Simulation device, test system and test method for fracturing process of tight reservoir

Abstract

The embodiment of the invention provides a simulation device, a test system and a test method for the fracturing process of a tight reservoir, and belongs to the field of oil and gas field reservoir fracturing. The simulation device comprises a shell used for containing injected confining pressure liquid; the shaft is located in the shell and used for containing injected fracturing fluid, and a perforation hole is formed in the side face of the shaft and communicates with the interior of the shaft; the branch-shaped hollow pipe is located in the shell, a pipe opening of the branch-shaped hollow pipe is communicated with the interior of the shaft through the perforation, the branch-shaped hollow pipe is made of an elastic piece, a plurality of cracks are formed in the branch-shaped hollow pipe, under the condition that air in the branch-shaped hollow pipe is exhausted, the cracks are in a closed state, and the shell and the shaft are made of transparent materials. The method is easy to operate, the tight reservoir fracturing process can be directly and visually simulated, and the crack initiation mechanism, the propping agent migration rule and the temporary plugging effect of the temporary plugging agent in the fracturing process can be represented.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas reservoir fracturing, in particular to a simulation device, a test system and a test method for the fracturing process of a tight reservoir. BACKGROUND

[0002] With the decrease of conventional oil and gas resources, the proportion of unconventional tight oil and gas reservoirs in the energy field gradually increases. However, such oil and gas reservoirs are extremely tight, the fluid seepage capacity is weak, and the development effect is poor, so volume fracturing means is often used to improve the fluid seepage space. However, the fracturing process is very complex and difficult to control, especially the fracture initiation mechanism and the proppant migration law have strong uncertainty, which leads to extremely high difficulty in formulating fracturing construction technology.

[0003] The existing research technology mainly simulates the fracture expansion and proppant migration process before and after fracturing through physical experiment, and explores the fracture formation mechanism by combining numerical simulation means after obtaining the basic parameters. However, the existing research physical simulation experiment means can only represent the fracture expansion and proppant migration law before and after fracturing, and cannot understand how the fracture is opened and how the proppant is migrated in the dynamic fracturing process, and the temporary plugging effect of the temporary plugging agent is unclear.

[0004] Therefore, it is necessary to provide an efficient and intuitive visual device, a measurement system and a measurement method for simulating the fracturing process of a tight reservoir. SUMMARY

[0005] The purpose of the embodiments of the present application is to provide a simulation device, a test system and a test method for the fracturing process of a tight reservoir, which can solve the problem that the fracture initiation mechanism, the proppant migration law and the temporary plugging effect in the dynamic fracturing process cannot be understood in the prior art.

[0006] In order to achieve the above-mentioned purpose, the simulation device for the fracturing process of a tight reservoir comprises: a shell for accommodating an injected confining pressure liquid; a wellbore located in the shell for accommodating an injected fracturing liquid, the side surface of the wellbore is provided with a perforation, and the perforation is communicated with the inside of the wellbore; and a branched hollow pipe located in the shell, the pipe opening of the branched hollow pipe is communicated with the inside of the wellbore through the perforation, wherein the branched hollow pipe is made of an elastic member and has a plurality of fractures inside, and the plurality of fractures are in a closed state under the condition that the air inside the branched hollow pipe is exhausted, wherein the shell and the wellbore are made of a transparent material.

[0007] Optionally, the simulation device comprises a distributed optical fiber, and the distributed optical fiber is distributed in the plurality of fractures, wherein each fracture in the plurality of fractures has a set size, a set length and a set tortuosity.

[0008] Optionally, the simulation device further comprises an inlet end pressure-bearing panel and an outlet end pressure-bearing panel, the fracturing fluid and the confining fluid are injected through the inlet end pressure-bearing panel, and the outlet end pressure-bearing panel provides back pressure to the outlet conduit of the wellbore, wherein the distributed optical fiber is connected to an optical fiber demodulator via the inlet end pressure-bearing panel.

[0009] Optionally, the side of the wellbore is provided with a plurality of perforations, each of the plurality of perforations is connected to a branch hollow tube, wherein the perforation comprises a hollow inner tube, and the outer diameter of the middle part of the perforation is smaller than the outer diameter of the two ends.

[0010] Optionally, the transparent material is tempered glass, the wall thickness of the shell is greater than 3 cm, and the wall thickness of the wellbore is greater than 2 cm.

[0011] Optionally, the fracturing fluid comprises proppants and temporary plugging agents, and the proppants and the temporary plugging agents have different colors.

[0012] Optionally, the proppants comprise a first proportion of quartz sand and a second proportion of ceramsite, the concentration of the proppants is 0.3-0.5 kg / L, the particle size of the temporary plugging agents is 40 / 60 mesh, and the concentration of the temporary plugging agents is 0.05-0.1 kg / L.

