A method for calculating remaining oil saturation of water-flooded layers in old wells based on multi-viscosity oil-water phase permeability experiment

Abstract

This invention discloses a method for calculating the remaining oil saturation of water-flooded layers in old wells based on multi-viscosity oil-water phase permeability experiments, relating to the field of petroleum extraction technology. The method includes: generating resistivity reduction rate curves based on multi-viscosity oil-water phase permeability experiments; establishing a quantitative relationship model between water cut and resistivity reduction rate of crude oils of different viscosities; calculating the resistivity reduction rate according to the target layer water cut and crude oil viscosity type using the appropriate quantitative relationship model, and calculating the resistivity of the water-flooded layer by combining it with the original oil layer resistivity; and calculating the remaining oil saturation of the water-flooded layer using the saturation formula. This invention, based on comparative experiments of multiple viscosities of oil-water phase permeability, obtains a relationship between resistivity reduction rate and water cut, resulting in higher accuracy of the calculation results. The method for calculating the remaining oil saturation of water-flooded layers avoids statistical bias and production losses caused by shutting down production wells for post-casing saturation logging. It is applicable to crude oil reservoirs of different viscosities, and its large-scale application in water-drive oilfield development will improve development efficiency.

Description

Technical Field

[0001] This invention relates to the field of petroleum extraction technology, and in particular to a method for calculating the residual oil saturation of water-flooded layers in old wells based on multi-viscosity oil-water phase permeability experiments. Background Technology

[0002] The existing technical solutions for calculating the remaining oil saturation of water-flooded layers in old wells mainly fall into three categories: well logging, dynamic analysis, and core experiments. Among them, well logging and dynamic analysis methods are the most widely used in the mining field. (1) Well logging methods: The main well logging methods for the remaining oil saturation of water-flooded layers in old wells include carbon-oxygen ratio energy spectrum logging, neutron lifetime logging, and casing resistivity logging. Although this method can directly measure the results, it will generate a lot of construction costs, and the shutdown of production wells for casing saturation logging will lead to production loss. (2) Dynamic analysis methods: Through production dynamic data or inter-well tracers, the time and space changes of remaining oil saturation are reflected. It is suitable for well group / block level evaluation. Specifically, there are material balance method, water drive characteristic curve method and tracer method. Among them, water drive characteristic curve method is the most widely used. At present, it is mainly obtained by regression analysis of the water cut and resistivity ratio of a large number of new wells. The quantitative relationship of resistivity ratio is obtained by reconstructing the original oil layer resistivity of the target old well and then calculating the remaining oil saturation through the saturation formula; the quantitative relationship of water cut and resistivity ratio obtained by the water drive characteristic curve method through multi-well regression analysis is a relatively rough empirical formula, which lacks experimental support for the water drive mechanism and is easily affected by various complex factors of production dynamics. Moreover, the existing water drive characteristic curve method does not consider the influence of crude oil viscosity; (3) Core test method: water drive oil test obtains the parameters of residual oil saturation and bound water saturation, and obtains the fixed relationship between water cut and remaining oil saturation. However, for reservoirs with strong heterogeneity, the relationship between water cut and remaining oil saturation is not fixed. In summary, the calculation of remaining oil saturation takes well logging interpretation as the core, dynamic analysis as a supplement, and core as verification.

[0003] Water injection development is currently the main development method in oilfields, utilizing water to displace oil from the reservoir and generate production. Evaluating the remaining oil saturation after water flooding is a core task in water injection development of older oilfields. Newly drilled wells have logging data, which can be interpreted to obtain relatively accurate remaining oil saturation levels in the producing formation. However, for older wells in high production volumes, obtaining accurate remaining oil saturation data requires shutting down production for costly post-casing saturation logging. To avoid impacting production while significantly reducing oilfield development costs, there is an urgent need to research a method for directly calculating remaining oil saturation using the water cut of the producing formation in older wells. Summary of the Invention

[0004] To address the aforementioned issues, this invention discloses a method for calculating the remaining oil saturation of water-flooded layers in old wells based on multi-viscosity oil-water phase permeability experiments. This method is based on relative permeability experiments of the oil-water two-phase flow of high-viscosity, medium-viscosity, and low-viscosity crude oils. It generates resistivity reduction rate curves that reflect the relative change in resistivity, and then establishes a quantitative relationship between the water production rate and resistivity reduction rate of crude oils with different viscosities. Finally, it calculates the resistivity of the water-flooded layer in old wells using the resistivity reduction rate of the water-flooded layer and the resistivity of the original oil layer, thereby quantitatively determining the remaining oil saturation of the water-flooded layer.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for calculating the residual oil saturation of a water-flooded layer in an old well based on a multi-viscosity oil-water phase permeability experiment includes the following steps:

[0007] S1. Based on the multi-viscosity oil-water phase penetration experiment, a resistivity decrease rate curve is generated;

[0008] S2. Establish a quantitative relationship model between water content and resistivity decrease rate of crude oil with different viscosities;

[0009] S3. Calculate the resistivity decrease rate by selecting the appropriate quantitative relationship model based on the target layer water cut and crude oil viscosity type, and calculate the water-flooded layer resistivity by combining the original oil layer resistivity.

