Device and method for evaluating seepage corrosion and mechanical properties of cement sheath

Abstract

The present invention discloses a device and method for evaluating the seepage corrosion and mechanical properties of cement rings in well cementing, which belongs to the field of corrosion evaluation of cementing materials in oil and gas wells. The device includes an acidic corrosive gas injection system, a formation water injection system, a high-pressure oil injection system, a control system, and a corrosion and testing system. The corrosion and testing system comprises a main body, an upper cover, and a base. The main body comprises, from the outside to the inside, a metal cylinder, a simulated formation, a simulated casing, and a center rod. A cement ring maintenance-corrosion space is formed between the simulated formation and the simulated casing. A temperature control device is provided in the annulus formed between the simulated casing and the center rod. Multiple displacement gauges are provided at different positions and angles on the center rod to measure the deformation displacement of the simulated casing-cement ring assembly. The method for evaluating the seepage corrosion and mechanical properties of cement rings using this device is simple to operate and simultaneously realizes three functions: cement ring maintenance under high temperature and high pressure, acidic medium corrosion, and cement ring mechanical integrity evaluation. It has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of corrosion evaluation of oil and gas well cementing materials, and specifically relates to a device and method for realizing high-temperature and high-pressure maintenance of cement sheath, seepage corrosion of cement sheath and cement sheath-formation interface, and mechanical integrity evaluation. Background Art

[0002] In cementing projects, the cement sheath, a critical component of the wellbore, supports the casing and provides stratum isolation, ensuring the safe and efficient extraction of oil and gas resources. However, compared to the wellbore's metal casing and the formation, the cement sheath has the weakest mechanical properties, making it a vulnerable link in the failure of the wellbore's sealing integrity. Furthermore, the cement sheath is subject to the high-temperature, high-pressure, and corrosive environment of formation fluids at the bottom of the well. Particularly in oil and gas wells with high H2S / CO2 content and CO2 storage wells, the neutralization reaction of acidic H2S and CO2 with the alkaline cement sheath alters the chemical and microstructure of the cement paste, impairing the cement sheath's bulk and the cement-formation interface, leading to the loss of the cement sheath's stratum isolation function. Therefore, it is imperative to accurately understand the evolution of the mechanical properties and porosity of cement paste in high-temperature, high-pressure, and corrosive media to provide tools and support for evaluating the corrosion resistance of cement paste and designing corrosion-resistant cement slurries for oil and gas wells with high acidic media and CO2 storage wells.

[0003] In recent years, researchers at home and abroad have focused on the corrosion effects of acidic media on cement paste by developing corrosion methods. The "Dynamic Corrosion Apparatus for Migrating High-Temperature and High-Pressure Corrosive Media" (CN109520878A) simulates the flow and alternation of corrosive media on the cement paste surface through a rotating mechanism. However, this device cannot reflect the complex process of corrosion within the cement paste, which requires seepage and subsequent reaction. The "High-Temperature and High-Pressure Seepage Corrosion Simulation Experimental Apparatus and Method" (CN118362491A) simulates the seepage corrosion process of high-temperature and high-pressure cement paste downhole by incorporating the seepage and corrosion reaction of corrosive media in the vertical direction of the cement paste, and can also be used to maintain cement paste samples under seepage corrosion conditions. The "Dual-Interface Seepage Corrosion Apparatus and Seepage Corrosion Method for Cementing Cement Paste" (CN118029947A) simultaneously simulates both gas and liquid corrosion processes. By applying confining pressure to the wellbore wall and adjusting the gas and liquid corrosive media, it simulates the high-pressure, multiple corrosion modes of cement paste at the bottom of the wellbore. Furthermore, considering that the cement stone forms a ring shape (also called a cement ring) at the bottom of the well, which may affect the corrosion evaluation results, the "A cement ring / plug corrosion integrity test device and method under high temperature and high pressure carbon dioxide" (CN118190766A) focuses on simulating the corrosion maintenance of the sealing cement ring / cement plug by injecting CO2 into the formation after the CCUS well is sealed. Liquid is injected at the upper end of the cement plug to observe the bubble situation and monitor the sealing of the cement ring and cement plug; "A full-scale cement ring corrosion test device and method simulating real downhole working conditions" (CN114878448A) injects cement slurry between two metal pipes to form a cement ring, and then injects a high-pressure corrosive medium into the end face of the cement ring to carry out unidirectional dynamic corrosion maintenance of the full-scale cement ring. After the corrosion is completed, cement stone cores are drilled from the cement ring to test performance indicators such as compressive strength, porosity and corrosion depth.

