A device and method for evaluating performance of drilling fluid for plugging leaks in marine hydrate reservoirs

Abstract

The present invention discloses a device and method for evaluating the performance of drilling fluid for plugging leaks in marine hydrate reservoirs. The device includes a hydrate reservoir simulation unit, a drilling fluid injection unit, and a leakage metering unit. The drilling fluid injection unit and the leakage metering unit are respectively connected to the hydrate reservoir simulation unit. The drilling fluid injection unit injects plugging drilling fluid into the hydrate reservoir simulation unit, and the leakage metering unit provides drilling fluid leakage measurement for the hydrate reservoir simulation unit. The device also includes a temperature control unit for providing temperature control for the entire device and a control system for data acquisition and control of the entire device. The hydrate reservoir simulation unit, drilling fluid injection unit, leakage metering unit, and temperature control unit are all electrically connected to the control system. The present invention can realize experimental simulation of the performance evaluation of drilling fluid for plugging leaks in marine hydrate reservoirs.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas exploration and development, and in particular to a device and method for evaluating the performance of marine hydrate reservoir plugging drilling fluid. Background Art

[0002] Natural gas hydrates are non-stoichiometric cage-like crystals formed by water and natural gas under high pressure and low temperature. They are an unconventional energy source with high density and high calorific value. Natural gas hydrates (hereinafter referred to as hydrates) have always attracted much attention as a new type of clean energy. The ocean hydrate reserves are huge, and hydrates are considered to be the most promising alternative energy source in the 21st century.

[0003] Although marine natural gas hydrates have enormous reserves and broad development prospects, the weak cementation strength of marine natural gas hydrates means that the bottomhole safety pressure window during drilling is very narrow. If the bottomhole pressure exceeds the fracture pressure of the marine natural gas hydrate reservoir, the marine natural gas hydrate reservoir will be fractured, forming cracks within the marine natural gas hydrate reservoir. As a result, well leakage is very likely to occur during the drilling of hydrate reservoirs, which seriously restricts the development of marine natural gas hydrates. Therefore, in order to solve the leakage problem during the drilling of marine natural gas hydrate reservoirs, it is urgent to carry out scientific and technological research in the optimization of marine natural gas hydrate reservoir plugging drilling fluid formula, plugging process optimization, and plugging drilling fluid performance evaluation. Therefore, the necessary laboratory simulation experimental equipment and methods are indispensable. At present, existing experimental equipment is unable to realize the study of the migration, bridging and distribution of plugging agent particles in the plugging drilling fluid in the cracks of marine hydrate reservoirs under different crack widths, plugging pressure differences and crack inclination conditions. It is also unable to realize the study of the invasion depth of plugging agent particles into the simulated cracks of the hydrate reservoir and the change law of the leakage volume of the plugging drilling fluid at different times. It is also unable to realize the optimization of the plugging drilling fluid formula and the plugging construction plan for different crack widths and crack inclination conditions. In turn, it seriously affects the research on plugging technology of marine natural gas hydrate reservoirs. Therefore, there is an urgent need to develop a performance evaluation device and method for plugging drilling fluid in marine hydrate reservoirs. Summary of the Invention

[0004] The purpose of the present invention is to provide a device and method for evaluating the performance of marine hydrate reservoir plugging drilling fluid, so as to solve the technical problem that the prior art cannot simulate the performance evaluation experimental device of marine hydrate reservoir plugging drilling fluid.

[0005] The objective of the present invention is achieved by adopting the following technical scheme: a marine hydrate reservoir plugging drilling fluid performance evaluation device, comprising a hydrate reservoir simulation unit, a drilling fluid injection unit and a leakage metering unit, wherein the drilling fluid injection unit and the leakage metering unit are respectively connected to the hydrate reservoir simulation unit, wherein the drilling fluid injection unit injects plugging drilling fluid into the hydrate reservoir simulation unit, and the leakage metering unit provides drilling fluid leakage measurement for the hydrate reservoir simulation unit; it also includes a temperature control unit for providing temperature control to the entire device and a control system for data acquisition and control of the entire device, wherein the hydrate reservoir simulation unit, the drilling fluid injection unit, the leakage metering unit and the temperature control unit are respectively electrically connected to the control system.

[0006] Furthermore, the hydrate reservoir simulation unit includes a plugging drilling fluid storage chamber and a protective cylinder, the plugging drilling fluid storage chamber is connected to the protective cylinder, a core clamp is provided in the protective cylinder, the core clamp is connected to the plugging drilling fluid storage chamber, and a stirring motor is also provided on the plugging drilling fluid storage chamber, and the stirring motor is electrically connected to the control system.

[0007] Furthermore, the outer layer of the plugging drilling fluid storage chamber is wrapped with a No. 1 flexible heating jacket, and the No. 1 flexible heating jacket and the plugging drilling fluid storage chamber are both provided with a plurality of sensors, and the sensors are respectively electrically connected to the control system.

[0008] Furthermore, the plugging drilling fluid storage chamber is connected to the rotating support shaft, and the rotating support shaft is connected to the movable bracket. The hydrate reservoir simulation unit is installed on the movable bracket through the rotating support shaft. The rotating support shaft is connected to the servo motor through a reduction gearbox, and the reduction gearbox and servo motor are both arranged on it, and the servo motor is electrically connected to the control system.

[0009] Furthermore, the core holder includes a core holder cylinder, a hydrate reservoir simulation core is arranged in the core holder cylinder, a core holder visual window and hydrate reservoir simulation cracks of different widths are arranged on the hydrate reservoir simulation core, and a drilling fluid outlet is also arranged at the bottom of the core holder cylinder; the outer layer of the protective cylinder is wrapped with a No. 2 flexible heating sleeve, and the protective cylinder and the No. 2 flexible heating sleeve are both provided with sensors, and the sensors are respectively electrically connected to the control system. A high-definition camera is also provided on the protective cylinder, and the high-definition camera is electrically connected to the control system.

