Initial yield splitting method for multi-section fractured horizontal well of tight sandstone gas reservoir

Abstract

The invention discloses a tight sandstone gas reservoir multi-section fractured horizontal well initial stage yield splitting method, and belongs to the field of tight sandstone, the method comprises the following steps: firstly obtaining reservoir data, crustal stress data and fracturing data of a reservoir corresponding to a fractured section, using an existing fracturing model to simulate according to the obtained data, and the like. The fracture control volume of the fracturing section is obtained; according to the obtained data and reservoir data, single-section fracture control reserves of the fracturing sections are calculated, and the sum value of the single-section fracture control reserves of all the fracturing sections in the single well serves as single-well fracture control reserves of the corresponding single well. Then the splitting gas production rate of the corresponding fracturing section is determined according to the ratio of the single-section fracture control reserves to the single-well fracture control reserves; according to the method, the initial productivity of each section of the multi-section fractured horizontal well can be known conveniently, a data basis is provided for guiding optimization of fracturing positions and fracturing construction parameters, and the larger the single-section fracture control reserves, the more gas production is facilitated, so that the fracturing contribution rate determined by the single-section fracture control reserves is accurate.

Description

Technical Field

[0001] The invention belongs to the field of tight sandstone, and in particular relates to an initial production splitting method for a multi-stage fractured horizontal well in a tight sandstone gas reservoir. Background Art

[0002] Tight sandstone gas reservoirs are mostly low-ultra-low porosity and low-ultra-low permeability gas reservoirs, with no natural production capacity or low natural production capacity, and usually need to be improved by sand fracturing. In recent years, multi-stage fracturing horizontal wells are often used for tight sandstone gas reservoir development. Due to factors such as reservoir heterogeneity and fracturing construction parameters, the reservoir thickness, reservoir, gas content and fracturing scale of each fracturing section of the horizontal well vary greatly. The contribution of each fracturing section to gas production in the same horizontal well varies greatly, and the contribution of each section will change at different production stages.

[0003] At present, the horizontal well gas production profile test is usually used to determine the contribution of each section of the fractured horizontal well to clarify the production characteristics of the fractured section. However, the gas production profile test is greatly affected by the ground and the wellbore. Not every horizontal well can achieve gas production profile testing, and the testing cost is high. To solve the above problems, a Chinese patent application document with application announcement number CN113006760B discloses a method for splitting the production of a multi-stage fractured horizontal well of tight sandstone gas. An ideal fracture section is constructed according to the actual fracture section, and the cosine similarity between the actual fracture section and the ideal fracture section is calculated. Then, based on the cosine similarity, the production contribution rate of the actual fracture section is calculated, and then the production of each section is determined based on the production contribution rate. Among them, the water saturation of the ideal fracture section is the minimum value of the water saturation of all actual fracture sections; the other basic data of the ideal fracture section are the maximum values ​​of the basic data of all actual fracture sections. That is to say, the contribution rate is determined based on the similarity between the actual fracturing section and the ideal section, that is, the conditions of the default ideal fracturing section are the most favorable for gas production, but the minimum water saturation and the maximum other basic data are not necessarily the most favorable for gas production. Therefore, when it cannot be determined that the ideal section is the most favorable for gas production, the contribution rate determined by the scheme based on the ideal fracturing section is also inaccurate.

[0004] In summary, the ideal fracturing section of the existing production splitting scheme is not necessarily the most favorable fracturing section for gas production, resulting in inaccurate contribution rate of the actual fracturing section determined based on the ideal fracturing section. Summary of the invention

[0005] The object of the present invention is to provide a method for splitting the initial production of a multi-stage fractured horizontal well in a tight sandstone gas reservoir, so as to solve the technical problem that the contribution rate of the actual fractured stage determined in the prior art is inaccurate.

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

[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: obtaining reservoir data, ground stress data and fracturing data of a reservoir corresponding to a fracturing stage, the reservoir data including porosity and gas saturation, obtaining fracture network characteristics of each fracturing stage according to the acquired data, and calculating the fracture control volume of each single stage of each fracturing stage based on the characteristics;

[0008] The single-stage fracture controlled reserves of the corresponding fracturing section are calculated according to the single-stage fracture controlled volume of each fracturing section and the reservoir data, and the sum of the single-stage fracture controlled reserves of each fracturing section in a single well is taken as the single-well fracture controlled reserves of the single well; the ratio of the single-stage fracture controlled reserves to the single-well fracture controlled reserves is taken as the fracturing contribution rate of the corresponding fracturing section, and the product of the single well gas production and the fracturing contribution rate is taken as the splitting gas production of the fracturing section.