[0004] Existing corrosion equipment focuses on corrosion maintenance of cement sheaths in high-temperature, high-pressure corrosive media. The cement sheath is removed only after cooling and depressurization, and its mechanical properties are then evaluated using other equipment. The cement sheath is a multi-component, porous, and brittle material, and the cooling and depressurization process can cause microstructural and performance changes. Furthermore, the cement sheath and metal casing have different material properties and significantly different thermal expansion coefficients, which can also damage the structure and performance of the cement sheath during the cooling and depressurization process.

[0005] With the development of technologies such as CO2 geological storage and oil recovery, the corrosion equipment and evaluation technology of cement sheath have become more challenging. The existing equipment has a single function and cannot accurately evaluate the corrosion status of cement sheath under bottom hole conditions and the influence of corrosion on the mechanical integrity of cement sheath. Summary of the Invention

[0006] The purpose of the present invention is to provide a cement sheath seepage corrosion and mechanical property evaluation device. The device can simultaneously realize three functions: cement sheath maintenance under high temperature and high pressure, corrosion of the cement sheath body and the formation-cement sheath interface by H2S / CO2 acidic medium, and mechanical integrity evaluation of the cement sheath after corrosion. It has broad market application prospects.

[0007] Another object of the present invention is to provide a method for evaluating the seepage corrosion and mechanical properties of cement sheaths using the above-mentioned device. The method has a reliable principle and is easy to operate. It solves the problem that existing corrosion devices cannot fully reflect the seepage corrosion of the cement sheath body in the formation and the formation-cement sheath interface, and directly evaluate the mechanical integrity of the cement sheath after corrosion under high temperature and high pressure.

[0008] In order to achieve the above technical objectives, the present invention adopts the following technical solutions.

[0009] The cement sheath seepage corrosion and mechanical property evaluation device includes an acidic corrosive gas injection system, a formation water injection system, a high-pressure oil injection system, a control system, and a corrosion and testing system.

[0010] The acidic corrosive gas injection system includes a gas cylinder, a control valve, a gas booster pump and a check valve, and the gas booster pump is connected to the control system. The formation water injection system includes a liquid storage tank, a liquid booster pump and a check valve, and the liquid booster pump is connected to the control system. The outlet ends of the acidic corrosive gas injection system and the formation water injection system are respectively equipped with check valves and converge into a high-pressure pipeline, which is connected to the corrosion and testing system.

[0011] The high-pressure oil injection system includes an oil storage tank, a high-pressure oil pump and a check valve. The high-pressure oil pump is connected to a control system. The outlet end of the high-pressure oil injection system is equipped with a check valve and connected to a corrosion and testing system.

[0012] The corrosion and testing system includes a main body, an upper cover and a base. The main body is composed of a metal cylinder, a simulated formation, a simulated casing and a center rod from the outside to the inside. The center rod is located at the center of the base and is connected to the upper cover through a nut. The metal cylinder and the simulated formation are sealed after epoxy resin is cured. A cement ring curing-corrosion space is formed between the simulated formation and the simulated casing. A temperature control device is arranged in the annulus formed between the simulated casing and the center rod. The temperature control device is connected to the control system to regulate the temperature in the corrosion and testing system.

