A device, method and application for evaluating the stability of natural gas hydrate formation wellbore

Abstract

The present invention aims to provide a device, method and application for evaluating the stability of the wellbore of a natural gas hydrate formation, and an indoor simulation device and method for simulating the changes in the stability of the wellbore of a hydrate formation during drilling. Through the present invention, the actual formation temperature and pressure environment can be simulated, and the effects of drilling fluid, temperature and pressure changes and other factors on the changes in the internal microstructure and mechanical properties of the hydrate formation can be studied. This is of great significance for understanding the characteristics of the hydrate formation and conducting the evaluation of the wellbore stability, and provides a basis and support for the safe drilling and development and production of the hydrate formation. The changes in mechanical properties described in the present invention are measured using a needle-penetration strength test module, which can effectively reflect the changes in the mechanical properties of the hydrate formation at different times; the microstructural characteristics described in the present invention are measured using tomographic scanning technology, which can effectively describe the changes in the internal microstructure during the drilling process.

Description

Technical Field

[0001] The invention belongs to the field of natural gas, and in particular relates to a device and method for evaluating the stability performance of a natural gas hydrate formation well wall and an application thereof. Background Art

[0002] Natural gas hydrate (hereinafter referred to as hydrate), also known as combustible ice, is an ice-like crystalline substance formed by natural gas and water under high pressure and low temperature conditions. Natural gas hydrate formations (hereinafter referred to as hydrate formations) are generally unconsolidated and semi-consolidated sandstone or mudstone sandstone formations. During the drilling process, changes in temperature and pressure will lead to the decomposition of hydrates, causing the formation rock to lose its cementation and skeleton support, causing the wellbore to collapse; the water produced by the decomposition increases the water content of the formation, reduces the strength of the formation rock, and makes the formation more prone to instability, causing complex situations such as stuck drill and well leakage. Therefore, how to simulate the changes in the internal microstructure and mechanical properties of the hydrate formation during drilling, and obtain the influencing factors and laws that affect the stability of the wellbore of the hydrate formation, is of great significance to the safe drilling of the hydrate formation.

[0003] In recent years, many scholars at home and abroad have carried out research on the relevant properties of natural gas hydrate formations. Chinese patent CN210071521U, Chinese patent CN210071522U and Chinese patent CN110441153A all disclose a triaxial test device for natural gas hydrates; however, the above-mentioned device cannot measure the changes in mechanical properties after coupling with fluids. Chinese patent CN209875149U provides an experimental device for simulating the destruction of pore walls of natural gas hydrate formations, which can measure the flow state of sand particles. Chinese patent CN110361420A discloses a test device for the acoustic and electrical characteristic parameters of natural gas hydrates. The United States Geological Survey and Nagasaki University in Japan have developed an experimental system that integrates in-situ synthesis of hydrates and triaxial mechanical testing. China University of Petroleum (East China) has also established a similar system. At present, some studies (Ning Fulong, Research on Borehole Stability of Natural Gas Hydrate Formation [D], China University of Geosciences, 2005; Xu Jiafang, Qiu Zhengsong, Research and Evaluation Simulation Device for Deepwater Drilling Fluid [J], Offshore Oil, 2010, 30(3):88-92) have developed a comprehensive simulation device for natural gas hydrate seepage mining, which can be used to study the changes in formation temperature, pressure and electrical properties after drilling fluid invasion, but it is not possible to measure the changes in microstructure during hydrate formation or decomposition. Therefore, there is currently no device and method that can effectively evaluate the changes in the microstructure of natural gas hydrate formations and their mechanical responses during drilling. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a device and method for evaluating the stability of the wellbore of a hydrate formation during a simulated drilling process. The device adopts a modular design concept, and each module is independent of each other. The device characterizes the instability of the formation through tomography and changes in mechanical properties, especially studying the changes in the internal microstructure and mechanical properties of the hydrate formation under the coupling conditions with the drilling fluid during the drilling process, thereby providing a basis and support for the future drilling and development and production of natural gas hydrate formations.

[0005] One of the purposes of the present invention is to provide a device for evaluating the stability of the wellbore of a hydrate formation, comprising a simulation reaction module, a gas injection module, a temperature and pressure test module, a needle penetration strength test module, a tomography scanning module, and an optional drilling fluid circulation module. The reaction module is placed on a test platform of the tomography scanning module and is connected to the drilling fluid circulation module by a hydraulic pipeline. A temperature and pressure test module is arranged inside the reaction module. The gas injection module is connected to the reaction module by a high-pressure pipeline, and a probe of the needle penetration strength test module is placed in the reaction module.

