Experimental device and method for simulating paving of proppant in multi-scale crack system

Abstract

The invention belongs to the technical field of oil and gas field development, and discloses an experimental device and method for simulating paving of a propping agent in a multi-scale crack system. The experimental device comprises a multi-scale crack system and a fracturing fluid preparation system, the multi-scale crack system comprises a main crack, a first-stage branch crack and a second-stage branch crack; the main crack, the first-stage branch crack and the second-stage branch crack are each of a visual flat plate structure and comprise two visual flat plates which are arranged in parallel, and the side edges of the two visual flat plates are sealed through edge wrapping frames; a plurality of first-stage branch seams are formed in the plate face of the main crack in a communicating mode, at least one second-stage branch seam is formed in the plate face of each first-stage branch seam in a communicating mode, the second-stage branch seams are connected back to the fracturing fluid preparation system through branch seam material returning pipelines, and valves and flow meters are arranged on the branch seam material returning pipelines. The experimental device and method are closer to a fracture network structure of an actual stratum, and the laying condition of the propping agent in the actual fracture network structure can be simulated more accurately.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field exploitation, and in particular to an experimental device and method for simulating the laying of proppants in a multi-scale fracture system. Background Art

[0002] Tight gravel reservoirs have low porosity and poor permeability, and conventional mining methods are difficult to achieve efficient development. Horizontal well volume fracturing technology can form a complex fracture network, increase the reservoir transformation volume, and significantly increase production and recovery rate. It is an important means to achieve large-scale and efficient development of gravel reservoirs. Since gravel reservoirs themselves are highly heterogeneous and contain a large amount of gravel, the artificial fractures produced by volume fracturing are mostly curved fractures extending around gravel and the fracture surface is rough, which has a significant impact on the long-distance migration of proppants and the formation of effective support for artificial fractures. In the process of pumping proppants in volume fracturing of tight gravel reservoirs, the proppants may all settle to the bottom of the fractures, resulting in no proppant filling in the upper part of the fractures, forming invalid fracture support. The settlement and distribution law of the proppant determines the final shape and conductivity of the proppant distribution in the complex fracture network, thereby determining the effect of the fracturing construction.

[0003] Chinese invention patent CN102590888A discloses an experimental device for simulating the laying of proppant in a crack, including an artificial crack, wherein the artificial crack includes two transparent plates arranged parallel to each other, the upper and lower ends of the two transparent plates are sealed by a frame respectively, a simulated wellbore is arranged at the left end of the transparent plate, and a liquid outlet pipe is arranged at the right end of the transparent plate, and the transparent plate, the frame, the wall of the simulated wellbore and the wall of the liquid outlet pipe together enclose a closed space; the top of the simulated wellbore is arranged There is a feed port, a discharge port is arranged at the bottom of the simulated wellbore, and multiple wall perforations are evenly arranged on the simulated wellbore wall and in the direction of the enclosed space, and the feed port, discharge port and wall perforations are interconnected; a flow meter and a pressure gauge are arranged at the feed port of the simulated wellbore; a return port is arranged at the top of the liquid outlet pipe, and a discharge port is arranged at the bottom of the liquid outlet pipe, and multiple holes are evenly arranged on the liquid outlet pipe wall and in the direction of the enclosed space, and the return port, discharge port and holes are interconnected; a flow meter and a pressure gauge are arranged at the return port of the liquid outlet pipe. The experimental device disclosed in this invention patent uses two transparent plates arranged in parallel to each other to simulate plane cracks, thereby simulating the settlement and distribution law of proppant in plane cracks. However, the experimental device of this patent has no secondary cracks outside the main cracks, and cannot simulate the migration of proppant under different secondary cracks, which is far from the crack network structure of the actual formation.

[0004] Therefore, how to provide an experimental device and method for simulating the placement of proppants in a multi-scale fracture system, fully consider the fracture network structure of the actual formation, and provide a theoretical basis and guidance for on-site construction is a problem that needs to be solved at present. Summary of the invention

[0005] In order to solve the technical problems existing in the prior art, the present invention provides an experimental device and method for simulating the laying of proppants in a multi-scale fracture system. The multi-scale fracture system composed of main fractures, primary branch fractures and secondary branch fractures is closer to the fracture network structure of the actual formation, and can more accurately simulate the laying of proppants in the actual fracture network structure, providing a theoretical basis and effective guidance for on-site construction.

