A method for determining regional stress field of underground coal mine by sectional hydraulic fracturing

Abstract

The present application belongs to the technical field of hydraulic fracturing in coal mine, and relates to a method for measuring regionalized stress field of staged hydraulic fracturing in coal mine. The method comprises the following steps: step S1, determining the staged parameters and position parameters of the fracturing section of the hydraulic fracturing borehole to be measured; step S2, designing the measuring point arrangement scheme of each fracturing section; step S3, constructing the stress detection special roadway for burying the stress detection equipment for each fracturing section; step S4, burying and constructing the stress detection special borehole for burying the stress detection equipment in the stress detection special roadway; step S5, installing the stress detection equipment into the stress detection special borehole and plugging the stress detection special borehole; and step S6, collecting and analyzing the detection data of the stress detection equipment. The present application can accurately measure the regionalized stress field of staged hydraulic fracturing, improve the accuracy and reliability of the measurement of the hydraulic fracturing stress field, and provide a more scientific guidance basis for the implementation of the staged hydraulic fracturing technology in coal mine.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of hydraulic fracturing in coal mine, and relates to a method for measuring regionalized stress field of staged hydraulic fracturing in coal mine. BACKGROUND

[0002] The rapid development of directional long borehole drilling technology in coal mine provides an effective solution to many technical problems in the process of coal mining. Especially in the fields of regionalized modification pressure relief and anti-collision in thick hard roof, gas permeation and extraction in coal seam, and increasing caving property of thick hard top coal, the staged hydraulic fracturing technology of directional long borehole drilling in coal mine shows significant advantages. The widespread application of this technology not only improves the efficiency of coal mining, but also helps to ensure the safety of coal production.

[0003] In the process of hydraulic fracturing, some key parameters are usually investigated to verify the fracturing effect and guide the subsequent construction. However, the current investigation parameters of staged hydraulic fracturing mainly focus on the hydraulic fracturing radius, and the investigation of hydraulic fracturing stress field is relatively less. In fact, due to rock mass rupture and high-pressure water injection in the process of hydraulic fracturing, stress concentration or pressure relief phenomenon will inevitably occur in a certain area of coal rock mass. Especially in staged hydraulic fracturing, the stress interference phenomenon between stages is particularly obvious, which has an important influence on the expansion of fracture and the effect of fracturing. Therefore, accurately measuring the regionalized stress field of staged hydraulic fracturing is of great significance to guide the implementation of fracturing technology.

[0004] However, in the field of oil and gas development, due to the inability to truly enter the underground space to install test sensor instruments, only indirect test means can be used to infer the stress field. In contrast, the coal mine being mined has the condition of constructing roadways and boreholes at any location, which provides a rare engineering basis for measuring the stress field. However, the existing stress field measurement methods still have many shortcomings, especially in terms of accuracy, which needs to be further improved.

[0005] At present, a commonly used stress field measurement method is to deduce and calculate through microseismic signals. However, this method has obvious inaccuracy. On the one hand, the microseismic signal formed by the coal rock rupture signal is not completely equivalent to the stress transmission signal, and there is a certain difference between the two; on the other hand, when fracturing in soft coal seam, there is often no microseismic signal or weak microseismic signal, which makes it impossible to accurately explore the relationship between the distribution of microseismic signal and the distribution of stress field. Therefore, there is an urgent need for a more accurate and reliable stress field measurement method to meet the needs of staged hydraulic fracturing technology in coal mine. SUMMARY

[0006] Therefore, the present application aims to provide a coal mine underground segmented hydraulic fracturing regionalized stress field measurement method, which can accurately measure the regionalized stress field of segmented hydraulic fracturing, improve the accuracy and reliability of the measurement of the hydraulic fracturing stress field, and provide a more scientific guidance basis for the implementation of the coal mine underground segmented hydraulic fracturing technology.

[0007] To achieve the above-mentioned purpose, the present application provides a coal mine underground segmented hydraulic fracturing regionalized stress field measurement method, comprising the following steps:

[0008] Step S1, determining the segmented parameters and position parameters of the hydraulic fracturing drilling fracturing section to be measured;

[0009] Step S2, designing a measurement point arrangement scheme for each fracturing section;

[0010] Step S3, constructing a stress detection special roadway for burying stress detection equipment for each fracturing section;

[0011] Step S4, burying and constructing a stress detection special drill hole for burying stress detection equipment in the stress detection special roadway;

[0012] Step S5, installing stress detection equipment in the stress detection special drill hole and plugging the stress detection special drill hole;

[0013] Step S6, collecting and analyzing the detection data of the stress detection equipment.

