Complex Formation Cementing Simulation and Gas-Water Reverse Invasion Evaluation Method and Evaluation System

Abstract

The present invention discloses a method and an evaluation system for simulating cementing in complex formations and evaluating gas and water back-invasion, which relate to the technology of oil and gas exploitation. The evaluation system is provided with a simulated formation, a buffer space, a cement sheath and a casing, and a movable bottom plate. Two sets of hydraulic cylinders are arranged below the movable bottom plate to respectively test the shear force at the second interface and the compressive strength of the cement sheath; the casing has a lumen and a cement return height hole, and a cement sheath is formed after the cement return height is solidified; a sonic logging probe and a gas detection device are arranged in the reaction kettle. The evaluation method uses the above evaluation system for evaluation. The evaluation system and the evaluation method can more accurately simulate the target formation, test the shear force at the second interface and the compressive strength of the cement sheath, and the visualization method is more convenient.

Description

Technical Field

[0001] The present invention relates to the technology of oil and gas exploitation, and particularly to a method and a system for evaluating cementing simulation and gas-water reverse invasion in complex formations. Background Art

[0002] The extraction of oil and gas needs to go through a series of complex processes, including drilling, cementing, well completion, perforating, water injection, oil production, etc. Cementing operation is an important process in the energy extraction process, which plays an important role in providing protection and support for the casing and effectively isolating adjacent formations; especially in the exploration and development of deep-water oil and gas, the quality of cementing directly determines the life of production wells and has an important impact on the smooth progress of subsequent links and the recovery rate. It is a key project for the long-term stable production of oilfields. Therefore, the evaluation of cementing quality is very necessary.

[0003] The key to cementing quality lies in the cementing quality of the second interface, mainly including cementing strength and interlayer isolation ability. At present, the methods for evaluating the cementing quality of the second interface can be mainly classified into two categories, namely, the well logging evaluation method in the field and the interface cementing strength evaluation method in laboratory experiments. The interface cementing strength evaluation method in laboratory experiments is mainly to first form a simulated formation, and then inject a certain amount of cement slurry into the space adjacent to the simulated formation and solidify it to form a cement sheath (the contact surface between the cement sheath and the simulated formation is the second interface); the cementing strength of the second interface is characterized by the shear strength measured by the shear behavior parallel to the second interface. At the same time, the interlayer isolation ability is characterized by the permeability of the second interface between the cement slurry and the simulated formation.

[0004] Deepwater oil and gas resources are widely distributed, including the coastal continental shelf area. At the same time, hydrates are also widely distributed in shallow marine surface sediments. The geographical locations of the two overlap highly, so it is very easy to encounter hydrate formations during surface cementing in the process of deepwater oil and gas exploration and development. Hydrates are stable solid compounds formed under specific temperature and pressure conditions. However, when external conditions such as temperature and pressure change, hydrates may decompose to produce a large amount of gas and water, posing challenges to cementing operations. During cementing, the heat released by the hydration of the cement slurry can cause the decomposition of hydrates in the simulated wellbore annulus wall, generating high-pressure free gas and water. These high-pressure free gas and water are very easy to back-invade into the cement slurry (i.e., gas-water back-invasion), seriously affecting the mechanical strength of the cement sheath and the sealing performance of the second interface of cementing, and even leading to the abandonment of cementing and wellbore instability, triggering safety accidents such as blowouts. In order to prevent the occurrence of gas-water back-invasion, it is crucial to determine the critical conditions of gas-water back-invasion under different geological conditions and cementing process conditions. By simulating and analyzing the physical property responses of hydrate formations and the laws of high-pressure gas-water back-invasion under different geological conditions and cementing process conditions, and evaluating the influence of gas-water back-invasion on the cementing quality such as the mechanical and impermeability properties of the cement sheath and the second interface, it can provide theoretical guidance and basis for the design of cementing programs and the optimization of cementing process parameters. Therefore, during the evaluation of the interfacial bonding strength in laboratory experiments, pore water and methane gas need to be injected into the simulated formation to form hydrates to make the simulated formation closer to the natural formation containing hydrates. However, due to the action of gravity, the distribution of pore water in the simulated formation is uneven, and it is difficult to ensure the uniform generation of hydrates in the simulated formation.

[0005] During cementing, since the cement slurry invades the simulated wellbore annulus wall to a certain extent, the morphology of the second interface is not a flat surface, and the hydrates in the simulated formation containing hydrates are very easy to decompose to produce high-pressure free gas and water back-invading into the cement. Therefore, the observation of the morphology and microcracks of the second interface is also conducive to the analysis and study of the strength and sealing performance of the second interface. Few existing cementing quality evaluation experimental devices take into account the observation of the morphology and microcracks of the second interface.

[0006] In addition, during the cementing process, to achieve the safety and stability of the wellbore and improve the bonding quality of the second interface, the pressure of the cement slurry is generally greater than the pore pressure of the simulated formation. When the cement slurry penetrates into the simulated formation under the action of the pressure difference, due to the limited thickness of the simulated formation, the pores in the simulated formation are subjected to the pressure generated by the intrusion of the cement slurry into the simulated wellbore annulus wall (the simulated wellbore annulus wall refers to the formation close to the wellbore), resulting in uneven pore distribution, pressure, and pressure buildup in the simulated formation, which is quite different from the in-situ formation cementing in the well (the in-situ formation in the well refers to the formation related to cementing formed after drilling), affecting the accuracy of the evaluation of the cement sheath and the second interface quality. At the same time, during the evaluation of the interface bonding strength in the laboratory experiment, the data analysis of the acoustic logging probe is used to evaluate the cementing quality of the cement slurry. Its setting method affects the airtightness of the device, thus affecting the pressure stability of the device. Poor pressure stability makes the test results inaccurate. The above problems increase the difficulty and accuracy of the evaluation of the bonding strength and the interlayer sealing ability.

[0007] There are already many existing technologies for the evaluation of cementing quality. For example, CN206707694A discloses an experimental device for evaluating the cementing quality of hydrate formations in deepwater cementing. This device only evaluates the cementing quality of the cement slurry through the data analysis of the acoustic logging probe, without considering the influence of the second interface strength, resulting in a low accuracy of the cementing quality evaluation result; the difference between the prefabricated artificial natural gas hydrate and the natural gas hydrate in the natural formation under actual conditions is large, and the credibility of the experimental results is low; the cement slurry is injected from the bottom of the kettle, which is contrary to the actual construction situation (in actual construction, the cement slurry is injected from the wellhead, that is, injected from top to bottom). The cementing pressure difference caused by the injection of the cement slurry (requiring the pressure of the cement slurry to be greater than the pressure of the simulated formation) is affected by the mud pump, and the credibility of the experimental results is low.

[0008] CN110778291 A discloses an experimental device for simulating cementing in a natural gas hydrate formation. This device only detects the temperature and pressure in the simulated hydrate formation during the cementing process and cannot accurately evaluate the cementing quality; due to reasons such as pressure buildup, local pressure unevenness, and excessive local pressure generated by the instrument itself, it affects the seepage process of the cement slurry in the pores of the simulated formation, resulting in a large difference between the prefabricated artificial natural gas hydrate and the natural gas hydrate in the natural formation under actual conditions, and the credibility of the experimental results is low; it is impossible to observe the hydrate thermal decomposition and back-invasion process in real time.