[0013] In another aspect, the present application also provides a test system for a fracturing process of a tight reservoir, the test system comprising: a simulation device for a fracturing process of a tight reservoir according to the above; a first injection unit for injecting confining fluid into the shell of the simulation device at a first injection pressure; a second injection unit for injecting fracturing fluid into the wellbore of the simulation device at a second injection pressure; a back pressure unit for providing back pressure to the outlet conduit of the wellbore; and a pressure acquisition system for monitoring the first injection pressure, the second injection pressure, and the back pressure.

[0014] In another aspect, the present application also provides a test method for a fracturing process of a tight reservoir, the test method comprising: discharging the internal air of the branch hollow tube to make the plurality of cracks in the branch hollow tube in a closed state; connecting the nozzle of the branch hollow tube to the inside of the wellbore through perforation, and placing the wellbore in a shell, wherein the shell and the wellbore are of a transparent material; injecting confining fluid into the shell and injecting fracturing fluid into the wellbore to make the fracturing fluid enter and prop open the plurality of cracks; and acquiring strain data of the plurality of cracks through a distributed optical fiber distributed in the plurality of cracks.

[0015] Optionally, the injecting the confining pressure fluid into the casing and the fracturing fluid into the wellbore comprises: injecting the confining pressure fluid into the casing at a first injection pressure until the casing is filled; injecting the fracturing fluid into the wellbore at a second injection pressure until the wellbore has a fracturing fluid flowing out of a liquid outlet pipe, wherein the second injection pressure is less than the first injection pressure; synchronously increasing the first injection pressure and the second injection pressure until the first injection pressure reaches a first set value; and continuously increasing the second injection pressure until the second injection pressure reaches a second set value, wherein the second set value is greater than the first set value.

[0016] By means of the technical scheme, the simulation device, the test system and the test method of the fracturing process of the tight reservoir are provided, which are used for intuitively characterizing the crack initiation mechanism, the proppant migration rule and the temporary plugging effect of the temporary plugging agent.

[0017] Other features and advantages of the embodiments of the present application will be described in detail in the following specific implementation part. BRIEF DESCRIPTION OF DRAWINGS

[0018] The accompanying drawings are included to provide a further understanding of the embodiments of the present application, and constitute a part of the specification, and are used together with the following specific implementation to explain the embodiments of the present application, but do not constitute a limitation on the embodiments of the present application. In the drawings:

[0019] Figure 1 A structure schematic diagram of the simulation device of the fracturing process of the tight reservoir provided by the embodiments of the present application is shown in the figure;

[0020] Figure 2 A structure schematic diagram of the casing provided by the embodiments of the present application is shown in the figure;

[0021] Figure 3 A structure schematic diagram of the horizontal wellbore provided by the embodiments of the present application is shown in the figure;

[0022] Figure 4 A structure sectional view of the perforation provided by the embodiments of the present application is shown in the figure;

[0023] Figure 5 A structure schematic diagram of the artificial fracture provided by the embodiments of the present application is shown in the figure;

[0024] Figure 6 A structure schematic diagram of the two sides of the liquid outlet, the liquid inlet end pressure bearing panel provided by the embodiments of the present application is shown in the figure;

[0025] Figure 7A connection mode schematic diagram of a pressure-bearing panel and a shell and a horizontal wellbore provided by an embodiment of the present application;

[0026] Figure 8 A structure schematic diagram of a pressurizing rod provided by an embodiment of the present application;

[0027] Figure 9 A structure schematic diagram of a test system of a fracturing process of a tight reservoir provided by an embodiment of the present application;

[0028] Figure 10 A flowchart of a test method of a fracturing process of a tight reservoir provided by an embodiment of the present application;

[0029] Figures 11a-11c A schematic diagram of an experimental result of a simulated triaxial experiment provided by an embodiment of the present application. DETAILED DESCRIPTION

[0030] The specific embodiments of the embodiments of the present application are described in detail below with reference to the accompanying drawings, and the typical implementation manners of the present application are introduced, so that those skilled in the art can more clearly understand the scheme of the present disclosure. It should be pointed out that, some or some of the structures of the different implementation manners introduced below can be replaced with each other, and the implementation manners of the present disclosure are not limited to the examples described below. It should be understood that, under the above concept, those skilled in the art can also obtain other possible implementation manners according to the examples below, and these manners should also be considered as the content of the present disclosure. The specific embodiments described herein are only used to illustrate and explain the embodiments of the present application, and are not used to limit the embodiments of the present application.

[0031] In addition, when the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementation manners described in the following exemplary embodiments do not represent all the implementation manners consistent with the present disclosure. Instead, they are only examples of devices and methods consistent with some aspects of the present disclosure as detailed in the appended claims.

