Complex formation well cementation simulation and gas-water anti-invasion evaluation method and evaluation system

Abstract

The invention discloses a complex stratum well cementation simulation and gas-water anti-invasion evaluation method and system, and relates to the petroleum and natural gas extraction technology, the evaluation system is provided with a simulated stratum, a buffer space, a cement sheath, a sleeve and a movable bottom plate, and two groups of hydraulic cylinders are arranged below the movable bottom plate to respectively test the shearing force of two interfaces and the compressive strength of the cement sheath; the casing pipe is provided with a pipe cavity and a cement height-returning hole, and a cement sheath is formed after cement height-returning solidification; and an acoustic logging probe and a gas detection device are arranged in the reaction kettle. The evaluation method adopts the evaluation system for evaluation. According to the evaluation system and the evaluation method, the target stratum can be simulated more accurately, the shearing force of the two interfaces and the compressive strength of the cement sheath can be tested, and the visualization mode is more convenient.

Description

Technical Field

[0001] The invention relates to oil and natural gas exploitation technology, and in particular to a complex formation cementing simulation and gas-water anti-invasion evaluation method and evaluation system. Background Art

[0002] The extraction of oil and natural gas requires a series of complex processes, including drilling, cementing, completion, perforation, water injection, oil production, etc. Cementing is an important process in the energy extraction process. It plays an important role in providing protection and support for the casing and effectively isolating adjacent strata. Especially in deepwater oil and gas exploration and development, the quality of cementing directly determines the life of the production well, 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 oil fields, so the evaluation of cementing quality is very necessary.

[0003] The key to cementing quality lies in the bonding quality of the two interfaces, which mainly includes bonding strength and interlayer isolation capacity. At present, the methods for evaluating the bonding quality of the two interfaces can be summarized into two categories, namely the on-site logging evaluation method and the interface bonding strength evaluation method of the indoor experiment. The interface bonding strength evaluation method of the indoor experiment 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 ring (the contact surface between the cement ring and the simulated formation is the two interfaces); the bonding strength of the two interfaces is characterized by the shear strength measured by the shear behavior parallel to the two interfaces, and at the same time, the interlayer isolation capacity is characterized by the permeability of the two interfaces between the cement slurry and the simulated formation.

[0004] Deepwater oil and gas resources are widely distributed, including coastal continental shelf areas. At the same time, hydrates are also widely distributed in shallow marine sediments. The geographical locations of the two are highly overlapped, 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 a challenge to cementing operations. During the cementing process, the heat released by cement slurry hydration will cause the decomposition of hydrates in the simulated wellbore annulus wall, producing high-pressure free gas and water. These high-pressure free gas and water are very easy to intrude into the cement slurry (i.e., gas-water intrusion), seriously affecting the mechanical strength of the cement ring and the sealing performance of the cementing interface, and even leading to cementing scrapping and wellbore instability, causing safety accidents such as blowouts. In order to prevent the occurrence of gas-water intrusion, it is very important to determine the critical conditions of gas-water intrusion under different geological conditions and cementing process conditions. By simulating and analyzing the physical property response of hydrate formations under different geological conditions and cementing process conditions and the law of high-pressure gas-water invasion, and evaluating the influence of gas-water invasion on cementing quality such as the mechanical and impermeability properties of cement sheath and two interfaces, theoretical guidance and basis can be provided for cementing scheme design and cementing process parameter optimization. Therefore, in the process of evaluating the interface bonding strength of indoor experiments, pore water and methane gas should be injected into the simulated formation to form hydrates so that the simulated formation is closer to the natural formation containing hydrates. However, due to the effect of gravity, the pore water in the simulated formation is unevenly distributed, and it is difficult to ensure that hydrates are uniformly generated in the simulated formation.

[0005] During the cementing process, the cement slurry invades the simulated wellbore annular wall to a certain extent, resulting in the two-interface morphology being not a flat surface. In addition, the hydrates in the simulated hydrate-containing formations are very easy to decompose to produce high-pressure free gas and water that invade the cement. Therefore, the observation of the two-interface morphology and microcracks is also conducive to the analysis and study of the two-interface strength and sealing performance. In the existing technology, few cementing quality evaluation experimental devices take into account the observation of the two-interface morphology and microcracks.

[0006] In addition, in order to achieve safety and stability of the wellbore wall and improve the bonding quality of the two interfaces during cementing, the cement slurry pressure is generally greater than the pore pressure of the simulated formation. When the cement slurry penetrates into the simulated formation under the action of 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 cement slurry invading the simulated wellbore annulus (the simulated wellbore annulus refers to the formation close to the wellbore wall), resulting in pore distribution, uneven pressure, and pressure holding in the simulated formation, which are quite different from those in the downhole in-situ formation cementing (the downhole in-situ formation refers to the formation related to cementing formed after drilling), affecting the accuracy of the cement ring and the evaluation of the two interface quality. At the same time, in the process of evaluating the interface bonding strength of the indoor experiment, the data analysis of the acoustic logging probe evaluates the cementing quality of the cement slurry. Its setting method affects the air tightness of the device and thus affects the pressure stability of the device. The poor pressure stability makes the test results inaccurate. The above problems increase the difficulty and accuracy of the evaluation of bonding strength and interlayer isolation capacity.

[0007] There are many existing technologies for evaluating cementing quality. For example, CN206707694A discloses an experimental device for evaluating cementing quality of hydrate formations in deep-water cementing. The device evaluates cementing quality of cement slurry only through data analysis of acoustic logging probes, without considering the influence of the two-interface strength, resulting in low accuracy of cementing quality evaluation results; prefabricated artificial natural gas hydrates are very different from hydrates in natural formations under actual conditions, and the credibility of the experimental results is low; cement slurry is injected from the bottom of the kettle, which is opposite to the actual construction situation (in actual construction situations, cement slurry is injected from the wellhead, that is, from top to bottom), and the cementing pressure difference caused by cement slurry injection (the pressure of cement slurry is required 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 of natural gas hydrate formations. The device only detects the temperature and pressure in the simulated hydrate formation during the cementing process and cannot accurately evaluate the cementing quality. The pressure build-up, uneven local pressure, excessive local pressure and other factors generated by the instrument itself affect the seepage process of cement slurry in the simulated formation pores, resulting in a large difference between the prefabricated artificial natural gas hydrate and the hydrate in the natural formation under actual conditions, and the credibility of the experimental results is low. It is impossible to observe the thermal decomposition and anti-invasion process of the hydrate in real time.

