0002] During water injection development in oilfields, as the injected water increases, it does not propel itself in a piston-like manner within heterogeneous oil reservoirs. Instead, it advances along areas with high porosity and permeability until most of the oil in the high-permeability zones is driven away by the water. However, a considerable amount of crude oil remains in the pores of the medium- and low-permeability zones. Therefore, during periods of high water cut, previously good oil-bearing layers become heavily water-flooded, while previously poorly permeable, low-porosity layers still possess significant potential production capacity and may become new major oil-bearing layers, becoming the primary targets for tapping potential in high and ultra-high water-cut oilfields. Therefore, a systematic and comprehensive method is needed to describe the electrical conductivity characteristics of low-porosity, low-permeability argillaceous sandstone, and to accurately calculate reservoir saturation, providing technical support for adjusting oilfield development plans, stabilizing oil production and controlling water, and calculating remaining oil reserves.

[0003] The electrical conductivity mechanism and model of argillaceous sandstone have been the subject of extensive theoretical and practical research abroad for a long time, but so far there is no universal and practical explanatory model or method, and many issues are still not understood in a unified manner.

[0004] Currently, the widely used WS model and dual-water model are used to determine the water saturation of sandstone reservoirs. However, neither of them can explain why the relationship between the rock resistivity increase index and water saturation I-Sw is not a completely exponential one. Therefore, traditional models are not suitable for calculating the water saturation S of low-porosity, low-permeability argillaceous sandstone reservoirs. w It has low accuracy and is poorly interpreted using conventional methods. Summary of the Invention

[0005] This invention proposes a method and apparatus for determining the saturation of low-porosity and low-permeability argillaceous sandstone reservoirs, in order to solve the problem that the existing technology cannot explain the relationship between the rock resistivity increase index and water saturation, resulting in low accuracy of the saturation of low-porosity and low-permeability argillaceous sandstone reservoirs.

[0006] According to one aspect of the present invention, a method for determining the saturation of low-porosity, low-permeability argillaceous sandstone reservoirs is provided, comprising:

[0007] Obtain well logging curves for the study area, wherein the well logging curves include at least: natural gamma, neutron, density, and resistivity well logging curves;

[0008] Based on the logging curves, determine the clay content and total porosity of the target formation, determine the clay content based on the clay content, and determine the bound water porosity based on the clay content and total porosity.

[0009] The clay water porosity is determined based on the clay content.

[0010] The microcapillary water porosity is determined based on the bound water porosity and clay water porosity.

[0011] The free water porosity is determined based on the total porosity and the bound water porosity.

[0012] The water saturation of the target layer is determined based on the free water porosity, microcapillary water porosity, clay water porosity, and resistivity logging curves.

[0013] Preferably, the method for determining the clay content of the target formation based on the well logging curve includes:

[0014] Based on the natural gamma, neutron and density logging curves in the logging curves, the clay content of the target layer is determined using Equation (1).

[0015] The clay content was calculated using equation (1);

[0016]

[0017] In the formula: Vsh is the clay content; Vshgr is the clay content obtained using natural gamma. denoted as neutron, density, and porosity, respectively, with a, b, and c being coefficients.

[0018] Preferably, the method for determining the clay content based on the mud content includes:

[0019] The clay content was calculated using equation (2);

[0020] V cl = a×Vsh-b (2);

[0021] In the formula: Vsh is the clay content, and a and b are coefficients.

[0022] Preferably, the method for determining the total porosity of the target formation based on the well logging curve includes:

[0023] Based on the density logging curve, the total porosity is determined using equation (3);

[0024] φ t =(ρ b -ρ ma ) / (ρ f -ρ ma (3);

[0025] In the formula: ρ b ρ f ρ maThese are the density values ​​of the target layer, formation fluid, and rock skeleton, respectively.

[0026] Preferably, the method for determining the bound water porosity based on the clay content and total porosity includes:

[0027] Obtain the effective porosity of the study area;

[0028] The bound water saturation is determined based on the effective porosity and clay content.

[0029] The bound water porosity is determined based on the bound water saturation and total porosity.

[0030] Preferably, the method for determining the bound water saturation based on the effective porosity and clay content includes:

[0031] The degree of saturation of bound water is calculated using equation (4);

[0032] S wb = a×Vsh / PORE+b (4);

[0033] In the formula: Vsh is the clay content; PORE is the effective porosity; a and b are coefficients.

[0034] Preferably, determining the bound water porosity based on the bound water saturation and total porosity includes:

[0035] The porosity of bound water is calculated using equation (5);

[0036] PORB=S wb φ t (5);

[0037] In the formula: S wb φ represents the bound water saturation. t Total porosity.

[0038] Preferably, the method for determining the water porosity of clay based on the clay content includes:

[0039] The water porosity of clay is calculated using equation (6);

[0040] φ c =V cl W cl (6);

[0041] In the formula: V cl Clay content; W cl This represents the moisture content of wet clay.

