Test device for simulating cement slurry plugging in oil and gas well formations, and method

Abstract

A test device for simulating cement slurry plugging in oil and gas well formations, and a method. The device comprises an upper kettle (13) and a lower kettle (16) which are snapped to form an inner cavity; the snap inner cavity is divided into an upper cavity (8), a middle cavity (11), and a lower cavity (17) by means of a floating piston (10) and a perforated isolation plate (15); the upper cavity, the middle cavity, and the lower cavity each are connected to a corresponding liquid feed and pressuring pipeline, a corresponding liquid discharge pipeline, a corresponding gas pipeline, and a corresponding overflow pipeline; heaters are arranged on the inner walls of the upper cavity, the middle cavity, and the lower cavity; temperature sensors and pressure sensors are arranged in the three cavities; a core barrel (27) is placed on the perforated isolation plate; a slurry containing barrel (25) is hung below the floating piston; and when the floating piston drives the slurry containing barrel to move downwards, the lower end of the slurry containing barrel sealedly abuts against the upper end of the core barrel. The test device can simulate various on-site working conditions, can analyze the process and result of squeezing cement slurry at multiple angles, and can provide sufficient test data for squeezing cement slurry to plug formations.

Description

Experimental apparatus and method for simulating formation cement slurry plugging in oil and gas wells Technical Field

[0001] This invention relates to the field of oil and gas well plugging technology, and in particular to a test apparatus and method for simulating formation cement slurry plugging in oil and gas wells. Background Technology

[0002] With the increasing demand for natural gas, pipeline transportation is no longer sufficient to solve the supply and demand problem, such as seasonal imbalances in gas consumption and transmission. In such cases, it is necessary to build gas storage facilities. Currently, approximately 70% of the world's underground gas storage facilities are converted from depleted oil and gas reservoirs. During the construction of gas storage facilities, the quality of sealing old wellbores is a major factor affecting the safety of the storage facility. Old wells typically have been in service for several decades, and the perforation and reservoir modification processes during the initial production phase essentially create numerous holes in the otherwise intact structure, making them highly susceptible to natural gas leaks. In severe cases, this can lead to wellhead leaks or even explosions. Therefore, one of the key technologies in constructing gas storage facilities for depleted oil and gas reservoirs is sealing all old wells in the storage structure.

[0003] Cement slurry sealing involves using liquid pressure to squeeze cement slurry into the formation or blast hole, stopping its flow and quickly solidifying to achieve a seal, thereby forming a permanent isolation zone inside the formation. This process is characterized by good sealing effect, low cost, and wide application in the field.

[0004] However, the current problem lies in the significant differences in the physical properties and pore-throat structures of different formations, which affect the ability of sealing cement slurry to penetrate different formations. Furthermore, different sealing cement slurry systems vary in composition and particle size, resulting in drastically different abilities to penetrate formation pores or perforations under pressure. The strength of the sealing cement slurry after setting may also differ. Therefore, it is impossible to effectively assess whether the cement slurry can penetrate the formation as expected, form a sufficient sealing zone near the wellbore, and seal pores of different sizes. Moreover, it is impossible to adjust the corresponding sealing parameters according to the specific well conditions of the oil and gas well, leading to unsatisfactory sealing results.

[0005] The "Abandoned Well Plugging Agent Test Device" (CN211179479U) applies periodic pressure to the test chamber using a simulated pressurization device, enabling it to test the reliability of the plugging agent in simulating formations and wellbore under alternating stress. However, its structure is flawed, relying solely on filter pores to simulate formations and failing to simulate the situation where cement slurry enters the formation core to form a plug. The "Full-Diameter High-Pressure Intelligent Leakage Plugging Tester" (CN203758993U) and the "High-Temperature High-Pressure Full-Diameter Core Fracture Plugging Tester" (CN103411750A) both evaluate the leakage plugging capability of drilling fluids by simulating the plugging of leaky formations by various solid particles in the drilling fluid.

[0006] In view of this, the present invention proposes a simulation experimental device for cement grouting oil and gas wells. Through a series of simulation experiments, the device studies the pressure required to squeeze different cement grouts into different formations, the depth of the cement grout squeezed into the formation core under a certain pressure, and the sealing ability of the core after solidification. This evaluates the adaptability of the cement grout to the formation to be sealed, and optimizes the formulation of the sealing system accordingly to ensure that the cement grout can penetrate into the formation or borehole to a certain depth, forming a sealing zone of sufficient thickness, and having sufficient strength after solidification to effectively seal the formation or borehole. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and to provide a test device and method for simulating formation cement slurry plugging in oil and gas wells. This invention solves the problem that existing simulation test devices require multiple devices to test various simulation items in the core sample and that the existing simulation items have insufficient parameters.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] Firstly, a test apparatus for simulating formation cement slurry plugging in oil and gas wells is provided, including an upper reactor and a lower reactor;

[0010] The upper and lower vessels can be locked together vertically to form a locking cavity. A floating piston that can move up and down is provided in the locking cavity, and a perforated partition plate is fixedly provided below the floating piston. The locking cavity is divided into an upper cavity, a middle cavity, and a lower cavity through the floating piston and the perforated partition plate.

[0011] The upper cavity is connected to the first liquid inlet pressurization line, the first liquid outlet line, the first gas line, and the first overflow line, respectively; the middle cavity is connected to the second liquid inlet pressurization line, the second liquid outlet line, the second gas line, and the second overflow line, respectively; and the lower cavity is connected to the third liquid inlet pressurization line, the third liquid outlet line, the third gas line, and the third overflow line, respectively. Heaters are installed on the inner walls of the upper cavity, the middle cavity, and the lower cavity, and corresponding temperature sensors and pressure sensors are installed in each of these three cavities.

[0012] A core tube is placed on the perforated isolation plate, and the core tube is snapped and fixed in the inner cavity; in addition, the core tube is sealed to the inner wall of the inner cavity by fitting a corresponding sealing ring; and a core is placed inside the core tube.

[0013] A slurry-holding cylinder is suspended below the floating piston. When the floating piston drives the slurry-holding cylinder to move downward, the lower end of the slurry-holding cylinder can be sealed and connected with the upper end of the core cylinder.

[0014] Ⅰ. When conducting the simulation test of "core water seepage capacity", the floating piston and slurry container need to be removed from the upper vessel; Ⅱ. When conducting the simulation test of "squeezing cement to seal the core", let the floating piston drive the slurry container downward to connect the slurry container with the core container. Cement slurry needs to be filled into the slurry container, and a positive pressure difference is formed between the middle cavity and the lower cavity to conduct the simulation test; Ⅲ. When conducting the simulation test of "testing the sealing effect after sealing the core with cement", a positive pressure difference is formed between the middle cavity and the lower cavity to conduct a positive sealing simulation test, and a positive pressure difference is formed between the lower cavity and the middle cavity to conduct a reverse sealing simulation test.

[0015] Furthermore, the upper vessel includes an upper vessel body and a top cover. The lower end of the upper vessel body is an opening, and the upper end of the upper vessel body is fitted with an openable top cover that can be sealed after being fastened. The lower vessel has an opening at the upper end and is closed at the lower end. A sedimentation tank and a perforated support cylinder are placed inside the lower vessel. The perforated support cylinder is fitted over the sedimentation tank, and the two form a certain annular gap. The height of the perforated support cylinder is greater than the height of the sedimentation tank, and a perforated partition plate is placed on top of the perforated support cylinder. After the upper and lower vessels are fastened together, the opening at the lower end of the upper vessel body aligns with the opening at the upper end of the lower vessel, and the fastening mechanism locks the connection securely.

[0016] Furthermore, the inner diameter of the upper vessel is smaller than that of the lower vessel, and a step A is formed at the engagement point when the upper and lower vessels are engaged. The outer cylindrical surface of the core tube is divided into a lower part, a middle part, and an upper part, with the outer diameters of the lower, middle, and upper parts decreasing sequentially. A step B is formed between the lower and middle parts. The outer diameter of the lower part is the same as the inner diameter of the lower vessel, the outer diameter of the middle part is the same as the inner diameter of the upper vessel, and the outer diameter of the upper part is smaller than the inner diameter of the upper vessel. When the core tube containing the core is placed in the engagement cavity: the core tube is inserted from the lower end of the upper vessel, with step B abutting against step A to secure the core tube. Furthermore, there is a corresponding sealing ring between the lower part of the tube and the inner wall of the lower vessel, a corresponding sealing ring between the middle part of the tube and the inner wall of the upper vessel, and an annular gap between the upper part of the tube and the inner wall of the upper vessel.

[0017] Furthermore, the upper end face of the upper part of the cylinder has an annular step C, and a core retaining ring is fixed to the upper end of the upper part of the cylinder by screws. The lower end face of the core retaining ring is adapted to the annular step C. The inner diameter of the core retaining ring is smaller than the inner diameter of the core cylinder. When the core retaining ring is fixed on the core cylinder, it can form a limiting structure for the core contained in the core cylinder. The upper end face of the core retaining ring is conical, and the lower end face of the slurry cylinder is also conical. The slurry cylinder fits against the core retaining ring and then connects with the core cylinder.