[0032] Firstly, the present application provides a simulation device 100 of a fracturing process of a tight reservoir, as shown in the figure, Figure 1 The simulation device 100 can include a shell 10, a wellbore 20 and a dendritic hollow tube 30. In a possible implementation manner, the wellbore 20 and the dendritic hollow tube 30 are both located in the shell 10, and the dendritic hollow tube 30 is in communication with the inside of the wellbore 20.

[0033] The shell 10 is used to accommodate the injected confining pressure liquid. The wellbore 20, for example, is a horizontal wellbore, used to accommodate the injected fracturing liquid. In order to better visualize the observation of the fracturing process, the shell 10 and the wellbore 20 are both made of transparent material, for example, tempered glass. In an embodiment, as shown in the figure,Figure 2 As shown, the shell 10 is a large-diameter super-thick tempered glass cylinder, and the wellbore 20 is a small-diameter super-thick tempered glass cylinder. The wall thickness of the shell 10 can be greater than 3 cm, and the wall thickness of the wellbore 20 can be greater than 2 cm.

[0034] In an embodiment, the fracturing fluid can include proppants and temporary plugging agents, and the alternating injection of the proppants and the temporary plugging agents can be achieved. In order to better distinguish the different injected fluids, the proppants and the temporary plugging agents have different colors. In an embodiment, the proppants can include a first proportion of quartz sand (for example, 80 / 100 mesh in particle size) and a second proportion of ceramsite (for example, 60 / 80 mesh in particle size), and the concentration thereof can be between 0.3-0.5 kg / L. The sum of the first proportion and the second proportion is 1, and the first proportion should be greater than the second proportion, for example, the first proportion can be 60-80%, and the corresponding second proportion is 40-20%. Preferably, the first proportion is 70%, and the second proportion is 30%. In addition, the particle size of the temporary plugging agent of the proppants is 40 / 60 mesh, and the concentration thereof can be between 0.05-0.1 kg / L.

[0035] At the same time, the side surface of the wellbore 20 is provided with a perforation, and the perforation is in communication with the inside of the wellbore 20 in a through connection manner, and the nozzle of the dendritic hollow tube 30 can be connected with the inside of the wellbore 20 through the perforation. In order to better simulate the effect, the nozzle of the dendritic hollow tube 30 needs to be sealingly connected with the perforation. In an embodiment, as shown in Figure 3 The side surface of the wellbore 20 can be provided with a plurality of perforations 21, for example, not less than three perforations. Each of the plurality of perforations 21 is connected with a dendritic hollow tube 30. The perforation 21 can include a hollow inner cylinder, and the outer diameter of the middle part of the perforation 21 is smaller than the outer diameter of the two ends. That is, a recess can be formed in the middle part of the perforation 21, which facilitates the sealing connection with the dendritic hollow tube 30. In an embodiment, as shown in Figure 4 The perforation 21 can be composed of cylinders and conical cylinders of different sizes, and is connected with the side surface of the wellbore 20 in a through connection manner. In a possible implementation manner, the dendritic hollow tube 30 is connected with the perforation 21 of the side surface of the wellbore 20 through strong glue, and an iron wire is used to strengthen the connection degree in the recess of the perforation 21.

[0036] As shown in Figure 5As shown, the dendritic hollow tube 30 can be made of elastic material, such as epoxy resin, and has multiple cracks inside. The dendritic hollow tube 30, also called artificial cracks, is a "tree-like" hollow tube of different sizes, lengths and tortuosity made of high-strength epoxy resin. In the case of air discharge inside the dendritic hollow tube 30, the multiple cracks are in a closed state. It should be noted that a small amount of phenolic resin glue is added to the "tree-like" artificial cracks of different sizes, lengths and tortuosity made of high-strength epoxy resin before the experiment, and the gas in the artificial cracks is discharged by extrusion and the artificial cracks are always kept in a closed state. During the experiment, when the back pressure value is greater than the confining pressure value, the artificial cracks can be opened to provide flow space for fracturing fluid and proppant.

[0037] In an embodiment, the simulation device 100 can also include a distributed optical fiber which can be distributed along the dendritic hollow tube 30 in the multiple cracks of the tortuous dendritic hollow tube 30, and the distributed optical fiber can be fixed along the multiple cracks by using strong glue. Each of the multiple cracks has a set size, a set length and a set tortuosity. This embodiment can simulate the compact reservoir by setting the distributed optical fiber in the multiple cracks, and can use the distributed optical fiber technology to simulate the crack initiation mechanism, proppant migration rule and temporary plugging effect of the temporary plugging agent in the fracturing process.

