A lost circulation evaluation device and method that considers formation rock mechanical properties and fracture characteristics

Abstract

This invention discloses a plugging evaluation device and method that considers the mechanical properties of formation rocks and fracture characteristics. The experimental device includes a wellbore simulation system, a pressure control system, a temperature control system, a leakage monitoring system, and a computer data acquisition system. The wellbore simulation system is connected to the pressure control system, temperature control system, and leakage monitoring system, respectively. All three systems are connected to the computer data acquisition system. This invention constructs a simulated three-dimensional fracture system equivalent to the mechanical properties and fracture characteristics of real fractured and leaky formations. This allows for testing the sealing pressure-bearing capacity of plugging materials under both positive and negative pressure differentials. It solves the technical problem that existing plugging evaluation devices cannot accurately simulate the mechanical properties and fracture characteristics of formation rocks, thus enabling a scientific and reasonable evaluation of the sealing pressure-bearing capacity and sealing effect of plugging materials.

Description

Technical Field

[0001] This invention relates to the field of leak sealing technology in oil drilling engineering, and in particular to a leak sealing evaluation device and method that takes into account the mechanical properties of formation rocks and fracture characteristics. Background Technology

[0002] Loss in wells occurs during various downhole operations throughout the well construction cycle, where drilling fluid, completion fluid, cement slurry, and other working fluids in oil and gas wells leak into the formation due to the pressure difference between the wellbore pressure and the formation fluid pressure. Therefore, during drilling and completion, to prevent loss of fluid, it is often necessary to add anti-loss and plugging materials to the drilling fluid to improve its ability to prevent loss of fluid and the formation's pressure-bearing capacity, or to stop drilling and plug the leak after it has already occurred. Currently, there are many different types of leakage prevention and plugging evaluation devices, such as the Chinese invention patent "A Crack Simulation Mechanism, Crack Simulation Experiment Instrument and Leakage Pluging Evaluation Experiment Device" (publication number CN112360432A), the Chinese invention patent "Formation Simulation Device and Crack Pluging Instrument" (publication number CN113622900A), the Chinese invention patent "An Experimental Device and Experimental Method for Crack Pluging Simulation" (publication number CN112326888B), and the Chinese utility model patent "Crack Simulation Device and Variable Crack Pluging Simulation Evaluation System" (publication number CN218522658U), etc.

[0003] However, the devices used in commonly used leak-sealing experimental instruments to simulate crack structures have the following problems:

[0004] 1) The mechanical characteristics of the simulated fracture device differ significantly from those of the actual leakage area. These geological mechanical characteristics are related to the stress sensitivity of the fractures, affecting fracture aperture, fracture propagation, leakage process, and leakage assessment. For example, the stainless steel plate used to simulate fractures in the Chinese invention patent "Evaluation Method for Plugging Formation Fractures" (publication number CN115248947A) has a Young's modulus, Poisson's ratio, and surface friction coefficient approximately in the range of 200-240 GPa, 0.29-0.33, and 0.1-0.4, respectively. However, the Young's modulus of the actual leakage area's rock formation is typically below 100 GPa, the Poisson's ratio is around 0.25, and the surface friction coefficient is usually above 0.6. This difference in mechanical parameters will affect the accuracy and effectiveness of the plugging experiment results.

[0005] 2) The simulated fracture device differs significantly from the fracture characteristic parameters of the actual leakage area. The fracture characteristics of the formation are related to the leakage sensitivity of the formation, affecting the degree of leakage, leakage evaluation, and selection of leakage prevention and plugging materials. For example, the fracture devices used to simulate leakage channels in the plugging instruments in the Chinese invention patent "A fracture simulation mechanism, fracture simulation experimental instrument and leakage evaluation test device" and the Chinese utility model patent "Friction simulation device and variable fracture plugging simulation evaluation system" (publication number CN218522658U) lack a definite source for setting key parameters such as fracture size, fracture width, and fracture morphology. Most of the data comes from geological workers observing the surface of the formation core, which cannot accurately reflect the complex three-dimensional fracture characteristics of the formation.

[0006] In summary, the current simulated fracture devices in leak-sealing evaluation devices do not consider the impact of formation rock mechanical properties and fracture characteristics on the leak-sealing evaluation results. Furthermore, the existing simulated fracture devices in leak-sealing evaluation devices have technical problems that make it difficult to realistically simulate formation rock mechanical properties and fracture characteristics. As a result, the leak-sealing evaluation devices lack rationality and fail to meet the requirements for reasonably evaluating the sealing performance of leak-sealing materials. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing leakage evaluation experimental devices and to provide a leakage evaluation device and method that considers the mechanical properties of formation rocks and the characteristics of fractures. This invention solves the technical problem that existing leakage evaluation devices cannot realistically simulate the mechanical properties of formation rocks and the characteristics of fractures. It can test the sealing pressure bearing capacity of leakage materials in fractures under positive and negative pressure differences, and scientifically and rationally evaluate the sealing pressure bearing capacity and sealing effect of leakage materials in leakage fractures.

[0008] The present invention adopts the following technical solution:

[0009] A plugging evaluation device that considers the mechanical properties of formation rocks and fracture characteristics includes a wellbore simulation system, a pressure control system, a temperature control system, a leakage monitoring system, and a computer data acquisition system.

[0010] The wellbore simulation system includes a simulated formation fracture system, plugging slurry, wellbore, top cover, base, upper metal filter, lower metal filter, upper sealing gasket, lower sealing gasket, upper metal shim, lower metal shim, and metal spring, wherein:

[0011] The cylinder is a metal cylindrical structure. The top cover is installed on the top of the cylinder, and the base is installed on the bottom of the cylinder. The top cover and the base are provided with threaded holes and sealing rings. The top cover is sealed to the air inlet valve core, and the base is sealed to the drain valve core. The upper metal filter and the lower metal filter are installed inside the cylinder. The upper metal filter is located on the lower side of the bottom cover, and the lower metal filter is installed on the upper side of the base.

[0012] Inside the cylinder, the upper metal filter screen is located below an upper metal gasket, the upper metal gasket is located below a metal spring and a sealing slurry, and the metal spring is located below a lower metal gasket.

[0013] The lower side of the inner metal gasket is the upper sealing gasket, the upper side of the lower metal filter screen is the lower sealing gasket, and the space between the upper and lower sealing gaskets is a simulated formation fracture system. The center of the simulated formation fracture device is a simulated fracture. Under experimental conditions, the slurry to be evaluated can form a sealing layer within it.

[0014] The pressure control system, which controls pressure changes, is connected to the wellbore simulation system via a pressure pipeline. The temperature control system heats the wellbore simulation system while monitoring the corresponding temperature. The leakage monitoring system, which measures the leakage of filtrate, is located at the bottom of the wellbore simulation system. The computer data acquisition system, which collects data, is connected to the pressure control system, the temperature control system, and the leakage monitoring system.

[0015] Both the upper and lower ends of the cylinder are threaded. The upper and lower sealing gaskets are high-temperature resistant rubber rings used to seal the annular gaps of the simulated crack system.

[0016] The upper and lower metal gaskets are annular gaskets used to fix and compress the simulated crack system.

[0017] The pressure control system includes an upper quick-release interface, an upper pressure relief port, an upper pressure relief valve, a first pressure control device, a first pressure valve, a second pressure valve, a pressure gauge, a pressure pump, a second pressure control device, a lower pressure relief valve, a lower pressure relief port, and a lower quick-release interface, wherein:

[0018] The upper quick-release interface is installed on the intake valve core via a sliding buckle. The intake valve core is connected to the first pressure control via pipeline I. An upper pressure relief valve is installed on pipeline I, and the outlet end of the upper pressure relief valve is the upper pressure relief port. The first pressure control device is connected to the pressure pump via pipeline II. A first pressure valve is installed on pipeline II. The first pressure control device is connected to the computer data acquisition system via a signal line.