[0018] Furthermore, after the locking structure is released, the lifting mechanism drives the lower vessel to move downwards. A sealing ring is fitted on the lower part and middle part of the core cylinder containing the core. The core cylinder is placed on the perforated isolation plate inside the lower vessel. After placement, the lower part of the cylinder is sealed to the inner wall of the lower vessel by the sealing ring. Then, a sealing ring is fitted on the middle part of the cylinder. Then, the lifting mechanism moves upwards, and the lower vessel gradually inserts the core cylinder containing the core into the upper vessel, so that the perforated isolation plate abuts the step B against the step A. Then, the locking structure is locked, so that the upper vessel and the lower vessel are connected and locked together.

[0019] Furthermore, the connection structures of the first, second, and third liquid inlet pressurization lines are all identical, each including an oil-water transition tank, a pressure regulator, and a liquid inlet pressurization switch valve connected in sequence. The connection structures of the first, second, and third drain lines are also identical, with each line equipped with a drain switch valve. The connection structures of the first, second, and third gas lines are all identical, with each line equipped with a gas switch valve. The connection structures of the first, second, third, and fourth overflow lines are all identical, with each line having its initial end connected to the inner cavity, and from the initial end to the final end, a separation valve, a condensate tank, and a back pressure valve are connected in sequence.

[0020] Furthermore, the first, second, and third liquid inlet pressurization lines are all connected to the main pipe, which is connected to the water source via a pressurization pump. The liquid inlet pressurization switch valve, drain switch valve, gas switch valve, and isolation valve are all electrically connected to the controller; the pressurization pump is electrically connected to the controller; and the controller is electrically connected to the display.

[0021] Secondly, a test method for a test apparatus simulating formation cement slurry plugging in oil and gas wells is provided, including the following steps:

[0022] S1. Prepare and encapsulate the core of the stratum to be sealed;

[0023] Prepare and encapsulate the core of the stratum to be sealed: Take a rock core with a similar pore structure to the stratum core as the core, and match the diameter and height of the core tube; put the core inside the core tube, and fill the annular space between the inner wall of the core tube and the outer wall of the core with consolidation material; after the consolidation material solidifies, the core is fixed and installed inside the core tube;

[0024] S2, “Core Clear Water Seepage Capacity” Simulation Test – that is, measuring the “clear water seepage capacity of the core before the core is sealed with cement slurry”;

[0025] The upper vessel is fixed in place by a mechanical mechanism. The locking structure is loosened, and the lower vessel is moved downward by the lifting mechanism. A sedimentation tank and a perforated support cylinder are placed in the lower vessel, and a perforated isolation plate is placed on the upper end of the perforated support cylinder. Clean water is poured into the lower vessel until the perforated isolation plate is submerged.

[0026] The lower part of both the perforated partition plate and the core tube is the same size as the inner wall of the lower reactor. Place the core tube with the core already sealed on the perforated partition plate. When placing it, the lower part of the tube should be fitted with a corresponding sealing ring before inserting it into the lower reactor. Let the lower part of the core tube sit in the lower reactor, and the lower part of the tube is sealed to the inner wall of the upper end of the lower reactor by the sealing ring. The lower part of the tube is supported by the perforated partition plate.

[0027] A corresponding sealing ring is installed on the middle part of the core tube; then the core limiting ring is fixed to the upper end of the core tube to limit the upper end of the core.

[0028] Then, the lower vessel and the core cylinder containing the core are slowly lifted upwards by the lifting mechanism, so that the middle and upper parts of the core cylinder are inserted into the upper vessel. The middle part of the core cylinder is fitted with the inner wall of the upper vessel through the corresponding sealing ring. At the same time, the step B formed by the lower part and the middle part of the core cylinder abuts against the step A formed by the upper and lower vessels. Then, the upper and lower vessels are locked together by the locking structure.

[0029] Open the top cover of the upper vessel, and remove the floating piston and the slurry cylinder upwards. At this time, the middle cavity and the upper cavity are connected - the middle cavity and the upper cavity together form the inner cavity of the upper vessel; pour clean water into the inner cavity of the upper vessel until it reaches the top of the inner cavity; then put the top cover back on.

[0030] Open the third liquid inlet pressurization line and the third gas line corresponding to the lower chamber, and introduce pressurized liquid through the pressurization pump to expel the gas in the lower chamber. After the gas is vented, close the third gas line. During the venting process, keep the pressure in the lower chamber at 0.2Mpa-0.3Mpa.

[0031] Similarly, the upper cavity is vented using the method of venting the lower cavity.

[0032] Open the back pressure valve on the third overflow line corresponding to the lower chamber and set the target back pressure value of the back pressure valve to 3-4 MPa. At the same time, open the back pressure valve on the first overflow line corresponding to the upper vessel cavity and set the target back pressure value of the back pressure valve to 3-4 MPa. Then, inject pressurized fluid through the corresponding first liquid inlet pressurization line, second liquid inlet pressurization line, and third liquid inlet pressurization line. When the back pressure valves on the first overflow line, second overflow line, and third overflow line drip liquid accordingly, it indicates that the 3-4 MPa back pressure value in the upper vessel cavity and the 3-4 MPa back pressure value in the lower chamber have been successfully set.

[0033] Close the first and second overflow lines in the upper chamber and open the third overflow line in the lower chamber; then open the first and second liquid inlet pressure lines corresponding to the upper chamber and gradually increase the pressure in the upper chamber until the pressure difference between the upper chamber and the lower chamber reaches the set target value. By measuring the amount of clear water flowing out of the third overflow line under different pressure differences, the simulation of "core water seepage capacity" can be completed.

[0034] S3, Simulation test of "squeezing cement to seal the formation core";

[0035] Open the top cover of the upper reactor, apply grease to the lower conical surface and inner wall of the slurry container to make its lower conical surface fit with the upper conical surface of the core limiting ring to achieve a seal; place the slurry container on the core limiting ring at the upper end of the core cylinder; pour a predetermined volume of pre-prepared cement slurry under high temperature and pressure into the slurry container; connect the upper end of the slurry container to the floating piston through the corresponding connecting mechanism; and then close the top cover.

[0036] Open the first liquid inlet pressure line of the upper chamber, open the first gas line of the upper chamber, start the pressure pump, and vent the liquid inlet of the upper chamber. During venting, maintain the pressure of the upper chamber at 0.2-0.3 MPa; after venting is complete, close the first gas line of the upper chamber.

[0037] Then, through the first liquid inlet pressurization line, a pressure of more than 2 MPa is applied to the upper cavity and maintained.

[0038] Open the second liquid inlet pressure line and the second gas line of the middle chamber, start the pressure pump, and vent the liquid inlet to the middle chamber. During venting, maintain the pressure in the middle chamber at 0.2-0.3 MPa; after venting is complete, close the second gas line.

[0039] An initial pressure of 1-2 MPa is applied to the middle cavity through the second liquid inlet pressurization line, and simultaneously, an initial pressure of 1-2 MPa is applied to the lower cavity through the third liquid inlet pressurization line.

[0040] Set the target temperature value and turn on the heater to heat the upper and lower vessels. Once the temperature inside the vessels reaches the set target value, gradually increase the pressure in the upper and middle chambers, ensuring a positive pressure difference of 2 MPa between the middle and lower chambers throughout the process. Observe and record the drainage of the third overflow pipeline under different pressure differences between the middle and lower chambers to obtain the overflow volume under different pressure differences, so as to analyze the cement slurry injection under different pressure differences, until the set sealing pressure difference is reached.

[0041] Gradually reduce the pressure in the middle and upper chambers, ensuring that the upper chamber always has a positive pressure difference of 2 MPa greater than that in the middle chamber, until the pressure difference between the middle and lower chambers reaches the set setting pressure difference. The cement grouting is then complete; settling is then complete.

[0042] S4. Simulation test of "testing the sealing effect after sealing the rock core with cement", including testing the positive sealing effect of the rock core after sealing by pressurizing the middle cavity;

[0043] After the cement slurry has cured, gradually reduce the pressure in the upper chamber to the pressure in the middle chamber; close the first liquid inlet pressure line in the upper chamber and open the first overflow line in the upper chamber to release the pressure in the upper chamber. At the same time, observe and record the amount of liquid overflowing from the upper chamber, and judge the situation where the floating piston drives the slurry container and the cement stone formed by the remaining cement slurry in it to move upward together.

[0044] If the volume of the overflow reaches the set percentage of the upper chamber's volume, it is considered that the floating piston has moved significantly upward and has opened the upper surface of the sealed core. The next test can proceed as planned. If there is no overflow or the overflow volume is significantly smaller than the initial volume of the upper chamber, the pressure difference between the upper and lower parts of the floating piston is too small to move the floating piston and other components upward together. In this case, the pressure in the middle and lower chambers is gradually increased synchronously until the volume of the overflow in the upper chamber reaches the set percentage of the upper chamber's volume, ensuring that the upper surface of the sealed core is opened and the first overflow line is closed.

[0045] Gradually reduce the pressure in the middle cavity to the initial pressure—0.2-0.3 MPa—while simultaneously reducing the pressure in the lower cavity to the set initial pressure—0.2-0.3 MPa. Open the third overflow line to gradually increase the pressure in the middle cavity, creating a pressure difference between the middle and lower cavities. Observe and record the time when the lower cavity begins to overflow—the time when the core is punctured. The pressure difference at this time is the puncture pressure difference of the core after sealing. Observe and record the seepage velocity of clear water under different pressure differences to evaluate the sealing capacity of the core after sealing, until the set test pressure difference is reached, completing the positive pressure sealing effect test. Gradually reduce the pressure in the middle cavity to its initial pressure.

