A method for splitting the initial production of multi-stage fractured horizontal wells in tight sandstone gas reservoirs

Abstract

This invention discloses a method for splitting the initial production of multi-stage fractured horizontal wells in tight sandstone gas reservoirs, belonging to the field of tight sandstone. The method includes the following steps: First, obtain reservoir data, geostress data, and fracturing data of the corresponding reservoir in the fractured section; then, perform simulations using existing fracturing models based on the obtained data to obtain the fracture-controlled volume of the fractured section; calculate the single-stage fracture-controlled reserves of the fractured section based on the obtained data and reservoir data; take the sum of the single-stage fracture-controlled reserves of all fractured sections in a single well as the single-well fracture-controlled reserves of the corresponding single well; then, determine the split gas production of the corresponding fractured section based on the ratio of the single-stage fracture-controlled reserves to the single-well fracture-controlled reserves. This method facilitates the understanding of the initial production capacity of each stage in a multi-stage fractured horizontal well, providing a data basis for guiding the optimization of fracturing location and fracturing construction parameters. Since a larger single-stage fracture-controlled reserve is more conducive to gas production, the fracturing contribution rate determined by the single-stage fracture-controlled reserve is accurate.

Description

Technical Field

[0001] This invention belongs to the field of tight sandstone, and in particular relates to a method for splitting the initial production of multi-stage fractured horizontal wells in tight sandstone gas reservoirs. Background Technology

[0002] Tight sandstone gas reservoirs are mostly low to ultra-low porosity and low to ultra-low permeability reservoirs, with no or very low natural production capacity. They typically require fracturing and proppant injection to increase single-well production. In recent years, multi-stage fracturing horizontal wells have been commonly used for the development of tight sandstone gas reservoirs. Due to factors such as reservoir heterogeneity and fracturing parameters, the reservoir thickness, reservoir properties, gas content, and fracturing scale vary significantly among the different fracturing stages of a horizontal well. The contribution of each fracturing stage to gas production in the same horizontal well varies greatly, and the contribution of each stage changes at different production stages.

[0003] Currently, the contribution of each segment in a fractured horizontal well is typically determined using horizontal well production profile testing to clarify the production characteristics of the fractured segment. However, production profile testing is significantly affected by surface and wellbore conditions, and not every horizontal well can be tested. Furthermore, the testing cost is high. To address these issues, Chinese patent application CN113006760B discloses a method for dividing the production of a multi-segment fractured horizontal well in tight sandstone gas. This method constructs an ideal fractured segment based on the actual fractured segments and calculates the cosine similarity between the actual and ideal fractured segments. Based on this cosine similarity, the production contribution rate of the actual fractured segment is calculated, and the production contribution rate of each segment is then determined. The ideal fractured segment's water saturation is the minimum water saturation of all actual fractured segments; other basic data for the ideal fractured segment are the maximum values ​​of the basic data for all actual fractured segments. In other words, the contribution rate is determined based on the similarity between the actual fracturing section and the ideal section. This means that the ideal fracturing section is assumed to be the one with the most favorable conditions for gas production. However, the minimum water saturation and the maximum other basic data do not necessarily mean that gas production is the most favorable. Therefore, when it cannot be determined that the ideal section is the most favorable fracturing section for gas production, the contribution rate determined by this scheme based on the ideal fracturing section is also inaccurate.

[0004] In summary, the ideal fracturing section in existing production splitting schemes is not necessarily the most favorable fracturing section for gas production, which leads to inaccurate contribution rates of actual fracturing sections determined based on the ideal fracturing section. Summary of the Invention

[0005] The purpose of this invention is to provide a method for splitting the initial production of multi-stage fractured horizontal wells in tight sandstone gas reservoirs, so as to solve the technical problem that the contribution rate of the actual fractured stage is not accurate in the prior art.

