A high temperature and high pressure seepage corrosion simulation experimental device and method

Abstract

The present invention discloses a high-temperature and high-pressure seepage corrosion simulation experimental device and method, which belongs to the field of oil and gas well cementing. The device includes a corrosive medium storage tank, a flow pump and a corrosion kettle, and the corrosion kettle includes a left end cover, a right end cover and a kettle body, and the kettle body is composed of a simulated sample, a rubber sleeve, a steel cylinder and a heating and insulation sleeve from the inside to the outside. The method includes: preparing a simulated sample; applying confining pressure to the simulated sample by a confining pressure pump; heating the corrosion kettle by a temperature controller; regularly or continuously injecting a corrosive medium into the corrosion kettle to ensure that the corrosive medium seeps through the formation surrounding rock and cement stone samples uninterruptedly; taking out the formation surrounding rock and cement stone samples, and measuring the corrosion parameters of the cement stone samples at different positions from the formation surrounding rock, including corrosion depth, compressive strength and permeability. The present invention is easy to operate, and by simulating the process of corrosive medium seepage from the formation surrounding rock to the cement stone sample and from the bottom of the well to the wellhead under high temperature and high pressure, the corrosion resistance of the cement stone can be more accurately evaluated.

Description

Technical Field

[0001] The invention belongs to the field of oil and gas well cementing, and in particular relates to a high-temperature and high-pressure seepage corrosion simulation experimental device and method. Background Art

[0002] Cementing is an important part of oil production technology, and cement stone corrosion is a major challenge and problem in the field of oil and gas well cementing engineering. With the improvement of people's understanding of the role of cement ring integrity in wellbore integrity and the in-depth development of gas fields with high corrosive media in my country, the corrosion research of cement stone under high temperature, high pressure and high corrosive media conditions has become a hot topic.

[0003] Generally speaking, when a well is built, only the casing and the cementing stone outside the casing remain in the well. Cementing cement not only supports and protects the casing, but also serves as an important wellbore isolation barrier unit to prevent formation fluid from flowing. Some of the cement stone in the well is sandwiched between the casing and the formation rock, and some is sandwiched between the casing and the casing. From bottom to top, the cement stone between the formation rock and the casing, and the cement stone between the casing and the casing face different corrosion conditions. The corrosive medium of the cement stone between the formation surrounding rock and the casing is the corrosive medium fluid that directly penetrates from the formation. The cement stone sandwiched between the casing and the casing can only contact the cement stone by slowly pushing upward through the corrosive medium below because the casing is impermeable. After cementing, perforation is performed to combine the formation and the wellbore. Oil and natural gas enter the wellbore through the blasthole. The corrosion near the blasthole may be closer to dynamic corrosion. Is there a seepage velocity far away from the blasthole? If there is a seepage velocity, it may gradually decrease. Beyond a certain range, the seepage velocity may be very slow, and the cement stone corrosion is closer to static corrosion.

[0004] According to the relative motion state between the corrosive medium and cement stone, it is divided into static corrosion (cement stone is directly placed in a high-temperature and high-pressure autoclave, and the corrosive medium is introduced into the autoclave) and dynamic corrosion (cement stone is fixed in the autoclave, and the corrosive medium is introduced to make relative motion between cement stone and the corrosive medium, simulating the dynamic corrosion process of cement stone under high temperature and high pressure). The corrosion of formation corrosive medium to oil well cement is inevitable. Due to the difference between the actual corrosion conditions (temperature, pressure, corrosion method, etc.) in the well and the corrosion conditions of cement stone in the laboratory, the cement stone corrosion process simulated in the laboratory is quite different from the actual situation in the well.

