Method for monitoring crack propagation in true triaxial hydraulic fracturing test

Abstract

The true triaxial hydraulic fracturing test crack propagation monitoring method of the present application comprises the following steps: adding a tracer to a fracturing fluid, injecting the fracturing fluid with the tracer into a borehole on the top surface of a rock to perform hydraulic fracturing on the rock; opening a plurality of monitoring holes extending in the up-down direction on the top surface of the rock; extending a bore scope into the plurality of monitoring holes to determine the location of the tracer in the rock, and determining the area of the crack in the rock according to the location of the tracer in the rock. Therefore, the true triaxial hydraulic fracturing test crack propagation monitoring method of the present application has the advantage of facilitating determination of the crack area.

Description

Technical Field

[0001] This invention relates to the field of hydraulic fracturing testing technology, specifically to a method for monitoring crack propagation in true triaxial hydraulic fracturing tests. Background Technology

[0002] True triaxial testing of hydraulic fracturing is a key experimental technique in rock mechanics, designed to simulate and evaluate the mechanical response of subsurface rocks during hydraulic fracturing. In this test, by precisely controlling vertical stress, horizontal stress, and the injection pressure of the fracturing fluid, the stress conditions in the formation can be reproduced, allowing for the study of the rock fracturing process and the dynamic propagation of fractures. This test not only helps to reveal the fracturing mechanism of rocks but also enables the analysis of fracture initiation, propagation, and interaction patterns, as well as changes in rock mechanical parameters. Related techniques for monitoring fracture propagation in true triaxial hydraulic fracturing include acoustic emission localization, CT scanning, and post-test rock sample sectioning. Acoustic emission localization can monitor the propagation range and dynamic behavior of fractures in real time during rock fracturing, but environmental noise has a significant impact, potentially affecting the accuracy and reliability of localization. Post-fracturing CT scanning of rock samples to capture and analyze internal fracture propagation is also a common technique; however, current technology limits the size of rock samples suitable for CT scanning to small sizes, failing to meet the requirements for large-size rock sample tests. Sectioning the rock sample along the fracture initiation surface after the test is another common method for investigating fracture propagation range, but this process inevitably causes severe damage to the rock sample, resulting in fracture misalignment or inseparable fractures, making it impossible to accurately determine the fracture distribution. Therefore, this patent proposes a true triaxial hydraulic fracturing test fracture propagation monitoring method. Summary of the Invention

[0003] This invention aims to at least partially address one of the technical problems in related technologies. To this end, embodiments of this invention propose a method for monitoring fracture propagation in true triaxial hydraulic fracturing tests.

[0004] The method for monitoring fracture propagation in a true triaxial hydraulic fracturing test according to an embodiment of the present invention includes the following steps:

[0005] A tracer is added to the fracturing fluid, and the fracturing fluid containing the tracer is injected into a borehole on the top surface of the rock to perform hydraulic fracturing on the rock.

[0006] Multiple monitoring holes extending vertically are made on the top surface of the rock;

[0007] A viewing instrument is inserted into multiple monitoring holes to determine the location of tracers in the rock, and the location of tracers in the rock is used to determine the area of ​​cracks in the rock.

[0008] Therefore, the true triaxial hydraulic fracturing test crack propagation monitoring method according to the embodiments of the present invention has the advantage of facilitating the determination of crack regions.

[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, Y-axis, and Z-axis are perpendicular to each other. The Z-axis extends in the vertical direction. The X-axis and Y-axis are located on the top surface of the rock. The coordinate position of each monitoring hole in the horizontal direction on the monitoring coordinate system is determined according to the X-axis and Y-axis.

[0010] The region of the crack is determined based on the position of the tracer detected by the peephole on the X, Y, and Z axes.

[0011] In some embodiments, 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 grid. The position of each monitoring hole in the horizontal direction is determined according to the X and Y coordinate axes.

[0012] In some embodiments, a first grid is first formed on the top surface of the rock, and a first monitoring hole is opened downward at the intersection of the first grid. The location 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, wherein the distance between the parallel grid lines in the second grid is less than the distance between the parallel grid lines in the first grid. The second grid covers the horizontal boundary position of the tracer in the rock determined by the first monitoring hole in the horizontal direction. A second monitoring hole is opened downward at the intersection of the second grid, and the horizontal boundary position of the tracer in the rock is determined again 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 grid includes at least one of a square grid and a triangular grid.

