Experimental device and method for evaluating drilling mode of natural gas hydrate reservoir

Abstract

The invention provides a natural gas hydrate reservoir horizontal well drilling mode evaluation experiment device and method. The natural gas hydrate reservoir horizontal well drilling mode evaluation experiment device comprises a constant-temperature box, a hydrate sediment synthesis system, a drilling system and a borehole shape observation system, the compound sediment synthesis system is provided with a gas inlet and a liquid inlet; the drilling system is arranged in the horizontal direction, communicates with the first side of the hydrate sediment synthesis system and is used for drilling into the hydrate sediment synthesis system. The well shape observation system is arranged on the opposite side of the drilling system in the horizontal direction, and the well shape observation system communicates with the second side of the hydrate sediment synthesis system and is used for observing the shape of a drilled well, the roughness degree of the well wall and the deformation degree of the long-term well. The device can simulate the drilling process of the natural gas hydrate reservoir horizontal well; the method realizes the analysis and evaluation of the borehole shape and well wall change characteristics of the horizontal well, and provides a reference basis for drilling parameters required in a natural gas hydrate drilling construction process.

Description

Technical Field

[0001] The invention relates to the technical field of natural gas hydrate drilling, and in particular to a natural gas hydrate reservoir drilling mode evaluation experimental device and method. Background Art

[0002] As an important potential strategic alternative energy source, natural gas hydrates have become the focus of world energy research, and realizing their commercial development has become an important development direction of my country's energy strategy. In 2017, my country successfully implemented the first round of natural gas hydrate trial production in the Shenhu area of ​​the South China Sea. In the same year, hydrates were listed as the 173rd mineral species in my country, and their industrial development was put on the agenda. In 2020, the second round of trial production was carried out in the Shenhu area of ​​the South China Sea for the first time using horizontal wells, which greatly increased natural gas production. The success of the two rounds of trial production proved that the natural gas hydrate reservoirs in the South my country Sea are technically feasible for exploitation, and the use of horizontal wells can greatly increase natural gas production. Therefore, in order to realize the commercial utilization of natural gas hydrates as soon as possible, complex structure wells have become an important way to develop hydrates in the future, and higher requirements have been put forward for the drilling of natural gas hydrate reservoirs.

[0003] Natural gas hydrate reservoirs have the characteristics of weak cementation, low strength, and non-diagenesis, which can easily cause problems such as wellbore instability and formation collapse during drilling. At the same time, temperature and pressure fluctuations during drilling can cause hydrate decomposition, resulting in a significant decrease in reservoir strength, further increasing drilling risks. Therefore, studying the pore formation characteristics and reservoir response characteristics during the drilling process of natural gas hydrate reservoirs is of great significance to the development and utilization of natural gas hydrates in my country.

[0004] The current hydrate reservoir drilling methods and drilling process simulation devices have the following shortcomings: First, it is not possible to simulate multiple drilling processes, and it is impossible to compare the differences in the hole-forming process and the formed holes under different drilling methods, making it difficult to optimize different drilling methods; second, it is impossible to observe and analyze the drilled wells, and the analysis of the wellbore morphology is not in-depth enough; third, there is a lack of analysis and discussion on parameters such as drill bit size, hydraulic parameters, drilling fluid properties, and drilling speed during the drilling of horizontal wells in hydrate reservoirs, making it difficult to clarify the relationship between drilling process parameters and rock breaking efficiency, which slows down the development of efficient drilling methods. Summary of the invention

[0005] In view of this, the present invention proposes an experimental device and method for evaluating the drilling method of a horizontal well in a natural gas hydrate reservoir, so as to study the key issues of the wellbore formation characteristics and stability evaluation of horizontal wells under the conditions of mechanical drill bit and hydraulic jet drilling.

[0006] The present invention proposes an experimental device for evaluating drilling methods of horizontal wells in natural gas hydrate reservoirs, comprising: a constant temperature box and a hydrate deposit synthesis system, a drilling system and a wellbore morphology observation system placed in the constant temperature box; wherein the hydrate deposit synthesis system is provided with a gas inlet and a liquid inlet, for respectively inputting the gas and water required for synthesizing hydrate deposits to synthesize hydrate deposits; the drilling system is arranged in a horizontal direction and is connected to a first side of the hydrate deposit synthesis system, for drilling into the hydrate deposits in the hydrate deposit synthesis system; the wellbore morphology observation system is arranged in a horizontal direction on the opposite side of the drilling system, and the wellbore morphology observation system is connected to a second side of the hydrate deposit synthesis system, for observing the shape of the drilled wellbore, the roughness of the well wall and the deformation degree of the long-term wellbore.