[0042] Preferably, the method for determining microcapillary water porosity based on the bound water porosity and clay water porosity includes:

[0043] The microcapillary water porosity is calculated using equation (7);

[0044] φ i =PORB-φ c (7);

[0045] In the formula: PORB is the bound water porosity; φ c This refers to the water porosity of clay.

[0046] Preferably, the method for determining free water porosity based on the total porosity and bound water porosity includes:

[0047] The porosity of free water is calculated using equation (8);

[0048] φ f =φ t -PORB (8);

[0049] In the formula: PORB is the bound water porosity; φ t Total porosity.

[0050] Preferably, the method for determining the water saturation of the target layer based on the free water porosity, microcapillary water porosity, clay water porosity, and resistivity logging curves includes:

[0051] The water saturation can be calculated using equation (9) or (10);

[0052]

[0053] in,

[0054] In the formula: S w φ represents water saturation. f φ i φ c These are free water porosity, capillary water porosity, and clay water porosity, respectively; R t R is the rock resistivity. W The resistivity of formation water; m f m i m c These represent the cementation indices of free water pores, microcapillary water pores, and clay water pores, respectively; α represents the Na... + Diffusion factor of ion diffusion layer; V q The cation exchange capacity Q V =1, the pore volume occupied by clay water; β is the equivalent conductivity of exchanged cations; S wfφ represents the water saturation in the free fluid pores; φ is the porosity, and n is the saturation index; φ t Total porosity.

[0055] Preferably, the oil saturation is determined using formula (11) based on the water saturation.

[0056] S O =1-S W (11);

[0057] Among them, S O S represents the oil saturation. W This represents the water saturation level.

[0058] According to one aspect of the present invention, an apparatus for determining the saturation of low-porosity, low-permeability argillaceous sandstone reservoirs is provided, comprising:

[0059] The acquisition unit is used to acquire well logging curves of the study area, wherein the well logging curves include at least: natural gamma, neutron, density and resistivity well logging curves; and to determine the clay content and total porosity of the target layer based on the well logging curves, determine the clay content based on the clay content, and determine the bound water porosity based on the clay content and total porosity.

[0060] The three-porosity determination unit is used to determine the clay water porosity based on the clay content, the microcapillary water porosity based on the bound water porosity and the clay water porosity, and the free water porosity based on the total porosity and the bound water porosity.

[0061] The saturation determination unit is used to determine the water saturation of the target layer based on the free water porosity, microcapillary water porosity, clay water porosity, and resistivity logging curves.

[0062] The present invention has at least the following beneficial effects:

[0063] This invention proposes a method and apparatus for determining the saturation of low-porosity and low-permeability argillaceous sandstone reservoirs. By introducing three porosities, free pores and micropores are treated separately, thereby explaining that the relationship between the rock resistivity increase index and water saturation is not a completely exponential relationship, and improving the accuracy of the interpretation of the saturation of low-porosity and low-permeability argillaceous sandstone reservoirs. Attached Figure Description

[0064] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present invention and, together with the specification, serve to explain the technical solutions of the present invention.

[0065] Figure 1 A flowchart illustrating a method for determining the saturation of low-porosity, low-permeability argillaceous sandstone reservoirs according to an embodiment of the present invention is shown.

[0066] Figure 2 This diagram shows a comparison of the clay content of the target layer according to an embodiment of the present invention.

[0067] Figure 3 This diagram shows a comparison of clay content in the target layer according to an embodiment of the present invention.

[0068] Figure 4 This diagram shows a comparison of the bound water saturation of the target layer according to an embodiment of the present invention.

[0069] Figure 5 This illustrates a comparison of water saturation in target wells according to an embodiment of the present invention. Figure 1 ;

[0070] Figure 6 This illustrates a comparison of water saturation in target wells according to an embodiment of the present invention. Figure 2 . Detailed Implementation

[0071] Various exemplary embodiments, features, and aspects of the present invention will now be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings denote elements that have the same or similar functions. Although various aspects of the embodiments are shown in the drawings, they are not necessarily drawn to scale unless specifically indicated otherwise.

[0072] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0073] In this document, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Furthermore, the term "at least one" in this document means any combination of at least two of any one or more elements. For example, including at least one of A, B, and C can mean including any one or more elements selected from the set consisting of A, B, and C.

[0074] Furthermore, to better illustrate the present invention, numerous specific details are set forth in the following detailed embodiments. Those skilled in the art will understand that the present invention can be practiced without certain specific details. In some instances, methods, means, elements, and circuits well known to those skilled in the art have not been described in detail in order to highlight the spirit of the invention.