[0014] Optionally, step S2 further comprises:

[0015] Step S21, starting from the center of the fracturing section to be measured, arranging a plurality of measurement points along the extension direction of the hydraulic fracturing drill hole and the direction perpendicular to the extension path of the hydraulic fracturing drill hole, respectively, and the plurality of measurement points are distributed in a cross shape as a whole, and the distance between each two adjacent measurement points is x, x is 5-15m.

[0016] Step S22, calculating the number of measurement points according to the following formula:

[0017] The number of measurement points in the extension direction of the hydraulic fracturing drill hole is c1, c1=d1 / x;

[0018] The number of measurement points in the direction perpendicular to the extension path of the hydraulic fracturing drill hole is c2, c2=d2 / x;

[0019] The total number of measurement points is c, c=c1+c2;

[0020] Wherein, d1 is the predicted fracturing range value of the fracturing section in the extension direction of the hydraulic fracturing drill hole, d2 is the predicted fracturing range value of the fracturing section perpendicular to the extension path of the hydraulic fracturing drill hole; the final calculation value of the total number of measurement points c is rounded to an integer.

[0021] Optionally, in step S3, a stress detection special roadway for burying stress detection equipment is arranged in the rock layer under the coal seam of the hydraulic fracturing area corresponding to each fracturing section in a manner perpendicular to the extension path of the hydraulic fracturing borehole, the stress detection special roadway passes through the projection of the center of the fracturing section on the horizontal plane, and the vertical distance between the stress detection special roadway and the coal seam is 20-30 m.

[0022] Optionally, in step S4, a stress detection special borehole for burying stress detection equipment is drilled to the measuring point in the stress detection special roadway in a see-coal-stop manner, and the actual depth k of each stress detection special borehole is recorded. n .

[0023] Optionally, step S5 further comprises:

[0024] Step S51, preparing u number of oil pillow stress gauges and u number of electronic pressure transmitters,

[0025] When c1 and c2 are both odd numbers, u=c-1,

[0026] When at least one of c1 and c2 is an even number, u=c; wherein,

[0027] The y of the oil pipe length of the oil pillow stress gauge is related to the actual depth of the stress detection special borehole, y=k n +2(m).

[0028] Step S52, pushing the oil pillow stress gauges into the corresponding stress detection special borehole bottoms one by one, and sealing the entire stress detection special borehole with cement slurry.

[0029] Step S53, after 10 days, installing an electronic pressure transmitter at the orifice of each stress detection special borehole, and supplementing the pressure in the oil pipe of the oil pillow stress gauge to 3 MPa.

[0030] Step S54, preparing 1 set of networking substation with a channel number greater than u, connecting all the electronic pressure transmitters to the networking substation, and debugging to make the signal transmittable to the ground computer.

[0031] Optionally, in step S6, the ground computer records the stress data before, during and after hydraulic fracturing, and calculates and analyzes the distribution of the stress field with time and space.

[0032] The beneficial effects of the present application are:

[0033] The technical effect of the present application is remarkable. A practical solution is proposed for the technical problem of regional stress field measurement of underground segmented hydraulic fracturing in coal mines.

[0034] Firstly, the present application effectively solves the problems of single point stress testing and the ineffective combination of stress testing and hydraulic fracturing by the method of close-range arrangement of multiple sensors. Compared with the traditional microseismic signal measurement method, the present application can more accurately reflect the real distribution of the stress field of the coal rock mass during the hydraulic fracturing process. This is because the arrangement of multiple sensors can cover a wider area and capture more information about the changes in the stress field, thereby improving the accuracy and reliability of the measurement.

[0035] Secondly, the method of the present application has the feature of regionalized measurement. By scientifically and reasonably designing the measurement point layout and the sensor embedding process, the present application can accurately measure the stress field of any segment of the segmented hydraulic fracturing. This regionalized measurement method not only improves the comprehensiveness of the stress field measurement, but also provides a more scientific basis for subsequent hydraulic fracturing construction.

[0036] In addition, the present application also takes full advantage of the convenient conditions of underground coal mine construction, and realizes the close-range measurement of the stress field by embedding stress detection special roadways and stress detection special boreholes. This measurement method not only reduces the measurement cost, but also improves the efficiency and accuracy of the measurement. At the same time, the present application also uses advanced electronic pressure transmitters and networking substation technology to realize real-time transmission and remote monitoring of stress data, providing a strong guarantee for coal mine safety production.

[0037] In summary, the technical effects of the present application mainly include improving the accuracy and reliability of the hydraulic fracturing stress field measurement, realizing regionalized measurement, fully utilizing the convenient conditions of underground coal mine construction, and reducing the measurement cost and improving the measurement efficiency. Not only does it provide a more scientific basis for the implementation of the segmented hydraulic fracturing technology in underground coal mines, but also provides strong support for coal mine safety production and efficient mining.