[0007] Furthermore, in the above-mentioned natural gas hydrate reservoir drilling method evaluation experimental device, the hydrate sediment synthesis system includes: a main reactor, a first connecting section, a second connecting section and a third connecting section connected to each other; wherein, the first side of the main reactor is connected to the drilling system through the first connecting section, the second side of the main reactor is connected to the wellbore morphology observation system through the second connecting section, and the top of the main reactor is connected to the collection system through the third connecting section.

[0008] Furthermore, in the above-mentioned natural gas hydrate reservoir drilling method evaluation experimental device, the main reactor is a T-shaped high-pressure reactor.

[0009] Furthermore, in the above-mentioned natural gas hydrate reservoir drilling method evaluation experimental device, a temperature sensor, a pressure sensor and an acoustic wave probe are arranged on the outside of the first connecting section to monitor the change pattern of the physical property parameters of the hydrate sediment during the drilling process.

[0010] Furthermore, in the above-mentioned natural gas hydrate reservoir drilling method evaluation experimental device, the hydrate sediment synthesis system also includes: a simulated screen pipe; wherein, The upper end of the simulated sieve tube is passed through the third connecting section, and the lower end of the simulated sieve tube is buried in the main reactor.

[0011] Furthermore, in the above-mentioned natural gas hydrate reservoir drilling method evaluation experimental device, the drilling system includes: a drilling rig, a thruster and a drilling fluid storage tank; wherein the drill bit of the drilling rig is arranged toward the reactor to contact the hydrate sediment; the drill rod of the drilling rig is arranged close to the driving end of the drilling rig, and a drilling fluid inlet and a drilling fluid outlet are provided on the drill rod to be connected to the drilling fluid storage tank respectively; one end of the thruster is connected to the driving end of the drilling rig, and the other end is connected to the first side of the reactor through a fixed frame.

[0012] Furthermore, in the above-mentioned natural gas hydrate reservoir drilling method evaluation experimental device, the liquid outlet end of the drilling fluid storage tank is connected to the second pump body, and a sixth valve is arranged between the two; the liquid outlet end of the second pump body is connected to the drilling fluid inlet on the drill pipe, and a fourth flow meter is arranged between the two; the liquid inlet end of the drilling fluid tank is connected to the drilling fluid outlet on the drill pipe, and a seventh valve is arranged between the two.

[0013] Furthermore, in the above-mentioned natural gas hydrate reservoir drilling method evaluation experimental device, the fixed frame includes: a first fixed plate and a plurality of fixed rods arranged in a horizontal direction; wherein each of the fixed rods is passed through the fixed plate and connected to the first side of the reactor, and the drilling rig is connected to the fixed frame through a support rod; wherein the support rod is slidably arranged between two relatively arranged fixed rods.

[0014] Furthermore, in the above-mentioned natural gas hydrate reservoir drilling method evaluation experimental device, the wellbore morphology observation system includes: an endoscope and a thrust rod; wherein, the endoscope passes through the first end cover and contacts the hydrate sediment in the hydrate sediment synthesis system; a fixed sleeve fixed to the center of the left end cover is provided on the outside of the thrust rod to maintain sealing and pressure during the pushing process of the endoscope.

[0015] The gas hydrate reservoir drilling method evaluation experimental device of the present invention prepares hydrate sediments through a hydrate sediment synthesis system, and by setting a horizontal drilling system, a mechanical drill bit or a hydraulic jet drill bit is used to simulate the drilling process of a gas hydrate reservoir horizontal well under conditions of different drill bit sizes and drilling parameters; further, the shape of the drilled wellbore, the roughness of the wellbore wall, and the long-term deformation degree of the wellbore are observed through a wellbore morphology observation system, thereby realizing the analysis and evaluation of the wellbore morphology and wellbore wall change characteristics, and providing a reference basis for the drilling parameters required for the gas hydrate drilling construction process.

