Diagnostic method for artificial fracture closure during production in tight gas fractured horizontal wells

Abstract

The present application relates to the diagnosis method of whether the artificial fracture is closed in the production process of the tight gas pressure fractured horizontal well, and belongs to the field of gas field development research. The method comprises the following steps: selecting typical wells; obtaining near-well parameters and far-well parameters of each typical well; establishing an unsteady seepage model of the tight gas pressure fractured horizontal well under constant pressure production by using the determined model parameters and the set effective half-length of the fracture; predicting the gas production data by using the seepage model and drawing a standard curve group of the tight gas pressure fractured horizontal well production; processing the historical gas production data of the tight gas pressure fractured horizontal well to be diagnosed, drawing a measured data curve on the same graph as the standard curve group, moving and adjusting the measured data curve, and then comparing the measured data curve with the standard curve group; and diagnosing whether the artificial fracture is closed in the production process of the pressure fractured horizontal well according to whether the measured data curve intersects with the multiple standard curves. The present application can quickly diagnose whether the artificial fracture is closed, greatly saves manpower and material resources, improves work efficiency, and has strong applicability.

Description

Technical Field

[0001] This invention belongs to the field of gas field development research, specifically relating to a method for diagnosing whether artificial fractures are closed during the production process of tight gas fractured horizontal wells. Background Technology

[0002] Multistage fracturing technology in horizontal wells is an important means to achieve economical and effective development of tight gas reservoirs and is currently widely used in tight gas reservoir development. As production continues, artificial fractures created during fracturing may close due to various reasons such as decreased formation pressure and proppant being carried away by the gas flow, resulting in a decrease in gas well productivity and seriously affecting the development effect of the gas well. Currently, the main method for diagnosing whether artificial fractures have closed during the production process of fracturing horizontal wells is the well testing method.

[0003] Well testing requires multiple pressure recovery tests on the target well (with a typical interval of 1-2 years between tests), collecting pressure recovery data, and then analyzing it using specialized software. This method requires understanding the reservoir geological characteristics and inputting numerous parameters of the reservoir and natural gas, such as effective thickness, porosity, saturation, natural gas density, and high-pressure properties of natural gas. The interpretation results include reservoir permeability, skin factor, effective length of horizontal sections, and effective half-length of artificial fractures. Multiple well tests are performed on the same gas well at regular intervals, and the effective half-length of artificial fractures is obtained from each test interpretation. If the effective half-length of artificial fractures gradually decreases over time, it indicates that the artificial fractures in the well have closed.

[0004] While well testing can diagnose whether artificial fractures in fractured horizontal wells have closed, it requires multiple well tests, which is expensive, time-consuming, and labor-intensive. Furthermore, it necessitates quantitatively interpreting the effective half-length of the artificial fracture before diagnosing closure based on changes in this length across multiple well tests. Additionally, it is ineffective for gas wells that have not undergone multiple well tests. Therefore, the application of this method is significantly limited.

[0005] The literature "Post-Fracturing Fracture Closure Model and Its Application" (Xu Lei, Journal of Chongqing University of Science and Technology (Natural Science Edition), 2021, 10: 47-49) establishes a mathematical model for the post-fracturing fracture closure process, mainly examining the change law of wellhead pressure during fracture closure, and provides a calculation method for determining fracture closure time and proppant settlement distance to predict fracture closure. The literature "Construction of Fracturing Closure Prediction Model" (Tang Feirui, Liaoning Chemical Industry, 2021, 10: 1537-1540) proposes a calculation model for hydraulic fracture closure based on rock mechanics theory, considering both proppant embedding in rock and proppant closure mechanisms during hydraulic fracture closure. This model is then applied to study the effects of proppant particle size, proppant elastic modulus, fracture width, and rock elastic modulus on fracture closure. The methods provided in these two literatures are only applicable to predicting artificial fracture closure before production after fracturing, and cannot be used to diagnose the closure of artificial fractures after gas well production over time.

