Well cementation interface stripping visualization test device and method

Abstract

The invention belongs to the technical field of oil exploitation simulation devices, and discloses a well cementation interface stripping visualization test device and method.The device comprises a visualization unit, an injection molding unit and a pressure stabilizing unit, fracturing fluid is injected into the visualization unit through the injection molding unit, and then the pressure stabilizing unit stabilizes the pressure of the visualization unit. The visualization unit, the injection pressure unit and the pressure stabilizing unit are arranged, and the interface debonding length caused by hydraulic fracturing can be reduced by simulating hydraulic fracturing conditions, testing well cementation interface stripping characteristics and optimizing fracturing parameters and a cement paste formula. According to the visual test method for well cementation interface stripping in the fracturing process, visualization of the interface stripping process under the liquid flooding effect can be achieved, the relation between the fracturing fluid channeling length and the fracturing pressure and displacement is clarified, the channeling risk in the fracturing process is reduced, and the problem of annulus pressure in the later period is avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum production simulation devices, and in particular relates to a cementing interface peeling visualization test device and method. Background Art

[0002] The horizontal well multi-stage hydraulic fracturing technology is to use the natural or induced fracture system of the reservoir, use fracturing fluid containing various additives to inject into the formation under high pressure, so as to expand the reservoir fracture network, and rely on proppants such as sand or ceramic particles to prevent the fractures from closing after the fracturing fluid returns, thereby improving the fracture network system of the reservoir, so that the oil and gas resources stored in it are continuously released and transported to the surface. Hydraulic fracturing technology has the characteristics of large displacement, high pressure, and long operation time. These characteristics lead to a harsh service environment for the casing-cement ring. Driven by high-pressure liquid, the fracturing fluid is easy to flow along the cementing interface, forming a fracture channel for fluid migration, inducing annular pressure problems.

[0003] At present, oil wells generally have cement ring integrity problems, which leads to annular pressure. Therefore, the annular pressure problem caused by multi-stage hydraulic fracturing seriously affects the safe and efficient development of low-permeability oil and gas reservoir resources, and there is a greater risk of environmental pollution. Summary of the invention

[0004] In order to solve at least one problem in the background technology, the present invention provides a cementing interface peeling visualization test device and method.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A cementing interface peeling visualization test device, comprising:

[0007] A visualization unit, comprising a see-through outer cylinder, an inner cylinder and a simulated wellbore, wherein the simulated wellbore is installed inside the inner cylinder, and the inner cylinder is installed inside the outer cylinder;

[0008] A casing is installed in the simulated wellbore, and cement is poured between the simulated wellbore and the casing to simulate a cement ring;

[0009] The injection unit includes a first constant pressure pump and a camera, wherein the first constant pressure pump is used to inject fracturing fluid into the inner surface and the outer surface of the cement sheath to simulate the crossflow process, and the camera is used to photograph the stripping interface;

[0010] The pressure stabilizing unit includes a second constant pressure pump and a third constant pressure pump, wherein the second constant pressure pump is used to stabilize the external pressure of the simulated wellbore, and the third constant pressure pump is used to simulate the internal pressure of the casing.

[0011] Preferably, the visualization unit further comprises a sealing cover, which is in a truncated cone shape, wherein the side surface of the end surface with a larger area is in contact with the inner wall of the outer cylinder, and the end surface with a smaller area is fixedly connected to the end of the simulated wellbore.

[0012] Preferably, the outer cylinder, the inner cylinder, the sealing cover, the casing and the simulated wellbore are all coaxially arranged;

[0013] One end of the outer cylinder is closed and the other end is open, and the sealing cover is located at the opening of the outer cylinder;

[0014] One end of the inner cylinder is closed and the other end is open;

[0015] A gap is arranged between the closed ends of the outer cylinder and the inner cylinder.

[0016] Preferably, flanges are provided at both ends of the simulated wellbore, and the flanges are in contact with the inner wall of the inner tube;

[0017] The sealing cover, the flange of the simulated wellbore, and the end gaps between the inner tube and the outer tube are all provided with reinforcement tubes;

[0018] Reinforcement steel bars are installed in the reinforcement tube.

