Method for quantitatively predicting dynamic permeability of fractured oil and gas reservoir fractures

Abstract

The invention relates to the technical field of oil exploration, in particular to a quantitative prediction method for dynamic permeability of fractures of fractured oil and gas reservoirs. According to the method, an underground crack-free rock core sample is adopted for artificial crack forming, and a relation chart of the confining pressure and the actually-measured crack permeability is obtained; the method comprises the following steps: predicting effective stress change in a development process by utilizing actual measurement formation pressure data of a single well, carrying out numerical simulation of effective stress in the development process on the basis of finite element modeling, and determining a relationship between effective stress of a target well and production time; and establishing a relationship between the effective stress of the target well and the fracture permeability in combination with a calculation result of the fracture permeability of the single well imaging logging, and further establishing a relationship between the production time and the fracture dynamic permeability, thereby realizing quantitative prediction of the change of the fracture dynamic permeability in the development process.

Description

Technical Field

[0001] The present disclosure relates to the technical field of petroleum exploration, and in particular to a quantitative prediction method for the dynamic permeability of fractures in fractured oil and gas reservoirs. Background Art

[0002] With the exploration and development of unconventional oil and gas, fractured reservoirs have become a key area of ​​exploration and development. In these reservoirs, fractures serve as crucial oil and gas storage spaces and primary seepage pathways, increasing matrix permeability by 2–3 orders of magnitude or even more. However, fractures are highly sensitive to effective stress. As formation pressure decreases and effective stress increases during oil and gas development, fracture permeability decreases rapidly. Without appropriate measures, well production may experience high initial yields followed by a rapid decline in later stages. Therefore, understanding the dynamics of fracture permeability during well development and initiating appropriate development strategies is crucial for maintaining long-term high and stable production in fractured reservoirs.

[0003] Existing technologies, through core experimental analysis and mathematical models, measure the fracture permeability under different confining pressures by changing the confining pressure, and study the variation characteristics of fracture permeability with effective stress. However, they cannot predict the quantitative variation law of fracture dynamic permeability at the gas reservoir scale. Therefore, they are only of theoretical significance or can only qualitatively propose macro-development measures for gas reservoirs, but cannot make quantitative predictions. Summary of the Invention

[0004] In response to the above problems, the present disclosure provides a method for quantitatively predicting the dynamic permeability of fractures in fractured oil and gas reservoirs, which is used to solve the problem that the existing technology cannot perform quantitative prediction.

[0005] A method for quantitatively predicting the dynamic permeability of fractures in fractured oil and gas reservoirs, the method comprising:

[0006] Establish a finite element model based on the structural contour data of the target layer and the formation rock mechanics parameters;

[0007] Apply boundary stress conditions to the finite element model to obtain the effective stress plane distribution diagram;

[0008] In the effective stress plane distribution map, the coordinate point without drilling where the fracture dynamic permeability prediction is to be carried out is used as a virtual well, and the effective stress of the virtual well coordinate point is read from the effective stress plane distribution map;

[0009] Based on the imaging logging data, a plane contour map of the fracture permeability in the current state is drawn, and the fracture permeability of the virtual well is read from it;

[0010] Artificial fractures were created using downhole core samples without fractures to obtain a graph showing the relationship between confining pressure and measured fracture permeability. The effective stress and fracture permeability of the virtual well were projected onto the graph showing the relationship between confining pressure and measured fracture permeability, and a curve showing the relationship between the effective stress and fracture permeability of the virtual well was obtained by interpolation.

[0011] Through multiple simulations in the effective stress plane distribution diagram, a relationship curve between the effective stress of the virtual well and the time from production was established;

[0012] Based on the relationship curves between the effective stress of the virtual well and the fracture permeability, and the relationship curves between the effective stress of the virtual well and the time to production, a relationship curve between the time to production and the dynamic permeability of the fracture is established;

[0013] The fracture permeability of the virtual well at a specific time from the start of gas reservoir production can be quantitatively predicted using the relationship curve between the time from production and the dynamic permeability of the fracture.

