A method for determining a dynamic saturation index of a watered-out layer

Abstract

This application relates to a method for determining the dynamic saturation index of a water-flooded formation, belonging to the field of oilfield development technology. The method includes: preparing experimental rock samples and obtaining pre-prepared experimental data; conducting oil-flooding and water-flooding experiments on the rock samples to obtain various experimental data; and calculating different water saturation levels (S) based on the various experimental data using a mixed formation water theoretical model. w The corresponding rock resistivity R tsim The mixed formation water theoretical model was then corrected; based on the corrected mixed formation water theoretical model, formation factor formula, resistivity increase formula, and various experimental data, the water saturation S at the measurement points in the waterflooding experiment was calculated. w The corresponding increase in rock resistivity I; based on relative permeability experimental data and flow fraction equations, flooding levels are classified, and saturation standards for different flooding levels are established; based on the increase in rock resistivity I and water saturation S w The saturation index n corresponding to different flood levels is calculated to obtain the dynamic saturation index that changes with the flood level.

Description

Technical Field

[0001] This application relates to the field of oilfield development technology, and in particular to a method for determining the dynamic saturation index of a water-flooded layer. Background Technology

[0002] With the continuous development of oil and gas resources, many oil fields have now entered the middle and late stages of development, and the reservoir water flooding situation is quite serious. Although a large amount of oil resources have been extracted, a considerable amount of remaining oil resources have not been developed, and the recovery rate of the remaining oil is low due to the impact of water flooding.

[0003] Currently, the commonly used method for calculating saturation in oil exploration and development is to use Archie's formula to calculate reservoir water saturation and oil saturation. Among these, the saturation index *n*, a rock electrical parameter, characterizes the distribution of oil and water in the pores and the surface electrical conductivity of the rock, significantly influencing saturation calculations. For water-injected reservoirs, the physical properties of the rock change significantly after water flooding, especially the saturation index *n*, which is extremely sensitive to the water flooding process and changes dynamically with it. Therefore, clarifying the dynamic changes of the saturation index *n* and accurately determining it is of great significance for improving the accuracy of remaining oil saturation calculations and tapping the potential of old wells.

[0004] Existing studies typically focus on two static endpoints—"before water flooding" and "after water flooding"—treating the water-flooded layer as a stratum with inherent rock electrical parameters. However, actual oil reservoirs exhibit strong heterogeneity, and water injection development leads to significant differences in the degree of water flooding across different areas, presenting various states such as no flooding, low, medium, and high water flooding. Under different water flooding stages, the distribution of oil and water within pores, the conductive network, and the salinity of mixed formation water continuously change dynamically, making the saturation index n a dynamic parameter that varies with the degree of water flooding.

[0005] The current method of calculating the saturation of water-flooded layers using static rock electrical parameters cannot reflect this change process, resulting in insufficient accuracy in evaluating the remaining oil saturation and making it difficult to meet the needs of mid-to-late stage oilfield development. Summary of the Invention

[0006] This application addresses, to at least some extent, one of the technical problems in the related art.

[0007] Therefore, this application aims to provide a method for determining the dynamic saturation index of a water-flooded layer. This method fully considers the dynamic change of the saturation index n with the water flooding process, solves the problem of low accuracy in calculating the remaining oil saturation using static parameters, improves the calculation accuracy of the remaining oil saturation of the water-flooded layer, and provides data support for the exploitation of remaining oil in old wells.

[0008] To achieve the above objectives, in a first aspect, this application provides a method for determining the dynamic saturation index of a flooded layer, comprising: Pre-fabricated experimental rock samples were prepared to obtain pre-fabricated experimental data. Oil-flooding and water-flooding experiments were conducted on rock samples to obtain data from the oil-flooding and water-flooding experiments, as well as the rock resistivity R during the water-flooding experiment. te With water saturation S w Change data and phase permeation experimental data; Based on pre-construction experimental data, oil-water flooding experimental data, and water-oil flooding experimental data, the water saturation S at different levels was calculated using a mixed formation water theoretical model. w The corresponding rock resistivity R tsim ; According to different water saturation S w Corresponding rock resistivity R tsim Rock resistivity R in water-driven oil recovery experiments te With water saturation S w Adjusting the mixed formation water theoretical model based on change data; The water saturation S at the measurement points in the waterflooding experiment was calculated based on the corrected mixed formation water theoretical model and formation factor formula. w The corresponding corrected actual rock resistivity R 0wz The formation factor formula is expressed as follows: In the formula, R0 is the resistivity of the rock sample saturated with formation water, and R w The resistivity of formation water in the reservoir pores. denoted as reservoir porosity, a as lithology coefficient, and m as cementation index; Based on the formula for resistivity increase rate and pre-constructed experimental data and the corrected actual rock resistivity R... 0wz Calculate the increase in rock resistivity I; the formula for the increase in resistivity is expressed as: In the formula, R t S represents the resistivity of the oil-bearing reservoir. w denoted as reservoir water saturation, b as lithology coefficient, and n as saturation index; Based on the relative permeability experimental data and the flow fraction equation, flooding levels are classified, and saturation standards for different flooding levels are established. Based on the rock resistivity increase rate I and water saturation S w The saturation index n corresponding to different flood levels is calculated to obtain the dynamic saturation index that changes with the flood level.

[0009] In this embodiment, firstly, oil-flooding and water-flooding experiments were conducted on the core samples to obtain the relationship between resistivity and water saturation. Secondly, the resistivity of the mixed formation water was simulated and calibrated using a mixed formation water theoretical model. Next, the relationship between the rate of increase in resistivity and saturation was calculated. Then, water flooding levels were classified based on relative permeability experiments and water production rates, and corresponding water saturation standards were established. Finally, the relationship between the rate of increase in resistivity and water saturation was fitted piecewise according to the water flooding level, and the dynamic saturation index n was calculated for each level. This method fully considers the dynamic changes of the saturation index during water flooding, significantly improving the accuracy of remaining oil saturation calculation and providing reliable data support for tapping the remaining oil potential of old wells.

[0010] In conjunction with the first aspect, in some implementations of the first aspect, methods for preparing experimental rock samples include: Core samples from the target study area were selected and cut into plunger samples. Surface pretreatment of the plunger sample; The pre-treated plunger samples were sequentially subjected to oil washing, salt washing, drying, and saturated brine treatment to obtain pre-prepared experimental rock samples.

[0011] In this embodiment of the application, the preparatory steps for the oil-drive water experiment provide an accurate quality benchmark for subsequent experiments, transforming the core rock sample into a standardized sample with a completely determined state under laboratory conditions, and providing a standardized physical model starting point with a known state for subsequent experiments.