[0006] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0007] An experimental device for simulating proppant laying in a multi-scale fracture system, comprising a multi-scale fracture system and a fracturing fluid configuration system, wherein the fracturing fluid configuration system is connected to the multi-scale fracture system via a feed pipe, and the multi-scale fracture system is connected back to the fracturing fluid configuration system via a main return pipe and a branch seam return pipe;

[0008] The multi-scale fracture system includes a main fracture, a primary branch fracture and a secondary branch fracture; the main fracture, the primary branch fracture and the secondary branch fracture are all visualization plate structures, including two visualization plates arranged parallel to each other, and the sides of the two visualization plates are sealed by a frame;

[0009] A feed shaft is provided at the left end of the two visualization plates and a return shaft is provided at the right end of the main crack, and the visualization plates, frame, feed shaft and return shaft together enclose a closed space; the bottom end of the feed shaft is closed, and a feed port is provided at the top end, the feed port is connected to the feed pipeline, and a flow meter and a pressure gauge are provided at the feed port; a plurality of wall perforations are provided on the wall of the feed shaft facing the closed space, and the wall perforations are connected with the feed port; the top end of the return shaft is closed, and a return port is provided at the bottom end, and a plurality of holes are provided on the wall of the return shaft facing the closed space, and the holes are connected with the return port; the return port is connected to the main return pipeline, and a flow meter and a valve are provided at the return port;

[0010] A plurality of primary branch seams are arranged on the plate surface of the main fracture, and at least one secondary branch seam is arranged on the plate surface of the primary branch seam. The secondary branch seam is connected back to the fracturing fluid configuration system through a branch seam return pipe, and a valve and a flow meter are arranged on the branch seam return pipe.

[0011] Furthermore, a plurality of perforations are evenly distributed on the wall of the feed shaft, and the aperture, number and azimuth of the perforations are set according to different simulation experiment requirements; a plurality of holes are evenly distributed on the wall of the return shaft.

[0012] Furthermore, a plurality of the multi-scale fracture systems are connected in series via an intermediate two-way joint.

[0013] Furthermore, the main crack, the primary branch crack and the secondary branch crack are connected via two intermediate connecting joints;

[0014] The intermediate connecting two-way joint is a straight-through connector, with an outlet at the top and a vent at the bottom, and is made of aviation aluminum alloy;

[0015] The turning angle and the width of the diameter of the intermediate two-way joint are of various specifications.

[0016] Furthermore, the turning angle of the intermediate connecting two-way joint is 30°, 45°, 60° or 90°, and the width of the through-hole is 2mm, 4mm, 6mm, 8mm or 10mm.

[0017] Furthermore, model covers are provided on both sides of the visualization panel for reinforcing and supporting the visualization panel; the model cover is a hollow frame structure, and a plurality of reinforcing ribs are provided at intervals in the middle of the model cover.

[0018] Furthermore, the pressure resistance range of the multi-scale crack system is 0-2MPa; the material of the visualization plate is borosilicate glass with a transmittance of ≥85%; the material of the model cover and the reinforcement ribs is 316L stainless steel or high-strength aluminum alloy.

[0019] Furthermore, the fracturing fluid configuration system comprises a liquid preparation tank, a sand adding device, a sand mixing tank and a settling tank; the liquid preparation tank and the sand adding tank are both connected to the sand mixing tank for sand mixing, and the discharge port of the sand mixing tank is connected to the feed pipe; the liquid discharge pipe of the liquid preparation tank and the discharge pipe of the sand mixing tank are both provided with a delivery pump;

[0020] The feed inlet of the settling tank is connected to the main return pipe and the branch seam return pipe respectively, and the top liquid outlet of the settling tank is connected to the liquid distribution tank through a delivery pump.

[0021] Furthermore, the liquid preparation tanks are two in parallel; the delivery pump is a screw pump.

[0022] Furthermore, the multi-scale crack system also includes a crack width adjustment mechanism, which includes a plurality of pads of different thicknesses, and the pads are clamped at both ends of two visualization plates.

[0023] Furthermore, the multi-scale crack system also includes a flipping mechanism; the two ends of the main crack are connected to the flipping mechanism through a short axis, and the flipping mechanism can drive the main crack to flip horizontally at any angle of 0-180° and then lock it, thereby simulating various situations from vertical to horizontal, including horizontal cracks, vertical cracks and angle cracks.

[0024] Furthermore, the flipping mechanism adopts a worm gear self-locking speed reduction mechanism, and the flipping mechanism adopts hydraulic control.

[0025] Furthermore, the multi-scale fracture system 1 also includes a high-pressure nozzle cleaning device, which includes a plurality of rotating high-pressure nozzles. The plurality of rotating high-pressure nozzles are respectively embedded and installed in two visualization plates at intervals, and ensure that the rotating high-pressure nozzles are provided at the entrance corresponding to the primary branch fracture.

[0026] Furthermore, a rotating high-pressure nozzle is arranged at the transition gap between the primary branch seam and the secondary branch seam.