[0019] Preferably, one end of the sleeve is threadedly connected to the sealing cover, and the other end is threadedly connected to the end of the outer cylinder;

[0020] The end of the sleeve close to the sealing cover is open, and the end away from the sealing cover is closed.

[0021] Preferably, the injection unit further comprises a first pipeline, a valve, a pressure gauge and a computer;

[0022] One end of the first pipeline is connected to the first constant pressure pump, and the other end is connected to the injection pipe, the injection pipe communicates with the annular gap between the simulated wellbore and the casing and is located at the end of the simulated wellbore;

[0023] The valve and the pressure gauge are both installed on the first pipeline;

[0024] The computer is electrically connected to the pressure gauge and the camera respectively.

[0025] Preferably, the pressure stabilizing unit further includes a second pipeline and a third pipeline;

[0026] One end of the second pipe is connected to the second constant pressure pump, and the other end is connected to the side of the outer cylinder, so as to stabilize the pressure of the gap between the outer cylinder and the simulated wellbore;

[0027] One end of the third pipeline is connected to the third constant pressure pump, and the other end is connected to the end of the sleeve, so as to inject pressure into the interior of the sleeve.

[0028] Preferably, a confining pressure pipe is connected between the outer cylinder and the inner cylinder, one end of the confining pressure pipe is communicated with the second pipeline, and the other end of the confining pressure pipe is communicated with the gap between the outer cylinder and the simulated wellbore.

[0029] Preferably, it further comprises a base, and the base is used to support the outer cylinder.

[0030] A cementing interface peeling visualization test method, used for the above-mentioned cementing interface peeling visualization test device, comprises the following steps:

[0031] The fracturing fluid with pigment is injected between the simulated wellbore and the casing through the injection unit, and the distribution of the fracturing fluid on the cement sheath is recorded by a camera until the cement sheath stops peeling off from the inner casing and the outer simulated wellbore;

[0032] At the same time, a transparent fluid is injected into the inside of the casing and the gap between the inner tube and the simulated wellbore through the pressure stabilizing unit to stabilize the pressure.

[0033] Preferably, the pressure injected between the simulated wellbore and the casing does not exceed 250 MPa, the pressure in the casing does not exceed 180 MPa, and the pressure between the inner tube and the simulated wellbore does not exceed 180 MPa.

[0034] Beneficial effects of the present invention:

[0035] 1. The present invention is provided with a visualization unit, a pressure injection unit and a pressure stabilization unit, which can reduce the interface debonding length caused by hydraulic fracturing by simulating hydraulic fracturing conditions, testing the cementing interface peeling characteristics, optimizing fracturing parameters and cement slurry formula.

[0036] 2. The present invention provides a visualization test method for cementing interface peeling during fracturing, which can realize the visualization of the interface peeling process under liquid drive, clarify the relationship between the crossflow length of the fracturing fluid and the fracturing pressure and displacement, reduce the risk of crossflow during the fracturing process, and avoid the problem of annular pressure in the later stage.

[0037] 3. The present invention records the crossflow length and the injection port pressure and flow rate data by setting up computers, pressure gauges and cameras, which can be used as verification data for related finite element models and provide a data basis for optimizing finite element calculation parameters and improving numerical simulation accuracy.

[0038] Other features and advantages of the present invention will be described in the following description, and partly become obvious from the description, or be understood by implementing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0040] Figure 1 A structural schematic diagram of a cementing interface peeling visualization test device of the present invention is shown;

[0041] Figure 2 A schematic diagram of the structure of a visual test unit of the present invention is shown;

[0042] Figure 3 A schematic diagram of a visualization test unit according to the present invention is shown;

[0043] Figure 4 A schematic diagram of a simulated wellbore external load according to the present invention is shown;

[0044] Figure 5 A test flow chart of the present invention is shown.