[0075] Figure 1 A flowchart illustrating a method for determining the saturation of low-porosity, low-permeability argillaceous sandstone reservoirs according to an embodiment of the present invention is shown. Figure 2 This diagram shows a comparison of the clay content of the target layer according to an embodiment of the present invention. Figure 3This diagram shows a comparison of clay content in the target layer according to an embodiment of the present invention. Figure 4 This diagram shows a comparison of the bound water saturation of the target layer according to an embodiment of the present invention. Figure 5 This illustrates a comparison of water saturation in target wells according to an embodiment of the present invention. Figure 1 ; Figure 6 This illustrates a comparison of water saturation in target wells according to an embodiment of the present invention. Figure 2 .like Figure 1-6 As shown, a method for determining the saturation of a low-porosity, low-permeability argillaceous sandstone reservoir includes: Step S01: Obtaining well logging curves for the study area, wherein the well logging curves include at least: natural gamma, neutron, density, and resistivity well logging curves; Step S02: Determining the argillaceous content and total porosity of the target formation based on the well logging curves, determining the clay content based on the argillaceous content, and determining the bound water porosity based on the argillaceous content and total porosity; Step S03: Determining the clay water porosity based on the clay content; Step S04: Determining the microcapillary water porosity based on the bound water porosity and clay water porosity; Step S05: Determining the free water porosity based on the total porosity and bound water porosity; Step S06: Determining the water saturation of the target formation based on the free water porosity, microcapillary water porosity, clay water porosity, and resistivity well logging curves.

[0076] The method for determining the saturation of low-porosity, low-permeability argillaceous sandstone reservoirs provided in this invention specifically includes the following steps:

[0077] Step S01: Obtain well logging curves for the study area, wherein the well logging curves include at least: natural gamma, neutron, density and resistivity well logging curves.

[0078] Step S02: Based on the logging curve, determine the clay content and total porosity of the target formation, determine the clay content based on the clay content, and determine the bound water porosity based on the clay content and total porosity.

[0079] In this invention, the method for determining the clay content of the target formation based on the logging curve includes: determining the clay content of the target formation using formula (1) based on the natural gamma, neutron and density logging curves in the logging curve; and calculating the clay content using formula (1).

[0080]

[0081] In the formula: Vsh is the clay content; Vshgr is the clay content obtained using natural gamma. denoted as neutron, density, and porosity, respectively, with a, b, and c being coefficients.

[0082] In this embodiment of the invention, the conventional method for calculating the clay content Vsh is to use the natural gamma logging curve. However, for low-porosity and permeable reservoirs, the effect of using only the natural gamma logging curve to calculate the clay content is not ideal, and the accuracy of the clay content calculation directly affects the accuracy of the clay content and bound water saturation calculation. Therefore, the method for calculating the clay content parameters in the study area has been improved. Different parameters, such as natural gamma, neutron, density-porosity difference, and spontaneous potential, are used to calculate the clay content. By comparing with the clay content obtained from actual experiments, natural gamma logging, neutron, and density are selected as the best parameters. The clay content is calculated by combining natural gamma and neutron density-porosity difference, i.e., Equation (1).

[0083] Taking Block A of the study area as an example, the framework parameters of the reservoir in the target block are collected, including natural gamma ray logging curve GR, density logging curve DEN, neutron logging curve CNL, and resistivity logging curve R. t .

[0084] Using the natural gamma, neutron, and density curves obtained from existing well logging in Block A, and the clay content calculated based on the natural gamma, neutron, and density values ​​respectively, a fitting chart was established. The coefficient values ​​of Equation (1) were obtained by fitting and regression. Finally, the formula for calculating the clay content of this block was established, as shown in Equation (1-1).

[0085]

[0086] The clay content corresponding to the target layer of the target well in Block A is calculated according to formula (1-1).

[0087] Where, Vshgr=(2 GCUR*GRI -1) / (2 GCUR -1);

[0088] In the formula: GCUR is the empirical coefficient of natural gamma for the study area, with a value of 3.7; GRI is the relative value of natural gamma, GRI = (GR - GR sd ) / (GR sh —GR sd ), where GR is the natural gamma logging value, GR sd To process the natural gamma logging values ​​of pure sandstone in the target well section (target formation), GR sh The natural gamma value is for pure mudstone.

[0089] 107 sample points were selected from the target stratigraphic section of Block A. The clay content calculated using Equation (1-1) was compared with the clay content analysis results obtained from core experiments. The results are as follows: Figure 2 As shown, the correlation coefficient is 0.843 and the average relative error is 17.05%, which verifies that the method of using formula (1-1) to determine the mud content has high accuracy.

[0090] In this invention, the method for determining the clay content based on the mud content includes: calculating the clay content using formula (2);

[0091] V cl = a×Vsh-b (2);

[0092] In the formula: Vsh is the clay content, and a and b are coefficients.

[0093] In this embodiment of the invention, by applying a large amount of core grain size analysis to perform correlation analysis on the clay content and mud content, it was found that the clay content V in the reservoir section... cl The ratio of Vsh to the mud content is basically stable, as shown in equation (2).

[0094] Taking Block A of the study area as an example, the clay content calculated using Equation (1) is used to establish a fitting chart with the clay content obtained from core experiments in the block. The coefficient value of Equation (2) is obtained by fitting and regression, and finally the clay content V of the block is established. cl The calculation formula is shown in equation (2-1).