[0009] The beneficial effects are as follows: firstly, reservoir data, ground stress data and fracturing data of the reservoir corresponding to the fracturing section are obtained, and then, the existing fracturing model is used for simulation according to the obtained data to obtain the fracture control volume of the fracturing section, and the single-stage fracture control reserve of the fracturing section is calculated according to the fracture control volume of the fracturing section and the reservoir data, and the sum of the single-stage fracture control reserves of all fracturing sections in a single well is taken as the single-well fracture control reserve of the corresponding single well, and then the fracturing contribution rate of the corresponding fracturing section is determined according to the ratio of the single-stage fracture control reserve to the single-well fracture control reserve; and the splitting gas production of the corresponding fracturing section is obtained according to the fracturing contribution rate of each fracturing section, that is, when the total gas production of a single well is known, the gas production corresponding to each fracturing section can be guided according to the contribution rate. Through the fracturing contribution rate, we can improve our understanding of the initial production capacity of each section of multi-stage fracturing horizontal wells, and provide a data basis for guiding the optimization of fracturing locations and fracturing construction parameters. In addition, this method mainly determines the fracturing contribution rate based on the fracture controlled reserves. Since the larger the single-stage fracture controlled reserves, the more conducive it is to gas production, the fracturing contribution rate determined by the single-stage fracture controlled reserves is also accurate.

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

[0011]

[0012] Among them, G i is the single-stage fracture controlled reserves of the i-th fracturing stage, Bg is the natural gas volume coefficient, V i is the single-segment fracture control volume of the i-th segment, is the porosity of the i-th segment, Sg i is the gas saturation of the ith section.

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

[0014] As a further improvement, the fracture network characteristics include fracture half-length, half-width and half-height, and the calculation formula for calculating the controlled volume of a single fracture segment is:

[0015]

[0016] Among them, V i is the single-segment crack control volume of the i-th segment, a i is the half length of the fracture in the i-th fracturing section, b i is the half-width of the i-th fracturing stage, c i is the half-height of the fracture in the i-th fracturing stage.

[0017] The beneficial effect is that the fractures created by the fracturing start to spread from the fracturing point to the surrounding areas, and the fracturing force gradually weakens, and the volume of the fractures formed is approximately an ellipsoid. Therefore, simplifying the fracture control volume to an ellipsoid facilitates volume calculation.

[0018] As a further improvement, the calculation formula for single well fracture controlled reserves is:

[0019]

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

[0021] As a further improvement, the calculation formula of fracturing contribution rate is:

[0022]

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

[0024] As a further improvement, the calculation formula for splitting gas production is:

[0025] Q pi =Q×W i

[0026] Among them, Q is the gas production of a single well, Q pi is the gas production of the i-th fracturing stage, W i is the contribution rate of the i-th stage fracturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1It is a plane characteristic diagram of single-stage hydraulic fracturing crack monitoring in the present invention;

[0028] Figure 2 It is a longitudinal characteristic diagram of a single-stage hydraulic fracturing fracture simulation in the present invention;

[0029] Figure 3 It is a well logging curve and production split comparison diagram of the horizontal section of Well A of the present invention;

[0030] Figure 4 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. The components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

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

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

[0034] Well A is a typical horizontal well in the Box 1 gas reservoir of the Lower Shihezi Formation in the X gas field. The actual horizontal section is 800m long, the sandstone is 667m long, and the gas-bearing sandstone is only 309m long. The average total hydrocarbon is 17.56%, the overall gas-bearing sandstone drilling rate is low, and the reservoir thickness and physical properties at different positions in the horizontal section vary greatly. Well A was selected for fracturing in 9 sections, and differentiated fracturing construction was carried out in September 2022. It was put into production in November 2022, and gas production profile testing was carried out at the end of December 2022. The initial production splitting method of multi-stage fracturing horizontal wells in tight sandstone gas reservoirs of this application is specifically adopted, such as Figure 4 As shown, the method comprises the following steps:

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

[0036] The reservoir data, ground stress data and fracturing data of the reservoir corresponding to the fracturing section are obtained. The reservoir data include gas layer thickness, porosity and gas saturation. The fracturing data include displacement, sand addition amount and net liquid volume entering the formation.