[0010] S4. Calculate the remaining oil saturation of the water-flooded layer using the saturation formula.

[0011] Optionally, in step S1, three types of crude oil—high viscosity (50-500 cP), medium viscosity (5-50 cP), and low viscosity (<5 cP)—are selected to conduct oil-water phase permeation experiments at different viscosities, obtaining oil-water phase permeation relationship curves. The water content of each sample is calculated using the phase flow function, as shown in the following formula:

[0012] ;

[0013] In the formula, Moisture content, For water flow rate, For the flow rate of oil, The relative permeability of water. The relative permeability of oil. The viscosity of water, The viscosity of the oil;

[0014] Since the resistivity of a rock is determined by the conductivity of water within its pores, the water saturation on the horizontal axis of the oil-water phase permeability curve is converted into a resistivity value using saturation formulas, such as the classic Archie formula used in well logging. The resistivity reduction rate is calculated using the following formula:

[0015] ;

[0016] In the formula, The rate of decrease in resistivity, The resistivity of the original oil layer in the water-flooded layer of the old well. The resistivity of the water-flooded layer in the old well.

[0017] Optionally, in step S2, a corresponding mathematical model is established through nonlinear fitting for quantitative calculation. The calculation model for the resistivity reduction rate of the high-viscosity oil-flooded layer is as follows:

[0018] ;

[0019] The calculation model for the resistivity reduction rate of medium-viscosity water-flooded layers is as follows:

[0020] ;

[0021] The calculation model for the resistivity reduction rate of low-viscosity oil-flooded layers is as follows:

[0022] .

[0023] Optionally, in step S3, the formula for calculating the resistivity of the flooded layer is as follows:

[0024] ;

[0025] In the formula, Resistivity of the old well water-flooded layer The original oil layer resistivity of the water-flooded layer in the old well is given. If the water-flooded layer was an oil layer during the initial open-hole logging, then the open-hole logging value is [value missing]. The water-flooded layer of the old well was water-flooded during the initial open-hole logging. The original oil layer resistivity was reconstructed using existing original oil layer resistivity reconstruction technology.

[0026] In step S4, the saturation formula is:

[0027] ;

[0028] in, The remaining oil saturation of the water-flooded layer. The water saturation level of the flooded layer. The resistivity of the water in the flooded layer. denoted as porosity of the water-flooded layer, and a, b, m, and n as the rock electrical parameters of the water-flooded layer. These parameters can be obtained through interpretation of early new wells.

[0029] A second aspect of the present invention provides a residual oil saturation calculation system for implementing the above method, comprising:

[0030] The data input module is used to receive core test data, well logging data, and water cut data;

[0031] The model processing module stores and calls quantitative relationship models of water content-resistivity reduction rate of crude oil with different viscosities;

[0032] The calculation output module is used to calculate and output the resistivity decrease rate, water-flooded layer resistivity, and residual oil saturation.

[0033] The beneficial effects of this invention are that, based on multiple viscosity oil-water phase permeability control experiments, the relationship between resistivity reduction rate and water cut obtained in this invention leads to higher accuracy in the final calculation results. The method for calculating the remaining oil saturation of water-flooded reservoirs described in this invention avoids various biases in extensive statistical work and also avoids production losses caused by shutting down production wells for post-casing saturation logging; it is applicable to crude oil reservoirs of different viscosities, and has particularly good applicability in old wells with strong heterogeneity and high water flooding; large-scale application of this method in water-drive oilfield development will lead to optimized development plans and improved development efficiency, thereby increasing oilfield recovery. Attached Figure Description

[0034] Figure 1 The above describes the experimental results of high-viscosity, medium-viscosity, and low-viscosity oil-water phase permeation according to an embodiment of the present invention.

[0035] Figure 2 The curves showing the water content and resistivity decrease rate of high-viscosity, medium-viscosity, and low-viscosity oil layers in an embodiment of the present invention are shown.

[0036] Figure 3 This is an embodiment of the present invention illustrating the relationship between water content and resistivity decrease rate after water flooding of high-viscosity, medium-viscosity, and low-viscosity oil layers;

[0037] Figure 4 This is an interpretation and evaluation diagram of the water-flooded layer in well 80XX, as shown in an embodiment of the present invention. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to represent selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] A method for calculating the residual oil saturation of a water-flooded layer in an old well based on a multi-viscosity oil-water phase permeability experiment includes the following steps:

[0040] S1. Based on the multi-viscosity oil-water phase penetration experiment, a resistivity decrease rate curve is generated.