[0012] In conjunction with the first aspect, in some implementations of the first aspect, the pre-constructed experimental data includes the original formation water resistivity R. wi Oil-driven water displacement experimental data include bound water saturation S wi The water-driven oil recovery experimental data includes the injected water resistivity R. wj and residual oil saturation S or Calculate S at different water saturation levels w The corresponding rock resistivity R tsim The methods include: Based on the mixed formation water theoretical model and the original formation water resistivity R... wi , Injected water resistivity R wj Bound water saturation S wi and residual oil saturation S or Calculate the resistivity R of mixed formation water wz The theoretical model for mixed formation water is a mass balance model, an ion exchange model, or a dynamic mixing model; the mass balance model is expressed as follows: The ion exchange model is expressed as follows: The dynamic hybrid model is expressed as: In the formula, C wz C wiC wj These represent the salinity of mixed formation water, original formation water, and injected water, respectively, with α being the mixing coefficient. Based on the resistivity R of the mixed formation water wz Calculations were made from pre-construction experimental data and oil-driven water displacement experimental data for different water saturation levels (S). w Corresponding rock resistivity R tsim .

[0013] In this embodiment of the application, the calculated water saturation S w With the corresponding rock resistivity R tsim This provides a theoretical simulation framework for the final experimental calibration and parameter determination.

[0014] In conjunction with the first aspect, in some implementations of the first aspect, the pre-constructed experimental data includes porosity. According to the resistivity R of the mixed formation water wz Calculations were made from pre-construction experimental data and oil-driven water displacement experimental data for different water saturation levels (S). w Corresponding rock resistivity R tsim The methods include: The lithology coefficient 'a' in the formula for obtaining the stratigraphic factor; The cementation index m was calculated based on the formation factor formula and pre-construction experimental data. The lithology coefficient b and static saturation index n0 were calculated based on oil-water flooding experimental data and the resistivity increase rate formula. According to the water saturation formula Lithology coefficient a, lithology coefficient b, cementation index m, static saturation index n0, and mixed formation water resistivity R wz Calculate S at different water saturation levels w Corresponding rock resistivity R tsim .

[0015] In this embodiment, parameters b, m, and n, calculated using pre-prepared experimental data and oil-driven water experimental data, reflect the electrical conductivity of the rock sample, ensuring the accuracy of subsequent calibration of the mixed formation water resistivity calculation model.

[0016] In conjunction with the first aspect, in some implementations of the first aspect, the pre-constructed experimental data includes the original formation water resistivity R. wi Porosity Oil-driven water displacement experimental data includes the rock sample resistivity R0 under saturated solution. Methods for calculating the cementation index m based on the formation factor formula and pre-constructed experimental data include: Based on the resistivity R of the saturated solution wi The formation factor F is calculated using the formation factor formula based on the resistivity R0 of the rock sample under saturated solution. Based on the formation factor formula, formation factor F, and porosity Calculate the cementation index m.

[0017] In this embodiment, the formation factor F is accurately calculated by measuring the known resistivity of the saturated solution and the resistivity R0 of the rock sample under the saturated solution, and then the cementation index m value is obtained, thereby providing a stable rock physics benchmark for subsequent water flooding process analysis, so as to realize the quantitative calculation of dynamic saturation index.

[0018] In conjunction with the first aspect, in certain implementations of the first aspect, the methods for calculating the lithology coefficient b and the static saturation index n0 include: Based on oil-driven water discharge experimental data and the rock resistivity increase rate formula, the resistivity increase rate I as a function of water saturation S was calculated. w Change data; According to the increase rate of rock resistivity I with water saturation S w The lithology coefficient b and the static saturation index n0 are used in the formula for calculating the increase in resistivity by fitting the change data in a double logarithmic coordinate system.

[0019] In this embodiment, the lithology coefficient b and static saturation index n0 are calculated using oil-water flooding experimental data to ensure the accuracy of subsequent model calibration.

[0020] In conjunction with the first aspect, in some implementations of the first aspect, based on the calculated rock resistivity R... tsim Methods for calibrating theoretical models of mixed formation water include: Based on the rock resistivity R of the water-drive oil experiment te With water saturation S w The changing data establishes the first change curve; According to different water saturation S w Corresponding rock resistivity R tsim Establish a second variation curve; Determine whether the second change curve matches the first change curve; If they match, the coefficient values ​​of the mixed formation water theory model and the selection of the mixed formation water theory model are appropriate; if they do not match, the mixed formation water theory model should be replaced or the coefficients in the mixed formation water theory model should be changed.

[0021] In this embodiment of the application, the theoretically calculated rock resistivity R is used... tsim With water saturation S w The variation curves are compared with those measured in actual experiments to determine whether the coefficients of the mixed formation water theoretical model or the model itself have been selected correctly. This allows the theoretical model to be modified into a calculation model suitable for this experiment, providing a reliable guarantee for the calculation of key variables.

[0022] In conjunction with the first aspect, in some implementations of the first aspect, the corrected actual rock resistivity R is calculated based on the corrected mixed formation water theoretical model and the formation factor formula. 0wz The methods include: Based on the rock resistivity R in the water-drive oil experiment te With water saturation S w Calculation of the resistivity R of mixed formation water using variable data and a corrected theoretical model of mixed formation water wz ; Based on the resistivity R of the mixed formation water wz The actual rock resistivity R after correction is calculated using the stratigraphic factor formula. 0wz .

[0023] In this embodiment of the application, the resistivity R of the mixed formation water is calculated using the corrected model. wz This solves the problem that traditional methods cannot calculate the resistivity R0 when the rock is saturated with mixed water, and thus facilitates the subsequent calculation of the rock resistivity increase rate I.

[0024] In conjunction with the first aspect, some implementations of the first aspect include methods for establishing saturation standards for different flood levels based on flood levels, such as: Based on the relative permeability experimental data, the oil-water relative permeability as a function of water saturation S was obtained. w The curve of change; Calculate the water production rate F based on the flow fraction equation. w The flow distribution equation is expressed as: In the formula, F w For water production rate, μ o μ w The viscosity of oil and water, respectively, K ro K rw These are the relative permeabilities of oil and water, respectively. According to the relationship between relative permeability and water saturation S w Change curve and water production rate F w Establish relative permeability and water production rate F w With water saturation S w The curve of change; Based on relative permeability and water production rate F w With water saturation S w The variation curves determine the water saturation range for each flood level, and establish saturation standards for different flood levels.

[0025] In this embodiment of the application, by establishing saturation standards for different flood levels based on the flood level, a quantitative correspondence is established between the macroscopic range of oilfield development divided according to water production rate and specific experimental data, providing a clear segmentation basis for subsequent calculation of dynamic saturation index n.