[0038] Other advantages, objects and features of the present application will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or can be learned by practice of the present application. The objects and other advantages of the present application can be realized and attained by the methods and instrumentalities set forth in the description. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to make the objects, technical solutions and advantages of the present application clearer, the preferred detailed description of the present application will be made below in combination with the drawings, in which:

[0040] Figure 1 The flowchart of the method for regionalized stress field measurement of segmented hydraulic fracturing in underground coal mines provided by the present application;

[0041] Figure 2A borehole layout plan for the method of measuring the regionalized stress field of segmented hydraulic fracturing in coal mines provided by the present invention;

[0042] Figure 3 The borehole layout profile along the I-I direction is shown in the method for determining the regionalized stress field of segmented hydraulic fracturing in coal mines provided by this invention. Detailed Implementation

[0043] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0044] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures, and should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0045] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0046] To address the numerous shortcomings of existing technologies, this invention proposes a regionalized stress field measurement method for segmented hydraulic fracturing in coal mines. This method not only solves the problems of single-point stress testing and ineffective integration of stress testing and hydraulic fracturing, but also improves the accuracy and reliability of stress field measurement. As a result, it can more effectively guide the implementation of segmented hydraulic fracturing technology and improve the efficiency and safety of coal mining.

[0047] like Figure 1 As shown, the method for determining the zoned stress field of underground hydraulic fracturing in coal mines according to the present invention specifically includes the following steps:

[0048] Step S1, determining the segmentation parameters and location parameters of the hydraulic fracturing drilling fracturing section to be measured;

[0049] Step S2, designing the measurement point arrangement scheme of each fracturing section;

[0050] Step S3, constructing a stress detection special roadway for burying stress detection equipment for each fracturing section;

[0051] Step S4, burying and constructing a stress detection special borehole for burying stress detection equipment in the stress detection special roadway;

[0052] Step S5, installing stress detection equipment in the stress detection special borehole and plugging the stress detection special borehole;

[0053] Step S6, collecting and analyzing the detection data of the stress detection equipment.

[0054] Further, step S2 includes:

[0055] Step S21, determining the layout range: as shown in the figure, taking the center of the fracturing section to be measured as the reference, designing the measurement points with a spacing of x along the hydraulic fracturing drilling extension path and in the direction perpendicular to the hydraulic fracturing drilling extension path, the measurement point shape is a cross, the cross center is at the fracturing section center, and the spacing x between adjacent two measurement points is 5-15m; Figure 2

[0056] Step S22, calculating the number of measurement points c: according to the predicted fracturing range value d1 of the hydraulic fracturing drilling extension and the predicted fracturing range value d2 in the direction perpendicular to the hydraulic fracturing drilling extension path, the number of measurement points c1 on the hydraulic fracturing drilling extension path is d1 / x, the number of measurement points c2 in the direction perpendicular to the hydraulic fracturing drilling extension path is d2 / x, the calculated value is rounded to an integer, and c=c1+c2

[0057] Specifically, in step S3, as shown in the figure, Figure 2 , Figure 3 In the rock layer below the coal seam in the hydraulic fracturing area, a stress detection special roadway perpendicular to the fracturing drilling direction is constructed, the stress detection special roadway passes through the fracturing section center projection, and the vertical distance of the stress detection special roadway from the coal seam is 20-30m.

[0058] Specifically, in step S4, in the stress detection special roadway, the stress detection special borehole is constructed to the designed measurement point, the stress detection special borehole is constructed to the coal seam, and the actual depth k of each stress detection special borehole is recorded n .

[0059] Further, step S5 includes:

[0060] ​Step S51, determining the type, quantity and parameters of the stress sensing device: preparing u number of oil pillow stress gauges and u number of electronic pressure transmitters, u=c-1 (center repetition) when c1 and c2 are both odd, and u=c in other cases, the oil pillow stress gauge oil pipe length y is prepared according to the actual depth of the stress detection special drill hole, y=k n +2(m);

[0061] Step S52, installing the stress gauge: after pushing the oil pillow stress gauge into the hole bottom of the corresponding stress detection special drill hole one by one, the entire stress detection special drill hole is blocked with cement slurry;

[0062] Step S53, installing the electronic pressure transmitter: after 10 days, the electronic pressure transmitter is installed at the orifice of the stress detection special drill hole, and the pressure in the oil pillow stress gauge oil pipe is supplemented to 3MPa;

[0063] Step S54, installing other supporting equipment: preparing 1 set of networking substation with a channel number greater than u, connecting all electronic pressure transmitters to the networking substation, and debugging to make the signal transmittable to the ground computer.

