A high-temperature and high-pressure true triaxial shale fracture slip test device and test method

Abstract

The present invention discloses a high-temperature and high-pressure true triaxial shale fracture slip test device and test method. The experimental device includes a rock sample, a true triaxial confining pressure device, a jack and a mold assembly, a true triaxial frame, a fracturing pump injection system, an acoustic emission system, and a digital sensor and control system. The test method includes using self-developed molds to prepare natural fractures with different cementation strengths and different cementation types, prefabricating cubic rock samples with built-in faults, using a true triaxial fracturing device to conduct shear slip experiments on large-scale natural fractures, exploring the slip amounts of various combinations of different natural fractures during shear slip under hydraulic fracturing, and at the same time effectively simulating the influence of high temperature on the fracturing construction process, providing technical support for the optimization of fracturing horizons and the optimization design of fracturing construction site parameters.

Description

Technical Field

[0001] The present invention relates to the technical field of shale reservoir reconstruction, and particularly to a high-temperature and high-pressure true triaxial shale fracture slip test device and test method. Technical Background

[0002] Different from single-stage and single-well fracturing, multi-cluster hydraulic fracturing within a horizontal well section has the periodic fracture-making characteristics of section by section and well by well (alternate or synchronous). According to the stress perturbation theory, the periodic fracture-making process will cause local in-situ stress alternating perturbation in the target layer of the horizontal well group. The in-situ stress alternating perturbation will also cause changes in the stress states of geological body weak planes such as natural fractures and artificial implants such as downhole casings, and further lead to casing deformation (referred to as casing change for short). After the casing change, the inner diameter of the wellbore becomes smaller, resulting in difficulties in lowering subsequent fracturing staging tools, and even the untransformed well sections below the casing change point cannot be transformed, greatly affecting the fracturing construction efficiency and reservoir reconstruction degree. Therefore, being able to effectively study the relevant laws of faults being activated and undergoing shear slip under the influence of hydraulic fracturing has extremely important guiding significance for fracturing construction.

[0003] Most of the faults in shale reservoirs are weakly cemented surfaces formed by mineral filling. Due to the different microstructures and sediment components of shale, the cementation strength in the faults has randomness. At present, in relevant literature, to achieve conventional triaxial shear slip, the axial confining pressure loading method is adopted and mostly small-sized core tests are carried out, which generally cannot truly simulate the underground environment; there are also some shear test literatures that apply different pressure values to the X, Y, and Z axes of large-sized true triaxial rock blocks, mostly adopting the general loading shear scheme of the plane pressure difference from the outside to the inside, and the influence of the fluid-solid-acoustic emission coupling effect and the filling material (cementation strength) in the fault on activating the fault slip is not considered. In addition, most tests do not consider the influence of temperature on the cementation effect. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-temperature and high-pressure true triaxial shale fracture slip test device and test method, which can better simulate the real underground form and study the influence of cemented natural fractures and hydraulic fracturing-activated faults on shear slip.

[0005] The technical solution of the present invention is as follows:

[0006] A high-temperature and high-pressure true triaxial shale fracture slip test device, which includes a rock sample, a true triaxial confining pressure device, a true triaxial frame, a fracturing pump injection system, a specimen picking and placing auxiliary device, an acoustic emission system, digital sensors (pressure, temperature, displacement), and a jack mold assembly, etc. It is invented to simulate the influence of heterogeneous reservoir rocks on the geometric shape of hydraulic fracturing fractures under high stratification stress, horizontal stress, and high temperature in different directions, and the results are closer to the reality and have strong guiding significance.

[0007] The true triaxial confining pressure device consists of three hydraulic loading cylinders, a hydraulic loading plate, and a nitrogen pressure tank. The pressure loading plate 12 is placed in the pressure chamber and is directly connected to the rock sample.

[0008] The true triaxial frame is of a frame structure, including a base 4, a box body 5, an upper end cover 7, a bearing plate 9, and support columns 6, etc. The base 4, the horizontal loading plate 12, the upper loading plate 8, the lower loading plate, and the bearing plate 9 together form a pressure chamber for holding the rock sample.

[0009] The base is provided with a fracturing fluid outflow channel.