[0006] Specifically,

[0007] The reaction module comprises a reaction kettle and a constant temperature system;

[0008] The reactor comprises a top cover and a kettle body, wherein the top cover and the kettle body are connected by flange or thread, and a pressure sensor and a temperature sensor are arranged on the top cover; the reactor is made of stainless steel; the inner diameter of the reactor body is 25-300 mm, preferably 50-150 mm; the length of the kettle body is 100-300 mm, preferably 150-200 mm; the wall thickness of the kettle body is 3-15 mm, preferably 5-10 mm; the thickness of the reactor top cover is 15-20 mm, preferably 18-20 mm;

[0009] The reactor body is divided into a space for storing circulating drilling fluid and gas, and a space for storing porous media and formation water. The upper part of the space for storing circulating drilling fluid and gas is provided with a drilling fluid outlet of a drilling fluid circulation module, and the lower part of the other side of the space for storing circulating drilling fluid and gas is provided with a drilling fluid inlet of the drilling fluid circulation module.

[0010] The reactor is the main body for hydrate formation and decomposition reactions, and also serves as the mother body of the needle penetration strength test module and the temperature and pressure test module; a plurality of pressure sensors, a plurality of temperature sensors and a plurality of needle penetration strength test modules are evenly distributed on the top cover of the reactor;

[0011] The constant temperature system comprises a temperature control device, a valve, a temperature sensor, and a constant temperature box connected in sequence by connecting pipes, wherein the temperature control device is an air-cooled compressor or an electric heating device; the temperature of the constant temperature system is -30 to 120°C, preferably -10 to 90°C; the temperature control device automatically adjusts according to the temperature required for the experiment, and an air-cooled fully enclosed compressor unit can be used for refrigeration, the fluid medium used can be water, saline solution or alcohol, and electric heating can be used for heating; the temperature sensor is used to measure the temperature of the fluid medium in the flow manifold; the constant temperature box is wrapped outside the reactor to provide the reactor with a constant temperature environment required for the experiment;

[0012] The drilling fluid circulation module includes a drilling fluid storage tank, a plunger pump, a pressure regulating valve, a valve, and a temperature sensor which are connected in sequence by connecting pipes, and is connected to the reactor by a hydraulic pipeline; a temperature regulating device is provided in the drilling fluid storage tank, which has an automatic cooling / heating function, and can realize precise control of the temperature under actual drilling conditions; the plunger pump is the power system of the drilling fluid circulation module, which continuously pumps out the drilling fluid at a constant flow rate to realize the circulation of the drilling fluid; the pressure regulating valve can simulate the working pressure under actual drilling conditions; the temperature sensor is used to detect the temperature of the flowing drilling fluid.

[0013] The above-mentioned device for evaluating the stability performance of the wellbore of the natural gas hydrate formation also includes a data acquisition and control module, which is connected to the gas injection module, the temperature and pressure test module, and the needle penetration strength test module through a circuit.

[0014] Specifically,

[0015] The gas injection module comprises a gas storage bottle, a buffer tank, a valve, a pressure regulating pump, a gas flow meter, and a pressure sensor connected in sequence by a connecting pipe; wherein the gas flow meter is used to measure the gas flow, and can be selected from one of an orifice plate type, a vortex type, a turbine type, and an ultrasonic type according to experimental needs; the gas in the gas injection module can be injected into the gas according to experimental needs, and is preferably selected from one of natural gas, carbon dioxide, and nitrogen, and more preferably natural gas; the buffer tank is a gas pressure buffer device, which provides the required gas for the pressure regulating pump; the pressure regulating pump is a regulating device for the pressure required for the experiment, which pressurizes the gas to the required experimental pressure; the pressure sensor is used to measure the pressure in the injection manifold;

