Mining simulation experiment device of natural gas hydrate multi-branch well and optimal well type arrangement determination method

Abstract

The invention relates to a natural gas hydrate multi-branch well exploitation simulation experiment device and an optimal well type arrangement determining method.The device comprises a natural gas hydrate reservoir synthesis unit, a multi-branch well exploitation simulation unit and a data monitoring and collecting unit, and the multi-branch well exploitation simulation unit is arranged in the natural gas hydrate reservoir synthesis unit; the multi-branch well exploitation simulation unit comprises a main well hole, a branch well and a sand control screen, and the main well hole and the branch well are each of a hollow structure with one closed end and one open end; a plurality of first eyelets are formed in the side wall of the main well hole, and a plurality of second eyelets are formed in the side wall of each branch well; the outer side of each branch well is wrapped with a sand control screen; by changing the number of the first eyelets or the number of the second eyelets connected with the multilateral wells, the spatial geometric arrangement parameters of the multilateral wells are adjusted; and the data monitoring and acquisition unit is connected with the natural gas hydrate reservoir synthesis unit. The system can be widely applied to the technical field of efficient development of natural gas hydrate resources.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of efficient development of natural gas hydrate resources, and in particular to a simulation experiment device for mining of a natural gas hydrate multi-lateral well and a method for determining an optimal well type arrangement. BACKGROUND

[0002] Natural gas hydrate, commonly known as "combustible ice", is a new type of energy with huge reserves, high energy density and low carbon and clean. How to increase production and efficiency is the biggest challenge in the current industrial development of natural gas hydrate. As a high-efficiency means of increasing production and efficiency, multi-lateral well has been widely used in the development of shale gas, shale oil and other new geological energy sources, significantly improving production efficiency and providing a valuable exploration path for natural gas hydrate production and efficiency.

[0003] However, the mining of natural gas hydrate multi-lateral well still faces many difficulties. First, in terms of actual production testing, there is no precedent for the mining of natural gas hydrate multi-lateral well, resulting in a lack of direct experience to learn from. Second, as an effective means of verifying the feasibility of natural gas hydrate multi-lateral well mining, there is currently a lack of experimental devices that can simulate various natural gas hydrate multi-lateral well mining scenarios. Third, how to scientifically optimize the arrangement of branch wells to maximize natural gas hydrate production capacity has not yet been studied, making it difficult to determine the best well type arrangement scheme in actual mining operations. These factors have seriously hampered the development of natural gas hydrate multi-lateral well mining technology and greatly hindered its industrialization application process.

[0004] Therefore, it is urgent to develop a simulation experiment device for mining of natural gas hydrate multi-lateral well and a method for determining an optimal well type arrangement to help achieve natural gas hydrate production and efficiency and promote the industrialization development process of natural gas hydrate. SUMMARY

[0005] To solve the above problems, the present application provides a simulation experiment device for mining of natural gas hydrate multi-lateral well and a method for determining an optimal well type arrangement to help achieve natural gas hydrate production and efficiency.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: on the one hand, a simulation experiment device for mining of natural gas hydrate multi-lateral well is provided, comprising a natural gas hydrate reservoir synthesis unit, a multi-lateral well mining simulation unit and a data monitoring and acquisition unit; The multi-lateral well mining simulation unit is arranged in the natural gas hydrate reservoir synthesis unit, and the multi-lateral well mining simulation unit comprises a main borehole, a branch well and a sand control screen, and the main borehole and the branch well are both hollow structures with one end closed and the other end open; The side wall of the main borehole is provided with a plurality of first holes for connecting the open end or the plug of the branch borehole, the side wall of each branch borehole is provided with a plurality of second holes for simulating the flow channel of reservoir fluid into the wellbore during the natural gas hydrate mining process, and the outer side of each branch borehole is provided with the sand control screen for simulating the sand control process of real natural gas hydrate mining; the spatial geometric arrangement parameters of the branch borehole are adjusted by changing the first holes connected by the branch borehole or changing the number of the second holes. The data monitoring and acquisition unit is connected with the natural gas hydrate reservoir synthesis unit, which is used for separating the gas-liquid mixture produced by the reservoir during the simulation of the natural gas hydrate mining process, monitoring the mass of water and the flow of gas in the produced gas-liquid mixture in real time, and simulating the real natural gas hydrate depressurization mining process.

[0007] Further, the natural gas hydrate reservoir synthesis unit includes a reaction kettle, a plunger pump, a gas cylinder and a cold water bath. The main borehole is longitudinally arranged in the reaction kettle, the open end of the main borehole is fixedly connected to the bottom center of the reaction kettle, the reaction kettle is filled with a sediment sample for simulating a natural gas hydrate reservoir, and the reaction kettle is used for simulating the formation space of natural gas hydrate in a natural environment. The top of the reaction kettle is connected with the plunger pump for providing water required for natural gas hydrate synthesis; the bottom center of the reaction kettle is connected with the gas cylinder for providing gas required for natural gas hydrate synthesis to the multi-branch well mining simulation unit; and the reaction kettle is completely immersed in the cold water bath. The bottom center of the reaction kettle is also connected with the data monitoring and acquisition unit.

[0008] Further, the data monitoring and acquisition unit includes a temperature sensor, a pressure sensor, a gas-liquid separation tank, a mass balance, a back pressure valve, a filter, a gas flow meter and a data acquisition terminal. The temperature sensor and the pressure sensor are arranged at the top of the reactor, and are used to monitor the temperature and pressure of the natural gas hydrate reservoir in the reactor in real time; the gas-liquid separation tank is placed on the mass balance, and the inlet of the gas-liquid separation tank is connected to the bottom center of the reactor through the back pressure valve and the filter in sequence, and the outlet of the gas-liquid separation tank is connected to the gas flow meter; the gas-liquid separation tank is used to separate the gas-liquid mixture produced from the reservoir in the simulation of the natural gas hydrate mining process, and store the separated water; the mass balance is used to weigh the mass of the water produced from the reservoir in the natural gas hydrate mining process in real time, so as to determine the water production rate in the natural gas hydrate mining process; the back pressure valve is used to control the reservoir pressure in the natural gas hydrate mining process; the filter is used to filter the gas-liquid mixture flowing into the well in the natural gas hydrate mining process; and the gas flow meter is used to collect the flow of the gas separated by the gas-liquid separation tank. The data acquisition terminal is electrically connected to the temperature sensor, the pressure sensor, the mass balance, the back pressure valve and the gas flow meter respectively, and is used to acquire the hydrate reservoir temperature, the hydrate reservoir pressure, the gas production rate and the water production rate, and control the work of the connected components.