[0046] S5-1, “Simulation test of sealing effect after cement sealing of rock core”, also includes reverse pressure test of reverse sealing effect;

[0047] If the core sample is not penetrated during the forward test, immediately conduct a reverse pressure test to assess the reverse sealing effect of the core sample after sealing. Close the third overflow line and open the second overflow line, gradually increasing the pressure in the lower chamber. Observe and record the time when the middle chamber begins to overflow—the time when the core sample is penetrated. The pressure difference at this point is the penetration pressure difference of the core sample after sealing. Observe and record the clear water seepage velocity under different pressure differences to evaluate the reverse sealing capability of the core sample after sealing. Continue until the set test pressure difference is reached to complete the reverse pressure sealing effect test. Gradually reduce the pressure in the lower chamber to its initial pressure.

[0048] S6. Experiment ends;

[0049] Stop heating and pressurizing, disassemble the entire test apparatus, and clean it.

[0050] S7. Analysis of experimental results;

[0051] The sealing effect of the core can be evaluated by comparing the breakdown pressure and water seepage rate of the core before and after sealing.

[0052] By analyzing the amount of initial cement slurry in the slurry container, the amount of cement stone formed by the remaining cement slurry, and the density distribution of the remaining cement stone, combined with the amount of liquid overflowing from the lower cavity during cement slurry extrusion, the amount of cement slurry components extruded into the core under the corresponding pressure difference can be analyzed.

[0053] By analyzing CT scan images of core samples before and after sealing, and the distribution of water-soluble and fine-particle tracer materials on the core profile, the process and results of cement slurry components entering the core under pressure differential were analyzed, thereby inferring the process of cement slurry components being squeezed into the core. By changing the sealing cement slurry, the core sample of the formation to be sealed, and the sealing pressure differential parameters, different sealing results and effects were obtained, thereby studying the influence of relevant factors on the sealing results and effects.

[0054] Furthermore, in S5-1, the reverse pressure test for the reverse sealing effect can also be performed using method S5-2;

[0055] S5-2, Reverse pressure test to test the reverse sealing effect;

[0056] After the cement slurry has set, directly perform a reverse pressure test to check the reverse sealing effect of the core after sealing; first reduce the pressure in the upper cavity, open the upper surface of the core after sealing, and then close the third overflow pipeline; then perform a reverse pressure test according to the method in S5-1, and then gradually reduce the pressure in the lower cavity to its initial pressure.

[0057] It should be noted that this scheme can simulate the high-temperature and high-pressure environment at the bottom of the well, formation cores with different lithologies, and cement slurry with different components and properties. It can accurately control the extrusion parameters, accurately measure the amount of cement slurry or its components extruded into the formation, and simulate the setting process of cement slurry under high temperature and pressure. Under high temperature and pressure, the remaining cement stone column can be hydraulically broken to expose the upper surface of the sealed core. Simultaneously, the core is fixed by a perforated isolation plate at the lower end and a top limiting ring at the upper end, thus achieving both top-down forward testing and bottom-up reverse testing. This tests the breakdown pressure and clear water seepage velocity of the sealed core, evaluating the sealing effect. Finally, after cooling and depressurization, the cement stone formed by extruding the remaining cement slurry can be... Analyzing data such as the volume and density distribution of remaining cement stone allows for the study of the distribution of cement slurry or its components squeezed into the core through methods such as core sectioning after sealing, CT scanning / XRD component analysis / tracer distribution analysis, etc. This enables the inversion of the squeezing process, exploration of relevant factors affecting the squeezing effect and their mechanisms of action, and evaluation of the adaptability of cement slurry to the formation to be sealed. This provides necessary research tools for the industry to conduct experimental research on squeezing cement slurry to seal formations / channels, evaluate the adaptability of cement slurry to the formation to be sealed, optimize cement slurry components based on the pore and fracture parameters of the formation to be sealed, optimize cement slurry performance, match reasonable squeezing parameters, strengthen the control of the squeezing process, and improve the effectiveness of squeezing cement slurry in sealing formations / channels.

[0058] The present invention has the following advantages:

[0059] I. This scheme can simulate various field conditions: (1) It can simulate the process of measuring the absorption of the formation to be sealed before the cement slurry is squeezed out; (2) It can simulate the process of squeezing the sealing cement slurry into the formation under high temperature and high pressure after it is injected into the well; (3) It can simulate the process of the cement slurry and its components squeezed into the core solidifying and hardening to seal the formation in the high temperature and high pressure environment in the well; (4) It can simulate the process of testing the wellbore pressure after the cement slurry solidifies and testing the sealing effect of the sealing strip under high temperature and high pressure; (5) It can simulate the process of testing the sealing effect of the sealing strip under high temperature and high pressure after the formation pressure of the gas storage rises.

[0060] II. During the test, several innovative functions are achieved through innovative structural design: (1) It can accurately control the pressure difference of the extruded cement slurry; (2) It can prepare and measure the amount of cement slurry and its components extruded into the core; (3) It can reduce the pressure of the upper cavity and move the floating piston up under the action of pressure difference to open the upper end face of the core after sealing without cooling or reducing pressure; (4) Without cooling or reducing pressure, after opening the overflow pipeline valve of the lower cavity, the middle cavity is pressurized to test the positive breakdown pressure and clear water seepage capacity of the core after sealing; (5) Without cooling or reducing pressure, after opening the overflow pipeline valve of the middle cavity, the lower cavity is pressurized to test the reverse breakdown pressure and clear water seepage capacity of the core after sealing.

[0061] III. The process and results of squeezing cement slurry can be analyzed from multiple perspectives: (1) The sealing effect on the core can be evaluated by the penetration pressure and clear water seepage velocity of the core before and after sealing; (2) The amount of liquid overflowing from the downstream chamber during squeezing cement slurry can be used to determine the situation where cement slurry is squeezed into the core or even passes through the core to enter the downstream chamber; (3) The time and pressure difference of the core being punctured can be inferred from the change in the overflow velocity of the downstream chamber during squeezing cement slurry; (4) The composition of cement slurry entering the core under pressure difference can be analyzed by the axial density distribution of cement stone formed by the remaining cement slurry in the slurry container; (5) The composition of cement slurry entering the core under pressure difference and its penetration depth can be analyzed by CT scanning of the core after sealing and the distribution of tracer material in the core.

[0062] Fourth, it can provide more reliable technical means for the relevant theories and technologies of cement slurry sealing of formations: By conducting relevant experiments, it can study the influence and mechanism of relevant factors such as cement slurry pressure difference, cement slurry composition and properties, and core pore size distribution on the effect of cement slurry sealing of cores. Based on this, it can optimize the composition of sealing cement slurry, improve the formulation of sealing cement slurry, and improve the adaptability of sealing cement slurry to the formation to be sealed, ultimately reducing the sealing pressure and improving the sealing effect. This provides a scientific, reasonable and reliable technical means for conducting indoor research on cement slurry sealing of formations and for field evaluation of the adaptability of sealing cement slurry to the formation to be sealed. Attached Figure Description

[0063] Figure 1 is a schematic diagram of the structure of the present invention;

[0064] In the diagram: 1-Top cover; 3-Back pressure valve; 4-Condensate tank; 5-Isolation valve; 7-Valve; 8-Upper chamber; 9-Clamping nut; 10-Floating piston; 11-Middle chamber; 12-Consolidation material; 13-Upper vessel; 14-Connecting bolt; 15-Perforated isolation plate; 16-Lower vessel; 17-Lower chamber; 18-Perforated support cylinder; 19-Settling tank; 20-Bottom cover; 21-Drainage switch valve; 22-Pressure regulator; 23-Oil-water transition tank; 24-Connecting rod; 25-Slurry container; 26-Core limiting ring; 27-Core cylinder; 29-Main pipe; 30-Pressure pump; 31-Controller; 32-Display. Detailed Implementation

[0065] The present invention will be further described below with reference to the accompanying drawings, but the scope of protection of the present invention is not limited to the following description.

[0066] It should be noted that the orientation or positional relationship indicated by terms such as "left" and "right" is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is usually placed during use, or the orientation or positional relationship in which those skilled in the art would conventionally understand it. Such terms are only for the convenience of describing the invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention.

[0067] Those skilled in the art will understand that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0068] It should be noted that, unless otherwise specified, the embodiments and features and technical solutions in the present invention can be combined with each other.

[0069] As shown in Figure 1, this embodiment discloses a test apparatus for simulating formation cement slurry plugging in oil and gas wells, including an upper vessel 13 and a lower vessel 16;

[0070] The upper vessel 13 and the lower vessel 16 can be fastened together vertically and form a fastening cavity after fastening. In the fastening cavity, a floating piston 10 that can move up and down is provided, and a perforated isolation plate 15 is fixedly provided below the floating piston 10. The fastening cavity is divided into an upper cavity 8, a middle cavity 11 and a lower cavity 17 through the floating piston 10 and the perforated isolation plate 15.

