Device and method for simulating high-temperature and high-pressure cement slurry plugging for oil and gas well

Abstract

The present invention relates to the technical field of oil and gas well plugging, and specifically discloses a device for simulating high-temperature and high-pressure cement slurry plugging for an oil and gas well, said device being a curing autoclave, comprising an outer cylinder, an inner cylinder A and an inner cylinder B, wherein the outer cylinder is provided with a vertical inner cavity, the top of the outer cylinder being openable whilst the bottom being sealed, the top being provided with a liquid and gas inlet, and the bottom being provided with a liquid and gas outlet; a cylindrical rock core specimen is mounted in the inner cylinder A, a gap between the cylindrical rock core specimen and the inner cylinder A being sealed with resin to form a sealing structure, which is sealingly mounted at the lower portion of the vertical inner cavity; and the inner cylinder B is located on the upper portion of the vertical inner cavity and is sealingly connected to the inner cylinder A. Further disclosed is a method for simulating high-temperature and high-pressure cement slurry plugging for an oil and gas well, wherein the state of parameters of a formation rock core is simulated and measured in a laboratory by means of the simulation of pores and fractures in said formation rock core. The present invention achieves the beneficial effects: the state of a formation rock core can be obtained in a laboratory by means of simulation, thereby optimizing the parameters of plugging cement slurry, improving the success rate of oil and gas well plugging; and the number of experimental operations is reduced.

Description

A device and method for simulating high-temperature and high-pressure cement slurry plugging of oil and gas wells Technical Field

[0001] The present invention relates to the technical field of oil and gas well plugging, in particular to a device and method for simulating high-temperature and high-pressure cement slurry plugging of oil and gas wells. Background Art

[0002] Cementing operations in oil and gas wells are a common method used in oil fields to seal leaking layers, perforation sections, and blastholes. The purpose is to force cement slurry into the formation or blasthole by applying pressure, and then seal the formation or blasthole after the cement slurry solidifies.

[0003] Referring to Figure 2, the conventional cementing operation in oil and gas wells involves the following process: a cement truck injects a predetermined amount of ultrafine cement slurry through the drill pipe. After the ultrafine cement slurry is injected into a designated location, the drill pipe is raised above the cement slurry level, and pressure is applied to squeeze the ultrafine cement slurry into the formation or blasthole. Whether the cement slurry has penetrated the formation is determined based on pressure changes. When the pressure continues to rise to a set value, the cementing is stopped, and the drill pipe is raised to a safe position to wait for the cement slurry to solidify. Once the cement slurry solidifies, the formation or blasthole is sealed.

[0004] However, problems with existing operating methods are: different formations have different conditions of pore development, and the ability of the plugging cement slurry to enter and penetrate them may vary. At the same time, different plugging cement slurries, due to differences in their components and the physical and chemical properties of their particles, have different abilities to enter formation pores and blastholes under pressure, and their strength after solidification may also vary. Therefore, it is impossible to effectively evaluate whether the cement slurry can enter the formation pores and fractures as expected, form a plugging zone of sufficient thickness, and whether it can form sufficient strength to plug pores of different sizes and achieve the expected plugging effect. As a result, it is impossible to adjust the corresponding extrusion parameters (currently only empirical parameters) according to the specific conditions of the oil and gas well, resulting in an inadequate plugging effect.

[0005] Based on this, our company designed a device to simulate the high-pressure cement slurry plugging of oil and gas wells, conducted indoor simulation experiments and evaluations, and based on the evaluation results, selected the plugging cement slurry components suitable for the size of the formation pores and fractures, optimized the formula of the plugging cement slurry, and ensured that the plugging cement slurry can penetrate into the formation pores or blastholes to a certain depth to form a plugging zone of sufficient thickness, and has sufficient strength after solidification to achieve the plugging of the predetermined pores or blastholes. Summary of the Invention

[0006] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a device and method for simulating high-temperature and high-pressure cement slurry plugging of oil and gas wells that can accurately provide extrusion parameters, thereby solving the problem that traditional oil and gas well plugging only uses empirical data, resulting in insufficient plugging effect.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] (Aspect 1) A device for simulating high-temperature and high-pressure cement slurry plugging of oil and gas wells, which is a curing kettle, comprises:

[0009] An outer cylinder having a vertical inner cavity; the top of the outer cylinder is openable and the bottom is sealed, the top of the outer cylinder has a liquid inlet and an air inlet, and the bottom of the outer cylinder has a liquid discharge and an air discharge port;

[0010] The inner cylinder A contains a cylindrical core specimen; the gap between the cylindrical core specimen and the inner cylinder A is sealed with resin, and the two form a sealing structure; the sealing structure is placed at the lower part of the vertical inner cavity of the outer cylinder, and the sealing structure seals and cuts off the lower part of the inner cylinder A;

[0011] The inner cylinder B is placed on the upper part of the vertical inner cavity of the outer cylinder. The inner cylinder B is connected to the inner cylinder A and the connection is sealed.

