Shale gas well production prediction method and system based on depletion development curve
By using a method based on depletion development curves and establishing a power function relationship through fracture-free matrix core experiments, the problem of accuracy in shale gas well production prediction was solved, achieving a simple and rapid production prediction effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2021-05-08
- Publication Date
- 2026-03-31
AI Technical Summary
Existing methods for predicting shale gas well production suffer from problems such as large prediction discrepancies, difficulty in handling mathematical analytical methods, and insufficient reasonableness of numerical simulation model assumptions, leading to inaccurate production capacity assessments.
Using a method based on the depletion development curve, a power function relationship between gas production rate and production time was established through laboratory simulation experiments with fracture-free matrix cores. The depletion development curve in the matrix-controlled stage was determined, and production was predicted in conjunction with gas well parameters.
It enables simple, fast, and accurate shale gas well production prediction, improving the accuracy of production capacity assessment.
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Figure CN115310252B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of shale gas exploration and development technology, and specifically relates to a method and system for predicting shale gas well production based on depletion development curves. Background Technology
[0002] Shale gas is an unconventional natural gas that is generated and stored in dark mudstone or high-carbon mudstone, with a wide distribution and great development potential. Currently, shale gas wells are generally commercially exploited after volumetric fracturing in horizontal wells. Production prediction and capacity evaluation are core indicators for assessing the development effectiveness of shale gas fields. Current production prediction methods include empirical methods, mathematical analytical methods, and numerical simulation methods. Empirical methods depend heavily on the processing of well production data and the selection of methods; the predictions from different empirical methods often vary significantly. Furthermore, the multi-scale, multi-flow, and transport mechanisms and characteristics of shale gas inevitably lead to multiple complex state equations in mathematical expression. Mathematical analytical methods struggle to perform equivalent processing and computational solutions. Numerical simulation methods typically employ shale gas fracturing horizontal well capacity prediction numerical models, such as dual-medium models, multi-medium models, and complex fracture network capacity models. However, the rationality and practicality of the model assumptions used in production analysis need further improvement. Summary of the Invention
[0003] The purpose of this invention is to provide a method that can more accurately predict the production of shale gas wells.
[0004] To achieve the above objectives, the present invention provides a method for predicting shale gas well production based on a depletion development curve, wherein the method includes:
[0005] The steps for determining the exponent of the matrix-controlled stage exhaustion development curve are as follows: A laboratory simulation experiment of exhaustion development is conducted using fracture-free matrix cores from the production layer of the target well's reservoir. A power function relationship (a power function relationship with coefficients, where the coefficients cannot be equal to 0) is established between the gas production rate and production time. Based on the exponent of the power function relationship, the exponent of the matrix-controlled stage exhaustion development curve is determined, thus obtaining the matrix-controlled stage exhaustion development curve with a determined exponent and undetermined coefficients. The matrix-controlled stage exhaustion development curve is a power function relationship (a power function relationship with coefficients, where the coefficients cannot be equal to 0).
[0006] Preliminary steps for determining the start time of the matrix control phase: Based on the existing development data of the target well, the start time of the matrix control phase is preliminarily determined;
[0007] The steps for verifying the start time of the matrix control stage and determining the coefficients of the matrix control stage depletion development curve are as follows: First, obtain the daily gas production data of the target well during the matrix control stage using the start time of the matrix control stage as the starting time. Second, fit the daily gas production data of the target well during the matrix control stage using the matrix control stage depletion development curve with the determined index and undetermined coefficients. If the highest fitting degree is less than 90%, it indicates that the start time of the matrix control stage is incorrect. Then, extend the start time of the matrix control stage by a certain step size to obtain a new start time. Use the new start time of the matrix control stage as the starting time to re-obtain the daily gas production data of the target well during the matrix control stage. Re-fit the daily gas production data of the target well during the matrix control stage using the matrix control stage depletion development curve with the determined index and undetermined coefficients until the highest fitting degree is not less than 90%. The start time of the matrix control stage at this point is the verified start time of the matrix control stage. The coefficients of the matrix control stage depletion development curve at the point of reaching the highest fitting degree are determined as the coefficients of the matrix control stage depletion development curve.
[0008] Production prediction steps: Using the depletion development curve of the matrix control stage combined with the verified start time of the matrix control stage, determine the daily gas production and / or cumulative gas production of the target well at the target time.
[0009] Generally, shale gas well development can be divided into two stages: the fracture network control stage and the matrix supply stage. In the early stages of development, production patterns are mainly controlled by the supply from the fracture network control zone and the flowback of fracturing fluid, resulting in a complex development pattern. During the fracture network control stage, the daily gas production curve fluctuates significantly due to the generation of free gas in the fractures and the flowback of fracturing fluid. In the matrix control stage, gas and water are produced simultaneously in the fractures, with daily water and gas production gradually decreasing, the supply range gradually expanding, and the gas production pattern becoming more uniform. In the later stages of production, matrix supply determines the well's output and stable production period. The matrix supply zone near the fractures can be considered as a one-dimensional flow of matrix towards the fractures. Using real reservoir cores, matrix depletion-type development simulation experiments are conducted to obtain the gas production patterns of the matrix under formation conditions. Combined with well parameters, this allows for the prediction of well production.
