A Rock Fracture Morphology and Fracture Width Monitoring System and Method

Abstract

The present invention relates to a system and method for monitoring the morphology and width of rock fractures. The system for monitoring the morphology and width of rock fractures includes: a true triaxial test rig for installing a rock sample with a simulated wellbore fixed inside, heating the rock sample, and applying confining pressure; a liquid injection device for heating and melting a fracturing alloy and injecting the melted fracturing alloy as a fracturing fluid into the simulated wellbore inside the rock sample to fracture the rock sample to form fractures; and a scanning device for scanning the fractured rock sample to obtain parameter information on the morphology and width of the rock sample fractures. The system for monitoring the morphology and width of rock fractures according to the present invention, based on the true triaxial test rig, heats the rock sample and applies confining pressure, and uses the liquid injection device to heat and melt the fracturing alloy and inject the melted fracturing alloy as a fracturing fluid into the simulated wellbore inside the rock sample. In combination with the scanning device, it can achieve non-destructive detection of the three-dimensional multi-scale fracture morphology and fracture width of tight rocks.

Description

Technical Field

[0001] The present invention relates to the field of monitoring of fracture morphology and fracture width, and particularly relates to a monitoring system and method for rock fracture morphology and fracture width. Background Art

[0002] Deep tight reservoirs are characterized by low porosity and low permeability. Hydraulic fracturing technology has become a key technology for improving the single-well production and recovery rate of tight reservoirs by inducing complex fracture networks in rock masses. As an important means to understand the propagation of fracture networks in hydraulic fracturing physical simulation experiments, the monitoring of three-dimensional fracture morphology and fracture width is the premise and foundation for evaluating the complexity of fracture networks.

[0003] Currently, in terms of fracture monitoring in hydraulic fracturing, although traditional methods are feasible, they all have certain limitations, especially the method of directly observing fractures. For example, a commonly used existing observation method is to split the rock sample after fracturing with tools such as a hacksaw and an iron needle to directly observe the shape of the fracture. This observation method has two disadvantages: one is that during the process of splitting the sample, the original fracture will be damaged, or new fractures will be generated on the basis of the original fractures, thus greatly affecting the accuracy of the experimental results; the other is that in the observation of multi-scale fractures, this direct observation method splits the sample along the main fracture, and the result can only observe the main fracture surface, and other micro-fractures are all damaged. In addition, the existing laboratory observation means for fractures also include: ① Using acoustic emission technology to monitor the fracture propagation process and morphology. The advantage of this technology is that it can detect the fracture propagation in real time; the disadvantage is that the error is relatively large, and finally the experimental results still need to be processed by a computer, and the simulation results are not intuitive enough. ② Making experimental samples with transparent materials to directly observe the propagation of hydraulic fractures. The advantage of this technology is that it can directly observe the fracture propagation; its limitation lies in the single selection of materials, and there are large differences between the transparent materials and the rock properties, so the representativeness is insufficient. ③ Ultrasonic monitoring of fracture technology. The advantage of this technology is high sensitivity, fast speed, and low cost; the disadvantage is that it can only monitor the depth of the fracture, the fracture display is not intuitive, and it is easily affected by subjective and objective factors. Similar technologies also include impact echo method detection technology. ④ Using technologies such as infrared thermal imaging to monitor fractures. This technology can directly observe the propagation morphology of fractures; the disadvantage is that the operation difficulty is large. ⑤ Using CT scanners to monitor fracture technology. This method can achieve non-destructive monitoring of fractures; however, it is difficult to monitor the closed fractures, and the denser the rock, the greater the monitoring difficulty. In addition, the above methods cannot achieve accurate monitoring of the actual fracture width in hydraulic fracturing. In view of this, in order to overcome the defects existing in the existing fracture monitoring technology, the present invention proposes a monitoring method for three-dimensional multi-scale fracture morphology and fracture width with simple operation. Summary of the Invention

[0004] The present invention provides a system and method for monitoring the morphology and width of rock fractures to solve one or several of the problems in the prior art.

[0005] The technical solution of the present invention to solve the above technical problems is as follows: A system for monitoring the morphology and width of rock fractures, comprising:

[0006] A true triaxial test rig for installing a rock sample with a simulated wellbore fixed inside, heating the rock sample, and applying confining pressure;

[0007] A liquid injection device for heating and melting a fracturing alloy and injecting the melted fracturing alloy as a fracturing fluid into the simulated wellbore inside the rock sample to fracture the rock sample to form fractures;

[0008] A scanning device for scanning the fractured rock sample to obtain parameter information on the morphology and width of the fractures in the rock sample.