[0038] In order to better fix the simulation device, in an embodiment, the simulation device 100 can also include a liquid inlet end pressure bearing panel and a liquid outlet end pressure bearing panel. As shown, Figure 6 As shown, the liquid outlet end pressure bearing panel has threaded through holes at four right angles, a through half-depth threaded hole at one side of the center, and two concentric annular grooves of different diameters at the other side. The annular groove of the smaller diameter has a protruding structure, and two annular grooves can be provided on the protruding structure for placing a sealing ring to further enhance the sealing degree of the horizontal wellbore. It should be noted that the outer diameter of the protruding structure of the concentric annular groove of the smaller diameter is consistent with the inner diameter of the horizontal wellbore, so that the protruding structure can be embedded in the horizontal wellbore, and the protruding structure is provided with two annular grooves for placing the annular sealing ring to enhance the sealing degree of the horizontal wellbore. Therefore, under the condition of sufficient sealing, the liquid outlet pipeline of the wellbore can be provided with back pressure by the liquid outlet end pressure bearing panel. The liquid inlet end pressure bearing panel is the same as the liquid outlet end pressure bearing panel, but has two through threaded holes in the two concentric annular grooves of different diameters, and the liquid inlet end pressure bearing panel can be used to inject fracturing fluid and confining pressure fluid. In particular, the distributed optical fiber can be connected to the external OFDR optical fiber demodulator through the liquid inlet end pressure bearing panel. That is, in the case of setting the distributed optical fiber along the tortuous artificial cracks by using strong glue, the distributed optical fiber is connected to the OFRD optical fiber demodulator through the through holes between the two concentric annular grooves of different diameters of the liquid inlet end pressure bearing panel after the distributed optical fiber is converged.

[0039] In a possible implementation form, as shown in Figure 7 The diameter of the half-depth threaded hole on one side of the pressure-bearing panel is consistent with the diameter of the liquid outlet pipe and the liquid inlet pipe, and is connected by screw rotation. Meanwhile, the concentric annular grooves with different diameters on one side of the pressure-bearing panel are consistent with the diameter of the casing and the horizontal wellbore, and can be connected by a sealing rubber ring and / or strong glue. That is, the two concentric annular grooves with different diameters of the liquid outlet end pressure-bearing panel and the liquid inlet end pressure-bearing panel are connected to the casing and the horizontal wellbore by a sealing rubber ring and strong glue, respectively, and the protrusion in the small-diameter annular groove can be embedded into the horizontal wellbore, so as to better realize overall sealing. In a possible implementation form, the two symmetric through-threaded holes in the middle of the two concentric annular grooves with different diameters of the liquid inlet end pressure-bearing panel also have a rubber ring sealing structure, and are connected to the confining pressure liquid injection port and the OFDR optical fiber strain demodulator, so as to further enhance the sealing degree of the horizontal wellbore.

[0040] In addition, in order to better fix the simulation device, the simulation device 100 can further include a pressurizing rod. As shown in Figure 8 The pressurizing rod has threads at both ends, and the liquid outlet end pressure-bearing panel and the liquid inlet end pressure-bearing panel can be connected by a nut, so as to better fix the simulation device and avoid deformation or disengagement of the liquid outlet end pressure-bearing panel and the liquid inlet end pressure-bearing panel due to excessive pressure of the injected liquid. In some optional implementation forms, the through-threaded holes at the four right angles of the liquid outlet end and the liquid inlet end pressure-bearing panel have the same diameter as the pressurizing rod, and the material can be stainless steel, for example, 304 type, 316 type, or 316L type alloy.

[0041] The beneficial effects of the present application relative to the prior art are that the existing dense reservoir fracturing simulation system used in the laboratory mainly uses a triaxial instrument to inject fracturing fluid into a cubic core, the core breaks from the inside, and the core is taken out after the experiment to observe the crack diffusion and proppant migration law. This method can only obtain the final experimental result, and cannot explore the dynamic process of crack initiation, diffusion, and proppant migration, resulting in incomplete experimental results, and the mathematical model established based on this also has the problem of unclear description.

[0042] In view of this, the shell and horizontal wellbore (including perforation) prepared by ultra-thick toughened glass and the "tree-shaped" artificial fracture of different sizes, lengths and tortuosity prepared by high-strength epoxy resin solve this problem well. In particular, the application of distributed optical fiber can quantitatively describe the whole process of crack opening. Specifically, the visualization device of the embodiment comprises a liquid outlet pressure-bearing panel, a liquid inlet pressure-bearing panel, a shell, a horizontal wellbore and a pressurizing rod. The four straight corners of the liquid outlet and the liquid inlet pressure-bearing panel have threaded through holes for placing four pressurizing rods with threaded ends, and the two pressure-bearing panels are connected by nuts, and one side is provided with two concentric annular grooves of different diameters, which are connected to the shell and the horizontal wellbore by sealing rubber rings and strong glue respectively. In particular, the small-diameter concentric annular groove is provided with a protruding structure, and the protruding structure is provided with two annular grooves for placing sealing rubber rings, which enhances the sealing degree between the horizontal wellbore and the liquid outlet and the liquid inlet pressure-bearing panel.

