A calculation method for dynamic oil displacement efficiency of water ridge cavity in bottom water reservoir

Abstract

The present invention discloses a method for calculating the dynamic oil recovery efficiency of a water ridge cavity in a bottom water reservoir, comprising step S10, collecting geological parameters, liquid production, and production time of the bottom water reservoir; step S20, calculating the maximum sweep radius of the bottom water reservoir based on the geological parameters; step S30, calculating the cumulative displacement volume based on the geological parameters, liquid production rate, and production time; and step S40, calculating the oil recovery efficiency based on the cumulative displacement volume, geological parameters, liquid production, and sweep radius. The present invention aims to combine the actual conditions of the oil field with numerical and physical modeling experiments to propose a method for finely characterizing the dynamic oil recovery efficiency inside the water ridge cavity. This method can calculate the oil recovery efficiency inside the water ridge cavity at any production stage of a horizontal well in a bottom water reservoir, and quantitatively calculate the degree of utilization of crude oil within the sweep range of the water ridge cavity. The calculation results can further guide the development of the potential of the oil field.

Description

Technical Field

[0001] The invention relates to a method for calculating the dynamic oil displacement efficiency of a water ridge cavity in a bottom water reservoir, and belongs to the technical field of oil reservoir engineering. Background Art

[0002] When developing horizontal wells in bottom-water reservoirs, a water ridge cavity with bottom water coning will be formed between the oil-water interface and the horizontal well, causing the oil well to see water quickly. At the same time, for bottom-water reservoirs, when the crude oil viscosity is in the thin oil range, it can be seen from the cross section perpendicular to the oil well that the lateral spread of the water ridge cavity is large, and the oil-water interface will rise at the same time, and the internal oil recovery efficiency distribution is relatively uniform (such as Figure 1 As the viscosity increases, the water content in the oil well rises faster, the lateral sweep range of the water ridge cavity gradually decreases, and the bottom water can easily break through along the middle of the water ridge cavity and establish a dominant channel. Once the bottom water breaks through, its lateral sweep range is limited and basically does not change (such as Figure 2 ), the output of crude oil in the subsequent development stage mainly comes from the continuous improvement of the oil recovery efficiency inside the water ridge cavity. Figure 3 It can be seen that the displacement factor at the center (core) of the water ridge cavity, and therefore the oil recovery efficiency, has a certain correlation with the water displacement factor. However, research shows that the closer to the edge of the water ridge cavity, the lower the water displacement factor, resulting in an uneven distribution of oil recovery efficiency. Clarifying the distribution of oil recovery efficiency within the scope of the water ridge cavity and achieving quantitative characterization of oil recovery efficiency are of great significance for the distribution of remaining oil in the oil field, the calculation of recovery factor, and the implementation of subsequent oil field infill adjustments.

[0003] At present, the conventional formula for calculating the recovery rate of bottom water reservoirs in the industry uses the oil displacement efficiency under the high displacement conditions of core experiments. Under actual mining conditions, the cumulative fluid production of a single well can reach more than 5 million cubic meters. Under enhanced fluid production conditions, the average displacement multiple within the water ridge cavity is difficult to reach the experimental conditions. Therefore, the recovery rate calculated by the oil displacement efficiency obtained by core experiments is much higher than the actual situation of the oil field. At the same time, the displacement multiples at different locations in the water ridge area vary greatly. The displacement multiple in the core area can reach nearly 10,000 times. Figure 1 As shown, the displacement ratio near the edge is very low. Due to the different displacement ratios, the corresponding oil-water relative permeability curve will also change accordingly. The residual oil saturation is low at locations with high water displacement ratios, while the residual oil saturation is high at locations with low water displacement ratios. Therefore, it is urgent to determine the dynamic oil displacement efficiency within the water ridge cavity of bottom water reservoirs to lay the foundation for accurately predicting the target recovery factor of the oil field and subsequently adjusting and tapping potential.

