Testing device and method for simulating oil and gas well stratum cement paste plugging

Abstract

The invention relates to the technical field of oil-gas well stratum simulation tests, and particularly discloses a test device and method for simulating oil-gas well stratum cement paste plugging. The test device comprises an upper kettle and a lower kettle which are buckled together to form an inner cavity; the buckling inner cavity is divided into an upper cavity, a middle cavity and a lower cavity through the floating piston and the perforated isolation plate; the upper cavity, the middle cavity and the lower cavity are respectively connected with a corresponding liquid inlet pressing pipeline, a liquid discharge pipeline, a gas pipeline and an overflow pipeline; heaters, temperature sensors and pressure sensors are arranged on the inner walls of the upper cavity, the middle cavity and the lower cavity; a rock core barrel is placed on the perforated isolation plate; a slurry containing barrel 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 can be in sealed butt joint with the upper end of the rock core barrel. The device has the beneficial effects that multiple field working conditions can be simulated through one device, the process and the result of squeezing cement slurry can be analyzed from multiple angles, and sufficient test data can be provided for plugging stratums by squeezing the cement slurry.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas well plugging, in particular to a test device and method for simulating oil and gas well formation cement slurry plugging. Background Art

[0002] As the demand for natural gas increases, pipeline transportation of natural gas is no longer sufficient to solve the problems of natural gas supply and demand, such as the imbalance between gas consumption and gas transmission caused by seasonal reasons. In this case, it is necessary to build a gas storage. At present, about 70% of the underground gas storage in the world are transformed from depleted oil and gas reservoirs. In the construction of gas storage, the plugging quality of old wells is the main reason affecting the safety of gas storage. The service time of old wells is generally from more than ten years to several decades. The perforation and reservoir transformation experienced in the early stage of production is equivalent to opening "a thousand holes" in the complete structure, which is very easy to cause natural gas leakage. In severe cases, it will cause wellhead leakage or even explosion. Therefore, one of the key technologies for the construction of depleted oil and gas reservoir gas storage projects is to plug all old wells in the reservoir construction structure.

[0003] Cement slurry well sealing is to use liquid pressure to squeeze cement slurry, squeeze it into the formation or blasthole, stop the flow and quickly solidify and harden to achieve sealing, thereby achieving the purpose of forming a permanent isolation zone inside the formation. This process has the characteristics of good sealing effect, low cost, and wide field application.

[0004] However, the current problem is that different formations have different physical properties and pore throat structures, and the ability of plugging cement slurry to enter different formations is also different. In addition, plugging cement slurries of different systems have different components and particle sizes, and their ability to enter formation pores or blastholes under pressure injection is also completely different. Moreover, the strength of the plugging cement slurry after solidification may also be different. Therefore, it is impossible to make an effective assessment of whether the cement slurry can enter the formation as expected, form a sufficient plugging zone in the near-well area, and plug pores of different sizes. In addition, it is impossible to adjust the corresponding squeezing parameters according to the specific well conditions of the oil and gas wells, resulting in unsatisfactory plugging effects.

[0005] The "Abandoned Well Plugging Agent Test Device" (CN211179479U) can test the plugging reliability of the plugging agent on the simulated formation and wellbore under the action of alternating stress by applying periodic pressure to the test chamber through a simulated pressurizing device. However, its structure is unreasonable. It only has filtration holes to simulate the formation, and cannot simulate the situation where cement slurry enters the formation core to form a plug. The "Full Diameter High Pressure Intelligent Plugging Tester" (CN203758993U) and the "High Temperature and High Pressure Full Diameter Core Fracture Plugging Tester" (CN103411750A) both evaluate the plugging ability of drilling fluid by simulating the plugging of various solid phase particles in the drilling fluid on the leaking layer.

[0006] In view of this, the present invention proposes a simulation experimental device for squeezing cement to plug oil and gas wells. Through a series of simulation experiments, the pressure required for squeezing different plugging cement slurries into different formations, the depth of cement slurries squeezed into the formation core under a certain pressure, and the plugging ability of the core after solidification are studied, so as to evaluate the adaptability of the plugging cement slurry to plugging the formation, and optimize the formula of the plugging system accordingly to ensure that the plugging cement slurry can enter the formation or blasthole to a certain depth to form a plugging zone of sufficient thickness, and has sufficient strength after solidification to achieve effective plugging of the formation or blasthole. Summary of the invention

[0007] The purpose of the present invention is to overcome the shortcomings of the prior art and to provide a test device and method for simulating cement slurry plugging in oil and gas well formations, which solves the problem that multiple devices are required in existing simulation test devices to test various simulation items of the core and solves the problem that the parameters in the tests of existing simulation items are not rich.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] In a first aspect, a test device for simulating cement slurry plugging in oil and gas well formations is provided, comprising an upper kettle and a lower kettle;

[0010] The upper kettle and the lower kettle can be buckled up and down, and after buckling, a buckling inner cavity is formed; a floating piston that can move up and down is provided in the buckling inner cavity, and a perforated isolation plate is fixedly provided below the floating piston; the buckling inner cavity is divided into an upper cavity, a middle cavity, and a lower cavity through the floating piston and the perforated isolation plate;

[0011] The upper chamber is respectively connected to the first liquid inlet pressure pipeline, the first liquid discharge pipeline, the first gas pipeline, and the first overflow pipeline; the middle chamber is respectively connected to the second liquid inlet pressure pipeline, the second liquid discharge pipeline, the second gas pipeline, and the second overflow pipeline; the lower chamber is respectively connected to the third liquid inlet pressure pipeline, the third liquid discharge pipeline, the third gas pipeline, and the third overflow pipeline; the inner walls of the upper chamber, the middle chamber, and the lower chamber are all provided with heaters, and the three chambers are all provided with corresponding temperature sensors and pressure sensors;

[0012] A core barrel is placed on the perforated isolation plate, and the core barrel is fixed in the buckle inner cavity by a buckle; in addition, the core barrel is sealed between the inner wall of the buckle inner cavity by sleeve-mounting a corresponding sealing ring; a core is installed in the core barrel;

[0013] A slurry barrel is suspended below the floating piston. When the floating piston drives the slurry barrel downward, the lower end of the slurry barrel can be sealed and docked with the upper end of the core barrel.

[0014] Ⅰ. When conducting the simulation test of "core clear water seepage capacity", the floating piston and the slurry barrel need to be taken out from the upper kettle; Ⅱ. When conducting the simulation test of "squeezing cement to seal the formation core", the floating piston is allowed to drive the slurry barrel downward - the slurry barrel is allowed to dock with the core barrel, and cement slurry is required to be loaded into the slurry barrel, and a positive pressure difference is formed on the lower chamber through the middle chamber to carry out the simulation experiment; Ⅲ. When conducting the simulation test of "testing the sealing effect after cement sealing the core", a positive pressure difference is formed on the middle chamber to carry out a forward sealing simulation experiment, and a positive pressure difference is formed on the lower chamber to carry out a reverse sealing simulation experiment.

[0015] Furthermore, the upper kettle comprises an upper kettle body and a top cover, the lower end of the upper kettle body is a through opening, and the upper end of the upper kettle body is buckled with an open top cover, which can be sealed after buckling. The upper end of the lower kettle is a through opening, and the lower end is closed; the lower kettle contains a sand settling tank and a perforated support cylinder, the perforated support cylinder is sleeved outside the sand settling tank and the two form a certain annular distance; the height of the perforated support cylinder is higher than the height of the sand settling tank, and a perforated isolation plate is placed on the top of the perforated support cylinder. After the upper kettle and the lower kettle are buckled, the through opening at the lower end of the upper kettle body is connected to the through opening at the upper end of the lower kettle, and the buckling can be locked by the locking structure after buckling.

[0016] Furthermore, the inner diameter of the upper kettle is smaller than the inner diameter of the lower kettle, and a step A is formed at the buckling position when the upper kettle and the lower kettle are buckled. The outer cylindrical surface of the core barrel is divided into the lower part, the middle part and the upper part of the barrel, and the outer diameters of the lower part, the middle part and the upper part of the barrel decrease successively, and a step B is formed between the lower part and the middle part of the barrel; and the outer diameter of the lower part of the barrel is the same as the inner diameter of the lower kettle, the outer diameter of the middle part of the barrel is the same as the inner diameter of the upper kettle, and the outer diameter of the upper part of the barrel is smaller than the inner diameter of the upper kettle. When placing the core barrel with the core in the buckled inner cavity: load the core barrel from the lower end of the upper kettle, let step B rest on step A, and realize the snap-on fixation of the core barrel; and there is a corresponding sealing ring between the lower part of the barrel and the inner wall of the lower kettle, there is a corresponding sealing ring between the middle part of the barrel and the inner wall of the upper kettle, and there is an annular gap between the upper part of the barrel and the inner wall of the upper kettle.