[0010] Furthermore, the drilling fluid injection unit includes an injection pump, a clean water tank and a plugging drilling fluid tank, the clean water tank and the plugging drilling fluid tank are respectively connected to the injection pump, the injection pump is connected to the plugging drilling fluid storage chamber of the hydrate reservoir simulation unit through pipeline 1, and the injection pump is connected to the drilling fluid outlet of the hydrate reservoir simulation unit through pipeline 2. Flow meters and multiple valves are provided on pipeline 1 and pipeline 2, and the injection pump, flow meter and multiple valves are respectively electrically connected to the control system.

[0011] Furthermore, the leakage metering unit includes a metering pump and a waste liquid tank, the metering pump and the waste liquid tank are respectively connected to the drilling fluid outlet of the hydrate reservoir simulation unit, and the metering pump is electrically connected to the control system.

[0012] Furthermore, the temperature control unit includes an air bath refrigeration box, flexible heating jacket No. 1 and flexible heating jacket No. 2, the hydrate reservoir simulation unit, drilling fluid injection unit and leakage metering unit are all arranged in the air bath refrigeration box, and the air bath refrigeration box, flexible heating jacket No. 1 and flexible heating jacket No. 2 are all electrically connected to the control system.

[0013] Furthermore, the control system includes a computer and a control cabinet, the computer is connected to the control cabinet via a data line, and the control cabinet is respectively connected to the hydrate reservoir simulation unit, the drilling fluid injection unit, the leakage metering unit and the temperature control unit.

[0014] A method for evaluating the performance of a marine hydrate reservoir plugging drilling fluid comprises the following steps:

[0015] Precooling process:

[0016] The temperature of the temperature control unit is controlled by the control system to reach the temperature required for the experiment, and pre-cooling is completed;

[0017] Hydrate reservoir simulated fracture drilling fluid filling process:

[0018] The control system controls the loss metering unit to inject the drilling fluid without plugging agent into the simulated fractures of the hydrate reservoir until the simulated fractures of the hydrate reservoir are completely filled with the drilling fluid without plugging agent as observed by the high-definition camera;

[0019] Hydrate reservoir simulation unit pressure maintenance process:

[0020] The control system controls the drilling fluid injection unit to inject high-pressure plugging drilling fluid into the hydrate reservoir simulation unit, so that the pressure in the hydrate reservoir simulation unit is equal to the actual marine hydrate reservoir formation pressure, thereby simulating the actual pressure environment of the actual marine hydrate reservoir;

[0021] Performance evaluation process of plugging drilling fluid:

[0022] Different plugging pressure differentials are set by a control system, and the control system controls the drilling fluid injection unit to inject high-pressure plugging drilling fluid into the hydrate reservoir simulation unit in multiple times according to the set different plugging pressure differentials. The flow of the plugging drilling fluid in the simulated fractures of the hydrate reservoir is simulated by the flow of the plugging drilling fluid in the fractures of the actual marine hydrate reservoir, thereby simulating the plugging process of the actual marine hydrate reservoir fractures by the plugging drilling fluid. Furthermore, the migration, bridging and distribution patterns of the plugging agent particles in the plugging drilling fluid in the simulated fractures of the hydrate reservoir are observed, and at the same time, the invasion depth of the plugging agent particles into the simulated fractures of the hydrate reservoir and the loss of the plugging drilling fluid at different times are obtained;

[0023] Flowback pressure test process:

[0024] The control system is used to control and adjust the pressure in the hydrate reservoir simulation unit to drop to the original experimental set pressure. The control system sets different injection pressures for the drilling fluid injection unit from low to high, and the flowback pattern of the plugging agent particles in the hydrate reservoir simulation fractures under different injection pressures provided by the drilling fluid injection unit is tested. Finally, the maximum flowback pressure under the experimental plugging pressure difference is determined.

[0025] The beneficial effects of the present invention are as follows: the device and method for evaluating the performance of leak-proof drilling fluid for marine hydrate reservoirs provided by the present invention can simulate the leak-proof process of marine hydrate reservoirs with different crack widths; can study the migration, bridging and distribution of plugging agent particles in the leak-proof drilling fluid in the cracks of marine hydrate reservoirs under different crack widths, leak-proof pressure differences and crack inclinations; at the same time, can study the invasion depth of the plugging agent particles into the simulated cracks of the hydrate reservoir and the change law of the leakage amount of the leak-proof drilling fluid at different times; can study the change law of the return pressure of the leak-proof drilling fluid under different crack widths, leak-proof pressure differences and crack inclinations of the marine hydrate reservoir; and can also realize the optimization of the leak-proof drilling fluid formula and the optimization of the leak-proof construction plan for different crack widths and crack inclinations. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0027] Figure 1 It is a schematic diagram of the structure of the present invention;

[0028] Figure 2 Schematic diagram of the core holder structure;

[0029] Figure 3 This is a schematic diagram of the end face structure of the core holder A;

[0030] Figure 4 This is a schematic diagram of the end structure of the core holder B;

