Fracture direction determination device and method

Abstract

The invention discloses a fracture direction determining device and method.The fracture direction determining device is arranged in a testing section of a hydraulic fracturing method and comprises a plurality of pressure sensors, a sensor support and an electronic compass with a storage function, the pressure sensors are fixed to the sensor support, and the electronic compass is arranged on the sensor support. The pressure sensors are fixed on the sensor support, the fixed pressure sensors are distributed at intervals in the circumferential direction of a drill hole of the test section, and the electronic compass is arranged on the sensor support, electrically connected with the pressure sensors and used for recording the direction change of the electronic compass and the pressure change of the pressure sensors. The pressure sensors which are annularly arranged are adopted to obtain the pressure around the hole, then the crack is accurately positioned, and the device is suitable for symmetric or asymmetric fracturing cracks.

Description

Technical Field

[0001] The invention belongs to the technical field of engineering geological survey, and in particular relates to a device and method for determining a crack direction. Background Art

[0002] Conventional hydraulic fracturing geostress testing is mainly divided into two parts: hydraulic fracturing test and fracture impression test. According to the mechanical theory of hydraulic fracturing, the stress value and stress direction of the test rock mass can be obtained respectively. At present, the conventional test method of hydraulic fracturing geostress is mainly achieved by independently testing the stress magnitude and direction, which is time-consuming, cumbersome to operate, and repeated testing can easily lead to borehole instability, requiring a lot of manpower and material resources. With the development of technology, some hydraulic fracturing geostress testing devices that can simultaneously collect stress magnitude and direction have also emerged. According to their main characteristics, they can be divided into three categories: the first is to characterize the direction of the fracture based on the wave velocity imaging method during the fracture test; the second is to directly show the fracture direction in the process of fracture formation by combining the borehole television imaging method; the third is to use a guide plate to determine the fracture direction (CN116816337A). All three methods can simultaneously collect the stress magnitude and direction of the test rock mass, but the manufacturing cost of the first two is very high and the degree of promotion is low. In the actual application process, the third method has a large fluctuation with the water flow during use because the pressure fracture is not completely symmetrical, resulting in a large error in the crack positioning. Therefore, it is necessary to develop a crack determination device and method that is more convenient to use and more accurately oriented.

[0003] Bernoulli's principle is a basic principle in fluid mechanics. It was proposed by Swiss fluid physicist Daniel Bernoulli in 1726. Its essence is the conservation of mechanical energy of an ideal fluid. Under ideal conditions, the sum of the kinetic energy, potential energy and pressure potential energy of a unit volume of fluid at any cross section of the same flow tube is a constant. Its most famous corollary is that when the flow is constant, the greater the flow velocity, the smaller the pressure. According to this principle, during the hydraulic fracturing process, when cracks are generated in the surrounding rock, the flow velocity at the crack position is the largest and the pressure is the smallest, so this feature can be used to locate the crack. Summary of the invention

[0004] One object of the present invention is to provide a device for determining the direction of a crack in order to address the deficiencies in the prior art. The device can accurately and conveniently determine the direction of the crack, is not affected by ground stress testing, and is effective for various forms of crack orientation.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A device for determining the direction of a fracture, which is arranged in a test section of a hydraulic fracturing method, and comprises: a plurality of pressure sensors, a sensor bracket and an electronic compass with a storage function, wherein the plurality of pressure sensors are fixed on the sensor bracket, and after being fixed, the plurality of pressure sensors are arranged at intervals along the circumference of a borehole of the test section, and the electronic compass is arranged on the sensor bracket, and the electronic compass is also electrically connected to the plurality of pressure sensors for recording changes in the azimuth of the electronic compass and changes in the pressure of each pressure sensor.

[0007] Furthermore, the sensor bracket includes a central rod, a plurality of support rods arranged along the circumference of the central rod, and a fixing ring fixed on the plurality of support rods, a plurality of pressure sensors are arranged at equal intervals on the fixing ring, and the electronic compass is arranged next to the central rod or on the end side of the central rod.

[0008] Furthermore, the number of the pressure sensors is determined according to the measurement accuracy, and the angle between adjacent sensors and the center of the hole is the measurement accuracy.

[0009] Furthermore, when the electronic compass is installed, the initial relative position between the electronic compass and one of the pressure sensors is recorded.

[0010] Furthermore, the volume of the pressure sensor is so small as not to interfere with the flow direction of the water.