[0009] The beneficial effects of the present invention are: The system for monitoring the morphology and width of rock fractures of the present invention is based on a true triaxial test rig, heating the rock sample and applying confining pressure, and using a liquid injection device to heat and melt a fracturing alloy and injecting the melted fracturing alloy as a fracturing fluid into the simulated wellbore inside the rock sample. Combined with a scanning device, it can realize non-destructive detection of the three-dimensional multi-scale fracture morphology and fracture width of tight rock fracturing. It can effectively avoid defects such as damage to the fracture morphology after fracturing, difficulty in identifying closed fractures, and difficulty in characterizing fracture width, providing a method for studying the multi-scale fracture network characteristics of deep tight reservoirs and optimizing pumping parameters such as proppant specifications, construction displacement, and viscosity, and the operation method is simple.

[0010] On the basis of the above technical solution, the present invention can be further improved as follows.

[0011] Further, the melting point of the fracturing alloy is 30 - 60 °C, and the density of the fracturing alloy is greater than 5 g / cm 3 .

[0012] The beneficial effects of adopting the above further solution are: By using a fracturing alloy with a low melting point and the fracturing fluid formed by the melted fracturing alloy, when the heating of the rock sample stops and it cools down, the fracturing fluid in the fractures will solidify. The solidified fracturing fluid can lock the width of the three-dimensional multi-scale fractures during the fracturing process of the rock sample, keep the fractures open, and overcome the shortcomings of traditional monitoring methods that cause fractures to close after fracturing and inaccurate monitoring of fracture width. Moreover, the solidified fracturing fluid can be taken out to more intuitively observe the fracture morphology. The melting point of the fracturing alloy is 30 - 60 °C, and the density is greater than 5 g / cm 3 . Excessively high temperatures are likely to cause damage to the rock sample and affect the accuracy of the experimental results. The higher the density of the alloy, the easier it is to identify and the higher the clarity of the fracture image obtained when scanning with a scanning device after fracturing.

[0013] Further, the set temperature for heating the rock sample by the true triaxial test rig is higher than the melting point of the fracturing alloy, and the absolute value of the difference between the set temperature and the melting point of the fracturing alloy is not higher than 10°C.

[0014] The beneficial effect of adopting the above further scheme is: to ensure the fluidity of the liquid alloy inside the rock sample during the fracturing process, and at the same time to prevent thermal damage to the rock sample.

[0015] Further, the true triaxial test rig includes a base, a heating plate, a heat insulation plate, a flat jack, an arc-shaped iron plate, and a sleeve. The rock sample is placed at the center of the base. Heating plates are respectively arranged around the outer sides of the rock sample. A heat insulation plate is arranged outside the heating plate. A flat jack is arranged outside the heat insulation plate. An arc-shaped iron plate is arranged outside the flat jack. The sleeve is arranged around the outside of the arc-shaped iron plate and wraps the arc-shaped iron plate, the flat jack, the heat insulation plate, the heating plate, and the rock sample.

[0016] The beneficial effect of adopting the above further scheme is: the heating plate can be used to heat the rock sample, and the heat insulation plate can be used to prevent the temperature from being transmitted outward, avoiding the external temperature rise of the true triaxial test rig and causing potential safety hazards.

[0017] Further, a temperature sensor is arranged on the heating plate. The rock sample is a cube. The flat jacks on three sides of the cube are respectively connected with confining pressure pumps. The heating plates on four sides of the cube, the temperature sensor on the heating plate, and the confining pressure pumps are respectively connected with a control device.

[0018] The beneficial effect of adopting the above further scheme is: the temperature sensor on the heating plate can monitor the temperature on the heating plate in real time. The temperature sensor is connected with the control device, and the temperature can be adjusted through the temperature control system in the control device. Moreover, in order to ensure the fluidity of the liquid alloy inside the rock sample during the fracturing process and prevent thermal damage to the rock sample, the set temperature of the heating plate can be controlled through the temperature control system in the control device, so that the absolute value of the difference between the set temperature and the melting point of the fracturing alloy is not higher than 10°C. The confining pressure pumps can apply three-way confining pressure to three sides of the cube. The three confining pressure pumps are independently controlled to meet the functions of synchronous equal pressurization rate or non-synchronous non-equal pressurization rate loading.

[0019] Further, a fracturing hole is arranged in the rock sample. The simulated wellbore is fixed in the fracturing hole. A barefoot section is reserved between the bottom of the simulated wellbore and the bottom of the fracturing hole. The length of the simulated wellbore is 175 - 180 mm, the inner diameter of the simulated wellbore is 6 - 8 mm, the outer diameter of the simulated wellbore is 10 - 12 mm, and the length of the barefoot section is 40 - 50 mm.

[0020] The beneficial effects of adopting the above further scheme are as follows: The setting of the bare-eye section can be used for the initiation and propagation of fractures.

[0021] Furthermore, the liquid injection device is connected to the simulated wellbore through a liquid injection pipeline, and the liquid injection pipeline adopts a steel pipe with a heat insulation layer on the outside.