[0095] V cl =0.5494Vsh-0.2049(2-1);

[0096] The clay content corresponding to the target layer of the target well in Block A is calculated according to formula (2-1).

[0097] Eighty-eight sample points were selected from the target stratigraphic section of Block A. The clay content calculated using equation (2-1) was compared with the clay content analysis results obtained from core experiments. The results are as follows: Figure 3 As shown, the average relative error is 15.7%, which verifies that the method of using formula (2-1) to determine the clay content has high accuracy.

[0098] In this invention, the method for determining the total porosity of a target formation based on the logging curve includes: determining the total porosity using equation (3) based on the density logging curve;

[0099] φ t =(ρ b -ρ ma ) / (ρ f -ρ ma (3);

[0100] In the formula: ρ b ρ f ρ ma These are the density values ​​of the target layer, formation fluid, and rock skeleton, respectively.

[0101] In this embodiment of the invention, when calculating the total porosity φ t At that time, the result calculated based on the reservoir logging density curve DEN is more accurate, as shown in Equation (3).

[0102] Substitute the density values ​​of the target layer, formation fluid, and rock skeleton on the density curve into equation (3) to calculate the total porosity corresponding to the target layer.

[0103] In this invention, the method for determining bound water porosity based on the clay content and total porosity includes: obtaining the effective porosity of the study area; determining the bound water saturation based on the effective porosity and clay content; and determining the bound water porosity based on the bound water saturation and total porosity.

[0104] In this invention, the method for determining the bound water saturation based on the effective porosity and clay content includes: calculating the bound water saturation using formula (4);

[0105] S wb = a×Vsh / PORE+b (4);

[0106] In the formula: Vsh is the clay content; PORE is the effective porosity; a and b are coefficients.

[0107] In this embodiment of the invention, the bound water saturation S, determined by mercury intrusion porosimetry data, was established as a standard. wb The formula for obtaining is shown in equation (4).

[0108] Taking Block A of the study area as an example, the clay content calculated by Equation (1) is used to establish a fitting chart with the bound water saturation obtained by the pump test and the effective porosity PORE obtained by the core test. The coefficient value of Equation (4) is obtained by fitting and regression. Finally, the formula for calculating the bound water saturation of the block is established, as shown in Equation (4-1).

[0109] S wb =0.4Vsh / PORE+0.1(4-1);

[0110] The bound water saturation corresponding to the target layer of the target well in Block A is calculated according to formula (4-1).

[0111] Forty-three sample points were selected from the target layer of Block A. The bound water saturation calculated by equation (4-1) was compared with the bound water saturation analysis results obtained by the pump pressure experiment. The results are as follows: Figure 4 As shown, the correlation coefficient is 0.845 and the mean absolute error is 8.43%, which verifies that the method of using formula (4-1) to calculate the saturation of bound water has high accuracy.

[0112] In this invention, determining the bound water porosity based on the bound water saturation and total porosity includes: calculating the bound water porosity using formula (5).

[0113] PORB=S wb φ t (5);

[0114] In the formula: S wb φ represents the bound water saturation. t Total porosity.

[0115] In this embodiment of the invention, the bound water porosity PORB is equal to the product of the bound water saturation and the total porosity, as shown in Equation (5). Substituting the bound water saturation calculated according to Equation (4) and the total porosity calculated according to Equation (3) into Equation (5), the bound water porosity corresponding to the target layer is calculated.

[0116] Step S03: Determine the clay water porosity based on the clay content.

[0117] In this invention, the clay water porosity φ is determined based on the clay content Vcl. c The methods include: calculating the water porosity of clay using equation (6);

[0118] φ c =V cl W cl (6);

[0119] In the formula: V cl Clay content; W cl This represents the moisture content of wet clay.

[0120] In an embodiment of the present invention, W cl =(ρ cl -ρ dcl ) / (ρ wc -ρ dcl ), where ρ dcl ρ cl ρ wc The densities of dry clay, wet clay, and clay-water are respectively. These may vary in different regions, but are generally constant for a given region or stratum. The density ρ of dry clay is... dcl By using X-ray diffraction data from the core, and by utilizing the relative content of each clay mineral and its corresponding theoretical density value, the density ρ of dry clay can be obtained. dcl This value is relatively stable for the same stratum; for the density ρ of wet clay... cl It can be selected using a density-neutron cross plot, which corresponds to the density response value of the clay point on the cross plot.

[0121] Substituting the clay content calculated according to equation (2) into equation (6), the clay water porosity φ corresponding to the target layer is calculated. c .

[0122] Step S04: Determine the microcapillary water porosity based on the bound water porosity and clay water porosity.

[0123] In this invention, the method for determining microcapillary water porosity based on the bound water porosity and clay water porosity includes: calculating the microcapillary water porosity using formula (7).

[0124] φ i =PORB-φ c (7);

[0125] In the formula: PORB is the bound water porosity; φ c This refers to the water porosity of clay.