[0019] The drain valve core is equipped with a quick-release interface via a sliding snap. The quick-release interface is connected to the second pressure control device via pipeline III. A pressure relief valve is installed on pipeline III, and the outlet end of the pressure relief valve is the pressure relief port. The second pressure control device is connected to the pressure pump via pipeline IV. A second pressure valve is installed on pipeline IV, and a pressure gauge is installed on the pressure pump. The second pressure control device is connected to the computer data acquisition system via a signal line.

[0020] The temperature control system includes a temperature control device, a temperature sensor, a power interface, and a heating sleeve, wherein:

[0021] The cylinder is placed inside the heating sleeve, and the temperature sensor is installed inside the cylinder. The temperature sensor is connected to the temperature control device and the computer data acquisition system through a data transmission line. One end of the temperature control device is connected to the heating sleeve, and the other end is connected to the power interface. The other end of the power interface is connected to the heating sleeve.

[0022] The leakage monitoring system includes a drain valve core, a drain switch, a leakage filtrate collector, and a leakage monitoring device, wherein:

[0023] A drain valve core is equipped with a drain switch, and the lower end of the drain switch is a leak filtrate collector. The leak filtrate collector is used to collect leaked filtrate. A leak monitoring device is installed at the bottom of the leak filtrate collector and is connected to a computer data acquisition system via a data transmission line.

[0024] The simulated formation fracture system is prepared by the following methods:

[0025] 1) Obtain stratigraphic rock samples from the lost area and test the mechanical characteristic parameters of the rock samples.

[0026] The aforementioned formation rock samples are core samples obtained from well drilling, and the aforementioned mechanical characteristics include Young's modulus. Poisson's ratio coefficient of friction Key parameter data.

[0027] 2) Prepare simulated strata rock samples.

[0028] Special simulated formation slurry was prepared according to experimental requirements and API standards. The simulated formation slurry formula included G-grade oil wells, aggregates, slurry preparation water, fluid loss reducing agent, and fibers. These were mixed in a certain proportion, poured into a curing mold, and the mold was placed in a high-temperature and high-pressure curing autoclave for curing for a certain period of time. The simulated formation rock sample was then taken out for later use.

[0029] 3) Determine the equivalence of mechanical characteristic parameters between simulated strata rock samples and strata rock samples.

[0030] The aforementioned principle of equivalent mechanical characteristic parameters includes the elastic modulus of simulated and actual geological rock samples. Equivalent, Poisson's ratio Equivalent, coefficient of friction Equivalently, suitable simulated strata rock samples are obtained.

[0031] The principle of equivalence between the simulated formation fracture system and the actual leakage region's formation mechanical characteristic parameters is as follows:

[0032]

[0033] 4) Obtain three-dimensional fracture parameter data of the formation in the lost area.

[0034] Perform CT scans on stratigraphic rock samples to obtain high-precision three-dimensional stratigraphic fracture data;

[0035] The CT scan mentioned is a non-destructive testing scanning technique;

[0036] Stratigraphic rock sample data were imported into data processing software for preprocessing to remove annular artifacts and irregular parts, and a Create Mask was created for fracture volume fraction. calculate;

[0037] Rock sample cracks and pores were extracted, and grayscale threshold segmentation and brightness difference segmentation methods were used to extract rock sample cracks and pores from the entire three-dimensional rock sample;

[0038] The pore portion of the rock sample is removed, and the pores in the three-dimensional rock sample are removed by a binarization data filtering method to obtain the rock sample cracks;

[0039] Calculate the fracture connectivity of the rock sample, with the fracture connectivity direction set as the rock sample axial direction (z-axis), to obtain all fracture leakage channels that are connected along the rock sample axial direction;

[0040] Calculate the fracture parameters of the rock sample and obtain the fracture volume fraction of the three-dimensional fracture using a formula. Crack width and crack tortuosity parameter.

[0041]

[0042]

[0043]

[0044] in, K Crack volume fraction, in % V Total volume of the rock sample, in mm. 3 n is the number of cracks; v i The volume of the i-th crack is in mm. 3 D represents the crack width, in mm. S i The area of ​​the i-th crack is in mm. 2 T represents the crack tortuosity; h i H represents the length of the i-th crack along the core axis, in mm; H represents the vertical height of the core axis, in mm.

[0045] 5) Construct a simulated formation fracture system.

[0046] Determine the equivalence of simulated formation fracture systems and formation rock sample fracture characteristic parameters, including fracture volume fraction. Equivalent, crack width Equivalent, crack tortuosity Equivalent;

[0047] The principle of equivalence between the simulated formation fracture system and the three-dimensional fracture characteristic parameters of the actual leakage area is as follows:

[0048]

[0049] A simulated formation fracture device with equivalent three-dimensional fracture characteristic parameters is fabricated; the simulated formation fracture device is used to prepare a simulated formation fracture system with equivalent three-dimensional fracture characteristic parameters to the actual leakage area.

[0050] To prepare a simulated formation fracture system, firstly, a simulated formation fracture device is installed, and a molding agent is injected into the device. After the molding agent cools and solidifies, the simulated formation fracture mold is disassembled and removed, then fixed in a suitable position in a curing device. The simulated formation rock sample slurry is poured into the curing mold, and it is first placed in a constant temperature curing chamber for pre-curing for a period of time, and then placed in a high-temperature and high-pressure curing autoclave for curing for a certain age, thus obtaining a simulated formation fracture system with mechanical characteristic parameters and three-dimensional fracture characteristic parameters equivalent to those of the formation rock sample. The molding agent is a solid molding agent that melts into a liquid state under high temperature conditions.

[0051] A plugging evaluation method considering the mechanical properties of formation rocks and fracture characteristics includes the following steps:

[0052] 1) Before starting the experiment, check that all valves and switches are in the closed position;

[0053] 2) Install the cylinder, place the simulated formation fracture system at the lower end of the cylinder's inner cavity, and then put in the lower sealing gasket, lower metal filter screen, base and drain valve core in sequence. From the upper end of the cylinder's inner cavity, put in the upper sealing gasket, lower metal gasket in sequence, inject the leak-proof and plugging slurry to be evaluated, and then put in the metal spring, upper metal gasket, upper metal filter screen in sequence. Install the top cover and air inlet valve core.

[0054] 3) Install the pressure control system. Attach the upper quick-release interface to the air intake valve core and the lower quick-release interface to the drain valve core. Connect the first pressure control device and the second pressure control device to the pressure pump via pressure lines. Connect the first pressure control device and the second pressure control device to the computer data acquisition system via data transmission lines.

[0055] 4) Install the temperature control system, connect the temperature control device to the heating sleeve, temperature sensor, and computer data acquisition system respectively, and connect the power interface;

[0056] 5) Install the leakage monitoring system, connect the leakage filtrate collector to the drain valve core, place it on the leakage monitoring device, and connect the leakage monitoring device to the computer data acquisition system through the data transmission line;

[0057] 6) Conduct a leak-stopping test, including:

[0058] Positive pressure differential leak sealing evaluation experiment;

[0059] Start the temperature control device, set the heating time, and use the annular heating sleeve to heat the simulated formation fracture system and the leakage prevention and plugging slurry to be evaluated in the cylinder. After the heating is completed, control the temperature at the target temperature, open the drain switch, and monitor the leakage through the leakage monitoring device.

[0060] Start the first pressure control device, set the target pressure, and use the pressure pump to pressurize the cylinder evenly and continuously until the target pressure is reached; set the pressurization rate and stabilization time; if no leakage or a small amount of leakage is detected when the drain switch is open, continue the pressurization process until the target pressure value is reached. Record the leakage amount, leakage rate, and positive pressure differential sealing pressure bearing capacity (pressure value) through the computer data acquisition system, and monitor the changes in the sealing performance of the anti-leakage slurry to be evaluated in real time.