[0012] When the cylindrical core specimen is placed in the curing kettle, plugging cement slurry is introduced through inner tube B. The curing kettle then controls pressure and temperature to allow the plugging cement slurry to penetrate the cylindrical core specimen. The amount of plugging cement slurry that penetrates the cylindrical core specimen is measured to evaluate the plugging cement slurry's ability to enter the pores and fissures of the cylindrical core specimen. The hydraulic breakdown pressure of the plugging band is tested and the pressure-bearing capacity of the plugging band is evaluated to determine the plugging effect of the used cement slurry on the experimental formation pores and fissures. CT scanning or cross-section observation is used to analyze and study the entry of the plugging cement slurry into the formation pores and fissures under different conditions and its consolidation within the formation pores and fissures. Compared to traditional empirical parameters, this solution evaluates and analyzes the corresponding situations to determine the actual parameters of the plugging cement slurry's blockage in the formation, thereby more realistically reflecting the core conditions of oil and gas wells and providing reference and guidance for optimizing the plugging cement slurry formulation and improving the blockage process.

[0013] As a preferred technical solution of the present application, the drain-vent port is connected to an adjustable high-pressure needle valve via a transparent graduated tube, so that the amount of plugging cement slurry that has seeped out of the drain-vent port can be better read via the transparent graduated tube.

[0014] Furthermore, the liquid drain and air exhaust port is provided on the lower base, and the lower base blocks the bottom of the outer cylinder.

[0015] As a preferred technical solution of this application, a support mesh is placed at the bottom of the vertical inner cavity of the outer cylinder, and the sealing structure is placed on the support mesh, which is conducive to blocking cement slurry from seeping from the entire end surface of the lower end surface of the columnar core specimen.

[0016] As a preferred technical solution of this application, the liquid-air inlet is a pressurized hole, which is provided on the upper cover; the upper cover is openably and hermetically mounted on the top of the outer cylinder. The pressurized hole can admit pressurized water, pressurized air, or normal pressure water.

[0017] As a preferred technical solution of the present application, when the sealing structure is placed at the lower part of the vertical inner cavity of the outer cylinder, the lower part of the inner cylinder A is sealed and cut off by disposing a sealing ring A outside the inner cylinder A.

[0018] As a preferred technical solution of this application, the inner cylinder B is tapered, with a larger top and smaller bottom. The opening at the upper end of the inner cylinder A is flared, with a larger top and smaller bottom. The two are adapted to be joined and greased at the joint before docking for easy disassembly. Inner cylinder B acts as a feed tube, preventing the sealing cement slurry from adhering to the inner wall of the outer cylinder, making it impossible to remove inner cylinder A.

[0019] In a second aspect, a method for simulating high-temperature and high-pressure cement slurry plugging of oil and gas wells comprises the following steps:

[0020] S1, pretreatment;

[0021] Take a cylindrical core specimen with pores and cracks similar to those of the formation core, and polish the cylindrical surface of the cylindrical core specimen;

[0022] Then, the cylindrical core specimen is placed into the inner cylinder A, and the annular gap between the two is filled with resin to form a sealing structure as a whole;

[0023] S2, water seepage;

[0024] After the resin in the sealing structure solidifies, the sealing structure is fitted with a sealing ring A and placed in the inner cavity of a curing kettle. The inner cavity is a vertical columnar cavity, and the sealing structure is located at the lower part of the inner cavity. The top of the inner cavity of the curing kettle is openable, and the upper part has a liquid inlet and air inlet, and the bottom has a liquid drain and exhaust port. The curing kettle also has a heating device.