[0027] Furthermore, the experimental device also includes an online monitoring system;

[0028] The online monitoring system is mainly composed of a carrying platform, a high-definition camera, a video-controlled mobile mechanism and a lighting auxiliary system; the frame of the carrying platform is built with aluminum alloy profiles, the high-definition camera is placed on the carrying platform, and the video-controlled mobile mechanism is used to freely adjust the movement of the high-definition camera in different positions, and the relevant video data is recorded and saved in real time, which is convenient for future analysis and research on the migration trajectory and migration law of the relevant sand-carrying fluid.

[0029] Furthermore, the experimental device also includes a data acquisition and processing system;

[0030] The data acquisition and processing system receives the measured values ​​of the pressure gauge and flow meter, and determines whether the pressure value and flow value are greater than or equal to the set upper and lower limit thresholds. If the pressure value and flow value are greater than or equal to the set upper and lower limit thresholds, a pressure or flow alarm is issued.

[0031] At the same time, the present invention also provides an experimental method for simulating the placement of proppants in a multi-scale fracture system, which is carried out using the experimental device as described in any of the above items, and the experimental method comprises the following steps:

[0032] Step S1: Based on the similarity principle and the width of the cracks in the field construction, the volume L1 of the proppant, the volume L2 of the fracturing fluid, the viscosity P of the fracturing fluid and the construction displacement V required for the experiment are calculated, and the fracturing fluid and various proppants are prepared according to the calculation results;

[0033] Step S2: Select a visualization plate with the same roughness as the fracture surface of the core in actual construction, set the number of perforations, perforation aperture and perforation azimuth on the wall of the feed shaft, assemble a multi-scale fracture system, and make the gap widths of the main fracture, primary branch fracture and secondary branch fracture consistent with the fracture width in the field construction;

[0034] Step S3: Adjust the angle of the main crack and connect the equipment pipeline;

[0035] Step S4: Put the prepared proppant and fracturing fluid into the liquid preparation tank 601 to mix and stir into the sand-carrying fracturing fluid, start the equipment to pump the sand-carrying fracturing fluid into the main fracture to form a circulation loop;

[0036] Step S5: photograph and track the migration trajectory of the proppant in the main fracture, collect experimental data, calculate the vertical settling velocity and horizontal migration velocity of the proppant, and record, save and display the output experimental data, the height and length of the sand bank, and the distribution map of the sand bank shape in real time;

[0037] Step S6: stop pumping the sand-carrying fracturing fluid into the main fracture, and use a rotating high-pressure nozzle to empty and clean the main fracture;

[0038] Step S7: Dry and weigh the proppant settled in the main fracture, calculate the mass ratio of the proppant settled in the main fracture to the total proppant, replace other proppant or fracturing fluid separately, repeat steps S4-S7, and complete the next round of experimental test.

[0039] Compared with the prior art, the beneficial effects of the present invention are:

[0040] (1) The multi-scale fracture system of the present invention includes a main fracture, a primary branch fracture and a secondary branch fracture, and the main fracture, the primary branch fracture and the secondary branch fracture are all visualized flat plate structures. Compared with the existing plane fracture model, the multi-scale fracture system of the present invention has a more complex fracture network structure, which is closer to the construction conditions of the actual formation. When simulating the settlement and distribution law of the proppant, it can more accurately reflect the laying conditions of the proppant in the actual formation fracture network structure, and provide a more accurate theoretical basis and guidance for on-site construction;

[0041] (2) The main crack, the primary branch crack and the secondary branch crack of the present invention are connected by an intermediate connecting two-way joint. The intermediate connecting two-way joint has a variety of specifications for the turning angle and the width of the diameter, which can respectively simulate the branch angles of 30°, 45°, 60° and 90° between the main crack 101 and the primary branch crack 102, and between the primary branch crack 102 and the secondary branch crack 103, and the crack width test of 2mm, 4mm, 6mm, 8mm or 10mm;

[0042] (3) The multi-scale crack system of the present invention also includes a crack width adjustment mechanism, which can change the crack width by replacing pads of different thicknesses, and the operation is simple and convenient;

[0043] (4) The multi-scale fracture system of the present invention further includes a hydraulic flip mechanism; the two ends of the main fracture are connected to the hydraulic flip mechanism through a short shaft, and the flip mechanism drives the fracture to flip horizontally at any angle of 0-180° and then locks it, thereby simulating various conditions from vertical to horizontal, including horizontal fractures, vertical fractures and angle fractures, and is applicable to more working conditions;

[0044] (5) The multi-scale fracture system of the present invention also includes a high-pressure nozzle cleaning device, which can clean and remove the residual sand in the multi-scale fracture system by rotating the high-pressure nozzle after the experiment. Compared with the conventional water cleaning and removal method, the method of the embodiment of the present invention not only reduces the difficulty of cleaning the residual sand in the corner gaps, but also makes the cleaning more thorough and efficient, and the cleaning speed is faster. At the same time, it can also greatly reduce the amount of cleaning water and save water resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is a schematic diagram of the structure of an experimental device according to Example 1 of the present invention;