[0010] In the aforementioned shale gas well production prediction method based on depletion development curves, the target well should have already entered the matrix control stage.
[0011] In the above-mentioned shale gas well production prediction method based on the depletion development curve, preferably, in the step of determining the index of the depletion development curve in the matrix control stage, the gas production rate is the average gas production rate; in the steps of verifying the start time of the matrix control stage and determining the coefficient of the depletion development curve in the matrix control stage, the daily gas production data is the average daily gas production data.
[0012] In the above-mentioned shale gas well production prediction method based on the depletion development curve, preferably, the exponent of the depletion development curve in the matrix control stage is determined based on the exponent of the power function relationship: the exponent of the power function relationship is used as the exponent of the depletion development curve in the matrix control stage.
[0013] In the above-mentioned shale gas well production prediction method based on the depletion development curve, preferably, the step of conducting a depletion-type development laboratory simulation experiment using a fracture-free matrix core of the target well's production reservoir to establish a power function relationship between gas production rate and production time includes:
[0014] A fracture-free matrix core from the production layer of the target well's development reservoir is placed in a core holder. The experimental temperature is the same as the temperature of the target well's development reservoir. The confining pressure is applied to the overlying pressure of the target well's development reservoir. The core is saturated with adsorbable methane gas until the pressure of the target well's development reservoir is reached.
[0015] After the core is fully saturated with adsorbable methane gas, let it stand for a period of time to allow the adsorption to reach equilibrium.
[0016] The back pressure valve is used to control the outlet pressure of the core holder to be consistent with the bottom pressure of the target well. Then, the outlet of the core holder is opened to start the simulated depletion development process and the gas production rate at different production times is recorded.
[0017] Based on the gas production rate at different production times, a power function relationship between the gas production rate and the production time is established.
[0018] In the above-mentioned shale gas well production prediction method based on depletion development curve, preferably, the existing development data of the target well includes at least one of the following parameters: daily gas production, daily liquid production, and gas-liquid ratio.
[0019] In the above-mentioned shale gas well production prediction method based on the depletion development curve, preferably, the daily gas production of the target well at the target time is determined by combining the depletion development curve of the matrix control stage with the verified start time of the matrix control stage in the following manner:
[0020] Based on the target time and the start time of the matrix control phase, determine the time when the target well enters the matrix control phase when it has reached the target time of production;
[0021] Based on the time it takes for the target well to enter the matrix control stage when it reaches the target production time, the daily gas production of the target well when it reaches the target production time is determined using the depletion development curve of the matrix control stage.
[0022] In the above-mentioned shale gas well production prediction method based on the depletion development curve, preferably, the cumulative gas production of the target well at the target time is determined by combining the depletion development curve of the matrix control stage with the verified start time of the matrix control stage in the following manner:
[0023] Based on the target time and the start time of the matrix control phase, determine the time when the target well enters the matrix control phase when it has reached the target time of production;
[0024] Based on the time when the target well enters the matrix control stage when it reaches the target time, and combined with the depletion development curve of the matrix control stage, the cumulative gas production of the target well in the matrix control stage when it reaches the target time is determined.
[0025] The cumulative gas production of the target well during the matrix control phase is determined by combining the cumulative gas production of the target well before entering the matrix control phase.
[0026] This invention also provides a shale gas well production prediction system based on a depletion development curve, wherein the system includes:
[0027] The exponent acquisition module for the matrix-controlled stage exhaustion development curve is used to obtain the power function relationship between gas production rate and production time established by the indoor simulation experiment of exhaustion development based on the fracture-free matrix core of the target well's production reservoir; the exponent of the matrix-controlled stage exhaustion development curve is determined based on the exponent of the power function relationship, thereby obtaining the matrix-controlled stage exhaustion development curve with a determined exponent and undetermined coefficients; wherein, the matrix-controlled stage exhaustion development curve is a power function relationship curve.
[0028] Preliminary determination module for the start time of the matrix control phase: used to preliminarily determine the start time of the matrix control phase based on existing development data of the target well;
[0029] The module for verifying the start time of the matrix control phase and determining the coefficients of the matrix control phase exhaustion development curve is used to acquire daily gas production data of the target well during the matrix control phase, using the start time of the matrix control phase as the starting time; to fit the daily gas production data of the target well during the matrix control phase using the matrix control phase exhaustion development curve with the determined index and undetermined coefficients; if the highest fitting degree is less than 90%, it indicates that the start time of the matrix control phase is incorrectly determined, and the start time of the matrix control phase is extended by a certain step to obtain a new start time of the matrix control phase. The new start time of the matrix control phase is used as the starting time to reacquire the daily gas production data of the target well during the matrix control phase, and the matrix control phase exhaustion development curve with the determined index and undetermined coefficients is used again to fit the daily gas production data of the target well during the matrix control phase until the highest fitting degree is not less than 90%. The start time of the matrix control phase at this time is the verified start time of the matrix control phase, and the coefficients of the matrix control phase exhaustion development curve at the highest fitting degree are determined as the coefficients of the matrix control phase exhaustion development curve.