[0016] On the other hand, the present invention also proposes an experimental method for evaluating the drilling method of a natural gas hydrate reservoir, comprising the following steps: Step 1, connecting a hydrate sediment synthesis system, a drilling system and a wellbore morphology observation system, and simultaneously connecting a gas supply system and a liquid supply system to test the air tightness of the entire device; Step 2, injecting gas and water required for synthesizing hydrate deposits into the hydrate deposit synthesis system through the gas supply system and the liquid supply system, setting the thermostat to a preset temperature, cooling the inside of the hydrate deposit, and synthesizing the hydrate deposit required for the test; Step 3, starting the drilling system, pushing the drill bit of the drilling rig forward at a certain speed, simulating the horizontal well section drilling process; and monitoring the dynamic response characteristics of the hydrate deposits during the drilling process; Step 4, withdrawing the drill bit, and then observing the morphology, roughness and deformation characteristics of the drilled wellbore through the wellbore morphology observation system, analyzing the morphological characteristics of the drilled wellbore in the hydrate deposit and evaluating the stability of the wellbore; Step 5, by comparing the morphological characteristics and stability of the drilled wells under different working conditions, combined with the drilling efficiency and hydrate reservoir fragmentation characteristics in the simulated drilling process, according to the characteristics of hydrate sediments, analyze the influence mechanism of various working parameters and construction process parameters on the drilling efficiency, and optimize the combination of natural gas hydrate reservoir drilling parameters.

[0017] The experimental method for evaluating the natural gas hydrate reservoir drilling method provided by the present invention can simulate the drilling process of a full-size drill bit in a natural gas hydrate reservoir horizontal well, and monitor the response characteristics of the reservoir during the drilling process in real time; according to different hydrate reservoir characteristics, hydrate sediment samples are synthesized in situ, and the drilling process of a full-size drill bit in the hydrate reservoir horizontal well is simulated through a drilling fluid circulation system and a drilling system. At the same time, the changes in reservoir physical properties during the drilling process are analyzed by monitoring the changes in acoustic parameters, electrical parameters and pressure, and the response characteristics and reservoir fragmentation of the reservoir during the drilling process are evaluated. After the drilling process is completed, the shape of the drilled wellbore, the roughness of the wellbore wall and the long-term deformation of the wellbore are observed through the wellbore morphology observation system, realizing the analysis and evaluation of the wellbore morphology and wellbore wall change characteristics; the morphological characteristics and stability of the drilled wellbore under different working conditions are compared and analyzed, and the full-size drill bit is optimized to simulate the drilling working parameters and hydraulic parameters during the drilling process, and the drill bit size, hydraulic parameters, drilling fluid properties and other parameters are determined. By comparing the drilling speed, the drilling efficiency is optimized, and then the best drilling plan is formulated in combination with the hydrate reservoir properties and drilling requirements, providing a reference basis for natural gas hydrate drilling construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings: Figure 1 A schematic diagram of the structure of a natural gas hydrate reservoir drilling method evaluation experimental device provided in an embodiment of the present invention; Figure 2 A schematic diagram of the arrangement of various sensors in a natural gas hydrate reservoir drilling method evaluation experimental device provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0019] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present disclosure and to be able to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features described in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0020] Device Example: See also Figure 1 The natural gas hydrate reservoir drilling method evaluation experimental device of the embodiment of the present invention includes: a constant temperature box 1 and a hydrate deposit synthesis system 2, a drilling system 3 and a wellbore morphology observation system 4 placed in the constant temperature box 1; wherein the hydrate deposit synthesis system 2 is provided with a gas inlet a and a liquid inlet b, for respectively inputting the gas and water required for synthesizing the hydrate deposit to synthesize the hydrate deposit c; the drilling system 3 is arranged in a horizontal direction and is connected to a first side of the hydrate deposit synthesis system 2, for drilling into the hydrate deposit in the hydrate deposit synthesis system 2; the wellbore morphology observation system 4 is arranged in a horizontal direction on the opposite side of the drilling system 3, and the wellbore morphology observation system 4 is connected to a second side of the hydrate deposit synthesis system 2, for observing the shape of the drilled wellbore, the roughness of the wellbore wall and the deformation degree of the long-term wellbore.