[0017] Furthermore, the upper end surface of the upper part of the barrel is provided with an annular step C, and a core stop ring is fixed to the upper end of the upper part of the barrel by screws, and the lower end surface of the core stop ring is adapted to the annular step C. The inner diameter of the core stop ring is smaller than the inner diameter of the core barrel, and when the core stop ring is fixed on the core barrel, it can form a limit structure for the core installed in the core barrel. The upper end surface of the core stop is conical, and the lower end surface of the slurry barrel is also conical. The slurry barrel is adapted to abut against the core stop ring and dock with the core barrel.

[0018] Furthermore, after the locking structure is released, the lifting mechanism drives the lower kettle to move downward, and sealing rings are sleeved on the lower and middle parts of the core barrel containing the core, and the core barrel is placed on the perforated isolation plate in the lower kettle. After placement, the lower part of the barrel and the inner wall of the lower kettle are sealed by the sealing ring; then a sealing ring is sleeved on the middle part of the barrel, and then the lifting mechanism moves upward, and the lower kettle gradually inserts the core barrel containing the core into the upper kettle, allowing the perforated isolation plate to press step B against step A, and then the locking structure is locked - the upper kettle and the lower kettle are docked and buckled.

[0019] Furthermore, the connection structures of the first liquid inlet pressure-pressing pipeline, the second liquid inlet pressure-pressing pipeline, and the third liquid inlet pressure-pressing pipeline are all consistent, and all include an oil-water transition tank, a pressure regulator, and a liquid inlet pressure-pressing switch valve connected in sequence. The connection structures of the first liquid discharge pipeline, the second liquid discharge pipeline, and the third liquid discharge pipeline are all consistent, and each pipeline is provided with a liquid discharge switch valve. The connection structures of the first gas pipeline, the second gas pipeline, and the third gas pipeline are all consistent, and each pipeline is provided with a gas switch valve. The connection structures of the first overflow pipeline, the second overflow pipeline, the third overflow pipeline, and the fourth overflow pipeline are all consistent, and each pipeline takes the end connected to the buckled inner cavity as the initial end, and is sequentially connected with an isolation valve, a condensation tank, and a back pressure valve from the initial end to the tail end.

[0020] Furthermore, the first liquid inlet pressure-pressing pipeline, the second liquid inlet pressure-pressing pipeline, and the third liquid inlet pressure-pressing pipeline are all connected to the main pipe, and the main pipe is connected to the water source via a pressure-pressing pump. The liquid inlet pressure-pressing switch valve, the liquid discharge switch valve, the gas switch valve, and the isolation valve are all electrically connected to the controller; the pressure-pressing pump is electrically connected to the controller; and the controller is electrically connected to the display.

[0021] In a second aspect, a test method for a test device simulating cement slurry plugging in oil and gas well formations is provided, comprising the following steps:

[0022] S1. Prepare and seal the core of the formation to be plugged;

[0023] Making and sealing the core of the formation to be plugged: taking a rock with a similar pore structure to the formation core as the core, the diameter and height of the core match the diameter and height of the core barrel; installing the core in the core barrel, and filling the annular space between the inner wall of the core barrel and the outer wall of the core; after the consolidation material solidifies, the fixation and installation of the core in the core barrel is completed;

[0024] S2, "core clear water seepage capacity" simulation test - that is, measuring the "core clear water seepage capacity before squeezing cement slurry to seal the core";

[0025] Fix the upper kettle with a mechanical mechanism, loosen the locking structure, and use the lifting mechanism to drive the lower kettle downward; place a sand settling tank and a perforated support cylinder in the lower kettle, and place a perforated isolation plate on the upper end of the perforated support cylinder; pour clean water into the lower kettle until the perforated isolation plate is submerged;

[0026] The hole-carrying isolation plate and the lower part of the core barrel are consistent with the inner wall size of the lower kettle; the core barrel with the core packaged is placed on the hole-carrying isolation plate. When placing, the lower part of the barrel needs to be covered with a corresponding sealing ring and then inserted into the lower kettle, so that the lower part of the core barrel is placed in the lower kettle, and the lower part of the barrel is sealed with the inner wall at the upper end of the lower kettle through the sealing ring, and the lower part of the barrel is supported by the hole-carrying isolation plate;

[0027] A corresponding sealing ring is arranged outside the middle of the core barrel; then a core limiting ring is fixed to the upper end of the core barrel to limit the upper end of the core;

[0028] Then, the lower kettle and the core barrel containing the core are slowly lifted upward by the lifting mechanism, so that the middle and upper parts of the core barrel are inserted into the upper kettle, and the middle part of the barrel is matched with the inner wall of the upper kettle through the corresponding sealing ring, and at the same time, the step B formed by the lower part and the middle part of the barrel abuts against the step A formed by the upper kettle and the lower kettle; then, the upper kettle and the lower kettle are locked by the locking structure;

[0029] Open the top cover of the upper kettle, and take out the floating piston and the pulp tube 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 kettle. Pour clean water into the inner cavity of the upper kettle until it reaches the top of the inner cavity of the upper kettle. Then install the top cover.

[0030] Open the third liquid inlet pressure pipeline and the third gas pipeline corresponding to the lower chamber, and introduce pressurized liquid through the pressure pump to discharge the gas in the lower chamber. After the exhaust is completed, close the third gas pipeline. During the exhaust process, keep the pressure of the lower chamber at 0.2Mpa-0.3Mpa;

[0031] Similarly, exhaust the inner cavity of the upper kettle by using the method of exhausting the lower cavity;

[0032] Open the back pressure valve on the third overflow pipeline corresponding to the lower chamber, and set the target back pressure value of the back pressure valve to 3-4Mpa, and at the same time open the back pressure valve on the first overflow pipeline corresponding to the upper kettle cavity and set the target back pressure value of the back pressure valve to 3-4Mpa, and open the back pressure valve on the third overflow pipeline corresponding to the upper kettle cavity and set the target back pressure value of the back pressure valve to 3-4Mpa; then inject pressure liquid through the corresponding first liquid inlet pressure pipeline, second liquid inlet pressure pipeline, and third liquid inlet pressure pipeline. When the back pressure valve on the first overflow pipeline, the back pressure valve on the second overflow pipeline, and the back pressure valve on the third overflow pipeline drip liquid accordingly, it indicates that the 3-4Mpa back pressure value in the upper kettle cavity and the 3-4Mpa back pressure value in the lower chamber are set successfully;

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

[0034] S3, "Squeezing cement to seal the formation core" simulation test;

[0035] Open the top cover on the upper kettle, apply butter on the lower conical surface of the slurry tube and its inner wall, so that the lower conical surface cooperates with the upper conical surface of the core stop ring to achieve sealing; place the slurry tube on the core stop ring at the upper end of the core tube; pour a predetermined volume of cement slurry prefabricated under high temperature and high pressure into the slurry tube; connect the upper end of the slurry tube with the floating piston through the corresponding connecting mechanism; and then buckle the top cover;

[0036] Open the first liquid inlet pressure pipeline of the upper chamber, open the first gas pipeline of the upper chamber, start the pressure pump, exhaust the liquid in the upper chamber, and keep the pressure of the upper chamber at 0.2-0.3Mpa during exhaust; after the exhaust is completed, close the first gas pipeline on the upper chamber;

[0037] Then, a pressure of more than 2Mpa is applied to the upper chamber through the first liquid inlet pressure pipeline, and the pressure is maintained;

[0038] Open the second liquid inlet pressure pipeline and the second gas pipeline of the middle cavity, start the pressure pump, exhaust the liquid inlet of the middle cavity, and keep the pressure of the middle cavity at 0.2-0.3Mpa during exhaust; close the second gas pipeline after exhausting;

[0039] Apply an initial pressure of 1-2Mpa to the middle cavity through the second liquid inlet pressure pipeline, and simultaneously and synchronously apply an initial pressure of 1-2Mpa to the lower cavity through the third liquid inlet pressure pipeline;

[0040] Set the target temperature value, and turn on the heater to increase the temperature in the upper and lower kettles; when the temperature in the kettle reaches the set target value, gradually increase the pressure of the upper chamber and the middle chamber, and ensure that there is always a positive pressure difference of 2Mpa between the middle chamber and the middle chamber during the process of gradually increasing the pressure; observe and record the drainage of the third overflow pipeline under different pressure differences between the middle chamber and the lower chamber, and obtain the overflow volume under different pressure differences to analyze the cement slurry squeezing situation under different pressure differences until the set plugging pressure difference is reached;

[0041] Gradually reduce the pressure of the middle cavity and the upper cavity, and ensure that the upper cavity always has a positive pressure difference of 2Mpa greater than that of the middle cavity during the gradual pressure reduction process, until the pressure difference between the middle cavity and the lower cavity reaches the set waiting pressure difference, and the squeezed cement slurry is completed; waiting for setting;

[0042] S4, "Testing the plugging effect after cement plugging the core" simulation test, including the positive plugging effect of the core after plugging by pressure testing the middle cavity;

[0043] After the cement slurry curing is completed, the pressure of the upper chamber is gradually reduced to the pressure of the middle chamber; the first liquid inlet pressure pipeline of the upper chamber is closed, and the first overflow pipeline of the upper chamber is opened to relieve the pressure of the upper chamber by overflowing liquid. At the same time, the amount of liquid overflowing from the upper chamber is observed and recorded, and the floating piston is used to judge the situation that the cement stone formed by the slurry cylinder and the remaining cement slurry therein is moved upward together;