[0004] The existing technologies have the following three main shortcomings: (1) There are few studies on the evolution of oil recovery efficiency and sweep coefficient for oil fields with strong bottom water production capacity, especially in the late stage of development and production when the oil field faces high water content. A considerable part of the crude oil comes from the high water content stage. After the reservoir is flushed with a large amount of liquid, its internal permeability will change to a certain extent. Therefore, the oil recovery efficiency and sweep coefficient calculated by the conventional phase permeability curve can no longer accurately reflect the changes inside the water ridge cavity. (2) There are many studies on the time-varying phase permeability, but there is no relevant research on the detailed characterization of the oil recovery efficiency in the water ridge cavity based on the time-varying phase permeability. In particular, there is little relevant research on the quantitative characterization of the oil recovery efficiency in different sweep ranges. (3) There is no relevant research on the dynamic oil recovery efficiency calculation formula for bottom water reservoirs. The oil recovery efficiency calculation formula obtained in this paper can predict the oil recovery efficiency in the water ridge cavity at any future development stage. Combined with the sweep coefficient, the recovery rate of bottom water reservoirs can be accurately calculated. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention provides a method for calculating the dynamic oil recovery efficiency of water ridges in bottom-water reservoirs. Based on the actual conditions of oil fields and combined with numerical and physical modeling experiments, this method proposes a method for finely characterizing the dynamic oil recovery efficiency within water ridges. This method can calculate the oil recovery efficiency within water ridges at any production stage in horizontal wells in bottom-water reservoirs and quantitatively calculate the extent of crude oil recovery within the water ridge's reach. The results can further guide oilfield potential development.

[0006] The present invention provides a technical solution to solve the above technical problems: a method for calculating the dynamic oil displacement efficiency of water ridge cavity in bottom water reservoir, comprising the following steps:

[0007] Step S10: collecting geological parameters, liquid production, and production time of the bottom water reservoir;

[0008] Step S20: Calculate the maximum sweep radius of the bottom water reservoir based on geological parameters;

[0009] Step S30: Calculate the cumulative displacement volume based on geological parameters, liquid production rate, and production time;

[0010] Step S40: Calculate the oil displacement efficiency based on the cumulative displacement volume, geological parameters, liquid production, and sweep radius.

[0011] A further technical solution is that the geological parameters in step S10 include permeability and crude oil viscosity.

[0012] A further technical solution is that the calculation formula in step S20 is:

[0013] R1=280μ -0.233

[0014] Where: μ is the viscosity of crude oil; R1 is the maximum sweep radius.

[0015] A further technical solution is that the calculation formula in step S30 is:

[0016] PV=-392.02ln(R)+0.433Q+50.519ln(k)-14.02ln(μ)+70.799t+142.37

[0017] Where: R is the distance between the oil in the water ridge cavity and the center of the water ridge at the water interface, which is called the water ridge radius; k is the permeability; μ is the crude oil viscosity; PV is the cumulative displacement volume; t is the production time; Q is the liquid production.

[0018] A further technical solution is that the calculation formula in step S40 is:

[0019] η=-1.363ln(Q)+1.154ln(k)-8.195(R)-2.593ln(PV)-4.754ln(μ)+81.35PV 0.071

[0020] Where: η is the oil displacement efficiency; R is the distance between the oil in the water ridge cavity and the center of the water ridge at the water interface, which is called the water ridge radius; k is the permeability; μ is the crude oil viscosity; PV is the cumulative displacement volume; Q is the liquid production.

[0021] The present invention has the following beneficial effects:

[0022] (1) The data basis of the technical method of the present invention is based on the analysis of the oil recovery efficiency results obtained from existing oil field tests, without increasing any cost.

[0023] (2) The calculation results are highly accurate and have small errors. Compared with existing technical solutions, the present invention can use known and conventional oil field production data to calculate the oil displacement efficiency within different sweep ranges, and the calculation is convenient and concise.

[0024] (3) This method has a wide range of applications, is flexible, and is easy to operate. It is not only applicable to the X oilfield in the Bohai Bay Basin, but also has been tested on other oilfields in the oilfield group. The calculation accuracy is high and the error is small, which shows that it is applicable to other oilfields in the oilfield group.

[0025] (4) Fewer parameters are required. All parameters are known data. Compared with numerical models, this method can quickly and accurately calculate the oil displacement efficiency within the corresponding swept area.

[0026] (5) The present invention can be used to predict the oil recovery efficiency at any production stage and within any sweep radius. It can also be used to predict the oil recovery efficiency within the future sweep radius of an oil field.

