True triaxial hydraulic fracturing test crack propagation monitoring method

Abstract

The true triaxial hydraulic fracturing test crack propagation monitoring method comprises the following steps that a tracer agent is added into fracturing fluid, and the fracturing fluid with the tracer agent is injected into a drill hole in the top face of a rock so that hydraulic fracturing can be carried out on the rock; a plurality of monitoring holes extending in the vertical direction are formed in the top face of the rock; and a peeping instrument is utilized to stretch into the multiple monitoring holes so as to determine the position of the tracer agent in the rock, and the area of the crack in the rock is determined according to the position of the tracer agent in the rock. Therefore, the true triaxial hydraulic fracturing test crack propagation monitoring method has the advantage that the crack area can be conveniently determined.

Description

Technical Field

[0001] The invention relates to the technical field of hydraulic fracturing tests, and in particular to a true triaxial hydraulic fracturing test crack extension monitoring method. Background Art

[0002] The true triaxial test of rock hydraulic fracturing is a key experimental technology in the field of rock mechanics, which aims to simulate and evaluate the mechanical response of underground rocks during hydraulic fracturing. In the test, by precisely controlling the vertical stress, horizontal stress and injection pressure of the hydraulic fracturing fluid, the stress conditions in the formation can be reproduced to study the rock fracture process and the dynamic expansion of the cracks. This test not only helps to reveal the fracture mechanism of rocks, but also analyzes the initiation, expansion and interaction of cracks, as well as changes in rock mechanical parameters. In related technologies, the true triaxial hydraulic fracturing crack expansion monitoring method includes acoustic emission positioning, CT scanning and sectioning of rock samples after the test. Acoustic emission positioning can monitor the expansion range and dynamic behavior of cracks in real time during rock sample fracturing, but environmental noise has a great impact on it, which may affect the accuracy and reliability of positioning; CT scanning of rock samples after fracturing is used to capture and analyze the expansion of internal cracks in rock samples, which is also a common technical means, but limited by the existing technical level, the size of rock samples that can be CT scanned is small and cannot meet the requirements of large-size rock sample tests; after the test, sectioning of rock samples along the fracture surface is also a common means to explore the expansion range of cracks, but the sectioning process will inevitably severely damage the rock samples, causing the fracturing cracks to be dislocated or some cracks to be unable to be separated, resulting in the inability to accurately judge the distribution of cracks. Based on this, this patent proposes a method for monitoring crack expansion in a true triaxial hydraulic fracturing test. Summary of the invention

[0003] The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, an embodiment of the present invention provides a method for monitoring crack propagation in a true triaxial hydraulic fracturing test.

[0004] The true triaxial hydraulic fracturing test crack extension monitoring method of the embodiment of the present invention comprises the following steps:

[0005] Adding a tracer to a fracturing fluid, and injecting the fracturing fluid with the tracer into a borehole on the top surface of the rock to hydraulically fracture the rock;

[0006] A plurality of monitoring holes extending in the up-down direction are opened on the top surface of the rock;

[0007] The position of the tracer in the rock is determined by inserting a peep instrument into the plurality of monitoring holes, and the area of ​​the fracture in the rock is determined according to the position of the tracer in the rock.

[0008] Therefore, the true triaxial hydraulic fracturing test crack extension monitoring method according to the embodiment of the present invention has the advantage of being easy to determine the crack area.

[0009] In some embodiments, a monitoring coordinate system is established according to the shape of the rock, the monitoring coordinate system includes an X-axis, a Y-axis and a Z-axis, any two of the X-axis, the Y-axis and the Z-axis are perpendicular to each other, the Z-axis extends in the up-down direction, the X-axis and the Y-axis are arranged on the top surface of the rock, and the coordinate position of each monitoring hole in the horizontal direction on the monitoring coordinate system is determined according to the X-axis and the Y-axis;

[0010] The area of ​​the crack is determined according to the position of the tracer detected by the peep instrument in the monitoring hole on the X-coordinate axis, the Y-coordinate axis and the Z-coordinate axis.