[0044] If the volume of the overflow reaches the percentage of the volume set in the upper chamber, it is considered that the floating piston has obviously moved upward and has uncovered the upper end surface of the plugged core, and 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 chamber, the pressure difference between the upper and lower parts of the floating piston is too small to drive the floating piston and other components to move upward together. At this time, the pressure of the middle chamber and the lower chamber is gradually increased synchronously until the volume of the overflow in the upper chamber reaches the percentage of the volume set in the upper chamber, ensuring that the upper end surface of the plugged core is uncovered, and the first overflow pipeline is closed;

[0045] Gradually reduce the pressure of the middle cavity to the initial pressure, i.e. 0.2-0.3Mpa, and also gradually reduce the pressure of the lower cavity to the set initial pressure, i.e. 0.2-0.3Mpa; open the third overflow pipeline, gradually increase the pressure of the middle cavity, and form a pressure difference between the middle cavity and the lower cavity; observe and record the time when the lower cavity begins to overflow, i.e. the time when the core is punctured, and the pressure difference at this time is the breakdown pressure difference of the plugged core; observe and record the clear water seepage rate under different pressure differences, so as to evaluate the plugging ability of the plugged core, until the set test pressure difference is reached, and the positive pressure plugging effect test is completed; gradually reduce the pressure of the middle cavity to its initial pressure;

[0046] S5-1, "Testing the plugging effect after cement plugging the core" simulation test, also includes reverse pressure testing the reverse plugging effect;

[0047] If the core is not penetrated in the forward test, immediately conduct a reverse pressure test to test the reverse plugging effect of the plugged core; close the third overflow pipeline, open the second overflow pipeline, gradually increase the pressure of the lower chamber, observe and record the time when the middle chamber begins to overflow - the time when the core is penetrated, and the pressure difference at this time is the breakdown pressure difference of the plugged core, observe and record the clear water seepage rate under different pressure differences, so as to evaluate the reverse plugging ability of the plugged core, until the set test pressure difference is reached, and the reverse pressure plugging effect test is completed; gradually reduce the pressure of the lower chamber to its initial pressure;

[0048] S6, end of experiment;

[0049] Stop heating and pressurizing, disassemble the entire test device, and clean it;

[0050] S7, Experimental results analysis;

[0051] By comparing the breakdown pressure and clear water seepage velocity of the core before and after plugging, the plugging effect of the core can be evaluated;

[0052] By analyzing the amount of initial cement slurry in the slurry tube, 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 when squeezing the cement slurry, the amount of cement slurry components squeezed into the core under the corresponding pressure difference is analyzed;

[0053] Through the CT scanning images of the core before and after plugging, the distribution of water-soluble tracer materials and fine-grained tracer materials on the core profile, the process and results of cement slurry components entering the core under pressure difference are analyzed, so as to infer the process of cement slurry components being squeezed into the core; by changing the plugging cement slurry, the core of the formation to be plugged, and the plugging pressure difference parameters, different plugging results and effects are obtained, so as to study the influence of relevant factors on the plugging results and effects.

[0054] Furthermore, in the above S5-1, the reverse pressure test for the reverse blocking effect can also be carried out in the manner of S5-2;

[0055] S5-2, reverse pressure test reverse blocking effect;

[0056] After the cement slurry is set, directly reverse pressure test the reverse plugging effect of the plugged core; first reduce the upper chamber pressure, uncover the upper end surface of the plugged core, 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 lower chamber pressure to its initial pressure.

[0057] It should be noted that this scheme can simulate the high temperature and high pressure environment of the bottom hole, formation cores of different lithologies, cement slurries of different components and properties, accurately control the extrusion parameters, accurately measure the amount of cement slurry or its components squeezed into the formation, simulate the coagulation process of cement slurry under high temperature and high pressure, and can hydraulically break the remaining cement stone column under high temperature and high pressure to expose the upper end face of the core after plugging. At the same time, the core is fixed by the perforated isolation plate at the lower end and the upper top limit ring at the upper end, so as to realize the forward test from top to bottom and the reverse test from bottom to top, test the breakdown pressure and clear water seepage rate of the core after plugging, and evaluate the plugging effect of the core accordingly; finally, after cooling and reducing the pressure, the cement stone formed by squeezing the remaining cement slurry can be By analyzing the volume and density distribution data of the remaining cement stone, the distribution of the cement slurry or its components squeezed into the core can be studied by dissecting the plugged core, performing CT scanning / XRD component analysis / tracer distribution data, inverting the squeezing process, exploring the relevant factors affecting the squeezing effect and their action rules, and evaluating the adaptability of the cement slurry to the plugged formation, etc., thereby providing the industry with the necessary research means to carry out relevant experimental research on squeezing cement slurry to plug the formation / crossflow channel, evaluate the adaptability of cement slurry to the plugged formation, select the cement slurry component according to the pore parameters of the formation to be plugged, optimize the cement slurry performance, match reasonable squeezing parameters, strengthen the control of the squeezing process, and improve the effect of squeezing cement slurry to plug the formation / crossflow channel.

[0058] The present invention has the following advantages:

[0059] 1. This scheme can simulate a variety of on-site working conditions: (1) It can simulate the process of measuring the absorption capacity of the formation to be plugged before squeezing cement slurry; (2) It can simulate the process of injecting plugging cement slurry into the well and squeezing it into the formation under high temperature and high pressure; (3) It can simulate the process of the cement slurry squeezed into the core and its components solidifying and hardening to plug the formation in the high temperature and high pressure environment in the well; (4) It can simulate the process of pressure testing the wellbore after the cement slurry solidifies and positively testing the plugging effect of the plugging belt under high temperature and high pressure; (5) It can simulate the process of reversely testing the plugging effect of the plugging belt under high temperature and high pressure after the formation pressure of the gas storage reservoir rises.

[0060] 2. During the test, multiple innovative functions are achieved through innovative structural design: (1) The pressure difference of squeezed cement slurry can be accurately controlled; (2) The amount of cement slurry and its components squeezed into the core can be prepared and measured; (3) The pressure in the upper chamber can be reduced without cooling or reducing pressure. Under the action of the pressure difference, the floating piston can drive the slurry tube and the remaining cement stone inside to move upward and uncover the upper end surface of the plugged core; (4) Without cooling or reducing pressure, the overflow pipeline valve of the lower chamber can be opened and the middle chamber can be pressurized to test the forward breakdown pressure and clear water seepage capacity of the plugged core; (5) Without cooling or reducing pressure, the overflow pipeline valve of the middle chamber can be opened and the lower chamber can be pressurized to test the reverse breakdown pressure and clear water seepage capacity of the plugged core.

[0061] 3. The process and results of squeezing cement slurry can be analyzed from multiple angles: (1) The plugging effect of the core can be evaluated by the breakdown pressure and clear water seepage velocity of the core before and after plugging; (2) The amount of liquid overflowing from the downstream chamber during squeezing cement slurry can be used to determine whether the cement slurry has been squeezed into the core or even passed through the core into the downstream chamber; (3) The time when the core was punctured and the pressure difference can be inferred based on the change in the velocity of the liquid overflowing from the downstream chamber during squeezing cement slurry; (4) The composition of the cement slurry entering the core under the pressure difference can be analyzed by the axial density distribution of the cement stone formed by the remaining cement slurry in the slurry tube; (5) The composition of the cement slurry entering the core under the pressure difference and its penetration depth can be analyzed by performing CT scanning on the plugged core and the distribution of tracer materials in the core;

[0062] 4. It can provide more reliable technical means for the theories and technologies related to squeezing cement slurry to plug formations: through conducting relevant experiments, it can study the influence of relevant factors such as squeezing cement slurry pressure difference, cement slurry components and properties, core pore size distribution, etc. on the effect of squeezing cement slurry plugging cores and their action mechanism, and accordingly optimize the components of the plugging cement slurry, optimize the formula of the plugging cement slurry, improve the adaptability of the plugging cement slurry to the plugged formation, and ultimately reduce the squeezing pressure and improve the plugging effect, thereby providing scientific, reasonable and reliable technical means for indoor research on squeezing cement slurry to plug formations and on-site evaluation of the adaptability of the plugging cement slurry to plugged formations. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0064] In the figure: 1-top cover; 3-back pressure valve; 4-condensate tank; 5-isolation valve; 7-valve; 8-upper chamber; 9-tightening nut; 10-floating piston; 11-middle chamber; 12-consolidation material; 13-upper kettle; 14-connecting bolts; 15-isolation plate with holes; 16-lower kettle; 17-lower chamber; 18-support cylinder with holes; 19-sand settling tank; 20-bottom cover; 21 drainage switch valve; 22-pressure regulator; 23-oil-water transition tank; 24-connecting rod; 25-slurry cylinder; 26-core limit ring; 27-core barrel; 29-main pipe; 30-boosting pump; 31 controller; 32 display. DETAILED DESCRIPTION

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

[0066] It should be noted that the directions or positional relationships indicated by "left", "right", etc. are based on the directions or positional relationships shown in the accompanying drawings, or are the directions or positional relationships in which the inventive product is usually placed when in use, or are the directions or positional relationships commonly understood by those skilled in the art. Such terms are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0067] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art to which this application belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with those in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless specifically defined as here.