[0009] The present team disclosed a visualization system for the bonding quality of the second interface of special-shaped cementing and the strength test of special-shaped bodies in CN109142192A. A simulated formation cavity and a cementing cement / cement stone cavity are connected to form an experimental cavity. The top and bottom of the experimental cavity are sealed, and a cement stone lifting die is provided at the lower part of the cementing cement / cement stone cavity. A thermocouple and multiple reaction gas injection pipes are arranged in the simulated formation cavity, and visual windows are respectively arranged on the sides of the simulated formation cavity and the cementing cement / cement stone cavity. This device can be used for evaluating the bonding quality of the second interface during the cementing process in hydrate-bearing formations and testing the quality of the bonding surface between the soil body and cement in soft soil formations, and to a certain extent, realizes the visualization of the second interface morphology and microcracks. However, this technology still has the following defects:

[0010] 1. Due to reasons such as pressure build-up, local pressure non-uniformity, and excessive local pressure generated by the instrument itself, the seepage process of cement slurry in the pores of the simulated formation is affected, resulting in a large difference between the prefabricated artificial natural gas hydrate and the natural gas hydrate in the natural formation under actual conditions, and the credibility of the experimental results is low;

[0011] 2. The visual observation head is outside the second interface. In order to achieve a sealed environment for confining pressure, an opaque rubber membrane tube is used, which makes it impossible to observe the thermal decomposition and reverse invasion processes of hydrates in real time. When observing the second interface, the rubber membrane tube needs to be disassembled, which is troublesome to operate; only when there is no need to use an additional rubber membrane tube to form a sealed environment can the rubber membrane tube be removed and a microscopic device can be used to observe the thermal decomposition and reverse invasion processes of hydrates in real time at the visual window, so the scenes that can be observed in real time are limited;

[0012] 3. When evaluating the cementing quality, it is necessary to calculate the permeability, the process is complex, and the error is large. Summary of the Invention

[0013] Aiming at a series of problems existing in the prior art, such as a large difference between the simulated formation and the natural formation, the quality of the second interface being damaged due to gas-water reverse invasion, the second interface being difficult to directly observe, the setting method of the acoustic logging probe affecting the airtightness of the device and thus affecting the pressure stability, and the compressive strength of the cement slurry and the shear strength of the second interface being difficult to measure simultaneously, the present invention provides a method and an evaluation system for simulating cementing in complex formations and evaluating gas-water reverse invasion.

[0014] The evaluation system for simulating cementing in complex formations and evaluating gas-water reverse invasion includes a reaction kettle. A simulated formation is arranged in the kettle body, and a buffer space is arranged between the simulated formation and the inner wall of the kettle body. A cement ring and a casing are sequentially arranged in the simulated formation, and the three are concentric circular cylinders. A movable bottom plate is arranged in the kettle body, and the kettle cover and the movable bottom plate respectively seal the upper and lower ends of the kettle body. The movable bottom plate supports the simulated formation, the cement ring and the casing. The upper end of the casing is hermetically connected to the kettle cover, and the lower end of the casing is hermetically connected to the movable bottom plate;

[0015] Two sets of hydraulic cylinders are arranged below the movable bottom plate. The first set of hydraulic cylinders is placed below the simulated formation; the second set of hydraulic cylinders is placed below the cement sheath.

[0016] The casing has a lumen. Cement return height holes are provided at the lower part of the casing, and the cement return height holes communicate with the cementing annulus where the cement sheath is located; an acoustic logging probe is arranged inside the reaction kettle; a gas detection device is arranged inside the reaction kettle, and the gas detection device includes probes for detecting temperature and / or pressure distributed in the cement sheath, the simulated formation and the buffer space; pipelines are provided in the buffer space, the lumen, the cementing annulus and the simulated formation.

[0017] The tube body of the casing has a sandwich layer, and the acoustic logging probes are evenly embedded and distributed in the sandwich layer of the tube body of the casing. The acoustic logging data lines are signal-connected to the acoustic logging probes, and the acoustic logging data lines are placed outside the sandwich layer of the casing.

[0018] A pressure relief hole is opened at one end of the inner wall of the casing close to the kettle cover, and the pressure relief hole communicates the sandwich layer of the casing and the lumen of the casing.

[0019] The probes for detecting temperature and / or pressure are one temperature probe, five temperature and pressure probes, and one pressure probe. The temperature probe is arranged inside the cement sheath, the five temperature and pressure probes are arranged side by side in the simulated formation, and the pressure probe is arranged inside the buffer space.

[0020] A visualization imaging device is arranged inside the reaction kettle. The visualization imaging device includes a glass tube and an imaging probe for imaging the second interface. Both ends of the glass tube are open, and the glass tube penetrates through the buffer space and the simulated formation, so that the inner port of the glass tube faces the second interface directly, and the outer port of the glass tube extends to the kettle body and is sealed and connected to the kettle body; the imaging probe is installed inside the glass tube.

[0021] The movable bottom plate includes a movable upper plate, a movable lower plate and a central plate which are nested. When the movable upper plate, the movable lower plate and the central plate are combined together, they form the bottom of the closed kettle body, and the joints of the movable upper plate, the movable lower plate and the central plate are filled with a sealing rubber cushion layer.

[0022] Each set of hydraulic cylinders includes two hydraulic cylinders. The first set of hydraulic cylinders is placed below the simulated formation with the second interface as the boundary, and the two hydraulic cylinders of the first set of hydraulic cylinders are distributed on the left and right sides at the lower end of the simulated formation; the second set of hydraulic cylinders is placed below the cement sheath with the first interface and the second interface as the boundary, and the two hydraulic cylinders of the second set of hydraulic cylinders are distributed on the left and right sides at the lower end of the cement sheath.

[0023] A water-soluble film is arranged on the inner side wall of the simulated formation, and a sand separation net is arranged on the outer side wall of the simulated formation; a plastic film is pasted on the outer surface of the casing. A rotating shaft is installed on the kettle body, and the rotating shaft is used to connect with a rotating device to realize the rotation of the kettle body.

[0024] A method for simulating cementing in complex formations and evaluating gas-water reverse invasion, using the above system, includes the following steps:

[0025] (1) Preparation stage:

[0026] Prepare a simulated formation in the reactor and install a gas detection device and a visualization imaging device; set up a water-soluble film and a sand separation net;

[0027] Adjust the porosity of the simulated formation until the difference between the porosity of the simulated formation and the average value of the "target formation porosity" / the average value of the target formation porosity < 10%;

[0028] Apply vaseline to the outside of the casing and wrap it with plastic film, then install it on the kettle cover and reseal the reactor;

[0029] Control the temperature of the kettle body by water bath until the temperature of the simulated formation reaches the target formation temperature;

[0030] (2) Hydrate formation stage:

[0031] Inject methane and pore water into the simulated formation, rotate the reactor to make the pore water evenly distributed, and keep the water bath temperature condition outside the kettle body unchanged until hydrates are formed;

[0032] (3) Cementing stage:

[0033] After washing the well, inject the cement slurry into the casing, close the reactor, and push the cement slurry back to the required height;

[0034] Use the method of injecting nitrogen into the simulated formation to make the pressure of the cement slurry higher than the pressure in the buffer space, and keep the pressure until the cement slurry solidifies;

[0035] (4) Obtain experimental data:

[0036] Obtain the temperature and pressure inside the reactor through temperature and / or pressure probes;

[0037] Observe the second interface through an imaging probe;

[0038] After the cement slurry solidifies, start the acoustic logging probe to emit acoustic waves, and the receiver obtains the acoustic waves; then start the first group of hydraulic cylinders to lift the simulated formation and record the pressure change of the first group of hydraulic cylinders; finally, start the second group of hydraulic cylinders to compress the cement sheath and record the pressure change of the second group of hydraulic cylinders.

[0039] The pipelines set in the buffer space, the lumen, the cementing annulus, and the simulated formation include: a backpressure valve interface / air outlet connected to the buffer space, an injection port connected to the lumen, a liquid and gas discharge port connected to the cementing annulus, and a gas-liquid inlet and a gas-liquid outlet that enable gas or liquid to enter and exit the simulated formation; the gas-liquid inlet penetrates the kettle cover and extends to the upper end of the simulated formation; one end of the gas-liquid outlet penetrates the movable bottom plate and extends to the lower end of the simulated formation.

[0040] Term Definitions:

[0041] Primary Interface: In the cementing and completion engineering, the bonding surface between the casing and the cement sheath is called the primary interface of cementing. Its sealing quality directly affects the safety and stability of oil and gas wells.

[0042] Secondary Interface: The bonding surface between the cement sheath and the formation is called the secondary interface of cementing. The sealing quality of the secondary interface is also crucial for the safety and stability of oil and gas wells. It can effectively prevent the crossflow of formation fluids, and its importance in quality assessment is greater than that of the primary interface.

[0043] Gas and Water Back-Invasion: During the cementing process, the phenomenon that formation gas or liquid invades into the cement sheath is called gas and water back-invasion. Gas and water back-invasion may lead to a decline in cementing quality and even cause safety accidents such as blowouts.

[0044] Pore Water: Injecting water into the simulated formation so that it is distributed in the pores of the simulated formation is pore water.

[0045] Hydrate Decomposition: Natural gas hydrates will decompose under certain conditions (such as a decrease in pressure or an increase in temperature), releasing gas (such as methane, etc.) and water. In deepwater drilling, the decomposition of natural gas hydrates may have a significant impact on drilling safety, such as causing an increase in wellbore pressure, wellbore instability, and cementing failure.

[0046] Natural Formation refers to the formation at the location where the well is drilled during the production of oil and gas. Corresponding to the simulated formation, the simulated formation is used to simulate the natural formation.