[0009] Further, the outlet of the gas flow meter is connected to a waste gas tank for storing the gas separated by the gas-liquid separation tank.

[0010] Further, the reactor comprises a cylinder and a flange plate, wherein the top of the cylinder is sealingly connected to the flange plate to form a closed chamber.

[0011] Further, the open end of the main borehole is sealingly connected to the bottom of the reactor, and is used as the gas and water outlet; the first boreholes on the main borehole are uniformly arranged in five groups in the vertical direction, and the included angle between adjacent first boreholes is 45°; the first boreholes on the main borehole are uniformly arranged in four groups in the horizontal direction, and the included angle between adjacent first boreholes is 90°.

[0012] Further, the open end of the branch borehole is sealingly connected to the first borehole; the second boreholes on the branch borehole are uniformly arranged in several groups in the vertical direction, and the included angle between adjacent second boreholes is 45°; the second boreholes on the branch borehole are uniformly arranged in four groups in the horizontal direction, and the included angle between adjacent second boreholes is 90°.

[0013] In another aspect, a method for determining the optimal well type arrangement of a natural gas hydrate multi-branch well is provided, comprising: The control variable method is adopted to design natural gas hydrate multi-branch well mining experimental schemes based on the spatial geometric arrangement parameters of the branch borehole, wherein a plurality of control experiments are arranged in each natural gas hydrate multi-branch well mining experimental scheme. Based on the natural gas hydrate multi-lateral well exploitation experimental scheme, the exploitation simulation experimental device is set according to any one of claims 1 to 6, and the natural gas hydrate synthesis process is simulated; Based on the set exploitation simulation experimental device, the natural gas hydrate exploitation process is simulated; Based on the simulation results of the natural gas hydrate synthesis process and the natural gas hydrate exploitation process of each natural gas hydrate multi-lateral well exploitation experimental scheme, the optimal well type arrangement of the multi-lateral well is determined.

[0014] Further, the natural gas hydrate multi-lateral well exploitation experimental scheme based on the design, the exploitation simulation experimental device is set, and the natural gas hydrate synthesis process is simulated, comprising: Based on the natural gas hydrate multi-lateral well exploitation experimental scheme, the multi-lateral well exploitation simulation unit is set; The natural gas hydrate reservoir synthesis unit is set, the set multi-lateral well exploitation simulation unit is placed in the reaction kettle of the natural gas hydrate reservoir synthesis unit, and the gas injection and exhaust operation is carried out in the reaction kettle through the gas cylinder and the back pressure valve, so as to completely remove the residual air in the reaction kettle, and obtain the prepared reaction kettle; Based on the prepared reaction kettle, the natural gas hydrate synthesis process is simulated.

[0015] Further, the natural gas hydrate exploitation process is simulated based on the set exploitation simulation experimental device, comprising: The plunger pump is started, the pressure of the back pressure valve is regulated, and the hydrate reservoir in the reaction kettle is depressurized; The temperature sensor and the pressure sensor collect the temperature and pressure change data of the reservoir in the natural gas hydrate exploitation process in real time; The gas-liquid separation tank separates the gas-liquid mixture produced in the natural gas hydrate exploitation process; The mass balance weighs the mass of the water collected in the gas-liquid separation tank; The gas flow meter monitors the gas flow of the gas-liquid separation tank; When the pressure of the natural gas hydrate reservoir in the reaction kettle is reduced to the preset threshold value, the plunger pump is switched from the constant rate depressurization mode to the constant pressure mode, so that the pressure of the back pressure valve is always maintained at the preset threshold value, and until the gas flow meter no longer detects gas production in the continuous preset time, it can be determined that the hydrate in the reaction kettle has been completely decomposed, and thus the natural gas hydrate exploitation process simulation ends.

[0016] Further, based on the simulation results of the natural gas hydrate synthesis process and the natural gas hydrate exploitation process of each natural gas hydrate multi-lateral well exploitation experimental scheme, the optimal well type arrangement of the multi-lateral well is determined, comprising: According to the designed natural gas hydrate multi-lateral well exploitation experiment scheme, the natural gas hydrate synthesis process and the natural gas hydrate exploitation process are simulated respectively, and the cumulative gas production data of each natural gas hydrate multi-lateral well exploitation experiment scheme is recorded through the data monitoring and acquisition unit; The cumulative gas production data corresponding to different control experiments in each natural gas hydrate multi-lateral well exploitation experiment scheme is compared and analyzed, the spatial geometric arrangement parameters of the branch well capable of realizing the maximum exploitation productivity of the natural gas hydrate multi-lateral well are determined, and then the optimal well type arrangement of the multi-lateral well is determined.

[0017] The present application has the following advantages: 1、The experimental device of the present application is extremely flexible in structural design, and through ingenious and convenient adjustment of the position of the branch well installed on the borehole of the main well, various spatial geometric arrangement modes of the branch well can be easily realized, and at the same time, a systematic and comprehensive natural gas hydrate multi-lateral well exploitation experiment scheme is designed by using the control variable method.

[0018] 2、In the experimental scheme design, the adjustable spatial geometric arrangement parameters of the branch well include the azimuth, phase angle, spacing, number and length of the branch well, which are multiple spatial geometric arrangement parameters that play a decisive role in the exploitation productivity; in the experimental implementation stage, the natural gas hydrate synthesis and natural gas hydrate exploitation operation are carried out according to the unified standard process, and the cumulative gas production data in the whole exploitation process is recorded in real time by using the data monitoring and acquisition unit; after the experiment, the hydrate exploitation productivity under different well type arrangement modes is compared and analyzed to determine the optimal well type arrangement mode capable of realizing the maximum hydrate exploitation productivity, which provides a solid and reliable scientific basis and technical support for the practical application of natural gas hydrate multi-lateral well exploitation.

