An experimental device and experimental method for staged multi-cluster fracturing of horizontal wells

Abstract

The present application provides an experimental device and experimental method for staged multi-cluster fracturing of horizontal wellbores. The experimental device includes a simulated wellbore, multiple perforating elements, and multiple connecting pipes. The simulated wellbore is used to be set in a rock formation sample. The interior of the simulated wellbore defines multiple fracturing spaces along its length. The multiple perforating elements are set outside the simulated wellbore and correspond one-to-one with the multiple fracturing spaces. Each perforating element is formed with multiple perforation channels connected to the corresponding fracturing spaces. The multiple connecting pipes are connected one-to-one with the multiple fracturing spaces and extend to the outside of the simulated wellbore. The experimental device of the present application has a simpler structure. When in use, there is no need to consider the correspondence accuracy between the fracturing section of the segmented injection string and the annular cutting groove, making operation simpler.

Description

Technical Field

[0001] The present application relates to the technical field of shale fracturing physical simulation experiments, and in particular to an experimental device and an experimental method for staged multi-cluster fracturing of horizontal wells. Background Art

[0002] Staged multi-cluster temporary fracturing in horizontal wells is a key tool for developing unconventional oil and gas reservoirs. This technology involves two main processes: first, the initiation and simultaneous propagation of multiple fracture clusters driven by fracturing fluid, known as primary fracturing; second, the injection of temporary plugging agents to temporarily plug both the fracture openings and within the fractures, followed by secondary fracturing to create new fractures and build a complex fracture network, known as temporary plugging fracturing. Clarifying the morphology of the initiation and simultaneous propagation of multiple fracture clusters during primary fracturing and revealing the patterns of fracture propagation during temporary plugging fracturing will help optimize the staged multi-cluster temporary fracturing process in horizontal wells and facilitate the efficient development of oil and gas resources.

[0003] The prior art has developed an experimental device for simulating multi-cluster fracturing of a horizontal wellbore on the ground. The experimental device comprises a casing, which is placed in the wellbore and the annular space is filled with glue; the casing is cut into a plurality of preset depths and cut into the rock sample to form a plurality of annular grooves to simulate the perforation clusters; a segmented injection string is inserted into the casing; a plurality of rubber sealing rings are provided on the outer surface of the string, which divide the wellbore into a plurality of fracturing sections, and the outlet of each injection line is located between two annular grooves in each fracturing section; and the simulation of multi-cluster fracturing of a horizontal wellbore is achieved by injecting liquid into the plurality of injection lines respectively.

[0004] The experimental device in the existing technology is not only complex in structure, but also the fracturing section of the segmented injection string must strictly correspond to the annular cutting groove, which requires the cutting groove depth to be precise. However, the operation is difficult during the actual experiment, and it is easy for the annular cutting groove to be outside the fracturing section. Summary of the Invention

[0005] An embodiment of the present application provides an experimental device for staged multi-cluster fracturing of horizontal wellbores. The experimental device does not require an additional injection string and has a simpler structure. Moreover, when in use, there is no need to consider the correspondence accuracy between the fracturing section of the staged injection string and the annular cutting groove, making operation simpler.

[0006] In a first aspect, an embodiment of the present application provides an experimental device for multi-cluster fracturing of segmented horizontal wellbores, comprising: a simulated wellbore for being arranged in a rock formation sample, wherein the interior of the simulated wellbore defines a plurality of fracturing spaces along the length direction; a plurality of perforating members, wherein the plurality of perforating members are arranged on the outside of the simulated wellbore and correspond one-to-one to the plurality of fracturing spaces, and each perforating member is formed with a plurality of perforating channels connected to the corresponding fracturing spaces; a plurality of connecting pipes, which are connected one-to-one to the plurality of fracturing spaces and extend to the outside of the simulated wellbore; the experimental device is configured to: introduce fracturing fluid into the fracturing space through the connecting pipes, so that the fracturing fluid flows through the perforating channels to the rock formation sample to perform a single fracturing on the rock formation sample; or introduce a temporary plugging agent and fracturing fluid into the fracturing space through the connecting pipes, so that the temporary plugging agent and fracturing fluid flow through the perforating channels to the rock formation sample to perform a temporary plugging and fracturing on the rock formation sample.

[0007] In one possible embodiment, each perforating element includes: multiple spacer rings, which are spaced apart along the length of the simulated wellbore, each spacer ring extending radially away from the simulated wellbore, and a perforating channel is formed between two adjacent spacer rings.

[0008] In a possible implementation, a fluid outlet is opened between two adjacent separation rings in the simulated wellbore, and the fluid outlet is used to connect the perforation channel and the fracturing space.