[0071] The upper cavity 8 is connected to the first liquid inlet pressurization line, the first liquid outlet line, the first gas line, and the first overflow line, respectively. The middle cavity 11 is connected to the second liquid inlet pressurization line, the second liquid outlet line, the second gas line, and the second overflow line, respectively. The lower cavity 17 is connected to the third liquid inlet pressurization line, the third liquid outlet line, the third gas line, and the third overflow line, respectively. Heaters are provided on the inner walls of the upper cavity 8, the middle cavity 11, and the lower cavity 17, and corresponding heat preservation devices are provided in these three cavities. Corresponding temperature sensors and pressure sensors are provided in these three cavities.

[0072] A core tube 27 is placed on the perforated isolation plate 15 and is snapped into the inner cavity; in addition, the core tube 27 is sealed to the inner wall of the inner cavity by fitting a corresponding sealing ring; and a core is contained inside the core tube 27.

[0073] A slurry container 25 is suspended below the floating piston 10. When the floating piston 10 drives the slurry container 25 to move downward, the lower end of the slurry container 25 can be sealed and connected with the upper end of the core cylinder 27.

[0074] It should be noted that: Ⅰ. When conducting the simulation test of "core water seepage capacity", the floating piston 10 and the slurry container 25 need to be removed from the upper vessel 13; Ⅱ. When conducting the simulation test of "squeezing cement to seal the formation core", the floating piston 10 drives the slurry container 25 downward to connect the slurry container 25 with the core container 27. Cement slurry needs to be filled into the slurry container 25, and a positive pressure difference is formed between the middle cavity 11 and the lower cavity 17 to conduct the simulation test; Ⅲ. When conducting the simulation test of "testing the sealing effect after sealing the core with cement", a positive pressure difference is formed between the middle cavity 11 and the lower cavity 17 to conduct a positive sealing simulation test, and a positive pressure difference is formed between the lower cavity 17 and the middle cavity 11 to conduct a reverse sealing simulation test.

[0075] The structure of the upper pot 13 and the lower pot 16 will be further explained below.

[0076] The upper vessel 13 includes an upper vessel body and a top cover 1. The lower end of the upper vessel body is an opening, and the upper end of the upper vessel body is fitted with an openable top cover 1 that can be sealed after being fastened. Furthermore, the upper vessel 13 includes an upper vessel body and a top cover 1. The top cover 1 is detachably fixed to the top of the upper vessel body by corresponding connecting bolts, and a corresponding sealing ring is provided between the top cover 1 and the upper vessel body. The lower vessel 16 includes a lower vessel body and a bottom cover 20. The bottom cover 20 is detachably fixed to the bottom of the lower vessel body by corresponding connecting bolts, and a corresponding sealing ring is also provided between the bottom cover 20 and the lower vessel body. The lower end of the upper vessel body and the upper end of the lower vessel body are sealed and fastened together by corresponding fastening bolts 14.

[0077] The lower vessel 16 includes a lower vessel body and a bottom cover 20. The upper end of the upper vessel body is an opening, and the lower end of the upper vessel body is sealed by the bottom cover 20. Furthermore, a settling tank 19 and a perforated support cylinder 18 are placed inside the lower vessel 16. The perforated support cylinder 18 is fitted over the settling tank 19, with a certain annular gap between them. The height of the perforated support cylinder 18 is greater than the height of the settling tank 19. A perforated partition plate 15 is placed on top of the perforated support cylinder 18. The perforated partition plate 15 is disc-shaped, and its outer diameter is approximately equal to the inner diameter of the lower vessel 16. When the perforated partition plate 15 is placed inside the support cylinder 18, it fits the inner wall of the lower vessel 16.

[0078] The upper vessel 13 has a flange at its lower end, and the lower vessel 16 has a flange at its upper end. After the upper vessel 13 and the lower vessel 16 are fastened together, the opening at the lower end of the upper vessel body is connected to the opening at the upper end of the lower vessel body. Then, the flanges between the upper vessel 13 and the lower vessel 16 are fastened together. After fastening, they are fixedly connected by fastening bolts 14 to form a locking structure at the fastening point.

[0079] The following section provides a further explanation of the installation structure between the core cylinder 27, the upper reactor 13, and the lower reactor 16.

[0080] The inner diameter of the upper vessel 13 is smaller than that of the lower vessel 16. When the upper vessel 13 and the lower vessel 16 are engaged, a step A is formed at the engagement point in the engagement cavity.

[0081] The outer cylindrical surface of the core tube 27 is divided into a lower part, a middle part, and an upper part, with the outer diameters of the lower part, the middle part, and the upper part decreasing sequentially. A step B is formed between the lower part and the middle part. Furthermore, the outer diameter of the lower part is the same as the inner diameter of the lower vessel 16, the outer diameter of the middle part is the same as the inner diameter of the upper vessel 13, and the outer diameter of the upper part is smaller than the inner diameter of the upper vessel 13.

[0082] When placing the core cylinder 27 containing the core into the locking cavity: insert the core cylinder 27 from the lower end of the upper vessel 13, so that the step B abuts against the step A, thereby achieving the snap-locking and fixing of the core cylinder 27; and, there is a corresponding sealing ring between the lower part of the cylinder and the inner wall of the lower vessel 16, a corresponding sealing ring between the middle part of the cylinder and the inner wall of the upper vessel 13, and an annular gap between the upper part of the cylinder and the inner wall of the upper vessel 13.

[0083] In addition, the upper end face of the upper part of the cylinder has an annular step C, and a core retaining ring 26 is fixed to the upper end of the upper part of the cylinder by screws. The lower end face of the core retaining ring 26 is adapted to the annular step C. The inner diameter of the core retaining ring 26 is smaller than the inner diameter of the core cylinder 27. When the core retaining ring 26 is fixed on the core cylinder 27, it can form a retaining structure for the core contained in the core cylinder 27. The upper end face of the core retaining ring 26 is conical, and the lower end face of the slurry container 25 is also conical. The slurry container 25 fits against the core retaining ring 26 and then connects with the core cylinder 27.

[0084] During installation:

[0085] The upper vessel 13 is fixed to a mechanical fixing mechanism, and the lower vessel 16 is installed on a lifting mechanism that can move up and down. After the locking structure is released, the lifting mechanism drives the lower vessel 16 to move downward. A sealing ring is fitted onto the lower part of the core cylinder 27 containing the core, and then the core cylinder 27 is placed inside the lower vessel 16, supported by the perforated partition plate 15, with the sealing ring at the lower part of the cylinder fitting and sealing against the inner wall of the lower vessel 16. Then, a corresponding sealing ring is fitted onto the middle part of the core cylinder 27, and a core limiting ring 26 is fixed at the upper end of the core cylinder 27. Under the action of the lifting mechanism moving upward, the core cylinder 27 containing the core is gradually inserted into the upper vessel 13, and the perforated partition plate 16 is pressed against the step A, with the middle part of the cylinder fitting and sealing against the inner wall of the upper vessel 13. After the locking structure is tightened, the upper vessel 13 and the lower vessel 16 can be connected and locked together.

[0086] It should be noted that the structure of the upper vessel 13, lower vessel 16, and core cylinder 27, as well as the installation structure between them, are designed in such a way that when the upper vessel 13 is separated from the lower vessel and the core cylinder 27 containing the core is placed on the perforated partition plate 15, the core cylinder 27 can be stably placed inside the lower vessel 16. When the lifting mechanism moves the lower vessel 16 upward, the core cylinder 27 inside the lower vessel 16 is stable and does not shake, thus facilitating the precise insertion of the core cylinder 27 into the upper vessel 13 and benefiting the lifting mechanism. The automated operation of the structure: When the core cylinder 27 is inserted into the upper vessel 13, it is secured in the inner cavity by corresponding steps A and B. The lifting mechanism facilitates the automated operation of this mechanism. Furthermore, after insertion, the sealing rings on the middle and lower parts of the cylinder seal the upper and lower vessels 13 and 16 at the connection point, preventing the inner cavity from communicating with the outside atmosphere – thus achieving automatic sealing. In addition, the venting, pressure build-up, and liquid drainage in the upper cavity 8, middle cavity 11, and lower cavity 17 are all controlled by the controller 31, which automatically measures the corresponding parameters, minimizing human interference and achieving automated measurement, thus ensuring measurement accuracy.

[0087] The following provides further explanation of each pipeline.

[0088] The connection structures of the first, second, and third inlet pressure lines are all identical, each including an oil-water transition tank 23, a pressure regulator 22, and an inlet pressure switch valve connected in sequence. Furthermore, the first, second, and third inlet pressure lines are all connected to a main pipe 29, which is connected to a water source via a pressure pump 30.

[0089] The connection structures of the first, second, and third drain lines are all identical, and each line is equipped with a drain switch valve 21.

[0090] The connection structures of the first, second, and third gas pipelines are all identical, and each pipeline is equipped with a gas switch valve 7. The connection structures of the first, second, third, and fourth overflow pipelines are all identical, with the end connected to the interlocking cavity as the initial end, and from the initial end to the tail end, an isolation valve 5, a condensate tank 4, and a back pressure valve 3 are connected in sequence.

[0091] It should be noted that the inlet pressure switch valve, the outlet switch valve 21, the gas switch valve 7, and the isolation valve 5 are all electrically connected to the controller 31; the pressure pump 30 is electrically connected to the controller 31; and the controller 31 is electrically connected to the display 32. Of course, other components that need to be controlled and monitored also need to be electrically connected to the controller 31, such as pressure sensors, temperature sensors, heaters, and other valves. These electrical connections are simply a basic PLC control method and will not be listed or elaborated upon here.