[0005] The existing indoor simulation devices for the corrosion of cement by corrosive media are mainly divided into the following two categories:

[0006] (1) Static corrosion simulation experimental device

[0007] This type of device can simulate the corrosion of cement stone by corrosive media in a static environment ("A high temperature and high pressure cement stone corrosion tester" CN102841048A), and directly place the cement specimen in a corrosion kettle or in a corrosion kettle containing formation water, and heat and pressurize it to perform corrosion simulation experiments. Most of these devices adopt a closed structure, and the generated corrosion products will not only not flow away but also precipitate and crystallize on the surface of the cement stone, thereby forming a protective layer on the surface of the cement stone, which greatly affects the subsequent corrosion reaction. As the corrosion time increases, due to the influence of the concentration of the corrosive medium, the corrosion rate becomes slower and slower. Compared with the actual underground formation with sufficient corrosive media, the corrosion rate of cement stone by corrosive media measured in the laboratory is much lower.

[0008] (2) Dynamic corrosion simulation experimental device

[0009] This type of device can realize the flow of acidic corrosive media ("Dynamic Corrosion Device for Migration of High-Temperature and High-Pressure Corrosive Media" CN109520878A). By stirring at a low speed and replacing the corrosive media regularly, the flow and replacement of the corrosive media on the surface of the cement stone are realized, which is more in line with the actual characteristics of the underground than the static corrosion simulation experimental device. However, this type of device still has shortcomings. Dynamic corrosion only allows the corrosive medium to flow on the surface of the cement stone. However, whether the underground is a high-permeability formation or a low-permeability formation, the corrosion rates of the two may be different. The seepage rate of the corrosive medium underground is too low or too high, which will affect the corrosion rate. Both of the above methods are difficult to simulate the process in which the corrosive medium passes through the cement stone between the formation surrounding rock and the casing, gradually penetrates into the cement stone between the casing and the casing, and corrodes it. At present, it is urgent to develop a cement stone corrosion indoor simulation device and method that can be closer to the actual situation underground, so as to provide new technical means for more realistic evaluation of the corrosion law and corrosion resistance of cement stone. Summary of the invention

[0010] The purpose of the present invention is to provide a high-temperature and high-pressure seepage corrosion simulation experimental device, which has a reliable principle and is easy to operate, and can more realistically and effectively simulate the seepage corrosion of corrosive media flowing upward through surrounding rocks and cement stone at different temperatures and pressures.

[0011] Another object of the present invention is to provide a method for conducting a high-temperature and high-pressure seepage corrosion simulation experiment using the above-mentioned device, by simulating the process of corrosive medium seeping from the formation surrounding rock to the cement stone and from the bottom of the well to the wellhead under high temperature and high pressure conditions, so as to more accurately evaluate the corrosion resistance of the cement stone.

[0012] In order to achieve the above technical objectives, the present invention adopts the following technical solutions.

[0013] A high-temperature and high-pressure seepage corrosion simulation experimental device mainly comprises an acid gas cylinder, a corrosive medium storage tank, a flow pump and a corrosion kettle.

[0014] The corrosion kettle comprises a left end cover, a right end cover and a kettle body, and the left and right end covers are connected to the kettle body by bolts.

[0015] The left end cover is provided with a liquid inlet and a liquid outlet. The liquid inlet is equipped with a matching one-way valve. The liquid outlet is provided with a pressure gauge and a back pressure valve. The liquid inlet is connected to a flow pump through a pipeline. The flow pump is connected to a corrosive medium storage tank and an acidic gas cylinder. The cavity in the middle of the left end cover accommodates the corrosive fluid delivered from the flow pump.

[0016] The right end cover is provided with a back pressure valve for adjusting the seepage corrosion pressure difference between the corrosive fluid and the cement stone sample. At the same time, if the corrosive medium slowly seeps through all the cement stone samples, the seeping corrosive medium is released through the back pressure valve.

[0017] The kettle body is composed of the inside of the kettle body, a rubber sleeve, a steel cylinder and a heating and insulation sleeve from the inside to the outside. The kettle body is provided with a confining pressure interface, which is connected to a pressure gauge and a confining pressure pump through a pipeline to ensure that there is no gap between the rubber sleeve and the sides of the surrounding rock and cement stone sample inside the kettle body, thereby ensuring that the corrosive medium seeps from left to right along the surrounding rock and cement water sample.