[0047] Simulated Formation refers to the formation in the experimental equipment that is simulated by mixing and piling up materials such as quartz sand, anhydrous calcium chloride, sodium silicate, and sodium-based bentonite. The structure formed by this part of the materials is called the simulated formation, which is used for evaluating the interfacial bonding strength in laboratory experiments.

[0048] Target Formation refers to the natural formation targeted for the evaluation of the interfacial bonding strength in laboratory experiments.

[0049] Confining Pressure generally refers to the pressure exerted on a rock by the surrounding rock mass, but in the present invention, the confining pressure refers to adjusting the air pressure in the space (referred to as the buffer space) set on the outer surface of the simulated formation so that the simulated formation is subjected to circumferential pressure.

[0050] Downhole In-Situ Cementing refers to the process of cementing after drilling in the natural formation.

[0051] And / or: A and / or B includes A and B, A or B.

[0052] In the present invention, the sealed connection can be sealed by conventional methods such as sealant, gasket, rubber sealing ring, etc.

[0053] Compared with the prior art, the present invention has at least achieved the following beneficial effects:

[0054] 1. Due to the limited thickness of the simulated formation and the pressure generated by the invasion of cement slurry into the simulated wellbore wall, the pore distribution and pressure in the simulated formation are uneven, which is quite different from the natural formation. The present invention improves this problem, improves the pore distribution and pressure unevenness in the simulated formation, makes the simulated formation closer to the natural formation, and increases the accuracy of quality evaluation.

[0055] 2. The present invention reduces the influence of the uneven distribution of pore water in the simulated formation caused by the factor of gravity on the accuracy of cementing quality evaluation by rotating the reaction kettle, enables the uniform generation of hydrates, and increases the accuracy of the evaluation of the bonding strength of the second interface and the interlayer sealing ability.

[0056] 3. In order to prevent the quality of the second interface from being damaged due to gas-water reverse invasion, the present invention adds a gas detection device and a visualization imaging device to the system, detects the temperature and pressure changes and conducts visualization imaging, providing a more comprehensive index analysis for cementing quality evaluation.

[0057] 4. The visualization imaging device can realize the real-time observation of a series of processes such as the hydrate generation process in pores, the seepage invasion process of cement slurry in formation pores, the decomposition process of hydrates by hydration heat, the process of high-pressure gas and water pushing back the cement slurry generated by hydrate decomposition, and the critical state of high-pressure gas and water invading the cement slurry from the simulated formation pores, solving the problem of difficult direct observation of the development of the second interface morphology and crack development.

[0058] 5. By using the gas detection device to monitor the decomposition of hydrates in the simulated formation in real time, it can be used as a basis for cementing quality evaluation. Probes are arranged at different diameters and depths in the simulated formation, and the decomposition of hydrates in the simulated formation can be judged through the temperature and pressure change data, which can be used to evaluate the gas-water reverse invasion index; and the temperature probe placed in the cement ring can monitor the cement temperature in real time, and the pressure probe placed in the buffer space can monitor the equilibrium pressure in the simulated formation in real time, which can be used to study the decomposition of hydrates under different cement heat release temperature and pressure conditions; solving the problem of difficult evaluation and low accuracy of the bonding strength of the second interface and the interlayer sealing ability due to gas-water reverse invasion in the hydrate-bearing formation.

[0059] 6. Through the acoustic logging probe and two groups of hydraulic cylinders, the acoustic logging data and shear compression strength data can be obtained conveniently and quickly, solving the problems of large operation difficulty and easy error generation in the original operation method; at the same time, the compressive strength of the cement slurry and the shear strength of the second interface are tested, increasing the use of the evaluation system and measuring and evaluating the cementing quality more comprehensively.

[0060] 7. By setting a buffer space separated by a sand separation net inside the reaction kettle and adjusting the air pressure in the buffer space, the uniform seepage process of the cement slurry in the simulated formation pores is realized, which is closer to the downhole in-situ cementing process and has higher accuracy, solving the problem that the complex simulated formation cementing process is quite different from the actual cementing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 is a cross-sectional view of the cementing simulation and gas-water back-invasion evaluation system for complex formations;

[0062] Figure 2 Top view of the cementing simulation and gas-water back-invasion evaluation system for complex formations;

[0063] Figure 3 is a schematic structural diagram of the movable bottom plate;

[0064] Figure 4 is a schematic diagram of the embedding of the acoustic logging probe (explosion);

[0065] Figure 5 is a partial schematic diagram of the embedding of the acoustic logging probe (section view);

[0066] Figure 6 is a schematic diagram of the setting of the gas detection device;

[0067] Figure 7 is a side view of the cementing simulation and gas-water back-invasion evaluation system for complex formations;

[0068] Reference numerals: 1, rotating shaft; 2, backpressure valve interface / outlet; 3, gas-liquid outlet; 4, connecting nut; 5, gas-liquid inlet; 6, hydraulic cylinder; 601, first group of hydraulic cylinders; 602, second group of hydraulic cylinders; 7, liquid and gas discharge port; 8, gas detection device connection port; 801, temperature probe; 802, temperature and pressure probe; 803, pressure probe; 9, simulated formation; 10, cement ring; 11, glass tube; 12, imaging probe; 13, buffer space; 14, permeable bottom plate; 15, casing; 16, acoustic logging probe; 17, injection port; 18, acoustic logging data line; 19, kettle cover; 20, rubber sealing ring; 21, sand separation net; 22, water-soluble film; 23, kettle body; 24, lumen; 25, movable bottom plate; 2501, movable upper plate; 2502, movable lower plate; 2503, center plate; 2504, sealing rubber cushion; 26, pressure relief hole; 27, cement return height hole; 28, spiral seal connection device; 29, first interface; 30, second interface. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0069] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the embodiments.

[0070] Cementing Simulation and Gas-Water Reverse Invasion Evaluation System for Complex Formations in Example 1

[0071] As Figure 1 , Figure 2 shown, the cementing simulation and gas-water reverse invasion evaluation system (hereinafter referred to as the evaluation system) includes a reactor, which includes a reactor body 23, a reactor cover 19 and a movable bottom plate 25. There is a cavity inside the reactor body 23, and the reactor body 23 is used to accommodate the reaction main body of the whole system and connect other auxiliary devices; optionally, the cross-section of the reactor body is circular, square or rectangular, preferably circular; on both sides of the reactor body 23, rotating shafts 1 are installed for connecting with a rotating device to realize the rotation of the reactor body; a reactor cover 19 is arranged on the top of the reactor body 23, and a rubber sealing ring 20 is placed inside the reactor cover 19 to seal the reactor body 23. The reactor cover 19 is connected to the reactor body 23 by six connection nuts 4 evenly distributed along the circumferential direction. An injection port 17 is arranged on the reactor cover 19. The injection port 17 is used to inject cement slurry into the lumen 24 of the casing 15 inside the reactor body. After injecting the cement slurry, the injection port 17 is connected to a high-pressure gas pump to inject high-pressure gas (also called post-positioned gas) into the lumen 24 to pressurize the cement slurry, so that the cement slurry returns to a high position and enters the cementing annulus. When the cement slurry solidifies in the cementing annulus, a cement ring 10 is formed.

[0072] A movable bottom plate 25 is slidably and sealedly arranged inside the bottom of the reactor body 23. The movable bottom plate 25 is slidably connected to the inner wall of the reactor body 23 to realize the up-and-down sliding of the movable bottom plate 25 in the reactor body by a certain distance, and the movable bottom plate 25 is sealed with the inner wall of the reactor body 23 to prevent pressure relief. As Figure 3 shown, the movable bottom plate 25 includes a movable upper plate 2501, a movable lower plate 2502, a central plate 2503 and a sealing rubber cushion layer 2504. When the movable upper plate 2501, the movable lower plate 2502 and the central plate 2503 are combined together, they form the bottom of the closed reactor body 23. For example, when the reactor body 23 is circular, both the movable upper plate 2501 and the movable lower plate 2502 are circular rings nested inside and outside, and the central plate 2503 is circular. When the three are combined, they form a complete circle; on one side where the movable upper plate 2501 and the movable lower plate 2502 are connected, there are steps respectively, and on one side where the movable lower plate 2502 and the central plate 2503 are connected, there are steps respectively. When the three are combined, the steps are buckled together. A sealing rubber cushion layer 2504 is filled between the steps of the movable upper plate 2501 and the movable lower plate 2502, and a sealing rubber cushion layer 2504 is filled between the steps of the movable lower plate 2502 and the central plate 2503, so that when the three do not move, they form a complete sealing structure, and there will be no leakage of gas or cement slurry between the steps of the movable upper plate 2501, the movable lower plate 2502 and the central plate 2503. The movable bottom plate 25 is located at the bottom end of the simulated formation 9, the casing 15 and the cement ring 10 to support the three.