[0006] To achieve the above objectives, the technical solution of the method for splitting the initial production of multi-stage fractured horizontal wells in tight sandstone gas reservoirs provided by this invention is as follows:

[0007] A method for splitting the initial production of a multi-stage fractured horizontal well in a tight sandstone gas reservoir, the method comprising the following steps: acquiring reservoir data, geostress data and fracture data of the reservoir corresponding to the fractured stage, the reservoir data including porosity and gas saturation, obtaining the fracture network characteristics of each fractured stage based on the acquired data, and calculating the single-stage fracture control volume of each fractured stage based on this.

[0008] The controlled reserves of each fractured section are calculated based on the controlled volume of each fractured section and reservoir data. The sum of the controlled reserves of each fractured section in a single well is taken as the controlled reserves of that single well. The ratio of the controlled reserves of each fractured section to the controlled reserves of the entire single well is taken as the fracturing contribution rate of the corresponding fractured section. The product of the gas production of a single well and the fracturing contribution rate is taken as the split gas production of that fractured section.

[0009] The beneficial effects are as follows: First, obtain reservoir data, geostress data, and fracturing data for the corresponding reservoir in the fracturing section. Then, use existing fracturing models to simulate the fracturing section based on the obtained data to obtain the fracture-controlled volume. Calculate the single-segment fracture-controlled reserves of the fracturing section based on the fracture-controlled volume and reservoir data. Use the sum of the single-segment fracture-controlled reserves of all fracturing sections in a single well as the single-well fracture-controlled reserves of the corresponding single well. Then, determine the fracturing contribution rate of the corresponding fracturing section based on the ratio of the single-segment fracture-controlled reserves to the single-well fracture-controlled reserves. Obtain the split gas production of the corresponding fracturing section based on the fracturing contribution rate of each fracturing section. In other words, when the total gas production of a single well is known, the contribution rate can guide the gas production of each fracturing section. By assessing the fracturing contribution rate, we can improve our understanding of the initial production capacity of each segment in a multi-stage fracturing horizontal well. This provides a data basis for optimizing fracturing locations and fracturing parameters. Furthermore, this method primarily relies on the fracture-controlled reserves to determine the fracturing contribution rate. Since a larger single-stage fracture-controlled reserve is more conducive to gas production, the fracturing contribution rate determined by the single-stage fracture-controlled reserve is also accurate.

[0010] As a further improvement, the formula for calculating the reserves controlled by a single fracture is as follows:

[0011]

[0012] Among them, G i Let Bg be the controlled reserves of a single fracture in the i-th fracturing stage, and V be the natural gas volume factor. i Let i be the single-segment seam control volume of the i-th segment. Let be the porosity of the i-th segment. Let be the gas saturation of the i-th segment.

[0013] The beneficial effect is that, since the single-segment fracture control volume has a positive impact on the controlled reserves, the single-segment fracture controlled reserves can be calculated by using the single-segment fracture control volume and reservoir data, so as to determine the accurate single-segment fracture controlled reserves.

[0014] As a further improvement, the seam mesh features include seam half-length, ripple half-width, and seam half-height. Therefore, the formula for calculating the volume of a single seam control segment is:

[0015]

[0016] Among them, V i Let a be the single-segment seam control volume of the i-th segment. i Let b be the half-length of the fracture in the i-th fracturing segment. i Let c be the sweep half-width of the i-th fracturing segment. i Let be the half-height of the fracture in the i-th fracturing segment.

[0017] The beneficial effect is that the fractures spread outwards from the fracturing point, and the fracturing force gradually weakens. The volume of the resulting fracture is approximately an ellipsoid. Therefore, simplifying the fracture volume to an ellipsoid facilitates volume calculation.

[0018] As a further improvement, the formula for calculating the fracture-controlled reserves of a single well is as follows:

[0019]

[0020] Among them, G i Let G be the single-segment fracture controlled reserves of the i-th fracturing segment, and G be the single-well fracture controlled reserves.

[0021] As a further improvement, the formula for calculating the fracturing contribution rate is:

[0022]

[0023] Among them, W i G is the contribution rate of the i-th stage of fracturing. i Let G be the single-segment fracture controlled reserves of the i-th fracturing segment, and G be the single-well fracture controlled reserves.