[0031] In the figure, 1-computer; 2-control cabinet; 3-injection pump; 4-clean water tank; 5-valve No. 1; 6-valve No. 2; 7-drilling fluid tank for plugging leaks; 8-back pressure regulating valve No. 1; 9-back pressure regulating valve No. 2; 10-valve No. 3; 11-valve No. 4; 12-flow meter No. 1; 13-check valve; 14-pressure sensor No. 1; 15-stirring motor; 16-motor fixing bracket; 17-safety valve; 18-temperature sensor No. 1; 19-temperature sensor No. 2; 20-flexible heating jacket No. 1; 21-reduction gearbox; 22-servo motor; 23-movable bracket; 24-stirring; 25-temperature sensor No. 3; 26-temperature sensor No. 4; 27-flexible heating jacket No. 2 Heat-shrink sleeve; 28-visual window of protective cylinder; 29-visual window of core holder; 30-simulated core of hydrate reservoir; 31-simulated fracture of hydrate reservoir; 32-sealing cap of protective cylinder; 33-rotating support shaft; 34-storage chamber for plugging drilling fluid; 35-protective cylinder; 36-pressure sensor No. 2; 37-pressure sensor No. 3; 38-valve No. 5; 39-flow meter No. 2; 40-valve No. 6; 41-valve No. 7; 42-metering pump; 43-valve No. 8; 44-waste liquid tank; 45-sealing ring; 46-core holder cylinder; 47-drilling fluid outlet; 48-air bath refrigeration box; 49-high-definition camera; 50-core holder; 51-valve No. 9. DETAILED DESCRIPTION

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0033] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0034] The following embodiments of the present invention are described in detail with reference to the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0035] Example 1:

[0036] See Figures 1 to 4A device for evaluating the performance of drilling fluid for plugging leaks in a marine hydrate reservoir comprises a hydrate reservoir simulation unit, a drilling fluid injection unit and a leakage metering unit, wherein the drilling fluid injection unit and the leakage metering unit are respectively connected to the hydrate reservoir simulation unit, wherein the drilling fluid injection unit injects plugging drilling fluid into the hydrate reservoir simulation unit, and the leakage metering unit provides drilling fluid leakage measurement for the hydrate reservoir simulation unit; the device also comprises a temperature control unit for providing temperature control to the entire device and a control system for performing data acquisition and control on the entire device, wherein the hydrate reservoir simulation unit, the drilling fluid injection unit, the leakage metering unit and the temperature control unit are respectively electrically connected to the control system.

[0037] In this embodiment, the hydrate reservoir simulation unit includes a plugging drilling fluid storage chamber 34 and a protective cylinder 35, and a core clamp 50 is provided in the protective cylinder 35. Furthermore, the plugging drilling fluid storage chamber 34 and the protective cylinder 35 are connected by welding, and the core clamp 50 is communicated with the plugging drilling fluid storage chamber 34. The core clamp 50 and the protective cylinder 35 are sealed by a sealing ring 45 to prevent the plugging drilling fluid from entering the gap between the core clamp 50 and the protective cylinder 35 during the experiment. The plugging drilling fluid can only enter the hydrate reservoir simulation fracture 31 through the core clamp 50, and then carry out the plugging experiment; the plugging drilling fluid storage chamber 34 is installed with a core clamp 50. There is a stirrer 24, and the stirrer 24 is sealed from the plugging drilling fluid storage chamber 34. The stirrer 24 is connected to the stirring motor 15. The stirring motor 15 drives the stirrer 24 to stir the plugging drilling fluid in the plugging drilling fluid storage chamber 34 through the rotation of the stirring motor 15 to prevent the plugging agent particles from settling and accelerate the heat exchange between the plugging drilling fluid and the plugging drilling fluid storage chamber 34. The stirring motor 15 is installed on the plugging drilling fluid storage chamber 34 through the motor fixing bracket 16. The stirring motor 15 is electrically connected to the control system.

[0038] Furthermore, the plugging drilling fluid storage chamber 34 is installed with a No. 1 pressure sensor 14, a safety valve 17, a No. 1 temperature sensor 18 and a No. 3 pressure sensor 37. The No. 1 pressure sensor 14 and the No. 3 pressure sensor 37 are respectively used to monitor the pressure at the upper and lower ends of the plugging drilling fluid storage chamber 34 during the experiment. The No. 1 temperature sensor 18 is used to monitor the temperature in the plugging drilling fluid storage chamber 34 during the experiment. The safety valve 17 prevents the pressure in the plugging drilling fluid storage chamber 34 from overloading during the experiment, and plays a protective role for the plugging drilling fluid storage chamber 34. The No. 1 pressure sensor 14, the No. 1 temperature sensor 18 and the No. 3 pressure sensor 37 are all electrically connected to the control system. The outer layer of the plugging drilling fluid storage chamber 34 is wrapped with a flexible heating jacket 20 No. 1, and a temperature sensor No. 2 19 is installed on the flexible heating jacket 20 No. 1. The flexible heating jacket 20 No. 1 is used to heat and regulate the plugging drilling fluid in the plugging drilling fluid storage chamber 34, and the temperature sensor No. 2 19 is used to monitor the temperature of the flexible heating jacket 20 No. 1. The flexible heating jacket 20 No. 1 and the temperature sensor No. 2 19 are both electrically connected to the control system.

[0039] Furthermore, the plugging drilling fluid storage chamber 34 is fixedly connected to the rotating support shaft 33, and the rotating support shaft 33 is connected to the movable bracket 23 through a bearing. The rotating support shaft 33 can rotate around the movable bracket 23, and then the hydrate reservoir simulation unit is installed on the movable bracket 23 through the rotating support shaft 33. The rotating support shaft 33 is connected to the servo motor 22 through the reduction gear 21. The reduction gear 21 and the servo motor 22 are fixed to the movable bracket 23. The reduction gear 21 is used to reduce the speed of the servo motor 22. The servo motor 22 provides power for the angle adjustment of the hydrate reservoir simulation unit. The simulation of different fracture formation inclinations is achieved by adjusting the angle of the hydrate reservoir simulation unit. The servo motor 22 is electrically connected to the control system.

[0040] In this embodiment, the core holder 50 is composed of a hydrate reservoir simulation core 30, a core holder barrel 46, a core holder visual window 29, a hydrate reservoir simulation fracture 31 and a drilling fluid outlet 47 at the bottom of the core holder barrel 46. The hydrate reservoir simulation core 30 is located in the core holder barrel 46. Hydrate reservoir simulation fractures 31 of different widths (the width can be 1 mm to 10 mm according to experimental requirements) exist in the middle of the hydrate reservoir simulation core 30. The core holder visual window 29 is opened on the core holder barrel 46, through which the migration, bridging and distribution of plugging agent particles in the hydrate reservoir simulation fracture 31 can be observed.