[0009] In a possible implementation, a ratio of a radial length of the separation ring protruding from the simulated wellbore to an outer diameter of the simulated wellbore is set to be greater than or equal to 0.15 and less than or equal to 0.25.

[0010] In a possible embodiment, among the multiple spacer rings in each perforating element, the spacer rings on both sides of the spacing direction are end spacer rings, and the spacer ring between the two end spacer rings is a middle spacer ring; the thickness of the end spacer rings is less than that of the middle spacer ring.

[0011] In one possible embodiment, the experimental device further includes: a plurality of connecting pipes, the plurality of connecting pipes corresponding one-to-one to the plurality of fracturing spaces, and each connecting pipe is arranged through a plurality of separation rings along the length direction of the simulated wellbore, and each connecting pipe has an open-ended structure at both ends; when the simulated wellbore is placed in the rock formation sample, the connecting pipe connects the annulus of the simulated wellbore between two adjacent perforating elements.

[0012] In a possible implementation, the outer surface of the simulated wellbore is configured to have an uneven structure.

[0013] In a possible implementation, the diameter of the connecting pipe is set to be greater than or equal to 5 mm and less than or equal to 8 mm.

[0014] In a possible embodiment, the experimental device further includes: a plurality of separators, which are arranged inside the simulated wellbore at intervals along the length direction, and two adjacent separators define a fracturing space.

[0015] In the second aspect, an embodiment of the present application provides an experimental method for segmented multi-cluster fracturing of a horizontal wellbore, which adopts any of the experimental devices mentioned above, and the experimental method includes: providing a rock sample and opening a horizontal wellbore in the rock sample; sealing and fixing a simulated wellbore in the horizontal wellbore; introducing fracturing fluid into the fracturing space through a connecting pipe to fracture the rock sample once; introducing a temporary plugging agent into the fracturing space through a connecting pipe, and introducing fracturing fluid to flush the temporary plugging agent into the cracks formed by the primary fracturing for temporary plugging, and after the temporary plugging is completed, using the fracturing fluid to form a temporary plugging fracturing.

[0016] The experimental device for staged multi-cluster fracturing of horizontal wellbores provided in the embodiment of the present application defines multiple fracturing spaces along the length direction inside the simulated wellbore, and multiple perforating members are arranged on the outside of the simulated wellbore and correspond one-to-one with the multiple fracturing spaces. Each perforating member is formed with multiple perforating channels connected to the corresponding fracturing spaces, and multiple connecting pipes are connected one-to-one with the multiple fracturing spaces and extend to the outside of the simulated wellbore. When in use, the connecting pipes are used to directly deliver fracturing fluid and temporary plugging agent to the fracturing space in the simulated wellbore, and the perforating members on the simulated wellbore are used to complete the primary fracturing and temporary plugging fracturing, and the installation of the connecting pipes and perforating members can be completed independently. Compared with the prior art, the experimental device of the embodiment of the present application does not require an additional injection string, and the structure is simpler. Moreover, when in use, there is no need to consider the correspondence accuracy between the fracturing section of the segmented injection string and the annular cutting groove, and the operation is simpler. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0018] Figure 1 This is a schematic diagram of the structure of an experimental device in one embodiment of the present application;

[0019] Figure 2 This is a schematic diagram of the use of the experimental device in one embodiment of this application Figure 1 ;

[0020] Figure 3 This is a schematic diagram of the use of the experimental device in one embodiment of this application Figure 2 ;

[0021] Figure 4 This is a schematic diagram of the use of the experimental device in one embodiment of this application Figure 3 ;

[0022] Figure 5 This is a schematic flow chart of the experimental method in one embodiment of the present application.

[0023] The above drawings illustrate specific embodiments of the present application, which will be described in more detail below. These drawings and the textual description are not intended to limit the scope of the present application in any way, but rather to illustrate the concepts of the present application to those skilled in the art by reference to specific embodiments. DETAILED DESCRIPTION

[0024] Staged multi-cluster fracturing in horizontal wells involves using packers to separate several horizontal sections along the horizontal well. Each horizontal section is a fracturing stage, and each fracturing stage contains multiple perforation clusters. Within a given fracturing stage, a surface high-pressure pump truck injects fluid at high speed, building up high pressure within the stage. This in turn triggers the initiation of fractures within the perforation clusters within the stage. Multiple perforation clusters initiate multiple fractures, which propel the fractures synchronously under the influence of the fracturing fluid. This process is applied sequentially to each fracturing stage to complete staged multi-cluster fracturing in horizontal wells.