[0046] Figure 2 is a schematic structural diagram of a crack width adjustment mechanism according to Embodiment 2 of the present invention;

[0047] Figure 3 is a schematic structural diagram of a high-pressure nozzle cleaning device according to Embodiment 4 of the present invention;

[0048] Description of the markings in the figure:

[0049] 1-Main fracture of multi-scale fracture system; 2-Feeding wellbore; 3-Returning wellbore; 4-Flowmeter; 5-Valve; 6-Fracturing fluid configuration system; 7-Pressure gauge; 8-Rotating high-pressure nozzle;

[0050] 101-main crack; 102-first-level branch crack; 103-second-level branch crack; 104-visualization plate; 105-pad; 106-reinforcement rib; 601-liquid distribution tank; 602-sand adding device; 603-sand mixing tank; 604-sedimentation tank; 605-delivery pump. DETAILED DESCRIPTION

[0051] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0052] In the description of the present invention, it is necessary to understand that the terms "coaxial", "bottom", "one end", "top", "middle", "the other end", "upper", "one side", "top", "inside", "front", "center", "both ends" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0053] In the present invention, unless otherwise clearly stipulated and limited, the terms such as "installation", "setting", "connection", "fixation" and "screw-on" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. Unless otherwise clearly defined, ordinary technicians in this field can understand the specific meanings of the above terms in the present invention according to the specific circumstances.

[0054] Example 1

[0055] Refer to the attached Figure 1 , is a schematic diagram of the structure of an experimental device for simulating the placement of proppant in a multi-scale fracture system provided by an embodiment of the present invention. Figure 1 As shown, the experimental device includes a multi-scale fracture system 1 and a fracturing fluid configuration system 6, wherein the fracturing fluid configuration system 6 is connected to the multi-scale fracture system 1 through a feed pipe, and the multi-scale fracture system 1 is connected back to the fracturing fluid configuration system 6 through a main return pipe and a branch seam return pipe;

[0056] The multi-scale fracture system 1 includes a main fracture 101, a primary branch fracture 102, and a secondary branch fracture 103; the main fracture 101, the primary branch fracture 102, and the secondary branch fracture 103 are all visualization plate structures, including two visualization plates arranged parallel to each other, and the sides of the two visualization plates are sealed by a frame;

[0057] The main fracture 101 is provided with a feed shaft 2 at the left end of the two visualization plates and a return shaft 3 at the right end, and the visualization plates, frame, feed shaft 2 and return shaft 3 together form a closed space; the bottom end of the feed shaft 2 is closed, and a feed port is provided at the top end, the feed port is connected to the fracturing fluid configuration system 6 through a feed pipe, and a flow meter 4 and a pressure gauge 7 are provided at the feed port; a plurality of wall perforations are provided on the wall of the feed shaft 2 facing the closed space, and the wall perforations are connected with the feed port; the top end of the return shaft 3 is closed, and a return port is provided at the bottom end, and a plurality of holes are provided on the wall of the return shaft 3 facing the closed space, and the holes are connected with the return port; the return port is connected to the fracturing fluid configuration system 6 through the main return pipe, and a flow meter 4 and a valve 5 are provided at the return port.

[0058] A plurality of primary branch seams 102 are provided on the plate surface of the main fracture 101, and at least one secondary branch seam 103 is provided on the plate surface of the primary branch seam. The secondary branch seam 103 is connected back to the fracturing fluid configuration system 6 through a branch seam return pipe, and a valve and a flow meter are provided on the branch seam return pipe.

[0059] The main fracture 101 , the primary branch fracture 102 and the secondary branch fracture 103 of the present invention constitute a multi-scale fracture system 1 .

[0060] According to a specific embodiment of the present invention, a plurality of perforations are evenly distributed on the wall of the feed shaft 2, and the aperture, number and azimuth (the angle between the axis of the perforation and the horizontal line) of the perforations can be set according to the requirements of different simulation experiments.

[0061] According to a specific embodiment of the present invention, a plurality of holes are evenly distributed on the wall of the return shaft 3.

[0062] According to a specific embodiment of the present invention, the size of the main crack 101 is: 6000mm long × 500mm high, and the crack width is adjustable from 2 to 10mm; the size of the first-level branch crack 102 is: 4000mm long × 500mm high, and the crack width is adjustable from 2 to 10mm; the size of the second-level branch crack 103 is: 2000mm long × 500mm high, and the crack width is adjustable from 2 to 10mm.