[0068] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features and technical solutions in the embodiments may be combined with each other.

[0069] like Figure 1 As shown, this embodiment discloses a test device for simulating cement slurry plugging of oil and gas well formations, including an upper kettle 13 and a lower kettle 16;

[0070] The upper kettle 13 and the lower kettle 16 can be buckled up and down to form a buckled inner cavity; a floating piston 10 that can move up and down is provided in the buckled inner cavity, and a perforated isolation plate 15 is fixedly provided below the floating piston 10; the buckled inner 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 chamber 8 is respectively connected to the first liquid inlet pressure pipeline, the first liquid discharge pipeline, the first gas pipeline, and the first overflow pipeline; the middle chamber 11 is respectively connected to the second liquid inlet pressure pipeline, the second liquid discharge pipeline, the second gas pipeline, and the second overflow pipeline; the lower chamber 17 is respectively connected to the third liquid inlet pressure pipeline, the third liquid discharge pipeline, the third gas pipeline, and the third overflow pipeline; the inner walls of the upper chamber 8, the middle chamber 11, and the lower chamber 17 are all provided with heaters, and corresponding heat preservation is provided at these three chambers, and corresponding temperature sensors and pressure sensors are provided in these three chambers;

[0072] A core barrel 27 is placed on the perforated isolation plate 15, and the core barrel 27 is fixed in the buckled inner cavity by snapping; in addition, the core barrel 27 is sealed between the inner wall of the buckled inner cavity by sleeve-mounting a corresponding sealing ring; a core is installed in the core barrel 27;

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

[0074] It should be noted that: Ⅰ. When conducting the "core clear water seepage capacity" simulation test, the floating piston 10 and the slurry barrel 25 need to be taken out from the upper kettle 13; Ⅱ. When conducting the "cement squeezing to seal the formation core" simulation test, the floating piston 10 drives the slurry barrel 25 to move downward - the slurry barrel 25 is connected with the core barrel 27, and cement slurry needs to be loaded into the slurry barrel 25, and a positive pressure difference is formed on the lower chamber 17 through the middle chamber 11 to carry out the simulation experiment; Ⅲ. When conducting the "testing the sealing effect after cement sealing the core" simulation test, the middle chamber 11 is allowed to form a positive pressure difference on the lower chamber 17 to carry out a forward sealing simulation experiment, and the lower chamber 17 is allowed to form a positive pressure difference on the middle chamber 11 to carry out a reverse sealing simulation experiment.

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

[0076] The upper kettle 13 includes an upper kettle body and a top cover 1. The lower end of the upper kettle body is a through opening. The upper end of the upper kettle body is buckled with an open top cover 1, which can be sealed after buckling. In addition, the upper kettle 13 includes an upper kettle body and a top cover 1. The top cover 1 is detachably fixed to the top of the upper kettle body by corresponding connecting bolts, and a corresponding sealing ring is arranged between the top cover 1 and the upper kettle body. The lower kettle 16 includes a lower kettle body and a bottom cover 20. The bottom cover 20 is detachably fixed to the bottom of the lower kettle body by corresponding connecting bolts, and a corresponding sealing ring is also arranged between the bottom cover 2 and the lower kettle body. The lower end of the upper kettle body and the upper end of the lower kettle body are sealed and buckled by corresponding buckling bolts 14.

[0077] The lower kettle 16 includes a lower kettle body and a bottom cover 20. The upper end of the upper kettle body is a through opening, and the lower end of the upper kettle body is blocked by the bottom cover 20. In addition, a sand settling tank 19 and a perforated support tube 18 are placed inside the lower kettle 16. Moreover, the perforated support tube 18 is sleeved outside the sand settling tank 19 and the two form a certain annular spacing. The height of the perforated support tube 18 is higher than the height of the sand settling tank 19. A perforated isolation plate 15 is placed on the top of the perforated support tube 18. The perforated isolation plate 15 is disc-shaped, and its outer diameter is equivalent to the inner diameter of the lower kettle 16. When the perforated isolation plate 15 is placed in the support tube 18, the perforated isolation plate 15 is adapted to the inner wall of the lower kettle 16.

[0078] The upper kettle 13 has a flange at the lower end, and the lower kettle 16 has a flange at the upper end. After the upper kettle 13 and the lower kettle 16 are buckled together, the through opening at the lower end of the upper kettle body is butted against the through opening at the upper end of the lower kettle body, and then the flanges between the upper kettle 13 and the lower kettle 16 are butted against each other and buckled. After buckling, they are fixedly connected by the buckling bolts 14 to form a locking structure at the buckling point.

[0079] The installation structure between the core barrel 27, the upper kettle 13 and the lower kettle 16 will be further described below.

[0080] The inner diameter of the upper kettle 13 is smaller than the inner diameter of the lower kettle 16 . When the upper kettle 13 and the lower kettle 16 are buckled together, a step A is formed in the buckled inner cavity at the buckled position.

[0081] The outer cylindrical surface of the core barrel 27 is divided into a lower part, a middle part and an upper part, and the outer diameters of the lower part, the middle part and the upper part decrease successively, forming a step B between the lower part and the middle part; and the outer diameter of the lower part is the same as the inner diameter of the lower kettle 16, the outer diameter of the middle part is the same as the inner diameter of the upper kettle 13, and the outer diameter of the upper part is smaller than the inner diameter of the upper kettle 13.

[0082] When placing the core barrel 27 containing the core in the buckled inner cavity: insert the core barrel 27 from the lower end of the upper pot 13, let the step B rest on the step A, so as to realize the snap-fit ​​fixation of the core barrel 27; and, there is a corresponding sealing ring between the lower part of the barrel and the inner wall of the lower pot 16, there is a corresponding sealing ring between the middle part of the barrel and the inner wall of the upper pot 13, and there is an annular gap between the upper part of the barrel and the inner wall of the upper pot 13.

[0083] In addition, an annular step C is provided at the upper end surface of the upper part of the barrel, and a core stop ring 26 is fixed to the upper end of the upper part of the barrel by screws, and the lower end surface of the core stop ring 26 is adapted to the annular step C. The inner diameter of the core stop ring 26 is smaller than the inner diameter of the core barrel 27. When the core stop ring 26 is fixed on the core barrel 27, a stop structure can be formed for the core installed in the core barrel 27. The upper end surface of the core stop ring 26 is conical, and the lower end surface of the slurry barrel 25 is also conical. The slurry barrel 25 is adapted to abut against the core stop ring 26 and then dock with the core barrel 27.

[0084] When installing:

[0085] The upper kettle 13 is fixed on a mechanical fixing mechanism, and the lower kettle 16 is installed on a lifting mechanism that can move up and down. After the locking structure is unlocked, the lifting mechanism drives the lower kettle 16 to move downward. A sealing ring is put on the lower part of the core barrel 27 containing the core, and then they are placed together in the lower kettle 16, so that the core barrel 27 is supported by the perforated isolation plate 15, and the sealing ring at the lower part of the barrel is adapted to seal with the inner wall of the lower kettle 16. Then, a corresponding sealing ring is put on the middle part of the core barrel 27, and then the core limiting ring 26 is fixed at the upper end of the core barrel 27. Under the action of the upward movement of the lifting mechanism, the core barrel 27 containing the core is gradually inserted into the upper kettle 13, and the perforated isolation plate 16 is pressed against the step A, and the middle part of the barrel is adapted to seal with the inner wall of the upper kettle 13. After the locking structure is locked again, the upper kettle 13 and the lower kettle 16 can be docked and buckled.

[0086] It should be noted that the structure of the upper kettle 13, the lower kettle 16, the core barrel 27, and the mounting structure therebetween are designed in such a way that when the upper kettle 13 is separated from the lower kettle and the core barrel 27 containing the core is placed on the perforated isolation plate 15, the core barrel 27 can be firmly seated in the lower kettle 16, and when the lifting mechanism drives the lower kettle 16 to move upward, the core barrel 27 in the lower kettle 16 is stable and does not shake, thereby facilitating the accurate insertion of the core barrel 27 into the upper kettle 13 and facilitating the lifting mechanism. The automatic action of the structure; when the core barrel 27 is inserted into the upper kettle 13, the core barrel 27 is fixed in the buckled inner cavity by the corresponding steps A and B - the core barrel 27 is fixed under the action of the lifting mechanism - which is conducive to the automatic action of the lifting mechanism, and after insertion, the upper kettle 13 and the lower kettle 16 are sealed at the buckle through the sealing ring arranged outside the middle part of the tube and the sealing ring arranged outside the lower part of the tube - to avoid the buckle inner cavity from being connected to the outside atmosphere - that is, automatic sealing is achieved. In addition, the exhaust, pressure holding, and liquid discharge in the upper cavity 8, the middle cavity 11, and the lower cavity 17 are all completed by the controller 31, which can automatically measure the corresponding parameters, reduce human interference as much as possible, realize automatic measurement, and ensure the accuracy of measurement.