[0009] This team disclosed in CN109142192A a visual test system for the bonding quality of the second interface of special-shaped cementing and the strength of special-shaped bodies. The simulated formation cavity and the 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 mold is provided at the bottom of the cementing cement / cement stone cavity. A thermocouple and multiple reaction gas injection pipes are provided in the simulated formation cavity, and visual windows are provided on the sides of the simulated formation cavity and the cementing cement / cement stone cavity. This device can be used to evaluate the bonding quality of the second interface during the cementing process of hydrate-containing formations, and to test the quality of the bonding surface between soft soil formations and cement, and to a certain extent realize the visualization of the second interface morphology and microcracks. However, this technology still has the following defects:

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

[0011] 2. The visualization observation head is outside the two interfaces. In order to achieve a sealed environment of confining pressure, an opaque rubber membrane tube is used, which makes it impossible to observe the thermal decomposition and anti-invasion process of hydrates in real time. The rubber membrane tube needs to be removed when observing the two interfaces, which is troublesome. Only when there is no need to use the rubber membrane tube to form a sealed environment can the rubber membrane tube be removed and the microscopic device can be used to observe the thermal decomposition and anti-invasion process of hydrates in real time at the visual window, thus limiting the scene that can be observed in real time;

[0012] 3. When evaluating cementing quality, it is necessary to calculate permeability, which is a complex process with large errors. Summary of the invention

[0013] In view of a series of problems existing in the prior art, such as large differences between simulated formations and natural formations, damage to the quality of the two interfaces due to gas-water counterinvasion, difficulty in visually observing the two interfaces, the setting method of the sonic logging probe affecting the air tightness of the device and thus affecting the pressure stability, and difficulty in simultaneously measuring the compressive strength of the cement slurry and the shear strength of the two interfaces, the present invention provides a complex formation cementing simulation and gas-water counterinvasion evaluation method and evaluation system.

[0014] The complex formation cementing simulation and gas-water anti-invasion evaluation system 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 arranged in sequence in the simulated formation, and the three are concentric ring columns; a movable bottom plate is arranged in the kettle body, and the kettle cover and the movable bottom plate seal the upper and lower ends of the kettle body respectively, and the movable bottom plate supports the simulated formation, the cement ring and the casing; the upper end of the casing is sealed and connected to the kettle cover, and the lower end of the casing is sealed and connected to the movable bottom plate;

[0015] Two groups of hydraulic cylinders are arranged under the movable bottom plate, the first group of hydraulic cylinders is placed under the simulated stratum; the second group of hydraulic cylinders is placed under the cement ring;

[0016] The casing has a lumen, a cement return hole is arranged at the lower part of the casing, and the cement return hole is connected to the cementing annulus where the cement ring is located; an acoustic logging probe is arranged in the reactor; a gas detection device is arranged in the reactor, and the gas detection device includes probes for detecting temperature and / or pressure distributed in the cement ring, simulated formation and buffer space; the buffer space, the lumen, the cementing annulus and the simulated formation are all provided with pipelines.

[0017] The casing body has an interlayer, the sonic logging probes are evenly embedded and distributed in the casing body interlayer, the sonic logging data line is connected to the sonic logging probe signal, and the sonic logging data line is placed outside the casing interlayer.

[0018] A pressure relief hole is opened on the inner wall of the sleeve at one end close to the kettle cover, and the pressure relief hole connects the interlayer of the sleeve with the tube cavity of the sleeve.

[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 in the cement ring, the five temperature and pressure probes are arranged side by side in the simulated formation, and the pressure probe is arranged in the buffer space.

[0020] A visualization imaging device is arranged in the reactor, and the visualization imaging device comprises a glass tube and an imaging probe for imaging the two interfaces. The glass tube has openings at both ends, and the glass tube passes through the buffer space and the simulated stratum, so that the inner end of the glass tube faces the two interfaces, and the outer end of the glass tube extends to the reactor body and is sealed and connected to the reactor body; the imaging probe is installed in the glass tube.

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

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

[0023] A water-soluble film is arranged on the inner wall of the simulated stratum, and a sand-isolating net is arranged on the outer wall of the simulated stratum; 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 the rotating device to realize the rotation of the kettle body.

[0024] A complex formation cementing simulation and gas-water anti-invasion evaluation method, using the above system, includes the following steps:

[0025] (1) Preparation stage:

[0026] Prepare simulated strata in the reactor and install gas detection devices and visualization imaging devices; set up water-soluble films and sand-blocking nets;

[0027] Adjust the simulated formation porosity until the difference between the simulated formation porosity and the “average value of the target formation porosity” / the average value of the target formation porosity is less than 10%;

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

[0029] The kettle is temperature-controlled by water bath until the simulated formation temperature 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 outside the reactor unchanged until hydrates are generated;

[0032] (3) Cementing stage:

[0033] After well washing, cement slurry is injected into the casing, the reactor is closed, and the cement slurry is pushed back up;

[0034] The pressure of cement slurry is made higher than the pressure of buffer space by injecting nitrogen into the simulated formation, and the pressure is maintained until the cement slurry solidifies;

[0035] (4) Obtaining experimental data:

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

[0037] Observe the two interfaces through an imaging probe;

[0038] After the cement slurry solidifies, the sonic logging probe is started to emit sound waves, and the receiver receives the sound waves; then the first group of hydraulic cylinders is started to lift the simulated formation, and the pressure changes of the first group of hydraulic cylinders are recorded; finally, the second group of hydraulic cylinders is started to compress the cement ring, and the pressure changes of the second group of hydraulic cylinders are recorded.

[0039] The pipelines arranged in the buffer space, the tubular cavity, the cementing annulus, and the simulated formation include: a back pressure valve interface / air outlet connected to the buffer space, an injection port connected to the tubular cavity, a liquid discharge and exhaust port connected to the cementing annulus, a gas-liquid inlet and a gas-liquid outlet to enable gas or liquid to enter and exit the simulated formation; the gas-liquid inlet passes through the kettle cover and extends to the upper end of the simulated formation; one end of the gas-liquid outlet passes through the movable bottom plate and extends to the lower end of the simulated formation.

[0040] Definition of terms:

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

[0042] Second interface: The bonding surface between the cement sheath and the formation is called the second interface of cementing. The sealing quality of the second interface is also crucial to the safety and stability of oil and gas wells. It can effectively prevent the cross-flow of formation fluids. In quality assessment, the importance of the second interface is greater than that of the first interface.

[0043] Gas-water reverse invasion: During the cementing process, the phenomenon of formation gas or liquid invading the cement sheath is called gas-water reverse invasion. Gas-water reverse invasion may lead to a decline in cementing quality and even cause safety accidents such as blowouts.

[0044] Pore ​​water: Water injected into a simulated formation and distributed in the pores of the simulated formation is called pore water.

[0045] Hydrate decomposition: Natural gas hydrates will decompose under certain conditions (such as reduced pressure and increased temperature), releasing gases (such as methane) and water. In deepwater drilling, the decomposition of natural gas hydrates may have a significant impact on drilling safety, such as increased wellbore pressure, instability of the wellbore wall, and cementing failure.

[0046] Natural formation refers to the formation where the well is located during the extraction of oil and gas. In contrast, simulated formation is used to simulate natural formation.

[0047] Simulated strata refer to simulating actual strata by mixing and stacking materials such as quartz sand, anhydrous calcium chloride, sodium silicate and sodium-based bentonite in experimental equipment. The structure formed by this part of materials is called simulated strata, which is used for the evaluation of interfacial bonding strength in indoor experiments.