[0014] Furthermore, a finite element model is established based on the structural contour data of the target layer and the rock mechanics parameters of the formation, including:

[0015] Import high-value data of the target layer structure into the finite element analysis software to establish a geological model; assign the formation rock mechanics parameters to the geological model, divide the grid to form a finite element model.

[0016] Furthermore, boundary stress conditions are applied to the finite element model to obtain the effective stress plane distribution diagram, including:

[0017] Taking the effective stress of several wells at a specific time from the current date as a constraint, boundary stress conditions are imposed on the finite element model, and a numerical simulation of the effective stress is performed to obtain a planar distribution diagram of the effective stress.

[0018] Furthermore, the effective stress of several wells at a specific time from the current date includes:

[0019] The effective stress of a well on different dates is obtained by subtracting the in-situ stress data interpreted from well logging and the formation pressure measured on multiple dates.

[0020] The difference between multiple different dates and the date of gas reservoir production is used as the horizontal axis, that is, the time from production is used as the horizontal axis, and the corresponding effective stress is used as the vertical axis to obtain the relationship curve between the two;

[0021] Calculate the effective stress of the well at a specific time from the date of production through the relationship curve;

[0022] The same method is used to calculate the effective stress of other wells at a specific time from the production date, and the effective stress of several wells at a specific time from the current date is obtained.

[0023] Furthermore, based on the imaging logging data, a plane contour map of the fracture permeability in the current state is drawn, and the fracture permeability of the virtual well is read from it, including:

[0024] The fracture permeability of a single well is calculated based on the fracture line density and effective aperture parameters obtained from the interpretation of single-well imaging logging. Based on the data from several wells, a plane contour map of the fracture permeability in the current state is drawn, from which the fracture permeability of the virtual well is read.

[0025] Furthermore, the fracture permeability of a single well is calculated based on the fracture line density and effective aperture parameters obtained from the interpretation of single-well imaging logging, including:

[0026] The fracture permeability of a single well is calculated using the following formula:

[0027] K=b 3 D / 12×10 15

[0028] Where K is the crack permeability, 10 -3 μm 2 ; b is the effective crack opening, m; D is the crack line density, m -1 .

[0029] Furthermore, artificial fractures are created using downhole core samples without fractures, including:

[0030] Core samples should be complete, relatively dense and uniform, with no obvious cracks on the surface and a length greater than 8 cm. The number of core samples should be no less than 3.

[0031] Cut the two ends of the selected core sample into smooth sections, place it in a rock pressurizing device, and pressurize along the axis of the core sample until cracks appear in the core;

[0032] The core analysis method was used to test the physical properties of the core samples with artificial fractures to obtain the measured fracture permeability.

[0033] Furthermore, when selecting cores, for cores containing oil and gas or drilled with oil-based mud, the drilled plug samples must be washed with oil and dried.

[0034] Furthermore, a graph showing the relationship between confining pressure and measured fracture permeability is obtained, including:

[0035] Select a core sample and gradually increase the confining pressure of the core sample at fixed pressure intervals. Use core analysis methods to test the physical properties of the core sample after each change in confining pressure to obtain the measured fracture permeability.

[0036] Count the confining pressure value and the corresponding measured fracture permeability at each time, and draw an intersection diagram of the two to obtain the relationship curve between confining pressure and measured fracture permeability;

[0037] Repeat the above steps for the remaining core samples to obtain the relationship curves between confining pressure and measured fracture permeability under different initial fracture permeabilities, and form a relationship chart between confining pressure and measured fracture permeability.