[0087] Each pipeline is further explained below.

[0088] The connection structures of the first liquid inlet pressure-pressing pipeline, the second liquid inlet pressure-pressing pipeline, and the third liquid inlet pressure-pressing pipeline are all the same, and all include an oil-water transition tank 23, a pressure regulator 22, and a liquid inlet pressure-pressing switch valve connected in sequence. In addition, the first liquid inlet pressure-pressing pipeline, the second liquid inlet pressure-pressing pipeline, and the third liquid inlet pressure-pressing pipeline are all connected to the main pipe 29, and the main pipe 29 is connected to the water source through a pressure pump 30.

[0089] The connection structures of the first liquid discharge pipeline, the second liquid discharge pipeline and the third liquid discharge pipeline are all consistent, and a liquid discharge switch valve 21 is provided on each pipeline.

[0090] 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 provided 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, and each pipeline has the end connected to the buckled inner cavity as the initial end, and is connected to the isolation valve 5, the condensation tank 4, and the back pressure valve 3 in sequence from the initial end to the tail end.

[0091] It should be noted that the liquid inlet pressure switch valve, the liquid discharge 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 connection methods are just simple PLC control methods and will not be listed here one by one.

[0092] In a second aspect, a test method for a test device simulating cement slurry plugging in oil and gas well formations is provided, comprising the following steps:

[0093] S1. Prepare and seal the core of the formation to be plugged;

[0094] Making and sealing the core of the formation to be plugged: taking a rock with a similar pore structure to the formation core as the core, the diameter and height of the core match the diameter and height of the core barrel 27; placing the core barrel 27 on a glass plate coated with sealing grease, and loading the core into the core barrel 27; after loading, there is an annular space between the core barrel 27 and the core, and filling the annular space with a consolidation material 12 such as a filling resin or cement slurry, and after the consolidation material 12 solidifies, the fixation and installation of the core in the core barrel 27 is completed;

[0095] It should be noted that if the obtained core does not have natural fractures, artificial fractures can be created by methods such as Brazilian splitting. After artificial fractures, a core with a hollow pore fracture structure similar to that of the formation core can be obtained;

[0096] S2, "core clear water seepage capacity" simulation test - that is, measuring the "core clear water seepage capacity before squeezing cement slurry to seal the core";

[0097] The upper kettle 13 is fixed by a mechanical mechanism, the locking structure is loosened, and the lower kettle 16 is driven downward by the lifting mechanism; a sand settling tank 19 and a support cylinder with holes 18 are placed in the lower kettle 16, the sand settling tank 19 is located at the center of the bottom of the lower kettle 16, and the support cylinder with holes 18 is sleeved outside the sand settling tank 19 with an annular gap between the two;

[0098] The height of the perforated support cylinder 18 is lower than that of the lower kettle 13, the height of the sand settling tank 19 is lower than that of the perforated support cylinder 18, and 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 upper opening height of the lower kettle 16; the perforated isolation plate 15 and the lower part of the core cylinder 27 are consistent with the inner wall size of the lower kettle 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 kettle 16, and the perforated isolation plate 15 is slightly lower than the upper opening of the lower kettle 16;

[0099] Pour clean water into the lower kettle 16 until the perforated isolation plate 15 is submerged;

[0100] When placing, a sealing ring is provided on the outer sleeve of the lower part of the core barrel 27 containing the core, and then the lower part of the barrel is inserted into the lower kettle 16 - the lower part of the barrel is placed on the perforated isolation plate 15 - the sealing ring is sealed between the lower part of the barrel and the inner wall of the lower kettle 16; it should be noted that the height of the lower part of the barrel is consistent with the height from the perforated isolation plate 15 to the upper opening of the lower kettle 16. When the lower part of the core barrel 27 is inserted into the lower kettle 16, the upper end surface of the lower part of the barrel is flush with the upper end surface of the upper opening of the lower kettle 16;

[0101] A corresponding sealing ring is disposed outside the middle of the core barrel 27; then the core limiting ring 26 is fixed to the upper end of the core barrel 27 to limit the upper end of the core;

[0102] Then, the lower kettle 16 and the core barrel 27 containing the core are slowly lifted upward by the lifting mechanism, so that the middle and upper parts of the core barrel 27 are inserted into the upper kettle 16 from bottom to top, so that the middle part of the barrel fits with the inner wall of the upper kettle 16 through the corresponding sealing ring, and at the same time, the step B formed by the lower part and the middle part of the barrel abuts against the step A formed by the upper kettle 13 and the lower kettle 16; then, the upper kettle 13 and the lower kettle 16 are locked by the locking structure;

[0103] Open the top cover 1 of the upper kettle 13, and take out the floating piston 10 and the pulp tube 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 kettle.

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

[0105] Open the third liquid inlet pressure pipeline and the third gas pipeline corresponding to the lower chamber 17, and introduce pressure liquid through the pressure pump 30 to discharge the gas in the lower chamber 17; during the exhaust process, maintain the pressure of 0.2Mpa-0.3Mpa in the lower chamber 12; after the exhaust is completed, close the third gas pipeline; during the exhaust, the third liquid discharge pipeline is always closed;

[0106] Similarly, according to the above-mentioned method of exhausting the lower chamber, the inner chamber of the upper kettle is exhausted. Since the upper chamber and the middle chamber are connected at this time, the exhaust can be achieved through the first liquid inlet pressure pipeline and the first gas pipeline, or through the second liquid inlet pressure pipeline and the second gas pipeline, or through the first liquid inlet pressure pipeline, the second liquid inlet pressure pipeline, the first gas pipeline and the second gas pipeline together; when exhausting, the first liquid discharge pipeline and the second liquid discharge pipeline are always closed;

[0107] Through the back pressure valve 3 on the corresponding overflow pipeline, the required target back pressure value - i.e. 3-4Mpa - is set for the lower chamber 17 and the upper kettle cavity; 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 kettle cavity are opened, and the pressure pump 30 is started to apply the set target pressure value - i.e. the target back pressure value - to the lower chamber 17 and the upper kettle 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 corresponding first overflow pipeline and the back pressure valve 3 on the second overflow pipeline in the upper kettle cavity are opened until these back pressure valves 3 all drip liquid, indicating that the back pressure value of the corresponding back pressure valve 3 is set successfully; when under back pressure, the corresponding first drainage pipeline, second drainage pipeline and third drainage pipeline are always closed;

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

[0109] S3, "Squeezing cement to seal the formation core" simulation test;

[0110] Open the top cover 1 on the upper kettle 13, apply butter on the lower end conical surface and the inner wall of the slurry tube 25, so that the lower end conical surface cooperates with the upper end conical surface of the core stop ring 26 to achieve sealing; place the slurry tube 25 on the core stop ring 26 at the upper end of the core tube 27; pour a predetermined volume of cement slurry prefabricated at high temperature and high pressure into the slurry tube 25; connect the upper end of the slurry tube 25 to the floating piston 10 through the corresponding connecting mechanism; and then buckle 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 and pressure-pressurizing pipeline of the upper chamber 8, open the first gas pipeline of the upper chamber 8, and open the second gas pipeline; start the pressure-pressurizing pump 30 to fill and exhaust the upper chamber 8. At this time, the floating piston 10 is pressed downward, and the paddle tube 25 is pressed against the core limit ring 26. During the process of filling and exhausting, the pressure of the upper chamber is maintained at 0.2-0.3Mpa; when the exhaust is completed, close the first gas pipeline on the upper chamber 8;

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

[0114] Open the second liquid inlet pressure pipeline and the second gas pipeline of the middle cavity 11, start the pressure pump 30, and fill the middle cavity 11 with liquid and exhaust the gas; during the process of filling the middle cavity 11 with liquid and exhausting the gas, the middle cavity 11 always maintains a pressure of 0.2-0.3Mpa; after the exhaust is completed, close the second gas pipeline;

[0115] Apply an initial pressure of 1-2 MPa to the middle cavity 11 through the second liquid inlet pressure pipeline;

[0116] The initial pressure of the lower chamber 17 is 1-2Mpa through the third liquid inlet pressure pipeline; at this time, the initial pressure of the lower chamber 17 can also be set to normal pressure, but considering that subsequent heating may cause thermal expansion of the liquid, it is preferred to keep the initial pressure of the lower chamber 17 at 1-2Mpa at this time;

[0117] Set the target temperature value, and turn on the heater to heat the upper kettle 13 and the lower kettle 16; when the temperature in the kettle reaches the set target value, gradually increase the pressure of the upper chamber 8 and the middle chamber 11, and ensure that the positive pressure difference of the upper chamber 8 is always about 2Mpa greater than that of the middle chamber 11 during the process of gradually increasing the pressure; in the process of gradually increasing the pressure, under different pressure differences between the middle chamber and the lower chamber, observe and record the drainage of the third overflow pipeline, and obtain the overflow amount under different pressure differences to analyze the cement slurry extrusion under different pressure differences (the overflow amount is the cement extrusion amount), until the set plugging pressure difference is reached; gradually reduce the pressure of the middle chamber 11 and the upper chamber 8, and ensure that the positive pressure difference of the upper chamber 8 is always about 2Mpa greater than that of the middle chamber 11 during the process of reducing the pressure, until the set waiting pressure difference of the middle chamber 11 to the lower chamber 17 is reached, and the extrusion and sealing of the cement slurry is completed; waiting for solidification;