[0043] In summary, the visualization device for simulating the fracturing process of a dense reservoir by using distributed optical fiber technology is provided by sealingly connecting the liquid outlet pressure-bearing panel, the liquid inlet pressure-bearing panel, the shell, the horizontal wellbore and the pressurizing rod. The device is used to intuitively characterize the crack initiation mechanism, proppant migration rule and temporary plugging effect of the dense reservoir. Specifically, when starting the simulation experiment, the confining pressure liquid injected into the shell can be used to simulate the pressure of the overburden rock layer of the reservoir, the "tree-shaped" artificial fracture can simulate the complex fracture network, and the phenolic resin glue can simulate the pressure required for the crushing of the rock skeleton structure to a certain extent. The crack is only lifted when the back pressure is increased to be greater than the sum of the confining pressure and the pressure required for "rock skeleton crushing", and the crack initiation mechanism is explored by the OFRD optical fiber strain demodulator. The proppant migrates into the crack along with the fracturing fluid, and the migration rule of the proppant of different colors is directly observed during the experiment. Finally, the temporary plugging agent is injected to evaluate the temporary plugging effect. The present application is simple to operate and can directly visualize the simulation of the fracturing process of a dense reservoir, and characterize the crack initiation mechanism, proppant migration rule and temporary plugging effect of the fracturing process.

[0044] In another aspect, the present application also provides a test system 200 for the fracturing process of a dense reservoir, as shown in Figure 9 The test system 200 can include: the simulation device 100 for the fracturing process of a dense reservoir as described above; a first injection unit for injecting confining pressure liquid into the shell of the simulation device at a first injection pressure; a second injection unit for injecting fracturing fluid into the wellbore of the simulation device at a second injection pressure; a back pressure unit for providing back pressure to the liquid outlet pipeline of the wellbore; and a pressure acquisition system for monitoring the first injection pressure, the second injection pressure and the back pressure.

[0045] The first injection unit is, for example, a confining fluid pressurizing unit. The confining fluid pressurizing unit is connected to the through-thread hole between the annular grooves of different diameters of the liquid inlet end pressure-bearing panel, so as to inject confining fluid into the casing at a first injection pressure.

[0046] The second injection unit is, for example, a displacement medium pressurizing unit. The displacement medium pressurizing unit can be composed of an ISCO pump and a fracturing fluid preparation tank containing water-based fracturing fluid, proppants of different colors and temporary plugging agents, and can realize the alternate injection of proppants and temporary plugging agents, and is connected to the threaded hole at the center of one side of the liquid inlet end pressure-bearing panel through the injection pipeline, so as to inject fracturing fluid into the wellbore at a second injection pressure. In an embodiment, the proppants can include a first proportion of 80 / 100 mesh quartz sand and a second proportion of 60 / 80 mesh ceramic, and the concentration can be 0.3-0.5 kg / L, and the particle size of the temporary plugging agent is 40 / 60 mesh, and the concentration can be 0.05-0.1 kg / L.

[0047] The back pressure unit is composed of an ISCO pump, a back pressure valve and a liquid collection barrel, and the ISCO pump provides back pressure to the back pressure valve at the outlet pipeline of the wellbore. Only when the pressure in the outlet pipeline is greater than the pressure provided by the ISCO pump, the fracturing fluid can flow into the liquid collection barrel, and the back pressure valve is connected to the threaded hole at the center of one side of the liquid outlet end pressure-bearing panel through the outlet pipeline.

[0048] The pressure acquisition system is connected to the displacement medium pressurizing unit, the confining fluid pressurizing unit and the back pressure unit, so as to monitor the pressure values at each place in the experimental process in real time, including the first injection pressure, the second injection pressure and the back pressure.

[0049] The specific method for testing by using the above-described measurement system can be: filling the casing with confining fluid by using the confining fluid pressurizing unit, injecting proppant-containing fracturing fluid into the horizontal wellbore by the displacement medium pressure unit in a constant flow mode, simultaneously increasing the confining fluid pressurizing unit and the back pressure unit in a constant pressure mode (for example, always keeping the back pressure less than 5 MPa of the confining pressure) to the first set value of the confining pressure, and then gradually increasing the back pressure to the second set value of the confining pressure while keeping the confining pressure unchanged, at which time the proppant-containing fracturing fluid begins to enter and prop open the artificial fracture, and the optical fiber strain data is collected on the OFDR optical fiber strain demodulator. After the proppant migration is completed, the temporary plugging agent is injected, and the temporary plugging effect is observed.