[0016] The needle penetration strength test module is mainly used for measuring the needle penetration strength of hydrate formations. The needle penetration strength test module includes a liquid storage tank, a plunger pump, a pressure sensor, a valve, a needle penetration strength meter, a pressure relief valve, and a hydraulic pipe connected in sequence by a hydraulic pipe. The fluid medium in the liquid storage tank of the needle penetration strength test module is selected from hydraulic oil, for example, preferably GB 7631.2-2003 L-HM, L-HV hydraulic oil, the plunger pump continuously and stably supplies fluid at a constant flow rate, and the needle penetration strength test module controls the probe penetration by ejecting the fluid medium volume through the high-precision plunger pump, the plunger pump flow control accuracy is 0.01-0.03ml / min, the fluid delivery capacity is 0.02-80ml / min, and the working pressure is 3-40MPa; the needle penetration strength test module includes at least 2 sets of needle penetration strength meters, the needle penetration strength meters can be used to measure the strength of natural gas hydrate formations at different periods to monitor its changes, the needle penetration strength meter includes a shell, a back cover, an inner piston, and a probe, wherein the shell is connected to the top cover of the reactor by a threaded connection, the back cover is connected to the shell by a threaded connection, the inner piston divides the shell into a hydraulic fluid medium space and a probe stroke space, and the probe is installed on the inner piston; the pressure sensor is used to measure the pressure change in the manifold during the operation of the high-precision plunger pump; the pressure relief valve is used to release the hydraulic pressure in the needle penetration strength test module;

[0017] The temperature and pressure test module is used to measure the temperature and pressure of the space for storing circulating drilling fluid and gas storage, and the space for storing porous media and formation water inside the reactor. The temperature and pressure test module includes at least two groups of temperature sensors and pressure sensors, one group is used to measure the temperature and pressure of the space for storing circulating drilling fluid and gas storage, and the other group is used to measure the temperature and pressure of the space for storing porous media and formation water; wherein the pressure sensor of the temperature and pressure test module has an accuracy of 0.1% to 0.3%, and a test range of 0.05 to 50 MPa; the temperature sensor of the temperature and pressure test module has an accuracy of ±0.1°C, and a test range of -20 to 100°C;

[0018] The tomographic scanning module can clearly, accurately, intuitively and non-destructively observe and describe the structural characteristics of natural gas hydrates such as density, porosity distribution, density changes, internal crack development, cavities, pores and fillings. It can describe the internal structural characteristics of natural gas hydrates at different times during the drilling and production process, and track and compare the impact of external factors such as drilling fluid intrusion, temperature and pressure changes on the internal microstructure of natural gas hydrate formations. The tomographic scanning module is mainly composed of high-precision industrial CT. During the experiment, the reactor is placed on the high-precision industrial CT test platform and fixed in position; after setting the scanning parameters, the container is fixed on the scanning bed to scan the original rock sample; after the scanning is completed, the CT image is processed by computer on the main console to obtain the ideal image effect; reconstructed into two-dimensional and three-dimensional photos of the CT image for observation and comparative analysis; the maximum resolution of the high-precision industrial CT is <1μm, the test sample diameter is 300mm, the length is 400mm, and the maximum weight of the test sample is 20kg;

[0019] The data acquisition and control module can collect data from the above-mentioned various temperature sensors, pressure sensors, gas flow and the like in real time, control the start, stop, flow and the like of high-precision plunger pumps, cooling / heating devices and the like, and the workflow of each module is displayed on the control interface, and various parameters can be monitored in real time, with flexible and convenient operation.

[0020] The second object of the present invention is to provide a method for evaluating the wellbore stability performance of hydrate formations using the above-mentioned device, including synthetic hydrate formations and performance evaluation, and simulated drilling fluid circulation hydrate formations and performance evaluation.

[0021] Specifically,

[0022] The synthetic hydrate formation and its performance evaluation include the following steps:

[0023] Step 1-1: Fill the reactor with porous media, inject formation water, and start the temperature control device;

[0024] Step 1-2: Open the valve of the gas injection module, inject the stored gas into the reactor, and adjust the pressure of the gas storage space in the reactor body;

[0025] Step 1-3: Start the reaction, and record the temperature and pressure during the reaction by the temperature and pressure test module;

[0026] Step 1-4 uses a chromatography scanning module to quickly scan and analyze the hydrate obtained after the reaction;

[0027] Steps 1-5 use a needle penetration strength test module to test the strength of the synthesized hydrate.

[0028] Preferably,

[0029] The porous medium is selected from at least one of sand and ceramsite, preferably at least one of sand and ceramsite with different particle sizes, for example, the particle size range is 10 -3 At least one of sand and ceramsite with a diameter of 10 to 10 mm;

[0030] The stored gas is selected from one of natural gas, carbon dioxide and nitrogen, preferably natural gas;

[0031] The reaction temperature in step 1-3 is -20 to 100°C, the reaction time is 0 to 240 hours, and the reaction pressure is 0 to 40 MPa. Preferably, the reaction temperature is 2 to 60°C, the reaction time is 1 to 48 hours, and the reaction pressure is 2 to 30 MPa.