[0025] Multi-cluster temporary plugging fracturing in horizontal wells involves injecting plugging material (temporary plugging powder, temporary plugging fiber, or temporary plugging balls) into a specific fracturing stage, thereby sealing a specific fracture or perforation hole. Field practice has shown that multi-cluster temporary plugging in horizontal wells generally fails to initiate fractures in all perforation clusters; that is, some perforation clusters initiate fractures, while others do not. To ensure that all perforation clusters initiate fractures, existing fractures and perforation clusters that have already initiated fractures are temporarily plugged. Fluid is then reinjected into the fracturing stage at high speed, and high pressure is re-established within that stage to force the uninitiated perforation clusters to initiate fractures. This process is applied sequentially to each fracturing stage to complete multi-cluster temporary plugging fracturing in horizontal wells.

[0026] Prior art has developed an experimental device for simulating multi-cluster fracturing in horizontal wellbores on the surface. The device comprises a casing, which is placed into the wellbore and filled with glue in the annulus. The casing is cut into the rock sample at multiple preset depths, forming multiple annular grooves to simulate perforation clusters. A segmented injection string is inserted into the casing. Multiple rubber seals are fitted on the outer surface of the string, dividing the wellbore into multiple fracturing segments. The outlet of each injection line is located between two annular grooves within each fracturing segment. By injecting fluid into each of the multiple injection lines, a simulation of multi-cluster fracturing in a horizontal wellbore is achieved. This experimental device is not only complex in structure, but also requires that the fracturing segments of the segmented injection string correspond strictly to the annular grooves. This requires precise groove depth, which is difficult to operate in actual experiments and can easily lead to the annular groove not being within the fracturing segment.

[0027] Based on this, the present application provides an experimental device for multi-cluster fracturing of horizontal wellbores. In the experimental device, multiple fracturing spaces are defined inside the simulated wellbore along the length direction. Multiple perforating members are arranged on the outside of the simulated wellbore and correspond one-to-one to the multiple fracturing spaces. Each perforating member is formed with multiple perforating channels connected to the corresponding fracturing spaces. Multiple connecting pipes are connected one-to-one to the multiple fracturing spaces and extend to the outside of the simulated wellbore. When in use, the connecting pipes are used to directly deliver fracturing fluid and temporary plugging agent to the fracturing space in the simulated wellbore, and the perforating members on the simulated wellbore are used to complete the primary fracturing and temporary plugging fracturing. The installation of the connecting pipes and the perforating members can be completed independently, the structure is simpler, and when in use, there is no need to consider the corresponding accuracy between the fracturing section of the segmented injection string and the annular cutting groove, and the operation is simpler.

[0028] See also Figure 1 , Figure 1 Schematic diagram of an experimental device in one embodiment of the present application. The present application provides an experimental device for staged multi-cluster fracturing of a horizontal wellbore, which may include a simulated wellbore 100, a plurality of perforating elements 200, and a plurality of connecting pipes 300.

[0029] A simulated wellbore 100 is disposed within a rock formation sample 10. Multiple fracture spaces 110 are defined along the length of the simulated wellbore 100. Perforating elements 200 are disposed outside the simulated wellbore 100, corresponding one-to-one with the fracture spaces 110. Each perforating element 200 is formed with multiple perforation channels 210 that communicate with a corresponding fracture space 110. Connecting pipes 300 are connected to the fracture spaces 110 in a one-to-one correspondence and extend to the exterior of the simulated wellbore 100.

[0030] The experimental device is configured as follows: fracturing fluid is introduced into the fracturing space 110 through the connecting pipe 300, so that the fracturing fluid flows through the perforation channel 210 to the rock formation sample 10, thereby fracturing the rock formation sample 10 once; or, a temporary plugging agent and fracturing fluid are introduced into the fracturing space 110 through the connecting pipe 300, so that the temporary plugging agent and fracturing fluid flow through the perforation channel 210 to the rock formation sample 10, thereby temporarily plugging and fracturing the fractures formed by the fracturing.

[0031] In this embodiment, a simulated wellbore 100 can be horizontally disposed within a horizontal wellbore 12 of a rock formation sample 10 to simulate a horizontal well. Steel casing can be used for the simulated wellbore 100. Multiple fracture spaces 110 are defined along the length of the simulated wellbore 100, simulating staged fracturing technology in horizontal wells. (Staged fracturing technology in horizontal wells involves using packers or bridge plugs to separate fracture stages, followed by stage-by-stage fracturing, creating multiple fractures within each stage.)

[0032] In this embodiment, outcrops (the exposed portions of rocks, mineral veins, and mineral deposits) can be processed into rock samples 10. Prior art also utilizes artificial cement samples for experiments. However, the physical properties of artificial cement (e.g., porosity, permeability, etc.) and rock mechanical properties (e.g., Young's modulus, compressive strength, etc.) differ significantly from those of real rock samples. Furthermore, it is difficult to accurately reproduce the structural weak planes of real rock samples, such as laminae, bedding, and natural fractures. The resulting experimental fracture morphology cannot represent the fracture morphology of reservoir fracturing. However, the physical properties, rock mechanical properties, and structural weak plane characteristics of outcrop samples are similar to those of reservoirs. Therefore, rock samples 10 processed from outcrops are closer to actual conditions, and experimental conclusions are more accurate and reliable.