[0021] Specifically, the hydrate sediment synthesis system 2 includes: a main reactor 21, a first connecting section 22, a second connecting section 23 and a third connecting section 24 connected to each other; wherein, the first side of the main reactor 21 is connected to the drilling system 3 through the first connecting section 22, the second side of the main reactor 21 is connected to the wellbore morphology observation system 4 through the second connecting section 23, and the top of the main reactor 21 is connected to the collection system 5 through the third connecting section 24.

[0022] Furthermore, the main reactor 21 can be a horizontally placed T-shaped high-pressure reactor, that is, it is composed of a vertical wellbore simulation part and a radial horizontal well simulation part. The main reactor 21 can withstand a pressure of 30 MPa and is filled with the prepared hydrate sediment.

[0023] The first connecting section 22 may be a cylindrical structure, and a cover 221 is provided at its end, and the cover 220 is connected to the main reactor 21 through a plurality of first screws 221. The drilling system 3 is connected to the first side of the main reactor 21 through a fixed frame, and the connection between the two has high sealing performance, which meets the requirements for hydrate sediment drilling. Furthermore, a temperature sensor, a pressure sensor and an acoustic wave probe are provided on the outside of the first connecting section 22 to monitor the change law of parameters such as hydrate sediment temperature, pore pressure, longitudinal and transverse wave waveforms and acoustic wave velocity during drilling.

[0024] The second connection section 23 may be a circular end cover structure, which is connected to the main reactor 21 via a plurality of second screws 231 ; the wellbore morphology observation system 4 is disposed through the second connection section 23 to contact the hydrate deposits in the main reactor 21 .

[0025] The third connecting section 24 is a cylindrical structure, which is connected to the main reactor 21 through a plurality of third screws 241 passing through the upper end cover 241. A fixed interface 240 is provided in the middle of the third connecting section 24, which seals the top of the main reactor 21 through a high-pressure pipeline and is connected to the collection system 5.

[0026] The drill bit of the drilling system 3 may be a mechanical drill bit or a hydraulic jet drill bit to simulate the drilling process of a horizontal well in a natural gas hydrate reservoir under conditions of different drill bit sizes and drilling parameters.

[0027] The inlet of the collecting system 5 is communicated with the top of the hydrate sediment synthesis system 2 to collect the hydrate decomposition and the sand-carrying fluid generated by the decomposition.

[0028] Specifically, the collection system 5 includes: a gas-solid-liquid separator 51 and a liquid collecting tank 52 which are connected; wherein the inlet of the gas-solid-liquid separator 51 is connected to the outlet of the main reactor 21; and the outlet of the gas-solid-liquid separator 51 is connected to the inlet of the liquid collecting tank 52.

[0029] During specific implementation, a third flowmeter 211 and a fourth valve 212 are provided between the outlet of the main reactor 21 and the inlet of the gas-solid-liquid separator 51 for discharging the produced gas-liquid-solid mixed fluid; a one-way valve is provided between the first outlet of the gas-solid-liquid separator 51 and the inlet of the liquid collecting tank 52 for collecting the produced liquid after separation of gas and solid; a fifth valve 213 is provided at the second outlet of the gas-solid-liquid separator 51 for discharging the separated gas.

[0030] In this embodiment, seals are provided at the connection points between the main reactor 21 and the first connection section 22 , the second connection section 23 and the third connection section 24 to ensure good air tightness of the entire device.

[0031] Preferably, the hydrate sediment synthesis system 2 further includes: a simulated screen tube 25; wherein the upper end of the simulated screen tube is passed through the third connecting section 24, and the lower end of the simulated screen tube 25 is buried in the main reactor 21, and the surrounding area is filled with hydrate sediments, playing the role of a sand-proof screen tube in the actual mining process, that is, it can prevent sand particles from entering the wellbore during the hydrate decomposition process. The simulated screen tube 25 can be a cylindrical variable diameter structure, and the diameter of the upper pipe section is smaller than the diameter of the lower pipe section. The simulated screen tube 25 is connected to the third connecting section 24 through a connecting pipe 251.