[0073] As shown Figure 1 in the figure, a water-permeable bottom plate 14 is fixed to the bottom of the kettle body 23, and the water-permeable bottom plate 14 supports the hydraulic cylinders. Two sets of hydraulic cylinders 6 (the first set of hydraulic cylinders 601 and the second set of hydraulic cylinders 602) are arranged between the movable bottom plate 25 and the water-permeable bottom plate 14. Each set of hydraulic cylinders includes two hydraulic cylinders. The first set of hydraulic cylinders 601 is placed under the simulated formation 9 with the second interface 30 between the cement ring 10 and the simulated formation 9 as the boundary. The first set of hydraulic cylinders 601 is distributed on the left and right sides at the lower end of the simulated formation 9. That is, when the piston rods of the first set of hydraulic cylinders 601 move upward, they can directly lift the simulated formation 9 at the second interface 30. The first set of hydraulic cylinders 601 lifts the simulated formation 9 upward to realize the detection of the shear of the second interface. Since the simulated formation is a circular cylinder and its bottom surface is a circle, the two hydraulic cylinders of the first set of hydraulic cylinders 601 are distributed on the same diameter line of the bottom surface of the simulated formation. In this way, when the first set of hydraulic cylinders 601 lifts the simulated formation 9 upward, the forces on the left and right sides of the simulated formation 9 are relatively uniform. The second set of hydraulic cylinders 602 is placed under the cement ring 10 with the first interface 29 formed by the casing 15 and the cement ring 10 and the second interface 30 formed by the cement ring 10 and the simulated formation 9 as the boundary. The second set of hydraulic cylinders 602 is distributed on the left and right sides at the lower end of the cement ring 10. That is, when the piston rods of the second set of hydraulic cylinders 602 move upward, they can directly lift the entire cement ring. The second set of hydraulic cylinders 602 lifts the cement ring upward so that the upper end of the cement ring is squeezed by the kettle cover to realize the compression detection of the cement ring 10. Since the cement ring is a circular cylinder and its bottom surface is a circle, the two hydraulic cylinders of the second set of hydraulic cylinders 602 are distributed on the same diameter line of the bottom surface of the cement ring 10. In this way, when the second set of hydraulic cylinders 602 lifts the cement ring upward, the forces on the left and right sides of the cement ring 10 are relatively uniform.

[0074] A simulated formation 9 is arranged inside the kettle body 23. The simulated formation is used to simulate the natural formation in reality, that is, the target formation. The simulated formation 9 is a circular cylinder, and the cavity inside the simulated formation 9 is a simulated wellbore. There is an annular gap between the simulated formation 9 and the inner wall of the kettle body 23, which is called the buffer space 13. Preferably, the height of the buffer space 13 is equal to the height of the simulated formation 9. The kettle body 23 is provided with a backpressure valve interface / outlet 2, which is communicated with the buffer space 13 and is used to inject gas into the buffer space 13 or release the pressure of the buffer space 13 so as to adjust the confining pressure, and solve the problems of uneven pore distribution and pressure in the simulated formation 9 caused by the invasion of cement slurry into the simulated formation 9. Controlling the pressure of the buffer space can realize the uniform seepage process of cement slurry in the pores of the simulated formation, making the evaluation process closer to the downhole in-situ cementing process, with higher accuracy, and reducing the influence of reasons such as pressure buildup, local pressure unevenness, and excessive local pressure generated by the evaluation system itself on the seepage of cement slurry in the formation pores. A filtering device (not shown in the figure) can be arranged at the backpressure valve interface / outlet 2 to avoid blockage of the backpressure valve interface / outlet 2 and the influence of sand particles on the sealing performance of the backpressure valve. The filtering device is arranged in the buffer space and does not directly contact the simulated formation, improving the effect and extending the service life. The filtering device adopts a quick-release structure, and the filter screen and filter element can be quickly replaced.

[0075] A cement sheath 10 is arranged in the simulated wellbore. The side of the simulated formation 9 close to the cement sheath 10 is the inner side of the simulated formation 9. The inner side wall of the simulated formation 9 is the simulated wellbore ring wall. A water-soluble film 22 is arranged on the simulated wellbore ring wall. The water-soluble film 22 will gradually dissolve when it meets water. Therefore, when the cement slurry contacts the water-soluble film, it will cause the water-soluble film 22 to dissolve, and part of the cement slurry will invade the simulated formation 9. The side of the simulated formation 9 close to the kettle body 23 is the outer side of the simulated formation 9. A sand separation net 21 is arranged on the outer side wall of the simulated formation 9. Both the water-soluble film 22 and the sand separation net 21 are used to ensure the stability of the soil inside the simulated formation 9 without collapse before the simulated formation 9 reacts and combines with the cement.

[0076] A casing 15 is also provided in the simulated wellbore. The casing 15 is tubular with openings at both the upper and lower ends, and a lumen 24 is formed inside. The casing 15, the cement sheath 10, and the simulated formation 9 have the same height and are concentric circular cylinders, and their cross-sections are concentric circles. Before injecting cement, the cement sheath 10 has not been formed yet. At this time, there is an annular cavity between the casing 15 and the wall of the simulated wellbore, which is called the cementing annulus. After the cement slurry is injected from the lumen of the casing 15 and returns upward (return height means flowing from bottom to top) in the cementing annulus, the cement slurry in the cementing annulus gradually consolidates to form the cement sheath 10. The interface where the cement sheath 10 contacts the casing 15 is an interface 29, and the interface where the cement sheath 10 contacts the simulated formation 9 is an interface 30. A plastic film is provided at the interface 29 of the casing 15 (i.e., the outer surface of the casing). The plastic film is pasted on the casing 15 through vaseline. When the cement sheath 10 moves upward under force, the plastic film at the interface 29 makes the shear force between the casing 15 and the cement sheath 10 almost zero at the interface. The upper and lower ends of the casing 15 have external threads. A spiral sealing connection device 28 is provided on the kettle cover 19 corresponding to the upper end of the casing 15. The spiral sealing connection device 28 has internal threads. The central plate 2503 corresponding to the lower end of the casing 15 has internal threads. The upper end of the casing 15 is hermetically connected to the kettle cover 19 through thread fitting, and the lower end of the casing 15 is hermetically connected to the central plate 2503. Four cement return height holes 27 are circumferentially distributed on the casing wall near the movable bottom plate 25 for the cement to return height. The four cement return height holes 27 are evenly spaced and are distributed on the casing wall at an equal distance from the movable bottom plate, so as to make the cement slurry returning height in the whole cementing annulus uniform. The injection port 17 is directly opposite to the lumen 24 of the casing 15, so that the cement slurry is first injected into the lumen 24, and then enters the cementing annulus through the cement return height holes 27.

[0077] As Figure 4 、 Figure 5 shown, there is a columnar lumen 24 in the center of the casing 15 for injecting cement slurry. The tube body of the casing 15 has a sandwich layer, which means a space is formed between the inner wall and the outer wall of the tube body. The acoustic logging probes 16 are evenly embedded and distributed in the sandwich layer of the tube body of the casing 15. The acoustic logging data lines 18 are signal-connected to the acoustic logging probes 16, and the acoustic logging data lines 18 are placed outside the sandwich layer of the casing 15. This setting method can solve the problem that it is difficult to place the acoustic logging probes 16 and their data lines after the kettle cover is sealed in general. The acoustic logging probes 16 are used to detect the quality of the cement sheath by acoustic waves; As Figure 7As shown in the figure, several acoustic logging probes 16 are connected in parallel and then connected to the acoustic logging data line 18 to form a set of acoustic logging probes, and the data is transmitted by the acoustic logging data line 18. The setting method of the embedded acoustic logging probe mainly considers that after the post-positioned gas propulsion, it will conflict with the acoustic logging probe arranged inside the casing cavity, and it is very easy to damage the sealing condition inside the reactor body when directly arranging the acoustic logging probe in the pipe cavity 24. Therefore, the acoustic logging probe is embedded inside the casing jacket, and the data in the acoustic logging probe is exported and analyzed by the data line. And a set of acoustic logging probes is embedded every 90° inside the casing. Four sets of acoustic logging probes are distributed in a ring, and a complete acoustic logging system is formed with 360° full coverage. The acoustic logging probe is quickly detachable and sealed from the outer wall of the casing. It can realize the detection of the cement sheath bonding condition in different hydration periods, return the acoustic wave data, and be used to analyze the cement sheath bonding quality. The design strength of the casing meets the influence of the cementing of the first and second interfaces and the cement sheath strength test process. A wire hole is provided in the kettle spiral seal connecting device 28 to meet the connection between the acoustic logging data line 18 and the acoustic logging probe inside the kettle body, and the spiral seal connecting device 28 and the acoustic logging data line 18 are sealed.