[0033] When fabricating the experimental device of this embodiment, a steel casing is first selected as the simulated wellbore 100. Separators 140 are then used to separate multiple fracturing spaces 110 within the simulated wellbore 100. Multiple liquid outlets 120 are then opened at locations corresponding to each fracturing space 110 in the simulated wellbore 100. Finally, a perforating element 200 with multiple perforation channels 210 is welded to the exterior of the simulated wellbore 100, ensuring one-to-one communication between the multiple perforation channels 210 and the multiple liquid outlets 120. This completes the fabrication process.

[0034] See also Figure 2 , Figure 2 This is a schematic diagram of the use of the experimental device in one embodiment of this application Figure 1 To prepare for an experiment using this experimental device, a horizontal wellbore 12 is first machined into the rock sample 10. Specifically, the rock sample 10 can be processed into an outcrop (the portion of rock, mineral veins, or mineral deposits exposed above ground). The entire experimental device is then placed into the horizontal wellbore 12 and sealed securely. Finally, the connecting pipe 300 is connected to the pump, completing all preparatory work for the experiment.

[0035] See also Figure 3 , Figure 3 This is a schematic diagram of the use of the experimental device in one embodiment of this application Figure 2 , Figure 3 The line with a solid arrow represents the fracturing fluid, and A represents the fracture formed by a single fracturing operation. During the experiment, during a single fracturing operation, fracturing fluid was introduced into the fracturing space 110 via the connecting pipe 300. The fracturing fluid then passed through the fracturing space 110 and into one or more perforation channels 210. The fracturing fluid concentrated its energy within the narrow perforation channels 210. The fracturing fluid flowing through the perforation channels 210 rapidly formed stress concentration points in the rock formation sample 10 near the perforation channels 210, ultimately hydraulically fracturing the rock formation sample 10.

[0036] In some specific embodiments, a primary fracturing process is performed as follows: a fracturing fluid is injected into one of the fracturing spaces 110 through the connecting pipe 300 at a flow rate of 10 mL / min to 20 mL / min, so that the fracturing fluid fills the fracturing space 110, and a high pressure is generated in the fracturing space 110 to initiate a fracture, thereby achieving a primary fracturing of the fracturing segment corresponding to the fracturing space 110. The pump is stopped after 200 mL of fracturing fluid has been injected.

[0037] See also Figure 4 , Figure 4 This is a schematic diagram of the use of the experimental device in one embodiment of this application Figure 3 , Figure 4 The line with a solid arrow represents fracturing fluid, the solid circle represents a temporary plugging agent, A represents a fracture formed by a primary fracturing operation, and B represents a fracture formed by a temporary plugging operation. During the experiment, temporary plugging fracturing was performed by introducing a temporary plugging agent into the fracturing space 110 via the connecting pipe 300. The temporary plugging agent passed through the perforation passages 210, thereby temporarily plugging the fractures formed by the fracturing operation, allowing for further temporary plugging fracturing.

[0038] In some specific embodiments, the temporary plugging and fracturing process is carried out as follows: first, 200 / 300 mesh, 15 cm 3 Quartz sand is placed into the fracturing space 110 through the connecting pipe 300, ensuring sufficient quartz sand temporary plugging agent is present near the fracture opening to facilitate temporary plugging of the fracture opening. Then, a quartz sand-containing fracturing fluid with a viscosity of 200 mPa·s and a sand concentration of 60 g / 100 mL is pumped in at a rate of 20 mL / min. The viscous resistance of the highly viscous fluid is used to carry the quartz sand into the fractures, thereby temporarily plugging the fractures. As the fracturing fluid is continuously injected, the temporary plugging agent gradually blocks the fractures and the fracture openings. The amount of fracturing fluid flowing into the previously fractured fracture begins to decrease, causing the fracturing space 110 to build up high pressure again, thereby initiating new fractures and achieving temporary plugging fracturing.

[0039] It should be noted that quartz sand can be used as a temporary plugging agent for simulation experiments. When conducting fracturing operations on site, it is necessary to select appropriate on-site temporary plugging agents based on actual conditions, such as acid-soluble temporary plugging agents, oil-soluble temporary plugging agents, water-soluble temporary plugging agents, one-way pressure temporary plugging agents, etc.