[0063] According to a specific embodiment of the present invention, a plurality of the multi-scale crack systems are connected in series through an intermediate connecting two-way joint to simulate crack settlement of sufficient length; the main crack 101, the primary branch seam 102 and the secondary branch seam 103 are connected through an intermediate connecting two-way joint; the intermediate connecting two-way joint is a straight-through connector with an outlet at the top and a vent at the bottom, and is made of high-strength aviation aluminum alloy; the turning angle and diameter seam width of the intermediate connecting two-way joint have a variety of specifications, which can simulate branch angles of 30°, 45°, 60° and 90° between the main crack 101 and the primary branch seam 102, and between the primary branch seam 102 and the secondary branch seam 103, as well as seam width tests of 2mm, 4mm, 6mm, 8mm or 10mm.

[0064] According to a specific embodiment of the present invention, a model cover is further provided on both sides of the visualization plate to reinforce and support the visualization plate; the model cover is a hollow frame structure, and a plurality of reinforcing ribs 106 (see Figure 2 ).

[0065] The pressure resistance range of the multi-scale crack system 1 is 0-2MPa; the material of the visualization plate constituting the main crack 101, the first-level branch crack 102 and the second-level branch crack 103 is borosilicate glass with a transmittance of ≥85%; the material of the model cover plate and the reinforcement ribs is 316L stainless steel or high-strength aluminum alloy.

[0066] According to a specific embodiment of the present invention, the inner wall surface of the visualization plate is provided with a single-sided rough visualization material representing different rock surface characteristics, and the transmittance of the single-sided rough visualization material is ≥85%. For example, 8 different specifications of roughness can be designed according to different rock surface characteristics.

[0067] According to a specific embodiment of the present invention, the range of the pressure gauge 7 is: 0-2MPa, and the accuracy is: 0.25%FS.

[0068] According to a specific embodiment of the present invention, the fracturing fluid configuration system 6 is used to mix the base fluid, cross-linking agent, proppant, fiber mixture and other materials, and stir them into sand-carrying fracturing fluid. The fracturing fluid configuration system 6 includes a liquid preparation tank 601, a sand adding device 602, a sand mixing tank 603 and a sedimentation tank 604; the liquid preparation tank 601 and the sand adding tank 602 are both connected to the sand mixing tank 603 for sand mixing, and the discharge port of the sand mixing tank 603 is connected to the feed pipe; the liquid discharge pipe of the liquid preparation tank 601 and the discharge pipe of the sand mixing tank 603 are both provided with a delivery pump 605;

[0069] The feed port of the settling tank 604 is respectively connected to the main return pipe and the branch seam return pipe, and the top liquid outlet of the settling tank 604 is connected to the liquid preparation tank 601 through the delivery pump 605, so that the fracturing fluid with settled and filtered sand particles in the settling tank 604 is re-pumped to the liquid preparation tank 601 to achieve the recovery and reuse of the fracturing fluid.

[0070] According to a specific embodiment of the present invention, the delivery pump 605 can be a screw pump, which is adjusted by a frequency converter, and the pumping flow rate is: 0-12m 3 / h; working pressure: 0-2MPa.

[0071] The volume of the liquid preparation tank 601 is 300L, the material can be 316L stainless steel, the working pressure range is 0-1.0MPa, and the stirring speed range is 0-500r / min.

[0072] According to a specific embodiment of the present invention, the fracturing fluid configuration system 6 may include two parallel liquid preparation tanks 601, and the two liquid preparation tanks may work simultaneously or independently. When the volume of fracturing fluid required for the experiment is smaller than the volume of the liquid preparation tank, one liquid preparation tank may be selected to complete the liquid preparation, and when the volume of fracturing fluid required for the experiment is larger than the volume of the liquid preparation tank, two liquid preparation tanks may be selected to complete the liquid preparation simultaneously.

[0073] The sand adding device 602 can add sand to the sand mixing tank 603 in a regular and quantitative manner. The material of the sand adding device can be 316 stainless steel. The sand adding ratio ranges from 10% to 30% and the sand adding speed ranges from 5kg / min to 20kg / min.

[0074] The volume of the sand mixing tank 603 is 300L, and the material can be 316L stainless steel. The working pressure range is: 0-1.0MPa, and the stirring speed range is: 0-500r / min.

[0075] The volume of the settling tank 604 is 300L, and the material can be 316L stainless steel. The working pressure range is 0-1.0MPa. The settling tank 604 is designed with a particle filter for separating sand particles in the sand-carrying fracturing fluid.

[0076] Example 2

[0077] The experimental device for simulating the placement of proppant in a multi-scale fracture system provided in the embodiment of the present invention has the following improvements on the basis of embodiment 1:

[0078] The multi-scale fracture system 1 also includes a fracture width adjustment mechanism, such as Figure 2 As shown, the crack width adjustment mechanism includes a plurality of pads 105 with different thicknesses, and the pads 105 are clamped and arranged at both ends of two visualization plates 104 .