[0026] In conjunction with the first aspect, some implementations of the first aspect include methods for calculating the saturation index n corresponding to different flooding levels, such as: Based on the rock resistivity increase rate I and water saturation S w The relationship establishes a third change curve. The saturation index n under different flood levels is obtained by piecewise fitting of the third variation curve on a double logarithmic coordinate system based on different flood levels.

[0027] In this embodiment of the application, by calculating the saturation index n corresponding to different flooding levels, the saturation index n dynamically changes with the degree of flooding, thereby achieving accurate quantification and ultimately improving the accuracy of the calculation of residual oil saturation in the flooded layer.

[0028] As can be seen from the above technical solutions, additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0029] Figure 1 This is a flowchart illustrating the method for determining the dynamic saturation index of the flooded layer according to an embodiment of this application. Figure 2 This is a flowchart illustrating a method for preparing experimental rock samples according to an embodiment of this application; Figure 3 It is a cross-plot of rock resistivity and saturation obtained from the oil-flooding experiment of the core in the embodiments of this application; Figure 4 It is a cross-plot of rock resistivity and saturation obtained from water-drive oil experiments of rock cores according to the embodiments of this application; Figure 5 This is a comparison diagram of rock resistivity and water saturation during core oil flooding and water flooding in the embodiments of this application; Figure 6 Based on the embodiments of this application, the water saturation S at different levels is calculated using the mixed formation water theoretical model. w The corresponding rock resistivity R tsim A flowchart illustrating the method; Figure 7 This is a graph showing the relationship between the resistivity of mixed formation water and water saturation, calculated based on the theoretical model of mixed formation water resistivity in the embodiments of this application. Figure 8 According to the embodiments of this application, based on the resistivity R of mixed formation water wz Calculate S at different water saturation levels w The corresponding rock resistivity R tsim A flowchart illustrating the method; Figure 9This is a schematic diagram of the process for calculating the cementation index m using the formation factor F formula according to an embodiment of this application; Figure 10 This is a flowchart illustrating the calculation method of lithology coefficient b and static saturation index n0 according to the embodiments of this application; Figure 11 It is a cross-plot of resistivity increase rate and saturation obtained from the oil-flooding experiment of the core in the embodiments of this application; Figure 12 This is a graph showing the relationship between rock resistivity and water saturation calculated based on the theoretical model of mixed formation water resistivity in the embodiments of this application. Figure 13 This is a flowchart illustrating the method for correcting a theoretical model of mixed formation water according to an embodiment of this application; Figure 14 This is a comparison chart of rock resistivity calculated according to the theoretical model in the embodiments of this application and rock resistivity from core experiments; Figure 15 This is a flowchart illustrating the method for calculating the increase rate of rock resistivity I based on the corrected mixed formation water theoretical model according to an embodiment of this application. Figure 16 This is a cross-plot of resistivity increase rate and water saturation calculated based on theoretical simulation and experimental results in the embodiments of this application; Figure 17 This is a flowchart illustrating a method for establishing saturation standards for different flood levels based on flood levels, according to an embodiment of this application. Figure 18 This is a diagram showing the results of a phase permeation experiment based on the embodiments of this application; Figure 19 This is a flowchart illustrating the method for calculating the saturation index n corresponding to different flooding levels according to the embodiments of this application; Figure 20 This is a flooding level classification diagram based on water production rate according to the embodiments of this application; Figure 21 This is a cross-plot of resistivity increase rate versus water saturation at different flooding levels according to the embodiments of this application; Figure 22 This is a graph showing the water saturation results calculated according to the embodiments of this application. Detailed Implementation

[0030] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0031] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between components; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0032] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0033] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0034] The present application will now be described in detail through exemplary embodiments. However, it should be understood that, without further description, elements, structures, and features in one embodiment may be advantageously incorporated into other embodiments.

[0035] In existing technologies, in oil exploration and development, Archie's formula is used to calculate reservoir water saturation S through resistivity logging. w This is a commonly used method for calculating saturation. Among the key rock electrical parameters, the cementation index *m* and the saturation index *n* can be obtained through core experiments for non-water-flooded layers. However, after water flooding of reservoirs during water injection development, the formation water salinity and oil-water distribution undergo dynamic changes. The value of *n* is sensitive to water flooding, causing the saturation index *n* to change accordingly, which seriously affects the accuracy of saturation calculation.

[0036] Previous studies have primarily focused on two static states: "before water flooding" and "after water flooding," assuming that the value of n is fixed after water flooding. However, in reality, oil reservoirs are highly heterogeneous, and the degree of water flooding varies significantly spatially. Using static parameters cannot accurately evaluate reservoirs with different levels of water flooding. Therefore, the static saturation index n0 in existing technologies cannot accurately characterize the dynamic relationship between the saturation index n and the degree of water flooding.

[0037] Based on this, this application proposes a method for determining the dynamic saturation index of the flooded layer.

[0038] Figure 1 This is a schematic flowchart of a method for determining the dynamic saturation index of a flooded layer according to the first aspect of this application. The method includes the following steps.

[0039] S1. Prepare experimental rock samples and obtain pre-prepared experimental data.

[0040] like Figure 2 The steps for preparing experimental rock samples are as follows.

[0041] S11. Select core samples from the target study area and cut them into plunger samples.

[0042] Specifically, before the oil-drive water experiment, a core sample that is representative of the study area is selected and cut into plunger samples.

[0043] S12. Perform surface pretreatment on the plunger sample.

[0044] Specifically, the core sample undergoes pretreatment such as surface smoothing and end face grinding to ensure good contact between the electrode and the rock during subsequent resistivity measurements, and to guarantee sealing and uniform fluid displacement.

[0045] S13. The pre-treated plunger sample is subjected to oil washing, salt washing, drying, and saturated brine treatment in sequence to obtain the pre-prepared experimental rock sample.

[0046] Specifically, the core sample is washed with a 3:1 volume ratio of toluene and alcohol to thoroughly remove residual crude oil and heavy hydrocarbons from the core pores. Next, it is washed with distilled water to dissolve and remove formation salt crystals from the core pores and particle surfaces, thus avoiding interference with resistivity measurements. Afterward, it is dried in a vacuum drying oven to constant weight to remove any remaining distilled water and any possible residual solvents from the pores after washing, preventing residual solvents from occupying pore space and hindering accurate saturation of the predetermined brine volume, thus providing an accurate mass benchmark for subsequent experiments. These steps transform the core sample into a standardized sample with a fully defined state under laboratory conditions, providing a standardized physical model starting point with a known state for subsequent experiments.