[0092] Secondly, a test method for a test apparatus simulating formation cement slurry plugging in oil and gas wells is provided, including the following steps:

[0093] S1. Prepare and encapsulate the core of the stratum to be sealed;

[0094] Prepare and encapsulate the core of the stratum to be sealed: Take a rock with a similar pore structure to the stratum core as the core, and match the diameter and height of the core tube 27; place the core tube 27 on a glass plate coated with sealant, and put the core into the core tube 27; after insertion, there is an annular space between the core tube 27 and the core, and fill the annular space with a solidifying material 12 such as resin or cement grout; after the solidifying material 12 solidifies, the fixing and installation of the core in the core tube 27 is completed;

[0095] It should be noted that if the obtained core does not have natural cracks, artificial cracks can be created through methods such as Brazilian splitting. After artificial cracking, a core with a porous and fractured structure similar to that of the stratum core can be obtained.

[0096] S2, “Core Clear Water Seepage Capacity” Simulation Test – that is, measuring the “clear water seepage capacity of the core before the core is sealed with cement slurry”;

[0097] The upper vessel 13 is fixed in place by a mechanical mechanism. The locking structure is loosened, and the lower vessel 16 is driven to move downward by the lifting mechanism. A sedimentation tank 19 and a perforated support cylinder 18 are placed inside the lower vessel 16. The sedimentation tank 19 is located at the center of the bottom of the lower vessel 16, and the perforated support cylinder 18 is sleeved on the outside of the sedimentation tank 19 with an annular gap between them.

[0098] The height of the perforated support cylinder 18 is lower than the height of the lower vessel 13, and the height of the settling tank 19 is lower than the height of the perforated support cylinder 18. A perforated isolation plate 15 is placed on the upper end of the perforated support cylinder 18, that is, the height of the perforated isolation plate 15 is lower than the height of the upper opening of the lower vessel 16. The lower part of both the perforated isolation plate 15 and the core cylinder 27 is consistent with the inner wall size of the lower vessel 16. When the perforated isolation plate 15 is placed on the perforated support cylinder 18, the perforated isolation plate 15 is fitted into the lower vessel 16 and the perforated isolation plate 15 is slightly lower than the upper opening of the lower vessel 16.

[0099] Pour clean water into the lower vessel 16 until it submerges the perforated isolation plate 15;

[0100] During placement, a sealing ring is fitted over the lower part of the core cylinder 27 containing the core, and then the lower part of the cylinder is inserted into the lower vessel 16—so that the lower part of the cylinder sits on the perforated isolation plate 15—the sealing ring seals between the lower part of the cylinder and the inner wall of the lower vessel 16; it should be noted that the height of the lower part of the cylinder is the same as the height of the perforated isolation plate 15 to the upper opening of the lower vessel 16, and when the lower part of the core cylinder 27 is inserted into the lower vessel 16, the upper end face of the lower part of the cylinder is flush with the upper end face of the upper opening of the lower vessel 16;

[0101] A corresponding sealing ring is fitted over the middle part of the core tube 27; then the core limiting ring 26 is fixed to the upper end of the core tube 27 to limit the upper end of the core.

[0102] Then, the lower vessel 16 and the core cylinder 27 containing the core are slowly lifted upwards by the lifting mechanism, so that the middle and upper parts of the core cylinder 27 are inserted into the upper vessel 16 from bottom to top, and the middle part of the cylinder is fitted with the inner wall of the upper vessel 16 through the corresponding sealing ring. At the same time, the step B formed by the lower part and the middle part of the cylinder abuts against the step A formed by the upper vessel 13 and the lower vessel 16. Then, the upper vessel 13 and the lower vessel 16 are locked together by the locking structure.

[0103] Open the top cover 1 of the upper vessel 13, and take out the floating piston 10 and the slurry cylinder 25 upwards. At this time, the middle cavity and the upper cavity are connected - the middle cavity and the upper cavity in the connected state together constitute the inner cavity of the upper vessel.

[0104] Pour clean water into the inner cavity of the upper vessel until it reaches the top of the inner cavity; then install the top cover 1.

[0105] Open the third liquid inlet pressurization line and the third gas line corresponding to the lower chamber 17, and introduce pressurized liquid through the pressurization pump 30 to expel the gas in the lower chamber 17; during the venting process, maintain the pressure in the lower chamber 12 at 0.2Mpa-0.3Mpa; after the venting is completed, close the third gas line; during the venting process, the third liquid outlet line is always closed;

[0106] Similarly, following the lower chamber venting method described above, venting is performed on the upper vessel's inner cavity. Since the upper and middle cavities are connected at this time, venting can be achieved through the first liquid inlet pressurization line and the first gas line, or through the second liquid inlet pressurization line and the second gas line, or through the first liquid inlet pressurization line, the second liquid inlet pressurization line, the first gas line, and the second gas line together. During venting, the first drain line and the second drain line are always closed.

[0107] The target back pressure value—3-4 MPa—is set for the lower chamber 17 and the upper vessel cavity through the back pressure valve 3 on the corresponding overflow pipeline. Specifically, the back pressure valve 3 is fully closed, the third overflow pipeline corresponding to the lower chamber 17 is opened, the first overflow pipeline and the second overflow pipeline corresponding to the upper vessel cavity are opened, and the pressure pump 30 is started to apply the set target pressure value—the target back pressure value—to the lower chamber 17 and the upper vessel cavity. The back pressure valve 3 on the third overflow pipeline of the lower chamber 17 is gradually opened, and the back pressure valve 3 on the first overflow pipeline and the second overflow pipeline corresponding to the upper vessel cavity is opened until all these back pressure valves 3 are dripping liquid, indicating that the back pressure value of the corresponding back pressure valve 3 has been successfully set. During the back pressure period, the corresponding first drain pipeline, second drain pipeline, and third drain pipeline are always closed.

[0108] Close the first and second overflow lines in the upper vessel cavity, and open the third overflow line in the lower cavity 17; then open the first and second liquid inlet pressure lines corresponding to the upper vessel cavity, gradually increasing the pressure in the upper vessel cavity until the pressure difference between the upper vessel cavity and the lower cavity reaches the set target value; then the clean water in the upper vessel cavity will flow through the gaps in the core to the lower cavity 17. Since the lower cavity 17 is filled with clean water, the excess clean water is discharged through the third overflow line; by measuring the amount of clean water flowing out of the third overflow line under different pressure differences between the upper vessel cavity and the lower cavity 17, the simulation of "core clean water seepage capacity" can be completed;

[0109] S3, Simulation test of "squeezing cement to seal the formation core";

[0110] Open the top cover 1 on the upper reactor 13, apply grease to the lower conical surface and inner wall of the slurry cylinder 25 to make its lower conical surface fit with the upper conical surface of the core limiting ring 26 to achieve a seal; place the slurry cylinder 25 on the core limiting ring 26 at the upper end of the core cylinder 27; pour a predetermined volume of pre-prepared cement slurry under high temperature and pressure into the slurry cylinder 25; connect the upper end of the slurry cylinder 25 to the floating piston 10 through the corresponding connecting mechanism; and then close the top cover 1.

[0111] In this way, the upper cavity 8, the middle cavity 11, and the lower cavity 17 are separated;

[0112] Open the first liquid inlet pressurization line of the upper chamber 8, open the first gas line of the upper chamber 8, and open the second gas line; start the pressurization pump 30 to inject liquid and vent gas into the upper chamber 8. At this time, the floating piston 10 is pressed down and the impeller cylinder 25 is pressed against the core limiting ring 26. During the liquid injection and venting process, maintain the pressure of 0.2-0.3 MPa in the upper chamber; after the venting is completed, close the first gas line on the upper chamber 8.

[0113] The upper chamber 8 is pressurized and maintained at 3-4 MPa through the first liquid inlet pressurization line. It should be noted that the purpose of setting 3-4 MPa here is to ensure that the upper chamber 8 always maintains positive pressure on the middle chamber 11. Of course, other values ​​that can maintain positive pressure can also be set.

[0114] Open the second liquid inlet pressure line and the second gas line of the middle cavity 11, start the pressure pump 30 to introduce liquid into the middle cavity 11 and vent it; during the process of introducing liquid into the middle cavity 11 and venting it, the middle cavity 11 should always maintain a pressure of 0.2-0.3 MPa; after venting is completed, close the second gas line.

[0115] An initial pressure of 1-2 MPa is applied to the middle cavity 11 through the second liquid inlet pressurization line;

[0116] The initial pressure of the lower chamber 17 is 1-2 MPa through the third liquid inlet pressurization line. At this time, the initial pressure of the lower chamber 17 can also be set to atmospheric pressure, but considering that subsequent heating may cause the liquid to expand thermally, it is preferable to keep the initial pressure of the lower chamber 17 at 1-2 MPa.