[0038] Furthermore, based on the relationship curves between the virtual well effective stress and the fracture permeability, and the relationship curves between the virtual well effective stress and the time to production, a relationship curve between the time to production and the dynamic permeability of the fracture is established, including:

[0039] Through the relationship curve between the effective stress of the virtual well and the time from production, multiple effective stress values ​​at a specific time from the production date are obtained and substituted into the relationship curve between the effective stress of the virtual well and the fracture permeability to calculate the corresponding fracture permeability. A relationship curve between the time from production and the corresponding fracture permeability is established with the time from production as the horizontal axis and the corresponding fracture permeability as the vertical axis.

[0040] The present disclosure has at least the following beneficial effects:

[0041] The present invention discloses an intuitive, quantitative and easy-to-operate method for quantitatively predicting the dynamic permeability of fractures during the development of fractured oil and gas reservoirs. Based on artificial fracture creation, fracture permeability testing under different confining pressures, effective stress numerical simulation and imaging logging fracture permeability calculation, the method can effectively quantitatively predict the dynamic permeability of fractures during the development of fractured oil and gas reservoirs and guide the formulation of development measures.

[0042] Other features and advantages of the present disclosure will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present disclosure. The purpose and other advantages of the present disclosure can be achieved and obtained through the structures indicated in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0044] Figure 1 This is a flow chart of a method for quantitatively predicting dynamic permeability of fractures according to an embodiment of the present disclosure;

[0045] Figure 2 Schematic diagram of the relationship curve between the experimental confining pressure and the measured fracture permeability in the embodiment;

[0046] Figure 3 Schematic diagram of effective stress change curve during the development process of the embodiment;

[0047] Figure 4 This is a schematic diagram of the numerical simulation results of effective stress 90 months after the embodiment was put into production;

[0048] Figure 5 Schematic diagram of the relationship between the effective stress of the virtual well and the fracture permeability;

[0049] Figure 6 Schematic diagram of the fracture dynamic permeability prediction curve during the virtual well development process. DETAILED DESCRIPTION

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present disclosure, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present disclosure without making any creative efforts shall fall within the scope of protection of the present disclosure.

[0051] Existing technologies, through core experimental analysis and mathematical models, measure the fracture permeability under different confining pressures by changing the confining pressure, and study the variation characteristics of fracture permeability with effective stress. However, they cannot predict the quantitative variation law of fracture dynamic permeability at the gas reservoir scale. Therefore, they are only of theoretical significance or can only qualitatively propose macro-development measures for gas reservoirs, but cannot make quantitative predictions.

[0052] To this end, this paper proposes a quantitative prediction method for the dynamic permeability of fractures in fractured oil and gas reservoirs. This method uses downhole core samples without fractures to artificially create fractures and obtain a relationship chart between confining pressure and measured fracture permeability. The method uses single-well measured formation pressure data to predict changes in effective stress during development. Based on finite element modeling, the method conducts numerical simulations of effective stress during development to clarify the relationship between the effective stress of the target well and the time to production. Combined with the calculation results of fracture permeability from single-well imaging logging, the method establishes a relationship between the effective stress of the target well and the fracture permeability, and further establishes a relationship between the time to production and the dynamic permeability of the fracture, thereby achieving a quantitative prediction of changes in the dynamic permeability of the fracture during development.

[0053] like Figure 1 As shown, a method for quantitatively predicting the dynamic permeability of fractures in fractured oil and gas reservoirs comprises:

[0054] Establish a finite element model based on the structural contour data of the target layer and the formation rock mechanics parameters;

[0055] Apply boundary stress conditions to the finite element model to obtain the effective stress plane distribution diagram;

[0056] In the effective stress plane distribution map, the coordinate point without drilling where the fracture dynamic permeability prediction is to be carried out is used as a virtual well, and the effective stress of the virtual well coordinate point is read from the effective stress plane distribution map;

[0057] Based on the imaging logging data, a plane contour map of the fracture permeability in the current state is drawn, and the fracture permeability of the virtual well is read from it;

[0058] Artificial fractures were created using downhole core samples without fractures to obtain a graph showing the relationship between confining pressure and measured fracture permeability. The effective stress and fracture permeability of the virtual well were projected onto the graph showing the relationship between confining pressure and measured fracture permeability, and a curve showing the relationship between the effective stress and fracture permeability of the virtual well was obtained by interpolation.