[0048] The target stratum refers to the natural stratum for which the interface bonding strength evaluation of the indoor experiment is conducted.

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

[0050] Downhole in-situ cementing refers to the process of cementing a well after drilling in a 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 means such as sealant, sealing gasket, rubber sealing ring, etc.

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

[0054] 1. Due to the limited thickness of the simulated formation and the pressure generated by cement slurry invading the simulated wellbore annular wall, the pore distribution and pressure in the simulated formation are uneven, which is quite different from the natural formation. The present invention aims to improve this problem, improve the pore distribution and pressure unevenness in the simulated formation, make the simulated formation closer to the natural formation, and increase the accuracy of quality evaluation.

[0055] 2. The present invention reduces the influence of uneven distribution of pore water in the simulated formation due to gravity on the accuracy of cementing quality evaluation by rotating the reactor, so that hydrates are generated evenly and the accuracy of the evaluation of the two-interface cementation strength and interlayer isolation capacity is increased.

[0056] 3. In order to prevent the quality of the two interfaces from being damaged due to gas-water back-invasion, the present invention adds a gas detection device and a visual imaging device to the system to detect temperature and pressure changes and perform visual imaging, providing a more comprehensive indicator analysis for cementing quality evaluation.

[0057] 4. The visualization imaging device can realize real-time observation of a series of processes such as the hydrate formation process in the pores, the seepage invasion process of cement slurry in the formation pores, the thermal decomposition process of hydrates due to hydration, the high-pressure gas and water generated by hydrate decomposition pushing back the cement slurry process, and the critical state of high-pressure gas and water invading the cement slurry from the simulated formation pores, thus solving the problem of difficulty in intuitively observing the development of the two-interface morphology and the development of cracks.

[0058] 5. Real-time monitoring of the decomposition of hydrates in simulated formations by gas detection devices can be used as a basis for cementing quality evaluation. Probes at different diameters and depths in simulated formations can be placed to determine the decomposition of hydrates in simulated formations through temperature and pressure change data, which can be used to evaluate gas-water reverse invasion indicators; 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 exothermic temperatures and pressure conditions; it solves the problem of difficulty and low accuracy in evaluating the two-interface bonding strength and interlayer isolation capacity of hydrate-containing formations due to gas-water reverse invasion.

[0059] 6. Through the sonic logging probe and two sets of hydraulic cylinders, the sonic logging data and shear compression strength data can be obtained quickly and conveniently, solving the problem of difficult operation and easy error in the original operation method; at the same time, the compressive strength of cement slurry and the shear strength of the two interfaces are tested, increasing the use of the evaluation system and more comprehensively measuring and evaluating the cementing quality.

[0060] 7. By setting up a buffer space separated by a sand screen in the reactor and adjusting the air pressure in the buffer space, a uniform seepage process of cement slurry in the simulated formation pores can be achieved, which is closer to the in-situ cementing process downhole and has higher accuracy, solving the problem of large differences between the complex simulated formation cementing process and the actual cementing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 It is a cross-sectional view of the complex formation cementing simulation and gas-water anti-invasion evaluation system;

[0062] Figure 2 Top view of complex formation cementing simulation and gas-water anti-invasion evaluation system;

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

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

[0065] Figure 5 It is a local schematic diagram (section view) of the sonic logging probe being embedded;

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

[0067] Figure 7 It is a side view of the complex formation cementing simulation and gas-water anti-invasion evaluation system;

[0068] Figure numerals: 1, rotating shaft; 2, back pressure valve interface / air 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, drain and exhaust 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. Sonic logging probe; 17. Injection port; 18. Sonic logging data line; 19. Kettle cover; 20. Rubber sealing ring; 21. Sand screen; 22. Water-soluble film; 23. Kettle body; 24. Tube cavity; 25. Removable bottom plate; 2501. Removable upper plate; 2502. Removable lower plate; 2503. Center plate; 2504. Sealing rubber cushion; 26. Pressure relief hole; 27. Cement return hole; 28. Spiral sealing connection device; 29. ​​First interface; 30. Second interface. DETAILED DESCRIPTION

[0069] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments.

[0070] Example 1 Complex formation cementing simulation and gas-water anti-invasion evaluation system

[0071] like Figure 1 , Figure 2 As shown, a complex formation cementing simulation and gas-water anti-invasion evaluation system (hereinafter referred to as the evaluation system) includes a reactor, and the reactor includes a reactor body 23, a reactor cover 19 and a movable bottom plate 25. The reactor body 23 has a cavity, and the reactor body 23 is used to accommodate the reaction body of the entire system and connect other auxiliary devices; optionally, the cross-section of the reactor body is circular, square or rectangular, preferably circular; rotating shafts 1 are installed on both sides of the reactor body 23 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 arranged in the reactor cover 19 to achieve the function of sealing the reactor body 23, and the reactor cover 19 is connected to the reactor body 23 through six connecting nuts 4 evenly distributed along the circumferential direction. An injection port 17 is provided on the kettle cover 19, and the injection port 17 is used to inject cement slurry into the tube cavity 24 of the casing 15 inside the kettle body. After the cement slurry is injected, the injection port 17 is connected to a high-pressure gas pump to inject high-pressure gas (also called post-gas) into the tube cavity 24 to pressurize the cement slurry, so that the cement slurry returns to the cementing annulus. When the cement slurry solidifies in the cementing annulus, a cement ring 10 is formed.