[0006] Therefore, there is an urgent need on-site for a diagnostic method that can reduce costs and shorten operation time, thereby achieving the goal of reducing costs and improving work efficiency, and is applicable to the prediction of artificial fracture closure after gas wells are put into production. Summary of the Invention

[0007] The purpose of this invention is to provide a method for diagnosing whether artificial fractures are closed during the production process of a tight gas fractured horizontal well, in order to solve the problems that existing methods for diagnosing whether artificial fractures are closed are expensive, time-consuming, labor-intensive, and not applicable to predicting whether artificial fractures will close after the gas well is put into production.

[0008] The technical solution provided by this invention for diagnosing whether artificial fractures are closed during the production process of tight gas fracturing horizontal wells is as follows: The method includes the following steps:

[0009] 1) Based on the development effect of each fractured horizontal well in the tight gas block, select typical wells; conduct unsteady well testing and analysis on each typical well to obtain the near-well parameters of each typical well; use the production instability method to adjust the near-well parameters of each typical well and determine the far-well parameters of each typical well.

[0010] 2) Based on the adjusted near-wellbore parameters and determined far-wellbore parameters of each typical well, determine the model parameters; using the model parameters and a preset set of effective half-lengths of artificial fractures, establish seepage models for constant-pressure production in horizontal wells with tight gas fracturing; use the seepage models to predict gas production data under constant-pressure conditions; process the gas production data, and plot a set of standard curves for different effective half-lengths of artificial fractures using a double logarithmic coordinate system with the gas production index as the ordinate and the material balance time as the abscissa.

[0011] 3) Process the historical gas production data of the tight gas fractured horizontal well to obtain the gas production index and the corresponding material balance time; plot the measured data curve of the tight gas fractured horizontal well to be diagnosed on the standard curve set graph with the gas production index as the vertical axis and the material balance time as the horizontal axis; adjust the measured data curve accordingly based on whether there is a curve segment in the later part of the measured data curve with a slope value that meets the set requirements; determine whether the early part of the measured data curve after adjustment intersects with the early part of the standard curve set. When the early part of the measured data curve intersects with the early part of at least two curves in the standard curve set along the vertical axis, the artificial fracture of the tight gas fractured horizontal well to be diagnosed is closed. If no intersection occurs, the artificial fracture of the tight gas fractured horizontal well to be diagnosed is not closed.

[0012] The beneficial effects of this invention are: 1) The method of this invention does not require multiple pressure recovery tests for each well; only a few typical horizontal wells with good development performance need to be selected for a single pressure recovery test, saving a significant amount of testing costs. 2) The method of this invention does not require production instability analysis for each well; only typical horizontal wells need to be analyzed and their parameters established, saving a significant amount of analysis time. 3) The method of this invention uses the parameters of typical wells to establish a set of standard curves, which can diagnose whether artificial fractures in other gas wells have closed. For situations where it is necessary to screen target wells from hundreds or thousands of fractured horizontal wells, this method can greatly save manpower and resources and improve work efficiency. 4) The method of this invention is applicable to diagnosing the closure of artificial fractures during production and can be applied to gas wells that have not undergone well testing; therefore, it has a wide range of applications and strong applicability.

[0013] Furthermore, in step 3), the method for adjusting the measured data curve based on whether there is a curve segment with a slope value that meets the set requirements in the later part of the measured data curve is as follows: If there is a curve segment with a slope that meets the set requirements in the later part of the measured data curve, then the measured data curve is moved as a whole until the later part of the measured data curve coincides with the later part of the standard curve group; if there is no curve segment with a slope that meets the set requirements in the later part of the measured data curve, then the measured data curve is moved as a whole until the end of the measured data curve is located at the position where the slope of the standard curve group begins to appear within the set slope range.