[0022] The beneficial effects of adopting the above further scheme are as follows: Reduce the heat loss along the way.

[0023] A method for monitoring the morphology and width of rock fractures by using the above system includes the following steps:

[0024] S1, Place the rock sample with a simulated wellbore fixed inside at the center of the true triaxial test frame;

[0025] S2, Heat and melt the fracturing alloy;

[0026] S3, Heat the rock sample and apply confining pressure to the rock sample through the true triaxial test frame;

[0027] S4, Use the liquid injection device to inject the fracturing fluid into the simulated wellbore inside the rock sample to fracture the rock sample to form fractures;

[0028] S5, In the stage of stable fracture propagation, the liquid injection device stops injecting liquid, the true triaxial test frame stops heating the rock sample, and after cooling the rock sample until the fracturing fluid inside the fracture solidifies, unload the confining pressure applied to the rock sample by the true triaxial test frame; among them, the stage of stable fracture propagation can be judged according to the fracturing curve, that is, the stage of stable fracture pressure propagation.

[0029] S6, Scan the fractured rock sample with a scanning device to obtain the parameter information of the fracture morphology and fracture width of the rock sample.

[0030] The beneficial effects of the present invention are as follows: The method for monitoring the morphology and width of rock fractures of the present invention uses the liquefied fracturing alloy as the fracturing fluid and combines scanning technology to achieve non-destructive monitoring of three-dimensional multi-scale fractures, overcoming the shortcoming of fracture morphology damage caused by traditional monitoring methods.

[0031] The present invention uses the fracturing alloy melted into a liquid state. When the liquid fracturing alloy cools and solidifies, it can lock the width of multi-scale fractures during the fracturing process, keep the fractures open, and overcome the shortcomings of traditional monitoring methods that cause the post-fracture closure and inaccurate measurement of fracture width. If an uncured liquid fracturing alloy is used, the liquid fracturing alloy will flow in the fracture, affecting the accuracy of fracture width measurement; moreover, it is necessary to close the servo control system and unload the three-way confining pressure after curing the fracture, so that the fracture width under the current confining pressure condition is obtained. If this order is not followed and the confining pressure is unloaded first, under the action of stress release, if it is a liquid fracturing alloy, the fracture width and morphology will also change and deviate from the true value.

[0032] The present invention realizes the non-destructive detection of the three-dimensional multi-scale fracture morphology and fracture width of tight rocks, overcomes the defects of existing fracture monitoring technologies such as fracture morphology damage, difficulty in identifying closed fractures, and difficulty in characterizing fracture width, and provides a method for studying the multi-scale fracture network characteristics of deep tight reservoirs and optimizing pumping parameters such as proppant specifications, construction displacement, and viscosity.

[0033] The fractures obtained by the method of the present invention include main hydraulic fractures, bedding fractures, natural fractures, and microfractures, and the distribution range of the fracture widths at different scales is 20um to 1000um.

[0034] Further, in S3, the rock sample is heated by a heating plate on a true triaxial test frame. After the heating plate reaches the set temperature and maintains for 4 to 5 hours, confining pressure is applied to the rock sample by a flat jack on the true triaxial test frame; triaxial confining pressure is applied to the rock sample in the shape of a cube by a flat jack on the true triaxial test frame.

[0035] The beneficial effect of adopting the above further scheme is that when heating the rock sample with a heating plate, due to the low heat conduction efficiency of the rock, after the temperature of the heating plate reaches the set value, it is stabilized for 4 to 5 hours to ensure that the rock is fully heated, and then triaxial confining pressure is applied. The triaxial confining pressure is controlled by three independent systems respectively, meeting the functions of synchronous equal-pressure-rate loading or non-synchronous non-equal-pressure-rate loading.

[0036] Further, in S4, the manner in which the liquid injection device injects fracturing fluid into the simulated wellbore inside the rock sample includes injecting fracturing fluid at a constant displacement and injecting fracturing fluid at a variable displacement.

[0037] The beneficial effect of adopting the above further scheme is that when the liquid injection device injects liquid alloy into the simulated wellbore inside the rock sample, the injection rate and injection manner can be adjusted according to the specific experimental purpose to obtain the fracture morphology and fracture width under different liquid injection conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic connection structure diagram of a rock fracture morphology and fracture width monitoring system of the present invention;

[0039] Figure 2 It is a top view structure diagram of the true triaxial test frame of the present invention;

[0040] Figure 3 It is a sectional view structure diagram of the true triaxial test frame of the present invention;

[0041] Figure 4 It is a connection block diagram of a rock fracture morphology and fracture width monitoring method of the present invention.