[0045] In the figure: 1. Visualization unit; 101. Outer tube; 102. Inner tube; 103. Sealing cover; 104. Reinforced steel bars; 105. Confining pressure pipe; 106. Injection pipe; 107. Simulated wellbore; 108. Casing; 109. Reinforced pipe; 2. Base; 3. First constant pressure pump; 4. First pipeline; 5. Valve; 6. Pressure gauge; 7. Computer; 8. Camera; 9. Second constant pressure pump; 10. Third constant pressure pump; 11. Second pipeline; 12. Third pipeline. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] A cementing interface peeling visualization test device, such as Figure 1 As shown, it includes a visualization unit 1, a base 2, an injection unit and a pressure stabilization unit. The device can simulate the hydraulic fracturing process, realize the visualization of the cementing interface crossflow process, evaluate the cement sheath anti-crossflow ability, and provide guidance for protecting the wellbore integrity during the horizontal well reservoir transformation process.

[0048] exist Figure 1In the figure, the visualization unit 1 includes a transparent outer cylinder 101, an inner cylinder 102, a sealing cover 103 and a simulated wellbore 107, wherein the simulated wellbore 107 is installed inside the inner cylinder 102, the inner cylinder 102 is installed inside the outer cylinder 101, and the sealing cover 103 is truncated cone-shaped, the side surface of the end face with a larger area is in contact with the inner wall of the outer cylinder 101, and the end face with a smaller area is fixedly connected to the end of the simulated wellbore 107.

[0049] Specifically, combined Figure 2 and Figure 3 It can be seen that the outer cylinder 101, the inner cylinder 102, the sealing cover 103, the casing 108 and the simulated wellbore 107 are all coaxially arranged, the outer cylinder 101 is closed at one end and open at the other end, and the sealing cover 103 is located at the opening of the outer cylinder 101; the inner cylinder 102 is closed at one end and open at the other end; a gap is set between the closed ends of the outer cylinder 101 and the inner cylinder 102. In addition, flanges are set at both ends of the simulated wellbore 107, and the flanges are fitted with the inner wall of the inner cylinder 102; the sealing cover 103, the flange of the simulated wellbore 107, and the end gap between the inner cylinder 102 and the outer cylinder 101 are all provided with a reinforcing tube 109; reinforcing steel bars are installed in the reinforcing tube 109. Moreover, one end of the casing 108 is threadedly connected to the sealing cover 103, and the other end is threadedly connected to the end of the outer cylinder 101; the end of the casing 108 close to the sealing cover 103 is open, and the end away from the sealing cover 103 is closed. In addition, a casing 108 is installed in the simulated wellbore 107, and cement is poured between the simulated wellbore 107 and the casing 108 to simulate a cement ring.

[0050] It should be noted that the sealing cover 103, the outer cylinder 101, and the simulated wellbore 107 are all made of high-strength transparent material polymethyl methacrylate (PMMA). The outer cylinder 101 has a confining pressure pipe 105 on its wall, through which liquid can be injected into the annulus between the inner wall of the outer cylinder 101 and the outer wall of the simulated wellbore 107 to exert confining pressure; during assembly, flexible silicone gaskets can be installed on the upper and lower end surfaces of the simulated wellbore 107 to play a sealing role.

[0051] The injection and pressure unit includes a first constant pressure pump 3, a first pipeline 4, a valve 5, a pressure gauge 6, a computer 7 and a camera 8. The first constant pressure pump 3 is used to inject fracturing fluid into the inner and outer surfaces of the cement ring to simulate the crossflow process, and the camera 8 is used to shoot the stripping interface. In addition, one end of the first pipeline 4 is connected to the first constant pressure pump 3, and the other end is connected to the injection pipe 106, which is connected to the annular gap between the simulated wellbore 107 and the casing 108 and is located at the end of the simulated wellbore 107; the valve 5 and the pressure gauge 6 are both installed on the first pipeline 4, and the computer 7 is electrically connected to the pressure gauge 6 and the camera 8 respectively.

[0052] It should be noted that, in the injection unit, the valve 5 can be a three-way valve, and the pressure gauge 6 can be an electronic pressure gauge. When the first constant pressure pump 3 injects fracturing fluid into the position of the cement ring, the pressure in the first pipeline 4 can be collected by the pressure gauge 6, and then the information is transmitted to the computer 7. At the same time, the camera 8 can capture the distribution of the fracturing fluid on the cement ring, so as to determine whether the cement ring is peeled off.