[0041] In this embodiment, the outer layer of the protective cylinder 35 is wrapped with a No. 2 flexible heating jacket 27, which can heat the protective cylinder 35, thereby heating the hydrate reservoir simulation core 30. The No. 3 temperature sensor 25 is installed on the No. 2 flexible heating jacket 27, and the No. 3 temperature sensor 25 is used to monitor the temperature of the No. 2 flexible heating jacket 27. The No. 4 temperature sensor 26 is installed on the protective cylinder 35, and the No. 4 temperature sensor 26 is used to monitor the temperature of the hydrate reservoir simulation core 30; the protective cylinder 35 is equipped with a protective cylinder visual window 28, which uses high-definition The camera 49 can observe and record the migration, bridging and distribution of the plugging agent particles through the protective cylinder visual window 28 and the core clamp visual window 29. The protective cylinder sealing cap 32 and the protective cylinder 35 are sealed and connected by a tapered thread. The No. 2 pressure sensor 36 is connected to the drilling fluid outlet 47 through the protective cylinder sealing cap 32 by a pipeline. The No. 2 pressure sensor 36 is used to monitor the pressure at the drilling fluid outlet 47. The No. 2 flexible heating jacket 27, No. 3 temperature sensor 25, No. 4 temperature sensor 26, the high-definition camera 49 and the No. 2 pressure sensor 36 are all electrically connected to the control system.

[0042] In this embodiment, the drilling fluid injection unit includes an injection pump 3, a clean water tank 4, a No. 1 valve 5, a No. 2 valve 6, a plugging drilling fluid tank 7, a No. 1 back pressure regulating valve 8, a No. 2 back pressure regulating valve 9, a No. 3 valve 10, a No. 4 valve 11, a No. 1 flow meter 12, a one-way valve 13, a No. 5 valve 38, a No. 2 flow meter 39 and a No. 6 valve 40; the injection pump 3 is connected to the clean water tank 4 via the No. 1 valve 5, and the injection pump 3 is connected to the plugging drilling fluid tank 7 via the No. 2 valve 6. The clean water tank 4 stores clean water for cleaning equipment. After the experiment is completed, the injection pump 3 can be used to inject clean water into the hydrate reservoir simulation unit to clean the injection pump 3 and the hydrate reservoir simulation unit. The plugging drilling fluid tank 7 is used to store the plugging drilling fluid required for the experiment. The pump 3 is connected to the plugging drilling fluid storage chamber 34 through a pipeline via the No. 2 back pressure regulating valve 9, the No. 3 valve 10, the No. 1 flow meter 12 and the one-way valve 13. This passage is mainly used to inject plugging drilling fluid into the plugging drilling fluid storage chamber 34 and increase the pressure of the plugging drilling fluid storage chamber 34. The No. 2 back pressure regulating valve 9 mainly functions to maintain the outlet pressure of the injection pump 3 at the set pressure required for the experiment. The No. 1 flow meter 12 is used to monitor the flow rate of the plugging drilling fluid injected into the plugging drilling fluid storage chamber 34. The one-way valve 13 is mainly used to prevent the high-pressure drilling fluid in the plugging drilling fluid storage chamber 34 from flowing back. The injection pump 3, the No. 1 valve 5, the No. 2 valve 6, the No. 2 back pressure regulating valve 9, the No. 3 valve 10 and the No. 1 flow meter 12 are all electrically connected to the control system.

[0043] Furthermore, the injection pump 3 forms another passage connected to the drilling fluid outlet 47 through back pressure regulating valve No. 2 9, valve No. 5 38, flow meter No. 2 39 and valve No. 6 40 in sequence. Flow meter No. 2 39 is used to monitor the flow of plugging drilling fluid flowing through this passage. The plugging drilling fluid tank 7 is connected to the plugging drilling fluid storage chamber 34 through pipelines through back pressure regulating valve No. 1 8 and valve No. 4 11 in sequence. Back pressure regulating valve No. 2 9, valve No. 5 38, flow meter No. 2 39, valve No. 6 40, back pressure regulating valve No. 1 8 and valve No. 4 11 are all electrically connected to the control system.

[0044] In this embodiment, the leakage metering unit includes valve No. 7 41, metering pump 42, valve No. 8 43, valve No. 9 51 and waste liquid tank 44; the metering pump 42 is connected to the drilling fluid outlet 47 via a pipeline through valve No. 7 41 and valve No. 9 51 in sequence. The metering pump 42 can be used to inject drilling fluid without plugging agent into the simulated fracture 31 of the hydrate reservoir, and can also be used to measure the leakage rate and leakage volume of the lost drilling fluid flowing out of the drilling fluid outlet 47. The waste liquid tank 44 is connected to the drilling fluid outlet 47 via a pipeline through valve No. 8 43 and valve No. 9 51 in sequence. The waste liquid tank 44 is used to collect the plugging drilling fluid after the experiment is completed and the waste liquid formed by the water purification equipment. Valve No. 7 41, metering pump 42, valve No. 8 43 and valve No. 9 51 are all electrically connected to the control system.