[0042] In the drawings, the list of components represented by each reference numeral is as follows:

[0043] 1. True triaxial test frame; 2. Constant temperature liquid injection container; 3. Servo booster; 4. Computer; 5. Control device; 6. First confining pressure pump; 7. Second confining pressure pump; 8. Third confining pressure pump; 9. Air compressor; 10. Distilled water container; 11. Liquid injection pipeline; 12. Simulated wellbore; 13. Heating plate; 14. Insulating board; 15. Flat jack; 16. Arc-shaped iron plate; 17. Sleeve; 18. Rock sample; 19. Base; 20. Upper cover plate; 21. Open hole section. Specific implementation manner

[0044] The principles and features of the present invention will be described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0045] Example 1

[0046] As Figures 1 to 3 shown, a monitoring system for rock fracture morphology and fracture width in this embodiment includes:

[0047] A true triaxial test frame 1 for installing a rock sample 18 with a simulated wellbore 12 fixed inside, heating the rock sample 18, and applying confining pressure;

[0048] A liquid injection device for heating and melting the fracturing alloy and injecting the melted fracturing alloy as a fracturing fluid into the simulated wellbore 12 inside the rock sample 18 to fracture the rock sample 18 to form fractures;

[0049] A scanning device for scanning the fractured rock sample 18 to obtain parameter information on the fracture morphology and fracture width of the rock sample 18.

[0050] Among them, the melting point of the fracturing alloy in this embodiment is 30 - 60 °C, and the density of the fracturing alloy is greater than 5 g / cm 3 . By using a low-melting-point fracturing alloy and the fracturing fluid formed by the melted fracturing alloy, when the heating of the rock sample stops and it cools down, the fracturing fluid in the fractures will solidify. The solidified fracturing fluid can lock the width of the three-dimensional multi-scale fractures during the fracturing process of the rock sample, keep the fractures open, and overcome the shortcomings of the traditional monitoring method that causes the fractures to close after fracturing and the inaccuracy of crack width monitoring. Moreover, the solidified fracturing fluid can be taken out to more intuitively observe the fracture morphology. The melting point of the fracturing alloy is 30 °C - 60 °C, and the density is greater than 5 g / cm 3 . Excessively high temperatures are likely to cause damage to the rock samples and affect the accuracy of the experimental results. The higher the density of the alloy, the easier it is to identify and the higher the clarity of the fracture images obtained when scanning with a scanning device after fracturing.

[0051] An alternative solution regarding the fracturing alloy in this embodiment is that the composition of the fracturing alloy includes one or a combination of several of the components Bi, Sn, Pb, and In. For example, 50% Bi and 50% Sn can be used, or 25% Bi, 25% Sn, 25% Pb, and 25% In can be used. When the composition of the fracturing alloy includes these four components of 25% Bi, 25% Sn, 25% Pb, and 25% In, the melting point of the fracturing alloy composed of these components is 52 °C, and the density is 5.8 g / cm 3 . Heat and melt the fracturing alloy, and use the melted fracturing alloy as a fracturing fluid and pour it into the liquid injection device;

[0052] Specifically, the set temperature at which the true triaxial test rig 1 of this embodiment heats the rock sample 18 is higher than the melting point of the fracturing alloy, and the absolute value of the difference between the set temperature and the melting point of the fracturing alloy is not higher than 10 °C. This ensures the fluidity of the liquid alloy inside the rock sample during the fracturing process and also prevents thermal damage to the rock sample. For example, when the melting point of the fracturing alloy is 52 °C, the rock sample can be heated to 60 °C.

[0053] As Figure 1 shown, a specific solution for the liquid injection device in this embodiment is that the liquid injection device includes a constant-temperature liquid injection container 2, a servo booster 3, a distilled water container 10, and an air compressor 9. The top of the constant-temperature liquid injection container 2 is connected to the simulated wellbore 12 through a liquid injection pipeline 11. The bottom of the constant-temperature liquid injection container 2 is connected to the servo booster 3 through a pipeline. The servo booster 3 is respectively connected to the distilled water container 10 and the air compressor 9. The servo booster 3 is connected to the computer 4, and the computer 4 is used to control and drive the operation of the servo booster 3. The constant-temperature liquid injection container 2 is a piston-type liquid injection mechanism, which can inject the fracturing fluid into the constant-temperature liquid injection container 2 and use the piston-type mechanism for pushing. The servo booster 3 provides the injection pressure for the constant-temperature liquid injection container 2, and the distilled water in the air compressor 9 and the distilled water container 10 respectively provides power for the servo booster 3, etc.