[0047] Pre-constructed experimental data includes porosity And permeability, after completing the above steps, the porosity of the core rock sample. And permeability is measured.

[0048] After completing the above experimental steps, a saturated brine solution with a salinity equivalent to that of the original formation water was prepared until the pores were completely saturated. The resistivity of this saturated brine solution was then measured. This saturated brine solution is equivalent to the original formation water, and its resistivity is denoted as the original formation water resistivity R. wi Through the above operations, the surface of the rock particles is covered with a water film, thereby restoring or establishing a relatively standard and repeatable water-wetted state, ensuring that subsequent oil-drive water experiments can obtain a reliable bound water saturation S that conforms to the actual underground conditions. wi Compared with the initial oil-water distribution state.

[0049] For example, in this embodiment of the application, the volume of the core sample is 24.95 cm³. 3 Porosity The resistivity is 0.368, the permeability is 1129.118 mD, and the formation water salinity in this study area is 4000 ppm. Therefore, a sodium chloride solution with a salinity of 4000 ppm was prepared. The original formation water resistivity R wi =1.365Ω·m.

[0050] S2. Conduct oil-flooding and water-flooding experiments on rock samples to obtain oil-flooding data, water-flooding data, and rock resistivity R during water-flooding experiments. te With water saturation S w Change data and phase permeation experimental data.

[0051] Specifically, oil-flooding experiments are first conducted on core samples from the water-flooded layer to simulate the original formation process of the oil reservoir; then, water-flooding experiments are conducted on the core samples to simulate the water injection development (water flooding) process of the oil field.

[0052] Petroleum generated from source rocks migrates to porous reservoirs filled with formation water under the influence of buoyancy and other factors, displacing the water and ultimately forming an oil reservoir. In oil-water displacement experiments, the water that cannot be displaced and adheres to the surface of the particles is called bound water. At the end of the oil-water displacement experiment, the core sample reaches bound water saturation S. wi The state is closest to the true state of the original oil reservoir. Therefore, oil-flooding water experiments are first conducted on core samples of the water-flooded layer to simulate the original formation process of the oil reservoir and provide an experimental basis for water-flooding oil experiments.

[0053] It should be noted that Archie's formula is a commonly used formula for calculating saturation in oil exploration and development. Archie's formula consists of two parts: the formation factor formula... Formula for increase in resistance Based on these two formulas, we can derive the formula for calculating reservoir water saturation from resistivity logging curves. .

[0054] Among them, S w The reservoir water saturation is typically represented by the oil saturation S. o =1-S w R t R0 is the resistivity of the oil-bearing reservoir, and R0 is the resistivity of the rock sample saturated with formation water. w The resistivity of formation water in the reservoir pores. The reservoir porosity is represented by a, b, m, and n, collectively known as rock electrical parameters. a and b are lithology coefficients, typically equal to 1. m is the cementation index, reflecting the tortuosity of the pore network; finer and more densely packed rock particles result in higher pore tortuosity and a larger m value. Conversely, greater porosity and more developed pore spaces result in a smaller m value. n is the saturation index, characterizing the distribution of oil and water in the pores and the surface electrical conductivity (wettability) of the rock.

[0055] Since the lithology, particle size and pore structure of rocks in water-injected oilfields do not change significantly after water flooding, the cementation index m does not change significantly in oil-flooding and water-flooding oil experiments and is usually assumed to remain unchanged.

[0056] In the oil-drive water experiment, the water saturation S of the core was measured at the measurement point. w and the corresponding rock resistivity R ta The number of measurement points should be no less than 5, until the water in the core cannot be displaced and the resistivity is stable. At this point, the water saturation of the core is the bound water saturation S. wi The oil-flooding experiment is complete, with bound water saturation S. wi Water-drive oil recovery experiments were conducted under specific conditions to simulate the water injection development process in an oilfield.

[0057] In the waterflooding experiment, the injected water was brine with a salinity comparable to that used in actual oilfield development, and the resistivity of the injected water was denoted as R. wj The water saturation S of the core sample was measured at the measurement point. w and the corresponding rock resistivity R te At least five measurement points should be used until only water and no oil are found in the core sample and the resistivity is stable. At this point, the oil saturation in the core sample is the residual oil saturation S. or .

[0058] In oil-drive water-drive and water-drive oil-drive experiments, the rock resistivity R was established respectively. t With water saturation S w The changing relationship curve.

[0059] For example, in this embodiment of the application, a total of 14 measurement points were used for the oil-flooding experiment (including the initial point, i.e., the point with 100% water saturation). The water saturation S of the core was measured at each measurement point. w and rock resistivity R ta The results are shown in Table 1. Table 1 shows that the final water saturation of the oil-driven water was 0.225, meaning the bound water saturation S of the core was... wi =0.225, such as Figure 3 The rock resistivity R in the oil-flooding experiment was obtained. ta With water saturation S w The changing relationship.

[0060] Table 1 Experimental data of oil-water displacement process

[0061] For example, in this embodiment of the application, the salinity of the brine used for water injection development is 9000 ppm. Therefore, the water-driven oil recovery experiment is prepared with a sodium chloride solution with a salinity of 9000 ppm. Under laboratory conditions (24°C), the water resistivity R is measured. wj =0.866Ω·m.

[0062] The water-driven oil recovery experiment used 13 measurement points, and the water saturation S of the core sample was measured at each point. w and rock resistivity R te The measured water saturation S w and the corresponding rock resistivity R te As shown in Table 2, the water-driven oil recovery process ultimately displaces the oil to a water saturation of 0.745, therefore the residual oil saturation S or =1-0.745=0.255, which represents the maximum level of oil recovery that can be achieved through water injection. For example... Figure 4 The rock resistivity R in the water-drive oil experiment was obtained. te With water saturation S wThe changing relationship.

[0063] Table 2 Experimental data for water-driven oil recovery process

[0064] It should be noted that, according to Figure 3 and Figure 4 Establishing the rock resistivity R in oil-drive water-drive and water-drive oil-drive experiments te With water saturation S w The change curves are compared, such as Figure 5 As shown, the resistivity curve during water-driven oil recovery does not coincide with that during water-driven oil recovery, and is generally lower than that during water-driven oil recovery. This is partly because the injection of highly salinized water into the pores increases the conductivity of the mixed water within the pores, and partly because the distribution of oil and water and the wettability of the rock surface change as the water-driven process progresses.

[0065] S3. Based on the pre-construction experimental data, oil-water flooding experimental data, and water-oil flooding experimental data, calculate the water saturation S at different levels using the mixed formation water theoretical model. w The corresponding rock resistivity R tsim .