[0030] Production prediction module: Used to determine the daily gas production and / or cumulative gas production of the target well at the target time by combining the exhaustion development curve of the matrix control phase with the verified start time of the matrix control phase.
[0031] In the above-mentioned shale gas well production prediction system based on the depletion development curve, preferably, in the index acquisition module of the depletion development curve in the matrix control stage, the gas production rate is the average gas production rate; in the matrix control stage start time verification and matrix control stage depletion development curve coefficient determination module, the daily gas production data is the average daily gas production data.
[0032] In the above-mentioned shale gas well production prediction system based on the depletion development curve, preferably, the exponent of the depletion development curve in the matrix control stage is determined based on the exponent of the power function relationship: the exponent of the power function relationship is used as the exponent of the depletion development curve in the matrix control stage.
[0033] In the aforementioned shale gas well production prediction system based on the depletion development curve, preferably, the power function relationship between the gas production rate and production time is established in the following manner:
[0034] A fracture-free matrix core from the production layer of the target well's development reservoir is placed in a core holder. The experimental temperature is the same as the temperature of the target well's development reservoir. The confining pressure is applied to the overlying pressure of the target well's development reservoir. The core is saturated with adsorbable methane gas until the pressure of the target well's development reservoir is reached.
[0035] After the core is fully saturated with adsorbable methane gas, let it stand for a period of time to allow the adsorption to reach equilibrium.
[0036] The back pressure valve is used to control the outlet pressure of the core holder to be consistent with the bottom pressure of the target well. Then, the outlet of the core holder is opened to start the simulated depletion development process and the gas production rate at different production times is recorded.
[0037] Based on the gas production rate at different production times, a power function relationship between the gas production rate and the production time is established.
[0038] In the aforementioned shale gas well production prediction system based on depletion development curves, preferably, the existing development data of the target well includes at least one of the following parameters: daily gas production, daily liquid production, and gas-liquid ratio.
[0039] In the aforementioned shale gas well production prediction system based on depletion development curves, preferably, the production prediction module includes:
[0040] First processing submodule: used to determine the time when the target well enters the matrix control phase when it has reached the target time, based on the target time and the start time of the matrix control phase;
[0041] The second processing submodule is used to determine the daily gas production of the target well when it enters the matrix control stage based on the time when the target well enters the matrix control stage, and to use the depletion development curve of the matrix control stage.
[0042] In the above-mentioned shale gas well production prediction method based on depletion development curves, the production prediction module preferably includes:
[0043] First processing module: used to determine the time when the target well enters the matrix control stage when it has reached the target time, based on the target time and the start time of the matrix control stage;
[0044] The third processing submodule is used to determine the cumulative gas production of the target well during the matrix control stage based on the time when the target well enters the matrix control stage from the time of production to the target time, combined with the depletion development curve of the matrix control stage.
[0045] The fourth processing submodule is used to determine the gas production volume of the target well at the target time by combining the cumulative gas production volume of the target well during the matrix control stage when it has reached the target time with the cumulative gas production volume of the target well before entering the matrix control stage.
[0046] The technical solution provided by this invention first obtains the gas production rate as a function of production time from the core sample of the target formation in the target well based on a depletion-type development simulation experiment. Second, it divides the well's production stages to preliminarily determine the start time of the matrix control stage. Then, it verifies the start time of the matrix control stage using the gas production rate as a function of production time combined with gas well production data. Finally, it predicts the gas well's production based on the verification results of the gas production rate as a function of production time and the start time of the matrix control stage. This method can achieve simple, fast, and accurate shale gas well production prediction. Attached Figure Description
[0047] Figure 1 This is a flowchart illustrating a shale gas well production prediction method based on a depletion development curve, provided in an embodiment of the present invention.
[0048] Figure 2 This is a schematic diagram of the structure of a shale gas well production prediction system based on a depletion development curve, provided in an embodiment of the present invention.
[0049] Figure 3 This is a depletion development curve during the matrix control stage in Example 1.
[0050] Figure 4 This is a diagram of the existing development data of the target well in Example 1.
[0051] Figure 5 This is a fitting graph of the exhaustion development curve of the target well and the gas production data of the matrix control stage in Example 1. Detailed Implementation
[0052] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.
[0053] The principles and spirit of the present invention will be explained in detail below with reference to several representative embodiments.
[0054] See Figure 1 To achieve the above objectives, this invention provides a method for predicting shale gas well production based on a depletion development curve, wherein the method includes:
[0055] Step S1: Conduct a depletion-type development laboratory simulation experiment using fracture-free matrix cores from the production layer of the target well's reservoir to establish a power function relationship between gas production rate and production time; determine the exponent of the depletion development curve in the matrix-controlled stage based on the exponent of the power function relationship, thereby obtaining a matrix-controlled stage depletion development curve with a determined exponent and undetermined coefficients; wherein, the matrix-controlled stage depletion development curve is a power function relationship curve.