[0018] The surrounding rock and cement stone samples are loaded into the kettle from left to right, which is equivalent to a permeability tester. At the beginning, 2-3cm can simulate the seepage of corrosive formation fluid passing through the surrounding rock and cement stone contact, and later simulate the situation of corrosive fluid flowing upward from the bottom of the well. After a certain corrosion time, the cement stone sample is taken out to observe the position where the corrosive medium finally seeps and corrodes the cement stone, whether the corrosion penetrates the cement stone, and the performance changes of the corroded cement stone; according to the corrosion of the corrosive medium seepage through the surrounding rock and cement stone at different positions, the seepage between the actual formation surrounding rock and cement stone, and the flow between cement stone from the bottom of the well to the wellhead are simulated.

[0019] Furthermore, one piece of surrounding rock and more than three cement stone samples are arranged in contact with each other from left to right in the kettle body. The surfaces of the surrounding rock and cement stone samples are regular and the sizes are the same. The cement stone samples are several samples of the same size obtained under the same curing conditions, and the number is determined according to the specific experimental conditions.

[0020] Furthermore, the rubber sleeve pressurizes the interior of the kettle body to seal the formation surrounding rock and cement stone samples, ensuring that the corrosive medium seeps from left to right along the surrounding rock and cement stone instead of flowing around the surrounding rock and cement stone.

[0021] Furthermore, the outer side of the kettle body is wrapped with a heating and heat-insulating sleeve, and the heating and heat-insulating sleeve is connected to a temperature controller.

[0022] Furthermore, if the underground corrosive medium contains acidic gas, the acidic gas provided by the acidic gas cylinder is injected into the corrosive medium storage tank. If there is no acidic gas, the one-way valve at the acidic gas cylinder is closed, the corrosive fluid is directly stored in the corrosive medium storage tank, and the corrosive fluid is injected into the corrosion kettle through a flow pump to make the corrosive medium flow regularly or continuously.

[0023] The method for conducting a high temperature and high pressure seepage corrosion simulation experiment using the above device comprises the following steps in sequence:

[0024] (1) Prepare a piece of formation surrounding rock, prepare cement slurry according to API specifications, pour it into a mold for curing to make at least three cement stone small round cakes or small cylindrical samples of the same size (prepare the number of cement stone samples according to specific experimental requirements, and multiple samples can facilitate the determination of permeability at different corrosion positions after the experiment). The formation surrounding rock and the cement stone sample are of the same height and have parallel and smooth surfaces; place the formation surrounding rock and cement stone samples in the kettle from left to right in sequence, so that the formation surrounding rock and cement stone samples are closely arranged to form a simulation sample;

[0025] (2) Inject the prepared corrosive solution into the corrosive medium storage tank;

[0026] (3) Turn on the confining pressure pump and apply confining pressure to the simulated sample through the confining pressure interface to ensure that the confining pressure is greater than the inlet pressure;

[0027] (4) Inject the corrosive medium into the cavity of the corrosion kettle through the flow pump, adjust the seepage pressure difference of the corrosive fluid on the cement stone sample and the pressure difference of the circulation of the corrosive fluid through the back pressure valve on the right end cover, and heat the corrosion kettle with the temperature controller to reach the temperature and pressure required for the experiment;

[0028] (5) Use a flow pump to regularly or continuously inject the corrosive medium into the corrosion kettle to ensure that the corrosive medium continuously seeps through the surrounding rock and cement stone samples;

[0029] (6) After the time required by the experimental design is reached, stop injecting the corrosive medium, turn off the temperature controller, and after the kettle temperature drops to room temperature or the set temperature, release the pressure of the corrosive fluid in the kettle cavity. After that, gradually reduce the confining pressure to zero, open the kettle, take out the surrounding rock and cement stone samples in turn, and conduct subsequent tests;

[0030] (7) Various corrosion parameters (corrosion depth, compressive strength, permeability, etc.) of cement stone samples at different positions away from the surrounding rock of the formation are measured. By simulating the seepage from the surrounding rock of the formation to the cement stone samples and the crossflow of the corrosive medium between cement stone samples, key data such as the seepage velocity of the corrosive medium through the surrounding rock to the cement stone underground in the actual formation and the crossflow velocity of the corrosive medium through the cement stone from the bottom of the well to the top are obtained.