[0032] The gas supply system 6 includes: a gas cylinder 61 and a gas booster pump 62 connected to each other; wherein the outlet of the gas cylinder 61 is connected to the inlet of the gas booster pump 62, and a first valve 63 is provided between the two; the outlet of the gas booster pump 62 is connected to the gas inlet of the reactor, and a first flow meter 64, a first pressure gauge 65 and a second valve 66 are provided between the two. In practice, the outlet of the gas booster pump 62 is connected to the gas inlet of the main reactor 21 through a high-pressure pipeline, so as to input methane and other gases into the main reactor 21, thereby realizing the gas supply in the process of hydrate sediment synthesis.

[0033] The liquid supply system 7 includes: a water tank 71 and a first pump body 72 which are connected to each other; wherein the outlet of the first pump body 72 is connected to the liquid inlet b of the main reactor 21, and a second flow meter 73, a second pressure gauge 74 and a third valve 75 are arranged between the two. In practice, the outlet of the first pump body 72 is connected to the liquid inlet b of the main reactor 21 through a high-pressure pipeline, so as to input liquids such as distilled water, deionized water or SDS solution into the reactor, thereby realizing the liquid supply in the process of hydrate sediment synthesis.

[0034] In this embodiment, the drilling system 3 includes: a drilling rig 31, a thruster 32 and a drilling fluid storage tank 33; wherein, the drill bit 311 of the drilling rig 31 is arranged toward the main reactor 21 to contact the hydrate sediment; the drill rod 312 of the drilling rig 31 is arranged close to the driving end of the drilling rig 31, and a drilling fluid inlet 3121 and a drilling fluid outlet 3122 are provided on the drill rod 312 to communicate with the drilling fluid storage tank 33 respectively; one end of the thruster 32 is connected to the driving end of the drilling rig 31, and the other end is connected to the first side of the main reactor 21 through a fixing frame 34.

[0035] Specifically, a sealing sleeve 313 is provided on the outside of the drill bit 311 to fix and protect the drill bit. The sealing sleeve 312 is embedded in the end cover on the second side of the main reactor 21, and a channel is provided inside the sealing sleeve to pass the drill rod 312. The shape of the accommodating cavity of the sealing sleeve 313 matches the drill bit. In this embodiment, mechanical drill bits of different sizes and hydraulic jet drill bits of different sizes and injection pressure conditions can be used. The hole formation characteristics and wellbore stability of the horizontal holes under the two drilling methods are different. The mechanical drill bit is a mechanical rock breaking under the combined action of cutting tooth pressure and torsion, while the hydraulic jet drill bit is a rock breaking by hydraulic impact and scouring. The hole shapes are different, and the drilling parameters such as drilling pressure, rotation speed, injection pressure, etc. have different effects on the hole size, shape, and wall roughness.

[0036] The liquid outlet of the drilling fluid storage tank 33 is connected to the second pump body 331, and a sixth valve 332 is provided between the two; the liquid outlet of the second pump body 331 is connected to the drilling fluid inlet 3121 on the drill pipe 312, and a fourth flow meter 333 is provided between the two; the liquid inlet of the drilling fluid tank is connected to the drilling fluid outlet 3122 on the drill pipe, and a seventh valve 334 is provided between the two. The drilling fluid storage tank 33 is used to provide the required drilling fluid during the drilling process, and to control the inflow and outflow of the drilling fluid, so as to realize the normal circulation of the drilling fluid during the drilling process, thereby assisting the drill bit of the drilling rig 31 to drill normally in the hydrate sediment.

[0037] Furthermore, the fixing frame 34 includes: a first fixing plate 341 and a plurality of fixing rods 342 arranged in a horizontal direction; wherein each of the fixing rods 342 is passed through the first fixing plate 341 and is connected to the first side of the main reactor 21, and the drilling rig 31 is connected to the fixing rod 342 via a support rod 35; wherein the support rod 35 is slidably arranged between two relatively arranged fixing rods 342.

[0038] Specifically, the support rod 35 is connected to the drilling rig 31, and the drilling rod is driven into the reactor by the drilling rig 31. The first fixing plate 341 is connected to the fixing rod 342 through a plurality of third bolts. The support rod 35 is slidably connected to the fixing rods 342 on both sides through the sliding sleeves 36 at both ends.