[0037] Specifically, the main lithologies encountered in the horizontal section of Well A are fine sandstone, medium sandstone, mudstone, etc. Due to the strong heterogeneity of the reservoir, the lithology, physical properties, and gas content encountered in the wellbore do not represent the reservoir characteristics of the entire region. Therefore, the reservoir data in different fracturing units are determined by combining the vertical and horizontal reservoir predictions of horizontal wells. The reservoir data of each fracturing section of Well A are shown in Table 1 below, and the corresponding fracturing data are shown in Table 1 below.

[0038] Table 1

[0039]

[0040] 2) Calculate the seam control volume.

[0041] According to the acquired data, the half-length and height of the fracturing crack are simulated by the fracturing model, and the affected width of the fracturing crack is determined according to the crack morphology of the crack monitoring. The fracture control volume is approximately an ellipsoid, and the major axis of the ellipsoid is the simulated fracture length. Since the fracture height is generally greater than the gas layer thickness of the target layer, the minor axes are the affected width and gas layer thickness, respectively, and finally the fracture control volume of each fracturing section is calculated. Therefore, the single-section fracture control volume is simplified to an ellipsoid, and the corresponding single-section fracture control volume is calculated according to the half-length, fracture height and affected width of the fracturing section. The calculation formula for calculating the single-section fracture control volume is:

[0042]

[0043] Among them, V i is the single-segment crack control volume of the i-th segment, a i is the half length of the fracture in the i-th fracturing section, b i is the half-width of the i-th fracturing stage, c i is the half-height of the fracture in the i-th fracturing stage.

[0044] 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 Specifically, the single-stage fracture control volume corresponding to each fracturing stage of Well A in this embodiment is shown in Table 2 below:

[0045] Table 2

[0046]

[0047] 3) Calculate the fracture-controlled reserves of a single well.

[0048] First, the single-stage fracture controlled reserves of the corresponding fracture section are calculated according to the single-stage fracture controlled volume of the fracture section and the reservoir data, and then the sum of the single-stage fracture controlled reserves of each fracture section in a single well is taken as the single-well fracture controlled reserves of the single well; the formula for calculating the single-stage fracture controlled reserves is:

[0049]

[0050] Among them, G i is the single-stage fracture controlled reserves of the i-th fracturing stage, Bg is the natural gas volume coefficient, V i is the single-segment fracture control volume of the i-th segment, is the porosity of the i-th segment, Sg i is the gas saturation of the ith section.

[0051] According to the above method for calculating the single-stage fracture controlled reserves, the single-stage fracture controlled reserves of each fracturing stage of Well A are calculated, as shown in Table 3 below:

[0052] Table 3

[0053]

[0054]

[0055] The half-height of the air layer refers to half of the thickness of the air layer, and the half-width of the sweep refers to half of the sweep width.

[0056] 4) Calculate the fracturing contribution rate and split the gas production of a single well.

[0057] like Figure 3 As shown in the figure, the ratio of single-stage fracture controlled reserves to single-well fracture controlled reserves is taken as the fracturing contribution rate of the corresponding fracturing stage, and the product of single-well gas production and fracturing contribution rate is taken as the split gas production of the fracturing stage. The calculation formula for single-well fracture controlled reserves is:

[0058]

[0059] Among them, G i is the single-stage fracture controlled reserves of the i-th fracturing stage, and G is the single-well fracture controlled reserves.

[0060] The calculation formula of the above fracturing contribution rate is:

[0061]

[0062] Among them, W i is the contribution rate of the i-th stage fracturing, G i is the single-stage fracture controlled reserves of the i-th fracturing stage, and G is the single-well fracture controlled reserves.

[0063] Using the above formula and the data in Table 3 above, the data of the fracturing contribution rate of each fracturing stage can be obtained as shown in Table 4 below. In addition, the gas production here is based on the daily gas production as an example. The daily gas production of Well A is 63500m 3 / d, then according to the fracturing contribution rate data in Table 4, the splitting daily gas production of each fracturing section of Well A can be obtained. The specific data are shown in Table 4 below.

[0064] Specifically, the above splitting gas production calculation formula is:

[0065]

[0066] Among them, Q is the gas production of a single well, Q pi is the gas production of the i-th fracturing stage, W i is the contribution rate of the i-th stage fracturing.