[0078] As Figure 1 shown, a small pressure relief hole 26 is opened at one end of the inner wall of the casing 15 close to the kettle cover 19. The pressure relief hole 26 connects the pipe body sandwich layer and the pipe cavity 24 of the casing 15 to balance the extrusion effect of the internal pressure of the reactor body on the sandwich layer of the casing 15. Since the pressure relief hole 26 is close to the kettle cover 19 and is set at a relatively high position, the cement slurry will not block the pressure relief hole 26 when injecting the cement slurry into the casing 15, and the cement slurry will not enter the sandwich layer of the casing 15 from the pressure relief hole 26.

[0079] As Figure 6As shown, the evaluation system further includes a gas detection device and a visualization imaging device for anti-invasion monitoring. The gas detection device includes seven probes (temperature probe 801, five temperature and pressure probes 802, and pressure probe 803). The temperature probe 801 is arranged inside the cement sheath. The five temperature and pressure probes 802 are arranged side by side in the simulated formation 9. The pressure probe 803 is arranged in the buffer space 13. The visualization imaging device includes a glass tube 11 and an imaging probe 12. Both ends of the glass tube 11 are open. The glass tube 11 penetrates through the buffer space 13 and the simulated formation 9, such that the inner port of the glass tube 11 faces the second interface 30 directly. The outer port of the glass tube extends to and is hermetically connected to the autoclave body 23. The glass tube 11 forms a visualization window through which the changes in the simulated formation can be directly observed with the naked eye. An imaging probe 12 is installed near the inner end of the glass tube 11 to achieve visualization imaging of the second interface 30. The visualization imaging device reaches deep into the simulated formation to the second interface. Cooperating with imaging probes of different precisions, a series of processes such as the hydrate formation process in the pores of the simulated formation, the seepage invasion process of the cement slurry in the pores of the simulated formation, the decomposition process of hydrates due to hydration heat, the process of high-pressure gas and water pushing back the cement slurry decomposed from hydrates, and the critical state of high-pressure gas and water invading the cement slurry from the pores of the simulated formation can be observed in real time. The prior art mainly determines the critical conditions for high-pressure gas and water to invade the cement slurry through numerical simulation methods. There are very few experimental research methods, and no visualization means through direct observation has been found so far. During the evaluation process of the present invention, an anti-fogging solution can be sprayed on the inner and outer surfaces of the glass tube 11 to prevent hydrates from aggregating and forming at the interface. The main components of the anti-fogging solution do not affect the hydrate phase equilibrium. In the present invention, the imaging probe is directly arranged at the second interface, and the imaging probe is arranged through the glass tube. Since the glass tube and the autoclave body are connected by a soft seal (such as a rubber seal), and the distance that the simulated formation is lifted by the cylinder is small, the cylinder will not damage the glass tube. The gas detection device arranges temperature and pressure probes at different diameters and depths in the simulated formation, and the decomposition situation of hydrates in the simulated formation can be judged through the temperature and pressure change data, which is used to evaluate the gas and water anti-invasion index. Moreover, the temperature probe arranged inside the cement sheath can monitor the cement temperature in real time, and the pressure probe arranged in the buffer space can monitor the equilibrium pressure in the simulated formation in real time, which is used to study the decomposition of hydrates under different cement heat release temperature and pressure conditions.

[0080] As Figure 1 、 Figure 7As shown, a gas-liquid inlet 5 is provided at the upper part of the kettle body 23. The gas-liquid inlet 5 penetrates through the kettle cover and extends to the upper end of the simulated formation 9. A gas-liquid outlet 3 is provided at the lower part of the kettle body 23. The gas-liquid outlet 3 is a telescopic pipe. One end of the gas-liquid outlet 3 penetrates through the movable bottom plate 25 and extends to the lower end of the simulated formation 9. And the gas-liquid inlet 5 is directly above the gas-liquid outlet 3. The gas-liquid inlet 5 can be used to inject methane and pore water into the simulated formation to generate hydrates in the simulated formation, and the excess methane and pore water are discharged through the lower gas-liquid outlet 3. In addition, high-pressure nitrogen is injected into the simulated formation through the gas-liquid inlet 5 to adjust the pore pressure in the simulated formation, so that the cement slurry pressure is only slightly higher than the pore pressure of the simulated formation (the pressure detected by the pressure probe 803 in the buffer space represents the pore pressure of the simulated formation) until the cement slurry is fully cured. A liquid and gas discharge port 7 is provided at the upper part of the kettle body 23, and one end of the liquid and gas discharge port 7 extends into the cementing annulus, which is mainly used for circulating and discharging the cement slurry. The liquid and gas discharge port 7 can be a pipe, with threads provided at its outer end, and threaded holes provided on the kettle cover 19. The liquid and gas discharge port 7 penetrates through the kettle cover and is threadedly and sealedly connected to the kettle cover. The gas-liquid inlet 5 is sealedly connected to the kettle cover 19 in the same way. After the cement slurry is injected into the lumen 24, high-pressure gas is injected into the lumen through the injection port 17. The high-pressure gas causes the cement slurry to return to a higher level in the cementing annulus. During the return process, the gas in the cementing annulus is discharged from the liquid and gas discharge port 7. After the return is completed, the excess cement slurry is discharged from the liquid and gas discharge port 7. In addition, the drilling fluid generated during well washing is also discharged from the liquid and gas discharge port 7.

[0081] The evaluation system requires the cooperation of a water bath constant temperature device and a rotating device (both are not shown in the figure). By placing the entire evaluation system in the water bath constant temperature device, the temperature of the evaluation system can be controlled. The kettle body 23 is connected to the rotating device through a rotating shaft 1, and the kettle body 23 is driven to rotate by the rotating device to achieve the purpose of rotating the simulated formation 9, so that the distribution of pore water in the simulated formation 9 can be made uniform. The rotating device can adopt any existing equipment that can be connected to the rotating shaft 1 and drive the kettle body 23 to rotate.

[0082] The evaluation system mainly evaluates the bonding strength through two groups of hydraulic cylinders. One group is placed under the simulated formation with the secondary interface between the cement sheath and the simulated formation as the boundary, used to shear the secondary interface and evaluate the bonding strength of the secondary interface. One group is placed under the cement sheath with the primary interface and secondary interface formed by the casing and the cement sheath as the boundary, used to compress the cement sheath and evaluate the compressive strength of the cement sheath. Usually, the secondary interface is sheared first, and then the cement sheath is compressed by lifting the hydraulic cylinder. This evaluation system not only comprehensively evaluates the bonding strength of the secondary interface of cementing and the compressive strength of the cement sheath, but also the test is carried out under the temperature and pressure conditions of the in-situ formation downhole, and the result is closer to the actual situation. Compared with the results of the tests carried out at room temperature and atmospheric pressure, it can more accurately reflect the actual cementing quality.

[0083] Example 1 Cementing in an anhydrous hydrate formation

[0084] Experimental steps for cementing in anhydrate formation:

[0085] To reduce variables in the experiment, when preparing the cement slurry, ensure that the mixing time and rotation speed of the solid-liquid mixture are the same for each experiment.

[0086] (0) Selection of target formation:

[0087] Select the GMGS3-W19 well site in the Baiyun Sag of the Pearl River Mouth Basin as the target well, and the hydrate formation in the well as the target layer. According to the logging and downhole in-situ core testing results of the target formation, the water depth at this well site is 1273.6 m, and the seabed temperature is about 4°C. The main components of the hydrate formation are quartz sand and clayey fine-grained sediments. The temperature of the hydrate layer is 14.46°C, the formation pressure is 14.68 MPa, and the average porosity is 0.4.