[0126] In this embodiment of the invention, the bound water porosity calculated according to equation (5) and the clay water porosity calculated according to equation (6) are substituted into equation (7) to calculate the microcapillary water porosity φ corresponding to the target layer. i .

[0127] Step S05: Determine the free water porosity based on the total porosity and the bound water porosity.

[0128] In this invention, the method for determining free water porosity based on the total porosity and bound water porosity includes: calculating the free water porosity using formula (8);

[0129] φ f =φ t -PORB (8);

[0130] In the formula: PORB is the bound water porosity; φ t Total porosity.

[0131] In this embodiment of the invention, the bound water porosity calculated according to equation (5) and the total porosity calculated according to equation (3) are substituted into equation (8) to calculate the free water porosity φ corresponding to the target layer. f .

[0132] Step S06: Determine the water saturation of the target layer based on the free water porosity, microcapillary water porosity, clay water porosity, and resistivity logging curves.

[0133] In this invention, the method for determining the water saturation of the target layer based on the free water porosity, microcapillary water porosity, clay water porosity, and resistivity logging curve includes: calculating the water saturation using formula (9) or (10).

[0134]

[0135] in,

[0136] In the formula: S w φ represents water saturation. f φ i φ c These are free water porosity, capillary water porosity, and clay water porosity, respectively; R t R is the rock resistivity. W The resistivity of formation water; m f m i m c These represent the cementation indices of free water pores, microcapillary water pores, and clay water pores, respectively; α represents the Na... + Diffusion factor of ion diffusion layer; V Q The cation exchange capacity Q V =1, the pore volume occupied by clay water; β is the equivalent conductivity of exchanged cations; S wf φ represents the water saturation in the free fluid pores; φ is the porosity, and n is the saturation index; φ t Total porosity.

[0137] In this embodiment of the invention, the rock is a porous medium, and its pores are divided into three parts: clay pore fluid, microcapillary pore fluid, and free pore fluid. Formation water in the clay pores and microcapillary pores is non-flowing, while hydrocarbons can only enter the free fluid pores. The clay water porosity, microcapillary water porosity, and free water porosity are calculated separately to establish a three-porosity logging interpretation model, i.e., equation (9) or equation (10). Based on this three-porosity model, the reservoir water saturation S can be calculated. w .

[0138] Due to the high electrical conductivity C of clay water cw for:

[0139]

[0140] In the formula: R cw β is the resistivity of clay water; β is the equivalent conductivity of exchanged cations; α is the Na+ resistivity. + Diffusion factor of ion diffusion layer; V Q The cation exchange capacity Q V=1, the pore volume occupied by water in clay.

[0141] When the rock contains water, the three-pore conductivity model equation of argillaceous sandstone is shown in Equation (9-1). Substituting Equation (9-1) into the basic calculation formula (9) for reservoir water saturation, the water saturation of the target layer is calculated.

[0142] In equation (9-1), In the formula: P w Formation water salinity;

[0143] In the formula: T is the formation temperature.

[0144] After simplifying equations (9) and (9-1), the three-pore conductivity model equation for muddy sandstone when the rock contains water is obtained as shown in equation (10). Equation (9) has higher accuracy than equation (10), but some parameters in equation (9) need to be obtained through a large amount of experimental data. The calculation process of equation (10) is simpler, but its accuracy is slightly lower than that of equation (9).

[0145] In this invention, the oil saturation is determined using formula (11) based on the water saturation.

[0146] S O =1-S W (11);

[0147] Among them, S O S represents the oil saturation. W This represents the water saturation level.

[0148] In this embodiment of the invention, the oil saturation is calculated based on the obtained water saturation, and the difference between the fixed value 1 and the water saturation is obtained as the oil saturation, as shown in formula (11).

[0149] like Figure 5 , Figure 6 The figure shown is the result of the target well in the study area after one interpretation based on the method of this invention and the three-porosity model. The comparison between the water saturation calculated by the model and the core experimental analysis results shows that the water saturation of the low-porosity and low-permeability argillaceous sandstone reservoir calculated by the method of this invention has a high degree of agreement with the water saturation analyzed by the core experiment. The average absolute error of water saturation is less than 6.5%, and the interpretation effect is good.

[0150] It is understood that the various method embodiments mentioned above in this invention can be combined with each other to form combined embodiments without violating the principle and logic. Due to space limitations, this invention will not elaborate further.

[0151] The execution entity for the method of determining the saturation of low-porosity and low-permeability argillaceous sandstone reservoirs can be a device for determining the saturation of low-porosity and low-permeability argillaceous sandstone reservoirs. For example, the method can be executed by a terminal device, a server, or other processing equipment. The terminal device can be a user equipment (UE), mobile device, user terminal, terminal, cellular phone, cordless phone, personal digital assistant (PDA), handheld device, computing device, vehicle-mounted device, wearable device, etc. In some possible implementations, the method for determining the saturation of low-porosity and low-permeability argillaceous sandstone reservoirs can be implemented by a processor calling computer-readable instructions stored in memory.