[0025] The curing kettle is fed with seepage water at normal temperature and pressure to saturate the cylindrical core specimens in the sealing structure with water, and the excess water is discharged through the drainage and exhaust ports;

[0026] S3. Place inner cylinder B in the upper part of the inner cavity of the curing kettle, and align the lower edge of inner cylinder B with the upper edge of inner cylinder A for sealing;

[0027] Pour a predetermined volume of plugging cement slurry prefabricated according to the plugging process into the inner tube B;

[0028] S4, congestion;

[0029] First, the curing kettle is sealed and initial pressure is applied to it, and then heated. After heating to the set temperature, the drain and exhaust ports are opened, creating an extrusion pressure differential for the plugging cement slurry. The plugging cement slurry enters the simulated gap, with part of the cement slurry being squeezed into the cylindrical core specimen and the rest being discharged through the drain and exhaust ports. The amount of plugging cement slurry discharged from the drain and exhaust ports is measured.

[0030] S5. After the plugging is completed according to the requirements of the plugging process, the drain and exhaust ports are closed, and the pressure in the curing kettle is gradually and slowly reduced. The plugging cement slurry is cured at a constant temperature and pressure and then allowed to solidify.

[0031] S6, testing;

[0032] After the predetermined solidification time, the curing kettle is cooled and the pressure is released, and then the inner cylinder B and the inner cylinder A are taken out. At this time, the simulated gap is sealed with cement to form a sealing band, and the sealing band solidifies. The cement slurry in the inner cylinder B also solidifies.

[0033] The cement plug formed by the remaining cement slurry in the inner tube B was removed and the volume of the cement plug was measured. The amount of the plugging cement slurry squeezed into the cylindrical core specimen was obtained by quantifying the total plugging cement slurry, subtracting the cement plug remaining in the inner tube B, and then subtracting the cement slurry discharged from the drainage-exhaust port. This allowed the ability of the plugging cement slurry to enter the pores of the cylindrical core specimen to be evaluated.

[0034] After step S6 is completed, step S7 is further performed. In step S7:

[0035] After removing the cement plug formed by the remaining cement slurry in inner tube B, inner tube A and the cylindrical core specimen therein are placed back into the curing kettle, and hydraulic pressure is applied from the top to test the hydraulic breakdown pressure of the plugging band, evaluate the pressure-bearing capacity of the plugging band, and then determine the plugging effect of the cement slurry on the experimental formation pores and fractures. Alternatively, using a jack and a compressive strength tester, the plugged cylindrical core specimen is removed from the inner tube of inner tube A, and then CT scanned or dissected for observation to analyze and study the entry of the plugging cement slurry into the formation pores and fractures under different conditions, and its consolidation in the formation pores and fractures.

[0036] As a preferred technical solution of the present application, in S4, the plugging cement slurry discharged from the drain-air outlet enters the transparent scale tube section and is then read.

[0037] As a preferred technical solution of the present application, in step S1, the columnar core specimen adopts a columnar formation core of standard size taken from an actual oil and gas well; if the taken out columnar formation core has cracks, it is directly loaded into the inner tube A and filled and sealed with resin; if the taken out columnar formation core does not have cracks, it is fractured into two symmetrical half-column cores by the Brazilian splitting method; after metal sheets of different thicknesses are placed on the fracture surfaces of the two half-column cores, the two semi-cylindrical cores are combined and tied together to form a structure simulating cracks; then the two tied semi-cylindrical cores are placed in the inner tube A and filled and sealed with resin.

[0038] As a preferred technical solution of the present application, in step S1, the columnar core specimen uses a simulated core that simulates the core of an actual oil and gas well formation; the simulated core has pores similar to those of the core of an actual oil and gas well formation; the simulated core is fractured into two symmetrical half-column cores by the Brazilian splitting method; after metal sheets of different thicknesses are placed on the fracture surfaces of the two half-column cores, the two semi-cylindrical cores are combined and tied together to form a structure simulating a fracture; then the two tied semi-cylindrical cores are placed in the inner tube A and filled and sealed with resin.

[0039] The present invention has the following advantages:

[0040] (1) The formation core conditions can be obtained through simulation in the laboratory, and the plugging cement slurry parameters can be optimized to improve the plugging success rate of oil and gas wells;

[0041] In traditional oil and gas well plugging operations (cementing operations), the extrusion parameters are empirical. However, cement slurries with different parameters have different abilities to penetrate formation pores and blastholes due to differences in composition and particle physical and chemical properties. Even cement slurries with the same parameters have different penetration abilities due to different pore development in different formations. Therefore, traditional empirical parameters cannot achieve the expected plugging effect.