[0041] Three crude oil types—high viscosity (316 cP), medium viscosity (19 cP), and low viscosity (4 cP)—were selected for oil-water phase permeability experiments at different viscosities. The oil-water phase permeability relationship curves were obtained, as shown below. Figure 1 As shown, the water content of each sample is calculated using the phase-separated flow function, as follows:

[0042] ;

[0043] In the formula, Moisture content, For water flow rate, For the flow rate of oil, The relative permeability of water. The relative permeability of oil. The viscosity of water, The viscosity of the oil;

[0044] The rate of decrease in resistivity is calculated using the following formula:

[0045] ;

[0046] In the formula, The rate of decrease in resistivity, The resistivity of the original oil layer in the water-flooded layer of the old well. The resistivity of the water-flooded layer in the old well.

[0047] S2. Establish a quantitative relationship model between water production rate and resistivity decrease rate of crude oil with different viscosities.

[0048] Figure 1 The water saturation on the horizontal axis is converted to resistivity using Archie's formula. The resistivity corresponding to the starting point of saturation at zero water permeability on the horizontal axis is set as the original oil layer resistivity of the water-flooded layer. The remaining resistivity values ​​on the right are set to the resistivity of the flooded layer. The curves showing the decrease in water content and resistivity after water flooding of oil layers of various viscosities were obtained, such as... Figure 2 As shown, a corresponding mathematical model is established through nonlinear fitting for quantitative calculation, such as... Figure 3 As shown, where,

[0049] The calculation model for the resistivity reduction rate of high-viscosity oil-flooded layers is as follows:

[0050] ;

[0051] The calculation model for the resistivity reduction rate of medium-viscosity water-flooded layers is as follows:

[0052] ;

[0053] The calculation model for the resistivity reduction rate of low-viscosity oil-flooded layers is as follows:

[0054] .

[0055] S3. Calculate the resistivity decrease rate by selecting the appropriate quantitative relationship model based on the target layer water cut and crude oil viscosity type, and calculate the water-flooded layer resistivity by combining it with the original oil layer resistivity.

[0056] The formula for calculating the resistivity of the flooded layer is as follows:

[0057] ;

[0058] In the formula, Resistivity of the old well water-flooded layer The original oil layer resistivity of the water-flooded layer in the old well is given. If the water-flooded layer was an oil layer during the initial open-hole logging, then the open-hole logging value is [value missing]. The water-flooded layer of the old well was water-flooded during the initial open-hole logging. The original oil layer resistivity was reconstructed using the existing original oil layer resistivity reconstruction technology. This embodiment uses the original oil layer resistivity reconstruction technology based on the oil layer resistivity-oil column height cross-plot for reservoir classification and multivariate regression modeling.

[0059] S4. Calculate the remaining oil saturation of the water-flooded layer using the saturation formula.

[0060] Residual oil saturation in water-flooded layer The calculation formula is:

[0061] ;

[0062] in, The remaining oil saturation of the water-flooded layer. The water saturation level of the flooded layer. The resistivity of the water in the flooded layer. denoted as porosity of the water-flooded layer, and a, b, m, and n as the rock electrical parameters of the water-flooded layer. These parameters can be obtained through interpretation of early new wells.

[0063] This embodiment also provides a residual oil saturation calculation system for implementing the above method, including:

[0064] The data input module is used to receive core test data, well logging data, and water cut data;

[0065] The model processing module stores and calls quantitative relationship models of water content-resistivity reduction rate of crude oil with different viscosities;

[0066] The calculation output module is used to calculate and output the resistivity decrease rate, water-flooded layer resistivity, and residual oil saturation.

[0067] Figure 4 This is an interpretation and evaluation diagram of the water-flooded layer in Well 80XX. The well was put into production in January 2019, with an initial oil production of 9.7 t / d, a water production of 27.4 t / d, and a water cut of 64.6%. In April 2025, the oil production was 2.7 t / d, the water production was 53.7 t / d, and the water cut was 95.2%. Using open-hole logging data, the oil saturation, reconstructed resistivity, and resistivity reduction rate were interpreted. Based on the relationship between the resistivity reduction rate and water cut, the initial water cut was calculated. Subsequent perforation production verified that the calculated water cut matched the actual values ​​(Table 1). This is because the perforated section contains two reservoirs, a thin and a thick one, with a dense limestone interlayer in between. The production is mainly contributed by the thicker layer, so the production water cut primarily reflects the water cut of the thicker layer, as shown in the KHK splitting calculation results (Table 2). In April 2025, the well's water cut rose to 95.2%, entering the ultra-high water cut stage. Based on the KHK water cut calculation results (Table 4), the water cuts of the two reservoirs are 97.3% and 94.7%, respectively. According to the relationship between water cut and resistivity decrease rate, the resistivity decrease rates are calculated to be 63.7% and 63.4%, respectively (Table 3). Furthermore, the current resistivities of the thin and thick reservoirs are calculated to be 2.82 ohms / mm² and 2.66 ohms / mm², respectively. Finally, the remaining oil saturation is calculated using the Alchian saturation formula to be 53.1% and 53.4%, respectively.