[0039] Preferably, the fixing frame 34 also includes: a second fixing plate 343; wherein the second fixing plate 343 is arranged opposite to the first fixing plate 341, and the second fixing plate 343 is connected to the end cover on the second side of the main reactor 21; the second end of each fixing rod 342 is passed through the second fixing plate 343 and then connected to the end cover on the second side of the main reactor 21.

[0040] The wellbore morphology observation system 4 includes: an endoscope 41 and a thrust rod 42; wherein, the endoscope 41 passes through the second connecting section 23 and contacts the hydrate sediment in the hydrate sediment synthesis system 2; a fixed sleeve 43 fixed at the center of the second connecting section 23 is provided on the outside of the thrust rod 42 to maintain sealing and pressure during the pushing process of the endoscope 41.

[0041] Combination Figure 1 and Figure 2 In this embodiment, a thermostat controller 9 is also included; wherein the thermostat controller is connected to the thermostat box 1 to cool the thermostat box 1 and maintain a constant temperature to assist the synthesis of hydrates in hydrate sediments. Of course, in this embodiment, a data processing system can also be included; wherein the data processing system is connected to the temperature sensor 10, the pressure sensor 11, the acoustic wave probe 12 and the thermostat controller 9 to process the collected parameters such as temperature, pressure, shear wave and longitudinal wave waveforms and speed. The data processing system includes a computer 13, a data processor 14 and related data lines, which play the role of data collection, data sorting and regulation.

[0042] It can be obviously concluded from the above that the experimental device for evaluating the drilling method of a horizontal well in a natural gas hydrate reservoir provided in this embodiment prepares hydrate sediments through a hydrate sediment synthesis system, and by setting a horizontal drilling system and using a mechanical drill bit or a hydraulic jet drill bit, it is possible to simulate the drilling process of a horizontal well in a natural gas hydrate reservoir under conditions of different drill bit sizes and drilling parameters; further, the shape of the drilled wellbore, the roughness of the wellbore wall, and the long-term deformation degree of the wellbore are observed through the wellbore morphology observation system, thereby realizing the analysis and evaluation of the wellbore morphology and wellbore wall change characteristics, and providing a reference basis for the drilling parameters required for the natural gas hydrate drilling construction process.

[0043] Method Example: The embodiment of the present invention also provides a natural gas hydrate reservoir drilling method evaluation experimental method, comprising the following steps: Step 1, connecting the hydrate sediment synthesis system, the drilling system and the wellbore morphology observation system, and connecting the gas supply system and the liquid supply system at the same time, and testing the air tightness of the entire device; Step 2, injecting gas and water required for synthesizing hydrate deposits into the hydrate deposit synthesis system through the gas supply system and the liquid supply system, setting the thermostat to a preset temperature, cooling the inside of the hydrate deposit, and synthesizing the hydrate deposit required for the test; Step 3, starting the drilling system, pushing the drill bit of the drilling rig forward at a certain speed, simulating the horizontal well section drilling process; and monitoring the dynamic response characteristics of the hydrate deposits during the drilling process; In specific implementation, the temperature, pressure, longitudinal and transverse wave waveforms and velocity and other parameters of the hydrate deposits during the drilling process are monitored by the pressure sensor, temperature sensor and acoustic probe, the change of hydrate saturation during the drilling process is predicted by the acoustic wave velocity, and the dynamic response characteristics of the hydrate deposits during the drilling process are analyzed by combining the above parameters.

[0044] Step 4, withdrawing the drill bit, and then observing the morphology, roughness and deformation characteristics of the drilled wellbore through the wellbore morphology observation system, analyzing the morphological characteristics of the drilled wellbore in the hydrate deposit and evaluating the stability of the wellbore; Step 5, by comparing the morphological characteristics and stability of the drilled wells under different working conditions, combined with the drilling efficiency and hydrate reservoir fragmentation characteristics in the simulated drilling process, according to the characteristics of hydrate sediments, analyze the influence of various working parameters and construction process parameters on the drilling efficiency of reservoirs with different physical properties, and optimize the optimal parameter combination for natural gas hydrate reservoir drilling.