[0013] The base is provided with injection ports and oil inlets at corresponding positions of the simulated formation and the annulus between the simulated casing and the center rod. The injection ports are connected to the formation water injection system and the acidic corrosive gas injection system respectively, and the oil inlet is connected to the high-pressure oil injection system.

[0014] The upper cover is provided with a discharge port and an oil outlet at corresponding positions of the simulated formation and the annulus between the simulated casing and the center rod, and the discharge port and the oil outlet are both connected to the back pressure valve through a high-pressure pipeline.

[0015] The simulated casing is used to simulate the casing of cementing operation, and plays the role of supporting the well wall and preventing oil and gas leakage.

[0016] The central rod is provided with multiple (not less than 3) displacement meters at different positions and angles, and the stress-strain of the material is calculated by measuring the deformation displacement of the simulated casing-cement sheath assembly when subjected to stress.

[0017] The acidic corrosive gas injection system and the formation water injection system provide the corrosion and testing system with acidic corrosive gas and formation water through the injection ports.

[0018] The high-pressure oil injection system injects high-temperature resistant oil into the corrosion and testing system through the oil inlet to control the pressure of the annulus between the simulated casing and the center rod, thereby achieving pressure control during high-temperature and high-pressure curing of the cement sheath and mechanical property testing.

[0019] The control system is used to control the temperature and pressure conditions during cement sheath maintenance and corrosion, and is used for pressure control during mechanical property testing.

[0020] The corrosion and testing system is used for curing and corroding cement sheaths under high temperature and high pressure, and evaluating the mechanical properties of the corroded cement sheaths.

[0021] The simulated formation can be processed by selecting outcrop rock samples according to actual formation data or using artificial rock samples with parameters close to the actual formation.

[0022] The method for evaluating the seepage corrosion and mechanical properties of cement sheath using the above-mentioned device comprises the following steps in sequence:

[0023] (1) Use epoxy resin to fix the simulated formation in the metal cylinder. After the epoxy resin is cured to form an effective seal, the center rod, simulated casing, and metal cylinder containing the simulated formation are installed on the base respectively;

[0024] (2) Inject cement slurry into the space between the simulated formation and the simulated casing, install the cover and tighten it with a nut;

[0025] (3) Open the high-pressure oil injection system to inject high-temperature resistant oil into the annulus between the simulated casing and the center rod, open the formation water injection system to inject formation water into the simulated formation, and close the back pressure valve when liquid flows out of the oil outlet and the discharge port; set the back pressure valve pressure, raise the temperature control device to the required temperature through the control system, start curing the cement sheath, and form a simulated casing-cement sheath combination;

[0026] (4) After the maintenance is completed, open the acid corrosive gas injection system to introduce acid corrosive gas H2S / CO2 into the corrosion and testing system to perform corrosion testing;

[0027] (5) After the corrosion is completed, pressure is injected into the annulus between the simulated casing and the center rod at a certain rate through the control system and the high-pressure oil injection system, forming a pressure difference between the simulated casing-cement sheath assembly and the simulated formation. The deformation displacement of the simulated casing-cement sheath assembly under the pressure difference is recorded by the radial displacement meter, and the data is collected and the stress-strain curve is drawn to analyze the mechanical properties of the cement sheath;

[0028] (6) After the experiment, cool down and reduce the pressure, unscrew the nut, open the upper cover, take out the cement ring, test the corrosion conditions of the cement ring and the simulated formation-cement ring interface (including microstructure, corrosion depth, etc.), and analyze the corrosion law of the cement ring in the H2S / CO2 corrosion environment.