[0019] 3、The present application simulates the formation of natural gas hydrate in nature by using a reaction kettle, and matches a plunger pump and a cold water bath to accurately control the pressure and temperature in the kettle, so as to ensure that the phase equilibrium condition of hydrate generation is reached, and a sand control screen and a filter are used to simulate the real sand control process of hydrate exploitation, and a main borehole and a branch well are used to simulate a production wellbore; through the cooperation of the above multiple components, the natural gas hydrate exploitation process can be highly restored.

[0020] 4、The present application adopts a modular detachable main borehole and branch well assembly structure design, and through flexible adjustment of the connection position of the branch well on the main borehole, the free combination of different spatial geometric arrangement parameters of the branch well can be realized, various natural gas hydrate multi-lateral well exploitation scenes can be simulated from multiple dimensions and all directions, and the limitation of the fixed branch well arrangement of the traditional experimental device is broken through.

[0021] 5、The natural gas hydrate multi-lateral well mining experiment scheme of the application can analyze the influence law of various spatial geometric arrangement parameters on the natural gas hydrate mining productivity, and through the comparative analysis of the hydrate mining productivity under different well type arrangement modes, the optimal well type arrangement mode is determined by taking the maximum productivity as the core evaluation standard, which helps to increase the productivity of hydrate mining and provides solid scientific support for the practical application of the natural gas hydrate multi-lateral well mining technology.

[0022] In summary, the application can be widely applied in the field of efficient development of natural gas hydrate resources. BRIEF DESCRIPTION OF DRAWINGS

[0023] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are included to provide a description of the preferred embodiments and are not intended to limit the scope of the application. Throughout the drawings, like reference numerals will be used to refer to like components. In the drawings: Figure 1 is a structural schematic diagram of a natural gas hydrate multi-lateral well mining simulation experiment device provided by an embodiment of the application; Figure 2 is a front view of the structure of a reaction kettle provided by an embodiment of the application; Figure 3 is a front view of the structure of a main borehole provided by an embodiment of the application; Figure 4 is a top view of the cross section of a first borehole in the main borehole provided by an embodiment of the application; Figure 5 is a front view of the structure of a branch well provided by an embodiment of the application; Figure 6 is a top view of the cross section of a second borehole in the branch well provided by an embodiment of the application; Figure 7 is a schematic diagram of a designed natural gas hydrate multi-lateral well mining experiment scheme provided by an embodiment of the application, wherein, Figure 7 (a) is for changing the azimuth of the branch well, Figure 7 (b) is for changing the phase angle of the branch well, Figure 7 (c) is for changing the number of the branch well, Figure 7 (d) is for changing the length of the branch well.

[0024] BRIEF DESCRIPTION OF DRAWINGS 1, natural gas hydrate reservoir synthesis unit; 2, multi-lateral well mining simulation unit; 3, data monitoring and acquisition unit; 4, first valve; 5, second valve; 6, third valve; 7, computer; 11, reactor; 12, plunger pump; 13, gas cylinder; 14, cold water bath; 15, deionized water; 111, barrel; 112, flange plate; 113, water inlet; 114, first sensor socket; 115, second sensor socket; 116, gas inlet; 21, main borehole; 22, branch borehole; 23, sand control screen; 24, plug; 211, first hole; 221, second hole; 31, temperature sensor; 32, pressure sensor; 33, gas-liquid separation tank; 34, mass balance; 35, back pressure valve; 36, filter; 37, gas flow meter; 38, data acquisition terminal; 39, waste gas tank. DETAILED DESCRIPTION

[0025] Example embodiments of the present application will be described herein below with reference to the accompanying drawings. While example embodiments of the present application are illustrated, it is to be understood that the present application is not limited to the illustrated embodiments. Rather, the present application is to be fully commensurate with the broadest scope equivalently substituted hereto as set forth in the claims. Furthermore, the described features, advantages, and characteristics of the application can be combined in any suitable manner.

[0026] It is to be understood that the terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises", "comprising", "includes", "including" and "has" are inclusive and therefore specify the presence of stated features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order

[0027] Although the terms first, second, third, etc. can be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms can be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as "first", "second", and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

[0028] For the sake of convenience, spatial relative terms can be used herein for describing a relationship of one element or feature to another element or feature as illustrated in the figures, such as "inner", "outer", "inside", "outside", "lower", "upper", etc. Such spatial relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures.

[0029] At present, there is no precedent for natural gas hydrate multi-lateral well production in actual production tests, resulting in the lack of directly applicable experience at present. As an effective means for verifying the feasibility of natural gas hydrate multi-lateral well production, indoor simulation experiments currently lack experimental devices that can simulate various natural gas hydrate multi-lateral well production scenarios. Furthermore, the problem of how to scientifically optimize the design of the arrangement of the lateral well to achieve the maximization of natural gas hydrate production capacity has not been studied so far, making it difficult to determine the optimal well type arrangement scheme in actual production operations. These factors seriously restrict the development of natural gas hydrate multi-lateral well production technology and greatly hinder the industrialization application process. Therefore, the embodiment of the present application provides a natural gas hydrate multi-lateral well production simulation experiment device, which comprises a natural gas hydrate reservoir synthesis unit, a multi-lateral well production simulation unit and a data monitoring and acquisition unit. The multi-lateral well production simulation unit is arranged in the natural gas hydrate reservoir synthesis unit, and the multi-lateral well production simulation unit comprises a main borehole, a lateral well and a sand control screen. The main borehole and the lateral well are both hollow structures with one end closed and one end open. A plurality of first holes for connecting the open end or the plug of the lateral well are formed on the sidewall of the main borehole. A plurality of second holes for simulating the flow of reservoir fluid into the wellbore flow channel during the natural gas hydrate production process are formed on the sidewall of each lateral well. A sand control screen for simulating the real natural gas hydrate production sand control process is arranged on the outside of each lateral well. By changing the first holes connected to the lateral well or changing the number of second holes, the spatial geometric arrangement parameters of the lateral well are adjusted. The data monitoring and acquisition unit is connected to the natural gas hydrate reservoir synthesis unit, which is used to separate the gas-liquid mixture produced by the reservoir during the simulation of the natural gas hydrate production process, monitor the mass of water and the flow rate of gas in the produced gas-liquid mixture in real time, and simulate the real natural gas hydrate depressurization production process. The present application can simulate various natural gas hydrate multi-lateral production scenarios, adjust the spatial geometric arrangement of the lateral well flexibly, study the hydrate production capacity under different well type arrangement modes, determine the optimal lateral well arrangement mode with the maximum capacity as the evaluation standard, and help to increase the production and efficiency of natural gas hydrate production.