[0027] (6) These research results of the present invention have been put into practical application in this oil field group, guiding the development of this oil field and providing a technical basis for the formulation of development plans for each block, determination of recovery rate and other oil field development decisions. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is the functional relationship diagram of displacement volume and oil displacement efficiency;

[0029] Figure 2 is the functional relationship diagram of permeability and oil displacement efficiency;

[0030] Figure 3 This is a functional relationship diagram between liquid volume and oil displacement efficiency;

[0031] Figure 4 is the functional relationship diagram of viscosity and oil displacement efficiency;

[0032] Figure 5 is the functional relationship between water ridge radius and oil displacement efficiency;

[0033] Figure 6 This is the field diagram of water ridge cavity oil displacement efficiency;

[0034] Figure 7 is the relationship diagram between oil displacement efficiency and displacement volume;

[0035] Figure 8 is the relationship between the derivative of oil displacement efficiency and displacement volume;

[0036] Figure 9 is the relationship diagram between oil displacement efficiency and water ridge area;

[0037] Figure 10 This is the relationship diagram between the sweep radius and the water ridge radius. DETAILED DESCRIPTION

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0039] A method for calculating the dynamic oil displacement efficiency of a water ridge cavity in a bottom water reservoir of the present invention comprises the following steps:

[0040] Step S10: collecting geological parameters, liquid production, and production time of the bottom water reservoir;

[0041] Step S10: collecting geological parameters and liquid production of the bottom water reservoir;

[0042] Step S20: Calculate the maximum sweep radius of the bottom water reservoir based on geological parameters;

[0043] R1=280μ -0.233

[0044] Where: μ is the viscosity of crude oil; R1 is the maximum sweep radius;

[0045] Step S30: Calculate the cumulative displacement volume based on geological parameters, liquid production rate, and production time;

[0046] PV=-392.02ln(R)+0.433Q+50.519ln(k)-14.02ln(μ)+70.799t+142.37

[0047] Where: R is the distance between the oil in the water ridge cavity and the center of the water ridge at the water interface, which is called the water ridge radius; k is the permeability; μ is the viscosity of crude oil; PV is the cumulative displacement volume; t is the production time; Q is the liquid production;

[0048] Step S40: Calculate the oil displacement efficiency based on the cumulative displacement volume, geological parameters, liquid production, and sweep radius.

[0049] η=-1.363ln(Q)+1.154ln(k)-8.195(R)-2.593ln(PV)-4.754ln(μ)+81.35PV 0.071

[0050] Where: η is the oil displacement efficiency; R is the distance between the oil in the water ridge cavity and the center of the water ridge at the water interface, which is called the water ridge radius; k is the permeability; μ is the crude oil viscosity; PV is the cumulative displacement volume; Q is the liquid production.

[0051] The derivation of the formula for calculating oil recovery efficiency first identified the most critical parameters affecting oil recovery efficiency: liquid production, permeability, viscosity, sweep radius, and production time. Through fitting, the functional relationship between these factors and oil recovery efficiency was obtained. By coupling multiple factors, a formula for calculating oil recovery efficiency was derived, in which the aforementioned factors serve as independent variables and oil recovery efficiency serves as the dependent variable. Simultaneously, based on actual oilfield production practices, the functional relationship between actual field data and measured oil recovery efficiencies was summarized, and the formula was corrected for a single factor, ultimately resulting in a formula for calculating oil recovery efficiency. This method is simple, fast, and accurate.

[0052] The fitting process of the oil displacement efficiency formula is as follows:

[0053] The functional relationship between displacement volume and oil displacement efficiency under different sweep radii was obtained by fitting the results obtained from the model, such as Figure 1 As shown in the figure, for example, when the sweep radius is 65m, the calculation formula for its oil displacement efficiency and displacement volume is:

[0054] η=8.7687ln(PV)+7.88

[0055] The functional relationship between permeability and oil displacement efficiency under different sweep radii was obtained by fitting the results obtained from the model, such as Figure 2 As shown in the figure, for example, when the sweep radius is 115m, the calculation formula for its oil displacement efficiency and permeability is:

[0056] η=1.8998ln(k)+39.117

[0057] The functional relationship between the liquid production rate and oil displacement efficiency under different sweep radii is obtained by fitting the results obtained from the model, such as Figure 3 As shown in the figure, for example, when the sweep radius is 115m, the calculation formula for its oil displacement efficiency and liquid production rate is:

[0058] η=4.57ln(Q)+8.63

[0059] The functional relationship between viscosity and oil displacement efficiency under different permeabilities was obtained by fitting the results obtained from the model, such as Figure 4 As shown, for example, when the viscosity is 1000mD, the calculation formula of its oil displacement efficiency and viscosity is:

[0060] η=-4.698ln(Q)+67.153

[0061] The functional relationship between the water ridge radius and oil displacement efficiency under different liquid volumes was obtained by fitting the results of the model, such as Figure 5 As shown, for example, when the daily liquid production is 1500 cubic meters / day, the calculation formula for oil displacement efficiency and water ridge radius is:

[0062] η=-7E-0.6R 3 +0.0024R 2 -0.3834R+74.666

[0063] The above formula is coupled with multiple factors according to the functional relationship between each factor and oil displacement efficiency, and the functional relationship between oil displacement efficiency and the above factors is finally obtained as follows:

[0064] η=-1.363ln(Q)+1.154ln(k)-8.195(R)-2.593ln(PV)-4.754ln(μ)+81.35PV 0.071

[0065] In the above formula, PV is affected by five factors: R, Q, k, μ, and t. These five factors cannot be directly introduced into the above formula. Therefore, the PV calculation formula obtained by fitting is:

[0066] PV=-392.02ln(R)+0.433Q+50.519ln(k)-14.02ln(μ)+70.799t+142.37

[0067] Where: R is the distance between the oil in the water ridge cavity and the center of the water ridge at the water interface, which is called the water ridge radius; k is the permeability; μ is the crude oil viscosity; PV is the cumulative displacement volume; t is the production time; Q is the liquid production.

[0068] The above formula can be used to calculate the oil displacement efficiency under any sweep radius. The calculation process is as follows:

[0069]

[0070]

[0071] Where: S1 and S2 are the average oil saturation within the sweep radius; l is the length of the horizontal well; r1 and r2 are the sweep radius. When calculating the oil saturation at any radius, two adjacent points can be randomly selected near the location, and their volume V can be calculated. Combined with the oil saturation, the saturation at that point can be obtained.

[0072] 2. Oil displacement efficiency zone division process:

[0073] The study found that the displacement multiple at the center of the water ridge cavity (core position) is different from the displacement multiple at the edge of the water ridge cavity. The displacement multiple at the core position is larger, up to tens of thousands of times, while the displacement multiple at the edge water ridge is extremely low. In order to facilitate the characterization of the boundary range of the water ridge cavity, this article combined the research findings and found that when the displacement multiple is lower than 0.05PV, its contribution to oil well production is less than 0.01%. This article uses 0.05PV as the characterization boundary of the water ridge cavity.

[0074] In the high-multiple water flooding process, the oil displacement efficiency can be divided into three stages according to the change of displacement volume. The first stage: the displacement volume is 0.5-5PV, and the oil displacement efficiency reaches 15%-25%. In this stage, the rate of change of oil displacement efficiency with displacement volume is the largest. Figure 7 、 Figure 8As shown, using 5PV as the threshold for oil recovery efficiency, when the displacement volume is less than 5PV, the reserves are readily accessible and have high potential. In this stage, oil recovery efficiency is significantly affected by displacement volume. In the early stages of development and production, this portion is widely distributed, but as development and production progress, the recovery efficiency shifts from 15% to 25% toward the edges of the water ridge cavity. In the second stage, when the displacement factor is between 5 and 2000PV, the oil recovery efficiency ranges from 25% to 70%. In this stage, the influence of displacement volume on oil recovery efficiency gradually decreases with increasing displacement factor. However, as displacement volume changes, a larger amount of crude oil is recovered in this stage. Judging by the absolute value of the increase in oil recovery efficiency, high-flooding waterflooding still offers a significant degree of recovery. In the third stage, when the displacement volume exceeds 2000PV, oil recovery efficiency exceeds 70%, reaching a local maximum of 80%. This is primarily due to the increased efficiency at the core water ridges of high-flooding waterflooding. Based on the zoning and division of displacement multiples, the oil recovery efficiency within the water ridge cavity was zoned. According to the oil recovery efficiency results, the marginal water ridge area has a low degree of crude oil recovery, with an oil recovery efficiency of only 15% to 25%, which can be further recovered. This has narrowed the well placement boundary from the marginal water ridge area to the transition water ridge area, further shortened the well placement boundary for different viscosities, and established the latest well spacing range for the well placement boundary for crude oils with different viscosities. The results are shown in the table below.