[0031] The present invention continuously or periodically injects corrosive medium into the kettle body through a flow pump, and finally makes the corrosive medium flow through the surrounding rock and contact the cement stone sample uninterruptedly, which is closer to the process of underground corrosive medium flowing from the surrounding rock to the cement stone and along the cement stone to the wellhead.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The present invention can simulate the seepage of corrosive media from surrounding rocks to cement stone samples, and can more realistically simulate the actual corrosion of cement stone at the bottom of the well, as well as the change in the seepage corrosion rate of the corrosive media during the process of flowing from underground through surrounding rocks and cement stone to the wellhead;

[0034] (2) The device and method provided by the present invention provide a favorable technical means for further studying the seepage corrosion conditions at different positions after the seepage corrosion of cement stone and improving the long-term sealing stability of the cement sheath. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a structural schematic diagram of a high-temperature and high-pressure seepage corrosion simulation experimental device of the present invention.

[0036] Figure 2 It is a schematic diagram of the structure of the corrosion kettle.

[0037] Description of reference numerals:

[0038] 1-acid gas cylinder; 2, 5-check valve; 3-corrosive medium storage tank; 4-flow pump; 6-liquid inlet; 7-corrosive kettle; 8-liquid outlet; 9, 12-back pressure valve; 10, 11, 28-pressure gauge; 13, 20-bolts; 14-left end cover; 15-cavity; 16-retaining ring; 17-surrounding rock; 18-inside kettle body; 19-cement stone sample; 21-steel cylinder; 22-rubber sleeve; 23-heating and insulation sleeve; 24-right end cover; 25-temperature controller; 26-kettle body; 27-confining pressure interface; 29-pressure relief valve; 30-confining pressure pump. DETAILED DESCRIPTION

[0039] In order to explain the present invention more clearly, the present invention is further described below in conjunction with preferred embodiments. It should be understood by those skilled in the art that the following specific description is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0040] See also Figure 1 , Figure 2 .

[0041] A high-temperature and high-pressure seepage corrosion simulation experimental device comprises a corrosion medium storage tank 3, a flow pump 4 and a corrosion kettle 7.

[0042] The corrosion kettle 7 includes a left end cover 14, a right end cover 24 and a kettle body 26 located in the middle. The left end cover, the right end cover and the kettle body are connected by bolts 13 and 20. The left end cover 14 is provided with a liquid inlet 6 and a liquid outlet 8. The liquid inlet is provided with a matching one-way valve 5, and the liquid outlet is provided with a matching back pressure valve 9 and a pressure gauge 10. The liquid inlet is connected to a flow pump 4 through a pipeline, and the flow pump is connected to a corrosive medium storage tank 3. There is a cavity 15 in the middle of the left end cover, which is communicated with the liquid inlet and the liquid outlet respectively, and is connected to the kettle body. A retaining ring 16 is provided at the connection, and the right end cover 24 is provided with a back pressure valve 12 and a pressure gauge 11; the kettle body 26 is composed of the kettle body interior 18, the rubber sleeve 22, the steel cylinder 21 and the heating and insulation sleeve 23 from the inside to the outside, and a simulated sample is installed inside the kettle body. The kettle body is provided with a confining pressure interface 27, which is connected to the pressure gauge 28, the pressure relief valve 29 and the confining pressure pump 30 through a pipeline. The simulated sample consists of formation surrounding rock 17 and at least three cement stone samples 19, which are arranged in contact from left to right inside the kettle body.

[0043] Furthermore, the surrounding rock 17 and cement stone sample 19 have regular surfaces and the same size. The cement stone sample is a number of samples of the same size obtained under the same curing conditions, and the number is determined according to the specific situation.

[0044] Furthermore, the confining pressure pump 30 pressurizes the interior of the kettle through the confining pressure interface, so that there is no gap between the rubber sleeve and the sides of the formation surrounding rock and cement stone samples inside the kettle, ensuring that the corrosive medium seeps from left to right along the surrounding rock and cement water samples, simulating the corrosion process of the corrosive medium seeping from left to right.

[0045] Furthermore, the heating and heat-insulating sleeve 23 is connected to a temperature controller 25 .

