Method for quantifying interwell fractures in pressure flooding process of low-permeability reservoir

Abstract

The invention provides an inter-well fracture quantification method in a low-permeability reservoir pressure-driving process, which comprises the following steps of: 1, calculating the theoretical pressure drop of an oil producing well in the pressure-driving process according to the actual daily water injection rate and daily liquid increase rate after pressure-driving; 2, according to the actual bottomhole flowing pressure data of the oil producing well before and after pressure driving, the actual pressure drop of the oil producing well in the pressure driving process is calculated; and 3, fitting the theoretical pressure drop according to the actual pressure drop of the oil producing well, and calculating the opening degree of the interwell fracture in the pressure driving process. According to the inter-well fracture quantification method in the pressure driving process of the low-permeability reservoir, the problems that in the pressure driving process of the low-permeability reservoir, the fracture development condition cannot be clearly known, and the water channeling risk is large are solved, and quantitative description of inter-well fractures generated in the pressure driving process is achieved; the method has important theoretical and practical significance in subsequent guidance of optimization and adjustment of a pressure-drive water injection scheme, design of plugging process parameters and improvement of pressure-drive water injection oil displacement efficiency and water injection utilization rate.

Description

Technical Field

[0001] The present invention relates to the technical field of fracture identification in pressure drive of low-permeability reservoirs, and particularly to a method for quantifying inter-well fractures during the pressure drive process in low-permeability reservoirs. Background Art

[0002] In the development of low-permeability reservoirs, there are often problems such as "difficult to inject and difficult to produce", resulting in a low level of energy maintenance in the development horizons, low liquid production, and low development efficiency. To solve the above problems, Shengli Oilfield creatively proposed pressure drive water injection. Compared with conventional water injection, pressure drive water injection uses a large-displacement high-pressure pump injection fracturing device to first fracture the formation into a network structure under conditions of overburden fracture pressure or near-overburden fracture pressure, and then injects water into the formation at a large displacement. By injecting water at high pressure and high speed in the short term and discharging liquid stably in the long term, the purpose of improving the oil displacement effect is achieved. However, the fracture network system generated between injection and production wells during pressure drive water injection makes the injected water easily conduct along the preferential seepage channels and main horizons, thus increasing the risk of directional water channeling. Therefore, quickly understanding the fracture development during pressure drive water injection is of great theoretical and practical significance for reducing the risk of reservoir water channeling, improving water injection utilization rate and oil displacement efficiency.

[0003] Currently, the main methods for predicting and identifying inter-well fractures include core analysis, logging interpretation, seismic interpretation, artificial intelligence prediction, and reservoir engineering analysis. Compared with the first three methods, artificial intelligence prediction and reservoir engineering analysis are two methods that have emerged in recent years and received relatively high attention.

[0004] In 2022, Dong Shaoqun et al. proposed an intelligent prediction method for fractures in tight carbonate reservoirs (artificial intelligence prediction method). The intelligent improvement of the proposed prediction method includes: ① Incorporating three artificial intelligence algorithms (support vector machine, multi-kernel Fisher discriminant analysis, random forest) into the conventional fracture identification method (fracture indicator parameter method), improving the identification model from three aspects: small sample classification, multi-scale non-linear feature extraction, and reduction of the variance of the prediction model, comprehensively identifying the fracture development of a single well to reduce the uncertainty of identification. ② Obtaining the inter-well fracture development trend through two ways: numerical simulation of reservoir geomechanics and seismic attribute prediction. Among them, seismic inversion of inter-well fracture development trend forms a relatively robust fracture prediction model through an artificial intelligence integrated learning algorithm (gradient boosting decision tree). ③ Based on single-well fracture identification and prediction of inter-well fracture development trend, a method for constructing an inter-well fracture density constraint body that can be used to directly constrain fracture network modeling is established. It realizes multi-scale information fusion and integrated intelligent prediction from single-well fracture identification to prediction of inter-well fracture development trend, to inter-well fracture density body, to fracture network modeling, and to fracture attribute coarsening.

[0005] In 2020, Zhang Shiming et al. proposed a method for quantifying the characteristic parameters of the inter-well fracture network after gas breakthrough in tight reservoirs (a reservoir engineering analysis method). After fracturing in tight reservoirs, a complex fracture network system is usually formed near the wellbore. The quantitative description of the characteristic parameters of the fracture network between injection and production wells is of great significance for formulating gas channeling plugging measures and adjusting development plans in the later stage. Based on the previous research results, according to the principle of mass conservation, the characterization functions of the main fracture network characteristic parameters such as fracture porosity, fracture permeability, fracture aperture, and fracture line density were improved, and a calculation method and solution steps for quantifying the characteristic parameters of the inter-well fracture network after gas breakthrough in tight reservoirs were proposed. Taking the XN well group in the Shengli Oilfield as an example, the quantification results of the inter-well fracture network characteristic parameters were obtained: the fracture porosity was 0.250% - 0.251%, the average fracture permeability was 42 - 1563 mD, the fracture aperture was 14 - 87 μm, and the fracture line density was 29 - 176 fractures / m. The analysis shows that: the fracture porosity of the XN well group is generally much smaller than the average porosity of the reservoir, and the fracture development degree is relatively strong; there are significant differences in the average fracture permeability and average gas channeling velocity between the inter-well of each gas channeling single well, mainly micro-fractures, and there are certain-scale gas channeling fracture channels; single wells with fast gas channeling velocity show characteristics such as high average fracture permeability, large fracture aperture, and small fracture line density. The quantitative description of the characteristic parameters of the inter-well fracture network after gas breakthrough in tight reservoirs was realized.