[0030] Example 1 As Figure 1 , Figure 2As shown, the embodiment provides a natural gas hydrate multi-lateral well exploitation simulation experiment device, which comprises a natural gas hydrate reservoir synthesis unit 1, a multi-lateral well exploitation simulation unit 2 and a data monitoring and acquisition unit 3. The natural gas hydrate reservoir synthesis unit 1 comprises a reaction kettle 11, a plunger pump 12, a gas cylinder 13 and a cold water bath 14. The multi-lateral well exploitation simulation unit 2 comprises a main borehole 21, a branch well 22 and a sand control screen 23. The main borehole 21 and the branch well 22 are both cylindrical structures with one end closed and one end open.

[0031] The main borehole 21 of the multi-lateral well exploitation simulation unit 2 is longitudinally arranged in the reaction kettle 11. The open end of the main borehole 21 is fixedly connected to the center of the bottom of the reaction kettle 11. The reaction kettle 11 is filled with sediment samples for simulating a natural gas hydrate reservoir. The reaction kettle 11 is used for simulating the formation space of natural gas hydrate in a natural environment. A plurality of first holes 211 are formed in the sidewall of the main borehole 21, and the first holes 211 are used for connecting the open end of the branch well 22 or a plug 24. A plurality of second holes 221 are formed in the sidewall of each branch well 22, and the second holes 221 are used for simulating the flow channel of reservoir fluid into the wellbore during the exploitation of natural gas hydrate. By changing the first holes 211 connected to the branch well 22 or changing the number of the second holes 221, the spatial geometric arrangement parameters of the branch well 22 (including the azimuth, phase angle, spacing, number and length of the branch well 22) can be flexibly adjusted. The sand control screen 23 is arranged outside each branch well 22, and all the second holes 221 on the branch well 22 are covered by the sand control screen 23. The sand control screen 23 is used for preventing the reservoir mud from entering the well during the exploitation of natural gas hydrate, thereby simulating the sand control process in the real exploitation of natural gas hydrate. The multi-lateral well exploitation simulation unit 2 is used for simulating the exploitation scene of the multi-lateral well 22 during the exploitation of natural gas hydrate.

[0032] The top of the reaction kettle 11 is connected to the plunger pump 12 through a first valve 4. The plunger pump 12 is used for providing water required for the synthesis of natural gas hydrate and controlling the pressure in the reaction kettle 11, so as to ensure that the pressure in the reaction kettle 11 reaches the phase equilibrium pressure required for the generation of hydrate during the generation of hydrate. The center of the bottom of the reaction kettle 11 is connected to the gas cylinder 13 through a second valve 5. The gas cylinder 13 is used for providing gas required for the synthesis of natural gas hydrate to the multi-lateral well exploitation simulation unit 2. The reaction kettle 11 is completely immersed in the cold water bath 14, and the cold water bath 14 is used for building a stable and controllable low-temperature environment.

[0033] The bottom center of the reactor 11 is also connected to the data monitoring and collecting unit 3, which is used to separate the gas-liquid mixture produced by the reservoir in the natural gas hydrate production process simulated by the multi-lateral well production simulation unit 2, to monitor the mass of water and the flow rate of gas in the produced gas-liquid mixture in real time, and to control the pressure in the reactor 11 by controlling the plunger pump 12, i.e., to control the reservoir pressure in the natural gas hydrate production process, thereby simulating the actual depressurization production process of natural gas hydrate.

[0034] In a preferred embodiment, the data monitoring and collecting unit 3 includes a temperature sensor 31, a pressure sensor 32, a gas-liquid separation tank 33, a mass balance 34, a back pressure valve 35, a filter 36, a gas flow meter 37, and a data collection terminal 38.

[0035] The temperature sensor 31 and the pressure sensor 32 are arranged at the top of the reactor 11 and are used to monitor the temperature and pressure of the natural gas hydrate reservoir in the reactor 11 in real time. The gas-liquid separation tank 33 is placed on the mass balance 34, the inlet of the gas-liquid separation tank 33 is connected to the bottom center of the reactor 11 in sequence through the back pressure valve 35, the filter 36, and the third valve 6, and the outlet of the gas-liquid separation tank 33 is connected to the gas flow meter 37. The gas-liquid separation tank 33 is used to separate the gas-liquid mixture produced by the reservoir in the natural gas hydrate production process by gravity and store the separated water. The mass balance 34 is used to weigh the mass of water produced by the reservoir in the natural gas hydrate production process in real time to determine the water production rate in the natural gas hydrate production process. The pressure of the back pressure valve 35 is directly driven by the plunger pump 12, and the back pressure valve 35 is used to control the reservoir pressure in the natural gas hydrate production process to simulate the actual depressurization production process of natural gas hydrate. The filter 36 is a higher sand retention precision sand filter screen, which is used to deeply filter the gas-liquid mixture flowing into the well in the natural gas hydrate production process, prevent extremely fine silt carried by water from entering the back pressure valve 35, and thereby avoid the problems of unstable pressure control, failure, and even damage of the back pressure valve 35. The gas flow meter 37 is used to collect the flow rate of the gas separated by the gas-liquid separation tank 33.