[0011] Another object of the present invention is to provide a method for determining a crack direction according to the above crack direction determining device, comprising the following steps:

[0012] S1: installing a fracture direction determination device, recording the initial relative position between the electronic compass baseline and one of the pressure sensors, placing the fracture direction determination device in a hydraulic fracturing drilling test section, and conducting a hydraulic fracturing ground stress test;

[0013] S2: During the test, the electronic compass records the pressure changes of each pressure sensor;

[0014] S3: After the test is completed, take out the electronic compass and read the data, compare the pressure of each pressure sensor during the closing and reopening stage, and the position of the pressure sensor with the two local minimum pressure values ​​is the crack position;

[0015] S4: Determine the crack's major azimuth according to the initial relative position between the electronic compass baseline and one of the pressure sensors, the electronic compass reading during the reopening phase, and the location of the pressure sensor with the lowest pressure value. That is, the angle between the electronic compass reading scale and the scale corresponding to the initial relative position is the crack's major azimuth.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: the fracture direction determining device of the present invention is oriented according to the Bernoulli principle, that is, the faster the water flow speed in the borehole, the lower the pressure, and around the borehole, the water flow rate close to the fracture position is the fastest, so the circumferential pressure of the borehole can be used to determine the orientation of the fracture. Therefore, the present invention adopts a ring-shaped pressure sensor to obtain the circumferential pressure, and then accurately locates the fracture, which is suitable for symmetrical or asymmetrical fractures, and has low manufacturing cost and is easy to use. In addition, the present invention can be carried out simultaneously with the hydraulic fracturing method without interfering with the ground stress. Since multiple pressure test sections can be set on the center rod at the same time, it is not necessary to lift the drill one section at a time, which effectively improves efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A top view of a crack direction determination device according to an embodiment of the present invention;

[0018] Figure 2 A schematic diagram of the structure of a device for determining the direction of cracks according to an embodiment of the present invention when multiple pressure test sections are set;

[0019] Figure 3 This is a schematic diagram of the structure of an electronic compass installed at the end of a center rod according to an embodiment of the present invention;

[0020] Figure 4 It is a schematic diagram of the structure when confirming the crack direction according to an embodiment of the present invention. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present invention will be described clearly and completely below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0023] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0024] like Figure 1As shown, an embodiment of the present invention discloses a device for determining the direction of a fracture, which is arranged in a test section of a hydraulic fracturing method, and includes: a plurality of pressure sensors 1, a sensor bracket 2, and an electronic compass 3 with a storage function. The sensor bracket 2 includes a central rod 20, a plurality of support rods 21 arranged circumferentially along the central rod 20, and a fixing ring 22 fixed on the plurality of support rods 21. The plurality of pressure sensors 1 are arranged at equal intervals on the fixing ring 22, and the plurality of pressure sensors 1 fixed on the fixing ring 22 are distributed in a circular array. The number of pressure sensors 1 is determined according to the measurement accuracy, and the angle of adjacent pressure sensors 1 relative to the center of the borehole 5 is the measurement accuracy. In this embodiment, 20 pressure sensors are arranged circumferentially of the borehole 5, and the accuracy thereof is 180° / 20=9°. In order to be able to simultaneously test the directions of fractures in multiple sections of boreholes 5, see Figure 2 , multiple pressure test sections 4 can be arranged in the borehole 5, that is, multiple circles of support rods 21 are arranged on the central rod 20, a fixing ring 22 is fixed on each circle of support rods 21, and the pressure test sections 4 formed by multiple pressure sensors 1 on each fixing ring 22 are arranged parallel to each other and are perpendicular to the axial direction of the borehole 5. In addition, in order to prevent the pressure sensor 1 from affecting the water flow and affecting the accuracy of the fracture orientation, the pressure sensor 1 is small enough not to interfere with the water flow too much. When the accuracy requirement is low, a micro pressure sensor can be used, and when the accuracy requirement is high, a distributed pressure sensor can be used.

[0025] The electronic compass 3 with storage function can be installed beside the center pole 20, or can be installed at the end of the center pole 20 (see Figure 3 ), but should not be installed on the test section. The installed electronic compass 3 is electrically connected to multiple pressure sensors 1, which are used to record the azimuth changes of the electronic compass 3 with storage function and the pressure changes of each pressure sensor 1. In order to facilitate the subsequent calculation of the direction of the crack based on the data recorded by the electronic compass 1 with storage function, the initial relative position of the electronic compass 1 with storage function and one of the pressure sensors 1 should be recorded before the test.