[0064] Specifically, in step S6, the ground computer records the stress data before, during and after hydraulic fracturing, and analyzes the distribution of the stress field with time and space.

[0065] The present application provides a kind of coal mine underground segmented hydraulic fracturing regionalized stress field determination method, by the close-range arrangement of multiple sensors and scientific and reasonable measuring point design and sensor burying process, accurate, comprehensive determination of stress field is realized, effectively solve the problem of traditional microseismic signal determination method inaccuracy, stress field distribution is not clear etc., fully utilize the convenient conditions of coal mine construction, reduce the determination cost, improve the determination efficiency and safety, provide strong support for the implementation of coal mine underground segmented hydraulic fracturing technology and coal mine safety production.

[0066] Finally, it should be pointed out that the above examples are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the spirit and scope of the present technical solutions, which should be covered in the scope of the claims of the present application.

Claims

1. A method for determining the regionalized stress field of segmented hydraulic fracturing in underground coal mines, characterized in that, Includes the following steps: Step S1: Determine the segmentation parameters and location parameters of the hydraulic fracturing borehole fracturing section that need to be measured; Step S2: Design the layout scheme of measuring points for each fracturing section; Step S3: Construct a dedicated stress testing tunnel for each fracturing section to install stress testing equipment; Step S4: Construct a special borehole for stress testing in the dedicated stress testing tunnel for installing stress testing equipment; Step S5: Install stress testing equipment into the stress testing borehole and seal the stress testing borehole; Step S6: Collect and analyze the detection data from the stress testing equipment; Step S2 further includes: Step S21: Starting from the center of the fracturing section to be measured, arrange multiple measuring points along the extension direction of the hydraulic fracturing borehole and in a direction perpendicular to the extension path of the hydraulic fracturing borehole. The multiple measuring points are arranged in a cross shape, and the distance between any two adjacent measuring points is x, where x is 5~15m. Step S22: Calculate the number of measuring points according to the following formula: The number of measuring points along the extension direction of the hydraulic fracturing borehole is c1, where c1 = d1 / x; The number of measuring points perpendicular to the extension path of the hydraulic fracturing borehole is c2, where c2 = d2 / x; The total number of measuring points is c, where c = c1 + c2; Wherein, d1 is the expected fracturing range of the fracturing section in the direction of extension of the hydraulic fracturing borehole, and d2 is the expected fracturing range of the fracturing section perpendicular to the extension path of the hydraulic fracturing borehole; the final calculated value of the total number of measuring points c is rounded to the nearest integer. In step S3, a dedicated stress detection roadway for burying stress detection equipment is arranged in the rock strata below the coal seam in the hydraulic fracturing area corresponding to each fracturing section, in a manner perpendicular to the extension path of the hydraulic fracturing borehole. The dedicated stress detection roadway passes through the projection of the center of the fracturing section on the horizontal plane, and the vertical distance between the dedicated stress detection roadway and the coal seam is 20~30m. Step S5 further includes: Step S51: Prepare u oil-filled stress gauges and u electronic pressure transmitters. When both c1 and c2 are odd numbers, u = c - 1. When at least one of c1 and c2 is an even number, u = c; where, The length y of the oil pipe of the oil conservator stress gauge is related to the actual depth of the stress detection borehole, y=k n +2 (m).

2. The determination method according to claim 1, characterized in that: In step S4, stress detection boreholes for burying stress detection equipment are drilled into the measuring point in the stress detection roadway in a manner that stops as soon as coal is encountered, and the actual depth k of each stress detection borehole is recorded. n .

3. The determination method according to claim 1, characterized in that: Step S5 further includes: Step S52: Push the oil-filled stress gauges one by one to the bottom of the corresponding stress detection borehole, and seal the entire stress detection borehole with cement grout.

4. The determination method according to claim 3, characterized in that: Step S5 further includes: Step S53, 10 days later, install an electronic pressure transmitter at the opening of each of the stress detection boreholes and pressurize the oil pipe of the oil tank stress gauge to 3MPa.

5. The determination method according to claim 4, characterized in that: Step S5 further includes: Step S54: Prepare a networked substation with more than u channels, connect all the electronic pressure transmitters to the networked substation, and debug to ensure that the signal can be transmitted to the ground computer.

6. The determination method according to claim 5, characterized in that: In step S6, the ground computer records stress data before hydraulic fracturing, stress data during hydraulic fracturing, and data after hydraulic fracturing, and calculates and analyzes the distribution of the hydraulic fracturing stress field over time and space.

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