[0066] Pre-construction experimental data includes the original formation water resistivity R. wi Oil-driven water displacement experimental data include bound water saturation S wi The water-driven oil recovery experimental data includes the injected water resistivity R. wj and residual oil saturation S or .like Figure 6 Calculate S at different water saturation levels w The corresponding rock resistivity R tsim The method is as follows.

[0067] S31. Based on the mixed formation water theoretical model and the original formation water resistivity R... wi , Injected water resistivity R wj Bound water saturation S wi and residual oil saturation S or Calculate the resistivity R of mixed formation water wz .

[0068] Specifically, the mixed formation water theoretical models currently used in the industry include the mass balance model, the ion exchange model, and the dynamic mixing model, each applicable to different stages of oil reservoir development.

[0069] The mass balance model is as follows: According to the mass balance equation, the sum of the number of ions in the original formation water (i.e., bound water) and the number of ions in the injected water equals the total number of ions in the mixed formation water after flooding, that is: (1) so: (2) Based on the relationship between solution resistivity, mineralization, and temperature, it can be known that (3) (4) In formulas (1)-(4), C wz C wi C wj The mineralization of mixed formation water, original formation water, and injected water, respectively, is represented by S. w and S wi These represent the water saturation and bound water saturation after flooding, respectively, S w -S wi R represents the increase in water saturation after water injection development, i.e., the amount of crude oil extracted. we R represents the resistivity of the mixed formation water at 24℃. wz The resistivity of the mixed formation water is given by T, where T is the formation temperature.

[0070] The ion exchange model considers the ion exchange between injected water and the original formation water during the later stages of water flooding, as well as the injection ratio. This means the injected water continuously exchanges ions with the original formation water within the pores. The salinity of the produced water is the same as the salinity of the mixed formation water. The total number of ions in all produced water is equal to the sum of the number of ions in all injected water and the number of ions in the original formation water. (5) Mixed formation water salinity can be obtained: (6) Where K is the water injection ratio, which is the ratio of the volume of water injected to the volume of oil produced. (S w -S wi ) represents the volume of produced oil. The method for converting mineralization to resistivity is shown in formulas (3)-(4).

[0071] The specific formula for the dynamic mixture model is as follows: (7) Among them, R wz R wi and R wj These represent the resistivity of mixed formation water, the resistivity of bound water, and the resistivity of injected water, respectively, S w S wi S orThese represent water saturation after flooding, bound water saturation, and residual oil saturation, respectively. α is the mixing coefficient, representing the degree of ion mixing between injected water and bound water. The value of α is related to reservoir lithology, physical properties, and pore structure. The value of α for each study area should be determined in conjunction with experiments.

[0072] It should be noted that, depending on the development situation of different oilfields, a mixed formation water theoretical model adapted to the development stage or the characteristics of the oilfield itself can be selected for calculation. In the embodiments of this application, a dynamic mixing model is selected to calculate the mixed formation water resistivity R. wz Perform simulation calculations.

[0073] Based on the previous example, the original formation water salinity is set to 4000 ppm, corresponding to a resistivity of 1.365 Ω·m, and the injected water salinity is set to 9000 ppm, corresponding to a resistivity of 0.866 Ω·m. wi =0.225. In the water flooding experiment, according to Table 2, the water flooding process eventually displaces the water to a water saturation point S. w The value is 0.745, therefore the residual oil saturation S or =1-0.745=0.255.

[0074] Based on the above oil-flooding water experiment and water-flooding oil experiment, the bound water saturation S is obtained. wi and residual oil saturation S or The resistivity of the mixed formation water is calculated using formula (7), and the water saturation S is obtained. w From S wi Initially, increase by 0.05 each time, until 1-S or ,coefficient The resistivity R of the mixed formation water was calculated by varying the value between (0, 5). wz As shown in Table 3, the resistivity R of the mixed formation water wz With water saturation S w Relationship diagram as follows Figure 7 As shown.

[0075] Table 3 Simulation results of resistivity of mixed formation water

[0076] S32, Based on the resistivity R of the mixed formation water wz Calculations were made from pre-construction experimental data and oil-driven water displacement experimental data for different water saturation levels (S). w Corresponding rock resistivity R tsim .

[0077] like Figure 8 As shown, based on the resistivity R of the mixed formation water wz Calculations were made from pre-construction experimental data and oil-driven water displacement experimental data for different water saturation levels (S). w Corresponding rock resistivity Rtsim The method is as follows.

[0078] S321. Obtain the lithology coefficient 'a' in the formation factor formula.

[0079] Specifically, in Archie's formula, the lithology coefficient 'a' is usually 1.

[0080] S322. Calculate the cementation index m based on the formation factor formula and prefabricated experimental data.

[0081] like Figure 9 As shown in the embodiments of this application, the method for calculating the cementation index m using the formation factor formula is as follows, and the pre-construction experimental data includes the original formation water resistivity R. wi Porosity The oil-driven water displacement experimental data include the rock sample resistivity R0 under saturated solution.

[0082] S3221, Based on the resistivity R of the saturated solution wi The formation factor F is calculated using the formation factor formula based on the resistivity R0 of the rock sample under saturated solution.

[0083] S3222, Based on the formation factor formula, formation factor F, and porosity Calculate the cementation index m.

[0084] For example, in an embodiment of this application, the resistivity of the saturated solution under laboratory conditions (24°C), i.e., the original formation water resistivity R, was measured in an oil-flooding experiment. wi =1.365Ω·m, resistivity of rock sample in saturated solution R0=7.287Ω·m, porosity =0.368, F=R0 / R wi =5.33, according to Set a=1, Substituting 0.368 into the equation, we get m = 1.675.

[0085] S323. Calculate the lithology coefficient b and static saturation index n0 based on the oil-water flooding experimental data and the resistivity increase rate formula.

[0086] like Figure 10 As shown, the calculation methods for the lithology coefficient b and the static saturation index n0 are as follows.

[0087] S3231. Calculate the rock resistivity increase rate I as a function of water saturation S based on oil-driven water experimental data and the resistivity increase rate formula. w Change data.

[0088] S3232, Based on the increase rate of rock resistivity I with water saturation S wThe lithology coefficient b and the static saturation index n0 are used in the formula for calculating the increase in resistivity by fitting the change data in a double logarithmic coordinate system.