[0045] In this embodiment, the temperature control unit comprises an air bath refrigeration box 48, a No. 1 flexible heating jacket 20, and a No. 2 flexible heating jacket 27; the hydrate reservoir simulation unit, the drilling fluid injection unit, and the leakage metering unit are all installed in the air bath refrigeration box 48. The air bath refrigeration box 48 provides a temperature-adjustable low-temperature environment for the hydrate reservoir simulation unit, the drilling fluid injection unit, and the leakage metering unit. The No. 1 flexible heating jacket 20 can increase the temperature of the plugging drilling fluid in the plugging drilling fluid storage chamber 34, and the No. 2 flexible heating jacket 27 can increase the temperature of the hydrate reservoir simulation core 30. The air bath refrigeration box 48, the No. 1 flexible heating jacket 20, and the No. 2 flexible heating jacket 27 work together to control the temperature of the hydrate reservoir simulation unit required for the experiment. The air bath refrigeration box 48, the No. 1 flexible heating jacket 20, and the No. 2 flexible heating jacket 27 are all electrically connected to the control system.

[0046] In this embodiment, the control system includes a computer 1 and a control cabinet 2; the computer 1 is connected to the control cabinet 2 via a data cable, and the control cabinet 2 is respectively connected to the hydrate reservoir simulation unit, the drilling fluid injection unit, the leakage metering unit and the temperature control unit. The control cabinet 2 mainly executes the control and data acquisition instructions issued by the computer 1 to the equipment in the hydrate reservoir simulation unit, the drilling fluid injection unit, the leakage metering unit and the temperature control unit. The computer 1 is mainly used to issue control and data acquisition instructions to the hydrate reservoir simulation unit, the drilling fluid injection unit, the leakage metering unit and the temperature control unit, and at the same time store and process the collected data fed back by the control cabinet 2.

[0047] The experimental method of the present invention comprises the following steps:

[0048] Equipment pre-cooling process:

[0049] The experimental operator sets the temperature of the air bath refrigeration box 48 to 2°C through computer 1 (this temperature should be the same as the temperature of the hydrate reservoir simulation core 30, and can be 1°C, 2°C, 3°C...). After receiving the instruction from computer 1 via control cabinet 2, the air bath refrigeration box 48 begins to cool until the hydrate reservoir simulation unit, drilling fluid injection unit, and leakage metering unit installed in the air bath refrigeration box 48 reach the required temperature of 2°C for the experiment. The purpose of the equipment pre-cooling process is to simulate the actual temperature environment of the marine hydrate reservoir. At the same time, in order to prevent the hydrate reservoir simulation core 30 from decomposing due to excessive temperature, the equipment pre-cooling process is completed.

[0050] Hydrate reservoir simulated fracture drilling fluid filling process:

[0051] After the equipment pre-cooling process is completed, the experimental operator installs the prepared core holder 50 with the hydrate reservoir simulation core 30 (the width of the seam is arbitrarily selected from 1mm to 10mm according to the experimental requirements, and 3mm is selected in this case) in the protective cylinder 35. The computer 1 and the control cabinet 2 jointly control to close the valve 8 43 and the valve 6 40, and open the valve 7 41. The experimental operator controls the computer 1 and the control cabinet 2 to start the metering pump 42. The metering pump 42 is filled with a sufficient amount of drilling fluid without plugging agent. The drilling fluid without plugging agent is injected into the hydrate reservoir through the drilling fluid outlet 47 by the metering pump 42. The simulated fracture 31 is observed by the high-definition camera 49 until the simulated fracture 31 of the hydrate reservoir is completely filled with the drilling fluid without the plugging agent. Then, valve No. 9 51 is closed and valve No. 8 43 is opened. The metering pump 42 injects the remaining drilling fluid without the plugging agent into the waste liquid tank 44. Then, the metering pump 42 is stopped and valves No. 7 41 and No. 8 43 are closed. The drilling fluid filling process of the simulated fracture of the hydrate reservoir is to prevent the plugging drilling fluid particles from entering the simulated fracture 31 of the hydrate reservoir in advance and affecting the implementation of the plugging drilling fluid performance evaluation process. The drilling fluid filling process of the simulated fracture of the hydrate reservoir is completed.

[0052] Hydrate reservoir simulation system pressure maintenance process:

[0053] After the filling process of the simulated fracture of the hydrate reservoir with drilling fluid is completed, the experimental operator immediately controls the computer 1 and the control cabinet 2 to open valve 1 5 and valve 3 10, adjusts the outlet pressure of the back pressure regulating valve 9 No. 2 to 10 MPa (it can be set arbitrarily within the range of 0-20 MPa according to the experimental needs), closes valve 4 11, valve 5 38 and valve 9 51, starts the injection pump 3 and the stirring motor 15, and the plugging drilling fluid tank 7 is injected into the plugging drilling fluid tank 7 by the injection pump 3 in sequence through the back pressure regulating valve 9 No. 2, valve 3 10, flow meter 1 12 and the one-way valve 13 are injected into the plugging drilling fluid storage chamber 34, and the stirring motor 15 drives the stirrer 24 to continuously stir the plugging drilling fluid in the plugging drilling fluid storage chamber 34 until the pressure monitored by the No. 1 pressure sensor 14 and the No. 2 pressure sensor 36 reaches 10 MPa. The pressure maintenance process of the hydrate reservoir simulation system is to simulate the pressure of the actual hydrate reservoir. At the same time, in order to prevent the hydrate reservoir simulation core 30 from decomposing due to pressure reduction, the injection pump 3 is stopped and the No. 3 valve 10 is closed. The pressure maintenance process of the hydrate reservoir simulation unit is completed.