[0117] Set the target temperature value and turn on the heater to heat the upper vessel 13 and lower vessel 16. Once the temperature inside the vessel reaches the set target value, gradually increase the pressure in the upper chamber 8 and the middle chamber 11, ensuring that the upper chamber 8 always has a positive pressure difference of about 2 MPa greater than the middle chamber 11 during the gradual pressure increase. During the gradual pressure increase, observe and record the discharge of the third overflow pipeline under different pressure differences between the middle and lower chambers to obtain the overflow volume under different pressure differences, in order to analyze the cement slurry extrusion under different pressure differences (the overflow volume is the cement extrusion volume), until the set sealing pressure difference is reached. Gradually decrease the pressure in the middle chamber 11 and the upper chamber 8, ensuring that the upper chamber 8 always has a positive pressure difference of about 2 MPa greater than the middle chamber 11 during the pressure reduction, until the set setting pressure difference between the middle chamber 11 and the lower chamber 17 is reached, and the cement slurry extrusion sealing is completed; wait for setting.

[0118] S4, “Simulation test of sealing effect after cement sealing of rock core”, including pressure test of the middle cavity 8 to test the positive sealing effect of the rock core after sealing;

[0119] After the cement slurry has cured, gradually reduce the pressure in the upper chamber 8 to the pressure in the middle chamber 11; close the first liquid inlet pressure line of the upper chamber 8, open the first overflow line of the upper chamber 8, and release the pressure of the upper chamber 8 by overflowing liquid. At the same time, observe and record the amount of liquid overflowing from the upper chamber 8, and judge the situation of the floating piston 10 moving the slurry cylinder 25 and the cement stone formed by the remaining cement slurry in it upward together.

[0120] If the volume of the overflow reaches more than 50% of the volume of the upper cavity 8 (that is, when the paddle cylinder 25 is against the core limiting ring 26, there is a fixed value of the height difference between the floating piston 10 and the top cover 1, and the volume corresponding to this fixed value of the height difference is recorded as the volume of the upper cavity; when the overflow liquid reaches half of the volume of the upper cavity, it is considered that the volume of the overflow reaches 50% of the volume of the upper cavity 8), then it is considered that the floating piston 10 has obviously moved upward and has opened the upper end face of the sealed core, and the next step of testing can be carried out as planned; if there is no overflow or the volume of the overflow is significantly smaller than the initial volume of the upper cavity, then the pressure difference between the upper and lower parts of the floating piston 10 is too small and insufficient to drive the floating piston 10 and other components to move upward together. At this time, the pressure of the middle cavity 11 and the lower cavity 17 is gradually increased synchronously until the volume of the overflow in the upper cavity 8 reaches more than 50% of the volume of the upper cavity, ensuring that the upper end face of the sealed core is opened and the first overflow pipeline is closed;

[0121] Gradually reduce the pressure in the middle cavity 11 to the initial pressure—1-2 MPa—and simultaneously gradually reduce the pressure in the lower cavity 17 to the initial pressure—1-2 MPa. The pressures in the middle cavity 11 and the lower cavity 17 are reduced synchronously, and the pressure reduction per unit time is the same. Open the third overflow line and gradually increase the pressure in the middle cavity 11 to form a pressure difference between the middle cavity 11 and the lower cavity 17. Observe and record the time when the lower cavity 17 begins to overflow—the time when the core is punctured. The pressure difference at this time is the puncture pressure difference of the core after sealing. Observe and record the clear water seepage velocity under different pressure differences to evaluate the sealing ability of the core after sealing, until the set test pressure difference is reached to complete the positive pressure sealing effect test. Gradually reduce the pressure in the middle cavity 11 to its initial pressure.

[0122] S5-1, “Simulation test of sealing effect after cement sealing of rock core”, also includes reverse pressure test of reverse sealing effect;

[0123] If the core sample is not punctured during the forward test, a reverse pressure test is immediately conducted to assess the reverse sealing effect of the core sample after sealing. Specifically, the third overflow line is closed, the second overflow line is opened, and the pressure in the lower chamber 17 is gradually increased. When the pressure in the lower chamber 17 increases, the impeller 25 separates from the core limiting ring 26—that is, the upper surface of the sealed core sample is uncovered. The time when the middle chamber 11 begins to overflow—the time when the core sample is punctured—is observed and recorded. The pressure difference at this time is the puncture pressure difference of the sealed core sample. The seepage velocity of the clear water under different pressure differences is observed and recorded to evaluate the reverse sealing capability of the sealed core sample until the set test pressure difference is reached, thus completing the reverse pressure sealing effect test. The pressure in the lower chamber 17 is then gradually reduced to its initial pressure.

[0124] It should be noted that in S5-1, the reverse pressure test for reverse blocking effect can also be performed using the S5-2 method;

[0125] S5-2, Reverse pressure test for reverse sealing effect: After the cement slurry has set, the reverse pressure test is performed on the core after sealing. Specifically, the pressure in the upper chamber 8 is reduced first, and then the floating piston 10 drives the slurry cylinder 25 to move upward, so that the slurry cylinder 25 separates from the core limiting ring 26 - that is, the upper end face of the core after sealing is opened. Then the third overflow line is closed; then the third overflow line is closed and the second overflow line is opened, and the pressure in the lower chamber 17 is gradually increased to perform the reverse pressure test. Then the pressure in the lower chamber is gradually reduced to its initial pressure.

[0126] S6. Experiment ends;

[0127] Stop heating and pressurizing, disassemble the entire test apparatus, and clean it.

[0128] After completing the test, stop heating the corresponding vessel, close the corresponding liquid inlet pressure lines for each chamber, and shut down the pressure pump 30. When the temperature of the upper vessel 13 and lower vessel 16 drops to room temperature or the set temperature, open the corresponding drain lines for each chamber to release the pressure in each chamber until the pressure in each chamber is zero. Then, allow air to enter and drain liquid from each chamber. Remove the top cover 1. Remove the locking structure of the upper vessel 13 and lower vessel 16, lower the lower vessel 16 to a suitable position, and remove and clean the core cylinder 27 and the perforated isolation plate 1. 5. Clean the perforated support cylinder 18 and settling tank 19 to remove any remaining cement stone from the inner cavity of the lower vessel 16; remove the core limiting ring 26 from the core cylinder 27 and clean the core limiting ring 26; use a special tool to remove the floating piston 10 and the slurry container 25 below it from the upper vessel 13; clean any remaining cement stone from the upper vessel 13; remove the floating piston 10 from the slurry container 25 and clean the floating piston 10; use a special tool to push out the remaining cement stone from the slurry container 25 and clean the slurry container 25.

[0129] S7. Analysis of experimental results;

[0130] The sealing effect of the core can be evaluated by comparing the breakdown pressure and water seepage rate of the core before and after sealing.

[0131] By analyzing the amount of initial cement slurry in the slurry container 25, the amount of cement stone formed by the remaining cement slurry, and the density distribution of the remaining cement stone, combined with the amount of overflow liquid in the lower cavity 17 when the cement slurry is squeezed, the amount of cement slurry components squeezed into the core under the corresponding pressure difference is analyzed.

[0132] By analyzing CT scan images of core samples before and after sealing, and the distribution of water-soluble and fine-particle tracer materials on the core profile, the process and results of cement slurry components entering the core under pressure differential were analyzed, thereby inferring the process of cement slurry components being squeezed into the core. By changing the sealing cement slurry, the core sample of the formation to be sealed, and the sealing pressure differential parameters, different sealing results and effects were obtained, thereby studying the influence of relevant factors on the sealing results and effects.

[0133] Test case

[0134] The experimental cement slurry formulation in this embodiment is as follows:

[0135] Note: The mass of quartz sand, barite, and each treatment agent is calculated based on ultrafine cement, and the mass of water is calculated based on dry ash.

[0136] Using the experimental apparatus and evaluation method of this invention, the compressive strength and seepage capacity of a 0.3 mm fractured rock core before injection of the aforementioned ultrafine cement slurry were tested. After curing with the aforementioned ultrafine cement slurry formulation under a pressure differential of 30 MPa and a temperature of 120°C, the compressive strength and seepage capacity of the core after sealing were also tested, as shown in Table 2. The experimental results show that the compressive strength of the 0.3 mm fractured rock core before sealing was 1 MPa, and the seepage capacity under a pressure differential of 1 MPa was 125 mL / min. After sealing with the ultrafine cement slurry, the forward compressive strength of the core was 16 MPa, and the reverse compressive strength was 20 MPa. The flow rate of the core decreased significantly under different pressure differentials, indicating a significant decrease in seepage capacity. This demonstrates that the sealing system effectively penetrated the 0.3 mm fractured rock core and achieved effective sealing.

[0137] It should be noted that the more uniform the distribution of cement slurry particles in the core and the deeper they penetrate into the core pores, the better the sealing effect of the cement slurry in penetrating the formation. A greater change in seepage capacity before and after sealing indicates a better sealing effect, and higher positive and negative bearing capacities after sealing also indicate a better sealing effect.

[0138] The above embodiments only illustrate preferred implementation methods, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of this invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this invention, and these all fall within the protection scope of this invention.