[0011] In some embodiments, lines are drawn on the top surface of the rock to form a grid, the monitoring holes are opened downward at the intersections of the grid, and the horizontal position of each monitoring hole is determined according to the X-coordinate axis and the Y-coordinate axis.

[0012] In some embodiments, a first grid is first formed on the top surface of the rock, a first monitoring hole is opened downward at the intersection of the first grid, and the position of the tracer in the rock is determined based on the first monitoring hole. Then, a second grid is formed on a portion of the top surface of the rock, the distance between parallel grid lines in the second grid is smaller than the distance between parallel grid lines in the first grid, the second grid horizontally covers the boundary position of the tracer in the rock in the horizontal direction determined according to the first monitoring hole, a second monitoring hole is opened downward at the intersection of the second grid, and the boundary position of the tracer in the rock in the horizontal direction is again determined based on the second monitoring hole.

[0013] In some embodiments, the distance between parallel grid lines in the second grid is 40 mm, and the distance between parallel grid lines in the second grid is less than or equal to 20 mm.

[0014] In some embodiments, the mesh comprises at least one of a square mesh and a triangular mesh.

[0015] In some embodiments, the top surface of the rock is rectangular, and the X-coordinate axis and the Y-coordinate axis of the monitoring coordinate system are respectively located on two intersecting edges on the top surface of the rock.

[0016] In some embodiments, each of the monitoring holes is numbered, and a table is created to record the X-axis position, Y-axis position, and Z-axis position of the tracer in the rock in each monitoring hole to determine the location of the tracer in the rock.

[0017] In some embodiments, the diameter of the monitoring hole is less than or equal to 3 mm.

[0018] In some embodiments, the tracer is a chemical fluorescent dye. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of a true triaxial hydraulic fracturing test device according to an embodiment of the present invention.

[0020] Figure 2 is a schematic diagram of rock after fracturing according to an embodiment of the present invention.

[0021] Figure 3 Schematic diagram of establishing a monitoring coordinate system and grid on a rock according to an embodiment of the present invention.

[0022] Figure 4 It is a schematic diagram of opening a monitoring hole on a rock according to an embodiment of the present invention.

[0023] Figure numerals: 1. rock, 2. drill hole, 3. monitoring hole, 4. crack, 5. peephole. DETAILED DESCRIPTION

[0024] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0025] The following describes the true triaxial hydraulic fracturing test crack extension monitoring method according to an embodiment of the present invention with reference to the accompanying drawings. Figures 1 to 4 As shown, the true triaxial hydraulic fracturing test crack extension monitoring method according to an embodiment of the present invention comprises the following steps:

[0026] A tracer is added to the fracturing fluid, and the fracturing fluid with the tracer is injected into the borehole 2 on the top surface of the rock 1 to hydraulically fracture the rock 1. Specifically, a true triaxial hydraulic fracturing test device is used to apply pressure to the rock sample (cubic rock 1) to simulate the stress state of the rock in the actual formation. A tracer is added to the fracturing fluid, and the tracer is a chemical fluorescent dye. The tracer is a chemical fluorescent dye. When the dye solution contacts the crack 4, it can quickly penetrate into the crack 4 due to its small molecular structure. In a short time, the dye molecules will form a uniform fluorescent film on the surface of the crack 4, thereby realizing the rapid detection of the crack 4. The fracturing fluid is injected into the rock through the true triaxial hydraulic fracturing test device, and the fracturing fluid will carry the tracer into the rock. As the crack 4 expands, the tracer will also be distributed in the crack network.

[0027] A plurality of monitoring holes 3 extending in the up-down direction are provided on the top surface of the rock 1. Specifically, a monitoring coordinate system is established according to the shape of the rock 1, and the monitoring coordinate system includes an X-coordinate axis, a Y-coordinate axis and a Z-coordinate axis, and any two of the X-coordinate axis, the Y-coordinate axis and the Z-coordinate axis are perpendicular to each other. The top surface of the rock 1 is a rectangle, and the X-coordinate axis and the Y-coordinate axis of the monitoring coordinate system are respectively located on two intersecting (right-angled) edges on the top surface of the rock 1, that is, the X-coordinate axis and the Y-coordinate axis are mutually perpendicular in the horizontal direction. The Z-coordinate axis extends in the up-down direction, and the X-coordinate axis and the Y-coordinate axis are located on the top surface of the rock 1. The coordinate position of each monitoring hole 3 in the horizontal direction on the monitoring coordinate system is determined according to the X-coordinate axis and the Y-coordinate axis.