[0059] Through multiple simulations in the effective stress plane distribution diagram, a relationship curve between the effective stress of the virtual well and the time from production was established;

[0060] Based on the relationship curves between the effective stress of the virtual well and the fracture permeability, and the relationship curves between the effective stress of the virtual well and the time to production, a relationship curve between the time to production and the dynamic permeability of the fracture is established;

[0061] The fracture permeability of the virtual well at a specific time from the start of gas reservoir production can be quantitatively predicted using the relationship curve between the time from production and the dynamic permeability of the fracture.

[0062] The specific implementation is as follows:

[0063] 1. Core sample selection and artificial fracture creation

[0064] (1) Core sample selection. Core samples should be complete, relatively dense and uniform in lithology, with no obvious cracks on the surface and a length greater than 8 cm. For cores containing oil and gas or drilled with oil-based mud, the drilled plug samples must be washed with oil and dried. The number of core samples should be no less than 3.

[0065] (2) Artificial cracking: Cut the two ends of the selected core sample into smooth sections, place it in a rock pressure device, and apply pressure along the axis of the core sample until cracks appear in the core.

[0066] (3) The physical properties of the artificially fractured core samples were tested using the conventional core analysis method (SY / T 5336-2006) to obtain the measured fracture permeability (gas phase fracture permeability or oil phase fracture permeability), which is the initial fracture permeability of the core sample.

[0067] 2. Establishment of a chart showing the relationship between confining pressure and measured fracture permeability

[0068] (1) Select a sample and gradually increase the confining pressure of the core sample at a certain pressure interval. Then, perform physical property tests on the core sample after each change of confining pressure according to the conventional core analysis method (SY / T 5336-2006) to obtain the measured fracture permeability.

[0069] (2) Count the confining pressure value and the corresponding measured crack permeability at each time, and draw an intersection diagram of the two to obtain the correlation formula between the confining pressure and the measured crack permeability.

[0070] (3) Repeat the above steps for the remaining core samples to obtain the correlation equation between the confining pressure and the measured fracture permeability under different initial fracture permeabilities, and form a relationship chart between the confining pressure and the measured fracture permeability.

[0071] 3. Calculation of effective stress during development

[0072] (1) The geostress data interpreted by well logging and the formation pressure measured on multiple dates are statistically analyzed, and the effective stress of the well on different dates is obtained by subtracting the two.

[0073] (2) Using the difference between the above-mentioned multiple dates and the gas reservoir's production date (i.e., the time since the start of production) as the horizontal axis and the corresponding effective stress as the vertical axis, a relationship curve and mathematical expression are obtained. The mathematical expression is used to calculate the effective stress of the well at a specific time from the start of production. The same method is used to calculate the effective stress of other wells at a specific time from the start of production.

[0074] 4. Numerical simulation of effective stress

[0075] (1) Import the target layer structure contour data into the finite element analysis software to establish a geological model. Then import the formation rock mechanics parameters and assign them to the geological model. Use the appropriate grid edge length to divide the grid and form a finite element model.

[0076] (2) Using the effective stress of multiple wells determined in step 3(2) at a specific time from the current date as a constraint, a boundary stress condition is imposed on the finite element model, and a numerical simulation of the effective stress is performed to obtain a plane distribution diagram of the effective stress. The coordinate point without a well for which the dynamic permeability prediction of the fracture is to be carried out is used as a virtual well, and the effective stress of the virtual well coordinate point is read from the plane distribution diagram of the effective stress. Through multiple simulations, a relationship curve and a mathematical relationship between the effective stress of the virtual well and the time from production are established.