[0036] The data collection terminal 38 is electrically connected to the temperature sensor 31, the pressure sensor 32, the mass balance 34, the back pressure valve 35, and the gas flow meter 37, respectively, and is used to collect data such as hydrate reservoir temperature, hydrate reservoir pressure, gas production rate, and water production rate, and to control the operation of the connected components.

[0037] Specifically, the outlet of the gas flow meter 37 is connected to a waste gas tank 39, which is used to store the gas separated by the gas-liquid separation tank 33.

[0038] Specifically, the data acquisition terminal 38 is also connected to the computer 7, which is used to store the data collected by the data acquisition terminal 38.

[0039] In a preferred embodiment, as shown in Figure 2 The reactor 11 includes a cylinder body 111 and a flange plate 112, wherein the top of the cylinder body 111 is sealingly connected to the flange plate 112 by an array of high-strength bolts, forming a cylindrical closed chamber with an inner diameter of 0.5 meters and a vertical height of 0.12 meters.

[0040] Specifically, the flange plate 112 is provided with a water inlet 113, a first sensor socket 114, and a second sensor socket 115, and the water inlet 113 is connected to the plunger pump 12. The first and second sensor sockets are used to set the temperature sensor 31 and the pressure sensor 32 inside the reactor 11.

[0041] Specifically, the cylinder body 111 is a hollow cylinder, constituting the chamber of the reactor 11. The bottom center of the cylinder body is provided with a gas inlet 116, which is connected to the main borehole 21 inside the reactor 11, and is connected to the gas cylinder 13 and the gas-liquid separation tank 33 outside the reactor 11. The gas inlet 116 is used to provide the gas required for the synthesis of natural gas hydrate into the reactor 11 during the synthesis of natural gas hydrate, and serves as a flow channel for gas and water production during the exploitation of natural gas hydrate.

[0042] In a preferred embodiment, the cold water bath 14 is composed of a cylindrical water tank filled with circulating cooling water, the temperature of which is controlled by a matching refrigeration system. The entire reactor 11 is completely immersed in the cold water bath 14 to build a stable and controllable low-temperature environment, thereby achieving precise control of the temperature of the sediment sample in the reactor 11, ensuring that the temperature in the reactor reaches the phase equilibrium temperature required for hydrate formation during hydrate synthesis.

[0043] In a preferred embodiment, as shown in Figure 3 The open end of the main borehole 21 is sealingly connected to the gas inlet 116 by threads, serving as the outlet for gas and water production. Five groups of first holes 211 are uniformly arranged in the vertical direction on the main borehole 21, with an included angle of 45° between adjacent first holes 211 and a spacing of 2 centimeters between adjacent first holes 211. Four groups of first holes 211 are uniformly arranged in the horizontal direction on the main borehole 21, with an included angle of 90° between adjacent first holes 211, as shown in Figure 4 By changing the position of the branch well 22 connected to the first hole 211, the spatial geometric arrangement parameters of the branch well can be flexibly adjusted.

[0044] In a preferred embodiment, as shown in Figure 5As shown, the open end of the branch well 22 is connected to the first hole 211 by a threaded sealing. The second holes 221 on the branch well 2 are evenly arranged in several groups in the vertical direction, and the included angle between adjacent second holes 221 is 45°, and the spacing between adjacent second holes 221 is 5 mm. The second holes 221 on the branch well 2 are evenly arranged in four groups in the horizontal direction, and the included angle between adjacent second holes 221 is 90°, as shown in Figure 6 As shown, by changing the number of groups of second holes 221 on the branch well 22, the length of the branch well 22 can be flexibly adjusted.

[0045] Specifically, the first hole 211 and the second hole 221 are both circular structures.

[0046] In a preferred embodiment, the gas required for the generation of natural gas hydrates is methane gas, and the water required for the generation of natural gas hydrates is deionized water 15.

[0047] Example 2 The present embodiment provides a method for determining the optimal well type arrangement of a natural gas hydrate multi-branch well, comprising the following steps: 1) Using the control variable method, based on the spatial geometric arrangement parameters of the branch well 22 (the azimuth of the branch well, the phase angle, the spacing, the number, the length, etc.), design a natural gas hydrate multi-branch well production experiment scheme, wherein several control experiments are set in each natural gas hydrate multi-branch well production experiment scheme.

[0048] Specifically, based on the azimuth of the branch well, the designed natural gas hydrate multi-branch well production experiment scheme is: Five groups of control experiments are designed, and each branch well 22 in each group of control experiments is on the same horizontal plane. Each time, only the position of each branch well 22 in the vertical direction of the main hole 21 is changed, including the top of the hydrate reservoir, the upper middle of the hydrate reservoir, the middle of the hydrate reservoir, the lower middle of the hydrate reservoir, and the bottom of the hydrate reservoir, while the other spatial geometric arrangement parameters of each branch well 22 remain unchanged.

[0049] Specifically, based on the phase angle of the branch well, the designed natural gas hydrate multi-branch well production experiment scheme is: Five groups of control experiments are designed, and each time only the phase angle of each adjacent branch well 22 (vertically the shortest distance) in the horizontal direction is changed, including 0°, 45°, 90°, 135° and 180°, while the other spatial geometric arrangement parameters of each branch well 22 remain unchanged, wherein the two branch wells 22 with the shortest vertical distance are adjacent branch wells 22.

[0050] Specifically, based on the spacing of the branch well, the designed natural gas hydrate multi-branch well production experiment scheme is: A control experiment is designed for 5 groups, and only the distance of each adjacent branch well 22 in the vertical direction is changed each time, including a first distance, a second distance, a third distance, a fourth distance and a fifth distance, wherein the first distance refers to the distance between adjacent branch wells 22 being zero, the second distance refers to the distance between adjacent branch wells 22 being one sixth of the vertical height of the reaction kettle 11, the third distance refers to the distance between adjacent branch wells 22 being two sixths of the vertical height of the reaction kettle 11, the fourth distance refers to the distance between adjacent branch wells 22 being three sixths of the vertical height of the reaction kettle 11, and the fifth distance refers to the distance between adjacent branch wells 22 being four sixths of the vertical height of the reaction kettle 11, while other spatial geometric arrangement parameters of each branch well 22 remain unchanged.