[0061] Negative pressure differential leak sealing evaluation experiment;

[0062] After completing the positive pressure differential leak-sealing evaluation experiment, the first pressure control device, the first pressure valve, and the drain switch are closed. Then, the upper pressure relief valve is opened and closed after pressure relief is completed. The second pressure control device is then started, and the pressure increase rate and pressure stabilization time are set. The pressure value fed back by the second pressure control device is monitored through the computer data acquisition system. If the pressure value is stable, the pressure continues to increase. If the pressure value drops significantly or drops to 0, the pressure value at the moment before the pressure drop is recorded through the computer data acquisition system. The pressure value at this moment is the pressure-bearing capacity of the leak-proof and leak-sealing slurry to be evaluated against negative pressure differential sealing.

[0063] 7) Disassemble the leak-sealing device. After the experiment, save the experimental data from the computer data acquisition system, turn off the pressure pump, the first pressure valve, the second pressure valve, and the temperature control device. After the leak-sealing device temperature drops to room temperature, open the upper and lower pressure relief valves to release the pressure in the inner cavity of the cylinder and the pressure pipeline. Turn off the first pressure control device, the second pressure control device, and the leakage monitoring device. Disconnect all pipelines of each control device, remove the top cover and the base, and take out the simulated formation fracture system.

[0064] 8) Evaluate the effectiveness of the leak sealing

[0065] The simulated formation fracture system was removed from the cylinder, and the sample was cut open to observe the distribution, location, proportion, and accumulation of the plugging material in the sealing layer. Photos were taken, and the plugging effect of the tested slurry was evaluated by combining the leakage rate of the filtrate, the positive pressure differential sealing capacity, and the negative pressure differential sealing capacity. Simultaneously, further microscopic testing experiments could be conducted on the plugging layer structure in the simulated formation fracture system to analyze the microscopic failure mechanism of the plugging material.

[0066] The beneficial effects of this invention are:

[0067] (1) This invention restores the leakage process and sealing process of the plugging material in the leakage channel of the downhole fracture, and comprehensively evaluates the sealing effect of the leakage prevention and plugging material by the leakage amount, leakage rate, positive pressure difference sealing pressure bearing capacity, negative pressure difference sealing pressure bearing capacity, distribution state, distribution location, distribution ratio and accumulation status of the sealing layer.

[0068] (2) By constructing a simulated three-dimensional fracture system that is equivalent to the rock mechanical properties and fracture characteristics of real fractured and leaky formations, this invention solves the technical problem that the simulated fracture device of the existing leakage evaluation device is difficult to truly simulate the rock mechanical properties and fracture characteristics of formations. It can test the sealing pressure bearing capacity of the leakage material in the wellbore simulation system under positive and negative pressure difference, and scientifically and rationally evaluate the sealing pressure bearing capacity and sealing effect of the leakage material in the fracture of the leaky formation.

[0069] (3) This invention establishes the principle of equivalent stratigraphic mechanical characteristic parameters, namely the elastic modulus of simulated stratigraphic rock samples and actual lost area stratigraphic rock samples. Equivalent, Poisson's ratio Equivalent, coefficient of friction Equivalent; simultaneously, an equivalence principle for the characteristic parameters of three-dimensional fractures in the formation was established, namely, the fracture volume fraction of the simulated formation fracture system and the actual leakage area formation rock samples. Equivalent, crack width D equivalent, crack tortuosity T equivalent. Attached Figure Description

[0070] Figure 1 This is a schematic diagram of the leak-sealing evaluation device of the present invention;

[0071] Figure 2 This is a flowchart illustrating the preparation process of the simulated formation fracture system of this invention.

[0072] Figure 3 This is a diagram of the formation fracture simulation device of the present invention;

[0073] Figure 4 This is a diagram of the maintenance device of the present invention;

[0074] Figure 5This is a diagram showing the experimental results of positive pressure differential leak plugging evaluation in Example 1 of the present invention;

[0075] Figure 6 This is a diagram showing the experimental results of negative pressure differential leak sealing evaluation in Example 1 of the present invention;

[0076] In the diagram: 1-Cylinder, 11-Top cover, 12-Base, 13-Upper sealing gasket, 14-Lower sealing gasket, 15-Upper metal gasket, 16-Lower metal gasket, 17-Metal spring, 18-Upper metal filter, 19-Lower metal filter, 110-Inlet valve core, 111-Drain valve core, 112-Drain switch;

[0077] 2-First pressure control device, 21-Upper quick-release interface, 22-Upper pressure relief port, 23-Upper pressure relief valve, 24-First pressure valve;

[0078] 3-Second pressure control device, 31-Second pressure valve, 32-Lower quick-release interface, 33-Lower pressure relief valve, 34-Lower pressure relief port;

[0079] 4-Pressure pump, 41-Pressure gauge;

[0080] 5-Temperature control device, 51-Temperature sensor, 52-Heating sleeve, 53-Power interface;

[0081] 6-Leakage monitoring device, 61-Plugging slurry, 62-Leakage filtrate collector, 63-Leakage filtrate;

[0082] 7-Simulated formation fracture device, 71-Simulated formation fracture system, 72-Sealing layer, 73-Simulated fracture;

[0083] 8-Computer data acquisition system;

[0084] 9-Maintenance equipment. Detailed Implementation

[0085] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0086] The technical solution adopted in this invention is:

[0087] 1) Key Methods

[0088] This invention takes the mechanical characteristics of the formation and the three-dimensional fracture characteristics of the formation as the research targets, and applies the mechanical characteristics of the formation and the three-dimensional fracture characteristics of the formation in the lost area to the simulated formation fracture system, thereby solving the problem of the equivalence between the simulated formation fracture system and the actual mechanical characteristics and three-dimensional fracture characteristics of the formation in the lost area.

[0089] The principle of equivalence between the simulated formation fracture system and the actual leakage region's formation mechanical characteristic parameters is as follows:

[0090]

[0091]

[0092]

[0093] The principle of equivalence between the simulated formation fracture system and the three-dimensional fracture characteristic parameters of the actual leakage area is as follows:

[0094]

[0095]

[0096]

[0097] E is the elastic modulus; Poisson's ratio; The coefficient of friction; This refers to the crack volume fraction; The width of the crack; The degree of tortuosity of the crack.

[0098] like Figure 1 As shown, the leakage evaluation device, which considers the mechanical characteristics of formation rocks and fracture characteristics, mainly includes a wellbore simulation system, a pressure control system, a temperature control system, a leakage monitoring system, and a computer data acquisition system.

[0099] The wellbore simulation system includes a simulated formation fracture system 71, a plugging slurry 61, a cylinder 1, a top cover 11, a base 12, an upper metal filter 18, a lower metal filter 19, an upper sealing gasket 13, a lower sealing gasket 14, an upper metal gasket 15, a lower metal gasket 16, and a metal spring 17, wherein:

[0100] The simulated formation fracture system 71 was prepared experimentally. The plugging slurry 61 is the plugging slurry to be evaluated.

[0101] The cylinder 1 is a metal cylindrical structure. The top cover 11 is installed on the top of the cylinder 1, and the base 12 is installed on the bottom of the cylinder 1. The top cover 11 and the base 12 are provided with threaded holes and sealing rings. The top cover 11 is sealed to the air inlet valve core 110, and the base 12 is sealed to the drain valve core 111. The upper metal filter screen 18 and the lower metal filter screen 19 are installed inside the cylinder 1. The upper metal filter screen 18 is located on the lower side of the top cover 11, and the lower metal filter screen 19 is installed on the upper side of the base 12. The upper metal filter screen 18 and the lower metal filter screen 19 can filter large particles in the sealing material to prevent the sealing particles from clogging the channels of the air inlet valve core 110 and the drain valve core 111.

[0102] Inside the cylinder 1, below the upper metal filter screen 18 is an upper metal gasket 15, below the upper metal gasket 15 are a metal spring 17 and the plugging slurry 61, and below the metal spring 17 is a lower metal gasket 16. The main function of the upper metal gasket 15, lower metal gasket 16 and metal spring 17 is to fix and compress the simulated formation fracture system 71, ensuring that the plugging material can only flow or remain in the simulated fracture 73, thus ensuring the accuracy and effectiveness of the plugging evaluation test results.