[0089] Specifically, in the oil-flooding experiment, based on the previous example, the rock sample resistivity R0 = 7.287 Ω·m, and the rock resistivity R measured in Table 1... ta According to the formula for the rate of increase in resistance Calculate the corresponding resistance increase rate, according to the resistance increase rate formula. The formula for the rate of increase in resistance is transformed into a linear equation through logarithmic transformation. The formula was then fitted using the least squares method, yielding the lithology coefficient before flooding: b = 1.0605, and the static saturation index: n0 = 1.552. The relationship between the rate of increase in resistivity and water saturation after fitting is as follows: Figure 11 As shown.

[0090] S324. Based on the water saturation formula, lithology coefficient a, lithology coefficient b, cementation index m, static saturation index n0, and mixed formation water resistivity R... wz Calculate S at different water saturation levels w Corresponding rock resistivity R tsim .

[0091] Specifically, according to the water saturation formula It can be deduced that The lithology coefficient a, lithology coefficient b, cementation index m, static saturation index n0, and mixed formation water resistivity R calculated in the previous step are then used as the basis for further analysis. wz By substituting the modified form of the water saturation formula, the rock resistivity R can be calculated. tsim With water saturation S w Relationship curve.

[0092] For example, porosity measured based on pre-constructed experimental data =0.368, the calculated m=1.675; the bound water saturation S measured in the oil-displacement water experiment wi =0.225, the calculated n=1.552; the residual oil saturation S calculated in the water-driven oil experiment. or =0.255, combined with the data calculated by the mixed formation water theoretical model in Table 3, and substituted into the water saturation formula, the rock resistivity R was obtained through simulation calculation. tsim With water saturation S w Relationship curves, such as Figure 12 As shown.

[0093] S4, according to different water saturation levels S w Corresponding rock resistivity R tsim Rock resistivity R in water-driven oil recovery experiments te With water saturation Sw Theoretical models of mixed formation water were corrected using variable data.

[0094] like Figure 13 As shown, the method for correcting the theoretical model of mixed formation water is as follows.

[0095] S41. Based on the rock resistivity R of the water-drive oil experiment... te With water saturation S w The changing data is used to establish the first change curve.

[0096] Specifically, such as Figure 4 As shown, the rock resistivity R is the result of experimental measurements. te With water saturation S w Change curve.

[0097] S42, according to different water saturation S w Corresponding rock resistivity R tsim Establish a second variation curve.

[0098] Specifically, such as Figure 12 As shown, the rock resistivity R is calculated using the dynamic hybrid model theory for different values ​​of coefficient α. tsim The curve showing the change.

[0099] S43. Determine whether the second change curve matches the first change curve.

[0100] Specifically, will Figure 12 All the calculated relationship curves and Figure 4 By comparing experimental data, we can observe at what value of coefficient α the second and first change curves have the highest degree of overlap in the low water saturation range.

[0101] It is important to note that when comparing the second variation curve with the first variation curve, the main focus should be on the agreement during the initial stage of water flooding (i.e., the stage with relatively low water saturation). This is because the saturation index n has not yet started to change during the initial stage of water flooding, and only then is the rock resistivity calculated using oil-driven water experimental data meaningful.

[0102] S44. If they match, the coefficient values ​​of the mixed formation water theory model and the selection of the mixed formation water theory model are appropriate; if they do not match, the mixed formation water theory model is replaced or the coefficients in the mixed formation water theory model are changed.

[0103] Specifically, in the embodiments of this application, such as Figure 14 As shown, by comparing the first and second change curves, it is found that when The calculated results match the experimental data, thus confirming that, in this embodiment of the application, the dynamic hybrid model is used for calculating the resistivity of the mixed formation water, and the formula ( )middle .

[0104] S5. Calculate the water saturation S at the measurement points in the waterflooding experiment based on the corrected mixed formation water theoretical model and formation factor formula. w The corresponding corrected actual rock resistivity R 0wz .

[0105] like Figure 15 As shown, the corrected actual rock resistivity R is calculated based on the corrected mixed formation water theoretical model and the formation factor formula. 0wz The method is as follows.

[0106] S51. Based on the rock resistivity R in the water-drive oil experiment... te With water saturation S w Calculation of the resistivity R of mixed formation water using variable data and a corrected theoretical model of mixed formation water wz .

[0107] Specifically, the water saturation measured during the water-drive oil recovery experiment is denoted as {S}. w1 S w2 ...S wN The resistivity of rock is denoted as {R}. te1 R te2 ...R teN}, where N is the number of measurement points during the water-driven oil recovery process.

[0108] Based on the mixed formation water resistivity R determined in step S4 wz The computational model simulates the waterflooding experiment, making the original formation water resistivity R... wi and the resistivity R of the injected water wj Similar to the data in the water flooding experiment, the water saturation was set to {S}. w1 S w2 ...S wN}, calculate the corresponding mixed formation water resistivity {R} wz1 R wz2 ...R wzN}

[0109] S52, Based on the resistivity R of the mixed formation water wz The actual rock resistivity R after correction is calculated using the stratigraphic factor formula. 0wz .

[0110] Specifically, based on the resistivity R of the mixed formation water wz The corrected actual rock resistivity R is calculated using the formation factor formula. 0wz Subsequently, the dynamic mixed formation water resistivity R was accurately calculated using the calibrated model. wz Furthermore, based on the variant of the stratigraphic factor formula... , to obtain the corresponding {R 0wz1 R 0wz2 ...R 0wzN}

[0111] It should be noted that residual oil remained in the rock samples after the waterflooding experiment, making it impossible to directly measure the resistivity when 100% saturated with mixed formation water. Therefore, the corrected actual rock resistivity R calculated here... 0wz The resistivity is assumed to be when the rock sample is completely saturated with mixed formation water.

[0112] S6. Based on the formula for the rate of increase in resistivity, pre-constructed experimental data, and the corrected actual rock resistivity R... 0wz Calculate the increase rate I of rock resistivity.

[0113] Specifically, according to the formula for resistance increase rate The corresponding {I1, I2, ..., I} are calculated. N Finally, the resistance increase rate {I1, I2, ..., I} is obtained. N} with water saturation {S w1 S w2 ...S wN The curve of change of}.

[0114] For example, based on the data obtained in the previous example, in the water-driven oil recovery experiment, the water saturation S at 13 measurement points was... w The values ​​are {0.225, 0.297, 0.329, 0.361, 0.425, 0.468, 0.495, 0.544, 0.619, 0.640, 0.673, 0.737, 0.745}. Substituting these saturations into formula (7), the corresponding mixed formation water resistivity R is calculated. wz Then, the corrected actual rock resistivity R is calculated based on the corrected mixed formation water theoretical model and the formation factor formula. 0wz .according to The corresponding {I1, I2, ..., I} are calculated. N The calculated data is shown in Table 4, from which the resistance increase rate can be obtained. With water saturation S w The change curve, such as Figure 16 It can be seen that the relationship between the two under the double logarithmic coordinate system is a phased change rather than a straight line.