[0014] Further, the setting requirement mentioned in step 3) refers to: the slope value is close to -1. The judgment method is: move the measured curve so that its later segment is compared with the later segment of the standard curve. If the data points of the later segment of the measured curve are all near the standard curve with a slope value of -1, then the later part of the measured curve has a curve segment with a slope close to -1; otherwise, the later part of the measured curve does not have a curve segment with a slope close to -1.

[0015] Furthermore, the gas production index is obtained by dividing the gas production data by the pressure square difference, where the pressure square difference is equal to the square of the original pressure minus the square of the bottom hole flowing pressure; the material balance time is obtained by dividing the cumulative production data by the production data.

[0016] Furthermore, the near-wellbore parameters include reservoir permeability, effective length of horizontal well, effective number of artificial fractures, effective half-length of artificial fractures, conductivity of artificial fractures, and fracture skin coefficient.

[0017] Furthermore, the far-well parameters include the boundary shape of the tight oil reservoir within the control range of the gas well and the distance from the boundary to the center of the well.

[0018] Furthermore, the method for determining the model parameters in step 3) is as follows: calculate the average value of each group of near-well parameters and far-well parameters, or select one group of near-well parameters and far-well parameters based on historical data of tight gas blocks.

[0019] Furthermore, a typical well is determined by comprehensively considering three factors: single well production, production rate and wellhead pressure decline rate, and cumulative gas production.

[0020] Furthermore, the instability test is a pressure recovery test method. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating a method for diagnosing whether artificial fractures are closed during the production process of a tight gas fracturing horizontal well, according to an embodiment of the present invention.

[0022] Figure 2 This is a set of standard production curves for tight gas fracturing horizontal wells according to an embodiment of the present invention;

[0023] Figure 3 This is a comparison chart of the measured data curve and the standard curve when the artificial crack is not closed in the later part of the embodiment of the present invention, where there is a slope of -1 segment.

[0024] Figure 4 This is a comparison chart of the measured data curve and the standard curve when the artificial crack has a slope of -1 in the later part of the embodiment of the present invention and is closed.

[0025] Figure 5 This is a comparison chart of the measured data curve and the standard curve when the artificial crack is closed in the later stage of the embodiment of the present invention without the slope -1 segment. Detailed Implementation

[0026] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0027] like Figure 1As shown, the method for diagnosing whether artificial fractures are closed during the production process of a tight gas fractured horizontal well according to the present invention includes the following steps:

[0028] 1) Selection of typical tight gas fractured horizontal wells: Based on the development effect of each fractured horizontal well in the tight gas block, a set number of typical wells are selected.

[0029] 2) Determination of near-wellbore and far-wellbore parameters: Conduct unsteady well testing and analysis on each typical well to determine the near-wellbore parameters of each typical well; use the production instability method to adjust the near-wellbore parameters of each typical well and determine the far-wellbore parameters of each typical well.

[0030] 3) Generation of standard curves for tight gas fractured horizontal wells: Based on the adjusted near-wellbore parameters and determined far-wellbore parameters of each typical well, the model parameters are determined; using the model parameters and a set of set effective half-lengths of artificial fractures, seepage models for constant-pressure production of tight gas fractured horizontal wells are established respectively; the seepage models are used to predict the gas production data under constant-pressure conditions; the gas production data is processed, and a set of standard curves with gas production index as the ordinate and material balance time as the abscissa are plotted under different effective half-lengths of artificial fractures.

[0031] 4) Diagnosis of whether artificial fractures in a tight gas fractured horizontal well are closed: The historical gas production data of the tight gas fractured horizontal well to be diagnosed is processed to obtain the gas production index data and material balance time. The gas production index-material balance time curve of the tight gas fractured horizontal well to be diagnosed is plotted on the same graph as the standard curve set, referred to as the measured data curve; the measured data curve is adjusted according to whether there is a curve segment in the later part of the measured data curve with a slope value that meets the set requirements, using the corresponding adjustment rules.