[0042] This scheme simulates the pores and cracks of the actual formation core to form a cylindrical core specimen; conducts a plugging cement slurry penetration test on the cylindrical core specimen in the laboratory; evaluates the ability of the plugging cement slurry to enter the pores and cracks of the cylindrical core specimen by measuring the amount of plugging cement slurry squeezed into the cylindrical core specimen; evaluates the pressure bearing capacity of the plugging tape by the hydraulic breakdown pressure of the plugging tape, and then determines the plugging effect of the cement slurry used on the pores and cracks of the experimental formation; analyzes and studies the penetration of the plugging cement slurry under different conditions through CT scanning or dissection observation. The conditions of the formation pores and fractures, and their consolidation in the pores and fractures of the formation; that is, through core penetration tests of different porosities, measuring the extrusion length to determine the extrusion amount and selecting the particle size of the dry mix material, thereby optimizing the components and formula of the plugging cement slurry, ensuring that the plugging cement slurry can penetrate the formation pores or blastholes to a certain depth to form a plugging zone of sufficient thickness, and has sufficient strength after solidification to achieve the plugging of the predetermined pores or blastholes, providing process parameter support for cementing operations, thereby improving the success rate of oil and gas well plugging;

[0043] (2) The upper temperature limit of this scheme is 200°C and the upper pressure limit is 30 MPa. It can simulate and evaluate the sealing effect of cement slurries with different temperatures, sealing pressures, and particle size distributions, quantify the depth of cement slurry squeezed into the formation, and effectively evaluate the sealing effect of the formation after squeezing ultrafine cement slurry;

[0044] (3) In one experiment, the amount of plugging cement slurry squeezed into the cylindrical core specimen, the hydraulic breakdown pressure of the plugging zone, and the consolidation of the plugging cement slurry in the pores and fissures of the formation can be measured simultaneously, which greatly simplifies the number of experimental operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIG1 is a schematic structural diagram of the device of the present invention;

[0046] Figure 2 is a schematic diagram of the cementing process in an oil and gas well before and after compression (left picture is before compression, right picture is after compression);

[0047] In the figure: 1-inner cylinder A, 2-outer cylinder, 3-lower base, 4-inner cylinder B, 5-support mesh plate, 6-pressurization hole, 7-core specimen, 8-sealing ring A, 9-sealing ring B, 10-adjustable high-pressure needle valve, 11-upper cover, 12-resin, 13-transparent scale tube. DETAILED DESCRIPTION

[0048] The present invention will be further described below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the following description.

[0049] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features and technical solutions therein can be combined with each other.

[0050] In the description of the invention, it should be noted that the terms "upper" and "lower" etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the invented product is usually placed when in use, or are the orientations or positional relationships commonly understood by those skilled in the art. Such terms are only used to facilitate the description of the invention and simplify the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the invention.

[0051] At least one embodiment of the present invention provides a device for simulating high-temperature and high-pressure cement slurry plugging of oil and gas wells, as shown in FIG1 , which is a curing kettle comprising an outer cylinder 2 , an inner cylinder A1 , and an inner cylinder B4 ;

[0052] The outer tube 2 has a vertical inner cavity, the top of the tube 2 is openable and the bottom is blocked, the top has a liquid inlet and air inlet, and the bottom has a liquid discharge and exhaust port;

[0053] An inner cylinder A1 is placed at the bottom of the vertical inner cavity; a cylindrical core specimen 7 is placed inside the inner cylinder A1; the gap between the cylindrical core specimen 7 and the inner cylinder A1 is sealed with resin 12, and the two form a sealing structure; the inner cylinder A1 of the sealing structure is covered with multiple sealing rings A8 and placed in the outer cylinder 2; the sealing rings A8 cut off and seal the gap between the sealing structure and the outer cylinder 2;

[0054] The inner cylinder B4 is placed on the upper part of the vertical inner cylinder; the lower end of the inner cylinder B4 is butted against the upper end of the inner cylinder A1 and the butt joint is sealed;

[0055] When the cylindrical core specimen 7 is installed in the curing kettle, the plugging cement slurry is loaded through the inner tube B4, and then the curing kettle allows the plugging cement slurry to penetrate into the cylindrical core specimen 7 through pressure control and temperature control; by measuring the amount of plugging cement slurry penetrating into the cylindrical core specimen 7, the ability of the plugging cement slurry to enter the pores of the cylindrical core specimen is evaluated; by testing the hydraulic breakdown pressure of the plugging belt and evaluating the pressure bearing capacity of the plugging belt, the plugging effect of the used cement slurry on the pores of the experimental formation is determined; through CT scanning or dissection observation, the situation of the plugging cement slurry entering the formation pores under different conditions and its consolidation in the formation pores are analyzed and studied; compared with traditional empirical parameters, this scheme obtains the actual parameters of the plugging cement slurry in the formation based on the evaluation and analysis of the corresponding conditions, so as to be more realistic about the core conditions of oil and gas wells, and provide reference and guidance for optimizing the plugging cement slurry formula and improving the squeezing and sealing process.