[0046] Furthermore, the retaining ring 16 is located on the left side of the kettle body and is symmetrical up and down, protecting the rubber sleeve from damage and fixing the simulation sample inside the kettle body.

[0047] Furthermore, the corrosive medium storage tank 3 is connected to the acid gas cylinder 1 via a one-way valve 2 .

[0048] The present invention places surrounding rock and several cement stone samples in sequence from left to right inside a kettle body, applies confining pressure, injects corrosive medium through a flow pump and pressurizes the medium to the pressure required for the experiment. The confining pressure is greater than the pressure required for the experiment, and the required temperature is set. After the temperature reaches the requirement, the flow rate of the flow pump is adjusted to regularly or continuously inject the corrosive medium into the reaction container to ensure that the surrounding rock and cement stone samples are in a seepage state.

[0049] The method for conducting a high temperature and high pressure seepage corrosion simulation experiment using the above device comprises the following steps in sequence:

[0050] (1) Obtain no less than three cement paste samples of the same size under the same curing conditions, prepare a piece of surrounding rock of the same height as the cement paste sample, and the surfaces of the surrounding rock and cement paste sample are regular and can be closely arranged together; prepare the number of cement paste samples according to the specific experimental requirements;

[0051] (2) Prepare the corrosive solution in the corrosive medium storage tank;

[0052] (3) Place the surrounding rock and cement stone samples into the kettle from left to right in sequence, so that the surrounding rock and cement stone are closely arranged, which is the simulated sample; fix the retaining ring and seal the left and right end covers with bolts;

[0053] (4) Seal the corrosion kettle, and connect the corrosion kettle, flow pump, corrosion medium storage tank, and acid gas cylinder in sequence;

[0054] (5) Turn on the confining pressure pump and apply confining pressure to the simulated surrounding rock and cement stone samples through the confining pressure interface to ensure that the confining pressure is greater than the inlet pressure;

[0055] (6) Use the back pressure valve on the right side to adjust the seepage pressure difference of the corrosive fluid on the cement stone sample, as well as the pressure difference of the corrosive fluid circulation. Cover the heating and insulation jacket outside the kettle body and set the temperature to the required temperature through the temperature controller. Turn on the flow pump to inject the corrosive medium into the cavity through the liquid inlet to reach the temperature and pressure required for the experiment, and start the simulation experiment.

[0056] (7) Use a flow pump to regularly or continuously inject the designed corrosive medium into the corrosion kettle, and dynamically seep through the surrounding rock and cement stone samples;

[0057] (8) After the time required by the experimental design is reached, stop injecting the corrosive medium, turn off the temperature controller, and after the kettle temperature drops to room temperature or the set temperature, release the pressure of the corrosive fluid in the cavity on the left side of the kettle. Then, gradually reduce the confining pressure to zero, open the kettle, take out the surrounding rock and cement stone samples in turn, and conduct subsequent tests;

[0058] (9) Measure various parameters of cement stone corrosion at different distances from the surrounding rock (corrosion depth, compressive strength, etc.), obtain the seepage from the surrounding rock to the cement stone in the experiment, and the crossflow of the corrosive medium between the cement stone and the cement stone, so as to simulate the seepage velocity of the corrosive medium through the surrounding rock to the cement stone underground in the actual stratum and the crossflow velocity of the corrosive medium through the cement stone from the bottom of the well to the top; simulate whether the corrosion near the borehole of the wellbore may be closer to dynamic corrosion, whether there is a seepage velocity away from the borehole, if there is a seepage velocity, it may gradually decrease, and the seepage velocity becomes very slow beyond a certain range, and whether the cement stone corrosion may be closer to static corrosion.