[0032] Specifically,

[0033] The hydrate bottom layer and performance evaluation thereof in the simulated drilling fluid circulation include the above steps 1-1 to 1-3, or include the above steps 1-1 to 1-5, and include the following steps thereafter:

[0034] Step 2-1: Turn on the temperature regulating device of the drilling fluid circulation module and set the experimental temperature;

[0035] Step 2-2: injecting drilling fluid into the storage circulating drilling fluid in the reactor, establishing a drilling fluid circulation, and setting the pressure and circulation time;

[0036] Step 2-3 uses a tomography scanning module to quickly scan and analyze hydrates under drilling fluid coupling conditions;

[0037] Step 2-4 uses a needle penetration strength test module to test the hydrate strength under drilling fluid coupling conditions.

[0038] Preferably,

[0039] Before step 2-1, the gas storage module needs to be closed to depressurize the gas storage space of the reactor;

[0040] The experimental temperature in step 2-1 is -10 to 80°C, preferably 0 to 60°C;

[0041] The pressure in step 2-2 is 0 to 60 MPa, preferably 6 to 40 MPa;

[0042] The cycle time in step 2-2 is 0 to 480 hours, preferably 2 to 240 hours.

[0043] The third object of the present invention is to provide an apparatus for evaluating the wellbore stability performance of a hydrate formation or an application of the method for evaluating the wellbore stability performance of a hydrate formation, which is used to detect the wellbore stability performance of a hydrate formation.

[0044] Preferably,

[0045] The application can be used to measure the changes in the internal structure and mechanical properties of hydrates;

[0046] The application can be used to determine the changes in the internal structure and mechanical properties of hydrates caused by different drilling fluid temperatures;

[0047] The application can be used to measure the changes in the internal structure and mechanical properties of hydrates caused by different drilling fluid circulation pressures.

[0048] The present invention provides an indoor simulation device and method for simulating the change of the wellbore stability performance of the hydrate formation during the drilling process. The device and method for evaluating the wellbore stability performance of the hydrate formation of the present invention can simulate the actual formation temperature and pressure environment, and study the changes in the microstructure and mechanical properties of the internal microstructure of the natural gas hydrate formation caused by factors such as drilling fluid and temperature and pressure changes, which is of great significance for understanding the characteristics of the natural gas hydrate formation and conducting the evaluation of the wellbore stability performance, and provides a basis and support for the safe drilling and development and production of the natural gas hydrate formation. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is a schematic diagram of the natural gas hydrate formation wellbore stability simulation device of the present invention;

[0050] Figure 2 It is a schematic diagram of a needle penetration strength meter;

[0051] Figure 3 The temperature and pressure variation curves during the formation of natural gas hydrate in step (6) of Example 1 are used to analyze the formation process of natural gas hydrate during the reaction;

[0052] Figure 4 is a CT microstructure photograph of the natural gas hydrate obtained in step (7) of Example 1, Figure 4 The internal structure of the gas hydrate layer can be clearly seen in the figure, where a is the gas hydrate, b is the pore, and c is the sand grain;

[0053] Figure 5 is the natural gas hydrate compressive strength curve measured in step (8) of Example 1, Figure 5 It is shown in the figure that the compressive strength with a needle penetration strength of 10 mm is 63.3 MPa;

[0054] Figure 6 The CT microstructure photograph of the natural gas hydrate obtained in step (4) of Example 2 after 3 hours of circulation is shown in FIG. Figure 6 It can be seen that the gas hydrate gradually disappears and the pores expand;

[0055] Figure 7is the compressive strength curve of natural gas hydrate measured in step (5) of Example 2 after 3 hours of circulation, Figure 7 It is shown in the figure that the compressive strength with a needle penetration strength of 10 mm is 55.1 MPa;

[0056] Figure 8 This is a CT microstructure photograph of the natural gas hydrate after 6 hours of circulation in Example 2. Figure 8 It can be seen that the area occupied by gas hydrate continues to shrink, and the pore part continues to expand;

[0057] Fig. 9 is the compressive strength curve of natural gas hydrate after 6 hours of circulation in Example 2, Fig. 9 It is shown in the figure that the compressive strength with a needle penetration strength of 10 mm is 46 MPa.