[0056] Step S2: Based on the existing development data of the target well, preliminarily determine the start time of the matrix control phase;
[0057] Step S3: Obtain daily gas production data of the target well during the matrix control stage, using the start time of the matrix control stage as the starting time; fit the daily gas production data of the target well during the matrix control stage using the exhaustion development curve of the matrix control stage with the determined index and undetermined coefficients; if the highest fitting degree is less than 90%, extend the start time of the matrix control stage by a certain step size to obtain a new start time of the matrix control stage, and re-obtain the daily gas production data of the target well during the matrix control stage using the new start time of the matrix control stage as the starting time. Re-fit the daily gas production data of the target well during the matrix control stage using the exhaustion development curve of the matrix control stage with the determined index and undetermined coefficients until the highest fitting degree is not less than 90%. The start time of the matrix control stage at this time is the verified start time of the matrix control stage, and the coefficient of the exhaustion development curve of the matrix control stage when the highest fitting degree is reached is determined as the coefficient of the exhaustion development curve of the matrix control stage.
[0058] Step S4: Using the depletion development curve of the matrix control stage combined with the verified start time of the matrix control stage, determine the daily gas production and / or cumulative gas production of the target well at the target time.
[0059] Generally, shale gas well development can be divided into two stages: the fracture network control stage and the matrix supply stage. In the early stages of development, production patterns are mainly controlled by the supply from the fracture network control zone and the flowback of fracturing fluid, resulting in a complex development pattern. During the fracture network control stage, the daily gas production curve fluctuates significantly due to the generation of free gas in the fractures and the flowback of fracturing fluid. In the matrix control stage, gas and water are produced simultaneously in the fractures, with daily water and gas production gradually decreasing, the supply range gradually expanding, and the gas production pattern becoming more uniform. In the later stages of production, matrix supply determines the well's output and stable production period. The matrix supply zone near the fractures can be considered as a one-dimensional flow of matrix towards the fractures. Using real reservoir cores, matrix depletion-type development simulation experiments are conducted to obtain the gas production patterns of the matrix under formation conditions. Combined with well parameters, this allows for the prediction of well production.
[0060] The target well should have already entered the matrix control stage.
[0061] The power function relationship between gas production rate and production time is a power function with coefficients, where the coefficients cannot be equal to 0. In the formula For the average gas production rate, For production time, For index, The coefficient is used. The depletion development curve in the matrix-controlled stage is a power function curve, i.e. In the formula This refers to the daily gas production during the substrate control phase. This refers to the production time during the matrix control stage. For index, is a coefficient.
[0062] In one embodiment, in step S1, the gas production rate is the average gas production rate; in step S3, the daily gas production data is the average daily gas production data.
[0063] In one embodiment, determining the exponent of the exhaustion development curve in the matrix control stage based on the exponent of the power function relationship means: using the exponent of the power function relationship as the exponent of the exhaustion development curve in the matrix control stage.
[0064] When fitting the daily gas production data of the target well's matrix control stage to the exhaustion development curve of the matrix control stage with the index determined and the coefficient to be determined, the degree of fitting is different under different coefficients. When the coefficient is a certain value, it will correspond to the highest degree of fitting. When the highest degree of fitting is reached, it will correspond to a certain coefficient.
[0065] In one embodiment, step S1 includes:
[0066] A fracture-free matrix core from the production layer of the target well's development reservoir is placed in a core holder. The experimental temperature is the same as the temperature of the target well's development reservoir. The confining pressure is applied to the overlying pressure of the target well's development reservoir. The core is saturated with adsorbable methane gas until the pressure of the target well's development reservoir is reached.
[0067] After the core is fully saturated with adsorbable methane gas, let it stand for a period of time to allow the adsorption to reach equilibrium.
[0068] The back pressure valve is used to control the outlet pressure of the core holder to be consistent with the bottom pressure of the target well. Then, the outlet of the core holder is opened to start the simulated depletion development process and the gas production rate at different production times is recorded.
[0069] Based on the gas production rate at different production times, a power function relationship between the gas production rate and the production time is established.
[0070] The exponent of the depletion development curve in the matrix control stage is determined based on the exponent of the power function relationship, thereby obtaining the depletion development curve in the matrix control stage with a determined exponent and undetermined coefficients; wherein, the depletion development curve in the matrix control stage is a power function relationship curve.
[0071] In one embodiment, the existing development data of the target well includes at least one of the following parameters: daily gas production, daily liquid production, and gas-liquid ratio.
[0072] In one implementation, the step size is no more than 10 days, for example, 10 days.
[0073] In one embodiment, the daily gas production of the target well at the target time is determined by combining the depletion development curve of the matrix control phase with the verified start time of the matrix control phase, in the following manner:
[0074] Based on the target time and the start time of the matrix control phase, determine the time when the target well enters the matrix control phase when it has reached the target time of production;
[0075] Based on the time it takes for the target well to enter the matrix control stage when it reaches the target production time, the daily gas production of the target well when it reaches the target production time is determined using the depletion development curve of the matrix control stage.
[0076] In one embodiment, the cumulative gas production of the target well at the target time is determined by combining the depletion development curve of the matrix control phase with the verified start time of the matrix control phase, in the following manner:
[0077] Based on the target time and the start time of the matrix control phase, determine the time when the target well enters the matrix control phase when it has reached the target time of production;
[0078] Based on the time when the target well enters the matrix control stage when it reaches the target time, and combined with the depletion development curve of the matrix control stage, the cumulative gas production of the target well in the matrix control stage when it reaches the target time is determined.