[0077] 5. Quantitative prediction of fracture dynamic permeability

[0078] (1) Based on the fracture line density, effective aperture and other parameters obtained from the interpretation of single-well imaging logging, the current fracture permeability is calculated. Using the data of multiple wells, a plane contour map of the fracture permeability under the current state is drawn, from which the fracture permeability of the above-mentioned virtual well is read.

[0079] (2) The current effective stress and fracture permeability of the virtual well are projected onto the relationship chart between the confining pressure and the measured fracture permeability established in step 2, and the relationship curve and mathematical relationship of the effective stress and fracture permeability of the virtual well are obtained by interpolation.

[0080] (3) Using the mathematical relationship between effective stress and time from production determined in step 4(2), obtain multiple effective stress values ​​at a specific time from the gas reservoir production date, and substitute them into the mathematical relationship in step 5(2) to calculate the corresponding fracture permeability. With the time from gas reservoir production (in months or years) as the horizontal axis and the corresponding fracture permeability as the vertical axis, a relationship curve and mathematical relationship are established between the two. Using this curve and mathematical relationship, the fracture permeability of the virtual well at a specific time from gas reservoir production can be quantitatively predicted.

[0081] By applying this disclosure, it is possible to quantitatively predict the changing patterns of fracture dynamic permeability during the development of fractured oil and gas reservoirs, thereby guiding the formulation of development measures. Compared with existing methods that rely solely on experiments, this disclosure combines experimental conclusions with effective stress calculations and numerical simulations of oil and gas reservoirs, fracture geological characteristics, and other factors for the first time, and applies them to the prediction of fracture dynamic permeability during the actual development of fractured oil and gas reservoirs. This method is more practical and highly operational. Using this disclosure, good application results have been achieved in the prediction of fracture dynamic permeability during actual gas reservoir development, accurately predicting the changing patterns of fracture dynamic permeability during the development process, which has important guiding significance for the formulation of next-step development measures.

[0082] In order to enable those skilled in the art to better understand the present disclosure, the principles of the present disclosure are described as follows with reference to the accompanying drawings:

[0083] Taking a gas reservoir as an example, the quantitative prediction method for the dynamic permeability of fractures in fractured oil and gas reservoirs described in this patent is explained.

[0084] 1. Core sample selection and artificial fracture creation

[0085] (1) Core sample selection. Core samples should be complete, relatively dense and uniform in lithology, with no obvious cracks on the surface and a length greater than 8 cm. For cores containing oil and gas or drilled with oil-based mud, the drilled plug samples must be washed with oil and dried. A total of three core samples were selected from this gas reservoir for sample preparation experiments.

[0086] (2) Artificial cracking. Cut the selected core sample into smooth sections at both ends and place it in a rock pressurization device. Pressurize the core sample along its axis until cracks appear in the core. The best sample is one with a vertical straight crack in the middle of the sample, followed by cracks at a certain angle. If the sample shatters during the pressurization process, it is an unqualified sample and should be resampled.

[0087] (3) The physical properties of the artificially fractured core samples were tested using the conventional core analysis method (SY / T 5336-2006) to obtain the measured fracture permeability (gas phase fracture permeability or oil phase fracture permeability), which is the initial fracture permeability of the core sample.

[0088] 2. Fracture permeability test under different confining pressures

[0089] (1) Select a sample and gradually increase the confining pressure of the core sample at a certain pressure interval. Physical properties of the core sample after each change in confining pressure are tested according to the conventional core analysis method (SY / T 5336-2006) to obtain the measured fracture permeability. The minimum confining pressure used in the gas reservoir rock sample experiment was 10 MPa, the maximum confining pressure was 90 MPa, and the confining pressure interval was 10 MPa.

[0090] (2) Statistically calculate the confining pressure value and the corresponding measured fracture permeability at each time, and draw a cross-plot of the two to obtain the correlation equation between the confining pressure and the measured fracture permeability. Use linear, exponential, logarithmic, and polynomial methods to fit the curve, and select the curve equation with the highest correlation coefficient. For this gas reservoir, the exponential equation is used to fit the curve ( Figure 2 ).