[0010] The acoustic emission system is equipped with eight probes respectively installed on the outside of the rock sample. The signal is amplified by an acoustic emission preamplifier, and finally the signal is simulated and processed in the digital system.

[0011] The center of the loading plate is distributed with hydraulic cylinders for applying hydraulic loads, and two round holes are reserved above it. The reserved holes are used for installing displacement sensors.

[0012] The specimen loading and unloading auxiliary device is connected by two brackets. The two transverse brackets are further fixed in the middle of the brackets by hexagon bolts. An electric hoist, a wire rope, a hook, etc. are fixed above the device.

[0013] The upper loading plate of the rock sample is specifically characterized in that a through hole is provided in the center.

[0014] The pore pressure loading system includes a hydraulic pump, fracturing fluid, and a pore pressure sensor.

[0015] The jack mold assembly is mainly assembled and connected by a top cover 15, a column 16, a hexagon bolt 17, a bottom plate 18, a fixture body 19, a fixture top cover 21, and a long hydraulic jack 22.

[0016] The fixture body is formed by connecting four fast baffle plates with hexagon bolts.

[0017] The rock sample is of a cube structure, and channels with a height of 1 / 2 times the core height are arranged on it for embedding the fracturing pipeline. Sealing glue is arranged in the annular space between the fracturing pipeline and the core sample block, and the sealing glue ensures the internal sealing of the core sample block.

[0018] A high-temperature and high-pressure true triaxial test simulation fault shale block shear slip device and test method are as follows:

[0019] S1. Prepare the jack pressure chamber and the mold. Take the fault filling similar material and perform a series of treatments such as air drying and crushing, configure it into the required filling material according to the ratio, and press it into a certain shape by using the jack device.

[0020] S2. Make a cubic rock sample with an internal fault.

[0021] S3, obtaining a cubic rock sample, and vertically drilling a hole on one side of the rock sample;

[0022] S4. Pre-buried wellbore tubulars in the hole drilled from the rock sample;

[0023] S5, pouring sealant into the gap between the wellbore tubular string and the hole wall to consolidate the wellbore tubular string;

[0024] S6. Sleeve the pressure head on the wellbore string to ensure that the pressure head and the rock sample fit tightly, weld the pressure head to the wellbore string, and apply sealant on the edge of the pressure head;

[0025] S7, heating the rock sample to a predetermined temperature before the experiment begins;

[0026] S8, placing the sealed and heated rock sample into a true triaxial pressure chamber using a pick-and-place auxiliary device to perform triaxial stress confining pressure loading;

[0027] S9, prepare fracturing fluid, inject it into the rock sample through a booster pump for hydraulic fracturing, and simultaneously turn on the acoustic emission system for data collection;

[0028] S10. The test can be stopped when the fracturing fluid flows out from the reserved channel;

[0029] S11. Analyze the acoustic emission data to obtain the distribution of rock sample cracks, obtain the shear slip of the rock sample through the displacement sensor, and perform result processing and analysis.

[0030] A high-temperature and high-pressure true triaxial shale fracture-slip test device and test method, characterized in that the fault filling similar material used in S2 is obtained by stratum survey sampling, and the cementing materials include chlorite, montmorillonite, calcite, quartz, metamorphic dolomite, sulfate and other minerals, which can prepare natural fractures with different cementation strengths and different cementation types.

[0031] A high-temperature and high-pressure true triaxial shale fracture-slip test device and test method, characterized in that the intersection angle position of the fault and the wellbore in the cubic rock sample can be set arbitrarily according to needs.

[0032] A high-temperature and high-pressure true triaxial shale fracture-slip test device and test method, characterized in that the hydraulic fracturing process is completed under high-temperature and high-pressure conditions.

[0033] Advantages of this patent:

[0034] 1. By using similar materials to fill faults to fit natural fractures of different types and with different bonding strengths, the slip amounts of natural fractures of different combinations and types when shear slip occurs under hydraulic fracturing can be explored.

[0035] 2. This experimental device system can achieve the vertical stratified stress difference and horizontal stress difference in heterogeneous reservoirs by changing the parameters of the pumping system and the stress loading system, and study the geometric morphology of fracturing cracks under various different stress combination states.

[0036] 3. The influence of high temperature on the fracturing construction process is effectively simulated by preheating, and the results are more in line with engineering practice.