[0053] It should be noted that, in some embodiments, in order to capture the distribution of the fracturing fluid on the entire surface of the cement sheath, it is generally necessary to use multiple cameras 8 to capture the cement sheath within a 360° range.

[0054] It should be further explained that, in some embodiments, in order to reduce the number of cameras 8, an annular guide rail can be provided on the peripheral side of the visualization unit 1, and then a copper bar for conducting electricity can be provided on the surface of the annular guide rail, and then a contact piece that slides with the copper bar can be provided on the camera 8, and the copper bar can be electrically connected to the computer 7. In this structure, the camera 8 can slide along the guide rail, so that a single camera 8 can shoot the cement ring at 360 degrees. In addition, in this structure, the position of the camera 8 on the guide rail can be manually adjusted, and a servo motor can be added to realize the sliding of the camera 8 along the guide rail through mechanical transmission.

[0055] The pressure stabilizing unit includes a second constant pressure pump 9, a third constant pressure pump 10, a second pipeline 11 and a third pipeline 12. The second constant pressure pump 9 is used to stabilize the pressure outside the simulated wellbore 107, and the third constant pressure pump 10 is used to simulate the internal pressure of the casing 108. In addition, one end of the second pipeline 11 is connected to the second constant pressure pump 9, and the other end is connected to the side of the outer cylinder 101, which is used to stabilize the pressure of the gap between the outer cylinder 101 and the simulated wellbore 107; one end of the third pipeline 12 is connected to the third constant pressure pump 9, and the other end is connected to the end of the casing 108, which is used to inject pressure into the casing 108.

[0056] It should be noted that if Figure 4 As shown, the pressure stabilizing unit is to maintain the pressure inside the casing 108 and outside the simulated wellbore 107 stable, simulate the pressure state of the underground oil well, and help ensure the accuracy of the test results. The second constant pressure pump 9 applies the confining pressure from the side of the simulated wellbore 107, and the third constant pressure pump 10 applies the confining pressure from the top of the casing 108.

[0057] Furthermore, a confining pressure pipe 105 is connected between the outer tube 101 and the inner tube 102 . One end of the confining pressure pipe 105 is communicated with the second pipeline 11 , and the other end is communicated with the gap between the outer tube 101 and the simulated wellbore 107 .

[0058] It should be noted that the second pipeline 11 can transport fluid through the confining pressure pipe 105 , and the interface of the confining pressure pipe 105 is located on the surface of the outer cylinder 101 , which facilitates fixed connection between the second pipeline 11 and the confining pressure pipe 105 .

[0059] The present invention discloses a cementing interface peeling visualization test method, which is used for the above-mentioned cementing interface peeling visualization test device, and comprises the following steps:

[0060] S1a: injecting a fracturing fluid with pigment between the simulated wellbore 107 and the casing 108 through the injection unit, and recording the distribution of the fracturing fluid on the cement sheath with a camera until the cement sheath stops peeling off from the inner casing 108 and the outer simulated wellbore 107;

[0061] S1b simultaneously injects transparent fluid into the interior of the casing 108 and the gap between the inner tube 102 and the simulated wellbore 107 through the pressure stabilizing unit to stabilize the pressure.

[0062] It should be noted that steps S1a and S1b are synchronously operated. In step S1a, the valve 5 of the injection unit is opened, and then the first constant pressure pump 3 injects the pigmented fracturing fluid into the annulus between the simulated wellbore 107 and the casing 108 through the first pipeline 4. Then the pigmented fracturing fluid will squeeze the cement ring and gradually penetrate into the contact surface between the cement ring and the casing 108 and the simulated wellbore 107. If the pigmented fracturing fluid gathers at a certain position, it means that the position is in a state of interface peeling. In addition, the pressure gauge 6 will also collect the pressure in the first pipeline 4 and transmit the information to the computer 7.