[0056] Referring to Figure 1, the bottom of the outer tube 2 is sealed by a lower base 3, which has a drain and exhaust port. After the sealing cement slurry seeps out from the lower end face of the columnar core specimen 7 and the bottom of the outer tube 2 solidifies, the lower base 3 can be removed for cleaning.

[0057] Referring to Figure 1 , the drain and exhaust port is also connected to the adjustable high-pressure needle valve 10 via a transparent graduated tube 13. When the plugging slurry seeps out from the lower end of the cylindrical core specimen 7, it falls into the transparent graduated tube 13, where a reading is taken to measure the amount of plugging slurry at the seepage site.

[0058] Referring to Figure 1 , a support mesh 5 is placed at the bottom of the vertical inner cavity of the outer tube 2, and the sealing structure is placed on the support mesh 5. This allows the sealing cement slurry to seep out from the entire lower end surface of the cylindrical core specimen 7, facilitating downward flow through the mesh of the support mesh 5, thus avoiding blockage.

[0059] Referring to Figure 1 , a removable upper cover 11 is installed on top of the outer tube 2. This cover is sealed to the upper end face of the outer tube 2 via a sealing ring B9. Upper cover 11 defines a liquid and air inlet. In this embodiment, the liquid and air inlet is a pressurized port 6. This port allows for the introduction of pressurized water, pressurized air, and normal-pressure water.

[0060] Referring to Figure 1, inner cylinder B4 is tapered, with a larger top and smaller bottom. The opening at the top of inner cylinder A1 is flared, with a larger top and smaller bottom. The two are designed to mate with each other, and grease the joints before docking for easy disassembly. Inner cylinder B4 acts as a feed tube, preventing the sealing cement slurry from adhering to the inner wall of outer cylinder 2 and preventing removal of inner cylinder A1.

[0061] It should be noted that the outer cylinder 2 is also provided with a heating device and a pressure gauge for measuring the internal pressure of the outer cylinder 2 .

[0062] At least one embodiment of the present invention provides a method for simulating high-temperature and high-pressure cement slurry plugging of oil and gas wells, which is implemented based on a device for simulating high-temperature and high-pressure cement slurry plugging of oil and gas wells, and includes the following steps:

[0063] S1, pretreatment;

[0064] Samples are taken according to the required dimensions of a standard core, 50 mm in diameter and 100 mm in height, to obtain authentic formation cores from oil and gas wells. If the formation core has clear pores and natural cracks, it is used as a cylindrical core specimen. After the surface of the cylindrical core specimen is smoothed, it is placed into the inner cylinder A1, and the annular space between the cylindrical core specimen and the inner cylinder A1 is filled with resin 12 to form a sealing structure. (The resin 12 not only seals the annular space between the cylindrical core specimen and the inner cylinder A1, preventing subsequent leakage of the sealing cement slurry from the annular space, but also secures the cylindrical core specimen within the inner cylinder A1. Furthermore, compared to the method of directly placing the cylindrical core specimen into the curing kettle, this method avoids the cylindrical core specimen being directly sealed to the curing kettle via the corresponding sealing ring, thus preventing the cylindrical core specimen from being squeezed by the sealing ring and damaged.)

[0065] Alternatively, a sample is taken according to the required dimensions of a standard core with a diameter of 50 mm and a height of 100 mm to obtain a true formation core from an oil and gas well. If the formation core has open pores but no natural cracks, artificial fractures are required. To create artificial fractures, the entire obtained formation core is fractured into two symmetrical half-cores using the Brazilian splitting method. Metal sheets of varying thickness are placed on the fracture surfaces of the two half-cores, with the metal sheets positioned close to the cylindrical surface, thereby forming fractures of varying thicknesses in the core with surface characteristics more closely resembling the actual downhole conditions. The two core halves are then tied and secured together and placed in an inner cylinder A1. The annular space between the corresponding core and inner cylinder A1 is also sealed with resin 12.