[0079] The cumulative gas production of the target well during the matrix control phase is determined by combining the cumulative gas production of the target well before entering the matrix control phase.
[0080] This invention also provides a shale gas well production prediction system based on a depletion development curve. Preferably, this system is used to implement the above-described method embodiments.
[0081] Figure 2 This is a structural block diagram of a shale gas well production prediction system based on a depletion development curve according to an embodiment of the present invention, as shown below. Figure 2 As shown, the system includes:
[0082] The exponent acquisition module 21 for the matrix-controlled stage exhaustion development curve is used to obtain the power function relationship between gas production rate and production time established by the indoor simulation experiment of exhaustion development based on the fracture-free matrix core of the target well's production reservoir; the exponent of the matrix-controlled stage exhaustion development curve is determined based on the exponent of the power function relationship, thereby obtaining the matrix-controlled stage exhaustion development curve with a determined exponent and undetermined coefficients; wherein, the matrix-controlled stage exhaustion development curve is a power function relationship curve.
[0083] Preliminary determination module 22 for the start time of the matrix control phase: used to preliminarily determine the start time of the matrix control phase based on the existing development data of the target well;
[0084] Module 23 for verifying the start time of the matrix control stage and determining the coefficients of the matrix control stage exhaustion development curve: This module is used to acquire daily gas production data of the target well during the matrix control stage, using the start time of the matrix control stage as the starting time; to fit the daily gas production data of the target well during the matrix control stage using the matrix control stage exhaustion development curve with the determined index and undetermined coefficients; if the highest fitting degree is less than 90%, it indicates that the start time of the matrix control stage is incorrectly determined. The start time of the matrix control stage is then extended by a certain step to obtain a new start time of the matrix control stage. The new start time of the matrix control stage is used as the starting time to reacquire the daily gas production data of the target well during the matrix control stage. The matrix control stage exhaustion development curve with the determined index and undetermined coefficients is then used to fit the daily gas production data of the target well during the matrix control stage again until the highest fitting degree is not less than 90%. The start time of the matrix control stage at this point is the verified start time of the matrix control stage, and the coefficients of the matrix control stage exhaustion development curve at the highest fitting degree are determined as the coefficients of the matrix control stage exhaustion development curve.
[0085] Production prediction module 24: Used to determine the daily gas production and / or cumulative gas production of the target well at the target time by combining the exhaustion development curve of the matrix control stage with the verified start time of the matrix control stage.
[0086] In one embodiment, in the index acquisition module 21 of the matrix control stage depletion development curve, the gas production rate is the average gas production rate; in the matrix control stage start time verification and matrix control stage depletion development curve coefficient determination module 23, the daily gas production data is the average daily gas production data.
[0087] In one embodiment, determining the exponent of the exhaustion development curve in the matrix control stage based on the exponent of the power function relationship means: using the exponent of the power function relationship as the exponent of the exhaustion development curve in the matrix control stage.
[0088] In one embodiment, the power function relationship between gas production rate and production time is established as follows:
[0089] A fracture-free matrix core from the production layer of the target well's development reservoir is placed in a core holder. The experimental temperature is the same as the temperature of the target well's development reservoir. The confining pressure is applied to the overlying pressure of the target well's development reservoir. The core is saturated with adsorbable methane gas until the pressure of the target well's development reservoir is reached.
[0090] After the core is fully saturated with adsorbable methane gas, let it stand for a period of time to allow the adsorption to reach equilibrium.
[0091] The back pressure valve is used to control the outlet pressure of the core holder to be consistent with the bottom pressure of the target well. Then, the outlet of the core holder is opened to start the simulated depletion development process and the gas production rate at different production times is recorded.
[0092] Based on the gas production rate at different production times, a power function relationship between the gas production rate and the production time is established.
[0093] In one embodiment, the existing development data of the target well includes at least one of the following parameters: daily gas production, daily liquid production, and gas-liquid ratio.
[0094] In one implementation, the step size is no more than 10 days, for example, 10 days.
[0095] In one embodiment, the production forecasting module 24 includes:
[0096] First processing submodule: used to determine the time when the target well enters the matrix control phase when it has reached the target time, based on the target time and the start time of the matrix control phase;
[0097] The second processing submodule is used to determine the daily gas production of the target well when it enters the matrix control stage based on the time when the target well enters the matrix control stage, and to use the depletion development curve of the matrix control stage.
[0098] In one embodiment, the production forecasting module 24 includes:
[0099] First processing module: used to determine the time when the target well enters the matrix control stage when it has reached the target time, based on the target time and the start time of the matrix control stage;
[0100] The third processing submodule is used to determine the cumulative gas production of the target well during the matrix control stage based on the time when the target well enters the matrix control stage from the time of production to the target time, combined with the depletion development curve of the matrix control stage.
[0101] The fourth processing submodule is used to determine the gas production volume of the target well at the target time by combining the cumulative gas production volume of the target well during the matrix control stage when it has reached the target time with the cumulative gas production volume of the target well before entering the matrix control stage.