[0091] (3) Repeat the above steps for the remaining two core samples to obtain the correlation equation between confining pressure and measured fracture permeability under different initial fracture permeabilities, and form a graph showing the relationship between confining pressure and measured fracture permeability ( Figure 2 ).

[0092] 3. Calculation of effective stress during development

[0093] (1) The in-situ stress data interpreted by well logging and the formation pressure measured on multiple dates are calculated and subtracted to obtain the effective stress of the well on different dates. For example, if the in-situ stress interpreted by well logging for Well 202 is 155 MPa and the formation pressure measured on a certain date is 103 MPa, then the effective stress is 155 - 103 = 52 MPa.

[0094] (2) With the difference between the above multiple dates and the date of gas reservoir commissioning (i.e., the time from commissioning) as the horizontal axis and the corresponding effective stress as the vertical axis, the relationship curve and mathematical relationship between the two are obtained ( Figure 3 ). Use this mathematical expression to calculate the effective stress of the well at a specific time from the date of commissioning. For example, when the well 201 is 30 months from the date of commissioning, substitute Figure 3 The mathematical relationship in [1] yields an effective stress of 64.1 MPa. The same method was used to calculate the effective stresses of the other eight wells in the gas reservoir 30 months after they were put into production.

[0095] 4. Numerical simulation of effective stress during development

[0096] (1) Import the target layer structural contour data into the finite element analysis software to establish a geological model. Then, import the formation rock mechanical parameters and assign them to the geological model. The grid is divided using an appropriate grid edge length to form a finite element model. The gas reservoir model was modeled using the general finite element analysis software ANSYS 10.0. The rock mechanical parameters were based on the results of rock mechanical experiments and well logging data interpretation. The grid unit type used was Solid45. The grid edge length of the formation was 300m, and the grid edge length of the fault was 100m.

[0097] (2) Taking the effective stress of multiple wells determined in step 3 (2) at a specific time from the current date as a constraint, the boundary stress condition is imposed on the finite element model, and the effective stress is numerically simulated to obtain the plane distribution map of the effective stress. The coordinate point without drilling where the dynamic permeability prediction of fractures is required is taken as the virtual well A, and the effective stress of the coordinate point of the virtual well A is read from the plane distribution map of the effective stress. And through multiple simulations, the relationship curve and mathematical relationship between the effective stress of the virtual well A and the time from production are established. For this gas reservoir, the effective stress every 10 months after 240 months of production is numerically simulated, and the numerical simulation results of the effective stress after 90 months of production are as follows. Figure 4 The location of the virtual well A where the dynamic permeability prediction of fractures needs to be carried out is shown in Figure 4 As shown, it can be seen from the figure that the effective stress of the virtual well A is 84.5 MPa.

[0098] 5. Quantitative prediction of fracture permeability during development

[0099] (1) Based on the fracture line density, effective aperture and other parameters obtained from the interpretation of single-well imaging logging, the current fracture permeability is calculated. Using the data of multiple wells, a plane contour map of the fracture permeability under the current state is drawn, from which the fracture permeability of the above-mentioned virtual well A is read. The formula for calculating fracture permeability using fracture density and aperture is:

[0100] K=b 3 D / 12×10 15

[0101] Where K is the crack permeability, 10 -3 μm 2 ; b is the effective crack opening, m; D is the crack line density, m -1 .