[0079] By placing pads 105 of set thickness at both ends of the two visualization plates 104, experimental simulation of multiple equal-width gaps (the pads at both ends have the same thickness) or multiple variable-width gaps (the pads at both ends have different thicknesses) can be achieved, and the gap width can be easily changed by replacing pads of different thicknesses, which is convenient to operate.

[0080] Example 3

[0081] The experimental device for simulating the placement of proppant in a multi-scale fracture system provided in the embodiment of the present invention has the following improvements on the basis of embodiment 1 or 2:

[0082] The multi-scale crack system 1 also includes a flipping mechanism; the two ends of the main crack are connected to the flipping mechanism through a short axis, and the flipping mechanism can drive the main crack to flip horizontally at any angle of 0-180° and then lock it, thereby simulating various situations from vertical to horizontal, including horizontal cracks, vertical cracks and angle cracks.

[0083] The flipping mechanism adopts a worm gear self-locking speed reduction mechanism, and the control method of the flipping mechanism can adopt hydraulic control, which can achieve the safety of the flipping process, ensure the safety of the operator, and is easy to operate and labor-saving.

[0084] Example 4

[0085] The experimental device for simulating the placement of proppant in a multi-scale fracture system provided in the embodiment of the present invention is improved as follows based on any one of the embodiments 1 to 3:

[0086] like Figure 3 As shown, the multi-scale fracture system 1 also includes a high-pressure nozzle cleaning device, which includes a plurality of rotating high-pressure nozzles 8. The plurality of rotating high-pressure nozzles 8 are respectively embedded and installed in two visualization plates 104 at intervals, and ensure that the rotating high-pressure nozzles 8 are provided at the entrance corresponding to the primary branch seam 102. The rotating high-pressure nozzles 8 can achieve 360° high-pressure cleaning without dead angles.

[0087] In some other embodiments, the rotating high-pressure nozzle 8 may also be additionally provided at the transition gap between the primary branch slit 102 and the secondary branch slit 103 to further improve the cleaning effect and cleaning efficiency.

[0088] By setting up a high-pressure nozzle cleaning device, after the experiment, the high-pressure nozzle can be rotated to perform 360° high-pressure cleaning without dead ends to remove the residual sand in the multi-scale fracture system 1. Compared with the conventional clean water cleaning and removal method, the method of the embodiment of the present invention not only reduces the difficulty of cleaning the residual sand in the corner gaps, and the cleaning is more thorough and efficient, but also has a faster cleaning speed. At the same time, it can also greatly reduce the amount of cleaning water and save water resources.

[0089] Example 5

[0090] The experimental device for simulating the placement of proppant in a multi-scale fracture system provided in the embodiment of the present invention is improved as follows based on any one of the embodiments 1 to 3:

[0091] The experimental device also includes an online monitoring system and a data acquisition and processing system.

[0092] The online monitoring system is mainly composed of a carrying platform, a high-definition camera, a video-controlled mobile mechanism and a lighting auxiliary system; the frame of the carrying platform is built with aluminum alloy profiles, the high-definition camera is placed on the carrying platform, and the video-controlled mobile mechanism is used to freely adjust the movement of the high-definition camera in different positions, and the relevant video data is recorded and saved in real time, which is convenient for future analysis and research on the migration trajectory and migration law of the relevant sand-carrying fluid.

[0093] The data acquisition and processing system receives the measured values ​​of the pressure gauge and flow meter, and determines whether the pressure value and flow value are greater than or equal to the set upper and lower limit thresholds. If the pressure value and flow value are greater than or equal to the set upper and lower limit thresholds, a pressure or flow alarm is issued.

[0094] According to a specific embodiment of the present invention, the experimental device can also be equipped with two computers, one computer can be used to store video data and image data captured by the shooting device, and the other computer can be used for data acquisition and processing system to process the received data. The two computers can communicate and transmit via a wireless network or a wired network.

[0095] It should be noted that the performance, memory size and hard disk storage size of the two computers can be set according to actual needs, and the present invention does not make specific limitations. For example, the performance of the computer can be higher than the processor i7, the memory size can be 32GB, the hard disk size can be 2000GB SSD, and the computer can use 380V or 220±20V, 50Hz AC power.