[0072] The bottom of the kettle 23 is provided with a movable bottom plate 25 in a sliding seal. The movable bottom plate 25 is slidably connected to the inner wall of the kettle 23 so that the movable bottom plate 25 can slide up and down a certain distance in the kettle, and the movable bottom plate 25 and the inner wall of the kettle 23 are sealed to prevent pressure release. Figure 3 As shown, the movable bottom plate 25 includes a movable upper plate 2501, a movable lower plate 2502, a center plate 2503 and a sealing rubber pad 2504. The movable upper plate 2501, the movable lower plate 2502 and the center plate 2503 form the bottom of the closed kettle body 23 when they are combined together. For example, when the kettle body 23 is circular, the movable upper plate 2501 and the movable lower plate 2502 are both circular rings nested inside and outside, and the center plate 2503 is circular. When the three are combined, a complete circle is formed; the movable upper plate 2501 and the movable lower plate 2502 are connected on one side. The movable lower plate 2502 and the center plate 2503 are respectively provided with steps on one side where they are connected. When the three are combined, the steps are buckled together. The sealing rubber pad 2504 is filled between the steps of the movable upper plate 2501 and the movable lower plate 2502, and the sealing rubber pad 2504 is filled between the steps of the movable lower plate 2502 and the center plate 2503, so that the three form a complete sealing structure when they are not moved, 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 center 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] like Figure 1 As shown, 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 cylinder. Two groups of hydraulic cylinders 6 (a first group of hydraulic cylinders 601 and a second group of hydraulic cylinders 602) are arranged between the movable bottom plate 25 and the permeable bottom plate 14, and each group of hydraulic cylinders includes two hydraulic cylinders. The first group of hydraulic cylinders 601 is placed under the simulated formation 9 with the two interfaces 30 between the cement ring 10 and the simulated formation 9 as the boundary. The first group of hydraulic cylinders 601 are distributed on the left and right sides of the lower end of the simulated formation 9, that is, when the piston rods of the first group of hydraulic cylinders 601 move upward, they can directly lift the simulated formation 9 located at the two interfaces 30. The first group of hydraulic cylinders 601 lifts the simulated formation 9 upward to realize the shear detection of the two interfaces; since the simulated formation is a circular ring column and its bottom surface is a circular ring, the two hydraulic cylinders of the first group of hydraulic cylinders 601 are distributed on the same diameter line of the bottom surface of the simulated formation, so that when the first group of hydraulic cylinders 601 lifts the simulated formation 9 upward, the force on the left and right sides of the simulated formation 9 is relatively uniform. The second group of hydraulic cylinders 602 are 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 stratum 9 as the boundaries. The second group of hydraulic cylinders 602 are distributed on the left and right sides of the lower end of the cement ring 10, that is, when the piston rod of the second group of hydraulic cylinders 602 moves upward, the entire cement ring can be directly lifted. The second group 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 achieve compression detection of the cement ring 10. Since the cement ring is a circular ring column and its bottom surface is a circular ring, the two hydraulic cylinders of the second group of hydraulic cylinders 602 are distributed on the same diameter line of the bottom surface of the cement ring 10, so that when the second group of hydraulic cylinders 602 lifts the cement ring upward, the left and right sides of the cement ring 10 are subjected to relatively uniform force.

[0074] A simulated formation 9 is arranged in the kettle 23, and the simulated formation is used to simulate the actual natural formation, that is, the target formation. The simulated formation 9 is a circular ring column, 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 23, which is called a buffer space 13. Preferably, the height of the buffer space 13 is equal to the height of the simulated formation 9. The kettle 23 is provided with a back pressure valve interface / air outlet 2, which is connected to the buffer space 13, and is used to inject gas into the buffer space 13 or release the pressure of the buffer space 13 to adjust the confining pressure, so as to solve the problem of uneven pore distribution and pressure of the simulated formation 9 caused by cement slurry invading the simulated formation 9. The pressure of the buffer space is controlled to achieve a uniform seepage process of cement slurry in the pores of the simulated formation, so that the evaluation process is closer to the in-situ cementing process in the well, with higher accuracy, and reduces the impact of the pressure holding, local pressure unevenness, and excessive local pressure generated by the evaluation system itself on the seepage of cement slurry in the pores of the formation. A filtering device (not shown in the figure) can be provided at the back pressure valve interface / air outlet 2 to avoid blockage of the back pressure valve interface / air outlet 2 and the influence of sand particles on the sealing of the back pressure valve. The filtering device is arranged in the buffer space and does not directly contact the simulated formation, thereby improving the effect and extending the service life. The filtering device adopts a quick-disassembly structure, and the filter screen and filter element are quickly replaced.

[0075] A cement ring 10 is set in the simulated wellbore, and the side of the simulated formation 9 close to the cement ring 10 is the inner side of the simulated formation 9. The inner wall of the simulated formation 9 is the simulated wellbore annular wall. A water-soluble film 22 is set on the simulated wellbore annular 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, and a sand-proof net 21 is set on the outer wall of the simulated formation 9. The water-soluble film 22 and the sand-proof net 21 are both used to ensure that the soil inside the simulated formation 9 is stable and does not collapse before the simulated formation 9 reacts with the cement.

[0076] A casing 15 is also arranged in the simulated wellbore. The casing 15 is tubular and has openings at both ends, forming a lumen 24 inside. The casing 15 and the cement ring 10 are at the same height as the simulated formation 9, and the three are concentric circular ring columns, and the cross-sections of the three are concentric circular rings. Before the cement is injected, the cement ring 10 has not yet been formed. At this time, there is an annular cavity between the casing 15 and the annular wall of the simulated wellbore, which is called the cementing annulus. When the cement slurry is injected from the lumen of the casing 15 and returns to the cementing annulus (returning refers to the flow from bottom to top), the cement slurry will flow to the cementing annulus. After the cementing ring 10 is moved, the cement slurry in the cementing annulus gradually solidifies to form a cement ring 10. The interface between the cement ring 10 and the casing 15 is an interface 29, and the interface between the cement ring 10 and the simulated formation 9 is a second interface 30. A plastic film is provided at the interface 29 of the casing 15 (i.e., the outer surface of the casing), and the plastic film is adhered to the casing 15 by vaseline. When the cement ring 10 is forced to move upward, the plastic film at the interface 29 makes an interface between the casing 15 and the cement ring 10 almost free of shear force. The upper and lower ends of the casing 15 have external threads, and a spiral sealing connection device 28 is arranged on the kettle cover 19 corresponding to the upper end position of the casing 15. The spiral sealing connection device 28 has internal threads, and the center plate 2503 corresponding to the lower end position of the casing 15 has internal threads. The upper end of the casing 15 is sealed and connected to the kettle cover 19 through threaded matching, and the lower end of the casing 15 is sealed and connected to the center plate 2503. Four cement return holes 27 are arranged circumferentially on the casing wall near the movable bottom plate 25 for cement return. The four cement return holes 27 are evenly spaced and distributed on the casing wall at an equal distance from the movable bottom plate, so that the cement slurry returned in the entire cementing annulus is 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 holes 27.

[0077] like Figure 4 , Figure 5 As shown, the center of the casing 15 has a columnar lumen 24 for injecting cement slurry, the body of the casing 15 has an interlayer, and the interlayer refers to the space formed between the inner wall and the outer wall of the body, the sonic logging probe 16 is evenly embedded and distributed in the interlayer of the casing 15, the sonic logging data line 18 is connected to the sonic logging probe 16 signal, and the sonic logging data line 18 is placed outside the interlayer of the casing 15. This arrangement can solve the problem that the sonic logging probe 16 and its data line are difficult to place after the kettle cover is sealed under normal circumstances. The sonic logging probe 16 is used to detect the quality of the cement ring with sound waves; as shown in FIG. Figure 7As shown, several acoustic logging probes 16 are connected in parallel with the acoustic logging data line 18 to form a group of acoustic logging probes, and the acoustic logging data line 18 transmits data. The setting method of the embedded acoustic logging probe mainly takes into account that the post-gas will conflict with the acoustic logging probe set inside the casing cavity after being propelled, and it is very easy to destroy the sealing conditions in the reactor body when the acoustic logging probe is directly placed in the lumen 24. Therefore, the acoustic logging probe is embedded in the casing jacket, and the data in the acoustic logging probe is exported and analyzed using the data line, and a group of acoustic logging probes is embedded in the casing every 90°. Four groups of acoustic logging probes are distributed in a ring, and 360° full coverage forms a complete acoustic logging system. The acoustic logging probe can be quickly removed from the outer wall of the casing and is sealed. The detection of cement sheath bonding conditions of different hydration ages is realized, and acoustic data is returned for analyzing the cement sheath bonding quality. The casing design strength meets the influence of the first and second interfaces of cementing and the cement sheath strength test process. A wire hole is provided in the kettle spiral sealing connection device 28 to meet the connection between the acoustic logging data line 18 and the acoustic logging probe in the kettle body, and the spiral sealing connection device 28 and the acoustic logging data line 18 are sealed.