[0102] Example 1
[0103] This embodiment provides a method for predicting shale gas well production based on a depletion development curve.
[0104] This method is used to predict the production of a shale gas well in Changning. The method includes:
[0105] I. Using fracture-free matrix cores from the production layers of the target well's reservoir, conduct laboratory simulation experiments on depletion-type development to establish an objective function of gas production rate (expressed as average gas production rate) versus production time as the depletion development curve for the matrix-controlled stage; specifically including:
[0106] A fracture-free matrix core (2.5 cm in diameter and 6 cm in length) from the production layer of the target well's development reservoir was placed in a core holder. The experimental temperature was 75°C, the same as the temperature of the target well's development reservoir. The confining pressure was increased to 45 MPa overburden pressure of the target well's development reservoir. The core was saturated with adsorbable methane gas until the pressure of the target well's development reservoir reached 35 MPa.
[0107] After the core is fully saturated with adsorbable methane gas, let it stand for 10-30 days to reach adsorption equilibrium.
[0108] The back pressure valve is used to control the outlet pressure of the core holder to be consistent with the bottom pressure of the target well, specifically 5 MPa. Then, the outlet of the core holder is opened to start the simulated depletion development process, and the gas production rate at different production times is recorded.
[0109] Based on the gas production rate at different production times, a power function relationship between the gas production rate and the production time was established, and the results are as follows: Figure 3 As shown.
[0110] The exponent of the depletion development curve in the matrix control stage is determined based on the exponent of the power function relationship, thereby obtaining the depletion development curve in the matrix control stage with a determined exponent and undetermined coefficients; wherein, the depletion development curve in the matrix control stage is a power function relationship curve.
[0111] like Figure 3 As shown, the shale gas production rate versus time curve is a decreasing straight line on a logarithmic coordinate system, indicating that the gas production rate and production time have a power function relationship during the shale matrix supply process. The objective function of the gas production rate versus production time, i.e., the depletion development curve of the matrix-controlled stage, can be expressed as:
[0112]
[0113] In the formula: The average gas production rate is expressed in mL / h. Cumulative gas production, in mL; , where h is the production time; a is the slope of the double logarithmic curve (representing the law or trend of decreasing output); b is the intercept of the double logarithmic curve.
[0114] like Figure 3 As shown in this embodiment, the objective function of gas production rate versus production time, i.e., the decay development curve of the matrix control stage, is specifically expressed as follows:
[0115] y = (1+a)eb x a = 6.9838x -0.54
[0116] In the formula: y is the average gas production rate, mL / h; x is the production time, h;
[0117] The expression for the decay development curve of the matrix-controlled stage with a determined exponent and undetermined coefficients is shown below:
[0118]
[0119] In the formula: The average daily gas production during the substrate control phase, 10 4 m 3 / d; t represents the production time, d.
[0120] II. Based on the existing development data of the target well (production curves, i.e., daily gas production curves and daily water production curves, such as...) Figure 4 (As shown) the initial start time of the matrix control phase is determined;
[0121] The production curve of this well includes a fracture network control stage and a matrix control stage. In the fracture network control stage, the daily gas production gradually increases and the daily water production gradually decreases. Due to the generation of free gas in the fractures and the backflow of fracturing fluid, the daily gas production curve fluctuates greatly. Analysis of the daily gas production and daily water production curves shows that after the production time is greater than 120 days, the gas production and water production patterns tend to stabilize, and it is preliminarily determined that the well enters the matrix control stage at 120 days.
[0122] 3. Using the start time of the matrix control phase as the starting time, obtain the average daily gas production data of the target well during the matrix control phase (i.e., average daily gas production data at different times; the average daily gas production at a certain time is equal to the cumulative gas production of the target well during the matrix control phase up to that time divided by the production time of the matrix control phase up to that time); fit the average daily gas production data of the target well during the matrix control phase using the exhaustion development curve of the matrix control phase with the determined index and undetermined coefficients; if the fitting degree is less than 90%, it indicates that the start time of the matrix control phase is incorrectly determined, and the start time of the matrix control phase should be adjusted according to a certain... The start time of the new matrix control stage is obtained by extending the step size (10 days). The average daily gas production data of the matrix control stage of the target well is obtained using the start time of the new matrix control stage. The average daily gas production data of the matrix control stage of the target well is then fitted again using the exhaustion development curve of the matrix control stage with the index determined and the coefficient to be determined, until the fitting degree is not less than 90%. The start time of the matrix control stage at this time is the verified start time of the matrix control stage. The coefficient of the exhaustion development curve of the matrix control stage when the highest fitting degree is reached is determined as the coefficient of the exhaustion development curve of the matrix control stage.
[0123] After normalizing and processing the experimental data, the gas production rate decline function was fitted with the production data of the gas well matrix control stage. The results showed a high degree of consistency in the decline pattern, with a goodness of fit of 98%. This indicates that the production well enters the matrix control stage after 170 days, and the coefficient of the exhaustion development curve of the matrix control stage, which reaches the highest degree of fit, is 271.79. The average gas production corresponding to 170 days of production is 149,500 cubic meters per day. The fitting results are as follows: Figure 5 As shown.