[0054] Performance evaluation process of plugging drilling fluid:

[0055] After the pressure maintenance process of the hydrate reservoir simulation system is completed, the experimental operator sets the temperature of the No. 1 flexible heating jacket 20 to 4°C through the computer 1 and the control cabinet 2 until the No. 1 temperature sensor 18 detects that the plugging drilling fluid temperature in the plugging drilling fluid storage chamber 34 reaches 4°C (used to simulate the situation that the plugging drilling fluid temperature is higher than the formation temperature during the actual plugging process), and maintains the plugging drilling fluid temperature in the plugging drilling fluid storage chamber 34 at 4°C; the experimental operator opens the No. 1 valve 5, the No. 3 valve 10, the No. 9 valve 51 and the No. 7 valve 41 through the computer 1 and the control cabinet 2, sets the outlet pressure of the No. 2 back pressure regulating valve 9 to 10.2 MPa, closes the No. 4 valve 11, the No. 5 valve 38, and the No. 6 valve 40 and No. 8 valve 43, then start the injection pump 3 and the metering pump 42, the injection pump 3 injects the plugging drilling fluid in the plugging drilling fluid tank 7 into the plugging drilling fluid storage chamber 34 through the No. 2 back pressure regulating valve 9, No. 3 valve 10, No. 1 flow meter 12 and the one-way valve 13, the computer 1 and the control cabinet 2 jointly control the injection pump 3 and the metering pump 42, so that the pressure of the No. 3 pressure sensor 37 is maintained at 10.2MPa, and the pressure of the No. 2 pressure sensor 36 is dynamically maintained at 10MPa (the metering pump 42 maintains the No. 2 pressure sensor 36 at 10MPa by adjusting the volume of the inner cavity of its pump body). Under the pressure difference of 0.2MPa, the plugging drilling fluid in the plugging drilling fluid storage chamber 34 is filled with water. The well fluid flows into the simulated fracture 31 of the hydrate reservoir. The drilling fluid without plugging agent in the simulated fracture 31 of the hydrate reservoir is displaced by the plugging drilling fluid along the fracture through the drilling fluid outlet 47 and into the metering pump 42. The high-definition camera 49 monitors the migration, bridging and distribution of plugging agent particles in the plugging drilling fluid in the simulated fracture 31 of the hydrate reservoir through the protective cylinder visual window 28 and the core holder visual window 29. At the same time, the invasion depth of the plugging agent particles into the simulated fracture 31 of the hydrate reservoir is monitored. The loss of plugging drilling fluid at different times is monitored through the metering pump 42. When the No. 2 pressure sensor 36 no longer changes, the outlet pressure of the No. 2 back pressure regulating valve 9 is reset to 10.4 MPa. a. The pressure of the No. 2 pressure sensor 36 is dynamically maintained at 10 MPa. Under the action of a pressure differential of 0.4 MPa, the plugging drilling fluid in the plugging drilling fluid storage chamber 34 continuously flows into the simulated fracture 31 of the hydrate reservoir. The plugging drilling fluid enters the metering pump 42 through the drilling fluid outlet 47. The high-definition camera 49 monitors the migration, bridging, and distribution of the plugging agent particles in the plugging drilling fluid in the simulated fracture 31 of the hydrate reservoir through the protective cylinder visual window 28 and the core holder visual window 29. At the same time, the penetration depth of the plugging agent particles into the simulated fracture 31 of the hydrate reservoir is monitored. The loss of the plugging drilling fluid at different times is monitored through the metering pump 42. According to the above operation, the flow rate is increased by 0.The process of injecting plugging drilling fluid into the plugging drilling fluid storage chamber 34 is repeated continuously, maintaining a pressure differential of 2 MPa until the required pressure differential of 3 MPa is reached (the pressure differential can be arbitrarily selected between 0 and 10 MPa). When the pressure of pressure sensor No. 2 36 remains constant at 10 MPa, the final depth of plugging agent particles penetrating the simulated fracture 31 in the hydrate reservoir is monitored using a high-definition camera 49. The final loss of plugging drilling fluid is read using metering pump 42. Injection pump 3 and metering pump 42 are stopped, and valve No. 3 10 and valve No. 7 41 are simultaneously closed. The plugging drilling fluid performance evaluation process is complete.

[0056] Flowback pressure test process:

[0057] After the plugging process is completed, the outlet pressure of the No. 1 back pressure regulating valve 8 is set to 10 MPa, the No. 7 valve 41, the No. 8 valve 43, the No. 3 valve 10, and the No. 9 valve 51 are closed, and the No. 4 valve 11 is opened. The plugging drilling fluid in the plugging drilling fluid storage chamber 34 enters the plugging drilling fluid tank 7 through the No. 4 valve 11 and the No. 1 back pressure regulating valve 8 under the action of the pressure difference (pressure difference 3 MPa) until the pressure in the plugging drilling fluid storage chamber 34 drops to 10 MPa. Set the No. 2 valve 41 and the No. 8 valve 43 to 10 MPa. The outlet pressure of the No. 2 back pressure regulating valve 9 is 10.2 MPa, the No. 2 valve 6 is closed, the No. 1 valve 5, the No. 5 valve 38, the No. 6 valve 40, and the No. 9 valve 51 are opened, the injection pump 3 is started, and the clean water in the clean water tank 4 is injected into the drilling fluid outlet 47 by the injection pump 3 through the No. 2 back pressure regulating valve 9, the No. 5 valve 38, the No. 2 flow meter 39, the No. 6 valve 40, and the No. 9 valve 51. The high-pressure clean water at the drilling fluid outlet 47 displaces the plugging drill bit in the simulated fracture 31 of the hydrate reservoir. The high-definition camera 49 is used to monitor whether the plugging agent particles migrate in the simulated fracture 31 of the hydrate reservoir. If there is no change, the outlet pressure of the No. 2 back pressure regulating valve 9 is adjusted by increasing the pressure by 0.1 MPa each time. Every time the pressure increases by 0.1 MPa, the high-definition camera 49 is used to monitor whether the plugging agent particles migrate in the simulated fracture 31 of the hydrate reservoir until the plugging agent particles in the simulated fracture 31 of the hydrate reservoir are observed to be returned to the plugging drilling fluid storage chamber 34. During the flowback process of the plugging particles, the maximum pressure of the No. 2 pressure sensor 36 is monitored to be the flowback pressure of the plugging pressure difference of 3 MPa. At the same time, it is monitored that the pressure of the No. 3 pressure sensor 37 is equal to that of the No. 2 pressure sensor 36, indicating that the plugging agent particles in the simulated fracture 31 of the hydrate reservoir are completely returned to the plugging drilling fluid storage chamber 34. The injection pump 3 and the air bath refrigeration box 48 are stopped, and the flowback pressure test process is completed.