[0040] As can be seen, the experimental device of the embodiment of the present application utilizes the connecting pipe 300 to directly deliver fracturing fluid and temporary plugging agent to the fracturing space 110 within the simulated wellbore 100, and utilizes the perforating element 200 on the simulated wellbore 100 to complete both primary fracturing and temporary plugging fracturing. The installation of the connecting pipe 300 and the perforating element 200 can be completed independently. Compared to the prior art, the experimental device of the embodiment of the present application does not require an additional injection string, resulting in a simpler structure. Furthermore, during use, there is no need to consider the alignment accuracy between the fracturing segments of the segmented injection string and the annular cut grooves, making operation much simpler.

[0041] In some embodiments, each perforating element 200 includes a plurality of separator rings 220 , which are spaced apart along the length of the simulated wellbore 100 . Each separator ring 220 extends radially away from the simulated wellbore 100 , and a perforating channel 210 is formed between two adjacent separator rings 220 .

[0042] In this embodiment, the spacer rings 220 can be made of high-strength steel. Each spacer ring 220 is sleeved onto the outside of the simulated wellbore 100 and fixedly connected to the outer wall of the simulated wellbore 100 by welding. The narrow passage formed between two adjacent spacer rings 220 serves as the perforation passage 210. This type of perforating element 200 offers a simple, robust structure and high reliability.

[0043] In some specific embodiments, the distance between two adjacent spacer rings 220 may be set to between 2 mm and 5 mm, such as 2 mm, 3 mm, 4 mm, 5 mm, etc. This facilitates simulation of primary fracturing and temporary plugging fracturing under different perforation cluster spacings.

[0044] In some specific embodiments, the radial heights of the plurality of perforating elements 200 are consistent, that is, the radial heights of the separation rings 220 of the plurality of perforating elements 200 are consistent, so as to reduce experimental errors.

[0045] In some specific embodiments, the radial height of each separator ring 220 can be set to be between 5 mm and 10 mm, for example, 5 mm, 6 mm, 7.5 mm, 8 mm, 10 mm, etc. Setting the radial height of the separator ring 220 within the above range ensures that the height of the perforation channel 210 is not too small, so that the fracturing fluid can achieve energy concentration in the perforation channel 210, while also preventing the separator ring 220 from protruding too much from the simulated wellbore 100, thereby reducing the difficulty of sealing the simulated wellbore 100.

[0046] In some embodiments, the outer diameter of the separator ring 220 can also be set according to the length of the simulated wellbore 100. As the length of the simulated wellbore 100 increases, the outer diameter of the separator ring 220 also increases, and the separator ring 220 protrudes more from the simulated wellbore 100. When the simulated wellbore 100 is embedded in the horizontal wellbore 12 of the rock formation sample 10, the larger the annulus between the simulated wellbore 100 and the horizontal wellbore 12, the thicker the sealant can be injected to secure the simulated wellbore 100.

[0047] Furthermore, the ratio of the radial length of the separator ring 220 protruding from the simulated wellbore 100 to the outer diameter of the simulated wellbore 100 is set to be greater than or equal to 0.15 and less than or equal to 0.25, for example, 0.15, 0.2, 0.25, etc. In some specific embodiments, the outer diameter of the simulated wellbore 100 is 35 mm, the radial length of the separator ring 220 protruding from the simulated wellbore 100 is 7.5 mm, and the outer diameter of the separator ring 220 is 50 mm.

[0048] In some embodiments, the simulated wellbore 100 further has a liquid outlet 120 between two adjacent separation rings 220 . The liquid outlet 120 is used to connect the perforation channel 210 with the fracturing space 110 .

[0049] For the same fracturing space 110 , the directions of the liquid outlets 120 thereon can be set according to actual conditions. For example, multiple liquid outlets 120 on the same fracturing space 110 can be set to be the same and can be arranged at any angle.

[0050] In some embodiments, among the multiple spacer rings 220 in each perforating element 200, the spacer rings 220 on both sides of the spacer rings 222 are end spacer rings 222, and the spacer ring 220 between the two end spacer rings 222 is a middle spacer ring 224. The thickness of the end spacer rings 222 is less than the thickness of the middle spacer ring 224.

[0051] As can be seen from the above, when using this experimental device, high-pressure fracturing fluid needs to flow through the perforation channel 210, which places certain demands on the fixing strength of the spacer ring 220. For the end spacer ring 222, after being fixed to the simulated wellbore 100, it can also be secondary fixed with the sealant 14 on one side. Therefore, the end spacer ring 222 has a good fixing effect, and the thickness of the end spacer ring 222 can be appropriately reduced to save material. For the middle spacer ring 224, it is only fixed to the simulated wellbore 100 and has no secondary fixing. Therefore, the thickness of the middle spacer ring 224 should be appropriately increased, and the contact area between the middle spacer ring 224 and the simulated wellbore 100 should be increased to ensure the fixing effect of the middle spacer ring 224.