[0124] IV. Using the depletion development curve of the matrix control stage and the verified start time of the matrix control stage, determine the average daily gas production and cumulative gas production of the target well at the target time.
[0125] The average daily gas production is achieved through the following methods:
[0126] Based on the target time and the start time of the matrix control phase, determine the time when the target well enters the matrix control phase when it has reached the target time of production;
[0127] Based on the time when the target well enters the matrix control stage when it reaches the target time, the average daily gas production of the target well when it reaches the target time is determined using the depletion development curve of the matrix control stage.
[0128] The cumulative gas production is achieved through the following methods:
[0129] Based on the target time and the start time of the matrix control phase, determine the time when the target well enters the matrix control phase when it has reached the target time of production;
[0130] Based on the time when the target well enters the matrix control stage when it reaches the target time, and combined with the depletion development curve of the matrix control stage, the cumulative gas production of the target well in the matrix control stage when it reaches the target time is determined.
[0131] The cumulative gas production during the substrate control stage is calculated using the following formula: Q = 271.79t 0.46 In the formula: Q is the cumulative gas production, 10 4 m 3 t represents production time, d represents production time;
[0132] The total cumulative gas production of the target well up to the target time is determined by combining the cumulative gas production of the target well during the matrix control stage with the cumulative gas production of the target well before entering the matrix control stage.
[0133] The predicted average daily gas production over 1180 days (3 years) is 59,600 cubic meters / day, corresponding to a daily gas production of 27,000 cubic meters / day, and the average daily gas production over 3600 days is 11,800 cubic meters / day; the total cumulative gas production of this well over 20 years (7200 days) is 162 million cubic meters.
[0134] Preferred embodiments of the invention have been described above with reference to the accompanying drawings. Many features and advantages of these embodiments are apparent from this detailed description, and therefore the claims are intended to cover all such features and advantages of these embodiments that fall within their true spirit and scope. Furthermore, since many modifications and alterations will readily occur to those skilled in the art, the embodiments of the invention are not intended to be limited to the precise structures and operations illustrated and described, but rather to encompass all suitable modifications and equivalents falling within their scope.
Claims
1. A method for shale gas well production prediction based on decline curve analysis, wherein, The method comprises: The index determination step of the matrix control stage depletion curve: performing a depletion development indoor simulation experiment on a no-fracture matrix core of a production interval of a reservoir developed by a target well, establishing a power function relationship between gas production rate and production time; determining the index of the matrix control stage depletion curve based on the index of the power function relationship, thereby obtaining the matrix control stage depletion curve with the index determined and the coefficient to be determined; wherein the matrix control stage depletion curve is a power function relationship curve; wherein the relationship between the gas production rate and the production time is: wherein: is the average gas production rate, mL / h; is the cumulative gas production, mL; is the production time, h; a is the log-log curve slope; b is the log-log curve intercept; The preliminary determination step of the start time of the matrix control stage: preliminarily determining the start time of the matrix control stage based on the existing development data of the target well; The coefficient determination step of the matrix control stage depletion curve and the start time verification of the matrix control stage: obtaining the daily gas production data of the target well in the matrix control stage with the start time of the matrix control stage as the starting time; fitting the daily gas production data of the target well in the matrix control stage by using the matrix control stage depletion curve with the index determined and the coefficient to be determined; if the highest fitting degree is lower than 90%, the start time of the matrix control stage is sequentially extended by a preset step to obtain a new start time of the matrix control stage, the daily gas production data of the target well in the matrix control stage is re-obtained with the new start time of the matrix control stage as the starting time, and the daily gas production data of the target well in the matrix control stage is fitted by using the matrix control stage depletion curve with the index determined and the coefficient to be determined again, until the highest fitting degree is not lower than 90%, at which time the start time of the matrix control stage is the verified start time of the matrix control stage, and the coefficient of the matrix control stage depletion curve at the time of the highest fitting degree is determined as the coefficient of the matrix control stage depletion curve; The production prediction step: determining the daily gas production and / or cumulative gas production of the target well at a target time by using the matrix control stage depletion curve in combination with the verified start time of the matrix control stage.
2. The prediction method according to claim 1, wherein In the index determination step of the matrix control stage depletion curve, the gas production rate is an average gas production rate; In the coefficient determination step of the matrix control stage depletion curve and the start time verification of the matrix control stage, the daily gas production data is average daily gas production data.
3. The prediction method of claim 1, wherein, The index determination of the matrix control stage depletion curve based on the index of the power function relationship means that the index of the power function relationship is taken as the index of the matrix control stage depletion curve.
4. The prediction method of claim 1, wherein, The power function relationship between the gas production rate and the production time is established by performing a depletion development indoor simulation experiment on a no-fracture matrix core of a production interval of a reservoir developed by a target well, which comprises: The no-fracture matrix core of the production interval of the reservoir developed by the target well is placed in a core holder, the experimental temperature is consistent with the temperature of the reservoir developed by the target well, the confining pressure is added to the overburden pressure of the reservoir developed by the target well, and the core is saturated with adsorbable methane gas to the pressure of the reservoir developed by the target well; After the core is fully saturated with the adsorbable methane gas, it is left for a period of time to allow adsorption to reach equilibrium; The back pressure valve is used to control the core holder outlet pressure to be consistent with the target well bottom hole pressure, and then the core holder outlet is opened to start the simulation of the depletion development process, and the gas production rate at different production times is recorded; Based on the gas production rate at different production times, a power function relationship between the gas production rate and the production time is established.