[0032] Determine whether the early part of the adjusted measured data curve intersects with the early part of the standard curve group. If the early part of the measured data curve intersects with the early parts of at least two curves in the standard curve group along the vertical axis, then the artificial fracture in the tight gas fractured horizontal well to be diagnosed has closed. If no intersection occurs, then the artificial fracture in the tight gas fractured horizontal well to be diagnosed has not closed.

[0033] As a further improvement to the above embodiments, for step 1), this invention selects fractured horizontal wells with longer production times and better development effects from among multiple wells in the tight gas block as typical wells. When evaluating the development effect of each fractured horizontal well in the tight gas block, this invention preferably uses a comprehensive evaluation based on three factors: single-well production, production rate and wellhead pressure decline rate, and cumulative production. A set number of fractured horizontal wells with higher single-well production, slower production and wellhead pressure decline rates, and larger cumulative gas production compared to other gas wells are selected as typical wells. The number of typical wells selected is generally 5 to 10. The production dynamic characteristics of these typical wells serve as benchmarks for other gas wells in the tight gas block.

[0034] As a further improvement to the above embodiment, for step 2), when performing unsteady well testing on selected typical wells, this embodiment preferably uses the pressure recovery well testing method, that is, using the measured pressure data to perform pressure instability analysis on these typical wells. Since the unsteady flow of tight gas is very slow, the response signal of the far-well parameters cannot be obtained, so this method can only obtain the near-well parameters. This step first determines the initial values ​​of the near-well parameters.

[0035] Near-wellbore parameters and far-wellbore parameters are defined by well test interpretation professionals based on the physical distance of the parameters from the wellbore. The distance of well test detection is positively correlated with the test time. Parameters that can be measured in a short well test time are considered near-wellbore parameters, while parameters that require a longer well test time are considered far-wellbore parameters.

[0036] Near-well parameters for conventional fractured horizontal wells include reservoir permeability, effective horizontal well length, effective number of artificial fractures, effective half-length of artificial fractures, fracture conductivity, and fracture skin factor. Of course, if the reservoir is complex or the fracture scale is large, near-well parameters may also include other parameters.

[0037] Remote well parameters typically refer to outer boundary parameters. In this embodiment, remote well parameters include the boundary shape of the tight oil reservoir within the control range of the gas well and the distance from the boundary to the center of the well.

[0038] As a further improvement to the above embodiment, for step 3), this step adopts the production instability method. The initial values ​​of the near-wellbore parameters obtained in step 2) are input, and historical data fitting is performed on the dynamic production data of these typical wells. The near-wellbore parameters are adjusted until a better fitting effect is achieved, thus obtaining the near-wellbore parameters. Initial values ​​of the far-wellbore parameters are obtained through fitting on typical charts, and then historical data fitting is performed by adjusting the initial values. After the historical data is fitted, the far-wellbore parameters are finally determined.

[0039] As a further improvement to the above embodiment, for step 4), this step requires statistically determining representative model parameters for these typical wells based on the determined near-wellbore and far-wellbore parameters. There are generally two ways to determine the model parameters: The first way is to calculate the average value of each group of near-wellbore and far-wellbore parameters to determine the representative model parameters. The second way is for experienced geologists and dynamic researchers to select one set of near-wellbore and far-wellbore parameters as model parameters based on historical research results and understanding of tight gas blocks.

[0040] Using model parameters and setting a set of effective half-lengths of artificial fractures (e.g., 80m, 60m, 40m, 20m, 0m), an unsteady flow model for constant-pressure production in a horizontally fractured tight gas well is established to predict gas production-time data under constant-pressure conditions until the gas production approaches the abandonment rate. The gas production index is obtained by dividing the predicted gas production data by the pressure square difference, and the square of the initial pressure minus the square of the bottomhole flowing pressure. The material balance time is obtained by dividing the cumulative production data by the production data. A set of standard curves is generated by plotting the gas production index data on the ordinate and the material balance time on the abscissa, with each curve corresponding to a half-length of an artificial fracture. Figure 2 As shown. The process of establishing the unsteady flow model is existing technology and will not be described in detail here.