[0066] Alternatively, a simulated core simulating an actual oil and gas well formation core is used; the simulated core has pores similar to those of the actual oil and gas well formation core; the simulated core is fractured into two symmetrical semi-cylindrical cores using the Brazilian splitting method; metal sheets of different thicknesses are placed on the fracture surfaces of the two semi-cylindrical cores, and the two semi-cylindrical cores are combined and tied together to form a structure simulating a fracture; the tied two semi-cylindrical cores are then placed in the inner cylinder A1 and filled and sealed with resin 12;

[0067] S2, water seepage;

[0068] After the resin 12 in the sealing structure solidifies, the upper cover 11 of the curing kettle is opened, and the sealing structure is sheathed with multiple sealing rings A8 and placed in the inner cavity of the curing kettle. The sealing structure is located at the lower part of the inner cavity, and the sealing rings A8 radially cut off the inner cavity of the curing kettle.

[0069] Close the upper cover 11 of the curing kettle, maintain normal temperature and pressure inside the curing kettle, open the drain and exhaust ports, add clean water or formation water through the liquid and air inlet ports, allow the water to penetrate into the corresponding cores in the sealing structure, saturate the corresponding cores with clean water or formation water, and drain excess water through the drain and exhaust ports; then close the drain and exhaust ports at the lower end of the curing kettle and remove the upper cover 11;

[0070] S3. Apply butter to the lower inclined surface of inner cylinder B4. Then, align it with inner cylinder A1 and rotate it appropriately so that the butter on the inclined surface covers as much of the inclined surfaces of inner cylinders A1 and B4 as possible. The butter on the inclined surfaces is engaged to form a seal between inner cylinders A1 and B4. Then, a predetermined volume of prefabricated plugging cement slurry prepared according to the plugging process is poured into inner cylinder B4.

[0071] S4, congestion;

[0072] The upper cover 11 is replaced and sealed with the inner cavity of the curing kettle via the sealing ring 8. An initial pressure of 2-3 MPa is applied to the inner cavity of the curing kettle via a pressure pump, and then the curing kettle is heated via a heating system (heating device). After heating to the set temperature, the drain and exhaust port at the lower end of the curing kettle is opened (the adjustable needle valve 10 is opened), and the extrusion pressure of the plugging cement slurry is increased at a predetermined time according to the extrusion sealing process to form an extrusion pressure differential, forcing the plugging cement slurry into the pores and cracks of the corresponding core of the sealing structure. Part of the cement slurry is extruded into the cylindrical core specimen, and the remaining part is discharged through the drain and exhaust port.

[0073] The amount of plugging cement slurry discharged from the drain-vent is read through the transparent graduated tube 13;

[0074] S5. After the plugging is completed according to the requirements of the plugging process, the drain and exhaust ports are closed, and the pressure in the curing kettle is gradually and slowly reduced. The plugging cement slurry is cured at a constant temperature and pressure and then allowed to solidify.

[0075] S6, testing;

[0076] After the predetermined solidification time, the curing kettle is cooled and depressurized, and then the inner cylinder B4 and the inner cylinder A1 are removed. At this time, the simulated gap is sealed with cement to form a sealing band, and the sealing band solidifies. The cement slurry in the inner cylinder B4 also solidifies.

[0077] Remove the cement plug formed by the remaining cement slurry in the inner tube B4 and measure its volume. Deduct the cement plug remaining in the inner tube B4 and the cement slurry discharged from the drainage and exhaust ports from the quantitative total plugging cement slurry to obtain the amount of plugging cement slurry squeezed into the cylindrical core specimen. This allows the ability of the plugging cement slurry to penetrate the pores of the cylindrical core specimen to be evaluated.

[0078] S7, retest;

[0079] After removing the cement plug formed by the remaining cement slurry in the inner tube B4, the inner tube A1 and the cylindrical core specimen therein are placed back into the curing kettle, and hydraulic pressure is applied from the top to test the hydraulic breakdown pressure of the plugging band, evaluate the pressure-bearing capacity of the plugging band, and then determine the plugging effect of the cement slurry on the experimental formation pores and fractures. Alternatively, using a jack and a compressive strength tester, the plugged cylindrical core specimen is removed from the inner tube of the inner tube A1 and then CT scanned or dissected for observation to analyze and study the penetration of the plugging cement slurry into the formation pores and fractures under different conditions and its consolidation in the formation pores and fractures.