[0115] Table 4 Simulated Water-Drive Oil Discharge Data

[0116] S7. Based on the relative permeability experimental data and the flow fraction equation, classify the flooding levels and establish saturation standards for different flooding levels.

[0117] like Figure 17 As shown, the method for establishing saturation standards for different flood levels based on flood levels is as follows.

[0118] S71. Obtain the relative permeability of oil and water as a function of water saturation based on relative permeability experimental data. w The curve showing the change.

[0119] S72. Calculate the water production rate F based on the flow rate equation. w .

[0120] Specifically, water production rate F w The calculation formula is: μ o μ w K represents the viscosity of oil and water, respectively, specifically the viscosity of the simulated oil and the displaced water used in the experiment. ro K rw These are the relative permeabilities of oil and water, respectively.

[0121] For example, Table 5 shows the relative permeability experimental data of this embodiment, and F is calculated according to the water production rate formula. w .

[0122] Table 5. Relative Permeability Experimental Data

[0123] S73, Based on the relationship between relative permeability and water saturation S w The variation curves and water production rate establish relative permeability and water production rate F. w With water saturation S w The curve showing the change.

[0124] Specifically, the water production rate is the most direct standard for classifying water flooding levels in oilfield water injection development. Water flooding levels can be classified according to general industry standards or based on the actual production conditions of each oilfield. For example... Figure 18 As shown, the relative permeability and water production rate F can be obtained. w With water saturation S w The curve showing the change.

[0125] S74, Based on relative permeability and water production rate F w With water saturation S w The variation curves determine the water saturation S for each flooding level. wThe scope was determined, and saturation standards for different flood levels were established.

[0126] Specifically, as shown in Table 6, based on the flooding level classification criteria, the water saturation S at each flooding level can be obtained. w The range.

[0127] Table 6. Classification Standards for Flooding Levels

[0128] S8. Based on the rock resistivity increase rate I and water saturation S w The saturation index corresponding to different flood levels is calculated to obtain the dynamic saturation index that changes with the flood level.

[0129] like Figure 19 As shown, the method for calculating the saturation index corresponding to different flooding levels is as follows.

[0130] S81, Based on the rock resistivity increase rate I and water saturation S w The relationship establishes a third change curve.

[0131] Specifically, the corrected mixed formation water theoretical model is used based on the water saturation S at the measurement point. w Calculate the increase rate of rock resistivity I, and establish the relationship between the increase rate of rock resistivity I and water saturation S. w The changing third curve.

[0132] S82. Based on the segmented fitting of the third variation curve under the double logarithmic coordinate system for different flood levels, the saturation index n under different flood levels is obtained.

[0133] Specifically, repeat step S323, according to the water saturation S of different flooding levels. w Distribution range, segmented for each water saturation S w Rock resistivity increase rate I and water saturation S within the range w The curves are displayed on a double logarithmic coordinate system. Under the double logarithmic coordinate system, the resistivity increase rate-water saturation curve in each segment is a straight line. Direct fitting can yield the saturation index n and the corresponding lithology coefficient b.

[0134] It should be noted that the dynamic saturation index n can be obtained for each core sample that has undergone oil-flooding and water-flooding experiments using the above method, and the results from multiple core samples can be used in combination.

[0135] For example, based on the water saturation S corresponding to different flooding levels obtained in step S7... w The range of variation is determined by adjusting the data in Table 4 according to the water saturation S at different flood levels. wThe ranges are plotted on a log-log coordinate system, with an additional (1,1) point added for each data set, as shown below. Figure 20 and Figure 21 As shown in the figure, in this embodiment, there is only one experimental data point in both the non-flooded and slightly flooded areas, making it impossible to fit the data. Furthermore, the water saturation S from the non-flooded to the slightly flooded area is not specified. w The variation range is very small, only 8%. Furthermore, based on the flooding mechanism analysis, the water flow has a very weak scouring effect on the rock during weak flooding, and it does not change the rock's pore structure or surface wettability. Therefore, the saturation index is calculated by combining the data from weak and non-flooded areas. The data points are fitted separately to obtain the b and n values ​​for different flooding levels, as shown in Table 7. The table shows that the saturation index n changes with the flooding level, and is a dynamic parameter. This is relevant when calculating the residual oil saturation S... or Using dynamic parameters during calculation will improve the accuracy of the saturation index n.

[0136] Table 7 Saturation Index for Different Flood Levels

[0137] Based on the dynamic saturation index n obtained above, the water saturation S is calculated. w The calculated residual oil saturation S or (1-S) w The oil saturation obtained from closed-loop coring analysis showed a higher agreement rate with that obtained from static saturation index analysis, demonstrating the accuracy of this method. Figure 22 As shown in the figure, the logging curves SP, GR, CAL, CN, DEN, DT, PERM, RDEEP, RSHLW, RXO, VSH, and PHIE represent spontaneous potential, natural gamma ray, well diameter, neutron porosity, density, sonic transit time, permeability, deep resistivity, shallow resistivity, microresistivity, clay content, porosity, and S, respectively. w1 and S w2 These represent the water saturation S calculated using the static saturation index. w and the water saturation S calculated using the method of the present invention w As can be seen from the figure, the saturation calculated by the method of the present invention is more consistent with the saturation of the core analysis.

[0138] It should be noted that this embodiment uses rock electrical and relative permeability test data from one rock core as an example to illustrate the method of the present invention, and is not intended to limit the number of rock cores. If there are more rock cores in other regions, multiple rock core test data of the same type can be combined and used.

[0139] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for determining the dynamic saturation index of a flooded layer, characterized in that, include: Pre-fabricated experimental rock samples were prepared to obtain pre-fabricated experimental data. Oil-flooding and water-flooding experiments were conducted on rock samples to obtain data from the oil-flooding and water-flooding experiments, as well as the rock resistivity R during the water-flooding experiment. te With water saturation S w Change data and phase permeation experiment data; Based on pre-construction experimental data, oil-water flooding experimental data, and water-oil flooding experimental data, the water saturation S at different levels was calculated using a mixed formation water theoretical model. w The corresponding rock resistivity R tsim ; According to different water saturation S w Corresponding rock resistivity R tsim Rock resistivity R in water-driven oil recovery experiments te With water saturation S w Adjusting the mixed formation water theoretical model based on change data; The water saturation S at the measurement points in the waterflooding experiment was calculated based on the corrected mixed formation water theoretical model and formation factor formula. w The corresponding corrected actual rock resistivity R 0wz The formation factor formula is expressed as follows: In the formula, R0 is the resistivity of the rock sample saturated with formation water, and R w The resistivity of formation water in the reservoir pores. denoted as reservoir porosity, a as lithology coefficient, and m as cementation index; Based on the formula for resistivity increase rate and pre-constructed experimental data and the corrected actual rock resistivity R... 0wz Calculate the increase in rock resistivity I; the formula for the increase in resistivity is expressed as: In the formula, R t S represents the resistivity of the oil-bearing reservoir. w denoted as reservoir water saturation, b as lithology coefficient, and n as saturation index; Based on the relative permeability experimental data and the flow fraction equation, flooding levels are classified, and saturation standards for different flooding levels are established. Based on the rock resistivity increase rate I and water saturation S w The saturation index n corresponding to different flood levels is calculated to obtain the dynamic saturation index that changes with the flood level.