[0006] In the Chinese patent application with the application number: CN201910131868.8, it involves a method for dynamically inverting the fracture aperture between wells in a tight reservoir, including the following steps: obtaining the actual pressure difference curve between injection and production wells according to the production dynamic data of injection and production wells; determining the fluid velocity in the cross-flow channel between injection and production wells according to the near-well fracture network range of the injection well; obtaining the theoretical pressure difference curve between injection and production wells according to the fluid velocity in the cross-flow channel between injection and production wells; determining the average permeability of the cross-flow channel between injection and production wells according to the actual pressure difference curve and the theoretical pressure difference curve between injection and production wells; and determining the fracture aperture between injection and production wells according to the average permeability of the cross-flow channel between injection and production wells. This invention solves the problem that the current fracture identification method cannot fully reflect the formation and disappearance process of inter-well fractures, resulting in a weak fracture identification and prediction effect in the process of water injection development in tight reservoirs. It not only greatly reduces the cost of inverting the fracture aperture between wells in tight reservoirs, but also provides the fracture aperture information between wells at different times, strongly supporting the development and management work of tight reservoirs.

[0007] In the Chinese patent application with the application number CN202211422234.6, a method for analyzing the fracture sensitivity of a fractured reservoir is involved, including: S1: determining the fracture properties to be analyzed; S2: setting the fluctuation range of each fracture property based on the fracture property parameters of the reservoir basic fracture model; S3: performing full-variable random sampling within the fluctuation range of each fracture property based on the Monte Carlo method to form a parameter combination for each fracture property; S4: inputting the parameter combination of each fracture property into the reservoir numerical simulator to calculate the production corresponding to the parameter combination of each fracture property; S5: performing global sensitivity analysis of the fracture properties based on the production corresponding to the parameter combination of each fracture property to obtain the fracture property sensitivity analysis result; which is used to simultaneously consider the sensitivity of multiple fracture properties to the reservoir production, and further realize the global sensitivity analysis of the reservoir fracture properties, providing a reliable basis for the dynamic analysis of fractured reservoirs and the adjustment of development plans.

[0008] However, although the artificial intelligence prediction method has a high recognition accuracy, it needs to comprehensively apply the data results of other fracture prediction or identification methods, requires a lot of data, and takes a long time for research, which is not conducive to the application research of short-term plans or adjustment measures. The reservoir engineering analysis method is simple and convenient, requires less data, and takes a short time for research, but is usually affected by the large differences in reservoir types and development characteristics, and the research methods and calculation formulas usually have obvious limitations in use.

[0009] According to the development characteristics of pressure drive water injection in low-permeability reservoirs, it is suitable to use the reservoir engineering analysis method to identify the inter-well fracture parameters, but the existing research methods and calculation formulas cannot be directly used.

[0010] The above existing technologies are quite different from the present invention and cannot solve the technical problems we want to solve. Therefore, we have invented a new method for quantifying inter-well fractures during the pressure drive process in low-permeability reservoirs. Summary of the Invention

[0011] The purpose of the present invention is to provide a method for quantifying inter-well fractures during the pressure drive process in low-permeability reservoirs, which solves the problems of unclear understanding of fracture development and high water channeling risk during the pressure drive process in low-permeability reservoirs, and realizes the quantitative description of inter-well fractures generated during the pressure drive process.

[0012] The purpose of the present invention can be achieved by the following technical measures: A method for quantifying inter-well fractures during the pressure drive process in low-permeability reservoirs, which includes:

[0013] Step 1, calculating the theoretical pressure drop of the production well during the pressure drive process according to the actual daily injection volume increase and daily production fluid volume increase after the pressure drive.

[0014] Step 2: Calculate the actual pressure drop of the production well during the pressure drive according to the actual bottom-hole flowing pressure data of the production well before and after the pressure drive.

[0015] Step 3: Fit the theoretical pressure drop based on the actual pressure drop of the production well and calculate the fracture aperture between wells during the pressure drive.

[0016] The object of the present invention can also be achieved by the following technical measures:

[0017] In Step 1, the bottom-hole flowing pressure curve and liquid production curve of the production well basically remain unchanged before the pressure drive. After the pressure drive, the bottom-hole flowing pressure curve and liquid production curve of the production well show obvious upward trends successively.

[0018] Step 1 includes:

[0019] Step 11: Calculate the theoretical pressure drop caused by the increased injection volume of the injection well at the production well according to the daily increased injection volume of the injection well after the pressure drive.

[0020] Step 12: Calculate the theoretical pressure drop caused by the increased liquid production of the production well at the production well according to the daily increased liquid production of the production well after the pressure drive.

[0021] Step 13: Calculate the theoretical pressure drop of the production well during the pressure drive according to the principle of pressure drop superposition.

[0022] In Step 11, the formula for calculating the theoretical pressure drop caused by the increased injection volume of the injection well at the production well is:

[0023]

[0024] Where Δp 注 (t) is the theoretical pressure drop caused by the increased injection volume of the injection well at the production well, MPa; Δq inj is the daily increased injection volume of the injection well after the pressure drive for enhanced injection, that is, the daily increased injection volume, m 3 / d; μ is the average viscosity of the fluid between the injection and production wells, mPa·s; K is the average permeability between the injection and production wells, mD; h is the average effective thickness of the reservoir between the injection and production wells, m; L is the well spacing between the injection and production wells, m; Δt 1 is the time corresponding to the start of the pressure drive for enhanced injection of the injection well, d; is the power integral function; η is the pressure conductivity coefficient between the injection and production wells; Ф is the average porosity of the reservoir, f; C t is the comprehensive compressibility coefficient of the reservoir, MPa -1 .