[0037] 4. Through the rock sample preparation method of this experiment, the influence of different angles and positions between faults and wellbores on activating fault slip can be studied.

[0038] 5. Using this sealing method, the problems of bypass seepage and boundary effect in the fracturing process can be solved, the stress concentration at the corner positions can be relieved, the pressure maintenance and seepage flow direction of the test path can be ensured, the net pressure in the artificial fracture can be maintained, and the closure of the fracture wall can be prevented, so that the fracturing experiment research can be effectively carried out. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is the overall view of a high-temperature and high-pressure true triaxial shale fracture slip test device and test method according to an embodiment of the present invention;

[0040] Figure 2 is the plane cross-sectional view of the overall view of a high-temperature and high-pressure true triaxial shale fracture slip test device and test method according to an embodiment of the present invention;

[0041] Figure 3 is the jack and mold assembly of a high-temperature and high-pressure true triaxial shale fracture slip test device and test method according to an embodiment of the present invention;

[0042] Figure 4 is the reserved hole on the loading plate according to an embodiment of the present invention;

[0043] Figure 5 is the cement rock sample with an internal fault according to an embodiment of the present invention;

[0044] Figure 6 is the cut shale outcrop with fractures according to an embodiment of the present invention;

[0045] Wherein 1 - lifting ring; 2 - set screw; 3 - threaded rod; 4 - base; 5 - box body; 6 - support column; 7 - upper end cover; 8 - upper loading plate; 9 - bearing plate; 10 - prefabricated outflow hole for fracturing fluid; 11 - lower loading plate; 12 - axial loading plate; 13 - wellbore; 14 - reserved central hole on the upper end cover; 15 - top cover; 16 - column; 17 - hexagon bolt; 18 - bottom plate; 19 - fixture body; 20 - cemented particles; 21 - fixture top cover; 22 - long hydraulic jack. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0046] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0047] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is 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 should not be construed as a limitation of the present invention. In addition, the terms "first", "second", and "third" are only used for descriptive purposes and should not be construed as indicating or implying relative importance.

[0048] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installation", "connection", and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection. 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.

[0049] As Figures 1 - 3 shown, a high-temperature and high-pressure true triaxial shale fracture and slip test device, the device includes an upper end cover 7 which is fixed in the Z-axis direction by tightening the set nut 2; a threaded rod 3 is installed in the threaded hole of the box body and connected to the bearing plate 9; the base 4 and the support column 6 are fixedly connected for supporting the frame device; prefabricated spring holes for installing acoustic emission sensors are left at both ends of the hydraulic axial load loading plate 12;

[0050] The rock sample is a cubic rock sample, the box body is cylindrical 5, and the inside of the box body is a true triaxial pressure chamber composed of a bearing plate 9, a hydraulic axial load loading plate 12, a rock sample, and a Z-axis upper loading plate 8 to form a true triaxial pressure loading chamber;

[0051] The jack mold assembly is mainly composed of a top cover 15, a column 16, a hexagon bolt 17, a bottom plate 18, a clamping body 19, a fixture top cover 21, and a long hydraulic jack 22 which are loaded and connected.

[0052] A high-temperature and high-pressure true triaxial shale fracture and slip test device and test method are as follows:

[0053] S1. Prepare the jack pressure chamber and the mold (as Figure 3), grind common natural fracture fillers (chlorite, montmorillonite and other minerals) into powder, add them into prefabricated molds in different proportions, add fracturing fluids with different mineralizations, and use a jack device to press them into a certain shape;

[0054] S2. Method 1: Use screws to fix the five faces of the iron plate to make a cubic box with standard sizes such as (300mm×300mm×300mm, 280mm×280mm×280mm, 500mm×500mm×500mm, etc.) for pouring cement cubic rock samples (such as Figure 5 ), preferably, the mass ratio of cement, standard sand and water can be 450g cement: 1350g standard sand: 220ml water. After pouring, demoulding is carried out at a predetermined time, and the demoulded artificial rock sample is placed under a preset temperature condition for water sprinkling and curing until the artificial core reaches the required strength; Method 2: Collect a number of shale outcrops in the target area, prepare them into 300×300×300mm cubes and cut fractures at a certain inclination angle to prepare fractures with different water saturation (such as Figure 6 );

[0055] S3. Select a side with bedding and microcracks and mark it diagonally. Select a drill bit with a diameter of Φ12 mm to drill vertically at the intersection. The drilling depth is 1 / 2 of the rock sample height to obtain a cubic rock sample.