[0118] S4, "Testing the plugging effect after cement plugging the core" simulation test, including the positive plugging effect of the core after the pressure test of the middle cavity 8;

[0119] After the cement slurry curing is completed, the pressure of the upper chamber 8 is gradually reduced to the pressure of the middle chamber 11; the first liquid inlet pressure pipeline of the upper chamber 8 is closed, and the first overflow pipeline of the upper chamber 8 is opened to relieve the pressure of the upper chamber 8 by overflowing liquid, and the amount of liquid overflowing from the upper chamber 8 is observed and recorded at the same time, and it is judged that the floating piston 10 drives the slurry cylinder 25 and the cement stone formed by the remaining cement slurry therein to move upward together;

[0120] If the volume of the overflow reaches more than 50% of the volume of the upper chamber 8 (that is, when the paddle tube 25 is against the core limit 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 the fixed value of the height difference is recorded as the volume of the upper chamber. When the overflowed liquid reaches half of the volume of the upper chamber, it is regarded as that the volume of the overflow reaches 50% of the volume of the upper chamber 8), it is considered that the floating piston 10 has obviously moved upward and has uncovered the upper end surface of the plugged core, and the next test can be carried out 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 10 is too small to drive the floating piston 10 and other components to move upward together. At this time, the pressure of the middle chamber 11 and the lower chamber 17 is gradually increased synchronously until the volume of the overflow of the upper chamber 8 reaches more than 50% of the volume of the upper chamber, ensuring that the upper end surface of the plugged core is uncovered and the first overflow pipeline is closed;

[0121] The pressure of the middle cavity 11 is gradually reduced to the initial pressure, i.e., 1-2Mpa. At the same time, the pressure of the lower cavity 17 is also gradually reduced to the initial pressure, i.e., 1-2Mpa. The pressures of the middle cavity 11 and the lower cavity 17 are reduced synchronously, and the pressure reduction values ​​per unit time are the same. The third overflow pipeline is opened to gradually increase the pressure of the middle cavity 11 to form a pressure difference between the middle cavity 11 and the lower cavity 17. The time when the lower cavity 17 starts to overflow is observed and recorded, i.e., the time when the core is punctured. The pressure difference at this time is the breakdown pressure difference of the core after plugging. The clear water seepage velocity under different pressure differences is observed and recorded to evaluate the plugging ability of the core after plugging. The test pressure difference is reached until the set test pressure difference is reached to complete the forward pressure plugging effect test. The pressure of the middle cavity 11 is gradually reduced to its initial pressure.

[0122] S5-1, "Testing the plugging effect after cement plugging the core" simulation test, also includes reverse pressure testing the reverse plugging effect;

[0123] If the core is not penetrated in the forward test, a reverse pressure test is immediately performed to test the reverse plugging effect of the plugged core; specifically, the third overflow pipeline is closed, the second overflow pipeline is opened, and the pressure of the lower chamber 17 is gradually increased. When the pressure of the lower chamber 17 increases, the paddle tube 25 is separated from the core limit ring 26 - that is, the upper end surface of the plugged core is uncovered, and the time when the middle chamber 11 begins to overflow - the time when the core is penetrated, and the pressure difference at this time is the breakdown pressure difference of the plugged core, and the clear water seepage rate under different pressure differences is observed and recorded to evaluate the reverse plugging ability of the plugged core, until the set test pressure difference is reached, and the reverse pressure plugging effect test is completed; the pressure of the lower chamber 17 is gradually reduced to its initial pressure;

[0124] It should be noted that in S5-1, the reverse pressure test to test the reverse blocking effect can also be carried out in the manner of S5-2;

[0125] S5-2, reverse pressure test reverse plugging effect: after the cement slurry is set, directly reverse pressure test the reverse plugging effect of the plugged core; specifically, first reduce the pressure of the upper chamber 8, so that the floating piston 10 drives the paddle cylinder 25 to move upward, so that the paddle cylinder 25 is separated from the core limit ring 26 - that is, the upper end surface of the plugged core is uncovered, and then the third overflow pipeline is closed; then the third overflow pipeline is closed, the second overflow pipeline is opened, and the pressure of the lower chamber 17 is gradually increased to perform a reverse pressure test, and then the pressure of the lower chamber is gradually reduced to its initial pressure;

[0126] S6, end of experiment;

[0127] Stop heating and pressurizing, disassemble the entire test device, and clean it;

[0128] After the test is completed, stop heating the corresponding kettle body, close the corresponding liquid inlet pressure pipeline of each chamber, and shut down the pressure pump 30; when the temperature of the upper kettle 13 and the lower kettle 16 drops to room temperature or the set temperature, open the corresponding liquid discharge pipeline of each chamber respectively, release the pressure of each chamber until the pressure of each chamber is zero, and then inlet and drain the air to each chamber; remove the top cover 1; remove the locking structure of the upper kettle 13 and the lower kettle 16, lower the lower kettle 16 to a suitable position, take out and clean the core barrel 27 and the perforated isolation plate 1 5. Use the perforated support tube 18 and the sand settling tank 19 to clean the cement stone that may remain in the inner cavity of the lower kettle 16; remove the core stop ring 26 from the core barrel 27 and clean the core stop ring 26; use special tools to remove the floating piston 10 and the slurry tube 25 below it from the upper kettle 13; clean the cement stone that may remain in the upper kettle 13; remove the floating piston 10 from the slurry tube 25 and clean the floating piston 10; use special tools to push out the remaining cement stone from the slurry tube 25 and clean the slurry tube 25;

[0129] S7, Experimental results analysis;

[0130] By comparing the breakdown pressure and clear water seepage velocity of the core before and after plugging, the plugging effect of the core can be evaluated;

[0131] By analyzing the amount of initial cement slurry in the slurry tube 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 overflowed liquid in the lower cavity 17 when squeezing the cement slurry, the amount of cement slurry components squeezed into the core under the corresponding pressure difference is analyzed;

[0132] Through the CT scanning images of the core before and after plugging, the distribution of water-soluble tracer materials and fine-grained tracer materials on the core profile, the process and results of cement slurry components entering the core under pressure difference are analyzed, so as to infer the process of cement slurry components being squeezed into the core; by changing the plugging cement slurry, the core of the formation to be plugged, and the plugging pressure difference parameters, different plugging results and effects are obtained, so as to study the influence of relevant factors on the plugging results and effects.

[0133] Test Case

[0134] The experimental cement slurry formula in this embodiment is:

[0135]

[0136] 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.

[0137]

[0138] The experimental device and evaluation method of the present invention were used to test the pressure bearing capacity and seepage capacity of the 0.3mm crack core before squeezing the above-mentioned ultrafine cement slurry. After the above-mentioned ultrafine cement slurry formula was used for curing under the conditions of squeezing pressure difference of 30Mpa and temperature of 120°C, the pressure bearing capacity and seepage capacity of the squeezed core were tested, as shown in Table 2. It can be seen from the experimental results that the pressure bearing capacity of the 0.3mm crack core before squeezing is 1MPa, and the seepage capacity under the pressure difference of 1MPa is 125mL / min. The forward pressure bearing capacity of the core after squeezing the ultrafine cement slurry is 16Mpa, and the reverse pressure bearing capacity is 20MPa. The flow rate of the core under different pressure differences is greatly reduced, and the seepage capacity is greatly reduced, indicating that the plugging system has entered the 0.3mm crack core in large quantities and has been effectively plugged.

[0139] It should be noted that if the cement slurry particles are more evenly distributed in the core and the depth of entering the core pores is deeper, the effect of plugging the cement slurry into the formation is better. The greater the change in seepage capacity before and after squeezing and sealing, the better the plugging effect. The higher the positive and reverse pressure bearing capacities after squeezing and sealing, the better the plugging effect.

[0140] The above embodiments only express preferred implementation modes, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention.