[0103] Inside the cylinder 1, the lower metal gasket 16 has an upper sealing gasket 13 below it, and the lower metal filter 19 has a lower sealing gasket 14 above it. Between the upper sealing gasket 13 and the lower sealing gasket 14 is a simulated formation fracture system 71. The center of the simulated formation fracture device is a simulated fracture 73, within which a sealing layer 72 can be formed. The upper sealing gasket 13 and the lower sealing gasket 14 primarily function to seal the tiny annular gap between the simulated formation fracture system 71 and the cylinder 1, preventing leakage of the sealing material from the annular gap and affecting the leakage evaluation test results.

[0104] The pressure control system includes an upper quick-release interface 21, an upper pressure relief port 22, an upper pressure relief valve 23, a first pressure control device 2, a first pressure valve 24, a second pressure valve 31, a pressure gauge 41, a pressure pump 4, a second pressure control device 3, a lower pressure relief valve 33, a lower pressure relief port 34, and a lower quick-release interface 32, wherein:

[0105] The upper quick-release interface 21 is installed on the intake valve core 110. The intake valve core 110 is connected to the first pressure control device 2 through pipeline I. An upper pressure relief valve 23 is installed on pipeline I, and the outlet end of the upper pressure relief valve 23 is the upper pressure relief port 22. The first pressure control device 2 is connected to the pressure pump 4 through pipeline II. A first pressure valve 24 is installed on pipeline II. The first pressure control device 2 is connected to the computer data acquisition system 8 through a signal line. The pressure supply and pressure relief functions at the upper end of the inner cavity of the cylinder 1 are provided by the intake valve core 110, the upper quick-release interface 21, the upper pressure relief port 22, the upper pressure relief valve 23, the first pressure control device 2, the first pressure valve 24, the pressure pump 4, and the pressure pipeline. The pressure data is fed back to the computer data acquisition system 8 in real time through the data transmission line.

[0106] A quick-release interface 32 is installed on the drain valve core 111. The quick-release interface 32 is connected to the second pressure control device 3 via pipeline III. A pressure relief valve 33 is installed on pipeline III, and the outlet end of the pressure relief valve 33 is a pressure relief port 34. The second pressure control device 3 is connected to the pressure pump 4 via pipeline IV. A second pressure valve 31 is installed on pipeline IV. A pressure gauge 41 is installed on the pressure pump 4. The second pressure control device 3 is connected to the computer data acquisition system 8 via a signal line. The pressure supply and pressure relief functions at the lower end of the inner cavity of the cylinder 1 are provided by the pressure pump 4, the second pressure control device 3, the pressure relief valve 33, the pressure relief port 34, the drain valve core 111, the quick-release interface 32, and the pressure pipelines. The pressure data is fed back to the computer data acquisition system 8 in real time via a data transmission line. The pressure pump can provide a pressure range of 0-15MPa.

[0107] The temperature control system includes a temperature control device 5, a temperature sensor 51, a power interface 53, and a heating sleeve 52, wherein:

[0108] The cylinder 1 is placed inside the heating sleeve 52. A temperature sensor 51 is installed inside the cylinder 1 and is connected to a temperature control device 5 and a computer data acquisition system 8 via a data transmission line. One end of the temperature control device 5 is connected to the heating sleeve 52, and the other end is connected to a power interface 53. The other end of the power interface 53 is also connected to the heating sleeve 52. The temperature control device 5 uses the temperature sensor 51 and the heating sleeve 52 to heat and control the temperature of the simulated formation fracture system and the leakage prevention and plugging slurry 61 to be evaluated within the cylinder 1, and feeds back the temperature data to the computer data acquisition system 8 in real time via the data transmission line. The heating sleeve can provide a temperature range of 0-260℃.

[0109] The leakage monitoring system includes a drain valve core 111, a drain switch 112, a leakage filtrate collector 62, and a leakage monitoring device 6, wherein:

[0110] A drain valve core 111 is equipped with a drain switch 112. The lower end of the drain switch 112 is a leakage filtrate collector 62, which is used to collect leakage filtrate 63. A leakage monitoring device 6 is installed at the bottom of the leakage filtrate collector 62 and is connected to the computer data acquisition system 8 through a data transmission line. During the experiment, the leakage filtrate 63 generated by the anti-leakage and plugging slurry 61 to be evaluated under the action of pressure difference enters the leakage filtrate collector 62 through the drain valve core 111 and the drain switch 112. The leakage monitoring device 6 feeds back the leakage data to the computer data acquisition system 8 in real time through the data transmission line.

[0111] The computer data acquisition system 8 is connected to the first pressure control device 2, the second pressure control device 3, the temperature control device 5, and the leakage monitoring device 6 via data transmission lines, and records in real time the pressure changes at the upper and lower ends of the cylinder 1, the temperature changes of the cylinder 1, and the leakage changes at the lower end of the cylinder 1.

[0112] A plugging evaluation method considering the mechanical properties of formation rocks and fracture characteristics includes the following steps:

[0113] Step 1. Before starting the experiment, check that all valves and switches are in the closed position;

[0114] Step 2. Wellbore simulation system: Place the simulated formation fracture system 71 at the lower end of the inner cavity of the wellbore 1, and then put in the lower sealing gasket 14, the lower metal filter screen 19 in sequence, install the base 12 and the drain valve core 111, and then put in the upper sealing gasket 13 and the lower metal gasket 16 in sequence from the upper end of the inner cavity of the wellbore 1, inject the plugging slurry 61 to be evaluated, and then put in the metal spring 17, the upper metal gasket 15, the upper metal filter screen 18 in sequence, and install the top cover 11 and the air inlet valve core 110.

[0115] Step 3. Install the pressure control system. Attach the upper quick-release interface 21 to the intake valve core 110 and the lower quick-release interface 32 to the drain valve core 111. Connect the first pressure control device 2 and the second pressure control device 3 to the pressure pump 4 via pressure lines. Connect the first pressure control device 2 and the second pressure control device 3 to the computer data acquisition system 8 via data transmission lines.

[0116] Step 4. Install the temperature control system and connect the temperature control device 5 to the heating sleeve 52, the temperature sensor 51, and the computer data acquisition system 8 respectively.

[0117] Step 5. Install the leakage monitoring system. Connect the leakage filtrate collector 62 to the drain valve core 111 and place it on the leakage monitoring device 6. The leakage monitoring device 6 is connected to the computer data acquisition system 8 through the data transmission line.

[0118] Step 6. Conduct a leak-sealing test, including:

[0119] 1) Positive pressure differential leak sealing evaluation test:

[0120] Start the temperature control device 5, set the heating time, and use the annular heating sleeve 52 to heat the simulated formation fracture system 71 and the anti-leakage and plugging slurry 61 in the cylinder 1. After the heating is completed, control the temperature at the target temperature, open the drain switch 112, and monitor the leakage through the leakage monitoring device 6.

[0121] Start the first pressure control device 2, set the target pressure, and use the pressure pump 4 to pressurize the cylinder evenly and continuously until the target pressure is reached; set the pressurization rate and stabilization time; if no leakage or a small amount of leakage is detected when the drain switch 112 is open, continue the pressurization process until the predetermined target pressure value is reached, and record the leakage amount, leakage rate and positive pressure differential sealing pressure bearing capacity (pressure value) through the computer data acquisition system 8, and monitor the changes in the sealing performance of the plugging slurry 61 to be evaluated in real time.

[0122] 2) Negative pressure differential leak sealing evaluation experiment:

[0123] After completing the positive pressure differential leak-sealing evaluation experiment, close the first pressure control device 2, the first pressure valve 24, and the drain switch 112. Then open the upper pressure relief valve 23 and keep it open after the pressure relief is completed. Start the second pressure control device 3, set the pressure increase rate to 0.5 MPa / cycle, and the pressure stabilization time to 5 mins. Monitor the pressure value fed back by the second pressure control device 3 through the computer data acquisition system 8. If the pressure value is stable, continue to increase the pressure. If the pressure value drops significantly or is about to become 0, record the pressure value before the pressure drop through the computer data acquisition system 8. The pressure value at this moment is the pressure resistance of the leak-proof and leak-sealing slurry 61 to be evaluated against negative pressure differential sealing pressure.