[0029] Furthermore, according to the requirements of experimental simulation working conditions, maintenance and corrosion can also be carried out simultaneously.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) It can simultaneously realize three functions: maintenance of cement sheath under high temperature and high pressure, corrosion of cement sheath body and simulated formation-cement sheath interface by H2S / CO2 acidic medium, and evaluation of mechanical integrity of cement sheath after corrosion. Traditional devices have single functions, and different equipment must be used to complete the above operations, which is not only cumbersome to operate but also easy to introduce human errors. The present invention can complete multiple operations in the same device, significantly improve experimental efficiency, reduce equipment footprint, and reduce cost investment;

[0032] (2) This method solves the problem that existing corrosion devices cannot directly evaluate the mechanical integrity of the cement sheath after corrosion under high temperature and high pressure. By installing a displacement meter in the device and applying pressure in conjunction with a control system, the present invention can directly measure the stress, deformation and displacement of the cement sheath under high temperature and high pressure environments, collect stress-strain data, and more accurately evaluate the mechanical properties of the cement sheath. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic diagram of the structure of the cement sheath seepage corrosion and mechanical properties evaluation device.

[0034] Figure 2 Schematic diagram of the corrosion and testing system structure.

[0035] In the figure: 100 - acidic corrosive gas injection system: 110 - gas cylinder, 120 - control valve, 130 - gas booster pump, 140 - check valve; 200 - formation water injection system: 210 - liquid storage tank, 220 - liquid booster pump, 230 - check valve; 300 - high-pressure oil injection system: 310 - oil storage tank, 320 - high-pressure oil pump, 330 - check valve; 400 - control system; 500 - corrosion and testing system System: 501-center rod, 502-nut, 503-back pressure valve, 504-back pressure valve, 505-metal cylinder, 506-simulated formation, 507-cement ring maintenance-corrosion space, 508-simulated casing, 509-annulus, 510-temperature control device, 511-oil outlet, 512-oil inlet, 513-injection port, 514-discharge port, 515-base, 516-upper cover, 517-radial displacement meter. DETAILED DESCRIPTION

[0036] The technical solution of the present invention is described clearly and completely below in conjunction with the embodiments and drawings.

[0037] See Figure 1 、 Figure 2 .

[0038] The cement sheath seepage corrosion and mechanical property evaluation device comprises an acidic corrosive gas injection system 100, a formation water injection system 200, a high-pressure oil injection system 300, a control system 400 and a corrosion and testing system 500.

[0039] The acidic corrosive gas injection system 100 includes a gas cylinder 110, a control valve 120, a gas booster pump 130 and a check valve 140. The formation water injection system 200 includes a liquid storage tank 210, a liquid booster pump 220 and a check valve 230. The gas booster pump and the liquid booster pump are respectively connected to the control system 400. The outlet ends of the acidic corrosive gas injection system and the formation water injection system are respectively equipped with check valves and converge into a high-pressure pipeline, which is connected to the corrosion and testing system 500.

[0040] The high-pressure oil injection system 300 includes an oil storage tank 310, a high-pressure oil pump 320 and a check valve 330. The high-pressure oil pump is connected to the control system 400. The outlet end of the high-pressure oil injection system is equipped with a check valve and connected to the corrosion and testing system 500.

[0041] The corrosion and testing system 500 includes a main body, an upper cover 516 and a base 515. The main body is composed of a metal cylinder 505, a simulated formation 506, a simulated casing 508 and a center rod 501 from the outside to the inside. The center rod is located at the center of the base and is connected to the upper cover by a nut 502. The metal cylinder and the simulated formation are effectively sealed after being cured with epoxy resin. A cement ring curing-corrosion space 507 is formed between the simulated formation and the simulated casing. An annulus 509 is formed between the simulated casing and the center rod, i.e., an annulus between the simulated casing and the center rod. A temperature control device 510 is provided in the annulus. The temperature control device is connected to the control system 400; the base 515 is respectively provided with an injection port 513 and an oil inlet 512 at corresponding positions of the simulated formation and the annulus between the simulated casing and the center rod, the injection ports are respectively connected to the formation water injection system and the acid corrosion gas injection system, and the oil inlet is connected to the high-pressure oil injection system; the upper cover 516 is respectively provided with a discharge port 514 and an oil outlet 511 at corresponding positions of the simulated formation and the annulus between the simulated casing and the center rod, the discharge port and the oil outlet are respectively connected to the back pressure valves 503 and 504 through high-pressure pipelines; the center rod 501 is provided with multiple radial displacement meters 517 at different positions and angles.