Claims

1. A test device for simulating cement slurry plugging in oil and gas well formations, characterized by: It comprises an upper kettle (13) and a lower kettle (16); The upper kettle (13) and the lower kettle (16) can be buckled up and down to form a buckled inner cavity; a floating piston (10) capable of moving up and down is provided in the buckled inner cavity, and a perforated isolation plate (15) is fixedly provided below the floating piston (10); the buckled inner 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); The upper chamber (8) is respectively connected to the first liquid inlet pressure pipeline, the first liquid discharge pipeline, the first gas pipeline, and the first overflow pipeline; the middle chamber (11) is respectively connected to the second liquid inlet pressure pipeline, the second liquid discharge pipeline, the second gas pipeline, and the second overflow pipeline; the lower chamber (17) is respectively connected to the third liquid inlet pressure pipeline, the third liquid discharge pipeline, the third gas pipeline, and the third overflow pipeline; the inner walls of the upper chamber (8), the middle chamber (11), and the lower chamber (17) are all provided with heaters, and the three chambers are all provided with corresponding temperature sensors and pressure sensors; A core barrel (27) is placed on the perforated isolation plate (15), and the core barrel (27) is fixed in the buckled inner cavity by snapping; in addition, the core barrel (27) is sealed between the inner wall of the buckled inner cavity by sleeve-mounting a corresponding sealing ring; a core is installed in the core barrel (27); A slurry cylinder (25) is suspended below the floating piston (10). When the floating piston (10) drives the slurry cylinder (25) to move downward, the lower end of the slurry cylinder (25) can be sealed and docked with the upper end of the core cylinder (27). Ⅰ. When conducting the simulation test of "core clear water seepage capacity", the floating piston (10) and the slurry tube (25) need to be taken out from the upper kettle (13); Ⅱ. When conducting the simulation test of "squeezing cement to plug the formation core", the floating piston (10) drives the slurry tube (25) to move downward - the slurry tube (25) is docked with the core tube (27), and cement slurry needs to be loaded into the slurry tube (25), and a positive pressure difference is formed on the lower chamber (17) through the middle chamber (11) to conduct the simulation test; Ⅲ. When conducting the simulation test of "testing the plugging effect after plugging the core with cement", the middle chamber (11) is allowed to form a positive pressure difference on the lower chamber (17) to conduct a forward plugging simulation test, and the lower chamber (17) is allowed to form a positive pressure difference on the middle chamber (11) to conduct a reverse plugging simulation test.

2. The test device for simulating oil and gas well formation cement slurry plugging according to claim 1, characterized in that: The upper kettle (13) comprises an upper kettle body and a top cover (1); the lower end of the upper kettle body is a through opening, and the upper end of the upper kettle body is buckled with an openable top cover (1) which can be sealed after being buckled; The upper end of the lower kettle (16) is open and the lower end is closed; a sand settling tank (19) and a perforated support cylinder (18) are placed inside the lower kettle (16); the perforated support cylinder (18) is sleeved outside the sand settling tank (19) and the two form a certain annular spacing; the height of the perforated support cylinder (18) is higher than the height of the sand settling tank (19), and a perforated isolation plate (15) is placed on the top of the perforated support cylinder (18) After the upper kettle (13) and the lower kettle (16) are buckled together, the through opening at the lower end of the upper kettle body is butted against the through opening at the upper end of the lower kettle (16), and after buckling, the buckled position can be locked via a locking structure.

3. The test device for simulating oil and gas well formation cement slurry plugging according to claim 2, characterized in that: The inner diameter of the upper kettle (13) is smaller than the inner diameter of the lower kettle (16), and when the upper kettle (13) and the lower kettle (16) are buckled together, a step A is formed at the buckling position; The outer cylindrical surface of the core barrel (27) is divided into a lower barrel portion, a middle barrel portion, and an upper barrel portion, and the outer diameters of the lower barrel portion, the middle barrel portion, and the upper barrel portion decrease in sequence, forming a step B between the lower barrel portion and the middle barrel portion; and the outer diameter of the lower barrel portion is the same as the inner diameter of the lower kettle (16), the outer diameter of the middle barrel portion is the same as the inner diameter of the upper kettle (13), and the outer diameter of the upper barrel portion is smaller than the inner diameter of the upper kettle (13); When placing the core barrel (27) containing the core in the buckled inner cavity: the core barrel (27) is inserted from the lower end of the upper kettle (13), and the step B is placed against the step A to achieve the snap-fit ​​fixation of the core barrel (27); and a corresponding sealing ring is provided between the lower part of the barrel and the inner wall of the lower kettle (16), a corresponding sealing ring is provided between the middle part of the barrel and the inner wall of the upper kettle (13), and an annular gap is provided between the upper part of the barrel and the inner wall of the upper kettle (13).

4. The test device for simulating cement slurry plugging of oil and gas well formations according to claim 3 is characterized by: The upper end surface of the upper part of the cylinder is provided with an annular step C, and a core limiting ring (26) is fixed to the upper end of the upper part of the cylinder by screws, and the lower end surface 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 barrel (27). When the core limiting ring (26) is fixed on the core barrel (27), a limiting structure can be formed for the core installed in the core barrel (27); The upper end surface of the core stop ring is conical, and the lower end surface of the slurry tube (25) is also conical. The slurry tube (25) fits against the core stop ring (26) and then docks with the core tube (27).

5. The test device for simulating cement slurry plugging in oil and gas well formations according to claim 4, characterized in that: The upper kettle (13) is fixed on a mechanical fixing mechanism, and the lower kettle (16) is installed on a lifting mechanism capable of moving up and down; After the locking structure is released, the lifting mechanism drives the lower kettle (16) to move downward, a sealing ring is sleeved on the lower part of the core barrel (27) containing the core, and the core barrel (27) is placed on the perforated isolation plate (15) in the lower kettle (16). After the placement, the lower part of the barrel and the inner wall of the lower kettle (16) are sealed by the sealing ring; a sealing ring is sleeved on the middle part of the barrel, and then the lifting mechanism moves upward, and the lower kettle (16) gradually inserts the core barrel (27) containing the core into the upper kettle (13), so that the perforated isolation plate (16) presses the step B against the step A, and then the locking structure is locked - the upper kettle (13) and the lower kettle (16) are butted and fastened.

6. The test device for simulating cement slurry plugging in oil and gas well formations according to claim 1, characterized in that: The connection structures of the first liquid inlet pressure-injection pipeline, the second liquid inlet pressure-injection pipeline, and the third liquid inlet pressure-injection pipeline are all the same, and all include an oil-water transition tank (23), a pressure regulator (22), and a liquid inlet pressure-injection switch valve connected in sequence; The connection structures of the first liquid discharge pipeline, the second liquid discharge pipeline and the third liquid discharge pipeline are consistent, and each pipeline is provided with a liquid discharge switch valve (21); The connection structures of the first gas pipeline, the second gas pipeline and the third gas pipeline are all consistent, and each pipeline is provided 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 consistent. Each pipeline has an end connected to the buckled inner cavity as the initial end, and is sequentially connected to an isolation valve (5), a condensation tank (4) and a back pressure valve (3) from the initial end to the tail end.