[0051] Specifically, based on the number of branch wells, the designed natural gas hydrate multi-branch well exploitation experiment scheme is as follows: A control experiment is designed for 5 groups, and only the number of branch wells 33 is changed each time, including 1, 2, 3, 4 and 5, while other spatial geometric arrangement parameters of each branch well 22 remain unchanged.

[0052] Specifically, based on the length of the branch well, the designed natural gas hydrate multi-branch well exploitation experiment scheme is as follows: A control experiment is designed for 5 groups, and only the number of branch wells 33 is changed each time, including 1, 2, 3, 4 and 5, while other spatial geometric arrangement parameters of each branch well 22 remain unchanged.

[0053] Specifically, as shown in Figure 7 , it is a schematic diagram of the designed natural gas hydrate multi-branch well exploitation experiment scheme.

[0054] 2) Based on the designed natural gas hydrate multi-branch well exploitation experiment scheme, the exploitation simulation experiment device of embodiment 1 is set up, and the natural gas hydrate synthesis process is simulated, specifically as follows: 2.1) Based on the designed natural gas hydrate multi-branch well exploitation experiment scheme, a multi-branch well exploitation simulation unit 2 is set up: 2.1.1) The sand control screen 23 is arranged on the side wall of the branch well 22, so as to ensure that the second hole 221 on the branch well 22 is covered by the sand control screen 23.

[0055] 2.1.2) Based on the designed natural gas hydrate multi-branch well exploitation experiment scheme, the branch well 22 is installed on the first hole 211 of the main well hole 21.

[0056] 2.1.3) For the first hole 211 of the main well hole 21 on which the branch well 22 is not installed, a thread protector 24 is used for sealing. 2.1.4) Install the main wellbore 21 at the gas injection port 116 of the reactor 11.

[0057] 2.2) Set up the natural gas hydrate reservoir synthesis unit 1, place the set up multi-branch well production simulation unit 2 into the reactor 11 of the natural gas hydrate reservoir synthesis unit 1, and perform gas injection and exhaust operation to the reactor 11 through the gas cylinder 13 and the back pressure valve 35, completely remove the residual air in the reactor 11, and obtain the prepared reactor 11: 2.2.1) Mix the dry coarse quartz sand, fine quartz sand, montmorillonite, illite, kaolin and chlorite according to the equal mass ratio to prepare the sediment sample.

[0058] 2.2.2) Fill the prepared sediment sample into the reactor 11, and weigh the sediment sample by the mass balance 34 before each filling, and record the mass of the sediment sample filled into the reactor 11.

[0059] 2.2.3) After the reactor 11 is filled with the sediment, the cylinder body 111 and the flange plate 112 are sealed and connected by bolts.

[0060] 2.2.4) Open the gas cylinder 13 and the second valve 5, and inject gas to pressurize the reactor 11, until the pressure sensor 32 detects that the pressure in the reactor 11 rises to 3 MPa, and then close the gas cylinder 13 and the second valve 5.

[0061] 2.2.5) Let the reactor 11 stand for a period of time to detect the air tightness of the reactor 11, if the pressure in the reactor 11 remains unchanged for five hours, it is determined that the chamber air tightness of the reactor 11 is good.

[0062] 2.2.6) After the sealing detection is completed, immerse the entire reactor 11 in the circulating cold water bath 7.

[0063] 2.2.7) Open the third valve 6 and the back pressure valve 35, and exhaust the gas in the reactor 11, until the pressure sensor 32 detects that the pressure in the reactor 11 decreases to 0, and then close the third valve 6 and the back pressure valve 35.

[0064] 2.2.8) Open the gas cylinder 13 and the second valve 5 again, and inject the gas required for the formation of natural gas hydrate into the reactor 11 through the gas injection port 116 again, until the pressure sensor 32 detects that the pressure in the reactor 11 rises to 3 MPa again.

[0065] 2.2.9) Repeat the above exhaust and gas injection operation 3 times to completely remove the residual air in the reactor 11.

[0066] 2.3) Based on the prepared reactor 11, simulate the natural gas hydrate synthesis process: 2.3.1 ) Open the gas cylinder 13 and the second valve 5 again, inject the gas required for the formation of natural gas hydrate into the reactor 11 through the gas injection port 116, and close the gas cylinder 13 and the second valve 5 when the pressure sensor 32 detects that the pressure in the reactor 11 rises from 3 MPa to 7 MPa.

[0067] 2.3.2) After the temperature and pressure in the reactor 11 are stable, collect the temperature and pressure data in the reactor 11 in real time through the temperature sensor 31 and the pressure sensor 32, and start the plunger pump 12, open the first valve 4, and slowly and uniformly inject the water required for the formation of natural gas hydrate into the reactor 11 through the water injection port 113 until the pressure in the reactor 11 rises from 7 MPa to 9 MPa, then close the plunger pump 12 and the first valve 4, and stop the water injection operation.

[0068] 2.3.3) Set the water bath temperature of the cold water bath 14 to 2°C, then start the refrigeration system of the cold water bath 14 to continuously cool the reactor 11. The decrease in the temperature of the deposits in the reactor 11 will trigger the formation of a large amount of hydrate, and the gas in the reactor 11 will be gradually consumed, thereby causing the pressure in the reactor 11 to decrease significantly.

[0069] 2.3.4) When the pressure sensor 32 detects that the pressure drop in the reactor 11 is less than 0.02 MPa / h for two hours, it indicates that the hydrate formation rate in the reactor 11 has slowed down significantly. Open the plunger pump 12 and the first valve 4 again, inject the water required for the formation of natural gas hydrate into the reactor 11, and close the plunger pump 12 and the first valve 4 when the pressure in the reactor 11 rises to 9 MPa again. Record the amount of water injected into the reactor 11 in detail. The increase in the pressure in the reactor 11 will again trigger the formation of a large amount of hydrate, and the remaining gas will continue to be consumed, thereby causing the pressure in the reactor 11 to decrease significantly again.