[0063] In step S1b, the second constant pressure pump 9 injects a transparent fluid (e.g., water, transparent fracturing fluid, etc.) into the annulus between the inner tube 102 and the simulated wellbore 107 through the second pipeline 11 to simulate the pressure outside the cement sheath. At the same time, the third constant pressure pump 10 injects a transparent fluid (e.g., water, transparent fracturing fluid, etc.) into the annulus between the inner tube 102 and the simulated wellbore 107 through the second pipeline 11 to simulate the pressure outside the cement sheath. Figure 2 A transparent fluid is injected into the top of the middle casing 108 to simulate the pressure inside the cement sheath.

[0064] Furthermore, the pressure between the simulated wellbore 107 and the casing 108 does not exceed 250 MPa, the pressure in the casing 108 does not exceed 180 MPa, and the pressure between the inner tube 102 and the simulated wellbore 107 does not exceed 180 MPa.

[0065] like Figure 5 As shown, it is a specific operation flow chart of the method of the present invention, which is as follows:

[0066] (1) Cement ring maintenance. Connect the casing 108, the outer tube 101 and the simulated wellbore 107, temporarily block the injection pipe 106 at the bottom of the outer tube 101, and inject cement slurry after confirming that the silicone seal is installed in place. After the grouting is completed, install the sealing cover 103, install the reinforcing steel bar 104, apply confining pressure and maintain for 7 days.

[0067] (2) Connecting the test pipeline. After the cement ring curing is completed, the visualization unit 1 and the first constant pressure pump 3 are connected by a high-pressure stainless steel pipe, and the sealing of the first pipeline 4 is checked before starting the pump.

[0068] (3) Turn on the pump to inject liquid and record the experimental data.

[0069] ① Adjust the outlet of valve 5 (three-way valve) to the outside of the first pipeline 4, start the pump at the minimum flow rate to discharge the residual gas in the manifold, stop the pump after confirming that it is completely discharged, and adjust the outlet of valve 5 to the inside of the first pipeline 4;

[0070] ② Turn on the camera 8, turn on the first constant pressure pump 3, restart the pump at a preset flow rate / pressure, pump colored fracturing fluid into the visualization unit 1, and observe the fluid pressure change and interface peeling;

[0071] ③ If the interface peels off, continue to pump the liquid until the interface stops peeling off or the interface peels off completely, then stop the pump and turn off the camera 8 and the pressure gauge 6;

[0072] ④If there is no peeling at the interface and the fluid pressure does not rise, turn off the pump, open valve 5 to release the pressure, and close valve 5 after the pressure is completely released; increase the fluid pump speed / pressure and repeat step ②.

[0073] (4) Analysis of sensitive factors. Experimental conditions such as pumping pressure, pumping speed, cement slurry formula, confining pressure, and casing internal pressure can be changed to analyze the interface peeling characteristics under different conditions and the influence of various parameters, thereby guiding the design of fracturing construction and achieving the purpose of reducing the risk of wellhead annular pressure.

[0074] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A cementing interface peeling visualization test device, characterized in that: include: A visualization unit (1) comprises a see-through outer cylinder (101), an inner cylinder (102) and a simulated wellbore (107), wherein the simulated wellbore (107) is installed inside the inner cylinder (102), and the inner cylinder (102) is installed inside the outer cylinder (101); A casing (108) is installed in the simulated wellbore (107), and cement is poured between the simulated wellbore (107) and the casing (108) to simulate a cement ring; The injection unit comprises a first constant pressure pump (3) and a camera (8), wherein the first constant pressure pump (3) is used to inject fracturing fluid into the inner surface and the outer surface of the cement sheath to simulate the crossflow process, and the camera (8) is used to photograph the peeling interface; The pressure stabilizing unit comprises a second constant pressure pump (9) and a third constant pressure pump (10), wherein the second constant pressure pump (9) is used to stabilize the external pressure of the simulated wellbore (107), and the third constant pressure pump (10) is used to simulate the internal pressure of the casing (108).