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

[0016] In some embodiments, each monitoring well is numbered, a table is created, and the X-axis, Y-axis, and Z-axis positions of the tracer in the rock within each monitoring well are recorded 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. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a true triaxial hydraulic fracturing test apparatus according to an embodiment of the present invention.

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

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

[0022] Figure 4 This is a schematic diagram of a monitoring hole being drilled in a rock according to an embodiment of the present invention.

[0023] Attached reference numerals: 1. Rock, 2. Borehole, 3. Monitoring hole, 4. Crack, 5. Sighting device. Detailed Implementation

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

[0025] The method for monitoring fracture propagation in a true triaxial hydraulic fracturing test according to an embodiment of the present invention is described below with reference to the accompanying drawings. Figures 1 to 4 As shown, the true triaxial hydraulic fracturing test crack propagation monitoring method according to an embodiment of the present invention includes the following steps:

[0026] A tracer is added to the fracturing fluid, and the fracturing fluid containing the tracer is injected into the borehole 2 on the top surface of rock 1 to perform hydraulic fracturing on rock 1. Specifically, a true triaxial hydraulic fracturing test apparatus is used to apply pressure to the rock sample (cubic rock 1) to simulate the stress state of rocks in actual formations. A tracer, a chemifluorescent dye, is added to the fracturing fluid. The chemifluorescent dye is chosen as the tracer. When the dye solution comes into contact with fracture 4, its small molecular structure allows it to quickly penetrate into the interior of fracture 4. Within a short time, the dye molecules form a uniform fluorescent film on the surface of fracture 4, thereby achieving rapid detection of fracture 4. The fracturing fluid is injected into the rock using the true triaxial hydraulic fracturing test apparatus. The fracturing fluid carries the tracer into the rock, and as fracture 4 expands, the tracer is also distributed throughout the fracture network.

[0027] Multiple monitoring holes 3 extending vertically are made on the top surface of rock 1. Specifically, a monitoring coordinate system is established based on the shape of rock 1. The monitoring coordinate system includes an X-axis, a Y-axis, and a Z-axis, with any two of the X, Y, and Z axes being perpendicular to each other. The top surface of rock 1 is rectangular, and the X and Y axes of the monitoring coordinate system are located on two intersecting (right-angled) edges of the top surface of rock 1, i.e., the X and Y axes are mutually perpendicular in the horizontal direction. The Z-axis extends vertically. The X and Y axes are located on the top surface of rock 1, and the horizontal coordinate position of each monitoring hole 3 in the monitoring coordinate system is determined based on the X and Y axes.

[0028] The probe of the viewing instrument 5 is inserted into multiple monitoring holes 3 to determine the location of the tracer in the rock 1. The region of the crack 4 in the rock 1 is determined based on the location of the tracer in the rock 1. The region of the crack 4 is determined based on the position of the tracer detected by the viewing instrument 5 in the monitoring holes 3 on the X, Y, and Z coordinate axes.

[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 downwards at the intersections of the grid, thereby facilitating the determination of the horizontal position of each monitoring hole 3 according to the X and Y coordinate axes. Specifically, the grid includes at least one of a square grid and a triangular grid. A square grid is a grid in which grid lines form multiple rectangles, and a triangular grid is a grid in which grid lines form multiple 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 reduces construction difficulty and improves the accuracy of the tracer's location.

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

[0032] The second grid horizontally covers the horizontal boundary position of the tracer in rock 1 determined by the first monitoring hole. This allows a portion of the multiple second monitoring holes to be located inside the horizontal boundary position of the tracer in rock 1 determined by the first monitoring hole, and another portion to be located outside the horizontal boundary position of the tracer in rock 1 determined by the first monitoring hole. The horizontal boundary position of the tracer in rock 1 is then determined again based on the second monitoring holes. In other words, the position of the tracer in rock 1 is roughly determined based on the first monitoring hole 3, and then a second grid is formed on a portion of the top surface of rock 1. The distance between parallel grid lines in the second grid is less than the distance between parallel grid lines in the first grid, resulting in a high density of the second grid. This leads to a denser network of monitoring holes (second monitoring holes) at the boundary of crack 4, meaning high accuracy of the second monitoring holes, allowing for precise determination of the horizontal boundary position of the tracer in rock 1. For example, both the first and second grids can be 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 well 3 is numbered, and a table is created to record the X-axis, Y-axis, and Z-axis positions of the tracer in the rock 1 within each monitoring well 3, in order to determine the location of the tracer in the rock 1. The table is shown below.