[0056] S4. First, use a high-pressure water gun nozzle to forcefully flush the rock and soil debris remaining in the previous step, invert the wellbore to remove the residue, and let it stand for a while until the wellbore wall is dry; select a position 10mm away from the bottom of the wellbore pipe to install a Φ12mm diameter annular rubber sleeve, and pre-embed the wellbore pipe in the cubic rock sample hole. When the liquid pressure contacts the annular rubber sleeve, it deforms and contacts the wall, preventing the sealant from reaching the hole at the bottom of the wellbore pipe and blocking the channel;

[0057] S5. Use polytetrafluoroethylene adhesive as a sealant to pour the sealant from the wellhead position along the wellbore wall to the annular space between the pipe string and the hole wall. During the pouring process, rotate and shake the wellbore so that the sealant can reach the annular rubber sleeve along the wall surface. When the liquid pressure contacts, the annular rubber sleeve is deformed and contacts the wall surface, completing the partition sealing of the lower part of the wellbore. The sealant densely fills the entire annular space. Wait for the sealant to dry and solidify, and then consolidate the wellbore;

[0058] S6. Apply sealant within 20mm along the edge of the square pressure head wall and the interface between the square pressure head and the rock sample wall, and use a dryer to dry it continuously to ensure that the wellhead is completely sealed;

[0059] S7. Before the experiment begins, the rock sample is heated by oven baking (oil bath heating, water bath heating, etc.) to a predetermined temperature (100°C to 280°C);

[0060] S8. Install a lifting ring on the prepared high-temperature sealed rock sample, and then use the picking and placing auxiliary device to place it into Figure 1 the large-scale true triaxial device in []. Install displacement sensors and acoustic emission sensors at the positions of the reserved holes on the loading plate, and conduct triaxial stress confining pressure loading. At the same time, turn on the sound acquisition system of the acoustic emission system (before this, it is necessary to calibrate the input parameters of the acoustic emission monitoring subsystem: connect the acoustic emission monitoring subsystem to the artificial core, based on the lead-breaking experiment of the artificial core, and according to the acoustic emission event positioning points monitored on the artificial core, calibrate the acoustic emission parameters input on the acoustic emission monitoring terminal until the acoustic emission event positioning points monitored after the artificial core breaks lead are close to the actual lead-breaking position);

[0061] S9. Prepare the corresponding fracturing fluid, including but not limited to slickwater, etc. Inject the fluid into the booster pump, and after boosting the energy, inject it into the fracturing pipeline for hydraulic fracturing. When the net pressure near the wellbore is greater than the fracture pressure, the rock sample fractures to generate artificial fracturing fractures;

[0062] S10. Under the condition of simulating that the specimen is under the influence of triaxial stress in the real formation, start the servo pump pressure control system, and pump the fracturing fluid into the specimen according to the set constant displacement parameter. As the fracturing fluid increases, the pump pressure increases rapidly. When the pump pressure curve shows an obvious point from rising to rapidly dropping, stop pumping the fracturing fluid. At this time, it means that the pump pressure has reached the fracture pressure. In short, when the pump pressure drops rapidly and tends to be stable, it can indicate that the pump pressure has reached the fracture pressure. At the same time, when the tester can visually see the fracturing fluid flowing out from the reserved channel, stop;

[0063] S11. Analyze the acoustic emission data to obtain the distribution of fractures in the rock sample, obtain the shear slip amount of the rock sample through the displacement sensor, and conduct result processing and analysis. Based on the above method, change the experimental conditions (composition of natural fracture fillings, salinity of fracturing fluid, water saturation, experimental temperature) to determine the variation laws of fracture friction coefficient and shear strength. According to the experimental data, fit the functional relationships between the friction coefficient, shear strength and salinity of fracturing fluid, water saturation, temperature, and filling composition. Comprehensively apply elastic-plastic mechanics, composite fracture mechanics, phase field method, and finite element method to construct a natural fracture slip prediction model. Simulate and obtain the natural fracture slip laws under different geological and engineering parameters. Provide technical support for the optimization of fracturing layer selection and the optimization design of fracturing construction site parameters, and at the same time have certain engineering significance for promoting the theory and technology of horizontal wellbore damage prevention and control and the optimization of on-site construction design.