[0152] Those skilled in the art will understand that, in the above-described method of the specific implementation, the order in which each step is written does not imply a strict execution order and does not constitute any limitation on the implementation process. The specific execution order of each step should be determined by its function and possible internal logic.

[0153] This invention also provides a device for determining the saturation of low-porosity, low-permeability argillaceous sandstone reservoirs, comprising: an acquisition unit for acquiring well logging curves of the study area, wherein the well logging curves include at least: natural gamma, neutron, density, and resistivity well logging curves; and determining the argillaceous content and total porosity of the target formation based on the well logging curves, determining the clay content based on the argillaceous content, and determining the bound water porosity based on the argillaceous content and total porosity; a three-porosity determination unit for determining clay water porosity based on the clay content, determining microcapillary water porosity based on the bound water porosity and clay water porosity, and determining free water porosity based on the total porosity and bound water porosity; and a saturation determination unit for determining the water saturation of the target formation based on the free water porosity, microcapillary water porosity, clay water porosity, and resistivity well logging curves.

[0154] In some embodiments, the functions or modules and units included in the apparatus provided by the present invention can be used to execute the methods described in the above method embodiments. The specific implementation can be referred to the description of the above method embodiments, and for the sake of brevity, it will not be repeated here.

[0155] To gain a deeper understanding of the conductivity mechanism of argillaceous sandstone reservoirs and provide meaningful insights, it is necessary to thoroughly understand and analyze the development history of previous conductivity mechanisms and models for argillaceous sandstone. This development history specifically includes:

[0156] (I) Archie's Pure Sandstone Conductivity Model: The earliest research on conductivity models was conducted on pure sandstone. Archie GE (1942), based on rock-electrical experiments, established the relationship between formation factor F and rock porosity Φ, thus practically proving the inverse exponential relationship between formation factor F and rock porosity Φ. The relationship between formation factor F and rock porosity Φ can be written as:

[0157] F = C w / C o =α / Φ m (13);

[0158] C o =Φ m C w / α (14);

[0159] In the formula: C o C represents the electrical conductivity of water-saturated strata rocks. w The electrical conductivity of the formation water.

[0160] Similarly, Archie GE (1942), based on rock-electrical experiments, established a relationship between rock resistivity and water saturation, namely, the rate of increase in resistivity I and the water saturation S. w The relationship between resistivity increase rate I and water saturation S has been proven in practice. w The inverse exponential relationship between resistivity increase rate I and pore water saturation S. w The relationship between them can be written as:

[0161] I = C o / C t =1 / S w n (15);

[0162] Thus, the electrical conductivity C of partially hydrous pure sandstone t With respect to the electrical conductivity C of the water contained w The relationship can be written as:

[0163] C t =Φ m C w S w n / α (16);

[0164] The above research results convert the measured rock resistivity into water saturation. Based on water saturation, oil and gas reservoirs can be evaluated, thus laying the theoretical and practical foundation for well logging interpretation of oil and gas reservoirs. To date, the two relationships mentioned above (the relationship between formation factor F and porosity φ, and the relationship between resistivity increase rate I and water saturation S) remain largely unchanged. wThe relationship between the two is still the theoretical basis for interpreting oil and gas reservoirs in well logging; for ease of use, it is also called the Archie formula, which is a conductivity model for pure sandstone.

[0165] The Archie formula played a crucial role in the initial exploration and development process, but in subsequent practice, it was found that the Archie formula did not adequately explain the electrical conductivity of argillaceous sandstone. When argillaceous material is present, C... o With C w A nonlinear relationship was observed between them; as the amount of clay increased, the electrical conductivity of the rock tended to increase, indicating that clay can improve the electrical conductivity of the rock.

[0166] Therefore, subsequent research on conductivity mechanisms and the development of models mainly revolved around how to account for the influence of the additional conductivity of clay on rock resistivity. This phenomenon continued until the 1980s, during which time the rock conductivity mechanism was further deepened and many conductivity models were proposed accordingly.

[0167] (II) WS Model: Hill and Millburn (1956) published extensive experimental data on the electrical conductivity and electrochemical potential of argillaceous sandstone. They were the first to study the electrical conductivity and electrochemical potential of argillaceous sandstone based on the cation exchange capacity of clay minerals, laying the foundation for a series of later models based on the double-layer theory. Hill's formula for fitting 450 experimental data points is as follows:

[0168] C o =(100 / C) w ) -blog(100 / Cw) C w / F (17);

[0169] Based on Hill's experimental data and their own test results, Waxman and Smits (1968) proposed a model considering the cation exchange capacity (WS model) of clay. They argued that clay has a high cation exchange capacity (CEC) because its surface is negatively charged. To achieve electrical balance, it must attract some electrolyte cations to its surface. However, the positions of these cations are interchangeable; that is, other cations in the electrolyte can exchange with these surface cations. Under the influence of an external electric field, the exchanged cations can also participate in conductivity, which is equivalent to adding a cation exchange conductivity to the electrolyte conductivity, thus improving the conductivity of argillaceous sandstone. Through their research, they concluded that the conductivity of the rock can be expressed as:

[0170] C o =(C w +BQ V ) / F (18);

[0171] C t =S w 2 (C w +BQ V / S w ) / F (19);

[0172] Because the Waxman and Smits model has both experimental evidence and theoretical basis, it has attracted attention and been widely used. However, during its use, it has been noted that the model has two shortcomings: one is the cation exchange capacity Q. v Regarding the determination of C0-C, people have found that... w Q derived from the curve v The value ratio is obtained from actual CEC measurements. v The value is much smaller. Secondly, it is difficult to explain the discrepancy between experimental and theoretical data on the electrical conductivity of mudstone water. According to this model, the electrical conductivity of mudstone water must be greater than that of sandstone water. However, actual conditions show that the electrical conductivity of mudstone may be less than that of sandstone. In addition, formation water extracted from mudstone also shows that its mineralization is lower than that of formation water from adjacent sandstone layers.

[0173] (III) Two-water model: Clavier (1977) et al. found that the WS model did not take into account the large amount of Na accumulated on the clay surface. + The resulting diffusion layer has a certain thickness, thus failing to account for the salt expulsion effect on the clay surface. In reality, due to surface adsorption and the characteristics of polar water molecules, the electrical conductivity of water within the diffusion layer on the clay surface differs from that of water outside the diffusion layer. Based on this, they proposed a dual-water model (DW model). This model divides the pore water of argillaceous sandstone into two parts: the water closer to the clay surface is called "clay water," also known as "near-water," which accumulates a large amount of Na. + But does not contain Cl - Therefore, it contains no salt. The water further away from the clay particles is called "free water," also known as "distant water," and it behaves similarly to ordinary formation water. From a seepage perspective, neither type of water is mobile. The corresponding electrical conductivity equation is:

[0174] C o =(C w +BQ V ) / F (20);

[0175] C t =S w 2 [(1-αV q Q V C w +BQ V / S w ] / Fo (twenty one);

[0176] Compared to the WS model, the two-water model has a more robust theoretical foundation and addresses the second problem encountered by the WS model. Nevertheless, Q in the two-water model... v Obtaining this value remains challenging. To date, there is no instrument available for direct field measurement of this crucial parameter; it can only be determined by measuring cation exchange capacity and pore volume from rock cores. Many researchers have explored this issue, but have only derived some localized empirical relationships.

[0177] In summary, extensive theoretical and practical research has been conducted both domestically and internationally on the electrical conductivity mechanism and models of argillaceous sandstone for a long time, but so far there is still no universal and practical explanatory model and method.

[0178] Calculating the saturation of low-porosity, low-permeability argillaceous sandstone reservoirs is a crucial step in tapping the potential of old oilfields. This invention addresses the low accuracy of existing technologies in calculating the saturation of low-porosity, low-permeability argillaceous sandstone reservoirs by deeply understanding and analyzing the development of previous conductive mechanisms and models. Focusing on better describing the conductive characteristics of low-porosity, low-permeability argillaceous sandstone, it introduces the concept of three porosities. This concept posits that when oil and gas enter the rock, they can only enter free pores and not micropores. By treating free pores and micropores separately, it can explain the relationship between the rock resistivity increase index and... The I-Sw relationship of water saturation is not a completely exponential relationship. By combining the physical parameters of rocks in different blocks, the methods for determining mud content, clay content, and bound water saturation have been improved, and a reasonable and more accurate interpretation model has been established. This lays the foundation for the determination of three porosities, thereby improving the accuracy and consistency of the first interpretation of saturation in low-porosity and low-permeability mudstone sandstone reservoirs. The average absolute error of the first interpretation saturation is less than 6.5%, the workload of manual secondary interpretation is significantly reduced, and the work efficiency is significantly improved. The processing results can improve both versatility and accuracy.

[0179] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for determining the saturation of low-porosity, low-permeability argillaceous sandstone reservoirs, characterized in that, include: Obtain well logging curves for the study area, wherein the well logging curves include at least: natural gamma, neutron, density, and resistivity well logging curves; Based on the logging curves, determine the clay content and total porosity of the target formation, determine the clay content based on the clay content, and determine the bound water porosity based on the clay content and total porosity. The clay water porosity is determined based on the clay content. The microcapillary water porosity is determined based on the bound water porosity and clay water porosity. The free water porosity is determined based on the total porosity and the bound water porosity. The water saturation of the target layer is determined based on the free water porosity, microcapillary water porosity, clay water porosity, and resistivity logging curves.

2. The method for determining the saturation of low-porosity, low-permeability argillaceous sandstone reservoirs according to claim 1, characterized in that, The method for determining the clay content of the target formation based on the well logging curve includes: Based on the natural gamma, neutron and density logging curves in the logging curves, the clay content of the target layer is determined using Equation (1). The clay content was calculated using equation (1); In the formula: Vsh is the clay content; Vshgr is the clay content obtained using natural gamma. denoted as neutron, density, and porosity, respectively, with a, b, and c being coefficients.