[0070] 2.3.5) Repeat the operation of the above step 2.3.4), and record the amount of water injected into the reactor 11 after each water injection operation in detail. When the amount of water injected into the reactor 11 in the next water injection stage is less than 30 mL, it is considered that the natural gas hydrate synthesis process is complete.

[0071] 3) Based on the set simulation experiment device, simulate the natural gas hydrate production process, specifically: 3.1) After the simulation of the natural gas hydrate synthesis process is complete, start the plunger pump 12, open the first valve 4, and finely control the pressure of the back pressure valve 35 through the data acquisition terminal 38 to depressurize the hydrate reservoir in the reactor 11 at a constant depressurization rate of 1 MPa / h.

[0072] 3.2) Temperature sensor 31 and pressure sensor 32 collect the temperature and pressure change data of the reservoir in real time during the natural gas hydrate exploitation process.

[0073] 3.3) Gas-liquid separation tank 33 separates the gas-liquid mixture produced during the natural gas hydrate exploitation process.

[0074] 3.4) Mass balance 34 weighs the mass of water collected in gas-liquid separation tank 33.

[0075] 3.5) Gas flow meter 37 monitors the gas flow separated by gas-liquid separation tank 33, and the final gas production is recycled to waste gas tank 39.

[0076] 3.6) When the pressure of the natural gas hydrate reservoir in reactor 11 drops to 2 MPa, plunger pump 12 is switched from constant rate decompression mode to constant pressure mode, so that the pressure of back pressure valve 35 is always maintained at 2 MPa. When gas flow meter 37 no longer detects gas production for a continuous half hour, it is determined that the hydrate in reactor 11 has been completely decomposed, and the simulation of the natural gas hydrate exploitation process ends. The gas production rate monitored by gas flow meter 37 during the natural gas hydrate exploitation process is recorded in detail for subsequent productivity evaluation.

[0077] 4) Based on the simulation results of the natural gas hydrate synthesis process and the natural gas hydrate exploitation process of each natural gas hydrate multi-lateral well exploitation experiment scheme, the optimal well type arrangement of the multi-lateral well is determined, specifically: 4.1) According to each natural gas hydrate multi-lateral well exploitation experiment scheme designed in step 1), the simulation of the natural gas hydrate synthesis process and the natural gas hydrate exploitation process of step 2) and step 3) is carried out respectively, and the cumulative gas production data of each natural gas hydrate multi-lateral well exploitation experiment scheme is recorded in detail through data monitoring and acquisition unit 3.

[0078] 4.2) Comparative analysis of the cumulative gas production data of different control experiments in each natural gas hydrate multi-lateral well exploitation experiment scheme determines the orientation, phase angle, spacing, number and length of the branch well that can maximize the productivity of the natural gas hydrate multi-lateral well exploitation, and further determines the optimal well type arrangement of the multi-lateral well.

[0079] Specifically, the productivity maximization means the highest cumulative gas production in the same length of natural gas hydrate exploitation, and when the productivity is maximized, the orientation, phase angle, spacing, number or length of the corresponding control experiment is the optimal orientation, phase angle, spacing, number or length of the multi-lateral well. The optimal well type arrangement of the multi-lateral well includes the optimal orientation, phase angle, spacing, number and length of the multi-lateral well.

[0080] The above embodiments are only used for illustrating the present application, wherein the structure, connection mode and manufacturing process of each component can be changed, and any equivalent transformation and improvement based on the technical scheme of the present application should not be excluded from the protection scope of the present application.

Claims

1. A simulation experimental device for the exploitation of multi-branch wells of natural gas hydrates, characterized in that, It includes a natural gas hydrate reservoir synthesis unit, a multi-branch well production simulation unit, and a data monitoring and acquisition unit; The multi-branch well production simulation unit is set up in the natural gas hydrate reservoir synthesis unit. The multi-branch well production simulation unit includes a main wellbore, branch wells and sand control screens. The main wellbore and branch wells are both hollow structures with one end closed and the other end open. The main wellbore has several first holes on its sidewall for connecting the opening end or plug of the branch well. Each branch well has several second holes on its sidewall for simulating the flow channel of reservoir fluid entering the wellbore during natural gas hydrate extraction. Each branch well is covered with a sand-proof screen to simulate the sand-proof process in real natural gas hydrate extraction. The spatial geometric arrangement parameters of the branch wells can be adjusted by changing the number of the first holes or the number of the second holes connected to the branch wells. The data monitoring and acquisition unit is connected to the natural gas hydrate reservoir synthesis unit and is used to separate the gas-liquid mixture produced by the reservoir during the simulated natural gas hydrate extraction process, monitor the water quality and gas flow rate in the produced gas-liquid mixture in real time, and simulate the real natural gas hydrate depressurization extraction process.

2. The experimental apparatus for simulating the exploitation of multi-branched natural gas hydrate wells as described in claim 1, characterized in that, The natural gas hydrate reservoir synthesis unit includes a reaction vessel, a plunger pump, gas cylinders, and a cold water bath; The main wellbore is arranged longitudinally inside the reactor. The opening end of the main wellbore is fixedly connected to the bottom center of the reactor. The reactor is filled with sediment samples to simulate natural gas hydrate reservoirs. The reactor is used to simulate the formation space of natural gas hydrates in the natural environment. The top of the reactor is connected to the plunger pump for providing water required for the synthesis of natural gas hydrates; the bottom center of the reactor is connected to the gas cylinder for providing gas required for the synthesis of natural gas hydrates to the multi-branch well production simulation unit; the reactor is completely submerged in the cold water bath. The data monitoring and acquisition unit is also connected to the center of the bottom of the reactor.