[0075] The displacement multiple in the middle of the water ridge cavity is greater than 2000PV. In the high-multiple water flooding process, when the displacement multiple is 0.5-5PV, the oil displacement efficiency reaches 15%-25%. Figure 7 、 Figure 8 It can be obtained that when the displacement volume reaches the range of 0.5~5PV, the oil recovery efficiency change rate reaches the maximum value, and crude oil can still be produced if the displacement continues. However, as the displacement multiple increases, the change rate gradually decreases. However, judging from the absolute value of the increase in its oil recovery efficiency, it can still be produced to a large extent. Therefore, 5PV is used as a dividing line for oil recovery efficiency. When the displacement volume is lower than 5PV, it can be regarded as a low degree of utilization and has the potential for further utilization. When the displacement volume is greater than 2000PV, the oil recovery efficiency is greater than 70%, and can reach a maximum of 80%. The oil recovery efficiency is relatively high, and the oil recovery efficiency remains basically unchanged if the displacement volume is continued to increase. When the displacement multiple is between 5 and 2000PV, the oil recovery efficiency is between 25% and 70%. Therefore, the displacement volume of 5PV is used as the dividing line for low oil recovery efficiency, and 2000PV is used as the dividing line for high oil recovery efficiency. Combined with the oil recovery efficiency calculation formula, the oil recovery efficiency is divided into regions, such as Figure 6 As shown, the oil recovery efficiency is divided into three areas: the core water ridge area, the transition water ridge area (oil recovery efficiency: and the edge water ridge area, the edge water ridge area, the oil recovery efficiency of the edge water ridge area is less than 25%, combined with Figure 7It can be found that after high-multiple water flooding, there is still a large degree of utilization. When arranging wells, the reference swept edge is set as the boundary of the marginal water ridge area, that is, the boundary of the displacement volume of 5PV. The utilization degree outside this boundary is low and can be further utilized. Inside this boundary, it can be utilized through old wells through strong liquid flushing. Therefore, when arranging wells, by shortening the well layout boundary from the marginal water ridge area to the transition water ridge area, the crude oil in the marginal water ridge area can be further utilized.

[0076] The highlights of the present invention are as follows: (1) The present invention combines the methods of numerical modeling and physical modeling experiments, fully considers the influence of liquid production, permeability, viscosity, sweep radius, and production time on oil recovery efficiency, and establishes a calculation method that can accurately calculate the oil recovery efficiency within the sweep range of the water ridge cavity. Combined with the above-mentioned prediction results of oil recovery efficiency and the law of change of oil recovery efficiency with displacement volume in high-multiple water drive, the oil recovery efficiency is divided into zones and zoning, which are divided into three areas: core water ridge area, transition water ridge area, and edge water ridge area. Among them, the edge water ridge area has low oil recovery efficiency and can be further utilized, shortening the well layout boundary from the edge water ridge area to the transition water ridge area. The utilization rate of oil field reserves is improved. (2) After the establishment of this method, the formula was calibrated and verified in combination with the actual drilling oil recovery efficiency of a large number of bottom water reservoir pass-through wells, and the prediction accuracy reached more than 85%. It has practical application value.

[0077] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A method for calculating the dynamic oil displacement efficiency of water ridge cavity in bottom water reservoir, characterized in that: The following steps are involved: Step S10: collecting geological parameters, liquid production and production time of the bottom water reservoir; Step S20: Calculate the maximum sweep radius of the bottom water reservoir based on geological parameters; R1=280μ -0.233 Where: μ is the viscosity of crude oil; R1 is the maximum sweep radius; Step S30: Calculate the cumulative displacement volume based on geological parameters, liquid production and production time; PV=-392.02ln(R)+0.433Q+50.519ln(k)-14.02ln(μ)+70.799t+142.37 Where: R is the distance between the oil in the water ridge cavity and the center of the water ridge at the water interface, which is called the water ridge radius; k is the permeability; μ is the viscosity of crude oil; PV is the cumulative displacement volume; t is the production time; Q is the liquid production; Step S40, calculating the oil displacement efficiency based on the cumulative displacement volume, geological parameters, liquid production, and water ridge radius; η=-1.363ln(Q)+1.154ln(k)-8.195(R)-2.593ln(PV)-4.754ln(μ)+81.35PV 0.071 Where: η is the oil displacement efficiency.

2. The method for calculating the dynamic oil displacement efficiency of the water ridge cavity in a bottom water reservoir according to claim 1, characterized in that: The geological parameters in step S10 include permeability and crude oil viscosity.

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