[0025] In Step 12, the formula for calculating the theoretical pressure drop caused by the increased liquid production of the production well at the production well is:

[0026]

[0027] Where: Δp采 (t) is the theoretical pressure drop caused by the increased liquid production volume at the oil production well, MPa; q pro is the increased daily liquid production volume of the oil production well after pressure drive, that is, the daily increased liquid production volume, m 3 / d; q con is the daily liquid production volume of the oil production well before pressure drive, m 3 / d; μ 2 is the average viscosity of the fluid near the oil production well, mPa·s; K 2 is the average permeability near the oil production well, mD; h 2 is the reservoir thickness at the well point of the oil production well, m; r w is the wellbore radius of the oil production well, m; η 2 is the pressure conductivity coefficient near the oil production well; Δt 2 is the time corresponding to the increase in the daily liquid production volume of the oil production well, d.

[0028] In step 13, the formula for calculating the theoretical pressure drop of the oil production well during the pressure drive process is:

[0029] Δp 理论 (t) = Δp 注 (t) - Δp 采 (t) (3)

[0031] In the formula, Δp 理论 (t) is the theoretical pressure drop of the oil production well during the pressure drive process, MPa. In step 2, the formula for calculating the actual pressure drop of the oil production well during the pressure drive process is:

[0032] Δp 实际 (t) = p 实际 (t) - p con (4)

[0034] In the formula, Δp 实际 (t) is the actual pressure drop of the oil production well during the pressure drive process, MPa; p 实际 (t) is the actual bottom-hole flowing pressure of the oil production well after pressure drive, MPa; p con is the actual bottom-hole flowing pressure of the oil production well before pressure drive, MPa.

[0035] In step 3, by fitting the theoretical pressure drop according to the actual pressure drop of the oil production well, the average permeability between the injection and production wells can be obtained.

[0036] In step 3, due to the generation of micro-fractures or fissures between the injection and production wells after pressure drive injection augmentation, which become the main source of the fluid seepage capacity during the pressure drive process; therefore, according to the functional relationship between the average permeability between the injection and production wells and the fracture aperture, the fracture aperture between the wells during the pressure drive process can be calculated.

[0037] In step 3, the formula for calculating the fracture aperture is:

[0038]

[0039] In the formula, b is the crack opening, in μm; K is the average permeability between the injection and production wells, in D; c is the influence coefficient of roughness and tortuosity on the crack permeability.

[0040] In the method for quantifying the inter-well cracks during the pressure drive process in a low-permeability reservoir of the present invention, by utilizing the significant differences in the bottom-hole flowing pressure response and production response of the production wells in the low-permeability reservoir before and after the pressure drive, the reservoir engineering method is applied to establish the functional relationship between different responses, and the crack parameters of the inter-well cracks generated during the pressure drive process are quickly identified; it solves the problems of unclear understanding of the crack development situation and high water channeling risk during the pressure drive process in the low-permeability reservoir, realizes the quantitative description of the inter-well cracks generated during the pressure drive process; it has important theoretical and practical significance for guiding the subsequent optimization and adjustment of the pressure drive injection plan and the design of plugging process parameters, and improving the oil displacement efficiency and water injection utilization rate of the pressure drive injection.

[0041] The present invention utilizes the significant differences in the bottom-hole flowing pressure response and production response of the production wells in the low-permeability reservoir before and after the pressure drive, applies the reservoir engineering method to establish the functional relationship between different responses, and quickly identifies the crack parameters of the inter-well cracks generated during the pressure drive process. It solves the problems of unclear understanding of the crack development situation and high water channeling risk during the pressure drive process in the low-permeability reservoir, and realizes the quantitative description of the inter-well cracks generated during the pressure drive process. It has important theoretical and practical significance for guiding the subsequent optimization and adjustment of the pressure drive injection plan and the design of plugging process parameters, and improving the oil displacement efficiency and water injection utilization rate of the pressure drive injection.

[0042] The present invention utilizes the significant differences in the bottom-hole flowing pressure response and production response of the production wells in the low-permeability reservoir before and after the pressure drive, applies the reservoir engineering method to establish the functional relationship between different responses, and quickly identifies the crack parameters of the inter-well cracks generated during the pressure drive process. Compared with the prior art, the present invention solves the problems of unclear understanding of the crack development situation and high water channeling risk during the pressure drive process in the low-permeability reservoir, and realizes the quantitative description of the inter-well cracks generated during the pressure drive process. It has important theoretical and practical significance for guiding the subsequent optimization and adjustment of the pressure drive injection plan and the design of plugging process parameters, and improving the oil displacement efficiency and water injection utilization rate of the pressure drive injection. Description of the Drawings

[0043] Figure 1 It is a schematic flow chart of a method for quantifying the inter-well cracks during the pressure drive process in a low-permeability reservoir provided by Embodiment 1 of the present invention;

[0044] Figure 2 It is a schematic diagram of the characteristic curves of the bottom-hole flowing pressure response and production response of the production wells in the low-permeability reservoir before and after the pressure drive provided by Embodiment 1 of the present invention;