3. The experimental apparatus for simulating the production of multi-branched natural gas hydrate wells as described in claim 2, characterized in that, The data monitoring and acquisition unit includes a temperature sensor, a pressure sensor, a gas-liquid separator, a mass balance, a back pressure valve, a filter, a gas flow meter, and a data acquisition terminal. The temperature and pressure sensors are located at the top of the reactor and are used to monitor the temperature and pressure of the natural gas hydrate reservoir inside the reactor in real time. The gas-liquid separator is placed on the mass balance. The inlet of the gas-liquid separator is connected to the bottom center of the reactor via the back pressure valve and a filter. The outlet of the gas-liquid separator is connected to the gas flow meter. The gas-liquid separator is used to separate the gas-liquid mixture produced from the reservoir during the simulated natural gas hydrate extraction process and to store the separated water. The mass balance is used to weigh the mass of water produced from the reservoir during the natural gas hydrate extraction process in real time to determine the water production rate during the extraction process. The back pressure valve is used to control the reservoir pressure during the natural gas hydrate extraction process. The filter is used to filter the gas-liquid mixture flowing into the well during the natural gas hydrate extraction process. The gas flow meter is used to collect the flow rate of the gas separated by the gas-liquid separator. The data acquisition terminal is electrically connected to the temperature sensor, pressure sensor, mass balance, back pressure valve, and gas flow meter, respectively, and is used to collect hydrate reservoir temperature, hydrate reservoir pressure, gas production rate, and water production rate, as well as control the operation of each connected component.

4. The experimental apparatus for simulating the production of multi-branched natural gas hydrate wells as described in claim 2, characterized in that, The reactor includes a cylindrical body and a flange, wherein the top of the cylindrical body is sealed to the flange to form a closed chamber.

5. The experimental apparatus for simulating the exploitation of multi-branched natural gas hydrate wells as described in claim 1, characterized in that, The opening end of the main wellbore is sealed to the bottom of the reactor and serves as the outlet for gas and water production; five sets of first holes are evenly distributed in the vertical direction on the main wellbore, with an included angle of 45° between adjacent first holes; four sets of first holes are evenly distributed in the horizontal direction on the main wellbore, with an included angle of 90° between adjacent first holes.

6. The experimental apparatus for simulating the exploitation of multi-branched natural gas hydrate wells as described in claim 1, characterized in that, The opening end of the branch well is sealed to the first hole; several groups of second holes on the branch well are evenly distributed in the vertical direction, and the included angle between adjacent second holes is 45°; four groups of second holes on the branch well are evenly distributed in the horizontal direction, and the included angle between adjacent second holes is 90°.

7. A method for determining the optimal well layout for multi-branched wells containing natural gas hydrates, characterized in that, include: Using the controlled variable method, an experimental scheme for the exploitation of multi-branch wells of natural gas hydrate was designed based on the spatial geometric arrangement parameters of the branch wells. Several control experiments were set up in each experimental scheme for the exploitation of multi-branch wells of natural gas hydrate. Based on the designed experimental scheme for the exploitation of multi-branch wells for natural gas hydrates, an exploitation simulation experimental device as described in any one of claims 1 to 6 is set up to simulate the natural gas hydrate synthesis process; The extraction process of natural gas hydrates was simulated using a set-up mining simulation experimental device. Based on the simulation results of the natural gas hydrate synthesis process and the natural gas hydrate extraction process in various experimental schemes for multi-branch well development of natural gas hydrate, the optimal well layout for multi-branch wells is determined.

8. The method for determining the optimal well layout of multi-branch wells for natural gas hydrates as described in claim 7, characterized in that, The experimental scheme for the production of multi-branch wells based on the design of natural gas hydrates includes setting up a production simulation experimental device and simulating the natural gas hydrate synthesis process, including: Based on the designed experimental scheme for multi-branch well exploitation of natural gas hydrates, a multi-branch well exploitation simulation unit was set up. A natural gas hydrate reservoir synthesis unit is set up, and the set multi-branch well production simulation unit is placed into the reaction vessel of the natural gas hydrate reservoir synthesis unit. Gas is injected and vented into the reaction vessel through gas cylinders and back pressure valves to completely remove the residual air in the reaction vessel and obtain the prepared reaction vessel. The natural gas hydrate synthesis process was simulated using the prepared reaction vessel.

9. The method for determining the optimal well layout of multi-branch wells for natural gas hydrates as described in claim 7, characterized in that, The established mining simulation experimental device simulates the natural gas hydrate mining process, including: Start the plunger pump and adjust the pressure of the back pressure valve to depressurize the hydrate reservoir in the reactor; Temperature and pressure sensors collect real-time data on temperature and pressure changes in the reservoir during the extraction of natural gas hydrates. Gas-liquid separators separate the gas-liquid mixture produced during the extraction of natural gas hydrates. The mass balance is used to weigh the mass of water collected in the gas-liquid separator. The gas flow meter monitors the flow rate of the gas separated by the gas-liquid separator. When the pressure of the natural gas hydrate reservoir in the reactor drops to the preset threshold, the plunger pump is switched from constant rate depressurization mode to constant pressure mode, so that the pressure of the back pressure valve is always maintained at the preset threshold until the gas flow meter no longer detects gas production for a continuous preset time. At this point, it can be determined that the hydrate in the reactor has been completely decomposed, and the simulation of the natural gas hydrate extraction process ends.

10. The method for determining the optimal well layout of multi-branch wells for natural gas hydrates as described in claim 7, characterized in that, Based on the simulation results of the natural gas hydrate synthesis and extraction processes in various multi-branch well production experiments, the optimal well layout for multi-branch wells is determined, including: According to the experimental schemes for the production of multi-branch wells of natural gas hydrates designed in the middle, the natural gas hydrate synthesis process and the natural gas hydrate production process were simulated respectively, and the cumulative gas production data of each experimental scheme for the production of multi-branch wells of natural gas hydrates were recorded through the data monitoring and acquisition unit. By comparing and analyzing the cumulative gas production data of different control experiments in various gas hydrate multi-branch well production experimental schemes, the spatial geometric layout parameters of the branch wells that can maximize the production capacity of gas hydrate multi-branch wells are determined, and then the optimal well type layout of multi-branch wells is determined.

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