3. The method for determining the saturation of low-porosity, low-permeability argillaceous sandstone reservoirs according to claim 1, characterized in that, The method for determining the clay content based on the mud content includes: The clay content was calculated using equation (2); V cl =a×Vsh-b (2); In the formula: Vsh is the clay content, and a and b are coefficients.

4. The method for determining the saturation of low-porosity, low-permeability argillaceous sandstone reservoirs according to claim 1, characterized in that, The method for determining the total porosity of the target formation based on the well logging curve includes: Based on the density logging curve, the total porosity is determined using equation (3); f t =(ρ b -r ma ) / (ρ f -r ma ) (3); In the formula: ρ b ρ f ρ ma These are the density values ​​of the target layer, formation fluid, and rock skeleton, respectively.

5. The method for determining the saturation of low-porosity, low-permeability argillaceous sandstone reservoirs according to claim 1, characterized in that, The method for determining bound water porosity based on the clay content and total porosity includes: Obtain the effective porosity of the study area; The bound water saturation is determined based on the effective porosity and clay content. The bound water porosity is determined based on the bound water saturation and total porosity.

6. The method for determining the saturation of low-porosity, low-permeability argillaceous sandstone reservoirs according to claim 5, characterized in that, The method for determining the bound water saturation based on the effective porosity and clay content includes: The degree of saturation of bound water is calculated using equation (4); S wb =a×Vsh / PORE+b (4); In the formula: Vsh is the clay content; PORE is the effective porosity; a and b are coefficients.

7. The method for determining the saturation of low-porosity, low-permeability argillaceous sandstone reservoirs according to claim 5, characterized in that, The determination of bound water porosity based on the bound water saturation and total porosity includes: The porosity of bound water is calculated using equation (5); PORB=S wb f t (5); In the formula: S wb φ represents the bound water saturation. t Total porosity.

8. The method for determining the saturation of low-porosity, low-permeability argillaceous sandstone reservoirs according to claim 1, characterized in that, The method for determining clay water porosity based on the clay content includes: The water porosity of clay is calculated using equation (6); φ c =V cl W cl (6); In the formula: V cl Clay content; W cl This represents the moisture content of wet clay.

9. The method for determining the saturation of low-porosity, low-permeability argillaceous sandstone reservoirs according to claim 1, characterized in that, The method for determining microcapillary water porosity based on the bound water porosity and clay water porosity includes: The microcapillary water porosity is calculated using equation (7); f i =PORB-φ c (7); In the formula: PORB is the bound water porosity; φ c This refers to the water porosity of clay.

10. The method for determining the saturation of low-porosity, low-permeability argillaceous sandstone reservoirs according to claim 1, characterized in that, The method for determining free water porosity based on the total porosity and bound water porosity includes: The porosity of free water is calculated using equation (8); f f =φ t -PORB (8); In the formula: PORB is the bound water porosity; φ t Total porosity.

11. The method for determining the saturation of low-porosity, low-permeability argillaceous sandstone reservoirs according to any one of claims 1-10, characterized in that, The method for determining the water saturation of the target layer based on the free water porosity, microcapillary water porosity, clay water porosity, and resistivity logging curves includes: The water saturation can be calculated using equation (9) or (10); in, In the formula: S w φ represents water saturation. f φ i φ c These are free water porosity, capillary water porosity, and clay water porosity, respectively; R t R is the rock resistivity. W The resistivity of formation water; m f m i m c These represent the cementation indices of free water pores, microcapillary water pores, and clay water pores, respectively; α represents the Na... + Diffusion factor of ion diffusion layer; V q The cation exchange capacity Q V =1, the pore volume occupied by clay water; β is the equivalent conductivity of exchanged cations; S wf φ represents the water saturation in the free fluid pores; φ is the porosity, and n is the saturation index; φ t Total porosity.

12. The method for determining the saturation of low-porosity, low-permeability argillaceous sandstone reservoirs according to claim 11, characterized in that: Based on the water saturation, the oil saturation is determined using formula (11); S O =1-S W (11); Among them, S O S represents the oil saturation. W This represents the water saturation level.

13. A device for determining the saturation of low-porosity, low-permeability argillaceous sandstone reservoirs, characterized in that, include: The acquisition unit is used to acquire well logging curves of the study area, wherein the well logging curves include at least: natural gamma, neutron, density and resistivity well logging curves; and to determine the clay content and total porosity of the target layer based on the well logging curves, determine the clay content based on the clay content, and determine the bound water porosity based on the clay content and total porosity. The three-porosity determination unit is used to determine the clay water porosity based on the clay content, the microcapillary water porosity based on the bound water porosity and the clay water porosity, and the free water porosity based on the total porosity and the bound water porosity. The saturation determination unit is used to determine the water saturation of the target layer based on the free water porosity, microcapillary water porosity, clay water porosity, and resistivity logging curves.

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