[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 borehole sight, the migration of tracers is observed and tracked, precisely locating the position of each tracer point. A 3D model of the fracture distribution can be created based on the data in the table. The 3D coordinates of all tracer points are imported into a computer for data processing and analysis using specialized software. These coordinates allow for the reconstruction of a 3D model of the fractures, thus visually demonstrating the propagation and distribution of hydraulic fracturing fractures.

[0037] Therefore, the true triaxial hydraulic fracturing test crack propagation monitoring method according to the embodiments of the present invention has the advantage of facilitating the determination of crack regions.

[0038] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to 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, they should not be construed as limitations on this invention.

[0039] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0040] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0041] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0042] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0043] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A true triaxial hydraulic fracturing test crack propagation monitoring method, characterized by, The method comprises the following steps: adding a tracer into a fracturing fluid, injecting the fracturing fluid with the tracer into a borehole on the top surface of a rock to perform hydraulic fracturing on the rock; opening a plurality of monitoring holes extending in the up-down direction on the top surface of the rock; extending a peeping instrument into the plurality of monitoring holes to determine the location of the tracer in the rock, and determining the area of the fracture in the rock according to the location of the tracer in the rock; establishing a monitoring coordinate system according to the shape of the rock, the monitoring coordinate system comprising an X coordinate axis, a Y coordinate axis and a Z coordinate axis, any two of the X coordinate axis, the Y coordinate axis and the Z coordinate axis being perpendicular to each other, the Z coordinate axis extending in the up-down direction, the X coordinate axis and the Y coordinate axis being arranged on the top surface of the rock, and determining the coordinate position of each monitoring hole in the horizontal direction in the monitoring coordinate system according to the X coordinate axis and the Y coordinate axis; determining the area of the fracture according to the location of the tracer detected by the peeping instrument in the monitoring hole in the X coordinate axis, the Y coordinate axis and the Z coordinate axis; drawing lines on the top surface of the rock to form a grid, opening the monitoring hole downward at the intersection of the grid, and determining the position of each monitoring hole in the horizontal direction according to the X coordinate axis and the Y coordinate axis; firstly forming a first grid on the top surface of the rock, opening a first monitoring hole downward at the intersection of the first grid, determining the location of the tracer in the rock according to the first monitoring hole, then forming a second grid on a part of the top surface of the rock, the distance between the parallel grid lines in the second grid being smaller than the distance between the parallel grid lines in the first grid, the second grid covering the boundary position of the tracer in the rock in the horizontal direction determined according to the first monitoring hole in the horizontal direction, opening a second monitoring hole downward at the intersection of the second grid, and determining the boundary position of the tracer in the rock in the horizontal direction again according to the second monitoring hole.

2. The true triaxial hydraulic fracturing test crack propagation monitoring method according to claim 1, characterized in that, The distance between the parallel grid lines in the first grid is 40 mm, and the distance between the parallel grid lines in the second grid is less than or equal to 20 mm.

3. The true triaxial hydraulic fracturing test crack propagation monitoring method according to claim 1, characterized by, The grid comprises at least one of a square grid and a triangular grid.

4. The true triaxial hydraulic fracturing test crack propagation monitoring method according to claim 1, characterized by, 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.

5. The true triaxial hydraulic fracturing test crack propagation monitoring method according to claim 1, characterized in that, Each monitoring hole is numbered, a table is established, and the X coordinate axis position, the Y coordinate axis position and the Z coordinate axis position of the tracer in the rock in each monitoring hole are recorded to determine the location of the tracer in the rock.

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

7. The true triaxial hydraulic fracturing test crack propagation monitoring method according to any one of claims 1-6, characterized in that, The tracer is a chemical fluorescent dye.

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