[0045] Figure 3 It is the production performance curve of Well Group H12 provided in the second embodiment of the present invention;

[0046] Figure 4 It is the measured bottom-hole flowing pressure curve of injection and production wells in Well Group H12 provided in the second embodiment of the present invention;

[0047] Figure 5 It is the injection-production pressure difference curve during the pressure drive process of Well Group H12 provided in the second embodiment of the present invention;

[0048] Figure 6 It is the distribution map of the average permeability between wells obtained by inverting the fitted injection-production pressure difference in Well Group H12 provided in the second embodiment of the present invention;

[0049] Figure 7 It is the fracture aperture map during the pressure drive process of Well Group H12 provided in the second embodiment of the present invention;

[0050] Figure 8 It is the injection-production pressure difference curve during the pressure drive process of Well Group HP6 provided in the third embodiment of the present invention;

[0051] Figure 9 It is the distribution map of the average permeability between wells obtained by inverting the fitted injection-production pressure difference in Well Group HP6 provided in the third embodiment of the present invention;

[0052] Figure 10 It is the fracture aperture map during the pressure drive process of Well Group HP6 provided in the third embodiment of the present invention. Detailed implementation manners

[0053] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0054] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0055] The method for quantifying the inter-well fractures during the pressure drive process of the low-permeability oil reservoir of the present invention includes:

[0056] Step 1, calculate the theoretical pressure drop of the production well during the pressure drive process according to the actual daily injection volume increase and daily production liquid volume increase after the pressure drive;

[0057] The pressure-driven water injection technology is a technology that aims to solve the problems of injection failure and production difficulties in low-permeability reservoirs during conventional water injection development. By injecting water at high pressure and high speed in a short period, it realizes the conversion of energy potential in the reservoir and improves the water injection utilization rate. Therefore, before pressure drive, the bottom-hole flowing pressure curve and liquid production curve of the production well basically remain unchanged. After pressure drive, the bottom-hole flowing pressure curve and liquid production curve of the production well show obvious upward trends successively, as Figure 2 shown.

[0058] Process 1: Calculate the theoretical pressure drop caused by the increased injection volume in the production well due to the increased daily water injection volume of the injection well after pressure drive. Specifically:

[0059]

[0060] In the formula, Δp 注 (t) is the theoretical pressure drop caused by the increased injection volume in the production well due to the increased daily water injection volume of the injection well, MPa; Δq inj is the increased daily water injection volume (daily increased water injection volume) of the injection well after pressure drive injection increase, m 3 / d; μ is the average viscosity of the fluid between the injection and production wells, mPa·s; K is the average permeability between the injection and production wells, mD; h is the average effective thickness of the reservoir between the injection and production wells, m; L is the well spacing between the injection and production wells, m; Δt 1 is the time corresponding to the start of pressure drive injection increase of the injection well, d; is the power integral function; η is the pressure conductivity coefficient between the injection and production wells; Ф is the average porosity of the reservoir, f; C t is the comprehensive compressibility coefficient of the reservoir, MPa -1 .

[0061] Process 2: Calculate the theoretical pressure drop caused by the increased liquid production in the production well due to the increased daily liquid production of the production well after pressure drive. Specifically:

[0062]

[0063] In the formula: Δp 采 (t) is the theoretical pressure drop caused by the increased liquid production in the production well due to the increased daily liquid production of the production well, MPa; q pro is the increased daily liquid production (daily increased liquid production) of the production well after pressure drive, m 3 / d; q con is the daily liquid production of the production well before pressure drive, m 3 / d; μ 2 is the average viscosity of the fluid near the production well, mPa·s; K 2 is the average permeability near the production well, mD; h 2 is the reservoir thickness at the well point of the production well, m; r w is the wellbore radius of the production well, m; η 2 is the pressure conductivity coefficient near the production well; Δt2 The time corresponding to the increase in the daily liquid production of the oil production well, d.

[0064] Process 3: According to the principle of pressure drop superposition, calculate the theoretical pressure drop of the oil production well during the pressure drive process, specifically:

[0065] Δp 理论 (t) = Δp 注 (t) - Δp 采 (t) (3)

[0067] In the formula, Δp 理论 (t) is the theoretical pressure drop of the oil production well during the pressure drive process, MPa.

[0068] Step 2: According to the actual bottom-hole flowing pressure data of the oil production well before and after the pressure drive, calculate the actual pressure drop of the oil production well during the pressure drive process;

[0069] The calculation formula for the actual pressure drop of the oil production well during the pressure drive process is:

[0070] Δp 实际 (t) = p 实际 (t) - p con (4)

[0072] In the formula, Δp 实际 (t) is the actual pressure drop of the oil production well during the pressure drive process, MPa; p 实际 (t) is the actual bottom-hole flowing pressure of the oil production well after the pressure drive, MPa; p con is the actual bottom-hole flowing pressure of the oil production well before the pressure drive (basically a fixed value p con ), MPa.

[0073] Step 3: Fit the theoretical pressure drop according to the actual pressure drop of the oil production well, and calculate the fracture aperture between wells during the pressure drive process.

[0074] By fitting the theoretical pressure drop according to the actual pressure drop of the oil production well, the average permeability between the injection and production wells can be obtained. Since microfractures or fissures are generated between the injection and production wells after pressure drive injection, which become the main source of fluid seepage ability during the pressure drive process; therefore, according to the functional relationship between the average permeability between the injection and production wells and the fracture aperture, the fracture aperture between wells during the pressure drive process can be calculated.