[0045] In the specific implementation, by comparing the morphological characteristics and stability of the drilled wells under different drill bit sizes, jet parameters, drilling parameters and reservoir physical properties, combined with the drilling efficiency and hydrate reservoir fragmentation characteristics in the simulated drilling process, the influence of jet parameters and drilling parameters on the drilling efficiency of reservoirs with different physical properties is analyzed, and the optimal parameter combination for natural gas hydrate reservoir drilling is determined by combining orthogonal experiments and optimization methods.

[0046] For example, drilling experiments with different structures of jet drill bits, such as multi-hole jet drill bits, straight-rotation mixed jet drill bits and self-rotating jet drill bits, were conducted. The effects of factors such as equivalent nozzle diameter and jet pressure of three jet drill bits on the drilling characteristics of hydrate reservoirs with different saturations were compared, with characteristics such as aperture, hole shape and inner wall roughness as evaluation indicators. Since hydrate reservoirs are soft and have low cementation strength, their pore formation characteristics are quite different from those of conventional sandstone and coal rock. The hole arrangement scheme and hole size on the jet drill bit were adjusted according to the experimental results. This experiment can clarify the relationship between the jet flow structure and the drilling characteristics of hydrate reservoirs, and also provide a basis for the structural optimization design of hydraulic jet drill bits for radial horizontal wells in hydrate reservoirs.

[0047] The related parts of the method embodiment and the above-mentioned device embodiment can be referred to each other and will not be described in detail here.

[0048] In summary, the method for evaluating the natural gas hydrate reservoir drilling method provided by the present invention can simulate the full-size drill bit drilling process of a horizontal well in a natural gas hydrate reservoir, and monitor the response characteristics of the reservoir during the drilling process in real time; according to the characteristics of different hydrate reservoirs, hydrate sediment samples are synthesized in situ, and the drilling process of the full-size drill bit on the horizontal well of the hydrate reservoir is simulated through the drilling fluid circulation system and the drilling system. At the same time, the changes in reservoir physical properties during the drilling process are analyzed by monitoring the changes in acoustic parameters, electrical parameters and pressure, and the response characteristics of the reservoir and the reservoir fragmentation during the drilling process are evaluated. After the drilling process is completed, the shape of the drilled wellbore, the roughness of the wellbore wall and the long-term deformation of the wellbore are observed through the wellbore morphology observation system, realizing the analysis and evaluation of the wellbore morphology and wellbore wall change characteristics; the morphological characteristics and stability of the drilled wellbore under different working conditions are compared and analyzed, and the full-size drill bit is optimized to simulate the drilling working parameters and hydraulic parameters during the drilling process, and the drill bit size, hydraulic parameters, drilling fluid properties and other parameters are determined. By comparing the drilling speed, the drilling efficiency is optimized, and then the best drilling plan is formulated in combination with the hydrate reservoir properties and drilling requirements, providing a reference basis for natural gas hydrate drilling construction.

[0049] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. An experimental device for evaluating the drilling method of horizontal wells in natural gas hydrate reservoirs. It is characterized in that include: A constant temperature box and a hydrate deposit synthesis system, a drilling system and a wellbore morphology observation system placed in the constant temperature box; wherein the hydrate deposit synthesis system is provided with a gas inlet and a liquid inlet for respectively inputting the gas and water required for synthesizing the hydrate deposit to synthesize the hydrate deposit; the drilling system is arranged in a horizontal direction and is communicated with a first side of the hydrate deposit synthesis system for drilling into the hydrate deposit in the hydrate deposit synthesis system; the wellbore morphology observation system is arranged in a horizontal direction on the opposite side of the drilling system, and the wellbore morphology observation system is communicated with a second side of the hydrate deposit synthesis system for observing the shape of the drilled wellbore, the roughness of the wellbore wall and the deformation degree of the wellbore over a long period of time.

2. The natural gas hydrate reservoir drilling method evaluation experimental device according to claim 1, It is characterized in that The hydrate sediment synthesis system includes: a main reactor, a first connecting section, a second connecting section and a third connecting section connected to each other; wherein the first side of the main reactor is connected to the drilling system through the first connecting section, the second side of the main reactor is connected to the wellbore morphology observation system through the second connecting section, and the top of the main reactor is connected to the collection system through the third connecting section.