2. A cementing interface peeling visualization test device according to claim 1, characterized in that: The visualization unit (1) further comprises a sealing cover (103), wherein the sealing cover (103) is in a truncated cone shape, the side surface of the end surface with a larger area is in contact with the inner wall of the outer cylinder (101), and the end surface with a smaller area is fixedly connected to the end of the simulated wellbore (107).

3. A cementing interface peeling visualization test device according to claim 2, characterized in that: The outer cylinder (101), the inner cylinder (102), the sealing cover (103), the casing (108) and the simulated wellbore (107) are all coaxially arranged; The outer cylinder (101) is closed at one end and open at the other end, and the sealing cover (103) is located at the opening of the outer cylinder (101); The inner cylinder (102) is closed at one end and open at the other end; A gap is provided between the closed ends of the outer cylinder (101) and the inner cylinder (102).

4. A cementing interface peeling visualization test device according to claim 3, characterized in that: Flanges are provided at both ends of the simulated wellbore (107), and the flanges are in contact with the inner wall of the inner tube (102); The sealing cover (103), the flange of the simulated wellbore (107), and the end gaps between the inner tube (102) and the outer tube (101) are all provided with a reinforcing tube (109); Reinforcement steel bars are installed in the reinforcement tube (109).

5. A cementing interface peeling visualization test device according to claim 3, characterized in that: One end of the sleeve (108) is threadedly connected to the sealing cover (103), and the other end is threadedly connected to the end of the outer cylinder (101); The end of the sleeve (108) close to the sealing cover (103) is open, and the end away from the sealing cover (103) is closed.

6. A cementing interface peeling visualization test device according to claim 1, characterized in that: The injection unit further comprises a first pipeline (4), a valve (5), a pressure gauge (6) and a computer (7); One end of the first pipeline (4) is connected to the first constant pressure pump (3), and the other end is connected to an injection pipe (106), wherein the injection pipe (106) communicates with the annular gap between the simulated wellbore (107) and the casing (108) and is located at the end of the simulated wellbore (107); The valve (5) and the pressure gauge (6) are both installed on the first pipeline (4); The computer (7) is electrically connected to the pressure gauge (6) and the camera (8) respectively.

7. The cementing interface peeling visualization test device according to claim 1, characterized in that: The pressure stabilizing unit further comprises a second pipeline (11) and a third pipeline (12); One end of the second pipe (11) is connected to the second constant pressure pump (9), and the other end is connected to the side of the outer cylinder (101), so as to stabilize the pressure of the gap between the outer cylinder (101) and the simulated wellbore (107); One end of the third pipeline (12) is connected to the third constant pressure pump (10), and the other end is connected to the end of the sleeve (108), so as to inject pressure into the sleeve (108).

8. A cementing interface peeling visualization test device according to claim 7, characterized in that: A confining pressure pipe (105) is connected between the outer cylinder (101) and the inner cylinder (102); one end of the confining pressure pipe (105) is in communication with the second pipeline (11), and the other end is in communication with the gap between the outer cylinder (101) and the simulated wellbore (107).

9. A cementing interface peeling visualization test device according to any one of claims 1 to 8, characterized in that: It also comprises a base (2), wherein the base (2) is used to support the outer cylinder (101).

10. A cementing interface peeling visualization test method, characterized in that: The cementing interface peeling visualization test device used in any one of claims 1 to 9 comprises the following steps: Injecting a fracturing fluid containing pigment between the simulated wellbore (107) and the casing (108) through an injection and pressure unit, and recording the distribution of the fracturing fluid on the cement sheath with a camera (8), until the cement sheath stops peeling off from the inner casing (108) and the outer simulated wellbore (107); At the same time, a transparent fluid is injected into the interior of the casing (108) and the gap between the inner tube (108) and the simulated wellbore (107) through a pressure stabilizing unit to stabilize the pressure.

11. A cementing interface peeling visualization test method according to claim 10, characterized in that: The pressure injected between the simulated wellbore (107) and the casing (108) does not exceed 250 MPa, the pressure in the casing (108) does not exceed 180 MPa, and the pressure between the inner tube (102) and the simulated wellbore (107) does not exceed 180 MPa.

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