Claims

1. A test apparatus for simulating formation cement slurry plugging in oil and gas wells, characterized in that: Including the upper pot (13) and the lower pot (16); The upper vessel (13) and the lower vessel (16) can be fastened together vertically and form a fastening cavity after fastening. In the fastening cavity, there is a floating piston (10) that can move up and down. A perforated partition plate (15) is fixedly provided below the floating piston (10). The fastening cavity is divided into an upper cavity (8), a middle cavity (11), and a lower cavity (17) through the floating piston (10) and the perforated partition plate (15). The upper cavity (8) is connected to the first liquid inlet pressurization line, the first liquid outlet line, the first gas line, and the first overflow line respectively. The middle cavity (11) is connected to the second liquid inlet pressurization line, the second liquid outlet line, the second gas line, and the second overflow line respectively. The lower cavity (17) is connected to the third liquid inlet pressurization line, the third liquid outlet line, the third gas line, and the third overflow line respectively. Heaters are provided on the inner walls of the upper cavity (8), the middle cavity (11), and the lower cavity (17). Corresponding temperature sensors and pressure sensors are provided in these three cavities. A core tube (27) is placed on the perforated isolation plate (15), and the core tube (27) is snapped and fixed in the inner cavity; in addition, the core tube (27) is sealed to the inner wall of the inner cavity by fitting a corresponding sealing ring; a core is contained in the core tube (27); A slurry container (25) is suspended below the floating piston (10). When the floating piston (10) drives the slurry container (25) to move downward, the lower end of the slurry container (25) can be sealed and connected with the upper end of the core cylinder (27). Ⅰ. When conducting the simulation test of "core water seepage capacity", the floating piston (10) and the slurry container (25) need to be removed from the upper vessel (13); Ⅱ. When conducting the simulation test of "squeezing cement to seal the core", let the floating piston (10) drive the slurry container (25) to move downward - let the slurry container (25) connect with the core container (27), and cement slurry needs to be filled into the slurry container (25) to form a positive pressure difference between the middle cavity (11) and the lower cavity (17) for simulation test; Ⅲ. When conducting the simulation test of "testing the sealing effect after sealing the core with cement", let the middle cavity (11) form a positive pressure difference between the lower cavity (17) for positive sealing simulation test, and let the lower cavity (17) form a positive pressure difference between the middle cavity (11) for reverse sealing simulation test.

2. The experimental apparatus for simulating formation cement slurry plugging in oil and gas wells according to claim 1, characterized in that: The upper vessel (13) includes an upper vessel body and a top cover (1). The lower end of the upper vessel body is a through opening, and the upper end of the upper vessel body is fitted with a top cover (1) that can be opened and can be sealed after being fitted. The lower vessel (16) has an open top and a closed bottom; a sedimentation tank (19) and a perforated support cylinder (18) are placed inside the lower vessel (16). The perforated support cylinder (18) is fitted over the sedimentation tank (19) and the two form a certain annular gap; the height of the perforated support cylinder (18) is higher than the height of the sedimentation tank (19), and a perforated partition plate (15) is placed on the top of the perforated support cylinder (18). After the upper vessel (13) and the lower vessel (16) are fastened together, the opening at the lower end of the upper vessel body is connected to the opening at the upper end of the lower vessel (16), and the fastening structure can lock the fastening point after fastening.

3. The experimental apparatus for simulating formation cement slurry plugging in oil and gas wells according to claim 2, characterized in that: The inner diameter of the upper vessel (13) is smaller than the inner diameter of the lower vessel (16). When the upper vessel (13) and the lower vessel (16) are fastened together, a step A is formed at the fastening point. The outer cylindrical surface of the core tube (27) is divided into a lower part, a middle part, and an upper part, with the outer diameters of the lower part, the middle part, and the upper part decreasing sequentially. A step B is formed between the lower part and the middle part. Furthermore, the outer diameter of the lower part is the same as the inner diameter of the lower vessel (16), the outer diameter of the middle part is the same as the inner diameter of the upper vessel (13), and the outer diameter of the upper part is smaller than the inner diameter of the upper vessel (13). When placing the core tube (27) containing the core into the inner cavity: insert the core tube (27) from the lower end of the upper vessel (13), and let the step B abut against the step A to achieve the snap-locking of the core tube (27); and, there is a corresponding sealing ring between the lower part of the tube and the inner wall of the lower vessel (16), a corresponding sealing ring between the middle part of the tube and the inner wall of the upper vessel (13), and an annular gap between the upper part of the tube and the inner wall of the upper vessel (13).

4. The experimental apparatus for simulating formation cement slurry plugging in oil and gas wells according to claim 3, characterized in that: The upper end face of the upper part of the cylinder has an annular step C. The upper end of the upper part of the cylinder is fixed with a core limiting ring (26) by screws. The lower end face of the core limiting ring (26) is adapted to the annular step C. The inner diameter of the core limiting ring (26) is smaller than the inner diameter of the core tube (27). When the core limiting ring (26) is fixed on the core tube (27), it can form a limiting structure for the core installed in the core tube (27). The upper end face of the core limiting ring is conical, and the lower end face of the slurry cylinder (25) is also conical. The slurry cylinder (25) fits against the core limiting ring (26) and then connects with the core cylinder (27).

5. The experimental apparatus for simulating formation cement slurry plugging in oil and gas wells according to claim 4, characterized in that: The upper vessel (13) is fixed on a mechanical fixing mechanism, and the lower vessel (16) is installed on a lifting mechanism that can move up and down; After the locking structure is released, the lifting mechanism drives the lower vessel (16) to move downward. A sealing ring is fitted on the lower part of the core cylinder (27) containing the core. The core cylinder (27) is placed on the perforated isolation plate (15) inside the lower vessel (16). After placement, the lower part of the cylinder is sealed with the inner wall of the lower vessel (16) by the sealing ring. Then, a sealing ring is fitted on the middle part of the cylinder. Then, the lifting mechanism moves upward, and the lower vessel (16) gradually inserts the core cylinder (27) containing the core into the upper vessel (13). The perforated isolation plate (16) presses the step B against the step A. Then, the locking structure is locked, so that the upper vessel (13) and the lower vessel (16) are connected and fastened.

6. The experimental apparatus for simulating formation cement slurry plugging in oil and gas wells according to claim 1, characterized in that: The connection structures of the first liquid inlet pressurization pipeline, the second liquid inlet pressurization pipeline, and the third liquid inlet pressurization pipeline are all the same, and all include an oil-water transition tank (23), a pressure regulator (22), and a liquid inlet pressurization switch valve connected in sequence. The connection structures of the first drain line, the second drain line, and the third drain line are all the same, and each line is equipped with a drain switch valve (21). The connection structures of the first gas pipeline, the second gas pipeline, and the third gas pipeline are all the same, and each pipeline is equipped with a gas switch valve (7). The connection structures of the first overflow pipeline, the second overflow pipeline, the third overflow pipeline and the fourth overflow pipeline are all the same. Each pipeline has an initial end connected to the end of the interlocking cavity, and from the initial end to the tail end, an isolation valve (5), a condenser (4) and a back pressure valve (3) are connected in sequence.

7. The experimental apparatus for simulating formation cement slurry plugging in oil and gas wells according to claim 6, characterized in that: The first liquid inlet pressurization line, the second liquid inlet pressurization line, and the third liquid inlet pressurization line are all connected to the main pipe (29), and the main pipe (29) is connected to the water source via the pressurization pump (30); The liquid inlet pressure switch valve, the liquid outlet switch valve (21), the gas switch valve (7), and the isolation valve (5) are all electrically connected to the controller (31); the pressure pump (30) is electrically connected to the controller (31); and the controller (31) is electrically connected to the display (32).