[0080] It should be noted that this solution has a maximum measurement temperature of 200°C and a maximum pressure of 30 MPa. This method can simulate and evaluate the sealing effect of cement slurries at different temperatures, sealing pressures, and particle size distributions, quantify the depth of cement slurry penetration into the formation, and effectively evaluate the sealing effect of the formation after the injection of ultrafine cement slurry.

[0081] It should be noted that during the test, the bearing capacity / breakdown pressure of the core is tested first, and then the bearing capacity / breakdown pressure after being blocked by ultrafine cement slurry is tested; if the bearing capacity / breakdown pressure after blocking is greater than the bearing capacity / breakdown pressure before blocking, the blocking is effective, and the greater the difference, the better the effect; the blocked core is cut open along the axis, and the depth of the blocking cement slurry entering the core pores shown by the tracer (such as red ink) is measured and observed; the deeper the penetration, the better the effect of the blocking cement slurry squeezing into the formation pores.

[0082] The above embodiments merely represent preferred implementations, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art will be able to make various modifications and improvements without departing from the scope of the present invention, and these modifications and improvements are all within the scope of protection of the present invention.

Claims

1. A device for simulating high-temperature and high-pressure cement slurry plugging of oil and gas wells, characterized in that: It is a curing kettle, comprising: The outer cylinder (2) has a vertical inner cavity; the top of the outer cylinder (2) can be opened and the bottom is blocked, the top has a liquid inlet and air inlet, and the bottom has a liquid discharge and air discharge port; An inner cylinder A (1) contains a columnar core specimen (7); a gap between the columnar core specimen (7) and the inner cylinder A (1) is sealed with resin (12), and the two form a sealing structure; the sealing structure is placed at the lower part of the vertical inner cavity of the outer cylinder (2), and the sealing structure seals and cuts off the lower part of the inner cylinder A (1); The inner cylinder B (4) is placed at the upper part of the vertical inner cavity of the outer cylinder (2). The inner cylinder B (4) is butt-jointed with the inner cylinder A (1) and the joint is sealed.

2. The device for simulating high temperature and high pressure cement slurry plugging of oil and gas wells according to claim 1, characterized in that: The liquid discharge and air discharge port is connected to the adjustable high-pressure needle valve (10) via a transparent graduated tube (13); The liquid discharge and air discharge port is provided on the lower base (3), and the lower base (3) blocks the bottom of the outer cylinder (2); The liquid inlet and air inlet is a pressurizing hole (6), and the pressurizing hole (6) is opened on the upper cover (11); the upper cover (11) is openably and hermetically mounted on the top of the outer cylinder (2).

3. The device for simulating high temperature and high pressure cement slurry plugging of oil and gas wells according to claim 1, characterized in that: A supporting mesh plate (5) is also placed at the inner bottom of the vertical inner cavity of the outer cylinder (2); and the sealing structure is placed on the supporting mesh plate (5).

4. The device for simulating high temperature and high pressure cement slurry plugging of oil and gas wells according to claim 1, characterized in that: When the sealing structure is placed at the lower part of the vertical inner cavity of the outer cylinder (2), the lower part of the inner cylinder A (1) is sealed and cut off by arranging a sealing ring A (8) outside the inner cylinder A (1).

5. The device for simulating high temperature and high pressure cement slurry plugging of oil and gas wells according to claim 1, characterized in that: The inner cylinder B (4) is in a conical shape with a larger top and a smaller bottom. The opening at the upper end of the inner cylinder A (1) is an expanded opening with a larger top and a smaller bottom. The two are adapted to be connected and butter is applied to the connection point before connection.