3. The natural gas hydrate reservoir drilling method evaluation experimental device according to claim 2, It is characterized in that The main reactor is a T-shaped high-pressure reactor.

4. The natural gas hydrate reservoir drilling method evaluation experimental device according to claim 2, It is characterized in that A temperature sensor, a pressure sensor and an acoustic wave probe are arranged on the outside of the first connecting section to monitor the changing patterns of the physical property parameters of the hydrate sediment during the drilling process.

5. The natural gas hydrate reservoir drilling method evaluation experimental device according to claim 2, It is characterized in that The hydrate sediment synthesis system further comprises: a simulated screen tube; wherein, The upper end of the simulated sieve tube is passed through the third connecting section, and the lower end of the simulated sieve tube is buried in the main reactor.

6. The natural gas hydrate reservoir horizontal well drilling method evaluation experimental device according to claim 1, It is characterized in that The drilling system includes: a drilling rig, a thruster and a drilling fluid storage tank; wherein the drill bit of the drilling rig is arranged toward the reactor to contact the hydrate sediment; the drill rod of the drilling rig is arranged close to the driving end of the drilling rig, and a drilling fluid inlet and a drilling fluid outlet are provided on the drill rod to communicate with the drilling fluid storage tank respectively; one end of the thruster is connected to the driving end of the drilling rig, and the other end is connected to the first side of the reactor through a fixing frame.

7. The natural gas hydrate reservoir drilling method evaluation experimental device according to claim 6, It is characterized in that The liquid outlet end of the drilling fluid storage tank is connected to the second pump body, and a sixth valve is arranged between the two; the liquid outlet end of the second pump body is connected to the drilling fluid inlet on the drill pipe, and a fourth flow meter is arranged between the two; the liquid inlet end of the drilling fluid tank is connected to the drilling fluid outlet on the drill pipe, and a seventh valve is arranged between the two.

8. The natural gas hydrate reservoir drilling method evaluation experimental device according to claim 6, It is characterized in that The fixing frame includes: a first fixing plate and a plurality of fixing rods arranged in a horizontal direction; wherein each of the fixing rods passes through the fixing plate and is connected to the first side of the reactor, and the drilling rig is connected to each of the fixing rods via a support rod; wherein the support rod is slidably arranged between two oppositely arranged fixing rods.

9. The natural gas hydrate reservoir drilling method evaluation experimental device according to claim 1, It is characterized in that The wellbore morphology observation system includes: an endoscope and a propulsion rod; wherein, the endoscope passes through the first end cover and contacts the hydrate sediment in the hydrate sediment synthesis system; a fixed sleeve fixed to the center of the left end cover is provided on the outside of the propulsion rod to maintain sealing and pressure during the pushing process of the endoscope.

10. An experimental method using the natural gas hydrate reservoir drilling method evaluation experimental device according to any one of claims 1 to 9, It is characterized in that The following steps are involved: Step 1, connecting the hydrate sediment synthesis system, the drilling system and the wellbore morphology observation system, and connecting the gas supply system and the liquid supply system at the same time, and testing the air tightness of the entire device; Step 2, injecting gas and water required for synthesizing hydrate deposits into the hydrate deposit synthesis system through the gas supply system and the liquid supply system, setting the thermostat to a preset temperature, cooling the inside of the hydrate deposit, and synthesizing the hydrate deposit required for the test; Step 3, starting the drilling system, pushing the drill bit of the drilling rig forward at a certain speed, simulating the horizontal well section drilling process; and monitoring the dynamic response characteristics of the hydrate deposits during the drilling process; Step 4, withdrawing the drill bit, and then observing the morphology, roughness and deformation characteristics of the drilled wellbore through the wellbore morphology observation system, analyzing the morphological characteristics of the drilled wellbore in the hydrate deposit and evaluating the stability of the wellbore; Step 5, by comparing the morphological characteristics and stability of the drilled wells under different working conditions, combined with the drilling efficiency and hydrate reservoir fragmentation characteristics in the simulated drilling process, according to the characteristics of hydrate sediments, analyze the influence mechanism of various working parameters and construction process parameters on the drilling efficiency, and optimize the combination of natural gas hydrate reservoir drilling parameters.

Images