[0088] (1) Preparation stage:

[0089] Preparation of skeleton materials. According to the test data of downhole in-situ core sampling of the target formation, select natural quartz sand with a matching particle size as the porous medium for simulating the formation skeleton. According to the previous experimental results, select natural quartz sand with a particle size of 10-60 mesh, then wash the natural quartz sand with distilled water 2-3 times until there are no obvious impurities in the water, and finally perform a drying treatment to obtain the simulated formation skeleton material.

[0090] Preparation of the simulated formation. Divide the cleaned quartz sand, anhydrous calcium chloride, sodium silicate, and sodium-based bentonite into three equal parts according to the required mass and stir evenly, then add them to the reaction kettle in three batches and in sequence. In the present invention, sodium-based bentonite with montmorillonite as the main component is used to simulate the clayey fine-grained sediments in the in-situ formation; during the process of adding to the reaction kettle, install a gas detection device and a visualization imaging device, and finally apply uniform pressure along the axial direction of the reaction kettle and maintain for the required time. During the preparation process, the uniformity of the pores can be improved by multiple batches of loading and pressing, and the joint surface can be made rough during adjacent filling times to prepare the simulated formation 9.

[0091] Physical property test (porosity of the simulated formation). Use the drainage method to test the porosity of the simulated formation. When the porosity of the simulated formation is relatively close to the average porosity of the target formation (close means that the difference between the porosity of the simulated formation and the "average porosity of the target formation") / the average porosity of the target formation < 10%), it indicates that the working conditions of the simulated formation 9 are consistent with those of the target formation; when the working conditions of the simulated formation 9 are consistent with those of the target formation, proceed to the next step. If not, apply uniform pressure along the axial direction of the reaction kettle to adjust the porosity of the simulated formation until it meets the requirements.

[0092] Air tightness inspection of the reactor. A water-soluble film 22 is arranged inside the simulated formation 9, and a sand separation net 21 is arranged outside it to prevent damage to the simulated formation and prevent sand from invading the buffer space 13. Immediately install a rubber sealing ring 20 on the kettle cover 19 and perform pre-tightening treatment on the contact area of the kettle cover to ensure that the height of the simulated formation 9 is not lower than the lower edge of the upper rubber sealing ring 20. Seal the reactor with the kettle cover 19. The pre-tightening treatment methods include but are not limited to pressing the upper end of the simulated formation 9 by hand or an object. Inject nitrogen into the reactor to 15 MPa and maintain the pressure for 12 h, and observe whether the pressure of the reactor changes. If there is no change, the air tightness of the reactor is good. If it is observed that the pressure changes significantly, it means that the air tightness of the reactor is not good, and the reactor needs to be resealed until the air tightness of the reactor is good.

[0093] Simulate and maintain the target formation temperature. After the physical property test of the simulated formation 9 and the air tightness inspection of the reactor, install the kettle cover 19, and install the casing 15 on the kettle cover 19, and fasten the kettle cover 19 and the kettle body 23 through the connecting nut 4. Among them, the outside of the casing 15 is first coated with a sufficient amount of vaseline, and then tightly wound with a plastic film around the outside of the casing to reduce the friction between the first interface 29 and the cement sheath 10, so that the cement sheath 10 and the casing 15 are completely separated in the subsequent shearing stage, and there is almost no shearing force on the first interface. Then install the kettle body 23 on the rotating device through the rotating shaft 1, and lift the water bath constant temperature device to submerge the reactor. The temperature probe in the reactor monitors the temperature of the simulated formation 9 in real time. When the temperature of the simulated formation reaches the target formation temperature condition (i.e., 4 °C), proceed to the next step.

[0094] (2) Cementing stage:

[0095] Cement slurry preparation. Prepare the cement slurry required for the experiment according to the operating specifications of the standard "Test Methods for Oil Well Cement" (GB / T 19139-2012).

[0096] Overbalanced cementing. Inject the prepared cement slurry into the casing 15 through the cement pump until the top of the pipe cavity, and strictly control the injection time and rate. The entire injection and pressure maintenance process adopts overbalanced cementing (the pressure of the cement slurry is slightly greater than the pressure of the buffer space 13). After all the cementing slurry is injected, a certain cementing pressure difference is still maintained to make the cement slurry slightly invade the wall of the simulated wellbore. Inject high-pressure nitrogen into the simulated formation through the gas-liquid inlet 5 and inject high-pressure nitrogen into the buffer space 13 to make the pressure of the cement slurry only slightly higher than the pore pressure of the simulated formation (the pressure of the buffer space 13 represents the pore pressure of the simulated formation, and the difference between the pressure of the cement slurry and the pore pressure of the simulated formation is less than or equal to 1 MPa, the same below) until the cement slurry is fully cured.

[0097] Maintain the simulated formation temperature and pressure conditions. According to the pressure data obtained from the temperature and pressure probe 802 in the simulated formation 9 and the pressure probe 803 in the buffer space 13, constantly monitor and timely adjust the air pressure in the buffer space 13 to balance the cementing differential pressure generated by the intrusion of the cement slurry into the simulated wellbore annulus wall during the cementing pressure maintenance process. During the entire experiment, maintain the temperature and pressure conditions of the simulated formation in the autoclave unchanged.

[0098] Post-treatment. After the injection of the cement slurry is completed, quickly close the autoclave. Since the initial setting time of the prepared cement slurry is relatively short, in order to ensure that the system is not damaged after the experiment, the following procedures need to be completed: close the cement pump and connect the high-pressure gas pump to the injection port 17, and pump high-pressure gas into the casing lumen to achieve the purpose of pushing the cement slurry back up and removing the residual cement slurry on the pipe wall.

[0099] (3) Experiment and result analysis:

[0100] Real-time observation of the intrusion amount of the cement slurry. Through the imaging probe 12 in the window of the glass tube 11, the morphological changes of the second cementing interface and the degree of intrusion of the cement slurry into the simulated wellbore annulus wall during the cement curing process can be observed in real time. The inside of the simulated formation can be directly observed through the wall of the glass tube 11.

[0101] Real-time monitoring of the temperature and pressure changes in the simulated formation. During the cementing process in the simulated formation 9, the temperature and pressure changes of the simulated formation 9 and the cement sheath 10 are monitored in real time through the gas detection device. This data can also be used as a cementing quality evaluation standard through experimental comparison.

[0102] Acoustic logging. After the cement slurry is fully cured, start the acoustic logging probe embedded in the casing 15 to emit acoustic waves, and the receiver converts acoustic waves of different frequencies into data. Through data analysis, the cementing quality of the second interface can be obtained.

[0103] In-situ test of the cementing strength of the second interface. Start the first group of hydraulic cylinders 601 to lift the simulated formation 9 at a constant speed of 0.5 mm / s, record the pressure changes of the first group of hydraulic cylinders 601, and calculate the shear strength; return the first group of hydraulic cylinders to their original positions, restart the first group of hydraulic cylinders 601 to lift the simulated formation 9 at a constant speed of 0.5 mm / s, record the pressure changes of the first group of hydraulic cylinders 601, and calculate the shear strength; compare the two shear strengths, and the difference between the two shear strengths is the cementing strength of the second interface.

[0104] In-situ test on the compressive strength of the cement sheath. After the shear at the second interface is completed, the cement sheath 10 is completely separated from both sides (due to the effect of vaseline and plastic film at the first interface, it can be approximately considered that there is no shear force between the first interface and the cement sheath 10, that is, the first interface and the cement sheath are already separated). Start the second group of hydraulic cylinders 602 to lift the cement sheath 10 at a constant speed of 0.5 mm / s, so that the cement sheath is compressed by the kettle cover, record the pressure change of the second group of hydraulic cylinders 602, and calculate the compressive strength of the cement sheath 10.

[0105] Pressure relief and cleaning. After the experiment is completed, relieve the confining pressure, the pressure in the kettle body, and the hydraulic pressure of the hydraulic cylinder 6 in the buffer space 13, open the kettle cover 19, and remove the simulated formation 9 and the cement sheath 10.

[0106] Analyze the experimental results.

[0107] Example 2: Cementing in hydrate-bearing formations

[0108] Experimental steps for cementing in hydrate-bearing formations:

[0109] To reduce the variables in the experiment, during the hydrate synthesis experiment, to ensure the same amount of hydrate synthesis, accurately control the initial temperature and pressure conditions, the methane input rate, and the reaction duration each time, and keep them consistent; when preparing the cement slurry, it is also necessary to ensure that the time and speed of solid-liquid mixing to stirring are consistent.