[0078] like Figure 1 As shown, a tiny pressure relief hole 26 is opened on the inner wall of the sleeve 15 at one end close to the kettle cover 19, and the pressure relief hole 26 connects the tube body interlayer of the sleeve 15 with the tube cavity 24 to balance the squeezing effect of the pressure inside the reactor body on the interlayer of the sleeve 15. Since the pressure relief hole 26 is close to the kettle cover 19 and is arranged at a higher position, when cement slurry is injected into the sleeve 15, the cement slurry will not block the pressure relief hole 26, and the cement slurry will not enter the interlayer of the sleeve 15 from the pressure relief hole 26.

[0079] like Figure 6As shown, the evaluation system also includes a gas detection device and a visual imaging device for anti-intrusion monitoring. The gas detection device includes seven probes (temperature probe 801, five temperature and pressure probes 802, and pressure probe 803), wherein the temperature probe 801 is arranged in the cement ring, 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; the visual imaging device includes a glass tube 11 and an imaging probe 12, the glass tube 11 is open at both ends, and the glass tube 11 passes through the buffer space 13 and the simulated formation 9, so that the inner end of the glass tube 11 is directly opposite to the second interface 30, and the outer end of the glass tube extends to the kettle body 23 and is sealed and connected to the kettle body 23, and the glass tube 11 forms a visual window, and the changes in the simulated formation can be directly observed with the naked eye; the imaging probe 12 is installed at the inner end of the glass tube 11 near the second interface 30 to achieve visual imaging of the second interface 30. The visualization imaging device goes deep into the simulated formation to reach the second interface, and cooperates with imaging probes of different precisions to realize real-time observation of a series of processes such as the hydrate generation process in the pores of the simulated formation, the seepage invasion process of cement slurry in the pores of the simulated formation, the hydration thermal decomposition process of hydrates, the high-pressure gas and water generated by hydrate decomposition to push back the cement slurry process, and the critical state of high-pressure gas and water invading the cement slurry from the pores of the simulated formation. The prior art mainly uses numerical simulation methods to determine the critical conditions of high-pressure gas and water invading cement slurry, while there are very few experimental research methods, and no visualization means of direct observation has been found so far. In the evaluation process of the present invention, the inner and outer surfaces of the glass tube 11 can be sprayed with an anti-fogging solution to prevent hydrates from aggregating and generating at the interface, and the main components of the anti-fogging solution do not affect the hydrate phase equilibrium. In the present invention, the imaging probe is directly set at the second interface, and the placement of the imaging probe is realized through the glass tube; because the glass tube and the kettle are soft-sealed (such as 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 places temperature and pressure probes at different diameter depths in the simulated formation, which can judge the hydrate decomposition in the simulated formation through the temperature and pressure change data, and is used to evaluate the gas-water anti-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 is used to study the decomposition of hydrates under different cement exothermic temperature and pressure conditions.

[0080] like Figure 1 , Figure 7As shown, a gas-liquid inlet 5 is arranged at the upper part of the kettle body 23, and the gas-liquid inlet 5 penetrates the kettle cover and extends to the upper end of the simulated formation 9; a gas-liquid outlet 3 is arranged at the lower part of the kettle body 23, and the gas-liquid outlet 3 is a retractable pipe, one end of the gas-liquid outlet 3 penetrates 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 gas-liquid outlet 3 at the lower part; 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 of the buffer space detected by the pressure probe 803 represents the pore pressure of the simulated formation) until the cement slurry is fully solidified. A liquid discharge and exhaust port 7 is arranged at the upper part of the kettle body 23, and one end of the liquid discharge and exhaust port 7 is derived into the cementing annulus, which is mainly used for cement slurry circulation discharge. The drain and exhaust port 7 can be a pipe, the outer end of which is provided with a thread, and the kettle cover 19 is provided with a threaded hole. The drain and exhaust port 7 penetrates the kettle cover and is sealed with the kettle cover thread. The gas-liquid inlet 5 is sealed with 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 rise in the cementing annulus. During the rising process, the gas in the cementing annulus is discharged from the drain and exhaust port 7. After the rising is completed, the excess cement slurry is discharged from the drain and exhaust port 7. In addition, the drilling fluid generated during the well washing is also discharged from the drain and exhaust port 7.

[0081] The evaluation system requires the cooperation of a water bath thermostat and a rotating device (neither of which is shown in the figure). The temperature of the evaluation system is controlled by placing the entire evaluation system in the water bath thermostat. The kettle 23 is connected to the rotating device via the rotating shaft 1 so that the rotating device drives the kettle 23 to rotate, thereby achieving the purpose of rotating the simulated formation 9. The rotation can make the pore water in the simulated formation 9 evenly distributed. The rotating device can be any existing device that can be connected to the rotating shaft 1 and drive the kettle 23 to rotate.

[0082] The evaluation system mainly uses two groups of hydraulic cylinders to evaluate the bonding strength. One group is placed under the simulated formation with the two interfaces between the cement sheath and the simulated formation as the boundary, used to shear the two interfaces and evaluate the bonding strength of the two interfaces; the other group is placed under the cement sheath with the first and second interfaces 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 two interfaces are sheared first and then the cement sheath is lifted and compressed by the hydraulic cylinder. This evaluation system not only comprehensively evaluates the bonding strength of the two interfaces 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 simulated in-situ formation downhole, and the results are closer to reality. Compared with the results of the test conducted at room temperature and normal pressure, it can more accurately reflect the actual cementing quality.

[0083] Example 1 Cementing of Hydrate-free Formation

[0084] Hydrate-free formation cementing experimental steps:

[0085] In order to reduce the variables in the experiment, when preparing cement slurry, ensure that the mixing time and speed of solid-liquid mixing are consistent in each experiment.

[0086] (0) Selection of target strata:

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

[0088] (1) Preparation stage:

[0089] Preparation of skeleton materials. According to the test data of the in-situ target formation coring in the well, natural quartz sand with matching particle size is selected as the porous medium for simulating the formation skeleton. According to the results of the previous experiments, natural quartz sand with a particle size of 10-60 mesh is selected. Then, the natural quartz sand is washed with distilled water 2-3 times until there are no obvious impurities in the water. Finally, it is dried to obtain the simulated formation skeleton material.