[0124] Step 7: Disassemble the leak sealing device. After the experiment, save the experimental data from the computer data acquisition system 8, turn off the pressure pump 4, the first pressure valve 24, the second pressure valve 31, and the temperature control device 5. After the device cools down, open the upper pressure relief valve 23 and the lower pressure relief valve 33 to release the pressure in the inner cavity of the cylinder 1 and the pressure pipeline. Turn off the first pressure control device 2, the second pressure control device 3, and the leakage monitoring device 6. Remove all pipelines of each control device, remove the top cover 11 and the base 12, and remove the simulated formation fracture system 71.

[0125] Step 8: Evaluate the effectiveness of the leak sealing.

[0126] The simulated formation fracture system 71 was removed from the cylinder, and the sample of the simulated formation fracture system 71 was cut open. The distribution state, location, proportion, and accumulation of the plugging material in the sealing layer 72 of the simulated formation fracture system 71 sample were observed and photographed. Combined with the leakage of filtrate, leakage rate, positive pressure differential sealing pressure bearing capacity, and negative pressure differential sealing pressure bearing capacity, the plugging effect of the plugging slurry 61 under test was evaluated. At the same time, further microscopic detection experiments can be conducted on the structure of the plugging layer 72 in the simulated formation fracture system 71 to analyze the microscopic failure mechanism of the plugging material in the plugging slurry 61.

[0127] Example 1

[0128] This embodiment uses a carbonate rock fractured leakage formation in the Shunbei area of ​​Xinjiang as an example for experimentation. The experimental process is described in detail below.

[0129] 1) Preparation of simulated rock samples

[0130] Step R1: Obtain stratigraphic rock samples from the lost area and test the mechanical characteristic parameters of the rock samples.

[0131] Collect stratigraphic rock samples from the lost area and test mechanical characteristic parameters including Young's modulus E and Poisson's ratio. coefficient of friction Key parameter data, among which Young's modulus and Poisson's ratio of rock are key parameters sensitive to crack deformation stress, and rock friction coefficient is a key parameter for the retention capacity of sealing materials in cracks.

[0132] Specifically, first, core samples of the leaking rock layer drilled downhole in the leaking area were obtained, and the Young's modulus of the core samples was measured using an RTR-1000 triaxial rock mechanics testing system. Poisson's ratio The parameters were measured using a COF-1 friction coefficient measuring instrument to determine the friction coefficient of the core sample from the leaking layer. parameter.

[0133] Experiments showed that the Young's modulus of carbonate rock samples from the fractured, leaky strata in the Shunbei area of ​​Xinjiang was 36.17 GPa, the Poisson's ratio was 0.31, and the coefficient of friction was 0.64.

[0134] Step R2: Prepare simulated stratigraphic rock samples

[0135] Specifically, firstly, according to experimental requirements and API standards, simulated formation rock samples were mixed in a certain proportion to prepare a special simulated formation slurry. The simulated formation slurry formula consisted of G-grade oil wells, aggregates, slurry preparation water, fluid loss control agent, and fibers. Then, the prepared slurry was injected into a curing mold and placed in a high-temperature, high-pressure curing autoclave for curing. The experimental conditions were set at a temperature of 150℃, a curing pressure of 20.7 MPa, and a curing time of 7 days. After reaching the required curing age, the simulated rock samples were removed for later use.

[0136] The Young's modulus of simulated strata rock samples was measured experimentally. 36.5 GPa, Poisson's ratio The coefficient of friction is 0.30. It is 0.61.

[0137] Step R3: Determine the equivalent of the simulated formation fracture coefficient and the actual leakage region's formation mechanical characteristic parameters.

[0138] Young's modulus in the mechanical characteristic parameters of the stratigraphic rock samples in the actual leakage area Poisson's ratio coefficient of friction Key parameters affect formation fracture aperture, fracture propagation, leakage process, and leakage assessment, significantly impacting the results of leakage plugging evaluation experiments. Therefore, it is necessary to test the aforementioned physical properties of simulated formation rock samples prepared with different formulations to ensure that the mechanical characteristics of the simulated formation rock samples are equivalent to those of the actual formation rock samples.

[0139] Specifically, determining the equivalent mechanical characteristic parameters includes steps R31-R33, where:

[0140] Step R31: Determine whether the elastic modulus of the simulated strata rock sample and the strata rock sample are equivalent. Specifically, the relative error of the elastic modulus between the simulated strata rock sample and the strata rock sample should not exceed 5%.

[0141] Step R32: Determine the Poisson's ratio equivalence between the simulated strata sample and the actual strata sample.

[0142] Specifically, the relative error of the Poisson's ratio between the simulated strata rock sample and the actual strata rock sample is required to be no more than 5%.

[0143] Step R33: Determine whether the friction coefficients of the simulated strata rock sample and the strata rock sample are equivalent. Specifically, the relative error of the friction coefficients of the simulated strata rock sample and the strata rock sample should not exceed 5%.

[0144] In step R3, multiple relevant parameters from steps R31-R33 are evaluated one by one. Only when all of the above mechanical parameters are physically equivalent to the lithological characteristics of the leakage area can the prepared simulated formation rock sample be determined to meet the design requirements, truly restore the formation mechanical parameter characteristics, and make the leakage evaluation results more reasonable and effective. The selected leakage plugging material and system can then achieve better leakage plugging effects in practical applications. If any of the above parameters does not meet the design requirements, the prepared simulated formation rock sample is determined to be unqualified. The slurry formula needs to be adjusted, and steps R2-R3 need to be repeated until the mechanical parameters of the simulated formation rock sample meet the requirements, thus obtaining a qualified simulated formation rock sample.

[0145] Specifically, this embodiment takes the carbonate-type fractured and leaky strata in the Shunbei area of ​​Xinjiang as an example to prepare simulated strata rock samples. The experimental results of the prepared simulated strata rock samples are shown in Table 1.

[0146] Table 1 Mechanical characteristic parameters of simulated and actual stratigraphic rock samples

[0147]

[0148] Note: The mechanical characteristic parameters of both the simulated and actual strata rock samples were tested three times, and the average value was taken.

[0149] The prepared simulated strata rock samples have similar mechanical characteristic parameters to the strata rock samples, satisfying the principle of equivalence of strata mechanical characteristics.

[0150] 2) Preparation of a simulated formation fracture system

[0151] The specific process for preparing the simulated formation fracture system is as follows:

[0152] Step L1: Obtain three-dimensional fracture parameter data of the formation in the lost area.

[0153] Obtaining three-dimensional fracture parameter data of the formation in the lost zone includes steps L11-L16, wherein:

[0154] Step L11. Perform CT scan of stratigraphic rock samples.

[0155] First, the strata samples from the missed area were scanned using a core CT 3D imaging system with X-rays under non-destructive conditions to obtain high-precision 3D strata fracture data.

[0156] Step L12: Preprocessing of stratigraphic rock sample data

[0157] After obtaining the three-dimensional core fracture parameter data of the lost area, the data was imported into AVIZO data processing software for data processing. The Crop editor and Volume edit commands were used to obtain a standard cylindrical core, irregular parts were removed, and a Create Mask was created for fracture volume fraction calculation.

[0158] Step L13: Extraction of fractures and pores from stratigraphic rock samples

[0159] Interactive thresholding, Interactive Top-hat, and Or Image commands are used to accurately extract core fracture and pore data parameters within the grayscale range of 0-65535. Interactive thresholding is a grayscale thresholding method, Interactive Top-hat is a brightness difference thresholding method, and Or Image is a logical algorithm.