[0110] (0) Selection of the target formation:

[0111] Select the GMGS3-W19 well site in the Baiyun Sag of the Pearl River Mouth Basin as the target well, and the hydrate-bearing formation in the well is the target layer. According to the logging and downhole in-situ core test results of the target formation: the water depth at this well site is 1273.6 m, the seabed temperature is about 4 °C. The main components of the hydrate-bearing formation are quartz sand and clayey fine-grained sediments. The temperature of the hydrate layer is 14.46 °C, the formation pressure is 14.68 MPa, and the average porosity is 0.4.

[0112] (1) Preparation stage:

[0113] Preparation of the skeleton material. According to the test data of the downhole in-situ core of the target formation, select natural quartz sand with a matching particle size as the porous medium for the simulated formation skeleton. According to the previous experimental results, select natural quartz sand with a particle size of 10-60 mesh, then wash the natural quartz sand with distilled water 2-3 times until there are no obvious impurities in the water, and finally perform a drying treatment to obtain the simulated formation skeleton material.

[0114] Prepare a simulated formation. Divide anhydrous calcium chloride, sodium silicate, sodium-based bentonite, and cleaned quartz sand into three equal parts according to the required mass, stir evenly, and then add them to the reaction kettle in three batches. In the present invention, sodium-based bentonite mainly composed of montmorillonite is used to simulate clayey fine-grained sediments in the in-situ formation; during the process of adding to the reaction kettle, install a gas detection device and a visualization imaging device, and finally apply uniform pressure along the axial direction of the reaction kettle and maintain for the required time. During the preparation process, the uniformity of pores can be improved by multiple batch loading and manual pressing, and the joint surface can be made rough during adjacent filling times to prepare the simulated formation 9.

[0115] Physical property test (porosity of the simulated formation). Use the drainage method to test the porosity of the simulated formation. When the average value of the porosity of the simulated formation and the target formation is relatively close (close means that the difference between the porosity of the simulated formation and the average value of the "porosity of the target formation") / the average value of the porosity of the target formation < 10%), it indicates that the working conditions of the simulated formation 9 and the target formation are in line; when the working conditions of the simulated formation 9 and the target formation are in line, proceed to the next step. If not, apply uniform pressure along the axial direction of the reaction kettle to adjust the porosity of the simulated formation until it meets the requirements.

[0116] Air tightness inspection. A water-soluble film 22 is arranged inside the simulated formation 9 to prevent formation damage, and a sand separation net 21 is arranged outside it to prevent formation damage and prevent sand from invading the buffer space 13. Immediately install a rubber sealing ring 20 on the kettle cover 19 and perform pre-tightening treatment on the contact area to ensure that the height of the simulated formation 9 is not lower than the lower edge of the upper rubber sealing ring 20. Inject nitrogen into the reaction kettle to 15 MPa and maintain the pressure for 12 h, and observe whether the pressure of the reaction kettle changes. If there is no change, the air tightness of the reaction kettle is good. After the air tightness is good, release the nitrogen, and then drain the nitrogen in the reaction kettle by injecting 2 MPa of methane.

[0117] Simulate and maintain the target formation temperature. After the simulated formation 9 passes the physical property test and air tightness inspection, install the kettle cover 19 and install the casing 15 on the kettle cover 19, and fasten the kettle cover 19 to the kettle body 23 through the connecting nut 4. Among them, the outside of the casing 15 is first coated with sufficient vaseline, and then tightly wound with a plastic film around the outside of the casing to reduce the friction between the interface 29 and the cement sheath 10, so that the cement sheath 10 and the casing 15 are completely separated in the subsequent shear stage, and there is no shear force at the interface. Then place the kettle body 23 on the rotating device of the rotating shaft 1, and lift the water bath constant temperature device to submerge the reaction kettle. The temperature probe in the reaction kettle monitors the temperature of the simulated formation 9 in real time. When the temperature of the simulated formation reaches the target formation temperature condition (i.e., 4 °C), proceed to the next step.

[0118] (2) Hydrate formation stage:

[0119] Inject water and methane. After the simulated formation temperature reaches 2°C, methane is injected through the gas-liquid inlet 5 to make the internal pressure of the reactor reach 8 MPa, and pore water (500 ml) is added by the immersion and drainage method. Then, the reactor is slowly rotated by the rotating device to make the pore water evenly distributed, reducing the influence of gravity on the distribution of pore water. Close the reactor and keep the water bath temperature condition outside the reactor unchanged. After the temperature and pressure inside the reactor are stable, it is regarded that the hydrate formation is completed. Then, adjust the simulated formation pore pressure and temperature to 14.68 MPa and 14.46°C respectively, which is the same as the in-situ hydrate formation.

[0120] (3) Cementing stage:

[0121] Well flushing process. Pump the prepared drilling fluid into the casing through the injection port 17, strictly control the injection time and rate. After the drilling fluid completes the well flushing process, apply air pressure at the injection port 17 to discharge the drilling fluid evenly from the liquid and gas discharge port 7 at the injection rate.

[0122] Cement slurry preparation. Prepare the cement slurry required for the experiment according to the operating specifications of the standard "Test Method for Oil Well Cement" (GB / T 19139 - 2012).

[0123] Overbalanced cementing. Inject the prepared cement slurry into the casing 15 through the cement pump until the top of the pipe cavity, strictly control the injection time and rate. The entire injection and pressure holding process adopts overbalanced cementing. After all the cementing slurry is injected, still maintain a certain cementing differential pressure to make the cement slurry slightly invade the simulated wellbore annulus wall. Inject high-pressure nitrogen through the gas-liquid inlet 5 to make the pressure of the cement slurry only slightly higher than the pore pressure of the simulated formation until the cement slurry is fully cured.

[0124] Maintain the simulated formation temperature and pressure conditions. According to the pressure data obtained from the temperature and pressure probes 802 in the simulated formation 9 and the pressure probe 803 in the buffer space 13, always pay attention to and adjust the air pressure in the buffer space 13 to balance the cementing differential pressure generated by the invasion of the cement slurry into the simulated wellbore annulus wall during the cementing pressure holding process. During the whole experiment, maintain the temperature and pressure conditions of the simulated formation inside the reactor unchanged.

[0125] Post-treatment. After the cement slurry injection is completed, quickly close the reactor. Since the initial setting time of this cement is short, in order to ensure that the system is not damaged after the experiment, the following processes need to be completed: turn off the cement pump and connect the high-pressure gas pump to the injection port 17, and pump high-pressure gas into the casing pipe cavity to achieve the purpose of pushing the cement slurry back up and removing the residual cement slurry on the pipe wall.

[0126] (4) Experiment and result analysis:

[0127] Monitoring of gas-water reverse invasion. Since hydrates can only be generated and stably exist within a very narrow temperature-pressure window, the heat of hydration released by the cement slurry hydration will cause the decomposition of hydrates. The decomposition of one unit of hydrate will produce more than 140 units of free gas and water, and these free gas and water will invade the well cement slurry under the action of pressure difference. The system monitors the temperature and pressure changes in the autoclave in real time through 7 temperature and pressure probes. Among them, a temperature probe 801 is installed in the cement sheath 10, a pressure probe 803 is installed in the buffer space 13, and 5 temperature-pressure probes 802 are installed in the simulated formation 9. These temperature and pressure probes can capture the temperature and pressure data in the autoclave. In the result analysis, these temperature and pressure change data will be used as the basis to judge the decomposition situation of hydrates in the simulated formation 9 and whether gas-water reverse invasion occurs.

[0128] Analysis of heat release during cement slurry hydration. The temperature probe 801 in the cement sheath 10 can monitor the temperature change of the cement sheath in real time, while the pressure probe 803 in the buffer space 13 can monitor the change of the equilibrium pressure in the simulated formation 9 in real time. The two can be used to study and analyze the influence of the heat release temperature of cement on the decomposition degree of hydrates and the equilibrium pressure.

[0129] Real-time observation of the intrusion amount of cement slurry. The imaging probe 12 in the glass tube 11 can be used to observe the morphological changes at the second interface during the cement solidification process and the degree of cement slurry intrusion into the simulated wellbore wall in real time. The glass tube 11 can directly observe the simulated formation.

[0130] Real-time monitoring of temperature and pressure changes in the simulated formation. During the well cementing process in the simulated formation 9, the temperature and pressure changes of the simulated formation 9 and the cement sheath 10 are monitored in real time through a gas detection device. Through experimental comparison, this data can also be used as a standard for evaluating well cementing quality.

[0131] Acoustic logging. After the cement slurry is fully solidified, start the acoustic logging probe embedded in the casing 15 to emit acoustic waves, and the receiver converts acoustic waves of different frequencies into data. Through data analysis, the cementing quality of the second interface can be obtained.