[0050] In summary, the test system for the fracturing process of the compact reservoir provided by the application can be used to intuitively characterize the crack initiation mechanism, the proppant migration rule and the temporary plugging effect of the temporary plugging agent. When starting the simulation experiment, the confining pressure liquid injected into the shell can be used to simulate the overburden pressure of the reservoir, the "tree-shaped" artificial crack can simulate the complex crack network, and the phenolic resin glue can simulate the pressure required for the crushing of the rock skeleton structure to a certain extent. The crack is only lifted when the back pressure is increased to be greater than the sum of the confining pressure and the pressure required for the crushing of the rock skeleton structure, and the crack initiation mechanism is explored through the OFRD optical fiber strain demodulator. The proppant migrates into the crack along with the fracturing fluid, and the migration rule of the proppant of different colors is directly observed during the experiment. Finally, the temporary plugging agent is injected, and the temporary plugging effect evaluation test is carried out. The application is simple to operate, can directly visually simulate the fracturing process of the compact reservoir, and can characterize the crack initiation mechanism, the proppant migration rule and the temporary plugging effect of the temporary plugging agent in the fracturing process.

[0051] In another aspect, the application also provides a test method 300 for the fracturing process of the compact reservoir for characterizing the crack opening mechanism, the proppant migration rule and the temporary plugging effect of the temporary plugging agent. The test method 300 can be implemented based on the measurement system 200 described above. As shown in the figure, Figure 10 The test method 300 can include steps S310-S340.

[0052] Step S310: The air in the branched hollow tube is discharged, so that the multiple cracks in the branched hollow tube are in a closed state.

[0053] Specifically, a small amount of phenolic resin glue can also be poured into the branched hollow tube, the phenolic resin glue is extruded by extrusion and the air is discharged, so that the multiple cracks are in a closed state. In addition, the multiple cracks can be coated with strong glue, and a distributed optical fiber can be arranged along the tortuous multiple cracks. The optical fiber is finally connected to the external OFRD optical fiber demodulator through the through hole between the annular grooves of different diameters of the liquid inlet end pressure bearing plate, so that the collected signals are sent to the optical fiber demodulator for subsequent analysis.

[0054] Step S320: The pipe opening of the branched hollow tube is connected to the inside of the wellbore through perforation, and the wellbore is placed in the shell. The shell and the wellbore are made of transparent material.

[0055] The purpose of this step S320 is to build a test system. Specifically, reference can be made to Figure 9The structure shown, according to the above description of the test system. For example, the need to be perforated surface coated with strong glue, the mouth of the hollow tube and perforated connected in perforated recess with iron wire to strengthen the mouth of the hollow tube and perforated connection degree. In addition, the horizontal wellbore, the shell through the sealing ring and strong glue and liquid outlet, liquid inlet end bearing panel connected and through the pressure rod to strengthen the connection degree, and the distributed optical fiber through the liquid inlet end bearing panel hole guide out. The connection and implementation of other components can refer to the above description, and will not be described here.

[0056] It is worth noting that in order to better perform the test method, the gas tightness of the test system needs to be specially set and checked.

[0057] Step S330, injecting confining fluid into the shell and injecting fracturing fluid into the wellbore, so that the fracturing fluid enters and props open the multiple fractures.

[0058] In an embodiment, step S330 can include:

[0059] Step S331, injecting confining fluid into the shell at a first injection pressure until the shell is full;

[0060] Step S332, injecting fracturing fluid into the wellbore at a second injection pressure until the fracturing fluid flows out of the liquid outlet pipe of the wellbore, wherein the second injection pressure is less than the first injection pressure;

[0061] Step S333, synchronously increasing the first injection pressure and the second injection pressure until the first injection pressure reaches a first set value; and

[0062] Step S334, continuing to increase the second injection pressure until the second injection pressure reaches a second set value, wherein the second set value is greater than the first set value.

[0063] The system pressurization process of S330 can be performed in combination with the measurement system of the fracturing process of the tight reservoir described above.

[0064] Specifically, step S331 injects confining fluid into the shell through the confining fluid pressurization unit in a constant flow mode (first injection pressure) until the shell is full.

[0065] Step S332 starts to inject proppant-containing fracturing fluid into the horizontal wellbore through the displacement medium pressure unit in a constant flow mode (second injection pressure) until the fracturing fluid flows out of the liquid outlet pipe.

[0066] Step S333 increases the confining pressure and the back pressure in a constant pressure mode (for example, the back pressure is always kept 5 MPa lower than the confining pressure) until the confining pressure reaches the first set value.