[0052] Therefore, the thickness of the end separation ring 222 is set to be smaller than the thickness of the middle separation ring 224 , which not only ensures the fixing effect of the separation ring 220 but also saves materials.

[0053] In some specific embodiments, the thickness of the end separation ring 222 can be set to between 1.5 mm and 3 mm, such as 1.5 mm, 2 mm, 3 mm, etc. The thickness of the middle separation ring 224 can be set to between 4 mm and 6 mm, such as 4 mm, 5 mm, 6 mm, etc.

[0054] In some embodiments, the experimental device may also include multiple connecting pipes 400, each of which corresponds one-to-one to the multiple fracturing spaces 110, and each connecting pipe 400 is arranged in the multiple separation rings 220 along the length direction of the simulated wellbore 100, and each connecting pipe 400 has an open-end structure, so that when the simulated wellbore 100 is placed in the rock formation sample 10, the connecting pipe 400 connects to the annulus between two adjacent perforating elements 200.

[0055] When the simulated wellbore 100 is placed and secured in the horizontal wellbore 12, a sealant 14 (e.g., epoxy resin) is used to seal the annulus between two adjacent perforating elements 200 of the simulated wellbore 100. However, because multiple spacer rings 220 protrude from the outer periphery of the simulated wellbore 100, the spacer rings 220 block the flow of the sealant 14 along the annulus. This hinders the sealant 14 from flowing sufficiently along the length of the simulated wellbore 100, thereby hindering the formation of a uniform sealing layer and failing to ensure a secure seal.

[0056] In this embodiment, each connecting tube 400 is provided along the length of the simulated wellbore 100 through the multiple separation rings 220 of each perforating element 200 and is open at both ends. That is, the connecting tube 400 is used to guide the sealant liquid 14 on one side of the perforating element 200 to the other side. In this way, the sealant liquid 14 can fully flow between two adjacent perforating elements 200 in the simulated wellbore 100, effectively isolating the fracturing section (the section with the perforating element 200) and the non-fracturing section (the section without the perforating element 200), so that the fracturing fluid will not flow into the non-fracturing section, thereby ensuring the reliability of the experiment.

[0057] In some specific embodiments, the inner diameter of the connecting tube 400 may be set to between 2 mm and 4 mm, and the length of the connecting tube 400 may be set according to the thickness of the perforating element 200 to ensure that the connecting tube 400 completely passes through the perforating element 200 .

[0058] In some embodiments, the outer surface of the simulated wellbore 100 is configured to have an uneven structure to increase the sealing strength when sealing the annulus between the simulated wellbore 100 and the rock sample 10 .

[0059] Specifically, the outer surface of the simulated wellbore 100 is roughened by processing densely distributed grooves 130 with a width of 4 mm and a depth of 1 mm, thereby increasing the bonding strength between the outer surface of the wellbore and the well wall.

[0060] In some embodiments, the diameter of the connecting pipe 300 is set to be greater than or equal to 5 mm and less than or equal to 8 mm, for example, 5 mm, 6 mm, 8 mm, etc. The diameter of the connecting pipe 300 within the above range is larger than the diameter of the injection channel of the existing design, so that the temporary plugging agent can be injected without clogging the pipeline.

[0061] In some embodiments, the experimental device may further include a plurality of separators 140 . The plurality of separators 140 are disposed inside the simulated wellbore 100 at intervals along the length direction, and two adjacent separators 140 define a fracturing space 110 .

[0062] The separators 140 may be welded inside the simulated wellbore 100 , and two adjacent separators 140 and the inner wall of the simulated wellbore 100 form a fracturing space 110 .

[0063] The following describes the working principle of the experimental device of this application based on a specific experimental process:

[0064] 1. Make an experimental device.

[0065] Step 1: Select a casing with a length of 360 mm, an outer diameter of 35 mm, and an inner diameter of 25 mm as the simulated wellbore 100. The outer surface of the simulated wellbore 100 is processed with densely distributed grooves 130 with a width of 4 mm and a depth of 1 mm to perform roughening treatment, thereby increasing the bonding strength between the outer surface of the wellbore and the well wall.

[0066] Step 2: Weld three sets of separators 140 inside the simulated wellbore 100 . The area between two separators 140 is the fracturing space 110 , and the area outside the two separators 140 is the non-fracturing space. The three sets of separators 140 form three fracturing spaces 110 .

[0067] Step 3: Multiple holes were drilled in each corresponding fracture space 110 of the simulated wellbore 100 to form multiple liquid outlets 120. Three perforating elements 200 were welded and installed in each corresponding fracture space 110. The multiple perforation channels 210 on each perforating element 200 corresponded one-to-one with the multiple liquid outlets 120. The outer diameter of the separator rings 220 of each perforating element 200 was 50 mm, the thickness of the end separator rings 222 was 2 mm, and the thickness of the middle separator ring 224 was 5 mm.