5. The prediction method of claim 1, wherein, The existing development data of the target well include at least one of the daily gas production, the daily liquid production, and the gas-liquid ratio parameter.
6. The prediction method of claim 1, wherein, The daily gas production of the target well at the target time is determined by using the depletion development curve of the matrix control stage and the verified start time of the matrix control stage in the following manner: Based on the target time and the start time of the matrix control stage, the time when the target well enters the matrix control stage at the target time is determined; Based on the time when the target well enters the matrix control stage at the target time, the daily gas production of the target well at the target time is determined by using the depletion development curve of the matrix control stage.
7. The prediction method of claim 1, wherein, The cumulative gas production of the target well at the target time is determined by using the depletion development curve of the matrix control stage and the verified start time of the matrix control stage in the following manner: Based on the target time and the start time of the matrix control stage, the time when the target well enters the matrix control stage at the target time is determined; Based on the time when the target well enters the matrix control stage at the target time, the cumulative gas production of the target well in the matrix control stage at the target time is determined by using the depletion development curve of the matrix control stage; The cumulative gas production of the target well at the target time is determined by using the cumulative gas production of the target well in the matrix control stage at the target time and the cumulative gas production of the target well before entering the matrix control stage.
8. A shale gas well production prediction system based on decline curve, wherein, The system comprises: An index acquisition module of the depletion development curve of the matrix control stage is configured to acquire a power function relationship between the gas production rate and the production time established based on the depletion development laboratory simulation experiment of the no-fracture matrix core of the target well development reservoir production horizon, determine the index of the depletion development curve of the matrix control stage based on the index of the power function relationship, and obtain the depletion development curve of the matrix control stage with the index determined and the coefficient undetermined; wherein the depletion development curve of the matrix control stage is a power function relationship curve; wherein the relationship between the gas production rate and the production time is: wherein: is the average gas production rate, mL / h; is the cumulative gas production, mL; is the production time, h; a is the log-log curve slope; b is the log-log curve intercept; A start time preliminary determination module of the matrix control stage is configured to preliminarily determine the start time of the matrix control stage based on the existing development data of the target well. The matrix control stage starting time verification and the coefficient determination module of the matrix control stage depletion development curve is configured to: acquire daily gas production data of the target well in the matrix control stage with the starting time of the matrix control stage; fit the daily gas production data of the target well in the matrix control stage by using the exponential determination and coefficient undetermined matrix control stage depletion development curve; if the highest fitting degree is lower than 90%, it is determined that the starting time of the matrix control stage is incorrect, the starting time of the matrix control stage is sequentially extended by a preset step to obtain a new starting time of the matrix control stage, the daily gas production data of the target well in the matrix control stage is reacquired with the new starting time of the matrix control stage, and the daily gas production data of the target well in the matrix control stage is re-fitted by using the exponential determination and coefficient undetermined matrix control stage depletion development curve, until the highest fitting degree is not lower than 90%, at this time, the starting time of the matrix control stage is the verified starting time of the matrix control stage, and the coefficient of the matrix control stage depletion development curve when the highest fitting degree is reached is determined as the coefficient of the matrix control stage depletion development curve; The production prediction module is configured to determine daily gas production and / or cumulative gas production of the target well at a target time by using the matrix control stage depletion development curve and the verified starting time of the matrix control stage.
9. The prediction system of claim 8, wherein, In the exponential acquisition module of the matrix control stage depletion development curve, the gas production rate is an average gas production rate. In the matrix control stage starting time verification and the coefficient determination module of the matrix control stage depletion development curve, the daily gas production data is average daily gas production data.
10. The prediction system of claim 8, wherein, The exponential determination of the matrix control stage depletion development curve based on the exponential of the power function relationship is that the exponential of the power function relationship is taken as the exponential of the matrix control stage depletion development curve.
11. The prediction system of any one of claims 8-10, wherein, The production prediction module includes: A first processing submodule is configured to determine the time when the target well enters the matrix control stage at the target time based on the target time and the starting time of the matrix control stage; A second processing submodule is configured to determine daily gas production of the target well at the target time by using the matrix control stage depletion development curve based on the time when the target well enters the matrix control stage at the target time.
12. The prediction system of any one of claims 8-10, wherein, The production prediction module includes: A first processing module is configured to determine the time when the target well enters the matrix control stage at the target time based on the target time and the starting time of the matrix control stage; A third processing submodule is configured to determine cumulative gas production of the target well in the matrix control stage at the target time by using the matrix control stage depletion development curve based on the time when the target well enters the matrix control stage at the target time; A fourth processing submodule is configured to determine total gas production of the target well at the target time by using the cumulative gas production of the target well in the matrix control stage at the target time and the cumulative gas production of the target well before entering the matrix control stage.
Citation Information
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Multiple state variable prediction-based voltage transformer state assessment method
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