[0068] Table 1. Open-hole logging interpretation and evaluation data of Well 80XX

[0069]

[0070] Table 2. Initial KHK production capacity allocation results of Well 80XX

[0071]

[0072] Table 3. Calculation data of remaining oil saturation in Well 80XX in 2025

[0073]

[0074] Table 4. KHK Production Capacity Allocation Results for Well 80XX in 2025

[0075]

[0076] The key point of this invention is to directly obtain the key parameter resistivity reduction rate from core experimental results. This ensures that the same rock sample obtains a quantitative relationship between the rate of decrease in resistivity and the rate of water production in the same experiment; moreover, the control experiment with different viscosities can better control the quality of the experimental results and is suitable for application in reservoirs with different viscosities.

[0077] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for calculating the residual oil saturation of a water-flooded layer in an old well based on a multi-viscosity oil-water phase permeability experiment, characterized in that, Includes the following steps: S1. Based on the multi-viscosity oil-water phase penetration experiment, a resistivity decrease rate curve is generated; S2. Establish a quantitative relationship model between water content and resistivity decrease rate of crude oil with different viscosities; S3. Calculate the resistivity decrease rate by selecting the appropriate quantitative relationship model based on the target layer water cut and crude oil viscosity type, and calculate the water-flooded layer resistivity by combining the original oil layer resistivity. S4. Calculate the remaining oil saturation of the water-flooded layer using the saturation formula.

2. The method for calculating the residual oil saturation of a water-flooded layer in an old well based on a multi-viscosity oil-water phase permeability experiment as described in claim 1, characterized in that, In step S1, three types of crude oil—high viscosity, medium viscosity, and low viscosity—were selected to conduct oil-water interpenetration experiments at different viscosities, obtaining oil-water interpenetration relationship curves. The water content of each sample was calculated using the phase flow function, as shown in the following formula: ； In the formula, Moisture content, For water flow rate, For the flow rate of oil, The relative permeability of water. The relative permeability of oil. The viscosity of water, The viscosity of the oil; Based on the relationship between water saturation and resistivity, the resistivity decrease rate is calculated as follows: ； In the formula, The rate of decrease in resistivity, The resistivity of the original oil layer in the water-flooded layer of the old well. The resistivity of the water-flooded layer in the old well.

3. The method for calculating the residual oil saturation of a water-flooded layer in an old well based on a multi-viscosity oil-water phase permeability experiment as described in claim 1, characterized in that, In step S2, a corresponding mathematical model is established through nonlinear fitting for quantitative calculation, wherein... The calculation model for the resistivity reduction rate of high-viscosity oil-flooded layers is as follows: ； The calculation model for the resistivity reduction rate of medium-viscosity water-flooded layers is as follows: ； The calculation model for the resistivity reduction rate of low-viscosity oil-flooded layers is as follows: 。 4. The method for calculating the residual oil saturation of a water-flooded layer in an old well based on a multi-viscosity oil-water phase permeability experiment as described in claim 1, characterized in that, In step S3, the formula for calculating the resistivity of the flooded layer is as follows: ； In the formula, Resistivity of the old well water-flooded layer The original oil layer resistivity of the water-flooded layer in the old well is given. If the water-flooded layer was an oil layer during the initial open-hole logging, then the open-hole logging value is [value missing]. The water-flooded layer of the old well was water-flooded during the initial open-hole logging. The original oil layer resistivity reconstruction technology was used to reconstruct the original oil layer resistivity of the water-flooded layer.

5. The method for calculating the residual oil saturation of a water-flooded layer in an old well based on a multi-viscosity oil-water phase permeability experiment as described in claim 1, characterized in that, In step S4, the saturation formula is: ； in, The remaining oil saturation of the water-flooded layer. The water saturation level of the flooded layer. The resistivity of the water in the flooded layer. denoted as porosity of the water-flooded layer, and a, b, m, and n are the rock electrical parameters of the water-flooded layer.

6. A system for calculating residual oil saturation for implementing the method according to any one of claims 1-5, characterized in that, include: The data input module is used to receive core test data, well logging data, and water cut data; The model processing module stores and calls quantitative relationship models of water content-resistivity reduction rate of crude oil with different viscosities; The calculation output module is used to calculate and output the resistivity decrease rate, water-flooded layer resistivity, and residual oil saturation.

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