[0068] Step 4: Drill holes in the multiple separation rings 220 of each perforating element 200, insert and fix the connecting pipe 400.

[0069] 2. Experimental process:

[0070] Step 5: Process the natural outcrop into a rock sample 10 of 400 mm×400 mm×400 mm, and drill a horizontal wellbore 12 with an inner diameter of 51 mm and a depth of 360 mm in the center of the rock sample 10.

[0071] Step 6: Tightly wrap the raw tape in the perforation channel 210 of each perforating element 200 until the perforation channel 210 is completely filled. This is to prevent the sealant 14 from seeping into the fracturing space 110 and clogging the fracturing space 110 .

[0072] Step 7: Pour 10 mL of epoxy resin glue into the horizontal wellbore 12, insert the experimental device into the horizontal wellbore 12, and the sealing glue 14 gradually returns to the annulus between the simulated wellbore 100 and the well wall through the connecting pipe 400, filling the annulus between the simulated wellbore 100 and the well wall. The sealing glue 14 finally returns to near the wellhead. For the annulus near the wellhead that has not been filled with the sealing glue 14, a small amount of sealing glue 14 is dripped from the wellhead to complete the filling of the remaining part. This process is similar to the on-site cementing process, which aims to tightly adhere the simulated wellbore 100 to the well wall, complete the effective isolation between the fracturing sections, and prevent the fluid from flowing along the outer wall of the wellbore during the fracturing experiment.

[0073] Step 8: Connect the corresponding connecting pipe 300 to a pump for one of the fracturing spaces 110. Inject fracturing fluid into the fracturing space 110 through the connecting pipe 300 at a rate of 10 to 20 mL / min. The fracturing fluid fills the fracturing space 110 and generates high pressure within the fracturing space 110, initiating fractures and achieving a primary fracturing of the corresponding fracturing segment of the fracturing space 110. Stop the pump after 200 mL of fracturing fluid has been injected.

[0074] Step 9, 200 / 300 mesh, 15cm 3 Quartz sand is placed in the fracturing space 110 to ensure sufficient temporary plugging agent near the fracture opening, facilitating temporary plugging. Then, a fracturing fluid containing quartz sand, with a viscosity of 200 mPa·s and a sand concentration of 60 g / 100 mL, is pumped in at a rate of 20 mL / min. The viscous resistance of the highly viscous fluid carries the quartz sand from the fracturing section into the fracture, facilitating temporary plugging within the fracture. As the temporary plugging agent is continuously injected, it gradually blocks the fracture interior and the fracture opening. The amount of temporary plugging agent flowing into the previously fractured fracture decreases, allowing the fracturing space 110 to build up high pressure again, thereby initiating new fractures and achieving temporary plugging.

[0075] Step 10: Repeat steps 8 and 9 for the remaining two fracturing spaces 110 .

[0076] See also Figure 5 , Figure 5 This is a schematic flow chart of an experimental method in one embodiment of the present application. In addition, the present application also provides an experimental method for staged multi-cluster fracturing of horizontal wells, which can use the experimental device in any of the above embodiments and can be implemented by the following steps:

[0077] Step S510 : providing a rock sample 10 , and opening a horizontal wellbore 12 in the rock sample 10 .

[0078] Step S520 : sealing and fixing the simulated wellbore 100 in the horizontal wellbore 12 .

[0079] Step S530 , fracturing fluid is introduced into the fracturing space 110 through the connecting pipe 300 , so that the fracturing fluid is ejected toward the rock sample 10 through the perforation channel 210 , thereby fracturing the rock sample 10 once.

[0080] Step S540: A temporary plugging agent is introduced into the fracturing space 110 through the connecting pipe 300, and a fracturing fluid is introduced to flush the temporary plugging agent into the cracks formed by the primary fracturing to perform temporary plugging. After the temporary plugging is completed, the fracturing fluid is used to temporarily plug and fracture the rock sample 10.

[0081] Step S520 may further include: pouring sealant into the horizontal wellbore 12; placing the simulated wellbore 100 in the horizontal wellbore 12, allowing the sealant to fill the annulus between two adjacent perforating elements 200 of the simulated wellbore 100 through the connecting pipe 400 to fix the simulated wellbore 100.

[0082] The fracturing process of step S530 and step S540 can be referred to the above description and will not be described in detail here.

[0083] In steps S530 and S540, dye tracers with different colors can be added to the fracturing fluid. This allows for the color-coded identification of the primary and temporary fracturing processes and hydraulic fracture morphology after fracturing. The diversion characteristics of the primary and temporary fracturing fractures can also be analyzed, along with the pump pressure curves for the primary and temporary fracturing fractures. This ultimately supports the design of process parameters for fracturing wells in shale reservoirs.