[0090] Prepare simulated strata. Cleaned quartz sand, anhydrous calcium chloride, sodium silicate and sodium bentonite are divided into three equal parts according to the required mass, and stirred evenly, and then added to the reactor three times and in sequence. The present invention uses sodium bentonite whose main component is montmorillonite to simulate the clay fine-grained sediment in the in-situ strata; during the process of adding to the reactor, the gas detection device and the visualization imaging device are installed, and finally the reactor is uniformly pressurized along the axial direction and maintained for the required time. During the preparation process, the uniformity of the pores can be improved by multiple batch loading and pressing, and the joint surface is roughened during adjacent fillings to prepare simulated strata 9.

[0091] Physical property test (porosity of simulated formation). Use the drainage method to test the porosity of the simulated formation. When the average values ​​of the porosity of the simulated formation and the porosity of the target formation are 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 is less than 10%), it means that the working conditions of the simulated formation 9 and the target formation are consistent; when the working conditions of the simulated formation 9 and the target formation are consistent, proceed to the next step. If not, uniformly pressurize along the axial direction of the reactor to adjust the porosity of the simulated formation until it is consistent.

[0092] Check the air tightness of the reactor. A water-soluble film 22 is set on the inner side of the simulated stratum 9, and a sand-proof net 21 is set on the outer side to prevent the simulated stratum from being damaged and to prevent sand from invading the buffer space 13. Then, a rubber sealing ring 20 is installed on the kettle cover 19 and the contact area of ​​the kettle cover is pre-tightened to ensure that the height of the simulated stratum 9 is not lower than the lower edge of the rubber sealing ring 20 above. The reactor is sealed with the kettle cover 19. The pre-tightening method includes but is not limited to pressing the upper end of the simulated stratum 9 with hands or objects. Inject nitrogen into the reactor to 15MPa and maintain the pressure for 12 hours. Observe whether the pressure of the reactor changes. If there is no change, the reactor has good air tightness. If a significant change in pressure is observed, it means that the reactor is not airtight, and the reactor needs to be resealed until the reactor has good air tightness.

[0093] Simulate and maintain the target formation temperature. After the simulated formation 9 passes the physical property test and the reactor passes the airtightness test, install the reactor cover 19, and install the casing 15 on the reactor cover 19, and fasten the reactor cover 19 and the reactor 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 a plastic film is tightly wrapped around the outside of the casing to reduce the friction between the interface 29 and the cement ring 10, so that the cement ring 10 and the casing 15 are completely separated in the subsequent shear stage, and there is almost no shear force on the interface. Then install the kettle body 23 on the rotating device through the rotating shaft 1, and lift the water bath thermostat to submerge the reactor. The temperature probe in the reactor monitors the temperature of the simulated formation 9 in real time. When the simulated formation temperature reaches the target formation temperature condition (i.e. 4°C), proceed to the next step.

[0094] (2) Cementing stage:

[0095] Preparation of cement slurry. Prepare the cement slurry required for the experiment according to the operating specifications of the oil well cement test method (GB / T19139-2012).

[0096] Overbalanced cementing. The prepared cement slurry is injected into the casing 15 through a cement pump until it reaches the top of the lumen, and the injection time and rate are strictly controlled. The entire injection and pressure-maintaining process uses overbalanced cementing (the pressure of the cement slurry is slightly greater than the pressure of the buffer space 13). After all the cementing cement slurry is injected, a certain cementing pressure difference is still maintained so that the cement slurry slightly invades the simulated wellbore annular wall. High-pressure nitrogen is injected into the simulated formation through the gas-liquid inlet 5, and high-pressure nitrogen is injected into the buffer space 13 so that the pressure of the cement slurry is 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 1MPa, the same below) until the cement slurry is fully solidified.

[0097] Maintain the temperature and pressure conditions of the simulated formation. According to the pressure data obtained by the temperature and pressure probe 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 in time to balance the cementing pressure difference caused by the cement slurry invading the simulated wellbore annular wall during the cementing pressure maintenance process. During the entire experiment, the temperature and pressure conditions of the simulated formation in the reactor are maintained unchanged.

[0098] Post-processing. After the cement slurry is injected, the reactor is quickly closed. Because the initial setting time of the prepared cement slurry is short, in order to ensure that the system is not damaged after the experiment is completed, the following procedures need to be completed: turn off the cement pumping machine and connect the high-pressure gas pump to the injection port 17, and pump the high-pressure gas into the casing cavity to achieve the purpose of pushing the cement slurry back and clearing the residual cement slurry on the pipe wall.

[0099] (3) Experiment and result analysis:

[0100] Real-time observation of cement slurry intrusion. The imaging probe 12 in the window of the glass tube 11 can be used to observe in real time the changes in the cementing interface morphology during cement curing and the extent of cement slurry intrusion into the simulated wellbore annular wall. The interior of the simulated formation can be directly observed through the wall of the glass tube 11.

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

[0102] Sonic logging: After the cement slurry is fully solidified, the sonic logging probe embedded in the casing 15 is started to emit sound waves, and the receiver converts the sound waves of different frequencies into data. Through data analysis, the bonding quality of the two interfaces can be obtained.

[0103] In-situ test of the bonding strength of the two interfaces. Start the first group of hydraulic cylinders 601 to lift the simulated stratum 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 stratum 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 bonding strength of the two interfaces.

[0104] In-situ test of cement ring compressive strength. After the shearing of the two interfaces is completed, the cement ring 10 is completely separated from both sides (due to the effect of vaseline and plastic film, the first interface can be regarded as having no shearing force with the cement ring 10, that is, the first interface and the cement ring are originally separated), the second group of hydraulic cylinders 602 are started to lift the cement ring 10 at a uniform speed of 0.5 mm / s, so that the cement ring is compressed by the kettle cover, the pressure change of the second group of hydraulic cylinders 602 is recorded, and the compressive strength of the cement ring 10 is calculated.

[0105] Pressure relief and cleaning: After the experiment is completed, the confining pressure in the buffer space 13, the pressure inside the kettle body, and the hydraulic pressure of the hydraulic cylinder 6 are relieved, the kettle cover 19 is opened, and the simulated stratum 9 and the cement ring 10 are removed.

[0106] Analyze the experimental results.

[0107] Example 2 Cementing of Hydrate Formation

[0108] Experimental steps for cementing hydrate-containing formations:

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

[0110] (0) Selection of target strata:

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

[0112] (1) Preparation stage:

[0113] Preparation of skeleton materials. According to the test data of the in-situ target formation coring in the well, natural quartz sand with matching particle size is selected as the porous medium for simulating the formation skeleton. According to the results of the previous experiments, natural quartz sand with a particle size of 10-60 mesh is selected. Then, the natural quartz sand is washed with distilled water 2-3 times until there are no obvious impurities in the water. Finally, it is dried to obtain the simulated formation skeleton material.