[0024] As a further improvement, the formula for calculating the gas production from the splitting process is as follows:

[0025]

[0026] Where Q is the gas production per well, Q pi W represents the gas production from the i-th fracturing stage. i The contribution rate of the fracturing in the i-th segment. Attached Figure Description

[0027] Figure 1 This is a planar feature diagram of single-stage hydraulic fracturing crack monitoring in this invention;

[0028] Figure 2 This is a longitudinal feature diagram of a single-stage hydraulic fracturing fracture in this invention;

[0029] Figure 3 This is a comparison chart of the horizontal section logging curve and production output of well A according to the present invention;

[0030] Figure 4 This is a flowchart illustrating the present invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are merely some embodiments of the invention, not all embodiments. The components of the embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0032] Example of an initial production splitting method for multi-stage fracturing horizontal wells in tight sandstone gas reservoirs:

[0033] This embodiment takes the He 1 gas reservoir of the Lower Shihezi Formation in the X gas field of a basin in China as an example. The He 1 gas reservoir of the Lower Shihezi Formation in this area is a braided river deposit with strong heterogeneity and rapid changes in sandstone reservoir. The reservoir thickness, physical properties and gas content vary greatly at different locations in the horizontal section.

[0034] Well A is a typical horizontal well in the He 1 gas reservoir of the Lower Shihezi Formation in the X gas field. The actual drilled horizontal section is 800m long, with 667m of sandstone and only 309m of gas-bearing sandstone. The average total hydrocarbon content is 17.56%, indicating a low overall gas-bearing sandstone encounter rate. The reservoir thickness and properties vary significantly at different locations within the horizontal section. Well A underwent fracturing in nine sections, with differentiated fracturing operations conducted in September 2022. Production commenced in November 2022, and gas production profile testing began at the end of December 2022. Specifically, the initial production splitting method for multi-stage fracturing of horizontal wells in tight sandstone gas reservoirs, as described in this application, is employed. Figure 4 As shown, the method includes the following steps:

[0035] 1) Obtain relevant data for the fracturing section.

[0036] Acquire reservoir data, geostress data, and fracturing data for the corresponding reservoir in the fracturing section. Reservoir data includes gas layer thickness, porosity, and gas saturation. Fracturing data includes displacement, proppant addition, and net fluid injection into the formation.

[0037] Specifically, the horizontal section of Well A mainly encountered lithologies such as fine sandstone, medium sandstone, and mudstone. Due to the strong heterogeneity of the reservoir, the lithology, physical properties, and gas-bearing capacity encountered in the wellbore do not represent the reservoir characteristics of the entire area. Therefore, reservoir data within different fracturing units were determined by combining the vertical and horizontal reservoir predictions of the horizontal well. The reservoir data for each fracturing section of Well A are shown in Table 1 below, and the corresponding fracturing data are also shown in Table 1 below. Table 1

[0038] 2) Calculate the seam control volume.

[0039] Based on the acquired data, the fracture half-length and fracture height are simulated using a fracturing model. The sweep width of the fracturing fracture is determined based on the fracture morphology monitored by the fracturing team. The controlled volume of the fracturing fracture is approximated as an ellipsoid, with the major axis representing the simulated fracture length. Since the fracture height is generally greater than the target gas layer thickness, the minor axes represent the sweep width and the gas layer thickness, respectively. Finally, the controlled volume of each fracturing segment is calculated. Therefore, the controlled volume of a single segment is simplified to an ellipsoid, and the corresponding controlled volume of a single segment is calculated based on the fracture half-length, fracture height, and sweep width of the fracturing segment. The formula for calculating the controlled volume of a single segment is:

[0040]

[0041] Among them, V i Let a be the single-segment seam control volume of the i-th segment. i Let b be the half-length of the fracture in the i-th fracturing segment. i Let c be the sweep half-width of the i-th fracturing segment. i Let be the half-height of the fracture in the i-th fracturing segment.