[0041] Once the standard curve is generated, the artificial fracture closure status of other gas wells besides the typical well can be diagnosed. First, the production history data of the gas well to be diagnosed is preprocessed, that is, the gas production data is divided by the pressure square difference to generate the gas production index data, and the cumulative production data is divided by the production data to obtain the material balance time. Second, the gas production index data and material balance time of the gas well to be diagnosed are interpolated to form a measured data curve, which is plotted on the same graph as the standard curve set.

[0042] Before cross-judging the standard curve and the measured data curve, the measured data curve needs to be adjusted. During the adjustment, it is necessary to adjust the measured data curve according to whether there are curve segments in the later part of the measured data curve with slope values ​​that meet the set requirements, and to use the corresponding adjustment rules.

[0043] The setting requirement is that the slope value is close to -1. By moving the measured curve and comparing its later segment with the later segment of the standard curve, it can be visually determined whether the slope of the later segment of the measured curve is close to -1. Specifically, if the data points of the later segment of the measured curve are all near the standard curve with a slope of -1, then the later part of the measured curve has a curve segment with a slope close to -1; otherwise, it is considered that the later part of the measured curve has a curve segment with a slope close to -1.

[0044] If the later part of the measured data curve has a segment with a slope that meets the set conditions, the adjustment rule is: move the entire measured data curve until the later part of the measured data curve coincides with the later part of the standard curve group. If the later part of the measured data curve does not have a segment with a slope that meets the set conditions, the adjustment rule is: move the entire measured data curve until the end of the measured data curve is located at the position where the standard curve group begins to show a slope within the set slope range.

[0045] The adjustment process can be found in [reference]. Figures 3-5 Specifically, if the later part of the measured data curve has a segment with a slope of approximately -1, the measured data curve is moved so that the later segment coincides with the later segment of the standard curve set, and the earlier segments of the two are compared. If the earlier segment of the measured data curve does not intersect with the earlier segment of the standard curve set, it is diagnosed that the artificial fracture in the well has not closed. Figure 3 As shown; when the early segment of the measured data curve intersects at least two curves from top to bottom of the standard curve set, it is diagnosed that the artificial fracture in the well has closed, such as... Figure 4 As shown; if the measured data curve does not have a segment with a slope of approximately -1 in the later stage, move the measured data curve so that its end is located where the standard curve group first appears with a slope of -1. Then compare the earlier segment of the measured data curve with the earlier segment of the standard curve group. When at least two curves of the earlier segment of the measured data curve and the earlier segment of the standard curve group intersect sequentially from top to bottom, it is diagnosed that the artificial fracture in the well has closed. Figure 5 As shown. If no intersection occurs, it is diagnosed that the artificial fractures in the well have not closed. When the early segment of the measured data curve intersects with the early segment of the standard curve set, the more intersections there are, the more obvious the fracture closure.

[0046] By plotting the gas production index data on the ordinate and the mass balance time on the abscissa, and using a double logarithmic method to create a curve, the seepage characteristics of the reservoir can be represented. For example, the better the fracturing effect, the longer the fracture half-length, which is reflected in the curve shape as a slope closer to -1 / 2. This allows for a clear assessment of the fracturing effect and fracture length.