[0067] Step S334 gradually increases the back pressure (the second injection pressure) until it exceeds the confining pressure and reaches the second set value while keeping the confining pressure (the first injection pressure) unchanged. Obviously, the second set value should be greater than the first set value. At this time, the fracturing fluid containing proppants starts to enter and prop open the artificial fractures.

[0068] Finally, after the proppants are completely transported, the temporary plugging agent is injected, and the temporary plugging effect is observed.

[0069] Step S340 collects strain data of the multiple fractures through the distributed optical fibers distributed in the multiple fractures.

[0070] In an embodiment, the optical fiber strain data can be collected by an OFRD optical fiber strain demodulator to analyze the fracture initiation mechanism. The dynamic transport rule of different color proppants in the fractures is observed, and the phase is distinguished through various image denoising algorithms, threshold segmentation and watershed algorithm to establish the dynamic transport rule of the proppants. After the temporary plugging agent is injected, the plugged perforations are directly observed, and the temporary plugging efficiency and temporary plugging time are calculated.

[0071] Specifically, for example, the diameters of the multiple fractures of the dendritic hollow tube can be set to 0.1 mm to 8.0 mm, the lengths can be set to 0.5 cm to 10 cm, and the tortuosity can be set to 2 to 35. The fracturing fluid with a viscosity of 1.1 mPa·s is configured, the proppants in the fracturing fluid are 80 / 100 mesh quartz sand (70%) + 60 / 80 mesh ceramic (30%) mixed together, the concentration is 0.3 kg / L, and the particle size of the temporary plugging agent is 40 / 60 mesh, and the concentration is 0.05 kg / L.

[0072] First, steps S331-S332 are performed. After the confining fluid fills the shell, the fracturing fluid containing proppants is injected into the horizontal wellbore at a rate of 0.5 ml / min until the fluid flows out of the outlet pipe.

[0073] Then, step S333 is performed to increase the confining pressure and the back pressure in a constant pressure mode (for example, the back pressure is always kept 5 MPa lower than the confining pressure) until the confining pressure reaches the first set value 20 MPa. As one implementation may be realized, the following steps are performed in sequence:

[0074] 1) P 围压 = 5 MPa, P 回压 = 0 MPa;

[0075] 2) P 围压 = 10 MPa, P 回压 = 5 MPa;

[0076] 3) P 围压 = 15 MPa, P 回压 = 10 MPa;

[0077] 4) P 围压 = 20 MPa, P 回压 = 15 MPa;

[0078] At this time, since the confining pressure reaches the first set value 20 MPa, the confining pressure is kept unchanged, and the back pressure is gradually increased to the second set value 22 MPa.

[0079] As another implementation as can be implemented, the above gradual increase of the back pressure to the second set value 22 MPa can sequentially perform the following steps: P 回压 = 18 MPa→P 回压 = 18.5 MPa→P 回压 = 19 MPa→P 回压 = 19.5 MPa→P 回压 = 20 MPa→P 回压 = 20.5→P 回压 = 21 MPa MPa→P 回压 = 21.5 MPa→P 回压 = 22 MPa.

[0080] Finally, the artificial fracture is gradually opened, and the fracturing fluid and the proppant flow into the fracture. When the proppant no longer flows into the fracture, the fracturing fluid containing the temporary plugging agent is injected at a speed of 0.5 ml / min, and the temporary plugging effect and the time length of the temporary plugging agent at the perforation are observed. The experimental results can be referred to FIG. 4, which respectively shows the change law of the fracture width with time, the proppant migration amount in the fracture with different tortuosity, and the temporary plugging time of the temporary plugging agent with different particle sizes. Figures 11a-11c It can be seen that, by the present application, the fracturing process of the dense reservoir can be directly visualized and simulated, and the fracture initiation mechanism, the proppant migration law and the temporary plugging effect of the temporary plugging agent in the fracturing process are characterized.

[0081] In summary, the test method for the fracturing process of the compact reservoir provided by the application can be used to intuitively characterize the crack initiation mechanism, the proppant migration rule and the temporary plugging effect of the temporary plugging agent. When starting the simulation experiment, the confining pressure liquid injected into the shell can be used to simulate the overburden pressure of the reservoir, the "tree-shaped" artificial crack can simulate the complex crack network, and the phenolic resin glue can simulate the pressure required for the crushing of the rock skeleton structure to a certain extent. The crack is only lifted when the back pressure is increased to be greater than the sum of the confining pressure and the pressure required for the crushing of the rock skeleton structure, and the crack initiation mechanism is explored through the OFRD optical fiber strain demodulator. The proppant migrates into the crack along with the fracturing fluid, and the migration rule of the proppants of different colors is directly observed during the experiment. Finally, the temporary plugging agent is injected, and the temporary plugging effect evaluation test is carried out. The application is simple to operate, can directly visually simulate the fracturing process of the compact reservoir, and can characterize the crack initiation mechanism, the proppant migration rule and the temporary plugging effect of the temporary plugging agent in the fracturing process.