[0075] The calculation formula for the fracture aperture is:

[0076]

[0077] In the formula, b is the fracture aperture, μm; K is the average permeability between the injection and production wells, D; c is the influence coefficient of roughness and tortuosity on the fracture permeability, and usually takes 0.75 for low-permeability oil reservoirs in China.

[0078] The following are several specific embodiments of applying the present invention

[0079] Embodiment 1

[0080] This embodiment provides a method for quantifying inter-well fractures during the pressure drive process in a low-permeability oil reservoir. As Figure 1 shown, this method includes:

[0081] Step S11: Calculate the theoretical pressure drop of the production well during the pressure drive process according to the actual daily injection water volume increase and daily produced liquid volume increase after the pressure drive.

[0082] Step S12: Calculate the actual pressure drop of the production well during the pressure drive process according to the actual bottom-hole flowing pressure data of the production well before and after the pressure drive.

[0083] Step S13: Fit the theoretical pressure drop according to the actual pressure drop of the production well, and calculate the opening of the inter-well fracture during the pressure drive process.

[0084] This embodiment utilizes the significant differences in the bottom-hole flowing pressure response and production response of production wells in low-permeability oil reservoirs before and after pressure drive, applies reservoir engineering methods to establish functional relationships between different responses, and quickly identifies the fracture parameters of inter-well fractures generated during the pressure drive process. Compared with the prior art, the present invention solves the problems of unclear understanding of fracture development and high water channeling risk during the pressure drive process in low-permeability oil reservoirs, and realizes the quantitative description of inter-well fractures generated during the pressure drive process. It has important theoretical and practical significance for guiding the optimization and adjustment of pressure drive injection water schemes and the design of plugging process parameters in the follow-up, and improving the oil displacement efficiency and water injection utilization rate of pressure drive injection water.

[0085] Preferably, in the above step S11, calculating the theoretical pressure drop of the production well during the pressure drive process according to the actual daily injection water volume increase and daily produced liquid volume increase after the pressure drive is specifically:

[0086] The pressure drive injection technology is a technology that solves the problems of difficult injection and difficult production in low-permeability oil reservoirs during conventional water injection development. By injecting water at high pressure and high speed in a short period of time, it realizes the conversion of energy potential in the reservoir and improves the water injection utilization rate. Therefore, the bottom-hole flowing pressure curve and the produced liquid volume curve of the production well basically remain unchanged before the pressure drive, and the bottom-hole flowing pressure curve and the produced liquid volume curve of the production well show obvious upward trends successively after the pressure drive, as Figure 2 shown.

[0087] Process 1: Calculate the theoretical pressure drop caused by the increased injection water volume of the injection well at the production well according to the daily injection water volume increase of the injection well after the pressure drive, specifically:

[0088]

[0089] In the formula, Δp 注(t) is the theoretical pressure drop caused by the increased injection volume at the production well in the injection well, MPa; Δq inj is the daily injection volume increased after pressure-driven injection enhancement in the injection well (daily injection volume increase), m 3 / d; μ is the average viscosity of the fluid between the injection and production wells, mPa·s; K is the average permeability between the injection and production wells, mD; h is the average effective thickness of the reservoir between the injection and production wells, m; L is the well spacing between the injection and production wells, m; Δt 1 is the time corresponding to the start of pressure-driven injection enhancement in the injection well, d; is the power integral function; η is the pressure conductivity coefficient between the injection and production wells; Ф is the average porosity of the reservoir, f; C t is the comprehensive compressibility coefficient of the reservoir, MPa -1 .

[0090] Process 2: Calculate the theoretical pressure drop caused by the increased liquid production volume at the production well according to the daily increased liquid production volume of the production well after pressure-driven injection. Specifically:

[0091]

[0092] In the formula: Δp 采 (t) is the theoretical pressure drop caused by the increased liquid production volume at the production well, MPa; q pro is the daily increased liquid production volume (daily increased liquid production volume) of the production well after pressure-driven injection, m 3 / d; q con is the daily liquid production volume of the production well before pressure-driven injection, m 3 / d; μ 2 is the average viscosity of the fluid near the production well, mPa·s; K 2 is the average permeability near the production well, mD; h 2 is the reservoir thickness at the production well point, m; r w is the wellbore radius of the production well, m; η 2 is the pressure conductivity coefficient near the production well; Δt 2 is the time corresponding to the increase in the daily liquid production volume of the production well, d.

[0093] Process 3: Calculate the theoretical pressure drop of the production well during the pressure-driven injection process according to the principle of pressure drop superposition. Specifically:

[0094] Δp 理论 (t) = Δp 注 (t) - Δp 采 (t) (3)

[0096] In the formula, Δp 理论 (t) is the theoretical pressure drop of the production well during the pressure-driven injection process, MPa.

[0097] Preferably, in the above step S12, according to the actual bottom-hole flowing pressure data of the production well before and after pressure drive, the actual pressure drop of the production well during the pressure drive is calculated, specifically as follows:

[0098] The calculation formula for the actual pressure drop of the production well during the pressure drive is:

[0099] Δp 实际 (t) = p 实际 (t) - p con (4)

[0101] In the formula, Δp 实际 (t) is the actual pressure drop of the production well during the pressure drive, MPa; p 实际 (t) is the actual bottom-hole flowing pressure of the production well after pressure drive, MPa; p con is the actual bottom-hole flowing pressure of the production well before pressure drive (basically a fixed value p con ), MPa.