[0064] As mentioned above, it is not any form of restriction on the present invention. Although the present invention has been disclosed through the above embodiments, it is not intended to limit the present invention. Any person skilled in the art can, within the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments of equivalent changes by using the technical content disclosed above. However, as long as it does not depart from the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A high temperature and high pressure true triaxial shale fracture slip test method, characterized in that: A high temperature and high pressure true triaxial shale fracture and slip test device is used to perform fracture and slip test, the high temperature and high pressure true triaxial shale fracture and slip test device comprising: a rock sample, a true triaxial confining pressure device, a true triaxial frame, a fracturing pumping system, a specimen taking and placing auxiliary device, an acoustic emission system, a digital sensor and a jack mold assembly, the digital sensor comprising a pressure sensor, a temperature sensor and a displacement sensor, the true triaxial confining pressure device comprising three hydraulic loading cylinders, a hydraulic loading plate and a nitrogen pressure tank; the hydraulic loading plate is placed in a pressure chamber and is directly connected to the rock sample; the true triaxial frame is a frame structure, comprising a base (4), a box The invention relates to a body (5), an upper end cover (7), a bearing plate (9), a lifting ring (1) and a supporting column (6); a base (4), an axial loading plate (12), a bearing plate (9) and an upper and lower loading plate together form a pressure chamber for containing a rock sample; the base (4) is provided with a fracturing fluid outflow channel (10); the acoustic emission system is equipped with eight probes respectively installed on the outside of the rock sample, and uses an acoustic emission preamplifier to amplify the signal, analyze the acoustic emission data, obtain the distribution of rock sample cracks, obtain the shear slip amount of the rock sample through a displacement sensor, and perform result processing and analysis; a reserved hole is reserved above the loading plate, and the reserved hole is used to load the displacement sensor; The test method comprises the following steps: Step 1: Prepare a jack pressure chamber and a mold, take similar materials for fault filling, air-dry and crush them, configure them into the required filling materials in proportion, and press them into a certain shape using a jack device; Step 2: Prepare a cubic rock sample with built-in faults; Step 3: Select a side with bedding and microcracks and draw lines along the diagonal to obtain a cubic rock sample, and drill vertically on one side of the rock sample; Step 4: pre-bury the wellbore string in the hole drilled from the rock sample; Step 5: pouring sealant into the gap between the wellbore tubular and the hole wall to consolidate the wellbore tubular; Step 6: Sleeve the pressure head on the wellbore string, ensure that the pressure head and the rock sample fit tightly, weld the pressure head to the wellbore string, and apply sealant on the edge of the pressure head; Step 7: Before the experiment begins, heat the rock sample to reach a predetermined temperature; Step 8: Place the sealed and heated rock sample into the true triaxial pressure chamber using a pick-and-place auxiliary device for triaxial stress confining pressure loading; Step 9: Prepare the fracturing fluid, inject it into the rock sample through a booster pump for hydraulic fracturing, and turn on the acoustic emission system for data collection; Step 10: The test is stopped when the fracturing fluid flows out from the reserved channel; Step 11: Analyze the acoustic emission data to obtain the distribution of rock sample cracks, obtain the shear slip of the rock sample through the displacement sensor, and perform result processing and analysis.

2. A high temperature and high pressure true triaxial shale fracture slip test method according to claim 1, characterized in that: The jack mold assembly is mainly composed of a top cover (15), a column (16), a hexagonal bolt (17), a bottom plate (18), a clamp body (19), a clamp top cover (21) and a long hydraulic jack (22) which are loaded and connected.

3. A high temperature and high pressure true triaxial shale fracture slip test method according to claim 1, characterized in that: The test device can determine the variation law of fracture friction coefficient and shear strength by changing experimental conditions, realize vertical stratification stress difference and horizontal stress difference of heterogeneous reservoirs, and study the geometric morphology of fracturing cracks under various stress combination states.

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