[0082] It should also be noted that the terms "comprising", "containing", or any other variant thereof are intended to cover non-exclusive inclusions, such that a process, method, article or apparatus that comprises a list of elements does not only include those elements, but can also include other elements not expressly listed or inherent to such process, method, article or apparatus. Without more limitations, the element defined by the phrase "comprising a" does not exclude the presence of additional identical elements in the process, method, article or apparatus that includes the element.

[0083] The above is only an embodiment of the application and is not intended to limit the application. Those skilled in the art can make various modifications and changes to the application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the application shall be included in the scope of the claims of the application.

Claims

1. A device for modeling a fracturing process of a compacted reservoir, characterized in that, The simulation device comprises: a housing for containing injected confining fluid; a wellbore located in the housing for containing injected fracturing fluid, the wellbore being provided with perforations on the side thereof, the perforations being in communication with the interior of the wellbore; and a dendritic hollow tube located in the housing, the tube mouth of the dendritic hollow tube being in communication with the interior of the wellbore through the perforations, wherein the dendritic hollow tube is made of elastic member and has a plurality of cracks in the interior thereof, the plurality of cracks being in a closed state in the case that the interior of the dendritic hollow tube is exhausted of air, wherein the housing and the wellbore are of transparent material.

2. The simulation device of claim 1, wherein, The simulation device comprises distributed optical fiber distributed in the plurality of cracks, wherein each of the plurality of cracks has a set size, a set length, and a set tortuosity.

3. The simulation device of claim 2, wherein, The simulation device further comprises an inlet end pressure-bearing panel and an outlet end pressure-bearing panel, the fracturing fluid and the confining fluid being injected through the inlet end pressure-bearing panel, and back pressure being provided to the outlet pipeline of the wellbore through the outlet end pressure-bearing panel, wherein the distributed optical fiber is connected to an optical fiber demodulator via the inlet end pressure-bearing panel.

4. The simulation device of claim 1, wherein, The wellbore is provided with a plurality of perforations on the side thereof, each of the plurality of perforations being connected to a dendritic hollow tube, wherein the perforation comprises a hollow inner cylinder, the outer diameter of the middle part of the perforation being smaller than the outer diameter of the two ends.

5. The simulation device of claim 1, wherein, The transparent material is tempered glass, the wall thickness of the housing is greater than 3 cm, and the wall thickness of the wellbore is greater than 2 cm.

6. The simulation device of claim 1, wherein, The fracturing fluid comprises proppant and temporary plugging agent, the proppant and the temporary plugging agent having different colors.

7. The simulation device of claim 6, wherein, The proppant comprises a first proportion of quartz sand and a second proportion of ceramsite, the concentration of the proppant being 0.3-0.5 kg / L, The particle size of the temporary plugging agent is 40 / 60 mesh, and the concentration of the temporary plugging agent is 0.05-0.1 kg / L.

8. A test system for a fracturing process of a tight reservoir, characterized in that, The test system comprises: a simulation device of a fracturing process of a tight reservoir according to any one of claims 1-7; a first injection unit for injecting confining fluid into the housing of the simulation device at a first injection pressure; a second injection unit for injecting fracturing fluid into the wellbore of the simulation device at a second injection pressure; a back pressure unit for providing back pressure to the outlet pipeline of the wellbore; and a pressure acquisition system for monitoring the first injection pressure, the second injection pressure, and the back pressure.

9. A method of testing a fracturing process of a tight reservoir, characterized in that, The test method comprises: exhausting the interior of the dendritic hollow tube to make the plurality of cracks in the dendritic hollow tube in a closed state; connecting the tube mouth of the dendritic hollow tube to the interior of the wellbore through the perforations, and placing the wellbore in the housing, wherein the housing and the wellbore are of transparent material; injecting confining fluid into the housing and injecting fracturing fluid into the wellbore to make the fracturing fluid enter and prop open the plurality of cracks; and acquiring strain data of the plurality of cracks through the distributed optical fiber distributed in the plurality of cracks.

10. The test method of claim 9, wherein, The injecting confining fluid into the housing and injecting fracturing fluid into the wellbore comprises: injecting the confining fluid into the casing at a first injection pressure until the casing is full; injecting the fracturing fluid into the wellbore at a second injection pressure until a flow of fracturing fluid exits the wellbore from a flow line, wherein the second injection pressure is less than the first injection pressure; synchronously increasing the first injection pressure and the second injection pressure until the first injection pressure reaches a first set value; and continuing to increase the second injection pressure until the second injection pressure reaches a second set value, wherein the second set value is greater than the first set value.

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