[0102] Preferably, in the above step S13, according to the actual pressure drop of the production well to fit the theoretical pressure drop, the fracture aperture between wells during the pressure drive is calculated, specifically as follows:

[0103] By fitting the theoretical pressure drop according to the actual pressure drop of the production well, the average permeability between the injection and production wells can be obtained. Since microfractures or fissures are generated between the injection and production wells after pressure drive injection increase, which become the main source of fluid seepage capacity during the pressure drive; therefore, according to the functional relationship between the average permeability between the injection and production wells and the fracture aperture, the fracture aperture between wells during the pressure drive can be calculated.

[0104] The calculation formula for the fracture aperture is:

[0105]

[0106] In the formula, b is the fracture aperture, μm; K is the average permeability between the injection and production wells, D; c is the influence coefficient of roughness and tortuosity on fracture permeability, and usually takes 0.75 for low-permeability oil reservoirs in China.

[0107] This embodiment utilizes the significant differences in the bottom-hole flowing pressure response and production response of low-permeability oil reservoir production wells before and after pressure drive, applies reservoir engineering methods to establish the functional relationship between different responses, and quickly identifies the fracture parameters of the fractures between wells generated during the pressure drive. It solves the problems of unclear understanding of fracture development and high water channeling risk during the pressure drive of low-permeability oil reservoirs, and realizes the quantitative description of the fractures between wells generated during the pressure drive. It has important theoretical and practical significance for guiding the optimization and adjustment of the pressure drive injection plan and the design of plugging process parameters in the follow-up, and improving the oil displacement efficiency and water injection utilization rate of pressure drive injection.

[0108] Embodiment 2

[0109] For a more intuitive understanding of the application effect of a method for quantifying inter-well fractures during pressure drive in a low-permeability reservoir provided in Example 1, taking the quantification of inter-well fractures during pressure drive in an actual low-permeability tight oil reservoir in China using the above method as an example, the specific implementation manner of the present invention will be described below.

[0110] The average permeability of the reservoir in this low-permeability tight oil reservoir is only 1.01 mD, and the average porosity of the reservoir is 8.95%. There is an obvious phenomenon of "injection failure and production difficulty" during the development process. Therefore, a pair of horizontal well injection-production well group H12 in this reservoir is selected as the test well group, and pressure drive water injection development technology is used for exploitation.

[0111] The production well in the H12 well group was fractured and put into production in December 2015, and the depletion development method was adopted at the initial stage of production. The production well had high water cut immediately after opening. At the initial stage of depletion exploitation, the daily liquid production was 30 t / d, and the daily oil production was about 1 t / d. After that, the production continued to decline. In May 2017, the injection well started to inject water, and the H12 well group adopted the conventional water injection development method. However, the development effect was not ideal, and there was an obvious phenomenon of "injection failure and production difficulty". During the conventional water injection development period, the average daily water injection was 24 t / d, the average daily liquid production was about 3.5 t / d, and the average daily oil production was about 0.3 t / d.

[0112] Recently, the H12 well group carried out a pressure drive water injection development test, and adopted the method of large-displacement intermittent water injection for the injection well for production. During the pressure drive water injection development period, the average daily water injection was about 90 t / d, the average daily liquid production was about 9 t / d, and the average daily oil production was about 0.8 t / d, and the oil displacement effect was improved. After early July 2018, it was changed to conventional water injection. The average daily water injection was about 19 t / d, the daily liquid production was stable at about 8 t / d, and the average daily oil production was about 0.5 t / d. The water injection utilization rate was significantly improved compared with that before pressure drive water injection.

[0113] The production performance curve of the H12 well group is as Figure 3 shown, and the measured bottom-hole flowing pressure curves of the injection and production wells in the H12 well group are as Figure 4 shown.

[0114] From Figure 3 it can be seen that the water cut of the H12 well group has always been relatively high since the start of production. The average water cut was about 91% before pressure drive water injection, 92% during pressure drive water injection, and about 96% after pressure drive water injection. Among them, the high water cut before pressure drive water injection was caused by the fractures or micro-fractures in the reservoir caused by fracturing; during pressure drive water injection, due to the large-displacement water injection of the injection well, the fractures or fissures in the reservoir further increased or expanded, resulting in a further increase in the water cut; the high water cut after pressure drive water injection was caused by the combined action of the reservoir fractures or fissures generated by the previous fracturing and pressure drive water injection. Therefore, the water cut is higher and the rising speed is faster.

[0115] From Figure 4It can be seen that before the pressure-driven water injection in Well Group H12, the bottom-hole flowing pressures of the injection wells and production wells remained basically constant. Therefore, the phenomena of injection failure, production failure, and ineffective water flooding occurred. During the pressure-driven water injection, the bottom-hole flowing pressure of the injection wells decreased significantly, while that of the production wells increased significantly, indicating that under the measure of short-term large-displacement water injection, a new fracture network system was formed, breaking the original flow field solidification phenomenon between the injection and production wells, not only increasing the production but also reducing the water cut. After the pressure-driven water injection ended, the fracture network system formed during the pressure-driven water injection did not close immediately. Therefore, compared with before the pressure-driven water injection, the injection-production pressure difference between the injection and production wells increased significantly (the bottom-hole flowing pressure of the injection wells increased and that of the production wells decreased). This is also the reason why long-term stable liquid production can still be maintained and the oil displacement effect can be improved after the short-term pressure-driven water injection ends.