[0084] Finally, it should be noted that those skilled in the art will readily identify other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. The present invention is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art not disclosed herein. The present invention is not limited to the precise structure described above and illustrated in the accompanying drawings, and various modifications and variations may be made without departing from the scope thereof. The scope of the present invention is limited solely by the appended claims.

Claims

1. An experimental device for staged multi-cluster fracturing of horizontal wells, characterized in that: include: A simulated wellbore (100) is used to be arranged in a rock formation sample (10), wherein a plurality of fracture spaces (110) are defined inside the simulated wellbore (100) along a length direction; a plurality of perforating elements (200), the plurality of perforating elements (200) being arranged outside the simulated wellbore (100) and corresponding one-to-one to the plurality of fracturing spaces (110), and each of the perforating elements (200) being formed with a plurality of perforating channels (210) communicating with the corresponding fracturing space (110); a plurality of connecting pipes (300), connected to the plurality of fracturing spaces (110) in a one-to-one correspondence and extending to the outside of the simulated wellbore (100); The experimental device is configured as follows: A fracturing fluid is introduced into the fracturing space (110) through the connecting pipe (300), so that the fracturing fluid flows toward the rock formation sample (10) through the perforation channel (210), thereby performing a primary fracturing on the rock formation sample (10); or, A temporary plugging agent and a fracturing fluid are introduced into the fracturing space (110) through the connecting pipe (300), so that the temporary plugging agent and the fracturing fluid flow toward the rock formation sample (10) through the perforation channel (210), thereby temporarily plugging and fracturing the rock formation sample (10); Each of the perforating elements (200) comprises: a plurality of spacer rings (220), the plurality of spacer rings (220) being spaced apart along the length direction of the simulated wellbore (100), each spacer ring (220) extending in a radial direction of the simulated wellbore (100) away from the simulated wellbore (100), and the perforation channel (210) being formed between two adjacent spacer rings (220); Among the plurality of separation rings (220) in each perforating element (200), the separation rings (220) located on both sides of the spacing direction are end separation rings (222), and the separation ring (220) located between the two end separation rings (222) is an intermediate separation ring (224); the separation rings (220) of the plurality of perforating elements (200) have the same radial height; the thickness of the end separation rings (222) is smaller than the thickness of the intermediate separation ring (224); The invention also includes: a plurality of connecting pipes (400), wherein the plurality of connecting pipes (400) correspond to the plurality of fracturing spaces (110) on a one-to-one basis; each connecting pipe (400) is provided through the plurality of separating rings (220) along the length direction of the simulated wellbore (100), and each connecting pipe (400) has an open structure at both ends; When the simulated wellbore (100) is placed in the rock formation sample (10), the connecting pipe (400) connects the annulus between two adjacent perforating elements (200) of the simulated wellbore (100).

2. The experimental device according to claim 1, characterized in that The simulated wellbore (100) is provided with a liquid outlet (120) between two adjacent separation rings (220), and the liquid outlet (120) is used to connect the perforation channel (210) and the fracturing space (110).

3. The experimental device according to claim 1, characterized in that The ratio of the radial length of the separation ring (220) protruding from the simulated wellbore (100) to the outer diameter of the simulated wellbore (100) is set to be greater than or equal to 0.15 and less than or equal to 0.

25.

4. The experimental device according to any one of claims 1 to 3, characterized in that include: The outer surface of the simulated wellbore (100) is configured as a concave-convex structure.

5. The experimental device according to any one of claims 1 to 3, characterized in that: The diameter of the connecting pipe (300) is set to be greater than or equal to 5 mm and less than or equal to 8 mm.

6. The experimental device according to any one of claims 1 to 3, characterized in that: Also includes: A plurality of separators (140) are provided inside the simulated wellbore (100) at intervals along the length direction, and two adjacent separators (140) define one fracturing space (110).

7. An experimental method for staged multi-cluster fracturing of a horizontal wellbore, the experimental method using the experimental device according to any one of claims 1 to 6, characterized in that: The experimental method includes: Providing a rock formation sample and drilling a horizontal wellbore in the rock formation sample; sealing and fixing the simulated wellbore in the horizontal wellbore; introducing fracturing fluid into the fracturing space through a connecting pipe to perform a primary fracturing on the rock formation sample; A temporary plugging agent is introduced into the fracturing space through the connecting pipe, and the fracturing fluid is introduced to flush the temporary plugging agent into the cracks formed by the primary fracturing to perform temporary plugging. After the temporary plugging is completed, the fracturing fluid is used to form a temporary plugging fracturing.

Images