[0028] The peep instrument 5 (probe) is inserted into the multiple monitoring holes 3 to determine the location of the tracer in the rock 1, and the area of ​​the crack 4 in the rock 1 is determined according to the location of the tracer in the rock 1. The area of ​​the crack 4 is determined according to the position of the tracer detected by the peep instrument 5 in the monitoring hole 3 on the X-axis, the Y-axis and the Z-axis.

[0029] like Figure 3 and Figure 4 As shown, in some embodiments, lines are drawn on the top surface of the rock 1 to form a grid, and monitoring holes 3 are opened downward at the intersection of the grid, so as to facilitate the determination of the horizontal position of each monitoring hole 3 according to the X-coordinate axis and the Y-coordinate axis. Specifically, the grid includes at least one of a square grid and a triangular grid. The square grid is a grid in which the grid lines form a plurality of rectangles, and the triangular grid is a grid in which the grid lines form a plurality of triangles.

[0030] In some embodiments, the diameter of the monitoring hole 3 is less than or equal to 3 mm. A smaller diameter of the monitoring hole 3 can reduce the construction difficulty and improve the position accuracy of the determined tracer.

[0031] In some embodiments, a first grid is first formed on the top surface of the rock 1, a first monitoring hole is opened downward at the intersection of the first grid, and the position of the tracer in the rock 1 is determined based on the first monitoring hole. Then a second grid is formed on a portion of the top surface of the rock 1, the distance between the mutually parallel grid lines in the second grid is smaller than the distance between the mutually parallel grid lines in the first grid, and a second monitoring hole is opened downward at the intersection of the second grid. Thus, the boundary of the rock 1 can be determined based on the first monitoring hole. The distance between the intersections of the second grid is smaller than the distance between the intersections of the first grid, that is, the distance between two adjacent second monitoring holes is smaller than the distance between two adjacent first monitoring holes, thereby improving the accuracy of the determined boundary position of the crack.

[0032] The second grid covers the boundary position of the tracer in the rock 1 in the horizontal direction determined by the first monitoring hole in the horizontal direction, so that a part of the plurality of second monitoring holes can be located inside the boundary position of the tracer in the rock 1 in the horizontal direction determined by the first monitoring hole, and another part of the plurality of second monitoring holes can be located outside the boundary position of the tracer in the rock 1 in the horizontal direction determined by the first monitoring hole, and the boundary position of the tracer in the rock 1 in the horizontal direction is determined again according to the second monitoring hole. That is, the position of the tracer in the rock 1 is roughly determined first according to the first monitoring hole 3, and then the second grid is formed on a part of the top surface of the rock 1, and the distance between the mutually parallel grid lines in the second grid is smaller than the distance between the mutually parallel grid lines in the first grid, so that the density of the second grid is high, so that the monitoring holes (second monitoring holes) at the boundary of the crack 4 are relatively dense, that is, the accuracy of the second monitoring holes is high, so as to accurately determine the boundary position of the tracer in the rock 1 in the horizontal direction again. For example, the first grid and the second grid are both square grids.

[0033] In some embodiments, the distance between parallel grid lines in the first grid is 40 mm, and the distance between parallel grid lines in the second grid is less than or equal to 20 mm. For example, the distance between parallel grid lines in the second grid is 20 mm or 10 mm.

[0034] In some embodiments, each monitoring hole 3 is numbered, and a table is established to record the X-axis position, Y-axis position, and Z-axis position of the tracer in the rock 1 in each monitoring hole 3, so as to determine the location of the tracer in the rock 1. The established table is shown in the following table.