[0102] (2) The current effective stress of virtual well A (for this gas reservoir, the current time is 60 months from the time of commissioning, so the numerical simulation result of the effective stress 60 months from the time of commissioning is used) and the fracture permeability are projected onto the relationship chart between confining pressure and measured fracture permeability established in step 2, and the relationship curve and mathematical relationship between the effective stress and fracture permeability of virtual well A are obtained by interpolation. The effective stress of virtual well A in the current state is 56.8 MPa, and the fracture permeability is 4.6×10 -3 μm 2 , project this point onto the relationship chart between the experimental confining pressure and the measured fracture permeability established in step 2(3), and obtain the permeability change curve passing through this point through mathematical interpolation, which is the relationship curve between the effective stress of virtual well A and the fracture permeability and the mathematical relationship ( Figure 5 Based on this curve, the fracture permeability of virtual well A under any effective stress can be calculated.

[0103] (3) Using the mathematical relationship between effective stress and time from production determined in step 4(2), obtain multiple effective stress values ​​at a specific time from the date of gas reservoir production, and substitute them into the mathematical relationship in step 5(2) to calculate the corresponding fracture permeability. With the time from gas reservoir production (in months or years) as the horizontal coordinate and the corresponding fracture permeability as the vertical coordinate, a relationship curve and mathematical relationship between the two are established. The curve and mathematical relationship can be used to quantitatively predict the fracture permeability of the virtual well at a specific time from gas reservoir production. The relationship between the time from production and fracture permeability of virtual well A is as follows: Figure 6 For example, 96 months after the start of production, Figure 6 The fracture permeability can be calculated as 1.13×10 -3 μm 2 .

[0104] Although the present disclosure has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present disclosure.

Claims

1. A method for quantitatively predicting the dynamic permeability of fractures in fractured oil and gas reservoirs, characterized in that: The method comprises: Establish a finite element model based on the structural contour data of the target layer and the formation rock mechanics parameters; Apply boundary stress conditions to the finite element model to obtain the effective stress plane distribution diagram; In the effective stress plane distribution map, the coordinate point without drilling where the fracture dynamic permeability prediction is to be carried out is used as a virtual well, and the effective stress of the virtual well coordinate point is read from the effective stress plane distribution map; Based on the imaging logging data, a plane contour map of the fracture permeability in the current state is drawn, and the fracture permeability of the virtual well is read from it; Artificial fractures were created using downhole core samples without fractures to obtain a graph showing the relationship between confining pressure and measured fracture permeability. The effective stress and fracture permeability of the virtual well were projected onto the graph showing the relationship between confining pressure and measured fracture permeability, and a curve showing the relationship between the effective stress and fracture permeability of the virtual well was obtained by interpolation. Through multiple simulations in the effective stress plane distribution diagram, a relationship curve between the effective stress of the virtual well and the time from production was established; Based on the relationship curves between the effective stress of the virtual well and the fracture permeability, and the relationship curves between the effective stress of the virtual well and the time to production, a relationship curve between the time to production and the dynamic permeability of the fracture is established; The fracture permeability of the virtual well at a specific time from the start of gas reservoir production can be quantitatively predicted using the relationship curve between the time from production and the dynamic permeability of the fracture.

2. The method for quantitatively predicting the dynamic permeability of fractures in fractured oil and gas reservoirs according to claim 1, characterized in that: Based on the structural contour data of the target layer and the formation rock mechanics parameters, a finite element model is established, including: Import high-value data of the target layer structure into the finite element analysis software to establish a geological model; assign the formation rock mechanics parameters to the geological model, divide the grid to form a finite element model.

3. The method for quantitatively predicting dynamic permeability of fractures in fractured oil and gas reservoirs according to claim 1, characterized in that: Apply boundary stress conditions to the finite element model to obtain the effective stress plane distribution diagram, including: Taking the effective stress of several wells at a specific time from the current date as a constraint, boundary stress conditions are imposed on the finite element model, and a numerical simulation of the effective stress is performed to obtain a planar distribution diagram of the effective stress.