[0042] like Figure 1 , Figure 2 As shown, where X f Y f h f Corresponding to a in Table 2 i 、b i c i Data. Specifically, the single-segment fracture control volume corresponding to each fracturing section of well A in this embodiment is shown in Table 2 below:

[0043] Table 2

[0044]

[0045] 3) Calculate the fracture-controlled reserves of a single well.

[0046] First, calculate the single-fracture controlled reserves of the corresponding fracturing section based on the single-fracture controlled volume and reservoir data. Then, sum the single-fracture controlled reserves of each fracturing section within a single well as the single-well fracture controlled reserves. The formula for calculating the single-fracture controlled reserves is:

[0047]

[0048] Among them, G i Let Bg be the controlled reserves of a single fracture in the i-th fracturing stage, and V be the natural gas volume factor. i Let i be the single-segment seam control volume of the i-th segment. Let be the porosity of the i-th segment. Let be the gas saturation of the i-th segment.

[0049] Based on the method described above for calculating the controlled reserves of a single fracture, the controlled reserves of each fractured section in Well A were calculated, as shown in Table 3 below:

[0050] Table 3

[0051]

[0052] The half-height of the gas layer refers to half the thickness of the gas layer, and the half-width of the sweep refers to half the width of the sweep.

[0053] 4) Calculate the fracturing contribution rate to divide the gas production of a single well.

[0054] like Figure 3 As shown, the ratio of the controlled reserves of a single fracture segment to the total controlled reserves of a single well is taken as the fracturing contribution rate of the corresponding fracturing segment, and the product of the gas production of a single well and the fracturing contribution rate is taken as the split gas production of that fracturing segment. The formula for calculating the controlled reserves of a single well fracture is:

[0055]

[0056] Among them, G i Let G be the single-segment fracture controlled reserves of the i-th fracturing segment, and G be the single-well fracture controlled reserves.

[0057] The formula for calculating the fracturing contribution rate mentioned above is:

[0058]

[0059] Among them, W i G is the contribution rate of the i-th stage of fracturing. i Let G be the single-segment fracture controlled reserves of the i-th fracturing segment, and G be the single-well fracture controlled reserves.

[0060] Using the above formula and based on the data in Table 3, the fracturing contribution rate of each fracturing section can be obtained as shown in Table 4 below. Furthermore, the gas production here is based on daily gas production; for example, well A has a daily gas production of 63,500 m³. 3 / d, then based on the fracturing contribution rate data in Table 4, the daily gas production of each fracturing section of Well A can be obtained, and the specific data are shown in Table 4 below.

[0061] Specifically, the formula for calculating the gas production from the splitting process is as follows:

[0062]

[0063] Where Q is the gas production per well, Q pi W represents the gas production from the i-th fracturing stage. i The contribution rate of the fracturing in the i-th segment.

[0064] Table 4

[0065]

[0066] Based on the data in Table 4, a comparison is made between the production yield obtained using this method and the production yield obtained using existing gas production profile testing methods. It can be seen that the production yields of each fracturing segment obtained in this application are basically consistent with those obtained by existing technologies. However, existing gas production profile testing requires certain conditions to be met at the surface and in the wellbore, and it suffers from drawbacks such as construction risks and high investment costs. In contrast, this application only requires obtaining the total production data of a single well. Based on the fracturing contribution rate of each segment, the production yield of each fracturing segment can be obtained. Furthermore, the fracturing contribution rate is stable over a certain period, and it is not necessary to repeatedly calculate the contribution rate in subsequent production segmentation processes. Only the total production data to be segmented needs to be obtained, and the production yield can be obtained through simple calculation based on the already obtained fracturing contribution rate. Therefore, the production yield calculated by this application is not only more accurate than that calculated by existing methods, but the calculation process is also relatively simple.

[0067] In addition, as shown in Table 4, the reservoir properties of sections 5 and 9 in well A are good, the gas content is good, and the fracturing scale is large. The calculated fracture-controlled reserves are also high, and the contribution of production per section is large. It can be determined that sections 5 and 9 are the main gas-producing sections. On the other hand, the reservoir properties of sections 1, 6, and 7 are poor, the gas content is poor, the fracturing scale is relatively small, the fracture-controlled reserves are low, and the contribution of production per section is small or non-existent.