7. The test device for simulating cement slurry plugging of oil and gas well formations according to claim 6, characterized in that: The first liquid inlet pressure-injection pipeline, the second liquid inlet pressure-injection pipeline, and the third liquid inlet pressure-injection pipeline are all connected to a main pipe (29), and the main pipe (29) is connected to a water source via a pressure-injection pump (30); The liquid inlet pressure switch valve, the liquid discharge 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 device for simulating cement slurry plugging in oil and gas well formations according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Prepare and seal the core of the formation to be plugged; Making and packaging a core of the formation to be plugged: taking a rock having a pore structure similar to that of the formation core as the core, the diameter and height of the core matching the diameter and height of the core barrel (27); placing the core in the core barrel (27), and filling the annular space between the inner wall of the core barrel (27) and the outer wall of the core with a consolidation material (12); after the consolidation material solidifies, the core is fixed and installed in the core barrel (27); S2, "core clear water seepage capacity" simulation test - that is, measuring the "core clear water seepage capacity before the core is plugged with cement slurry"; The upper kettle (13) is fixed by a mechanical mechanism, the locking structure is loosened, and the lower kettle (16) is driven downward by the lifting mechanism; a sand settling tank (19) and a perforated support cylinder (18) are placed in the lower kettle (16), and a perforated isolation plate (15) is placed on the upper end of the perforated support cylinder (18); clean water is poured into the lower kettle (16) until the perforated isolation plate (15) is submerged; The bottom of the perforated isolation plate (15) and the core barrel (27) are consistent with the inner wall size of the lower kettle (16); the core barrel (27) with the core packaged is placed on the perforated isolation plate (15); when placing, the bottom of the barrel is covered with a corresponding sealing ring and then inserted into the lower kettle (16), so that the bottom of the core barrel (27) is placed in the lower kettle (16), and the bottom of the barrel is sealed with the inner wall of the upper end of the lower kettle (16) through the sealing ring, and the bottom of the barrel is supported by the perforated isolation plate (15); A corresponding sealing ring is disposed outside the middle of the core barrel (27); then a core limiting ring (26) is fixed to the upper end of the core barrel (27) to limit the upper end of the core; Then, the lower kettle (16) and the core barrel (27) containing the core are slowly lifted upward by the lifting mechanism, so that the middle and upper parts of the core barrel (27) are inserted into the upper kettle (16), and the middle part of the barrel is adapted to the inner wall of the upper kettle (16) through the corresponding sealing ring, and at the same time, the step B formed by the lower part and the middle part of the barrel abuts against the step A formed by the upper kettle (13) and the lower kettle (16); then, the upper kettle (13) and the lower kettle (16) are locked by the locking structure; Open the top cover (1) of the upper kettle (13), and remove the floating piston (10) and the pulp tube (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 kettle. Pour clean water into the inner cavity of the upper kettle until it reaches the top of the inner cavity of the upper kettle. Then install the top cover (1); Open the third liquid inlet pressure pipeline and the third gas pipeline corresponding to the lower chamber (17), and introduce pressurized liquid through the pressure pump (30) to discharge the gas in the lower chamber (17). After the gas is discharged, close the third gas pipeline, and keep the pressure of the lower chamber (17) at 0.2Mpa-0.3Mpa during the discharge process; Similarly, exhaust the inner cavity of the upper kettle by using the method of exhausting the lower cavity; Open the back pressure valve (3) on the third overflow pipeline corresponding to the lower chamber (17), and set the target back pressure value of the back pressure valve (3) to 3-4Mpa, and at the same time open the back pressure valve (3) on the first overflow pipeline corresponding to the upper kettle cavity and set the target back pressure value of the back pressure valve (3) to 3-4Mpa, and open the back pressure valve (3) on the third overflow pipeline corresponding to the upper kettle cavity and set the target back pressure value of the back pressure valve (3) to 3-4Mpa; then inject pressure liquid through the corresponding first liquid inlet pressure pipeline, second liquid inlet pressure pipeline, and third liquid inlet pressure pipeline. When the back pressure valve (3) on the first overflow pipeline, the back pressure valve (3) on the second overflow pipeline, and the back pressure valve (3) on the third overflow pipeline drip liquid accordingly, it indicates that the 3-4Mpa back pressure value in the upper kettle cavity and the 3-4Mpa back pressure value in the lower chamber (17) are set successfully; The first overflow pipeline and the second overflow pipeline in the upper kettle cavity are closed, and the third overflow pipeline of the lower cavity (17) is opened; then the first liquid inlet pressure pipeline and the second liquid inlet pressure pipeline corresponding to the upper kettle cavity are opened, and the pressure of the upper kettle cavity is gradually increased until the pressure difference between the upper kettle cavity and the lower cavity reaches the set target value, and the simulation of the "core clear water seepage capacity" can be completed by measuring the amount of clean water flowing out of the third overflow pipeline under different pressure differences; S3, "squeezing cement to seal the formation core" simulation test; Open the top cover (1) on the upper kettle (13), apply butter on the lower end conical surface of the slurry tube (25) and its inner wall, so that the lower end conical surface cooperates with the upper end conical surface of the core stop ring (26) to achieve sealing; place the slurry tube (25) on the core stop ring (26) at the upper end of the core tube (27); pour a predetermined volume of cement slurry prefabricated at high temperature and high pressure into the slurry tube (25); connect the upper end of the slurry tube (25) to the floating piston (10) through a corresponding connecting mechanism; and then buckle the top cover (1); Open the first liquid inlet pressure pipeline of the upper chamber (8), open the first gas pipeline of the upper chamber (8), start the pressure pump (30), exhaust the liquid in the upper chamber (8), and maintain the pressure of the upper chamber (8) at 0.2-0.3Mpa during exhaust; after the exhaust is completed, close the first gas pipeline on the upper chamber (8); Then, a pressure of more than 2 Mpa is applied to the upper chamber (8) through the first liquid inlet pressure pipeline, and the pressure is maintained; Open the second liquid inlet pressure pipeline and the second gas pipeline of the middle cavity (11), start the pressure pump (30), exhaust the liquid inlet of the middle cavity (11), and maintain the pressure of the middle cavity (11) at 0.2-0.3Mpa during exhaust; after the exhaust is completed, close the second gas pipeline; Applying an initial pressure of 1-2 Mpa to the middle chamber (11) through the second liquid inlet pressure pipeline, and simultaneously and synchronously applying an initial pressure of 1-2 Mpa to the lower chamber (17) through the third liquid inlet pressure pipeline; A target temperature value is set, and a heater is turned on to increase the temperature inside the upper kettle (13) and the lower kettle (16); when the temperature inside the kettle reaches the set target value, the pressure of the upper chamber (8) and the middle chamber (11) is gradually increased, and in the process of gradually increasing the pressure, a positive pressure difference of 2 Mpa is ensured between the middle chamber (11) and the middle chamber (11); under different pressure differences between the middle chamber (11) and the lower chamber (17), the discharge of the third overflow pipeline is observed and recorded to obtain the overflow amount under different pressure differences, so as to analyze the squeeze-in of cement slurry under different pressure differences, until the set plugging pressure difference is reached; Gradually reducing the pressure of the middle chamber (11) and the upper chamber (8), ensuring that the upper chamber (8) always has a positive pressure difference of 2 MPa greater than that of the middle chamber (11) during the gradual pressure reduction process, until the pressure difference between the middle chamber (11) and the lower chamber (17) reaches the set waiting pressure difference, and the squeeze-sealing cement slurry is completed; waiting for setting; S4, "Testing the plugging effect after cement plugging the core" simulation test, including testing the positive plugging effect of the core after plugging by pressure test in the middle cavity (8); After the cement slurry curing is completed, the pressure of the upper chamber (8) is gradually reduced to the pressure of the middle chamber (11); the first liquid inlet pressure-injection pipeline of the upper chamber (8) is closed, and the first overflow pipeline of the upper chamber (8) is opened to relieve the pressure of the upper chamber (8) by overflowing liquid, and the amount of liquid overflowing from the upper chamber (8) is observed and recorded at the same time, and it is judged based on this that the floating piston (10) drives the slurry holding barrel (25) and the cement stone formed by the remaining cement slurry therein to move upward together; If the volume of the overflowed liquid reaches a percentage of the set volume of the upper chamber (8), it is considered that the floating piston (10) has obviously moved upward and has uncovered the upper end surface of the plugged core, and the next test can be carried out as planned; if there is no overflow or the volume of the overflowed liquid is obviously smaller than the initial volume of the upper chamber, the pressure difference between the upper and lower parts of the floating piston (10) is too small to drive the floating piston (10) and other components to move upward together. At this time, the pressure of the middle chamber (11) and the lower chamber (17) is gradually increased synchronously until the volume of the overflowed liquid in the upper chamber (8) reaches a percentage of the set volume of the upper chamber (8), ensuring that the upper end surface of the plugged core is uncovered and the first overflow pipeline is closed; The pressure of the middle chamber (11) is gradually reduced to the initial pressure, i.e., 0.2-0.3 MPa, and the pressure of the lower chamber (11) is also gradually reduced to the set initial pressure, i.e., 0.2-0.3 MPa; the third overflow pipeline is opened to gradually increase the pressure of the middle chamber (11) to form a pressure difference between the middle chamber (11) and the lower chamber (17); the time when the lower chamber (17) begins to overflow, i.e., the time when the core is punctured, is observed and recorded, and the pressure difference at this time is the puncture pressure difference of the core after plugging; the clear water seepage velocity under different pressure differences is observed and recorded, so as to evaluate the plugging ability of the core after plugging, until the set test pressure difference is reached, and the positive pressure plugging effect test is completed; the pressure of the middle chamber (11) is gradually reduced to its initial pressure; S5-1, "Testing the plugging effect after cement plugging the core" simulation test, also includes reverse pressure testing the reverse plugging effect; If the core is not penetrated in the forward test, the reverse pressure test is immediately carried out to test the reverse plugging effect of the plugged core; Specifically, the third overflow pipeline is closed, the second overflow pipeline is opened, the pressure of the lower chamber (17) is gradually increased, the time when the middle chamber (11) begins to overflow - the time when the core is broken down, the pressure difference at this time is the breakdown pressure difference of the core after plugging, the clear water seepage velocity under different pressure differences is observed and recorded, so as to evaluate the reverse plugging ability of the core after plugging, until the set test pressure difference is reached, and the reverse pressure plugging effect test is completed; the pressure of the lower chamber (17) is gradually reduced to its initial pressure; S6, end of experiment; Stop heating and pressurizing, disassemble the entire test device, and clean it; S7, Experimental results analysis; By comparing the breakdown pressure and clear water seepage velocity of the core before and after plugging, the plugging effect of the core can be evaluated; By analyzing the amount of initial cement slurry in the slurry tube, 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 when squeezing the cement slurry, the amount of cement slurry components squeezed into the core under the corresponding pressure difference is analyzed; Through the CT scanning images of the core before and after plugging, the distribution of water-soluble tracer materials and fine-grained tracer materials on the core profile, the process and results of cement slurry components entering the core under pressure difference are analyzed, so as to infer the process of cement slurry components being squeezed into the core; by changing the plugging cement slurry, the core of the formation to be plugged, and the plugging pressure difference parameters, different plugging results and effects are obtained, so as to study the influence of relevant factors on the plugging results and effects.

9. The test method of the test device for simulating oil and gas well formation cement slurry plugging as claimed in claim 8, characterized in that: In the above S5-1, the reverse pressure is applied to test the reverse blocking effect, and the method of S5-2 can also be adopted; S5-2, reverse pressure test reverse blocking effect; After the cement slurry is set, directly reverse pressure test the reverse plugging effect of the plugged core; Specifically, the pressure of the upper chamber (8) is first reduced, the upper end surface of the plugged core is uncovered, and then the third overflow pipeline is closed; then a reverse pressure test is performed according to the method in S5-1, and then the pressure of the lower chamber is gradually reduced to its initial pressure.

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