[0096] Example 6

[0097] The embodiment of the present invention provides an experimental method for simulating the placement of proppant in a multi-scale fracture system using the above experimental device, the method comprising the following steps:

[0098] Step S1: Based on the similarity principle and the width of the cracks in the field construction, the volume L1 of the proppant, the volume L2 of the fracturing fluid, the viscosity P of the fracturing fluid and the construction displacement V required for the experiment are calculated, and the fracturing fluid and various proppants are prepared according to the calculation results;

[0099] Step S2: Select a visualization plate with the same roughness as the fracture surface of the core in actual construction, set the number of perforations, perforation aperture and perforation azimuth on the wall of the feed shaft, assemble a multi-scale fracture system, and make the gap widths of the main fracture, primary branch fracture and secondary branch fracture consistent with the fracture width in the field construction;

[0100] Step S3: Adjust the angle of the main crack and connect the equipment pipeline;

[0101] Step S4: Put the prepared proppant and fracturing fluid into the liquid preparation tank 601 to mix and stir into the sand-carrying fracturing fluid, start the equipment to pump the sand-carrying fracturing fluid into the main fracture to form a circulation loop;

[0102] Step S5: photograph and track the migration trajectory of the proppant in the main fracture, collect experimental data, calculate the vertical settling velocity and horizontal migration velocity of the proppant, and record, save and display the output experimental data, the height and length of the sand bank, and the distribution map of the sand bank shape in real time;

[0103] Step S6: stop pumping the sand-carrying fracturing fluid into the main fracture, and use a rotating high-pressure nozzle to empty and clean the main fracture;

[0104] Step S7: Dry and weigh the proppant settled in the main fracture, calculate the mass ratio of the proppant settled in the main fracture to the total proppant, replace other proppant or fracturing fluid separately, repeat steps S4-S7, and complete the next round of experimental test.

[0105] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. An experimental device for simulating proppant placement in a multi-scale fracture system, characterized in that: It comprises a multi-scale fracture system and a fracturing fluid configuration system, wherein the fracturing fluid configuration system is connected to the multi-scale fracture system through a feed pipe, and the multi-scale fracture system is connected back to the fracturing fluid configuration system through a main return pipe and a branch seam return pipe; The multi-scale fracture system includes a main fracture, a primary branch fracture and a secondary branch fracture; the main fracture, the primary branch fracture and the secondary branch fracture are all visualization plate structures, including two visualization plates arranged parallel to each other, and the sides of the two visualization plates are sealed by a frame; A feed shaft is provided at the left end of the two visualization plates and a return shaft is provided at the right end of the main crack, and the visualization plates, frame, feed shaft and return shaft together enclose a closed space; the bottom end of the feed shaft is closed, and a feed port is provided at the top end, the feed port is connected to the feed pipeline, and a flow meter and a pressure gauge are provided at the feed port; a plurality of wall perforations are provided on the wall of the feed shaft facing the closed space, and the wall perforations are connected with the feed port; the top end of the return shaft is closed, and a return port is provided at the bottom end, and a plurality of holes are provided on the wall of the return shaft facing the closed space, and the holes are connected with the return port; the return port is connected to the main return pipeline, and a flow meter and a valve are provided at the return port; A plurality of primary branch seams are arranged on the plate surface of the main fracture, and at least one secondary branch seam is arranged on the plate surface of the primary branch seam. The secondary branch seam is connected back to the fracturing fluid configuration system through a branch seam return pipe, and a valve and a flow meter are arranged on the branch seam return pipe.

2. The experimental device according to claim 1, characterized in that: A plurality of perforations are evenly distributed on the wall of the feed shaft, and the aperture, number and azimuth of the perforations are set according to different simulation experiment requirements; a plurality of holes are evenly distributed on the wall of the return shaft.

3. The experimental device according to claim 1, characterized in that: A plurality of the multi-scale fracture systems are connected in series via intermediate two-way joints.

4. The experimental device according to claim 1, characterized in that: The main crack, the primary branch crack and the secondary branch crack are connected via two intermediate connecting joints; The intermediate connecting two-way joint is a straight-through connector, with an outlet at the top and a vent at the bottom, and is made of aviation aluminum alloy; The turning angle and the width of the diameter of the intermediate two-way joint are of various specifications.

5. The experimental device according to claim 3 or 4, characterized in that: The turning angle of the intermediate connecting two-way joint is 30°, 45°, 60° or 90°, and the width of the through-hole is 2mm, 4mm, 6mm, 8mm or 10mm.

6. The experimental device according to claim 1, characterized in that: Model covers are also provided on both sides of the visualization flat panel for reinforcing and supporting the visualization flat panel; the model cover is a hollow frame structure, and a plurality of reinforcing ribs are provided at intervals in the middle of the model cover.

7. The experimental device according to claim 6, characterized in that: The pressure resistance range of the multi-scale crack system is 0-2MPa; the material of the visualization plate is borosilicate glass with a transmittance of ≥85%; the material of the model cover plate and the reinforcement ribs is 316L stainless steel or high-strength aluminum alloy.