[0042] The cement sheath seepage corrosion and mechanical property evaluation device can realize cement sheath maintenance under high temperature and high pressure, and seepage corrosion and mechanical integrity evaluation of the cement sheath body and the formation-cement sheath interface, and specifically includes the following steps:

[0043] Step 1: Install the metal cylinder on the base, inject resin to fill the gap between the metal cylinder and the simulated formation, prepare H2S / CO2 gas cylinders, connect all high-pressure pipelines, and select outcrop rocks or artificial cores with corresponding porosity and permeability according to the simulated formation to be tested;

[0044] Step 2: After the resin solidifies, prepare cement slurry according to GB / T 19139-2012 and inject the cement slurry into the space formed between the simulated formation and the simulated casing. Use nuts to tighten the upper cover to ensure that the device is sealed completely.

[0045] Step 3: Open the high-pressure oil injection system to inject crude oil into the annulus between the simulated casing and the center rod. Open the formation water injection system to inject formation water into the simulated formation. When crude oil and formation water flow out of the oil outlet and the discharge port, close the back pressure valve and the check valve. Raise the temperature control device to the required temperature through the control system to cure and form the cement ring.

[0046] Step 4: Open the control valve and the check valve to introduce H2S / CO2 corrosive gas into the corrosion and testing system to perform corrosion testing;

[0047] Step 5: After corrosion is complete, the control system applies pressure to the annulus between the simulated casing and the center rod. The cement sheath expands toward the simulated formation. The displacement of the cement sheath under pressure is recorded using a displacement meter. The strain of the cement sheath is calculated. Combined with known parameters such as the elastic modulus of the material, the stress on the material is indirectly calculated based on the measured displacement and strain data, and a stress-strain diagram is drawn.

[0048] Step 6: After the experiment, open the upper cover and take out the cement ring. By observing and testing the corrosion of the cement ring, the corrosion condition of the cement ring under H2S / CO2 corrosion is obtained, and the corrosion law of the cement ring is analyzed.

[0049] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. Any obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A cement ring seepage corrosion and mechanical property evaluation device, comprising an acidic corrosive gas injection system (100), a formation water injection system (200), a high-pressure oil injection system (300), a control system (400) and a corrosion and testing system (500), characterized in that: The acidic corrosive gas injection system (100) includes a gas cylinder (110), a gas booster pump (130) and a check valve. The formation water injection system (200) includes a liquid storage tank (210), a liquid booster pump (220) and a check valve. The gas booster pump and the liquid booster pump are respectively connected to the control system (400). The outlet ends of the acidic corrosive gas injection system and the formation water injection system are respectively connected to the corrosion and testing system (500). The high-pressure oil injection system (300) includes an oil storage tank (310), a high-pressure oil pump (320) and a check valve. The high-pressure oil pump is connected to the control system (400). The outlet end of the high-pressure oil injection system is connected to the corrosion and testing system (500). The corrosion and testing system (500) includes a main body, an upper cover (516) and a base (515). The main body is composed of a metal cylinder (505), a simulated formation (506), a simulated casing (508) and a center rod (501) from the outside to the inside. The center rod is located on the base. The center position of the base is connected by a nut and an upper cover, the metal cylinder and the simulated formation are effectively sealed after being cured by epoxy resin, a cement ring curing-corrosion space (507) is formed between the simulated formation and the simulated casing, an annulus (509) is formed between the simulated casing and the center rod, that is, the annulus between the simulated casing and the center rod, a temperature control device (510) is set in the annulus, and the temperature control device is connected to the control system (400); the base is respectively provided with an injection port (513) and an oil inlet (512) at corresponding positions of the simulated formation and the annulus between the simulated casing and the center rod, the injection ports are respectively connected to the formation water injection system and the acid corrosion gas injection system, and the oil inlet is connected to the high-pressure oil injection system; the upper cover is respectively provided with a discharge port (514) and an oil outlet (511) at corresponding positions of the simulated formation and the annulus between the simulated casing and the center rod, the discharge port and the oil outlet are respectively connected to the back pressure valve through a high-pressure pipeline; the center rod is provided with multiple radial displacement gauges (517) at different positions and angles.