Claims

1. A method for diagnosing whether artificial fractures are closed during the production process of a tight gas fractured horizontal well, characterized in that... The method includes the following steps: 1) Based on the development effect of each fractured horizontal well in the tight gas block, select typical wells; conduct unsteady well testing and analysis on each typical well to obtain the near-well parameters of each typical well; use the production instability method to adjust the near-well parameters of each typical well and determine the far-well parameters of each typical well. 2) Based on the adjusted near-wellbore parameters and determined far-wellbore parameters of each typical well, determine the model parameters; using the model parameters and a preset set of effective half-lengths of artificial fractures, establish seepage models for constant-pressure production in horizontal wells with tight gas fracturing; use the seepage models to predict gas production data under constant-pressure conditions; process the gas production data, and plot a set of standard curves for different effective half-lengths of artificial fractures in a double logarithmic coordinate system with the gas production index as the ordinate and the material balance time as the abscissa. 3) Process the historical gas production data of the tight gas fractured horizontal well to obtain the gas production index and the corresponding material balance time; plot the measured data curve of the tight gas fractured horizontal well to be diagnosed on the standard curve set graph with the gas production index as the vertical axis and the material balance time as the horizontal axis; adjust the measured data curve accordingly based on whether there is a curve segment in the later part of the measured data curve with a slope value that meets the set requirements; determine whether the early part of the measured data curve after adjustment intersects with the early part of the standard curve set. When the early part of the measured data curve intersects with the early part of at least two curves in the standard curve set along the vertical axis, the artificial fracture of the tight gas fractured horizontal well to be diagnosed is closed. If no intersection occurs, the artificial fracture of the tight gas fractured horizontal well to be diagnosed is not closed.

2. The method for diagnosing whether artificial fractures are closed during the production process of a tight gas fractured horizontal well according to claim 1, characterized in that, In step 3), the method for adjusting the measured data curve based on whether there is a curve segment with a slope value that meets the set requirements in the later part of the measured data curve is as follows: If there is a curve segment with a slope that meets the set requirements in the later part of the measured data curve, then the measured data curve is moved as a whole until the later part of the measured data curve coincides with the later part of the standard curve group; if there is no curve segment with a slope that meets the set requirements in the later part of the measured data curve, then the measured data curve is moved as a whole until the end of the measured data curve is located at the position where the slope of the standard curve group begins to appear within the set slope range.

3. The method for diagnosing whether artificial fractures are closed during the production process of a tight gas fractured horizontal well according to claim 1 or 2, characterized in that, The setting requirement mentioned in step 3) refers to the slope value being close to -1. The judgment method is to move the measured curve so that its later segment is compared with the later segment of the standard curve. If the data points of the later segment of the measured curve are all near the standard curve with a slope value of -1, then the later part of the measured curve has a curve segment with a slope close to -1; otherwise, the later part of the measured curve does not have a curve segment with a slope close to -1.

4. The method for diagnosing whether artificial fractures are closed during the production process of a tight gas fractured horizontal well according to claim 1 or 2, characterized in that, The gas production index is obtained by dividing the gas production data by the pressure square difference, which is equal to the square of the original pressure minus the square of the bottom hole flowing pressure; the material balance time is obtained by dividing the cumulative production data by the production data.

5. The method for diagnosing whether artificial fractures are closed during the production process of a tight gas fractured horizontal well according to claim 1 or 2, characterized in that, The near-wellbore parameters include reservoir permeability, effective length of horizontal well, effective number of artificial fractures, effective half-length of artificial fractures, conductivity of artificial fractures, and fracture skin coefficient.

6. The method for diagnosing whether artificial fractures are closed during the production process of a tight gas fractured horizontal well according to claim 1 or 2, characterized in that, The remote well parameters include the boundary shape of the tight oil reservoir within the control range of the gas well and the distance from the boundary to the center of the well.

7. The method for diagnosing whether artificial fractures are closed during the production process of a tight gas fractured horizontal well according to claim 1 or 2, characterized in that, The method for determining the model parameters in step 3) is as follows: calculate the average value of each group of near-well parameters and far-well parameters, or select one group of near-well parameters and far-well parameters based on historical data of tight gas blocks.

8. The method for diagnosing whether artificial fractures are closed during the production process of a tight gas fractured horizontal well according to claim 1 or 2, characterized in that, The typical well is determined by comprehensively considering three factors: single well production, production rate and wellhead pressure decline rate, and cumulative gas production.

9. The method for diagnosing whether artificial fractures are closed during the production process of a tight gas fractured horizontal well according to claim 1 or 2, characterized in that, The instability test is a pressure recovery test method.

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