8. The experimental device according to claim 1, characterized in that: The fracturing fluid configuration system comprises a liquid preparation tank, a sand adding device, a sand mixing tank and a sedimentation tank; the liquid preparation tank and the sand adding tank are both connected to the sand mixing tank for sand mixing, and the discharge port of the sand mixing tank is connected to the feed pipeline; the liquid discharge pipeline of the liquid preparation tank and the discharge pipeline of the sand mixing tank are both provided with a delivery pump; The feed inlet of the settling tank is connected to the main return pipe and the branch seam return pipe respectively, and the top liquid outlet of the settling tank is connected to the liquid distribution tank through a delivery pump.

9. The experimental device according to claim 8, characterized in that: The liquid dispensing tanks are two connected in parallel; the delivery pump is a screw pump.

10. The experimental device according to claim 1, characterized in that: The multi-scale crack system further includes a crack width adjustment mechanism, which includes a plurality of pads of different thicknesses, and the pads are clamped and arranged at both ends of two visualization plates.

11. The experimental device according to claim 1, characterized in that: The multi-scale crack system also includes a flipping mechanism; the two ends of the main crack are connected to the flipping mechanism through a short axis, and the flipping mechanism can drive the main crack to flip horizontally at any angle of 0-180° and then lock it, thereby simulating various situations from vertical to horizontal, including horizontal cracks, vertical cracks and angle cracks.

12. The experimental device according to claim 11, characterized in that: The turning mechanism adopts a worm gear self-locking speed reduction mechanism, and the turning mechanism adopts hydraulic control.

13. The experimental device according to claim 1, characterized in that: The multi-scale fracture system 1 also includes a high-pressure nozzle cleaning device, which includes a plurality of rotating high-pressure nozzles. The plurality of rotating high-pressure nozzles are embedded and installed in two visualization plates at intervals, and ensure that the rotating high-pressure nozzles are provided at the entrance corresponding to the primary branch fracture.

14. The experimental device according to claim 13, characterized in that: A rotating high-pressure nozzle is arranged at the transition gap between the first-level branch seam and the second-level branch seam.

15. The experimental device according to any one of claims 1-4, 6-14, characterized in that: The experimental device also includes an online monitoring system; The online monitoring system is mainly composed of a carrying platform, a high-definition camera, a video-controlled mobile mechanism and a lighting auxiliary system; the frame of the carrying platform is built with aluminum alloy profiles, the high-definition camera is placed on the carrying platform, and the video-controlled mobile mechanism is used to freely adjust the movement of the high-definition camera in different positions, and the relevant video data is recorded and saved in real time, which is convenient for future analysis and research on the migration trajectory and migration law of the relevant sand-carrying fluid.

16. The experimental device according to claim 15, characterized in that: The experimental device also includes a data acquisition and processing system; The data acquisition and processing system receives the measured values ​​of the pressure gauge and flow meter, and determines whether the pressure value and flow value are greater than or equal to the set upper and lower limit thresholds. If the pressure value and flow value are greater than or equal to the set upper and lower limit thresholds, a pressure or flow alarm is issued.

17. An experimental method for simulating proppant placement in a multi-scale fracture system, using the experimental device according to any one of claims 1 to 16, characterized in that: The experimental method comprises the following steps: Step S1: Based on the similarity principle and the width of the cracks in the field construction, the volume L1 of the proppant, the volume L2 of the fracturing fluid, the viscosity P of the fracturing fluid and the construction displacement V required for the experiment are calculated, and the fracturing fluid and various proppants are prepared according to the calculation results; Step S2: Select a visualization plate with the same roughness as the fracture surface of the core in actual construction, set the number of perforations, perforation aperture and perforation azimuth on the wall of the feed shaft, assemble a multi-scale fracture system, and make the gap widths of the main fracture, primary branch fracture and secondary branch fracture consistent with the fracture width in the field construction; Step S3: Adjust the angle of the main crack and connect the equipment pipeline; Step S4: Put the prepared proppant and fracturing fluid into the liquid preparation tank 601 to mix and stir into the sand-carrying fracturing fluid, start the equipment to pump the sand-carrying fracturing fluid into the main fracture to form a circulation loop; Step S5: photograph and track the migration trajectory of the proppant in the main fracture, collect experimental data, calculate the vertical settling velocity and horizontal migration velocity of the proppant, and record, save and display the output experimental data, the height and length of the sand bank, and the distribution map of the sand bank shape in real time; Step S6: stop pumping the sand-carrying fracturing fluid into the main fracture, and use a rotating high-pressure nozzle to empty and clean the main fracture; Step S7: Dry and weigh the proppant settled in the main fracture, calculate the mass ratio of the proppant settled in the main fracture to the total proppant, replace other proppant or fracturing fluid separately, repeat steps S4-S7, and complete the next round of experimental test.

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