[0160] Step L14: Remove the porous portion of the formation rock sample

[0161] The Label analysis and Analysis filter commands were used to remove the pore portion of the formation rock samples. Shape_VA3D≥5 was defined as fractures and Shape_VA3D<5 as pores, thus obtaining the fracture data of the formation rock samples.

[0162] Step L15: Calculate the fracture connectivity of the formation rock samples

[0163] The Axis connectivity command was used to remove isolated fractures in the formation samples. The Neighborhood value was set to 6 (interface-to-face connectivity between adjacent voxels), and the Orientation was set to the z-axis direction. The connectivity direction was set to the axial direction of the formation sample (z-axis), preserving all fracture leakage channels with connectivity along the axial direction of the formation sample.

[0164] Step L16: Calculate fracture parameters of formation rock samples

[0165] The volume fraction, label analysis, and centroid path tortuosity commands were used to obtain the key characteristic parameter of the crack, which is the crack volume fraction. K、 Crack width D and crack tortuosity T The fracture volume fraction K, fracture width D, and fracture tortuosity of a three-dimensional fracture in a formation rock sample can be calculated using the following formulas. T parameter.

[0166]

[0167]

[0168]

[0169] in, Crack volume fraction, in % Total volume of the rock sample, in mm. 3 ; This represents the number of cracks. The volume of the i-th crack is in mm. 3 D represents the crack width, in mm. The area of ​​the i-th crack is in mm. 2 ; The degree of tortuosity of the crack; The length of the i-th crack along the rock sample axis, in mm. The vertical height of the rock sample along its axis is expressed in mm.

[0170] Through the above data processing and calculations, the fracture volume fraction of carbonate-type fractured and lost-flow strata in the Shunbei area of ​​Xinjiang was obtained. The crack width was 5.78%. The crack tortuosity is 2.51 mm. It is 1.29.

[0171] Step L2: Constructing a simulated formation fracture system

[0172] After completing step L1, the fracture volume fraction of the three-dimensional fractures in the formation is obtained. Based on the principle that the simulated formation fracture system is equivalent to the three-dimensional fracture characteristic parameters of the actual leakage area, the parameters of fracture width D and fracture tortuosity T are used to construct a simulated formation fracture system.

[0173] Specifically, constructing a simulated formation fracture system includes steps L21-L25, wherein:

[0174] Step L21: Determine the equivalence of the simulated formation fracture system with the actual three-dimensional fracture characteristic parameters of the lost-flow region.

[0175] Key parameters such as the volume, width, and morphology of three-dimensional fractures in the rock samples of the leakage area are related to the sensitivity of fracture leakage, affecting the degree of fracture leakage, leakage evaluation and judgment, and the selection of leakage prevention and plugging materials. They have a significant impact on the evaluation results of leakage and plugging. Therefore, based on the principle of equivalence of three-dimensional fracture characteristic parameters, the simulated formation fracture system is made equivalent to the three-dimensional fracture characteristic parameters of the actual leakage area.

[0176] Specifically, determining the equivalence of the simulated formation fracture system with the actual leakage region's three-dimensional fracture characteristic parameters includes steps L211-L213, where:

[0177] Step L211: Determine whether the fracture volume ratio of the simulated formation fracture system is equivalent to that of the actual lost area formation rock sample. Specifically, the relative error between the fracture volume ratio of the simulated formation fracture system and the actual lost area formation rock sample should not exceed 2%.

[0178] Step L212: Determine whether the fracture width of the simulated formation fracture system is equivalent to that of the actual lost area formation rock sample. Specifically, the relative error between the fracture width of the simulated formation fracture system and the actual lost area formation rock sample should not exceed 2%.

[0179] Step L213: Determine whether the fracture tortuosity of the simulated formation fracture system is equivalent to that of the actual lost area formation rock sample. Specifically, the relative error of the fracture tortuosity between the simulated formation fracture system and the actual lost area formation rock sample should not exceed 2%.

[0180] A simulated formation fracture device was fabricated based on the aforementioned principle of equivalent three-dimensional fracture characteristic parameters, and its fracture volume fraction was... The crack width was 5.8%. The crack tortuosity is 2.5mm. It is 1.3.

[0181] Step L22: Prepare a simulated formation fracture system

[0182] The process of preparing a simulated formation fracture system is as follows: Figure 2 As shown, first install a simulated formation fracture device (such as...) Figure 3As shown), the molding agent is injected into the device. After the molding agent cools and solidifies, the simulated formation fracture mold is disassembled and removed, and then fixed to the curing device (such as...). Figure 4 At a suitable location (as shown), the simulated formation rock sample slurry is poured into a curing mold. It is first pre-cured in a constant temperature curing chamber for a period of time, and then cured in a high-temperature, high-pressure curing autoclave for a certain age, resulting in a simulated formation fracture system equivalent to the mechanical and three-dimensional fracture characteristic parameters of the formation rock sample. The plasticizer is a solid plasticizer that melts into a liquid state under high temperature conditions.

[0183] The simulated formation fracture system was cured under low-temperature, normal-pressure conditions at 60℃ for 1 day, and under high-temperature, high-pressure conditions at 150℃, 20.7 MPa, and 7 days. After reaching the required curing age, the simulated formation fracture system was removed to observe the integrity of the fractures. Only complete fracture samples can accurately represent the formation's mechanical and fracture characteristics, leading to more reasonable and effective plugging evaluation results.

[0184] Specifically, this embodiment takes the carbonate rock-type fractured leakage strata in the Shunbei area of ​​Xinjiang as an example to prepare a simulated strata fracture system. The experimental results of the prepared simulated strata fracture system are shown in Table 2.

[0185] Table 2. Three-dimensional fracture characteristic parameters of the simulated formation fracture system and formation rock samples.

[0186]

[0187] The simulated formation fracture system prepared has similar three-dimensional fracture characteristic parameters to the formation rock sample, satisfying the principle of equivalence of three-dimensional formation fracture characteristic parameters.

[0188] 3) Conduct positive pressure differential leak sealing evaluation experiments.

[0189] The positive pressure differential leakage plugging evaluation experiment method described in this embodiment uses a simulated formation fracture system leakage prevention and plugging experimental device. It mainly evaluates the leakage prevention and plugging capabilities of plugging materials and systems under formation temperature and positive pressure differential conditions.

[0190] Before starting the experiment, check that all valves and switches are in the closed position.

[0191] Step D1: Install the wellbore simulation system. First, place the simulated formation fracture system 71 at the lower end of the inner cavity of the cylinder 1, then place the lower sealing gasket 14 and the lower metal filter 19 in sequence, install the base 12 and the drain valve core 111, and place the upper sealing gasket 13 and the upper metal gasket 15 in sequence from the upper end of the inner cavity of the cylinder 1. Inject the anti-leakage and plugging slurry 61 to be evaluated, then place the metal spring 17, the upper metal gasket 15, and the upper metal filter 18 in sequence, and install the top cover 11 and the air inlet valve core 110.

[0192] Step D2: Install the pressure control system. Attach the upper quick-release interface 21 to the intake valve core 110 and the lower quick-release interface 32 to the drain valve core 111. Connect the first pressure control device 2 and the second pressure control device 3 to the pressure pump 4 via pressure lines. Connect the first pressure control device 2 and the second pressure control device 3 to the computer data acquisition system 8 via data transmission lines.

[0193] Step D3: Install the temperature control system and connect the temperature control device 5 to the heating sleeve 52, the temperature sensor 51, and the computer data acquisition system 8 respectively.

[0194] Step D4: Install the leakage monitoring system, connect the leakage filtrate collector 62 to the drain valve core 111, place it on the leakage monitoring device 6, and connect the leakage monitoring device 6 to the computer data acquisition system 8 through the data transmission line;

[0195] Step D5: Conduct a leak-sealing test, which includes the following steps D51-D52, wherein...

[0196] Step D51: Heating experiment. Start the temperature control device 5, set the heating time, and use the annular heating sleeve 52 to heat the simulated formation fracture system 71 and the anti-leakage and plugging slurry 61 in the cylinder 1. After the heating is completed, control the temperature at the target temperature, open the drain switch 112, and monitor the leakage through the leakage monitoring device 6.