[0059] 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 on the basis of the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A high-temperature and high-pressure seepage corrosion simulation experimental device, comprising a corrosive medium storage tank (3), a flow pump (4) and a corrosion kettle (7), characterized in that: The corrosion kettle (7) comprises a left end cover (14), a right end cover (24) and a kettle body (26) located in the middle. The left end cover, the right end cover and the kettle body are connected by bolts. The left end cover (14) is provided with a liquid inlet and a liquid outlet. The liquid inlet is provided with a one-way valve. The liquid outlet is provided with a back pressure valve and a pressure gauge. The liquid inlet is connected to a flow pump (4) through a pipeline. The flow pump is connected to a corrosion medium storage tank (3). A cavity (15) is provided in the middle of the left end cover. The cavity is communicated with the liquid inlet and the liquid outlet respectively. A retaining ring (16) is provided at the connection with the kettle body. The right end cover (24) is provided with a back pressure valve and a pressure gauge. The kettle body (26) is, from the inside to the outside, The kettle body is provided with a confining pressure interface, which is connected to a confining pressure pump (30) through a pipeline. The simulated sample consists of formation surrounding rock (17) and at least three cement stone samples (19). The formation surrounding rock and cement stone samples have regular surfaces and the same size, and are arranged in contact from left to right in the kettle body. The confining pressure pump pressurizes the inside of the kettle body through the confining pressure interface so that there is no gap between the rubber sleeve and the formation surrounding rock and cement stone samples in the kettle body, thereby ensuring that the corrosive medium seeps from left to right along the formation surrounding rock and cement stone samples.

2. A high temperature and high pressure seepage corrosion simulation experimental device as claimed in claim 1, characterized in that: The cement paste samples are several samples of the same size obtained under the same curing conditions, and the number is determined according to the specific situation.

3. A high temperature and high pressure seepage corrosion simulation experimental device as claimed in claim 1, characterized in that: The heating and heat-insulating sleeve is connected to a temperature controller (25).

4. A high temperature and high pressure seepage corrosion simulation experimental device as claimed in claim 1, characterized in that: The retaining ring is located on the left side of the kettle body and is symmetrical up and down, protects the rubber sleeve from damage, and fixes the simulation sample inside the kettle body.

5. The high temperature and high pressure seepage corrosion simulation experimental device according to claim 1, characterized in that: The corrosive medium storage tank is connected to the acid gas cylinder (1) via a one-way valve.

6. A method for conducting a high temperature and high pressure seepage corrosion simulation experiment using the device of claim 1, 2, 3, 4 or 5, comprising the following steps in sequence: (1) Prepare a piece of surrounding rock, make cement slurry according to API specifications, pour it into a mold for curing to make at least three cement stone samples of the same size, and place the surrounding rock and cement stone samples in the kettle from left to right in sequence, and arrange them closely to form a simulated sample; (2) Injecting the prepared corrosive medium into the corrosive medium storage tank; (3) Turn on the confining pressure pump and apply confining pressure to the simulated sample through the confining pressure interface to ensure that the confining pressure is greater than the inlet pressure; (4) Inject the corrosive medium into the cavity of the corrosion kettle through the flow pump, adjust the seepage pressure difference of the corrosive fluid on the cement stone sample and the pressure difference of the circulation of the corrosive fluid through the back pressure valve on the right end cover, and heat the corrosion kettle with the temperature controller to reach the temperature and pressure required for the experiment; (5) Use a flow pump to regularly or continuously inject the corrosive medium into the corrosion kettle to ensure that the corrosive medium continuously seeps through the surrounding rock and cement stone samples; (6) After the time required by the experimental design is reached, stop injecting the corrosive medium, turn off the temperature controller, and after the kettle temperature drops to room temperature or the set temperature, release the pressure in the kettle cavity to reduce the confining pressure, open the kettle and take out the surrounding rock and cement stone samples in turn; (7) Determine the corrosion parameters of cement paste samples at different distances from the surrounding rock, including corrosion depth, compressive strength and permeability.

7. The method according to claim 6, characterized in that By simulating the seepage from the surrounding rock to the cement stone sample and the crossflow of the corrosive medium between the cement stone samples, the seepage velocity of the corrosive medium in the actual formation through the surrounding rock to the cement stone underground and the data of the corrosive medium seepage through the cement stone from the bottom of the well to the top are obtained.

8. The method according to claim 6, characterized in that If the underground corrosive medium contains acid gas, the acid gas provided by the acid gas cylinder is injected into the corrosive medium storage tank.

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