[0114] Prepare simulated strata. Divide anhydrous calcium chloride, sodium silicate, sodium bentonite and cleaned quartz sand into three equal parts according to the required mass, stir evenly, and then add them into the reactor three times. The present invention uses sodium bentonite whose main component is montmorillonite to simulate clay fine-grained sediments in the in-situ strata; during the process of adding into the reactor, install the gas detection device and the visualization imaging device, and finally uniformly pressurize along the axial direction of the reactor and maintain it for the required time. During the preparation process, the uniformity of the pores can be improved by multiple batch loading and manual pressing, and the joint surface can be roughened during adjacent fillings to prepare simulated strata 9.

[0115] Physical property test (porosity of simulated formation). The porosity of the simulated formation is tested by the drainage method. When the average values ​​of the simulated formation porosity and the target formation porosity are relatively close (close means that the difference between the simulated formation porosity and the "average value of the target formation porosity" / the average value of the target formation porosity is less than 10%), it indicates that the working conditions of the simulated formation 9 and the target formation are consistent; when the working conditions of the simulated formation 9 and the target formation are consistent, the next step is performed. If not, the porosity of the simulated formation is adjusted by uniformly applying pressure along the axial direction of the reactor until it is consistent.

[0116] Air tightness check. A water-soluble film 22 is set on the inner side of the simulated stratum 9 to prevent stratum damage, and a sand-isolating net 21 is set on the outer side to prevent stratum damage and prevent sand from invading the buffer space 13. Then install the rubber sealing ring 20 on the kettle cover 19 and pre-tighten the contact area to ensure that the height of the simulated stratum 9 is not lower than the lower edge of the rubber sealing ring 20 above. Inject nitrogen into the reactor to 15MPa and maintain the pressure for 12h, observe whether the pressure of the reactor changes, if there is no change, the reactor has good air tightness. After the air tightness is good, release the nitrogen, and then exhaust the nitrogen in the reactor by injecting 2MPa 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, 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 a sufficient amount of vaseline, and then a plastic film is tightly wrapped around the outside of the casing to reduce the friction between an interface 29 and the cement ring 10, so that the cement ring 10 and the casing 15 are completely separated in the subsequent shear stage, and there is no shear force on the interface. Then place the kettle body 23 on the rotating device of the rotating shaft 1, and lift the water bath thermostat to submerge the reactor. The temperature probe in the reactor monitors the temperature of the simulated formation 9 in real time. When the simulated formation temperature 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. When the simulated formation temperature reaches 2°C, inject methane through the gas-liquid inlet 5 to make the internal pressure of the reactor reach 8MPa, and add pore water (500ml) by immersion and drainage method. Then slowly rotate the reactor through the rotating device to make the pore water evenly distributed and reduce the influence of gravity on the pore water distribution. Close the reactor and keep the water bath temperature outside the reactor unchanged. Wait until the temperature and pressure in the reactor are stable, then the hydrate formation is considered complete, and then adjust the simulated formation pore pressure and temperature to 14.68MPa and 14.46°C respectively, which are the same as the in-situ hydrate formation.

[0120] (3) Cementing stage:

[0121] Well washing process. The prepared drilling fluid is pumped into the casing through the injection port 17, and the injection time and rate are strictly controlled. After the drilling fluid completes the well washing process, the injection port 17 is pressurized to discharge the drilling fluid at a uniform speed from the liquid discharge and exhaust port 7 according to the injection rate.

[0122] Preparation of cement slurry. Prepare the cement slurry required for the experiment according to the operating specifications of the oil well cement test method (GB / T19139-2012).

[0123] Overbalanced cementing. The prepared cement slurry is injected into the casing 15 through a cement pump until it reaches the top of the lumen, and the injection time and rate are strictly controlled. Overbalanced cementing is used in the entire injection and pressure-maintaining process. After all the cement slurry is injected, a certain cementing pressure difference is still maintained to allow the cement slurry to slightly invade the simulated wellbore annular wall. High-pressure nitrogen is injected 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 solidified.

[0124] Maintain the temperature and pressure conditions of the simulated formation. According to the pressure data obtained by the temperature and pressure probe 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 pressure difference caused by the cement slurry invading the simulated wellbore annular wall during the cementing pressure maintenance process. During the entire experiment, the temperature and pressure conditions of the simulated formation in the reactor are maintained unchanged.

[0125] Post-processing. After the cement slurry is injected, the reactor is quickly closed. Because the initial setting time of the cement is short, in order to ensure that the system is not damaged after the experiment is completed, the following steps need to be completed: turn off the cement pumping machine and connect the high-pressure gas pump to the injection port 17, and pump the high-pressure gas into the casing cavity to achieve the purpose of pushing the cement slurry back and clearing the residual cement slurry on the pipe wall.

[0126] (4) Experiment and result analysis:

[0127] Gas-water reverse invasion monitoring. Since hydrates can only be produced and stably exist in a very narrow temperature and pressure window, the hydration heat released by cement slurry hydration will lead to the decomposition of hydrates. One unit of hydrate decomposition will produce more than 140 units of free gas and water. These free gas and water invade into the cementing cement slurry under the action of pressure difference. The system monitors the temperature and pressure changes in the reactor in real time through 7 temperature and pressure probes, among which a temperature probe 801 is placed in the cement ring 10, a pressure probe 803 is placed in the buffer space 13, and 5 temperature and pressure probes 802 are placed in the simulated formation 9. These temperature and pressure probes can capture the temperature and pressure data in the reactor. In the result analysis, these temperature and pressure change data will be used as a basis to judge the decomposition of hydrates in the simulated formation 9 and whether gas-water reverse invasion occurs.

[0128] Cement slurry hydration exothermic analysis. The temperature probe 801 in the cement sheath 10 can monitor the temperature change of the cement sheath in real time, and the pressure probe 803 in the buffer space 13 can monitor the equilibrium pressure change in the simulated formation 9 in real time. Both can be used to study and analyze the influence of cement exothermic temperature on the degree of hydrate decomposition and equilibrium pressure.

[0129] Real-time observation of cement slurry intrusion. The imaging probe 12 in the glass tube 11 can be used to observe the changes in the morphology of the two interfaces during cement solidification and the extent of cement slurry intrusion into the simulated wellbore annular wall in real time. The glass tube 11 can directly observe the simulated formation.

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

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

[0132] In-situ test of the bonding strength of the two interfaces. Start the first group of hydraulic cylinders 601 to lift the simulated stratum 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 stratum 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 bonding strength of the two interfaces.

[0133] In-situ test of cement ring compressive strength. After the shearing of the two interfaces is completed, the cement ring 10 is completely separated from both sides (due to the effect of vaseline and plastic film, the first interface can be regarded as having no shearing force with the cement ring 10, that is, the first interface and the cement ring are originally separated), and the second group of hydraulic cylinders 602 are started to uniformly compress the cement ring 10 at a speed of 0.5 mm / s, so that the cement ring is compressed by the kettle cover, and the pressure change of the second group of hydraulic cylinders 602 is recorded to calculate the compressive strength of the cement ring 10.