[0197] Specifically, this embodiment takes the carbonate rock-type lost formation in the Shunbei area as an example, and sets the experimental temperature at 150℃ and the heating time at 20mins.

[0198] Step D52: Pressure Increase Experiment. Start the first pressure control device 2, set the target pressure, and use the pressure pump 4 to continuously and uniformly pressurize the cylinder 1 until the target pressure is reached. Set the pressurization rate to 0.5 MPa / cycle and the pressure stabilization time to 5 mins. If no leakage or a small amount of leakage is detected with the drain switch 112 open, continue the pressurization process until the predetermined pressure value (≤7 MPa) is reached. Record the leakage amount M, leakage rate V, and positive pressure differential sealing pressure bearing capacity through the computer data acquisition system 8. (Pressure value) Real-time monitoring of the sealing performance changes of the anti-leakage and plugging slurry 61 to be evaluated. Experimental results are shown in […]. Figure 5 .

[0199] 4) Conduct a negative pressure differential leak sealing evaluation experiment.

[0200] The negative pressure differential plugging evaluation experiment method described in this embodiment uses a simulated formation fracture system leak prevention and plugging experimental device. It mainly simulates the situation where, after the plugging operation is completed, the pumping pressure generated during drilling or other construction processes causes a drop in the hydrostatic column pressure in the well, resulting in a negative pressure differential downhole. The experiment evaluates the ability of the plugging layer 72 in the simulated formation fracture system 71 to resist negative pressure differential plugging.

[0201] Specifically, after completing steps D1-D5, close the first pressure control device 2, the first pressure valve 24, and the drain switch 112. Then open the upper pressure relief valve 23 and keep it open after the pressure relief is completed. Start the second pressure control device 3, set the pressure increase rate to 0.5 MPa / cycle, and the pressure stabilization time to 5 minutes. Monitor the pressure value fed back by the second pressure control device 3 through the computer data acquisition system 8. If the pressure value is stable, continue to increase the pressure. If the pressure value drops significantly or drops to 0, record the pressure value before the pressure drop through the computer data acquisition system 8. The pressure value at this time is the pressure bearing capacity of the leak-proof and plugging slurry 61 to be evaluated against negative pressure differential sealing. The experimental results are shown in Figure 6 .

[0202] 5) Disassemble the leak sealing device

[0203] After the experiment, save the experimental data from the computer data acquisition system 8, close the second pressure control device 3 and the second pressure valve 31, close the temperature control device 5, and after the device temperature drops to room temperature, open the upper pressure relief valve 23 and the lower pressure relief valve 33 to release the pressure in the inner cavity of the cylinder 1 and the pressure pipeline, close the first pressure control device 2 and the leakage monitoring device 6, remove all pipelines of each control device, remove the top cover 11 and the base 12, and take out the simulated formation fracture system 71.

[0204] 6) Evaluate the effectiveness of the leak sealing

[0205] After removing the simulated formation fracture system 71 from the cylinder, the sample of the simulated formation fracture system 71 was cut open. The distribution state, distribution location, distribution ratio, and aggregation of the plugging material of the sealing layer 72 in the sample were observed, and photographs were taken. Combined with the leakage of filtrate M, leakage rate V, and positive pressure differential sealing pressure bearing capacity, the results were analyzed. Negative pressure differential sealing pressure bearing capacity The leakage-stopping effect of the tested leakage-stopping slurry 61 is comprehensively evaluated. At the same time, further microscopic detection experiments can be conducted on the simulated formation fracture system 71 structure to analyze the microscopic failure mechanism of the leakage-stopping slurry 61.

[0206] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A plugging evaluation device considering the mechanical properties of formation rocks and fracture characteristics, characterized in that... It includes a wellbore simulation system, a pressure control system, a temperature control system, a leakage monitoring system, and a computer data acquisition system; The wellbore simulation system includes a simulated formation fracture system, plugging slurry, wellbore, top cover, base, upper metal filter, lower metal filter, upper sealing gasket, lower sealing gasket, upper metal shim, lower metal shim, and metal spring, wherein: The cylinder is a metal cylindrical structure. The top cover is installed on the top of the cylinder and the base is installed on the bottom of the cylinder. The top cover and the base are provided with threaded holes and sealing rings. The top cover is sealed to the air inlet valve core and the base is sealed to the drain valve core. The upper metal filter screen and the lower metal filter screen are installed in the cylinder. The upper metal filter screen is located on the lower side of the top cover and the lower metal filter screen is installed on the upper side of the base. Inside the cylinder, the upper metal filter screen is located below an upper metal gasket, the upper metal gasket is located below a metal spring and a sealing slurry, and the metal spring is located below a lower metal gasket. The lower metal gasket inside the cylinder has an upper sealing gasket on the lower side, and the upper metal filter screen has a lower sealing gasket on the upper side. Between the upper and lower sealing gaskets is a simulated formation fracture system. The center of the simulated formation fracture system is a simulated fracture. Under experimental conditions, the slurry to be evaluated forms a sealing layer inside it. The pressure control system, which controls pressure changes, is connected to the wellbore simulation system via a pressure pipeline. The temperature control system heats the wellbore simulation system while monitoring the corresponding temperature. The leakage monitoring system, which measures the leakage of filtrate, is located at the bottom of the wellbore simulation system. The computer data acquisition system, which collects data, is connected to the pressure control system, the temperature control system, and the leakage monitoring system. The pressure control system includes an upper quick-release interface, an upper pressure relief port, an upper pressure relief valve, a first pressure control device, a first pressure valve, a second pressure valve, a pressure gauge, a pressure pump, a second pressure control device, a lower pressure relief valve, a lower pressure relief port, and a lower quick-release interface, wherein: The upper quick-release interface is installed on the intake valve core via a sliding buckle. The intake valve core is connected to the first pressure control via pipeline I. An upper pressure relief valve is installed on pipeline I, and the outlet end of the upper pressure relief valve is the upper pressure relief port. The first pressure control device is connected to the pressure pump via pipeline II. A first pressure valve is installed on pipeline II. The first pressure control device is connected to the computer data acquisition system via a signal line. The lower quick-release interface is installed on the drain valve core via a sliding snap. The lower quick-release interface is connected to the second pressure control device via pipeline III. A pressure relief valve is installed on pipeline III, and the outlet end of the pressure relief valve is the pressure relief port. The second pressure control device is connected to the pressure pump via pipeline IV. A second pressure valve is installed on pipeline IV. A pressure gauge is installed on the pressure pump. The second pressure control device is connected to the computer data acquisition system via a signal line.

2. The plugging evaluation device considering the mechanical properties of formation rocks and fracture characteristics according to claim 1, characterized in that, The upper and lower ends of the cylinder are threaded, the upper and lower sealing gaskets are high-temperature resistant rubber rings, and the upper and lower metal gaskets are annular gaskets.

3. The plugging evaluation device considering the mechanical properties of formation rocks and fracture characteristics according to claim 1, characterized in that, The temperature control system includes a temperature control device, a temperature sensor, a power interface, and a heating sleeve, wherein: The cylinder is placed inside the heating sleeve, and the temperature sensor is installed inside the cylinder. The temperature sensor is connected to the temperature control device and the computer data acquisition system through a data transmission line. One end of the temperature control device is connected to the heating sleeve, and the other end is connected to the power interface. The other end of the power interface is connected to the heating sleeve.

4. The plugging evaluation device considering the mechanical properties of formation rocks and fracture characteristics according to claim 1, characterized in that, The leakage monitoring system includes a drain valve core, a drain switch, a leakage filtrate collector, and a leakage monitoring device, wherein: A drain valve core is equipped with a drain switch, and the lower end of the drain switch is a leak filtrate collector. The leak filtrate collector is used to collect leaked filtrate. A leak monitoring device is installed at the bottom of the leak filtrate collector and is connected to a computer data acquisition system via a data transmission line.