[0132] In-situ test of the cementing strength of the second interface. Start the first group of hydraulic cylinders 601 to lift the simulated formation 9 at a constant speed of 0.5 mm / s, record the pressure change of the first group of hydraulic cylinders 601, and calculate the shear strength; return the first group of hydraulic cylinders to their original positions, restart the first group of hydraulic cylinders 601 to lift the simulated formation 9 at a constant speed of 0.5 mm / s, record the pressure change of the first group of hydraulic cylinders 601, and calculate the shear strength; compare the two shear strengths, and the difference between the two shear strengths is the cementing strength of the second interface.

[0133] In-situ test on the compressive strength of the cement sheath. After the shear at the second interface is completed, the cement sheath 10 is completely separated from both sides (due to the effect of vaseline and plastic film, the first interface can be approximately regarded as having no shear force with the cement sheath 10, that is, the first interface is already separated from the cement sheath). Start the second set of hydraulic cylinders 602 to compress the cement sheath 10 at a uniform speed of 0.5 mm / s, so that the cement sheath is compressed by the kettle cover, record the pressure change of the second set of hydraulic cylinders 602, and calculate the compressive strength of the cement sheath 10.

[0134] Pressure relief and cleaning. After the experiment is completed, relieve the confining pressure in the buffer space 13, the pressure in the kettle body, and the hydraulic pressure of the hydraulic cylinders 6, open the kettle cover 19, and remove the simulated formation 9 and the cement sheath 10.

[0135] Analyze the experimental results.

[0136] Although the present invention has been described here with reference to the illustrative embodiments of the present invention, it should be understood that those skilled in the art can design many other modifications and embodiments that will fall within the scope and spirit of the principles disclosed in this application.

Claims

1. A cementing simulation and gas-water reverse invasion evaluation system for complex formations, characterized in that It includes a reactor. A simulated formation (9) is arranged inside the reactor body (23), and a buffer space (13) is arranged between the simulated formation (9) and the inner wall of the reactor body (23); inside the simulated formation (9), a cement sheath (10) and a casing (15) are sequentially arranged, and the three are concentric circular cylinders; a movable bottom plate (25) is arranged inside the reactor body (23), and the reactor cover (19) and the movable bottom plate (25) respectively seal the upper and lower ends of the reactor body (23), and the movable bottom plate (25) supports the simulated formation (9), the cement sheath (10) and the casing (15); the upper end of the casing (15) is hermetically connected to the reactor cover (19), and the lower end of the casing (15) is hermetically connected to the movable bottom plate (25). Two groups of hydraulic cylinders (6) are arranged below the movable bottom plate (25). The first group of hydraulic cylinders (601) is arranged below the simulated formation (9); the second group of hydraulic cylinders (602) is arranged below the cement sheath (10). The casing (15) has a pipe cavity (24). Cement return height holes (27) are arranged at the lower part of the casing (15), and the cement return height holes (27) communicate with the cementing annulus where the cement sheath (10) is located. An acoustic logging probe (16) is arranged inside the reactor. A gas detection device is arranged inside the reactor. The gas detection device includes probes for detecting temperature and / or pressure distributed in the cement sheath, the simulated formation and the buffer space. Pipes are arranged in the buffer space (13), the pipe cavity (24), the cementing annulus and the simulated formation. The pipe body of the casing (15) has a sandwich layer. The acoustic logging probes (16) are evenly embedded and distributed in the sandwich layer of the pipe body of the casing (15). The acoustic logging data line (18) is signal-connected to the acoustic logging probe (16), and the acoustic logging data line (18) is arranged outside the sandwich layer of the casing (15). A pressure relief hole (26) is opened at one end of the inner wall of the casing (15) close to the reactor cover (19), and the pressure relief hole (26) communicates the sandwich layer of the casing (15) and the pipe cavity (24) of the casing (15).

2. The complex formation cementing simulation and gas-water reverse invasion evaluation system according to claim 1, characterized in that The probes for detecting temperature and / or pressure are one temperature probe (801), five temperature and pressure probes (802), and one pressure probe (803). The temperature probe (801) is arranged inside the cement sheath, the five temperature and pressure probes (802) are arranged side by side in the simulated formation (9), and the pressure probe (803) is arranged in the buffer space (13).

3. The cementing simulation and gas-water reverse invasion evaluation system for complex formations according to claim 1, wherein A visualization imaging device is arranged inside the reactor. The visualization imaging device includes a glass tube and an imaging probe (12) for imaging the second interface (30). Both ends of the glass tube (11) are open. The glass tube (11) penetrates through the buffer space (13) and the simulated formation (9) so that the inner port of the glass tube (11) faces the second interface (30) directly, and the outer port of the glass tube extends to the reactor body (23) and is hermetically connected to the reactor body (23); the imaging probe (12) is installed inside the glass tube (11).

4. The cementing simulation and gas-water back-invasion evaluation system for complex formations according to claim 1, wherein The movable bottom plate (25) includes a nested movable upper plate (2501), a movable lower plate (2502), and a central plate (2503). When the movable upper plate (2501), the movable lower plate (2502), and the central plate (2503) are combined together, they form the bottom of the closed kettle body (23). The joints of the movable upper plate (2501), the movable lower plate (2502), and the central plate (2503) are filled with a sealing rubber cushion layer (2504).

5. The complex formation cementing simulation and gas-water reverse invasion evaluation system according to claim 4, characterized in that Each group of the hydraulic cylinders includes two hydraulic cylinders. The first group of hydraulic cylinders (601) is placed under the simulated formation (9) with the two-interface (30) as the boundary. The two hydraulic cylinders of the first group of hydraulic cylinders (601) are distributed on the left and right sides at the lower end of the simulated formation (9); the second group of hydraulic cylinders (602) is placed under the cement sheath (10) with the one-interface (29) and the two-interface (30) as the boundary. The two hydraulic cylinders of the second group of hydraulic cylinders (602) are distributed on the left and right sides at the lower end of the cement sheath (10).

6. The cementing simulation and gas-water reverse invasion evaluation system for complex formations according to any one of claims 1 to 5, characterized in that A water-soluble film (22) is provided on the inner side wall of the simulated formation (9), and a sand separation net (21) is provided on the outer side wall of the simulated formation (9); a plastic film is pasted on the outer surface of the casing (15).

7. The cementing simulation and gas-water reverse invasion evaluation system for complex formations according to claim 6, characterized in that A rotating shaft (1) is installed on the kettle body (23), and the rotating shaft (1) is used to connect with a rotating device to realize the rotation of the kettle body.

8. A method for simulating cementing in complex formations and evaluating gas and water back-invasion, characterized in that, Using the system according to any one of claims 1 to 7, includes the following steps: (1) Preparation stage: Prepare the simulated formation in the reaction kettle and install a gas detection device and a visualization imaging device; set the water-soluble film and the sand separation net; Adjust the porosity of the simulated formation until the difference between the porosity of the simulated formation and the "average value of the target formation porosity" / the average value of the target formation porosity < 10%; Apply vaseline on the outside of the casing and wind the plastic film, then install it on the kettle cover and reseal the reaction kettle; Perform water bath temperature control on the kettle body until the temperature of the simulated formation reaches the target formation temperature; (2) Hydrate formation stage: Inject methane and pore water into the simulated formation, rotate the reaction kettle to make the pore water evenly distributed, and keep the water bath temperature condition outside the kettle body unchanged until hydrates are formed; (3) Cementing stage: After washing the well, inject the cement slurry into the casing, close the reaction kettle, and push the cement slurry back to the top; Use the method of injecting nitrogen into the simulated formation to make the pressure of the cement slurry higher than the pressure of the buffer space, and keep the pressure until the cement slurry solidifies; (4) Obtain experimental data: Obtain the temperature and pressure inside the reaction kettle through a temperature and / or pressure probe; Observe the two-interface through an imaging probe; After the cement slurry solidifies, start the acoustic logging probe to emit acoustic waves, and the receiver obtains the acoustic waves; then start the first group of hydraulic cylinders to lift the simulated formation twice, record the pressure changes of the first group of hydraulic cylinders twice, calculate the two shear strengths through the pressure changes, obtain the difference between the two shear strengths, and use it as the shear strength of the two-interface; finally, start the second group of hydraulic cylinders to compress the cement sheath, and record the pressure changes of the second group of hydraulic cylinders as the compressive strength of the cement sheath.

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