2. The cement sheath seepage corrosion and mechanical performance evaluation device according to claim 1, characterized in that: The acidic corrosive gas injection system and the formation water injection system provide the corrosion and testing system with acidic corrosive gas and formation water through the injection ports.

3. The cement sheath seepage corrosion and mechanical performance evaluation device according to claim 1, characterized in that: The high-pressure oil injection system injects high-temperature resistant oil into the corrosion and testing system through the oil inlet to control the pressure of the annulus between the simulated casing and the center rod, thereby achieving pressure control during high-temperature and high-pressure curing of the cement sheath and mechanical property testing.

4. The cement sheath seepage corrosion and mechanical performance evaluation device according to claim 1, characterized in that: The control system is used to control the temperature and pressure conditions during cement sheath maintenance and corrosion, and is used for pressure control during mechanical property testing.

5. The cement sheath seepage corrosion and mechanical performance evaluation device according to claim 1, characterized in that: The corrosion and testing system is used for curing and corroding cement sheaths under high temperature and high pressure, and evaluating the mechanical properties of the corroded cement sheaths.

6. The cement sheath seepage corrosion and mechanical performance evaluation device according to claim 1, characterized in that: The simulated formation is processed by selecting outcrop rock samples according to actual formation data or using artificial rock samples with parameters close to the actual formation.

7. A method for evaluating the seepage corrosion and mechanical properties of cement sheath using the apparatus of claim 1, 2, 3, 4, 5 or 6, comprising the following steps: (1) Use epoxy resin to fix the simulated formation in the metal cylinder. After the epoxy resin is cured to form an effective seal, the center rod, simulated casing, and metal cylinder containing the simulated formation are installed on the base respectively; (2) Inject cement slurry into the space between the simulated formation and the simulated casing, install the cover and tighten it with a nut; (3) Open the high-pressure oil injection system to inject high-temperature resistant oil into the annulus between the simulated casing and the center rod, open the formation water injection system to inject formation water into the simulated formation, and close the back pressure valve when liquid flows out of the oil outlet and the discharge port; set the back pressure valve pressure, raise the temperature control device to the required temperature through the control system, start curing the cement sheath, and form a simulated casing-cement sheath combination; (4) After the maintenance is completed, open the acid corrosive gas injection system to introduce acid corrosive gas H2S / CO2 into the corrosion and testing system to perform corrosion testing; (5) After the corrosion is completed, pressure is injected into the annulus between the simulated casing and the center rod at a certain rate through the control system and the high-pressure oil injection system, forming a pressure difference between the simulated casing-cement sheath assembly and the simulated formation. The deformation displacement of the simulated casing-cement sheath assembly under the pressure difference is recorded by the radial displacement meter, and the data is collected and the stress-strain curve is drawn to analyze the mechanical properties of the cement sheath; (6) Cool down and reduce pressure, unscrew the nut, open the upper cover and remove the cement ring, test the cement ring, simulate the corrosion of the formation-cement ring interface, and analyze the corrosion law of the cement ring in the H2S / CO2 corrosion environment.

8. The method according to claim 7, wherein According to the needs of experimental simulation working conditions, maintenance and corrosion are carried out simultaneously.

Images