[0035] Tracer Point X Y Z 1 20 20 30 2 40 40 40 3 60 40 12 4 80 60 34 5 1 00 40 46 … … … …

[0036] Using a high-precision peep instrument, we can observe and track the migration of tracers in the borehole, accurately locate the position of each tracer point, and build a three-dimensional model of the crack distribution based on the data in the table. We can import the three-dimensional coordinates of all tracer points into the computer and use professional software for data processing and analysis. Through these coordinates, we can reconstruct the three-dimensional model of the cracks, thereby intuitively showing the expansion and distribution of hydraulic fracturing cracks.

[0037] Therefore, the true triaxial hydraulic fracturing test crack extension monitoring method according to the embodiment of the present invention has the advantage of being easy to determine the crack area.

[0038] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0039] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0040] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0041] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0042] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0043] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A true triaxial hydraulic fracturing test crack expansion monitoring method, characterized in that: The following steps are involved: Adding a tracer to a fracturing fluid, and injecting the fracturing fluid with the tracer into a borehole on the top surface of the rock to hydraulically fracture the rock; A plurality of monitoring holes extending in the up-down direction are opened on the top surface of the rock; The position of the tracer in the rock is determined by inserting a peep instrument into the plurality of monitoring holes, and the area of ​​the fracture in the rock is determined according to the position of the tracer in the rock.

2. The true triaxial hydraulic fracturing test crack extension monitoring method according to claim 1, characterized in that: A monitoring coordinate system is established according to the shape of the rock, wherein the monitoring coordinate system includes an X-axis, a Y-axis and a Z-axis, any two of which are perpendicular to each other, the Z-axis extends in the up-down direction, the X-axis and the Y-axis are arranged on the top surface of the rock, and the coordinate position of each monitoring hole in the horizontal direction on the monitoring coordinate system is determined according to the X-axis and the Y-axis; The area of ​​the crack is determined according to the position of the tracer detected by the peep instrument in the monitoring hole on the X-coordinate axis, the Y-coordinate axis and the Z-coordinate axis.

3. The true triaxial hydraulic fracturing test crack extension monitoring method according to claim 2, characterized in that: Lines are drawn on the top surface of the rock to form a grid, and the monitoring holes are opened downward at the intersections of the grids. The position of each monitoring hole in the horizontal direction is determined according to the X-coordinate axis and the Y-coordinate axis.

4. The true triaxial hydraulic fracturing test crack extension monitoring method according to claim 3, characterized in that: First, a first grid is formed on the top surface of the rock, and a first monitoring hole is opened downward at the intersection of the first grid. The position of the tracer in the rock is determined according to the first monitoring hole. Then, a second grid is formed on a part of the top surface of the rock, and the distance between parallel grid lines in the second grid is smaller than the distance between parallel grid lines in the first grid. The second grid horizontally covers the boundary position of the tracer in the rock in the horizontal direction determined according to the first monitoring hole. A second monitoring hole is opened downward at the intersection of the second grid, and the boundary position of the tracer in the rock in the horizontal direction is determined again according to the second monitoring hole.

5. The true triaxial hydraulic fracturing test crack extension monitoring method according to claim 4, characterized in that: The distance between the parallel grid lines in the second grid is 40 mm, and the distance between the parallel grid lines in the second grid is less than or equal to 20 mm.

6. The true triaxial hydraulic fracturing test crack extension monitoring method according to claim 4, characterized in that: The mesh includes at least one of a square mesh and a triangular mesh.

7. The method for monitoring crack expansion in a true triaxial hydraulic fracturing test according to claim 4, characterized in that: The top surface of the rock is a rectangle, and the X-coordinate axis and the Y-coordinate axis of the monitoring coordinate system are respectively located on two intersecting edges on the top surface of the rock.

8. The true triaxial hydraulic fracturing test crack extension monitoring method according to claim 2, characterized in that: Each of the monitoring holes is numbered, and a table is established to record the X-axis position, Y-axis position and Z-axis position of the tracer in the rock in each of the monitoring holes, so as to determine the location of the tracer in the rock.

9. The true triaxial hydraulic fracturing test crack extension monitoring method according to claim 1, characterized in that: The diameter of the monitoring hole is less than or equal to 3 mm.

10. The method for monitoring crack expansion in a true triaxial hydraulic fracturing test according to any one of claims 1 to 9, characterized in that: The tracer is a chemical fluorescent dye.

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