5. The plugging evaluation device considering the mechanical properties of formation rocks and fracture characteristics according to claim 1, characterized in that, in, The simulated formation fracture system is prepared by the following methods: 1) Obtain stratigraphic rock samples from the lost area and test the mechanical characteristic parameters of the rock samples. The geological rock samples mentioned are core samples taken from wells, and the mechanical characteristic parameters include Young's modulus. Poisson's ratio coefficient of friction Key parameter data; 2) Preparation of simulated stratigraphic rock samples Special simulated formation slurry was prepared according to experimental requirements and API standards. The simulated formation slurry formula included G-grade oil wells, aggregates, slurry preparation water, fluid loss control agent, and fiber. These were mixed in a certain proportion, poured into a curing mold, and the mold was placed in a high-temperature and high-pressure curing autoclave for curing for a certain period of time. The simulated formation rock sample was then taken out for later use. 3) Determine the equivalent mechanical characteristic parameters of simulated stratigraphic rock samples and actual stratigraphic rock samples. The principle of equivalent mechanical characteristic parameters includes the elastic modulus of simulated and actual strata rock samples. Equivalent, Poisson's ratio Equivalent, coefficient of friction Equivalently, suitable simulated stratigraphic rock samples are obtained; The equivalence principle between the simulated formation fracture system and the actual leakage region's formation mechanical characteristic parameters is as follows: 4) Obtain three-dimensional fracture parameter data of the formation in the lost area. Perform CT scans on stratigraphic rock samples to obtain high-precision three-dimensional stratigraphic fracture data; The CT scan mentioned is a non-destructive testing scanning technique; Stratigraphic rock sample data were imported into data processing software for preprocessing to remove annular artifacts and irregular parts, and a Create Mask was created for fracture volume fraction. calculate; Rock sample cracks and pores were extracted, and grayscale threshold segmentation and brightness difference segmentation methods were used to extract rock sample cracks and pores from the entire three-dimensional rock sample; The pore portion of the rock sample is removed, and the pores in the three-dimensional rock sample are removed by a binarization data filtering method to obtain the rock sample cracks; Calculate the fracture connectivity of the rock sample, with the fracture connectivity direction set as the rock sample axial direction, to obtain all fracture leakage channels that are connected along the rock sample axial direction; Calculate the fracture parameters of the rock sample and obtain the fracture volume fraction of the three-dimensional fracture using a formula. Crack width and crack tortuosity parameter: in, K Crack volume fraction, in % V Total volume of the rock sample, in mm. 3 n is the number of cracks; v i The volume of the i-th crack is in mm. 3 D represents the crack width, in mm. S i The area of ​​the i-th crack is in mm. 2 T represents the crack tortuosity; h i H represents the length of the i-th crack along the core axis, in mm; H represents the vertical height of the core axis, in mm. 5) Construct a simulated formation fracture system Determine the equivalence of simulated formation fracture systems and formation rock sample fracture characteristic parameters, including fracture volume fraction. Equivalent, crack width Equivalent, crack tortuosity Equivalent; The equivalence principle between the simulated formation fracture system and the actual leakage region's three-dimensional fracture characteristic parameters is as follows: A simulated formation fracture device with equivalent three-dimensional fracture characteristic parameters is fabricated; the simulated formation fracture device is used to prepare a simulated formation fracture system with equivalent three-dimensional fracture characteristic parameters to the actual leakage area. To prepare a simulated formation fracture system, firstly, a simulated formation fracture device is installed, and a plasticizer is injected into the device. After the plasticizer cools and solidifies, the simulated formation fracture mold is disassembled and removed, and then fixed in a suitable position in the curing device. The simulated formation rock sample slurry is poured into the curing mold, and it is first placed in a constant temperature curing chamber for pre-curing for a period of time. Then, it is placed in a high temperature and high pressure curing autoclave for curing for a certain period of time, thus obtaining a simulated formation fracture system that is equivalent to the mechanical characteristic parameters and three-dimensional fracture characteristic parameters of the formation rock sample.

6. A leakage evaluation method using a leakage evaluation device considering the mechanical properties of formation rocks and fracture characteristics as described in any one of claims 1-5, characterized in that, Includes the following steps: 1) Before starting the experiment, check that all valves and switches are in the closed position; 2) Install the cylinder, place the simulated formation fracture system at the lower end of the cylinder's inner cavity, and then put in the lower sealing gasket, lower metal filter screen, base and drain valve core in sequence. From the upper end of the cylinder's inner cavity, put in the upper sealing gasket, lower metal gasket in sequence, inject the leak-proof and plugging slurry to be evaluated, and then put in the metal spring, upper metal gasket, upper metal filter screen in sequence. Install the top cover and air inlet valve core. 3) Install the pressure control system. Attach the upper quick-release interface to the air intake valve core and the lower quick-release interface to the drain valve core. Connect the first pressure control device and the second pressure control device to the pressure pump via pressure lines. Connect the first pressure control device and the second pressure control device to the computer data acquisition system via data transmission lines. 4) Install the temperature control system, connect the temperature control device to the heating sleeve, temperature sensor, and computer data acquisition system respectively, and connect the power interface; 5) Install the leakage monitoring system, connect the leakage filtrate collector to the drain valve core, place it on the leakage monitoring device, and connect the leakage monitoring device to the computer data acquisition system through the data transmission line; 6) Conduct a leak-stopping test, including: Positive pressure differential leak sealing evaluation experiment; Start the temperature control device, set the heating time, and use the annular heating sleeve to heat the simulated formation fracture system and the leakage prevention and plugging slurry to be evaluated in the cylinder. After the heating is completed, control the temperature at the target temperature, open the drain switch, and monitor the leakage through the leakage monitoring device. Start the first pressure control device, set the target pressure, and use the pressure pump to pressurize the cylinder evenly and continuously until the target pressure is reached; set the pressurization rate and pressure stabilization time; if no leakage or a small amount of leakage is detected when the drain switch is open, continue the pressurization process until the target pressure value is reached, and record the leakage amount, leakage rate and positive pressure differential sealing pressure bearing capacity through the computer data acquisition system, and monitor the changes in the sealing performance of the anti-leakage slurry to be evaluated in real time; Negative pressure differential leak sealing evaluation experiment; After completing the positive pressure differential leak-stopping evaluation experiment, the first pressure control device, the first pressure valve, and the drain switch are closed. Then, the upper pressure relief valve is opened and closed after pressure relief is completed. The second pressure control device is started, and the pressure increase rate and pressure stabilization time are set. The pressure value fed back by the second pressure control device is monitored through the computer data acquisition system. If the pressure value is stable, the pressure continues to increase. If the pressure value drops significantly or drops to 0, the pressure value before the pressure drop is recorded through the computer data acquisition system. The pressure value at this moment is the leak-stopping slurry's ability to resist negative pressure differential sealing pressure. 7) Disassemble the leak-sealing device. After the experiment, save the experimental data from the computer data acquisition system, turn off the pressure pump, the first pressure valve, the second pressure valve, and the temperature control device. After the leak-sealing device temperature drops to room temperature, open the upper and lower pressure relief valves to release the pressure in the inner cavity of the cylinder and the pressure pipeline. Turn off the first pressure control device, the second pressure control device, and the leakage monitoring device. Disconnect all pipelines of each control device, remove the top cover and the base, and take out the simulated formation fracture system. 8) Evaluate the effectiveness of the leak sealing The simulated formation fracture system was removed from the cylinder, and the sample was cut open. The distribution, location, proportion, and accumulation of the plugging material in the sealing layer were observed and photographed. The plugging effect of the slurry was evaluated by combining the leakage of filtrate, leakage rate, positive pressure differential sealing pressure bearing capacity, and negative pressure differential sealing pressure bearing capacity. At the same time, further microscopic detection experiments could be conducted on the structure of the plugging layer in the simulated formation fracture system to analyze the microscopic failure mechanism of the plugging material.

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