[0026] See Figure 4 When using the crack direction determining device to determine the crack direction, the following steps are included:

[0027] Step 1: Install the crack direction determination device first, record the initial relative position between the baseline of the electronic compass 3 with storage function and one of the pressure sensors, and in order to facilitate subsequent calculation and positioning, the pressure sensors 1 located on the same pressure test section 4 can be numbered. In this embodiment, the pressure sensors 1 are numbered as S1 to S2. 20 , the initial relative orientation between the electronic compass and the pressure sensor 1 numbered S1 can be recorded before the test, and then the installed fracture direction determination device is placed in the drilling test section of the hydraulic fracturing method to perform the hydraulic fracturing method ground stress test;

[0028] Step 2: During the test, the electronic compass 3 with storage function records the changes in its azimuth and the changes in the pressure of each pressure sensor 1;

[0029] Step 3: After the test is completed, take out the electronic compass 3 with storage function and read the data, compare the pressure of each pressure sensor 1 in the closing and reopening stage, and the direction of the pressure sensor 1 with the two local minimum pressure values ​​is the direction of the crack 6. In this embodiment, it is found that the two sensors with the lowest pressure values ​​are S3 and S14, that is, the direction where the two pressure sensors 1 are located is the direction of the crack 6, and the reading scale of the electronic compass in this measuring section is 20°;

[0030] Step 4: According to the initial relative orientation of the baseline of the electronic compass 3 with storage function and one of the pressure sensors (i.e., S1 in this embodiment) and the electronic compass reading and the location of the pressure sensors (S3 and S14) with the lowest pressure value in the reopening stage, determine the great local azimuth of the crack 6, that is, the angle between the electronic compass reading scale rotated clockwise to the scale corresponding to the initial relative orientation is the great local azimuth of the crack 6; in this embodiment, the scales corresponding to the initial relative orientations of S3 and S14 are 30° and 210° respectively, then the azimuth of the hydraulic fracture 6 is 10° and 190°, that is, the principal stress orientation is 10° east of north.

[0031] The above are only preferred embodiments of the present invention, and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of the specification of the present invention should be included in the protection scope of the present invention.

Claims

1. A crack direction determination device, characterized in that: The fracture direction determination device is arranged in a test section of the hydraulic fracturing method, and includes: a plurality of pressure sensors, a sensor bracket, and an electronic compass with a storage function. The plurality of pressure sensors are fixed on the sensor bracket, and after being fixed, the plurality of pressure sensors are arranged at intervals along the circumference of the borehole of the test section. The electronic compass is arranged on the sensor bracket, and the electronic compass is also electrically connected to the plurality of pressure sensors for recording the azimuth changes of the electronic compass and the pressure changes of each pressure sensor.

2. The crack direction determining device according to claim 1, characterized in that: The sensor bracket includes a central rod, a plurality of support rods arranged along the circumference of the central rod, and a fixing ring fixed on the plurality of support rods. A plurality of pressure sensors are arranged on the fixing ring at equal intervals. The electronic compass is arranged beside the central rod or at the end side of the central rod.

3. The crack direction determining device according to claim 1, characterized in that: The number of pressure sensors is determined according to the measurement accuracy, and the angle between adjacent sensors and the center of the hole is the measurement accuracy.

4. The crack direction determining device according to claim 1, characterized in that: When installing the electronic compass, record the initial relative position of the electronic compass and one of the pressure sensors.

5. The crack direction determining device according to claim 1, characterized in that: The volume of the pressure sensor is so small that it does not interfere with the flow direction of water.

6. A method for determining a crack direction using a crack direction determining device according to any one of claims 1 to 5, characterized in that: The steps include: S1: installing a fracture direction determination device, recording the initial relative position between the electronic compass baseline and one of the pressure sensors, placing the fracture direction determination device in a hydraulic fracturing drilling test section, and conducting a hydraulic fracturing ground stress test; S2: During the test, the electronic compass records the pressure changes of each pressure sensor; S3: After the test is completed, take out the electronic compass and read the data, compare the pressure of each pressure sensor during the closing and reopening stage, and the position of the pressure sensor with the two local minimum pressure values ​​is the crack position; S4: Determine the crack's major azimuth according to the initial relative position between the electronic compass baseline and one of the pressure sensors, the electronic compass reading during the reopening phase, and the location of the pressure sensor with the lowest pressure value. That is, the angle between the electronic compass reading scale and the scale corresponding to the initial relative position is the crack's major azimuth.

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