[0058] Subsequent processing:

[0059] After the backflow pressure test process is completed, valve No. 4 11 is opened, and the outlet pressure of back pressure regulating valve No. 1 is gradually adjusted downward to make the plugging drilling fluid in the plugging drilling fluid storage chamber 34 flow into the plugging drilling fluid tank 7 until the pressure in the plugging drilling fluid storage chamber 34 is "0". When the pressure in the plugging drilling fluid storage chamber 34 drops to exceed the phase equilibrium pressure of the hydrate, the hydrate reservoir simulation core 30 begins to decompose. In order to accelerate the decomposition rate of the hydrate reservoir simulation core 30, the flexible heating jacket No. 2 is started, and the temperature of the flexible heating jacket No. 2 reaches 50°C (it can be set arbitrarily within 0~100°C according to experimental requirements. The higher the temperature setting, the faster the hydrate reservoir simulation core 30 decomposes). At the same time, valve No. 5 38, valve No. 6 40, and valve No. 9 51 are opened, and the outlet pressure of back pressure regulating valve No. 2 is set to "0". The injection pump 3 is started, and the clean water in the clean water tank 4 is injected into the pump 3 through valve No. 5 38, flow meter No. 2, and valve No. 6. 40, valve 9 51, and hydrate reservoir simulated fracture 31 are injected into the plugging drilling fluid storage chamber 34. Clean water displaces the plugging drilling fluid in the plugging drilling fluid storage chamber 34 and enters the plugging drilling fluid tank 7 through valve 4 11 and back pressure regulating valve 1 8 until the plugging drilling fluid storage chamber 34 is filled with clean water. Stop the injection pump 3, close valve 4 11, valve 5 38, valve 6 40, and valve 7 41, open valve 3 10 and valve 8 43, and start the injection pump 3. Clean water enters the plugging drilling fluid storage chamber 34 in sequence through the No. 2 back pressure regulating valve 9, the No. 3 valve 10, the No. 1 flow meter 12, and the one-way valve 13. Then, the clean water displaces the decomposed substances of the hydrate reservoir simulation core 30 and enters the waste liquid tank 44 through the drilling fluid outlet 47, the No. 9 valve 51, and the No. 8 valve 43 until the plugging drilling fluid storage chamber 34 and the core clamp 50 are completely cleaned. The injection pump 3 and the No. 2 flexible heating jacket 27 are stopped, and the subsequent treatment process is completed.

[0060] The present invention has at least the following technical effects:

[0061] The device and method for evaluating the performance of leak-proof drilling fluid for marine hydrate reservoirs provided by the present invention can simulate the leak-proof process of marine hydrate reservoirs with different crack widths; can study the migration, bridging and distribution of plugging agent particles in the leak-proof drilling fluid within the cracks of marine hydrate reservoirs under different crack widths, plugging pressure differences and crack inclinations; at the same time, can study the invasion depth of the plugging agent particles into the simulated cracks of the hydrate reservoir and the change in the leakage amount of the leak-proof drilling fluid at different times; can study the change in the return pressure of the leak-proof drilling fluid under different crack widths, plugging pressure differences and crack inclinations of the marine hydrate reservoir; and can also achieve the optimization of the leak-proof drilling fluid formula and the optimization of the leak-proof construction plan for different crack widths and crack inclinations.

[0062] It should be noted that for the aforementioned embodiments, for simplicity of description, they are all expressed as a series of action combinations, but those skilled in the art should be aware that this application is not limited by the order of the actions described, because according to this application, some steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in this specification are preferred embodiments, and the actions involved are not necessarily required by this application.

[0063] The above embodiments describe the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Without departing from the spirit and scope of the present invention, modifications and variations made by those skilled in the art without departing from the spirit and scope of the present invention should be within the scope of protection of the appended claims.