2. The method for determining the dynamic saturation index of the flooded layer according to claim 1, characterized in that, Methods for preparing experimental rock samples include: Core samples from the target study area were selected and cut into plunger samples. Surface pretreatment of the plunger sample; The pre-treated plunger samples were sequentially subjected to oil washing, salt washing, drying, and saturated brine treatment to obtain pre-prepared experimental rock samples.

3. The method for determining the dynamic saturation index of the flooded layer according to claim 1, characterized in that, Pre-construction experimental data includes the original formation water resistivity R. wi Oil-driven water displacement experimental data include bound water saturation S wi The water-driven oil recovery experimental data includes the injected water resistivity R. wj and residual oil saturation S or Calculate S at different water saturation levels w The corresponding rock resistivity R tsim The methods include: Based on the mixed formation water theoretical model and the original formation water resistivity R... wi , Injected water resistivity R wj Bound water saturation S wi and residual oil saturation S or Calculate the resistivity R of mixed formation water wz The theoretical model for mixed formation water is a mass balance model, an ion exchange model, or a dynamic mixing model; the mass balance model is expressed as follows: The ion exchange model is expressed as follows: The dynamic hybrid model is expressed as: In the formula, C wz C wi C wj These represent the salinity of mixed formation water, original formation water, and injected water, respectively, with α being the mixing coefficient. Based on the resistivity R of the mixed formation water wz Calculations were made from pre-construction experimental data and oil-driven water displacement experimental data for different water saturation levels (S). w Corresponding rock resistivity R tsim .

4. The method for determining the dynamic saturation index of the flooded layer according to claim 3, characterized in that, Pre-constructed experimental data includes porosity According to the resistivity R of the mixed formation water wz Calculations were made from pre-construction experimental data and oil-driven water displacement experimental data for different water saturation levels (S). w Corresponding rock resistivity R tsim The methods include: The lithology coefficient 'a' in the formula for obtaining the stratigraphic factor; The cementation index m was calculated based on the formation factor formula and pre-construction experimental data. The lithology coefficient b and static saturation index n0 were calculated based on oil-water flooding experimental data and the resistivity increase rate formula. According to the water saturation formula Lithology coefficient a, lithology coefficient b, cementation index m, static saturation index n0, and mixed formation water resistivity R wz Calculate S at different water saturation levels w Corresponding rock resistivity R tsim .

5. The method for determining the dynamic saturation index of the flooded layer according to claim 4, characterized in that, Pre-construction experimental data includes the original formation water resistivity R. wi Porosity Oil-driven water displacement experimental data includes the rock sample resistivity R0 under saturated solution. Methods for calculating the cementation index m based on the formation factor formula and pre-constructed experimental data include: Based on the resistivity R of the saturated solution wi The formation factor F is calculated using the formation factor formula based on the resistivity R0 of the rock sample under saturated solution. Based on the formation factor formula, formation factor F, and porosity Calculate the cementation index m.

6. The method for determining the dynamic saturation index of the flooded layer according to claim 4, characterized in that, The methods for calculating the lithology coefficient b and the static saturation index n0 include: Based on oil-driven water discharge experimental data and the rock resistivity increase rate formula, the rock resistivity increase rate I as a function of water saturation S was calculated. w Change data; According to the increase rate of rock resistivity I with water saturation S w The lithology coefficient b and the static saturation index n0 are used in the formula for calculating the increase in resistivity by fitting the change data in a double logarithmic coordinate system.

7. The method for determining the dynamic saturation index of the flooded layer according to claim 1, characterized in that, Methods for calibrating theoretical models of mixed formation water include: Based on the rock resistivity R of the water-drive oil experiment te With water saturation S w The changing data establishes the first change curve; According to different water saturation S w Corresponding rock resistivity R tsim Establish a second change curve; Determine whether the second change curve matches the first change curve; If they match, the coefficient values ​​of the mixed formation water theory model and the selection of the mixed formation water theory model are appropriate; if they do not match, the mixed formation water theory model should be replaced or the coefficients in the mixed formation water theory model should be changed.

8. The method for determining the dynamic saturation index of the flooded layer according to claim 1, characterized in that, The corrected actual rock resistivity R was calculated based on the corrected mixed formation water theoretical model and the formation factor formula. 0wz The methods include: Based on the rock resistivity R in the water-drive oil experiment te With water saturation S w Calculation of the resistivity R of mixed formation water using variable data and a corrected theoretical model of mixed formation water wz ; Based on the resistivity R of the mixed formation water wz The actual rock resistivity R after correction is calculated using the stratigraphic factor formula. 0wz .

9. The method for determining the dynamic saturation index of the flooded layer according to claim 1, characterized in that, Methods for establishing saturation standards for different flood levels based on flood severity include: Based on the relative permeability experimental data, the oil-water relative permeability as a function of water saturation S was obtained. w The curve of change; Calculate the water production rate F based on the flow fraction equation. w The flow distribution equation is expressed as: In the formula, F w For water production rate, μ o μ w The viscosity of oil and water, respectively, K ro K rw These are the relative permeabilities of oil and water, respectively. According to the relationship between relative permeability and water saturation S w Change curve and water production rate F w Establish relative permeability and water production rate F w With water saturation S w The curve of change; Based on relative permeability and water production rate F w With water saturation S w The variation curves determine the water saturation range for each flood level, and establish saturation standards for different flood levels.

10. The method for determining the dynamic saturation index of the flooded layer according to claim 1, characterized in that, Methods for calculating the saturation index n corresponding to different flood levels include: Based on the rock resistivity increase rate I and water saturation S w The relationship establishes a third change curve; The saturation index n under different flood levels is obtained by piecewise fitting of the third variation curve on a double logarithmic coordinate system based on different flood levels.

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