[0116] It can be seen from this that quickly understanding the fracture development during the pressure-driven process and timely understanding the development location and degree of the dominant seepage channels are of great significance for reducing the risk of water channeling, improving the utilization rate of pressure-driven water injection, and enhancing the oil displacement efficiency. Therefore, using the method for quantifying inter-well fractures during the pressure-driven process in low-permeability oil reservoirs described in this paper and utilizing the actual dynamic monitoring data of the pressure-driven well group, the inter-well fracture parameters are quickly identified through reservoir engineering methods. The specific process is as follows:

[0117] Step 1: According to the actual daily injection volume increase and daily liquid production increase after pressure-driven, the theoretical pressure drop of the production wells during the pressure-driven process is calculated using Formulas (1) to (3), as Figure 5 shown;

[0118] Step 2: According to the actual bottom-hole flowing pressure data of the production wells before and after pressure-driven, the actual pressure drop of the production wells during the pressure-driven process is calculated using Formula (4), as Figure 5 shown;

[0119] Step 3: The theoretical pressure drop is fitted to the actual pressure drop of the production wells to obtain the average inter-well permeability during the pressure-driven water injection, as Figure 6 shown, and the inter-well fracture aperture during the pressure-driven process is calculated using Formula (5), as Figure 7 shown.

[0120] From Figure 6 and Figure 7 it can be seen that during the pressure-driven water injection in Well Group H12, the inter-well fracture network permeability first increased and then gradually decreased. The average permeability of the dominant channels between wells was 28.36 md, and the equivalent fracture aperture was 23.35 μm. Controlled by the inter-well pressure gradient, when the injection volume increased, the inter-well fracture network permeability could increase to more than 40 mD.

[0121] The structure of the present invention is simple. By using the actual dynamic monitoring data of the pressure-driven well group and applying reservoir engineering methods, the inter-well fracture parameters can be quickly identified. It solves the problems such as unclear understanding of fracture development and high water breakthrough risk during the pressure-driven process in low-permeability reservoirs, and realizes the rapid identification of inter-well flow channels and the quantitative description of inter-well fracture parameters. It has important theoretical and practical significance for guiding the optimization and adjustment of the pressure-driven water injection plan and the design of plugging process parameters in the follow-up, and improving the oil displacement efficiency and water injection utilization rate of pressure-driven water injection.

[0122] Embodiment III

[0123] In the specific Embodiment 3 of applying the present invention, the average permeability of the reservoir in a certain actual low-permeability tight oil reservoir in China is only 0.53 mD, and the average porosity of the reservoir is 8.21%. There is an obvious phenomenon of "difficult to inject and difficult to produce" during the development process. Therefore, a pair of horizontal well injection-production well group HP6 in this reservoir is selected as the test well group, and pressure-driven water injection development technology is used for exploitation.

[0124] The production well in the HP6 well group was fractured and put into production in March 2013. In the initial stage, the fracturing fluid was back-produced, and the initial stable water cut was about 20%. The reservoir has good oil-bearing property. In the depletion exploitation stage, the initial stable daily liquid production was 20 t / d, the daily oil production was 10 t / d, and the daily liquid production showed a decreasing trend. In February 2015, the injection well in the HP6 well group started to inject water. The development effect was not ideal by adopting the conventional water injection development method. The average daily water injection was 10 t / d, the average daily liquid production was about 0.5 t / d, and the average daily oil production was about 0.2 t / d.

[0125] Recently, the HP6 well group carried out a pressure-driven water injection development test and adopted the method of large-displacement intermittent water injection for the injection well for production. During the pressure-driven water injection development period, the average daily water injection was about 35 t / d, the average daily liquid production was about 15 t / d, and the average daily oil production was about 2.8 t / d. The oil displacement effect was improved. Then it was changed to conventional water injection. The average daily water injection was about 15 t / d, the daily liquid production was stable at about 10 t / d, and the average daily oil production was about 1.5 t / d. The water injection utilization rate was significantly improved compared with that before pressure-driven water injection.

[0126] Adopt the method for quantifying inter-well fractures during the pressure-driven process in low-permeability reservoirs described in this article. By using the actual dynamic monitoring data of the pressure-driven well group, the inter-well fracture parameters can be quickly identified through reservoir engineering methods. The specific process is as follows:

[0127] Step 1, according to the actual daily increased water injection volume and daily increased liquid production volume after pressure-driven, apply Formulas (1) to (3) to calculate the theoretical pressure drop of the production well during the pressure-driven process, as Figure 8 shown;

[0128] Step 2, according to the actual bottom-hole flowing pressure data of the production well before and after pressure-driven, apply Formula (4) to calculate the actual pressure drop of the production well during the pressure-driven process, as Figure 8 shown;

[0129] Step 3: Fit the theoretical pressure drop according to the actual pressure drop of the oil production well to obtain the average permeability between wells during pressure-driven water injection, as Figure 9 shown. Calculate the fracture aperture between wells during the pressure-driven process using formula (5), as Figure 10 shown.

[0130] From Figure 9 and Figure 10 it can be seen that during the pressure-driven water injection in the HP6 well group, the permeability of the fracture network between the injection and production wells shows a gradually increasing trend, indicating the generation of preferential channels such as fractures or microfractures between the injection and production wells. Among them, the average permeability of the preferential channel between wells is 216.1 md, and the equivalent fracture aperture is 40.05 μm. Controlled by the pressure gradient between wells, the permeability of the fracture network between wells can increase to more than 980 mD when the injection volume increases.