[0134] Pressure relief and cleaning: After the experiment is completed, the confining pressure in the buffer space 13, the internal pressure of the kettle body and the hydraulic pressure of the hydraulic cylinder 6 are relieved, the kettle cover 19 is opened, and the simulated stratum 9 and the cement ring 10 are removed.

[0135] Analyze the experimental results.

[0136] Although the invention has been described herein with reference to illustrative embodiments thereof, it should be understood that numerous other modifications and implementations can be devised by those skilled in the art that will fall within the scope and spirit of the principles disclosed herein.

Claims

1. Complex formation cementing simulation and gas-water anti-invasion evaluation system, characterized by: The reactor comprises a reactor, wherein a simulated stratum (9) is arranged in a reactor body (23), and a buffer space (13) is arranged between the simulated stratum (9) and the inner wall of the reactor body (23); a cement ring (10) and a casing (15) are arranged in sequence in the simulated stratum (9), and the three are concentric circular ring columns; a movable bottom plate (25) is arranged in the reactor body (23), and a 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 stratum (9), the cement ring (10) and the casing (15); the upper end of the casing (15) is sealedly connected to the reactor cover (19), and the lower end of the casing (15) is sealedly 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 placed below the simulated stratum (9), and the second group of hydraulic cylinders (602) is placed below the cement ring (10); The casing (15) has a lumen (24), a cement return hole (27) is arranged at the lower part of the casing (15), and the cement return hole (27) is communicated with the cementing annulus where the cement ring (10) is located; An acoustic logging probe (16) is arranged in the reactor; A gas detection device is arranged in the reactor, and the gas detection device includes probes for detecting temperature and / or pressure distributed in the cement sheath, the simulated stratum and the buffer space; The buffer space (13), the pipe cavity (24), the cementing annulus, and the simulated formation are all provided with pipelines.

2. The complex formation cementing simulation and gas-water anti-invasion evaluation system according to claim 1 is characterized in that: The casing (15) has a tube body with an interlayer, the sonic logging probe (16) is evenly embedded and distributed in the tube body interlayer of the casing (15), the sonic logging data line (18) is connected to the sonic logging probe (16) by signal, and the sonic logging data line (18) is placed outside the casing (15) interlayer.

3. The complex formation cementing simulation and gas-water anti-invasion evaluation system according to claim 2 is characterized in that: A pressure relief hole (26) is formed on the inner wall of the sleeve (15) at one end close to the kettle cover (19), and the pressure relief hole (26) connects the interlayer of the sleeve (15) and the lumen (24) of the sleeve (15).

4. The complex formation cementing simulation and gas-water anti-invasion evaluation system according to claim 1 is characterized in that: The probes for detecting temperature and / or pressure are a temperature probe (801), five temperature and pressure probes (802), and a pressure probe (803). The temperature probe (801) is arranged in the cement ring, 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).

5. The complex formation cementing simulation and gas-water anti-invasion evaluation system according to claim 1 is characterized in that: A visualization imaging device is arranged in the reactor, comprising a glass tube and an imaging probe (12) for imaging the two interfaces (30); the glass tube (11) has openings at both ends, and the glass tube (11) passes through the buffer space (13) and the simulated stratum (9), so that the inner end of the glass tube (11) faces the two interfaces (30), and the outer end of the glass tube extends to the reactor body (23) and is sealedly connected to the reactor body (23); the imaging probe (12) is installed in the glass tube (11).

6. The complex formation cementing simulation and gas-water anti-invasion evaluation system according to claim 1 is characterized in that: The movable bottom plate (25) comprises a movable upper plate (2501), a movable lower plate (2502), and a center plate (2503) which are nested. When the movable upper plate (2501), the movable lower plate (2502), and the center plate (2503) are combined together, they form the bottom of the closed kettle body (23). The joints between the movable upper plate (2501), the movable lower plate (2502), and the center plate (2503) are filled with a sealing rubber pad layer (2504).

7. The complex formation cementing simulation and gas-water anti-invasion evaluation system according to claim 6 is characterized in that: Each group of hydraulic cylinders comprises two hydraulic cylinders. The first group of hydraulic cylinders (601) is placed below the simulated stratum (9) with the two interfaces (30) as the boundary, and the two hydraulic cylinders of the first group of hydraulic cylinders (601) are distributed on the left and right sides of the lower end of the simulated stratum (9); the second group of hydraulic cylinders (602) is placed below the cement ring (10) with the first interface (29) and the second interface (30) as the boundary, and the two hydraulic cylinders of the second group of hydraulic cylinders (602) are distributed on the left and right sides of the lower end of the cement ring (10).

8. The complex formation cementing simulation and gas-water anti-invasion evaluation system according to any one of claims 1 to 7, characterized in that: A water-soluble film (22) is arranged on the inner wall of the simulated stratum (9), and a sand-isolating net (21) is arranged on the outer wall of the simulated stratum (9); and a plastic film is pasted on the outer surface of the casing (15).

9. The complex formation cementing simulation and gas-water anti-invasion evaluation system according to claim 8 is characterized in that: The kettle body (23) is provided with a rotating shaft (1), and the rotating shaft (1) is used to be connected with a rotating device so as to realize the rotation of the kettle body.

10. A complex formation cementing simulation and gas-water anti-invasion evaluation method, characterized in that: The system according to any one of claims 1 to 9 comprises the following steps: (1) Preparation stage: Prepare simulated strata in the reactor and install gas detection devices and visualization imaging devices; set up water-soluble films and sand-blocking nets; Adjust the simulated formation porosity until the difference between the simulated formation porosity and the "average value of the target formation porosity" / the average value of the target formation porosity is less than 10%; Apply vaseline to the outside of the sleeve and wrap it with plastic film, then install it on the kettle cover and reseal the reactor; The kettle is temperature-controlled by water bath until the simulated formation temperature reaches the target formation temperature; (2) Hydrate formation stage: 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 outside the reactor unchanged until hydrates are generated; (3) Cementing stage: After well washing, cement slurry is injected into the casing, the reactor is closed, and the cement slurry is pushed back up; The pressure of cement slurry is made higher than the pressure of buffer space by injecting nitrogen into the simulated formation, and the pressure is maintained until the cement slurry solidifies; (4) Obtaining experimental data: Obtain the temperature and pressure in the reactor through temperature and / or pressure probes; Observe the two interfaces through an imaging probe; After the cement slurry solidifies, the sonic logging probe is started to emit sonic waves, and the receiver receives the sonic waves; then the first group of hydraulic cylinders is started twice to lift the simulated formation, and the pressure changes of the first group of hydraulic cylinders are recorded twice. The two shear strengths are calculated through the pressure changes, and the difference between the two shear strengths is obtained as the shear strength of the two interfaces; finally, the second group of hydraulic cylinders is started to compress the cement ring, and the pressure changes of the second group of hydraulic cylinders are recorded as the compressive strength of the cement ring.

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