[0068] This application is primarily used in the analysis of the contribution rate of each fractured segment in a single well during staged fracturing of highly heterogeneous reservoirs. Based on reservoir data and fracture-controlled volume, the controlled reserves of a single fracture segment are obtained, further leading to the controlled reserves of the entire well. The production contribution of each fractured segment is then determined based on its proportion within the total controlled reserves of the entire well. This method avoids situations where surface or wellbore conditions prevent production profiling to determine the contribution of each fractured segment, reduces construction risks and investment costs during gas production profiling, and is easy to operate and highly practical. It also solves the problem of inaccurate contribution rate determination in existing methods. This provides a data foundation for understanding the initial production capacity of each segment in multi-stage fracturing horizontal wells and facilitates guidance and optimization of fracturing location and construction parameters, which is of great significance for the refined development of gas fields.

[0069] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still make modifications to the technical solutions described in the foregoing embodiments without creative effort, or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for splitting the initial production of a multi-stage fractured horizontal well in a tight sandstone gas reservoir, characterized in that, The method includes the following steps: Acquire reservoir data, geostress data and fracturing data for each fracturing section of a horizontal well. The reservoir data includes porosity and gas saturation. Based on the acquired data, the fracture network characteristics of each fracturing segment are obtained, and the single-segment controlled volume of each fracturing segment is calculated accordingly. The fracture network characteristics include the fracture half-length, the swept half-width, and the fracture half-height. The formula for calculating the single-segment controlled volume is as follows: ， Among them, V i Let a be the single-segment seam control volume of the i-th segment. i Let b be the half-length of the fracture in the i-th fracturing segment. i Let c be the sweep half-width of the i-th fracturing segment. i Let be the half-height of the fracture in the i-th fracturing segment; The controlled fracture volume of each fractured section and reservoir data are used to calculate the controlled fracture reserves of the corresponding fractured section. The sum of the controlled fracture reserves of each fractured section in a single well is taken as the controlled fracture reserves of that single well. The ratio of the controlled reserves of a single fracture segment to the controlled reserves of a single well fracture is used as the fracture contribution rate of the corresponding fracture segment. The split gas production of the corresponding fracture segment is determined by using the fracture contribution rate of each fracture segment and the gas production of a single well.

2. The method for splitting the initial production of multi-stage fractured horizontal wells in tight sandstone gas reservoirs according to claim 1, characterized in that, The formula for calculating the controlled reserves of a single fracture is: ， Among them, G i Let Bg be the controlled reserves of a single fracture in the i-th fracturing stage, and V be the natural gas volume factor. i Let i be the single-segment seam control volume of the i-th segment. Let be the porosity of the i-th segment. Let be the gas saturation of the i-th segment.

3. The method for splitting the initial production of multi-stage fractured horizontal wells in tight sandstone gas reservoirs according to claim 2, characterized in that, The formula for calculating the controlled reserves of a single well due to fractures is: ， Among them, G i Let G be the single-segment fracture controlled reserves of the i-th fracturing segment, and G be the single-well fracture controlled reserves.

4. The method for splitting the initial production of multi-stage fractured horizontal wells in tight sandstone gas reservoirs according to claim 3, characterized in that, The formula for calculating the fracturing contribution rate is: ， Among them, W i G is the contribution rate of the i-th stage of fracturing. i Let G be the single-segment fracture controlled reserves of the i-th fracturing segment, and G be the single-well fracture controlled reserves.

5. The method for initial production splitting of multi-stage fracturing horizontal wells in tight sandstone gas reservoirs according to any one of claims 1-4, characterized in that, The formula for calculating the gas production from the splitting process is as follows: ， Where Q is the gas production per well, Q pi W represents the gas production from the i-th fracturing stage. i The contribution rate of the fracturing in the i-th segment.

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