[0054] As Figures 1 to 3As shown, the true triaxial test rig 1 includes a base 19, a heating plate 13, a heat insulation plate 14, a flat jack 15, an arc-shaped iron plate 16, and a sleeve 17. The rock sample 18 is placed at the center of the base 19. Heating plates 13 are respectively arranged around the outer periphery of the rock sample 18. A heat insulation plate 14 is arranged outside the heating plate 13. A flat jack 15 is arranged outside the heat insulation plate 14. An arc-shaped iron plate 16 is arranged outside the flat jack 15. The sleeve 17 is arranged around the outside of the arc-shaped iron plate 16 and wraps the arc-shaped iron plate 16, the flat jack 15, the heat insulation plate 14, the heating plate 13, and the rock sample 18. The heating plate 13 can be used to heat the rock sample 18, and the heat insulation plate 14 can prevent the temperature from being transmitted outward, avoiding the external temperature rise of the true triaxial test rig 1 and causing potential safety hazards. The arrangement order of each component on the true triaxial test rig 1 is specifically as follows: the rock sample 18 is placed at the center of the base 19, and outward in sequence are the heating plate 13, the heat insulation plate 14, the flat jack 15, the arc-shaped iron plate 16, and the sleeve 17. The sleeve 17 can be a circular sleeve, and each component is arranged inside the sleeve 17. The arc-shaped iron plate 16 is equivalent to the function of a gasket. The inner side surface of the arc-shaped iron plate 16 is a planar structure, and the outer side surface is an arc-shaped structure. The arc-shaped iron plate 16 is press-connected to the flat jack 15 by the planar structure on the inner side, and the arc-shaped iron plate 16 is adaptively press-connected to the inner side surface of the sleeve 17 by the arc-shaped structure on the outer side. The four arc-shaped iron plates 16 arranged on the outer side surfaces of the four flat jacks 15 enclose a cylindrical structure. The sleeve 17 is in a cylindrical structure and is appropriately sleeved outside the cylindrical structure, providing structural support for components such as the arc-shaped iron plate 16, the flat jack, the heat insulation plate 14, and the heating plate 13, ensuring the smooth implementation of the confining pressure. The true triaxial test rig 1 can press and position the rock sample 18, the heating plate 13, the heat insulation plate 14, the flat jack 15, the arc-shaped iron plate 16, and the sleeve 17 through the upper cover plate 20.

[0055] As Figures 1 to 3As shown in the figure, a temperature sensor is provided on the heating plate 13 of this embodiment. The rock sample 18 is a cube. Although flat jacks 15 are provided on the four side surfaces of the cube, the flat jacks 15 on three side surfaces of the cube are respectively connected to confining pressure pumps. The heating plates 13 on the four side surfaces of the cube, the temperature sensor on the heating plate 13, and the confining pressure pumps are respectively connected to the control device 5. Specifically, the flat jacks 15 on three side surfaces of the cube can be respectively connected to the first confining pressure pump 6, the second confining pressure pump 7, and the third confining pressure pump 8. The temperature sensor on the heating plate 13 can monitor the temperature of the heating plate 13 in real time. The temperature sensor is connected to the control device 5, and the control device 5 can be connected to the computer 4. The temperature can be adjusted through the temperature control system in the control device 5. Moreover, in order to ensure the fluidity of the liquid alloy inside the rock sample 18 during the fracturing process and prevent thermal damage to the rock sample, the set temperature of the heating plate 13 can be controlled through the temperature control system in the control device 5, so that the absolute value of the difference between the set temperature and the melting point of the fracturing alloy is not higher than 10°C. The confining pressure pumps can apply triaxial confining pressure to three side surfaces of the cube. The three confining pressure pumps are independently controlled to meet the functions of synchronous equal pressurization rate or asynchronous non-equal pressurization rate loading.

[0056] As Figures 1 to 3 shown in the figure, a fracturing hole is provided in the rock sample 18 of this embodiment. The simulated wellbore 12 is fixed in the fracturing hole, and a barefoot section 21 is reserved between the bottom of the simulated wellbore 12 and the bottom of the fracturing hole. The length of the simulated wellbore 12 is 175 - 180 mm, the inner diameter of the simulated wellbore 12 is 6 - 8 mm, the outer diameter of the simulated wellbore 12 is 10 - 12 mm, and the length of the barefoot section 21 is 40 - 50 mm. The setting of the barefoot section can be used for the initiation and propagation of fractures.

[0057] As Figures 1 to 3 shown in the figure, the liquid injection device of this embodiment is communicated with the simulated wellbore 12 through a liquid injection pipeline 11. The liquid injection pipeline 11 is a steel pipe with an adiabatic layer on the outside. The length of the liquid injection pipeline 11 is as short as possible, less than 5 m, to reduce the heat loss along the way.