Claims

1. A method for evaluating the performance of a marine hydrate reservoir plugging drilling fluid, implemented using a marine hydrate reservoir plugging drilling fluid performance evaluation device, characterized in that: The evaluation device includes a hydrate reservoir simulation unit, a drilling fluid injection unit and a leakage metering unit, wherein the drilling fluid injection unit and the leakage metering unit are respectively connected to the hydrate reservoir simulation unit, wherein the drilling fluid injection unit injects plugging drilling fluid into the hydrate reservoir simulation unit, and the leakage metering unit provides drilling fluid leakage metering for the hydrate reservoir simulation unit; and further includes a temperature control unit for providing temperature control for the entire device and a control system for data acquisition and control of the entire device. The hydrate reservoir simulation unit, the drilling fluid injection unit and the leakage metering unit are respectively connected to the hydrate reservoir simulation unit, wherein the drilling fluid injection unit injects plugging drilling fluid into the hydrate reservoir simulation unit, and the leakage metering unit provides drilling fluid leakage metering for the hydrate reservoir simulation unit. The element, the leakage metering unit and the temperature control unit are electrically connected to the control system respectively; the hydrate reservoir simulation unit includes a plugging drilling fluid storage chamber (34) and a protective cylinder (35), the plugging drilling fluid storage chamber (34) is connected to the protective cylinder (35), a core holder (50) is provided in the protective cylinder (35), the core holder (50) is communicated with the plugging drilling fluid storage chamber (34), and a stirring motor (15) is also provided on the plugging drilling fluid storage chamber (34), and the stirring motor (15) is electrically connected to the control system; The evaluation method comprises the following steps: Precooling process: The temperature of the temperature control unit is controlled by the control system to reach the temperature required for the experiment, and pre-cooling is completed; Hydrate reservoir simulated fracture drilling fluid filling process: The control system controls the leakage metering unit to inject the drilling fluid without plugging agent into the simulated fracture (31) of the hydrate reservoir until the simulated fracture (31) of the hydrate reservoir is completely filled with the drilling fluid without plugging agent as observed by the high-definition camera (49); Hydrate reservoir simulation unit pressure maintenance process: The control system controls the drilling fluid injection unit to inject high-pressure plugging drilling fluid into the hydrate reservoir simulation unit, so that the pressure in the hydrate reservoir simulation unit is equal to the actual marine hydrate reservoir formation pressure, thereby simulating the actual pressure environment of the actual marine hydrate reservoir; Performance evaluation process of plugging drilling fluid: Different plugging pressure differences are set by the control system, and the control system controls the drilling fluid injection unit to inject high-pressure plugging drilling fluid into the hydrate reservoir simulation unit in multiple times according to the set different plugging pressure differences. The flow of the plugging drilling fluid in the hydrate reservoir simulation fracture (31) is simulated by the flow of the plugging drilling fluid in the actual marine hydrate reservoir fracture, thereby simulating the plugging process of the actual marine hydrate reservoir fracture by the plugging drilling fluid. Furthermore, the migration, bridging and distribution of the plugging agent particles in the plugging drilling fluid in the hydrate reservoir simulation fracture (31) are observed, and at the same time, the invasion depth of the plugging agent particles into the hydrate reservoir simulation fracture (31) and the loss amount of the plugging drilling fluid at different times are obtained; Flowback pressure test process: The control system is used to control and adjust the pressure in the hydrate reservoir simulation unit to drop to the original experimental set pressure. The control system sets different injection pressures for the drilling fluid injection unit from low to high, and the backflow pattern of the plugging agent particles in the hydrate reservoir simulation fracture (31) under different injection pressures provided by the drilling fluid injection unit is tested. Finally, the maximum backflow pressure under the experimental plugging pressure difference is determined.

2. The method for evaluating the performance of a marine hydrate reservoir plugging drilling fluid according to claim 1, wherein: The outer layer of the plugging drilling fluid storage chamber (34) is wrapped with a No. 1 flexible heating jacket (20), and a plurality of sensors are provided on the No. 1 flexible heating jacket (20) and the plugging drilling fluid storage chamber (34), and the sensors are electrically connected to the control system respectively.

3. The method for evaluating the performance of a marine hydrate reservoir plugging drilling fluid according to claim 1, wherein: The plugging drilling fluid storage chamber (34) is connected to a rotating support shaft (33), and the rotating support shaft (33) is connected to a movable bracket (23). The hydrate reservoir simulation unit is installed on the movable bracket (23) through the rotating support shaft (33). The rotating support shaft (33) is connected to a servo motor (22) through a reduction gear box (21). The reduction gear box (21) and the servo motor (22) are both arranged on top, and the servo motor (22) is electrically connected to a control system.

4. The method for evaluating the performance of a marine hydrate reservoir plugging drilling fluid according to claim 1, wherein: The core holder (50) includes a core holder barrel (46), a hydrate reservoir simulation core (30) is arranged in the core holder barrel (46), a core holder visual window (29) and hydrate reservoir simulation cracks (31) of different crack widths are arranged on the hydrate reservoir simulation core (30), and a drilling fluid outlet (47) is also arranged at the bottom of the core holder barrel (46); the outer layer of the protective barrel (35) is wrapped with a No. 2 flexible heating jacket (27), and the protective barrel (35) and the No. 2 flexible heating jacket (27) are both provided with sensors, and the sensors are respectively electrically connected to the control system. The protective barrel (35) is also provided with a high-definition camera (49), and the high-definition camera (49) is electrically connected to the control system.

5. The method for evaluating the performance of a marine hydrate reservoir plugging drilling fluid according to claim 1, wherein: The drilling fluid injection unit comprises an injection pump (3), a clean water tank (4) and a plugging drilling fluid tank (7); the clean water tank (4) and the plugging drilling fluid tank (7) are respectively connected to the injection pump (3); the injection pump (3) is connected to the plugging drilling fluid storage chamber (34) of the hydrate reservoir simulation unit via pipeline 1; the injection pump (3) is connected to the drilling fluid outlet (47) of the hydrate reservoir simulation unit via pipeline 2; a flow meter and a plurality of valves are provided on both pipeline 1 and pipeline 2; the injection pump (3), the flow meter and the plurality of valves are respectively electrically connected to a control system.

6. The method for evaluating the performance of a marine hydrate reservoir plugging drilling fluid according to claim 1, wherein: The leakage metering unit comprises a metering pump (42) and a waste liquid tank (44), wherein the metering pump (42) and the waste liquid tank (44) are respectively connected to the drilling fluid outlet (47) of the hydrate reservoir simulation unit, and the metering pump (42) is electrically connected to a control system.

7. The method for evaluating the performance of a marine hydrate reservoir plugging drilling fluid according to claim 1, wherein: The temperature control unit includes an air bath refrigeration box (48), a No. 1 flexible heating jacket (20) and a No. 2 flexible heating jacket (27); the hydrate reservoir simulation unit, the drilling fluid injection unit and the leakage metering unit are all arranged in the air bath refrigeration box (48); the air bath refrigeration box (48), the No. 1 flexible heating jacket (20) and the No. 2 flexible heating jacket (27) are all electrically connected to the control system.

8. The method for evaluating the performance of a marine hydrate reservoir plugging drilling fluid according to claim 1, wherein: The control system comprises a computer (1) and a control cabinet (2); the computer (1) is connected to the control cabinet (2) via a data line; and the control cabinet (2) is respectively connected to a hydrate reservoir simulation unit, a drilling fluid injection unit, a leakage metering unit, and a temperature control unit.

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