4. The method for quantitatively predicting dynamic permeability of fractures in fractured oil and gas reservoirs according to claim 3, characterized in that: The effective stress of several wells at a specific time from the current date, including: The in-situ stress data interpreted from well logging and the formation pressure measured on multiple dates are statistically analyzed. The effective stress of the well on different dates is obtained by subtracting the in-situ stress from the formation pressure. The difference between multiple different dates and the date of gas reservoir production is used as the horizontal axis, that is, the time from production is used as the horizontal axis and the corresponding effective stress is used as the vertical axis to obtain the relationship curve between the time from production and the effective stress; Calculate the effective stress of the well at a specific time from the date of production through the relationship curve; The same method is used to calculate the effective stress of other wells at a specific time from the production date, and the effective stress of several wells at a specific time from the current date is obtained.

5. The method for quantitatively predicting dynamic permeability of fractures in fractured oil and gas reservoirs according to claim 1, characterized in that: Based on the imaging logging data, a plane contour map of the fracture permeability in the current state is drawn, and the fracture permeability of the virtual well is read from it, including: The fracture permeability of a single well is calculated based on the fracture line density and effective aperture parameters obtained from the interpretation of single-well imaging logging. Based on the data from several wells, a plane contour map of the fracture permeability in the current state is drawn, from which the fracture permeability of the virtual well is read.

6. The method for quantitatively predicting dynamic permeability of fractures in fractured oil and gas reservoirs according to claim 5, characterized in that: The fracture permeability of a single well is calculated based on the fracture line density and effective aperture parameters obtained from the interpretation of single-well imaging logging, including: The fracture permeability of a single well is calculated using the following formula: K=b 3 D / 12×10 15 Where K is the crack permeability, 10 -3 μm 2 ; b is the effective crack opening, m; D is the crack line density, m -1 .

7. The method for quantitatively predicting dynamic permeability of fractures in fractured oil and gas reservoirs according to claim 1, characterized in that: Artificial fracture creation is performed using downhole core samples without fractures, including: The core samples should be complete, relatively dense and uniform, with no obvious cracks on the surface and a length greater than 8 cm. The number of core samples should be no less than 3. Cut the two ends of the selected core sample into smooth sections, place it in a rock pressurizing device, and pressurize along the axis of the core sample until cracks appear in the core; The core analysis method was used to test the physical properties of the core samples with artificial fractures to obtain the measured fracture permeability.

8. The method for quantitatively predicting dynamic permeability of fractures in fractured oil and gas reservoirs according to claim 7, characterized in that: When selecting cores, for cores containing oil and gas or drilled with oil-based mud, the drilled plug samples must be washed with oil and dried.

9. The method for quantitatively predicting dynamic permeability of fractures in fractured oil and gas reservoirs according to claim 1, characterized in that: Obtain a graph showing the relationship between confining pressure and measured fracture permeability, including: Select a core sample and gradually increase the confining pressure of the core sample at a fixed pressure interval. Use the core analysis method to test the physical properties of the core sample after each change in confining pressure to obtain the measured fracture permeability. Count the confining pressure value and the corresponding measured fracture permeability at each time, and draw a cross-plot of the confining pressure value and the measured fracture permeability to obtain a relationship curve between the confining pressure and the measured fracture permeability; Repeat the above steps for the remaining core samples to obtain the relationship curves between confining pressure and measured fracture permeability under different initial fracture permeabilities, and form a relationship chart between confining pressure and measured fracture permeability.

10. The method for quantitatively predicting dynamic permeability of fractures in fractured oil and gas reservoirs according to claim 1, characterized in that: Based on the relationship curves between the virtual well effective stress and the fracture permeability, and the relationship curves between the virtual well effective stress and the time to production, a relationship curve between the time to production and the dynamic permeability of the fracture is established, including: Through the relationship curve between the effective stress of the virtual well and the time from production, multiple effective stress values ​​at a specific time from the production date are obtained and substituted into the relationship curve between the effective stress of the virtual well and the fracture permeability to calculate the corresponding fracture permeability. With the time from production as the horizontal axis and the corresponding fracture permeability as the vertical axis, a relationship curve between the time from production and the dynamic permeability of the fracture is established.

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