[0058] The rock fracture morphology and fracture width monitoring system of this embodiment can be used for monitoring the three-dimensional multi-scale fracture morphology and fracture width of tight rocks. Tight rocks generally refer to rocks with high density, low porosity, and low permeability, such as carbonate rocks, shales, tight sandstones, etc. Based on a true triaxial test rig, this monitoring system heats the rock sample and applies confining pressure, and uses a liquid injection device to heat and melt the fracturing alloy, and injects the melted fracturing alloy as fracturing fluid into the simulated wellbore inside the rock sample. Combined with a scanning device, it can achieve non-destructive detection of the three-dimensional multi-scale fracture morphology and fracture width of tight rock fracturing. It can effectively avoid defects such as the fracture morphology being damaged after fracturing, the difficulty in identifying closed fractures, and the difficulty in characterizing fracture width, providing a method for studying the multi-scale fracture network characteristics of deep tight reservoirs and optimizing pumping parameters such as proppant specifications, construction displacement, and viscosity. The operation method is simple.

[0059] Example 2

[0060] As Figure 4 shown, a method for monitoring the rock fracture morphology and fracture width using the system of the above-mentioned Example 1 in this embodiment includes the following steps:

[0061] S1, Place the rock sample 18 with a simulated wellbore 12 fixed inside at the center of the true triaxial test rig 1, and assemble the equipment and pipelines. When assembling, the placement order of the rock sample 18 and other components on the true triaxial test rig 1 is as follows: The tight sandstone is placed as the rock sample 18 at the center of the base 19, and outward are the heating plate 13, the adiabatic plate 14, the flat jack 15, the arc-shaped iron plate 16, and the sleeve 17 in sequence. The size of the rock sample 18 is 400mm×400mm×400mm, the length of the simulated wellbore 12 is 180mm, the inner diameter is 8mm, the outer diameter is 12mm, and the open hole section 21 at the bottom of the simulated wellbore 12 is 40mm, which is used for the initiation and propagation of fractures. The injection pipeline 11 connecting the simulated wellbore and the liquid injection device is a special steel pipe with a layer of thermal insulation material outside, and the pipeline length is 3m;

[0062] S2, Select an alloy composed of Bi, Sn, Pb, and In, with a melting point of 52°C and a density of 5.8g / cm3. Heat and melt the alloy, and pour the melted liquid alloy as fracturing fluid into the constant temperature liquid injection container 2; Specifically, the fracturing alloy can be heated and melted by other equipment and then poured into the constant temperature liquid injection container of the liquid injection device, or the fracturing alloy can be directly heated in the constant temperature liquid injection container;

[0063] S3, Heat the rock sample 18 through the heating plate 13 on the true triaxial test rig 1, raise the temperature to 60°C, and after stabilizing for 4h, apply triaxial confining pressure to the rock sample 18 using the flat jack 15 on the true triaxial test rig 1, with the magnitudes being 20Mpa, 23Mpa, and 30MPa respectively;

[0064] S4. Use the servo booster 3 to pump the liquid alloy into the interior of the rock sample 18 at a constant rate of 20 ml / min, fracturing the rock sample 18 to form fractures.

[0065] S5. After the fracture propagation stabilizes for 15 minutes, stop injecting the liquid. Lower the heating plate 13 to room temperature. After cooling the rock sample 18 to ensure that the liquid alloy inside the fractures solidifies, turn off the servo booster 3 and unload the triaxial confining pressure, and the fracturing experiment ends.

[0066] S6. After the experiment, perform a three-dimensional CT scan on the fractured rock sample 18. Use image processing technology to process the CT image data, extract multi-scale fracture parameter information, obtain the fracture network morphology and fracture width distribution law, and the distribution range of fracture widths at different scales is 40 μm to 500 μm.

[0067] Example 3

[0068] As Figure 4 shown, a method for monitoring the rock fracture morphology and fracture width using the system of Example 1 above includes the following steps:

[0069] S1. Place the rock sample 18 with the simulated wellbore 12 fixed inside at the center of the true triaxial test rig 1, and assemble the equipment and pipelines. When assembling, the placement order of the rock sample 18 and other components on the true triaxial test rig 1 is as follows: the tight sandstone is placed as the rock sample 18 at the center of the base 19, and outward in sequence are the heating plate 13, the adiabatic plate 14, the flat jack 15, the arc-shaped iron plate 16, and the sleeve 17. The size of the rock sample 18 is 400 mm × 400 mm × 400 mm, the length of the simulated wellbore 12 is 175 mm, the inner diameter is 6 mm, the outer diameter is 10 mm, and the open-hole section 21 at the bottom of the simulated wellbore 12 is 50 mm, which is used for the initiation and propagation of fractures. The injection pipeline 11 connecting the simulated wellbore 12 and the injection device is a special steel pipe, with a layer of heat-insulating material outside, and the pipeline length is 4 m.

[0070] S2. Select an alloy composed of Bi, Sn, Pb, and In, with a melting point of 52 °C and a density of 5.8 g / cm 3 . Heat and melt the alloy, and pour the melted liquid alloy as the fracturing fluid into the constant-temperature injection container 2; specifically, it can also heat and melt the fracturing alloy through other equipment and then pour it into the constant-temperature injection container of the injection device, or directly heat the fracturing alloy in the constant-temperature injection container.