[0067] Table 4

[0068]

[0069] According to the data in Table 4, the splitting production obtained according to this method is compared with the production profile test production obtained by the existing gas production profile test method. It can be seen that the production of each fracturing section obtained by this application is basically consistent with that of the prior art. However, the existing gas production profile test requires the ground and the wellbore to meet certain conditions before it can be implemented, and there are disadvantages of high construction risks and investment costs during the test process; while this application only needs to obtain the total production data of a single well, and according to the fracturing contribution rate of each section, the splitting production of each fracturing section can be obtained, and the fracturing contribution rate is stable within a certain period of time. In the subsequent production splitting process, there is no need to repeatedly calculate the contribution rate, only the total production data that needs to be split is obtained, and the splitting production can be obtained by a simple calculation based on the already obtained fracturing contribution rate. It can be seen that the splitting production calculated by this application relative to the existing method is not only accurate, but also the calculation process is relatively simple.

[0070] In addition, it can be seen from Table 4 that the reservoir properties of the 5th and 9th sections of Well A are good, the gas content is good, the fracturing scale is large, the calculated fracture-controlled reserves are also high, and the single-section production contribution ratio is large. It can be determined that the 5th and 9th sections are the main gas-producing sections; while the reservoir properties of the 1st, 6th and 7th sections are poor, the gas content is poor, the fracturing construction scale is relatively small, the fracture-controlled reserves are low, and the single-section production contribution ratio is small or no contribution.

[0071] The main application of this application is the analysis of the contribution rate of each fracturing stage in a single well of a highly heterogeneous reservoir. The single-stage fracture controlled reserves are obtained based on the reservoir data and the fracture controlled volume, and the single-well fracture controlled reserves are further obtained. The production contribution of each fracturing stage is determined based on the proportion of the single-stage fracture controlled reserves in the single-well fracture controlled reserves. In the process of production splitting, this method not only avoids the situation where the contribution of each fracturing stage cannot be grasped by production profile testing due to reasons such as the ground and the wellbore, but also reduces the construction risk and investment cost during the gas production profile test. It is easy to operate and has strong practicality. At the same time, it solves the problem of inaccurate determination of the existing contribution rate. It provides a data basis for understanding the initial production capacity of each stage of multi-stage fracturing horizontal wells, and is also convenient for guiding and optimizing the fracturing location and fracturing construction parameters, which is of great significance for the fine development of gas fields.

[0072] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions recorded in the aforementioned embodiments without creative work, or replace some of the technical features therein with equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for splitting the initial production of multi-stage fractured horizontal wells in tight sandstone gas reservoirs, characterized in that: The method comprises the following steps: Acquire reservoir data, geostress data and fracturing data of reservoirs corresponding to each fracturing section of the horizontal well, wherein the reservoir data includes porosity and gas saturation; The fracture network characteristics of each fracturing stage are obtained based on the acquired data, and the fracture control volume of each fracturing stage is calculated based on this; The single-stage fracture controlled reserves of the corresponding fracture stage are calculated according to the single-stage fracture controlled volume of each fracture stage and the reservoir data, and the sum of the single-stage fracture controlled reserves of each fracture stage in a single well is taken as the single-well fracture controlled reserves of the single well; The ratio of single-stage fracture controlled reserves to single-well fracture controlled reserves is taken as the fracturing contribution rate of the corresponding fracturing stage, and the splitting gas production of the corresponding fracturing stage is determined by using the fracturing contribution rate of each fracturing stage and the gas production of the 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 is the single-stage fracture controlled reserves of the i-th fracturing stage, Bg is the natural gas volume coefficient, V i is the single-segment fracture control volume of the i-th segment, is the porosity of the i-th segment, Sg i is the gas saturation of the ith section.

3. 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 fracture network characteristics include fracture half-length, half-width and half-height, and the calculation formula of the controlled volume of a single fracture segment is: Among them, V i is the single-segment crack control volume of the i-th segment, a i is the half length of the fracture in the i-th fracturing section, b i is the half-width of the i-th fracturing stage, c i is the half-height of the fracture in the i-th fracturing stage.

4. 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 calculation formula for single well fracture controlled reserves is: Among them, G i is the single-stage fracture controlled reserves of the i-th fracturing stage, and G is the single-well fracture controlled reserves.

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

6. The method for splitting the initial production of multi-stage fractured horizontal wells in tight sandstone gas reservoirs according to any one of claims 1 to 5, characterized in that: The calculation formula of splitting gas production is: Q pi =Q×W i Among them, Q is the gas production of a single well, Q pi is the gas production of the i-th fracturing stage, W i is the contribution rate of the i-th stage fracturing.

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