8. The test method of the test apparatus for simulating formation cement slurry plugging of oil and gas wells as described in any one of claims 1 to 7, characterized in that: Includes the following steps: S1. Prepare and encapsulate the core of the stratum to be sealed; Prepare and encapsulate the core of the stratum to be sealed: Take a rock with a similar pore structure to the stratum core as the core, and match the diameter and height of the core tube (27) with the diameter and height of the core tube (27); put the core into the core tube (27), and fill the annular space between the inner wall of the core tube (27) and the outer wall of the core with consolidation material (12); after the consolidation material solidifies, the core is fixed and installed in the core tube (27); S2, "Core water seepage capacity" simulation test - that is, measuring the "core water seepage capacity before the core is sealed with cement slurry"; The upper vessel (13) is fixed in place by a mechanical mechanism. The locking structure is loosened, and the lower vessel (16) is driven downward by the lifting mechanism. A sedimentation tank (19) and a perforated support cylinder (18) are placed in the lower vessel (16). A perforated isolation plate (15) is placed at the upper end of the perforated support cylinder (18). Clean water is poured into the lower vessel (16) until the perforated isolation plate (15) is submerged. The lower part of the perforated partition plate (15) and the core tube (27) are consistent with the inner wall size of the lower vessel (16); place the core tube (27) with the core already sealed on the perforated partition plate (15). When placing it, the lower part of the tube should be fitted with a corresponding sealing ring and then inserted into the lower vessel (16) so that the lower part of the core tube (27) sits in the lower vessel (16) and the lower part of the tube is sealed to the inner wall at the upper end of the lower vessel (16) by the sealing ring. The lower part of the tube is supported by the perforated partition plate (15). A corresponding sealing ring is installed on the middle part of the core tube (27); then the core limiting ring (26) is fixed on the upper end of the core tube (27) to limit the upper end of the core. Then, the lower vessel (16) and the core cylinder (27) containing the core are slowly lifted upward by the lifting mechanism, so that the middle and upper parts of the core cylinder (27) are inserted into the upper vessel (16), and the middle part of the cylinder is fitted with the inner wall of the upper vessel (16) through the corresponding sealing ring. At the same time, the step B formed by the lower part and the middle part of the cylinder abuts against the step A formed by the upper vessel (13) and the lower vessel (16); then the upper vessel (13) and the lower vessel (16) are locked by the locking structure. Open the top cover (1) of the upper vessel (13), and take out the floating piston (10) and the slurry cylinder (25) upwards. At this time, the middle cavity and the upper cavity are connected - the middle cavity and the upper cavity together form the inner cavity of the upper vessel; pour clean water into the inner cavity of the upper vessel until the top of the inner cavity of the upper vessel; then install the top cover (1). Open the third liquid inlet pressure line and the third gas line corresponding to the lower chamber (17), and introduce pressurized liquid through the pressure pump (30) to allow the gas in the lower chamber (17) to be discharged. After the gas is discharged, close the third gas line. During the gas discharge process, keep the pressure in the lower chamber (17) at 0.2Mpa-0.3Mpa. Similarly, the upper cavity is vented using the method of venting the lower cavity. Open the back pressure valve (3) on the third overflow line corresponding to the lower chamber (17) and set the target back pressure value of the back pressure valve (3) to 3-4 MPa. At the same time, open the back pressure valve (3) on the first overflow line corresponding to the upper vessel cavity and set the target back pressure value of the back pressure valve (3) to 3-4 MPa. Open the back pressure valve (3) on the third overflow line corresponding to the upper vessel cavity and set the target back pressure value of the back pressure valve (3) to 3-4 MPa. Then inject pressurized liquid through the corresponding first liquid inlet pressurization line, second liquid inlet pressurization line, and third liquid inlet pressurization line. When the back pressure valve (3) on the first overflow line, the back pressure valve (3) on the second overflow line, and the back pressure valve (3) on the third overflow line drip liquid accordingly, it indicates that the 3-4 MPa back pressure value in the upper vessel cavity and the 3-4 MPa back pressure value in the lower chamber (17) are successfully set. Close the first overflow line and the second overflow line in the upper vessel cavity, and open the third overflow line in the lower cavity (17); then open the first liquid inlet pressure line and the second liquid inlet pressure line corresponding to the upper vessel cavity, and gradually increase the pressure in the upper vessel cavity until the pressure difference between the upper vessel cavity and the lower cavity reaches the set target value. By measuring the amount of clear water flowing out of the third overflow line under different pressure differences, the simulation of "core clear water seepage capacity" can be completed. S3, Simulation test of "Cement-squeezed formation core"; Open the top cover (1) on the upper vessel (13), apply grease to the lower conical surface and inner wall of the slurry cylinder (25) so that the lower conical surface matches the upper conical surface of the core limiting ring (26) to achieve a seal; place the slurry cylinder (25) on the core limiting ring (26) at the upper end of the core cylinder (27); pour a predetermined volume of cement slurry pre-prepared under high temperature and high pressure into the slurry cylinder (25); connect the upper end of the slurry cylinder (25) to the floating piston (10) through the corresponding connecting mechanism; and then close the top cover (1). Open the first liquid inlet pressure line of the upper chamber (8), open the first gas line of the upper chamber (8), start the pressure pump (30), and vent the liquid inlet of the upper chamber (8). When venting, maintain the pressure of the upper chamber (8) at 0.2-0.3 MPa; after venting is completed, close the first gas line on the upper chamber (8); Then, through the first liquid inlet pressurization line, a pressure of more than 2 MPa is applied to the upper cavity (8) and the pressure is maintained; Open the second liquid inlet pressure line and the second gas line of the middle cavity (11), start the pressure pump (30), and vent the liquid into the middle cavity (11). When venting, maintain the pressure of the middle cavity (11) at 0.2-0.3 MPa; after venting is completed, close the second gas line. An initial pressure of 1-2 MPa is applied to the middle cavity (11) through the second liquid inlet pressurization line, and an initial pressure of 1-2 MPa is applied to the lower cavity (17) through the third liquid inlet pressurization line simultaneously. Set the target temperature value and turn on the heater to heat the upper vessel (13) and lower vessel (16); when the temperature inside the vessel reaches the set target value, gradually increase the pressure in the upper cavity (8) and the middle cavity (11), and ensure that there is always a positive pressure difference of 2 MPa between the middle cavity (11) and the middle cavity (17) during the gradual increase of pressure; observe and record the discharge of the third overflow pipeline under different pressure difference values ​​between the middle cavity (11) and the lower cavity (17) to obtain the overflow volume under different pressure differences, so as to analyze the cement slurry squeezing under different pressure differences until the set sealing pressure difference is reached; Gradually reduce the pressure between the middle cavity (11) and the upper cavity (8), ensuring that the upper cavity (8) always has a positive pressure difference of 2 MPa greater than that of the middle cavity (11) during the gradual pressure reduction process, until the pressure difference between the middle cavity (11) and the lower cavity (17) reaches the set waiting-to-cure pressure difference, and the cement grouting is completed; waiting to set; S4, "Testing the sealing effect after sealing the core with cement" simulation test, including the positive sealing effect of the core after sealing by pressure testing of the middle cavity (8); After the cement slurry curing is completed, the pressure in the upper chamber (8) is gradually reduced to the pressure in the middle chamber (11); the first liquid inlet pressure line of the upper chamber (8) is closed, the first overflow line of the upper chamber (8) is opened, and the upper chamber (8) is overflowed to release pressure. At the same time, the amount of liquid overflowing from the upper chamber (8) is observed and recorded, and the floating piston (10) is used to determine the situation in which the slurry cylinder (25) and the cement stone formed by the remaining cement slurry in it move upward together. If the volume of the overflow reaches the set percentage of the upper cavity (8), it is considered that the floating piston (10) has moved significantly upward and has opened the upper end face of the sealed core. The next test can be carried out as planned. If there is no overflow or the volume of the overflow is significantly smaller than the initial volume of the upper cavity, the pressure difference between the upper and lower parts of the floating piston (10) is too small and insufficient to drive the floating piston (10) and other components to move upward together. At this time, the pressure of the middle cavity (11) and the lower cavity (17) is gradually increased synchronously until the volume of the overflow in the upper cavity (8) reaches the set percentage of the upper cavity (8) to ensure that the upper end face of the sealed core is opened and the first overflow pipeline is closed. Gradually reduce the pressure in the middle cavity (11) to the initial pressure - i.e. 0.2-0.3 MPa, and simultaneously gradually reduce the pressure in the lower cavity (11) to the set initial pressure - i.e. 0.2-0.3 MPa; open the third overflow line and gradually increase the pressure in the middle cavity (11) to form a pressure difference between the middle cavity (11) and the lower cavity (17); observe and record the time when the lower cavity (17) begins to overflow - the time when the core is punctured, and the pressure difference at this time is the puncture pressure difference of the core after sealing. Observe and record the clear water seepage velocity under different pressure differences to evaluate the sealing ability of the core after sealing, until the set test pressure difference is reached to complete the positive pressure sealing effect test; gradually reduce the pressure in the middle cavity (11) to its initial pressure; S5-1, "Testing the sealing effect after sealing the rock core with cement", also includes reverse pressure testing the reverse sealing effect; If the core sample is not penetrated during the forward test, the reverse pressure test is immediately performed to test the reverse sealing effect of the core sample after sealing. Specifically, close the third overflow line, open the second overflow line, gradually increase the pressure in the lower chamber (17), observe and record the time when the middle chamber (11) begins to overflow - the time when the core is punctured, and the pressure difference at this time is the puncture pressure difference of the core after sealing. Observe and record the seepage velocity of clear water under different pressure differences to evaluate the reverse sealing ability of the core after sealing, until the set test pressure difference is reached to complete the reverse pressure sealing effect test; gradually reduce the pressure in the lower chamber (17) to its initial pressure. S6. Experiment ends; Stop heating and pressurizing, disassemble the entire test apparatus, and clean it. S7. Analysis of experimental results; The sealing effect of the core can be evaluated by comparing the breakdown pressure and water seepage rate of the core before and after sealing. By analyzing the amount of initial cement slurry in the slurry container, the amount of cement stone formed by the remaining cement slurry, and the density distribution of the remaining cement stone, combined with the amount of liquid overflowing from the lower cavity during cement slurry extrusion, the amount of cement slurry components extruded into the core under the corresponding pressure difference can be analyzed. By analyzing CT scan images of core samples before and after sealing, and the distribution of water-soluble and fine-particle tracer materials on the core profile, the process and results of cement slurry components entering the core under pressure differential were analyzed, thereby inferring the process of cement slurry components being squeezed into the core. By changing the sealing cement slurry, the core sample of the formation to be sealed, and the sealing pressure differential parameters, different sealing results and effects were obtained, thereby studying the influence of relevant factors on the sealing results and effects.

9. The test method of the test apparatus for simulating formation cement slurry plugging in oil and gas wells as described in claim 8, characterized in that: In S5-1, the reverse pressure test for reverse sealing effect can also be performed using method S5-2; S5-2, Reverse pressure test to test the reverse sealing effect; After the cement grout has set, the reverse pressure test is performed directly on the core sample to test the reverse sealing effect. Specifically, first reduce the pressure in the upper chamber (8), open the upper end face of the core after sealing, and then close the third overflow pipeline; then perform a reverse pressure test according to the method in S5-1, and then gradually reduce the pressure in the lower chamber to its initial pressure.

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