[0071] S3. Heat the rock sample 18 through the heating plate 12 on the true triaxial test rig 1. When the temperature rises to 58 °C and stabilizes for 5 h, apply triaxial confining pressures to the rock sample 18 using the flat jack 15 on the true triaxial test rig 1, with magnitudes of 21 Mpa, 22 Mpa, and 29 MPa respectively.

[0072] S4. Use the servo booster 3 to pump the liquid alloy into the inside of the rock sample 18 at a variable displacement starting from a rate of 1 ml / min and increasing at a rate of 0.5 ml / min to fracture the rock sample 18 to form fractures.

[0073] S5. After the fractures have propagated and stabilized for 20 minutes, stop injecting the liquid. Lower the heating plate 13 to room temperature. After cooling the rock sample 18 to ensure that the liquid alloy inside the fractures solidifies, turn off the servo booster 3 and unload the triaxial confining pressure, and the fracturing experiment ends.

[0074] S6. After the experiment, perform three-dimensional CT scanning on the fractured rock sample 18, process the CT image data using image processing technology, extract multi-scale fracture parameter information, obtain the fracture network morphology and fracture width distribution law, and the distribution range of fracture widths at different scales is 50 μm to 800 μm.

[0075] Example 4

[0076] As Figure 4 shown, a method for monitoring the fracture morphology and fracture width of rocks using the system of the above Example 1 in this example includes the following steps:

[0077] S1. Place the rock sample 18 with the simulated wellbore 12 fixed inside at the center of the true triaxial test frame 1, and assemble the equipment and pipelines. When assembling, the placement order of the rock sample 18 and other components on the true triaxial test frame 1 is that the tight sandstone is placed as the rock sample 18 at the center of the base 19, and outward are the heating plate 13, the heat insulation plate 14, the flat jack 15, the arc iron plate 16, and the sleeve 17 in sequence. The size of the rock sample 18 is 400 mm × 400 mm × 400 mm, the length of the simulated wellbore 12 is 178 mm, the inner diameter is 7 mm, the outer diameter is 11 mm, and the open hole section 21 at the bottom of the simulated wellbore 12 is 45 mm, which is used for the initiation and propagation of fractures. The injection pipeline 11 connecting the simulated wellbore and the injection device is a special steel pipe with a layer of heat insulation material on the outside, and the pipeline length is 4 m.

[0078] S2. Select an alloy composed of Bi, Sn, Pb, and In, with a melting point of 52 °C and a density of 5.8 g / cm3. Heat and melt the alloy, and pour the melted liquid alloy as the fracturing fluid into the constant temperature injection container; specifically, it can also be heated and melted by other equipment and then poured into the constant temperature injection container of the injection device, or the fracturing alloy can be directly heated in the constant temperature injection container.

[0079] S3. Heat the rock sample 18 through the heating plate 13 on the true triaxial test frame 1. When the temperature rises to 58 °C and stabilizes for 4.5 h, use the flat jack 15 on the true triaxial test frame 1 to apply triaxial confining pressures to the rock sample 18, with magnitudes of 15 Mpa, 18 Mpa, and 27 MPa respectively.

[0080] S4. Use the servo booster 3 to pump the liquid alloy into the inside of the rock sample 18 at a variable displacement starting from a rate of 1 ml / min and increasing at a rate of 0.5 ml / min, and fracture the rock sample 18 to form fractures.

[0081] S5. After the fracture propagation stabilizes after 25 minutes, stop injecting the liquid. Lower the heating plate 13 to room temperature. After cooling the rock sample 18 to ensure that the liquid alloy inside the fractures solidifies, turn off the servo booster 3 and unload the triaxial confining pressure, and the fracturing experiment ends.

[0082] S6. After the experiment, perform three-dimensional CT scanning on the fractured rock sample 18, process the CT image data using image processing technology, extract multi-scale fracture parameter information, obtain the fracture network morphology and fracture width distribution law, and the distribution range of the fracture widths at different scales is 20 μm to 400 μm.

[0083] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation to the present invention.

[0084] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, "a plurality" means at least two, such as two, three, etc., unless otherwise specifically and clearly defined.

[0085] In the present invention, unless otherwise clearly specified and defined, the terms "mounted", "connected", "connected to", "fixed", etc. should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the internal communication of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0086] In the present invention, unless otherwise clearly specified or limited, the first feature being "on" or "under" the second feature may mean that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Further, the first feature being "above", "over" and "on top of" the second feature may mean that the first feature is directly above or obliquely above the second feature, or merely indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature being "under", "below" and "beneath" the second feature may mean that the first feature is directly below or obliquely below the second feature, or merely indicates that the horizontal height of the first feature is less than that of the second feature.