6. A method for simulating high temperature and high pressure cement slurry plugging of oil and gas wells, characterized in that: The following steps are involved: S1, pretreatment; Take a columnar core specimen with pores and cracks similar to those of the formation core, and polish the cylindrical surface of the columnar core specimen; Then, the columnar core specimen is placed in the inner cylinder A (1), and the annular gap between the two is filled with resin (12), thereby forming a sealing structure as a whole; S2, water seepage; After the resin (12) in the sealing structure is solidified, the sealing structure is sleeved with a sealing ring A (8) and placed in the inner cavity of the curing kettle, the inner cavity is a vertical columnar inner cavity, and the sealing structure is located at the lower part of the inner cavity; the top of the inner cavity of the curing kettle can be opened, the upper part thereof has a liquid inlet and air inlet, and the bottom thereof has a liquid discharge and air outlet; the curing kettle also has a heating device; The curing kettle is fed with seepage water at normal temperature and pressure, so that the columnar core specimens in the sealing structure are saturated with water, and the excess water is discharged through the drainage-air outlet; S3, placing the inner cylinder B (4) in the upper part of the inner cavity of the curing kettle, and butting the lower edge of the inner cylinder B (4) with the upper edge of the inner cylinder A (1) to seal; A predetermined volume of plugging cement slurry prefabricated according to the plugging process is poured into the inner tube B (4); S4, congestion; First, the curing kettle is closed and initial pressure is applied to the inside, and then heated; when heated to the set temperature, the drain-vent is opened to form an extrusion pressure difference for the plugging cement slurry, and the plugging cement slurry enters the simulated gap, a part of the cement slurry is squeezed into the columnar core specimen, and the other part of the cement slurry is discharged through the drain-vent; Measure the amount of plugging cement slurry discharged from the drain-vent port; S5. After the plugging is completed according to the requirements of the plugging process, the drain-exhaust port is closed, and the pressure in the curing kettle is gradually and slowly reduced, and the plugging cement slurry is cured at a constant temperature and pressure, and then solidified; S6, testing; After the curing kettle has solidified for a predetermined time, the temperature is lowered and the pressure is released, and then the inner cylinder B (4) and the inner cylinder A (1) are taken out. At this time, the simulated gap is sealed by cement to form a sealing band, and the sealing band solidifies, and the cement slurry in the inner cylinder B (4) also solidifies; The cement plug formed by the remaining cement slurry in the inner tube B (4) is removed and the volume of the cement plug is measured; the amount of the plugging cement slurry squeezed into the columnar core specimen is obtained by quantitatively calculating the total plugging cement slurry, subtracting the cement plug remaining in the inner tube B (4), and then subtracting the cement slurry discharged from the drainage-air outlet, thereby evaluating the ability of the plugging cement slurry to enter the pores of the columnar core specimen.

7. A method for simulating high temperature and high pressure cement slurry plugging of oil and gas wells according to claim 6, characterized in that: After step S6 is completed, step S7 is further performed. In step S7: After removing the cement plug formed by the remaining cement slurry in the inner tube B (4), the inner tube A (1) and the columnar core specimen therein are placed back into the curing kettle, and hydraulic pressure is applied from the top to test the hydraulic breakdown pressure of the plugging belt, evaluate the pressure bearing capacity of the plugging belt, and then determine the plugging effect of the cement slurry on the experimental formation pores and fractures; alternatively, the plugged columnar core specimen is taken out of the inner tube of the inner tube A (1) by using a jack and a compressive strength tester, and then CT scan or dissection observation is performed to analyze and study the situation of the plugging cement slurry entering the formation pores and fractures under different conditions, and the situation of its consolidation in the formation pores and fractures.

8. A method for simulating high temperature and high pressure cement slurry plugging of oil and gas wells according to claim 6 or 7, characterized in that: In S4, the plugging cement slurry discharged from the drain and exhaust port enters the transparent scale tube section (13) and is then read.

9. The device and method for simulating high-temperature and high-pressure cement slurry plugging of oil and gas wells according to claim 6 or 7, characterized in that: In step S1, the columnar core specimen is a columnar formation core of standard size taken from an actual oil and gas well; If the obtained columnar formation core has cracks, it is directly placed in the inner tube A (1) and filled and sealed with resin (12); If the extracted columnar formation core has no cracks, it is fractured into two symmetrical half-column cores by the Brazilian splitting method; after metal sheets of different thicknesses are placed on the fracture surfaces of the two half-column cores, the two semi-cylindrical cores are combined and tied together to form a structure simulating cracks; then the two tied semi-cylindrical cores are placed in an inner tube A (1) and filled and sealed with resin (12).

10. The device and method for simulating high-temperature and high-pressure cement slurry plugging of oil and gas wells according to claim 6 or 7, characterized in that: In the step S1, the columnar core specimen is a simulated core that simulates an actual oil and gas well formation core; The simulated core has pores similar to those of actual oil and gas well formation cores; The simulated core is fractured into two symmetrical half-cylindrical cores by the Brazilian splitting method; after metal sheets of different thicknesses are placed on the fracture surfaces of the two half-cylindrical cores, the two half-cylindrical cores are combined and tied together to form a structure simulating fractures; and then the two tied half-cylindrical cores are placed in an inner tube A (1) and filled and sealed with resin (12).

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