[0131] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

[0132] Except for the technical features described in the specification, the rest are known technologies to those skilled in the art.

Claims

1. A method for quantifying interwell fractures during pressure flooding of low permeability reservoirs, characterized in that: The interwell fracture quantification method during the pressure flooding process of the low permeability reservoir includes: Step 1, calculating the theoretical pressure drop of the oil production well during the pressure drive process according to the actual daily increased water injection volume and the daily increased liquid production volume after the pressure drive; Step 2, calculating the actual pressure drop of the oil production well during the pressure drive process according to the actual bottom hole flow pressure data of the oil production well before and after the pressure drive; Step 3: Fit the theoretical pressure drop according to the actual pressure drop of the oil production well to calculate the aperture of the inter-well fractures during the pressure drive process.

2. The method for quantifying interwell fractures during pressure flooding of low permeability reservoirs according to claim 1, characterized in that: In step 1, the bottom hole pressure curve and the liquid production curve of the oil production well before the pressure drive remain basically unchanged, and the bottom hole pressure curve and the liquid production curve of the oil production well after the pressure drive show a significant rise phenomenon.

3. The method for quantifying interwell fractures during pressure flooding of low permeability reservoirs according to claim 2, characterized in that: Step 1 includes: Step 11, based on the daily increased water injection volume of the water injection well after pressure drive, calculate the theoretical pressure drop caused by the increased water injection volume of the injection well at the oil production well; Step 12, calculating the theoretical pressure drop at the oil production well caused by the increase in liquid production according to the daily increase in liquid production of the oil production well after pressure drive; Step 13, according to the principle of pressure drop superposition, calculate the theoretical pressure drop of the oil production well during the pressure drive process.

4. The method for quantifying interwell fractures during pressure flooding of low permeability reservoirs according to claim 3, characterized in that: In step 11, the formula for calculating the theoretical pressure drop caused by increasing the water injection volume at the oil production well is: In the formula, Δp 注 (t) is the theoretical pressure drop at the production well caused by increasing the water injection rate, MPa; Δq inj The daily water injection volume increased after the injection well is injected by pressure drive, i.e., the daily increased water injection volume, m 3 / d; μ is the average viscosity of the fluid between the injection and production wells, mPa·s; K is the average permeability between the injection and production wells, mD; h is the average effective reservoir thickness between the injection and production wells, m; L is the distance between the injection and production wells, m; Δt1 is the time corresponding to the start of pressure drive and injection of the injection well, d; is the power integral function; η is the pressure conductivity between injection and production wells; Ф is the average porosity of the reservoir, f; C t is the comprehensive compressibility coefficient of the reservoir, MPa -1 .

5. The method for quantifying interwell fractures during pressure flooding of low permeability reservoirs according to claim 4, characterized in that: In step 12, the formula for calculating the theoretical pressure drop at the oil production well caused by the increase in liquid production is: Where: Δp 采 (t) is the theoretical pressure drop caused by the increase in liquid production at the oil well, MPa; q pro is the daily increased liquid production of the oil well after pressure drive, i.e., the daily increased liquid production, m 3 / d;q con is the daily liquid production of the oil well before pressure drive, m 3 / d; μ2 is the average viscosity of the fluid near the oil well, mPa·s; K2 is the average permeability near the oil well, mD; h2 is the reservoir thickness at the oil well point, m; r w is the wellbore radius of the oil well, m; η2 is the pressure conductivity coefficient near the oil well; Δt2 is the time corresponding to the increase in daily liquid production of the oil well, d.

6. The method for quantifying interwell fractures during pressure flooding of low permeability reservoirs according to claim 5, characterized in that: In step 13, the formula for calculating the theoretical pressure drop of the oil production well during the pressure drive process is: Δp 理论 (t)=Δp 注 (t)-Δp 采 (t) (3) In the formula, Δp 理论 (t) is the theoretical pressure drop of the oil well during the pressure drive process, MPa.

7. The method for quantifying interwell fractures during pressure flooding of low permeability reservoirs according to claim 1, characterized in that: In step 2, the actual pressure drop calculation formula of the oil well during the pressure drive process is: Δp 实际 (t)=p 实际 (t)-p con (4) In the formula, Δp 实际 (t) is the actual pressure drop of the oil well during the pressure drive process, MPa; p 实际 (t) is the actual bottom hole pressure of the oil well after pressure drive, MPa; p con It is the actual bottom hole flowing pressure of the oil well before pressure drive, MPa.

8. The method for quantifying interwell fractures during pressure flooding of low permeability reservoirs according to claim 1, characterized in that: In step 3, the theoretical pressure drop is fitted according to the actual pressure drop of the production well, and the average permeability between the injection and production wells can be obtained.

9. The method for quantifying interwell fractures during pressure flooding of low permeability reservoirs according to claim 8, characterized in that: In step 3, microcracks or fissures are generated between the injection and production wells after the pressure drive, which become the main source of fluid seepage capacity during the pressure drive process; therefore, the inter-well fracture aperture during the pressure drive process can be calculated based on the functional relationship between the average permeability between the injection and production wells and the fracture aperture.

10. The method for quantifying interwell fractures during pressure flooding of low permeability reservoirs according to claim 9, characterized in that: In step 3, the calculation formula of the crack opening is: Where b is the fracture aperture, μm; K is the average permeability between injection and production wells, D; and c is the influence coefficient of roughness and tortuosity on fracture permeability.

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