[0087] In the description of the present specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In the present specification, the schematic representations of the above terms are not necessarily directed to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art may combine and combine the different embodiments or examples described in the present specification and the features of the different embodiments or examples.

[0088] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A monitoring system for rock fracture morphology and fracture width, characterized in that, Comprising: A true triaxial test rig (1) for installing a rock sample (18) with a simulated wellbore (12) fixed therein, heating the rock sample (18), and applying confining pressure thereto; A liquid injection device for heating and melting the fracturing alloy and injecting the melted fracturing alloy as fracturing fluid into the simulated wellbore (12) inside the rock sample to fracture the rock sample to form fractures; A scanning device for scanning the fractured rock sample to obtain information on the fracture morphology and fracture width parameters of the rock sample; The melting point of the fracturing alloy is 30 to 60 °C, and the density of the fracturing alloy is greater than 5 g / cm 3 ; The true triaxial test rig (1) includes a base (19), a heating plate (13), a heat insulation plate (14), a flat jack (15), an arc-shaped iron plate (16), and a sleeve (17). The rock sample (18) is placed at the center of the base (19). Heating plates (13) are respectively arranged around the outer sides of the rock sample (18). A heat insulation plate (14) is arranged outside the heating plate (13). A flat jack (15) is arranged outside the heat insulation plate (14). An arc-shaped iron plate (16) is arranged outside the flat jack (15). The sleeve (17) is arranged around the outside of the arc-shaped iron plate (16) and covers the arc-shaped iron plate (16), the flat jack (15), the heat insulation plate (14), the heating plate (13), and the rock sample (18).

2. The rock fracture morphology and fracture width monitoring system according to claim 1, wherein The set temperature for heating the rock sample (18) by the true triaxial test rig (1) is higher than the melting point of the fracturing alloy, and the absolute value of the difference between the set temperature and the melting point of the fracturing alloy is not higher than 10°C.

3. The monitoring system for rock fracture morphology and fracture width according to claim 1, wherein A temperature sensor is arranged on the heating plate (13). The rock sample (18) is a cube. Flat jacks (15) on three sides of the cube are respectively connected with confining pressure pumps. The heating plates (13) on four sides of the cube, the temperature sensor on the heating plate (13), and the confining pressure pumps are respectively connected with a control device (5).

4. The monitoring system for the morphology and width of rock fractures according to claim 1, characterized in that, Fracturing holes are arranged in the rock sample (18). The simulated wellbore (12) is fixed in the fracturing holes. A barehole section (21) is reserved between the bottom of the simulated wellbore (12) and the bottom of the fracturing holes. The length of the simulated wellbore (12) is 175 - 180 mm, the inner diameter of the simulated wellbore (12) is 6 - 8 mm, the outer diameter of the simulated wellbore (12) is 10 - 12 mm, and the length of the barehole section (21) is 40 - 50 mm.

5. The rock fracture morphology and fracture width monitoring system according to claim 1, characterized in that The liquid injection device is communicated with the simulated wellbore (12) through a liquid injection pipeline (11). The liquid injection pipeline (11) is a steel pipe with a heat insulation layer on the outside.

6. A method for monitoring the morphology and width of rock fractures using the system according to any one of claims 1 to 5, characterized in that, Including the following steps: S1, placing a rock sample (18) with a simulated wellbore (12) fixed therein at the center of the true triaxial test rig (1); S2, heating and melting the fracturing alloy; S3, heating the rock sample (18) and applying confining pressure to the rock sample through the true triaxial test rig (1); S4, using the liquid injection device to inject the fracturing fluid into the simulated wellbore (12) inside the rock sample (18) to fracture the rock sample to form fractures; S5. During the stable crack propagation stage, the liquid injection device stops injecting liquid, the true triaxial test rig (1) stops heating the rock sample (18), and after cooling the rock sample (18) until the fracturing fluid in the crack solidifies, the confining pressure applied by the true triaxial test rig (1) to the rock sample (18) is unloaded. S6. The fractured rock sample (18) is scanned using a scanning device to obtain information on the crack morphology and crack width parameters of the rock sample (18).

7. The method according to claim 6, characterized in that, In S3, the rock sample (18) is heated by the heating plate (13) on the true triaxial test rig (1). After the heating plate (13) reaches the set temperature and maintains for 4 - 5 hours, the confining pressure is applied to the rock sample (18) using the flat jack (15) on the true triaxial test rig (1); the flat jack (15) on the true triaxial test rig (1) is used to apply three-way confining pressure to the rock sample (18) in the shape of a cube.

8. The method according to claim 6, characterized in that, In S4, the methods for the liquid injection device to inject fracturing fluid into the simulated wellbore (12) inside the rock sample (18) include injecting fracturing fluid at a constant displacement and injecting fracturing fluid at a variable displacement.

Images