[0058] Reference numerals:

[0059] 1 Reactor

[0060] 7 High-precision industrial CT

[0061] 11 Cooling / Heating Device

[0062] 12 First Valve

[0063] 13. First temperature sensor

[0064] 14 Constant temperature box

[0065] 21 Drilling fluid storage tank

[0066] 22 First plunger pump

[0067] 23 First pressure regulating valve

[0068] 24 Second valve

[0069] 25 Second temperature sensor

[0070] 31 Natural gas cylinder

[0071] 32 Buffer tank

[0072] 33 Third valve

[0073] 34 Second pressure regulating pump

[0074] 35 Gas flow meter

[0075] 36 Fourth Valve

[0076] 37 First pressure sensor

[0077] 38 Fifth Valve

[0078] 41 Liquid storage tank

[0079] 42 Second plunger pump

[0080] 43 Second pressure sensor

[0081] 44~48 The sixth to tenth valves

[0082] 49~52 First to fourth needle penetration strength meter

[0083] 53 Third pressure sensor

[0084] 54 Fourth pressure sensor

[0085] 55 First temperature sensor

[0086] 56 Second temperature sensor

[0087] 57 Eleventh pressure relief valve

[0088] 61 Back cover

[0089] 62 Shell

[0090] 63 inner piston

[0091] 64 Probe DETAILED DESCRIPTION

[0092] The present invention is described in detail below in conjunction with specific embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the contents of the present invention still fall within the scope of protection of the present invention.

[0093] The device for evaluating the stability of the wellbore of a hydrate formation according to the present invention:

[0094] like Figure 1 As shown, a device for evaluating the stability of the wellbore of a hydrate formation includes a reactor and a constant temperature module, a drilling fluid circulation module, a natural gas injection module, a temperature and pressure test module, a tomography scanning module, a needle penetration strength test module, and a data acquisition and control module.

[0095] The specifications of the reactor body are 80mm in inner diameter, 160mm in length, and 10mm in wall thickness. There is a dividing line at 1 / 4 of the bottom of the reactor body, which divides the reactor body into two parts: upper ① and lower ②. The upper ① part is mainly used for circulating drilling fluid and natural gas; the lower ② part is used to fill the porous medium and formation water simulating the natural gas hydrate formation, and generate natural gas hydrate in it. The porous medium can be a particle size of 10 -3~10mm sand, ceramsite, etc. The lower part ② can also be filled with natural hydrate cores taken from underground for experiments. There are 2 pressure sensors, 2 temperature sensors and 4 needle penetration strength test modules evenly distributed on the top cover of the reactor to detect temperature and pressure changes and natural gas hydrate formation mechanical parameters.

[0096] The reactor top cover is 18 mm thick to withstand the force generated during the needle penetration strength test.

[0097] The working pressure of the reactor is 30 MPa.

[0098] The constant temperature system provides a temperature range of -10℃~90℃, and a temperature control accuracy of ±0.05℃. The constant temperature system uses a water bath as the main means, and is composed of a cooling / heating device 11, a first valve 12, a first temperature sensor 13, a constant temperature box 14 and an auxiliary manifold connected in sequence. The cooling / heating device 11 can automatically adjust according to the temperature required for the experiment; the refrigeration device uses Peltier electric refrigeration, and the heating device uses electric heating. The valve 12 is used to control the flow state of the constant temperature fluid medium. The temperature sensor 13 is used to measure the temperature of the fluid medium in the flow manifold. The constant temperature box 14 is wrapped outside the reactor 1 to provide the reactor 1 with a constant temperature environment required for the experiment.

[0099] The drilling fluid circulation module can simulate the flow state of drilling fluid during drilling and simulate the process of interaction between drilling fluid and hydrate formation under actual formation temperature and pressure conditions. The module is mainly composed of a drilling fluid storage tank 21, a plunger pump 22, a first pressure regulating valve 23, a second valve 24, a second temperature sensor 25 and an auxiliary hydraulic manifold connected in sequence. The drilling fluid storage tank 21 has a volume of 5000ml and has an automatic cooling / heating function, which can achieve precise control of the temperature state under actual drilling conditions. The plunger pump 22 has a flow control accuracy of 0.1ml / s, a maximum flow of 10ml / s, and a maximum working pressure of 30MPa. The first pressure regulating valve 23 can simulate the working pressure under actual drilling conditions, with a pressure control accuracy of ±1.0Pa. The second valve 24 is used to control the flow of drilling fluid. The temperature sensor is used to detect the temperature of the flowing drilling fluid. The inlet of the drilling fluid flow manifold is located at the lower part ① of the reactor 1 space, and the outlet is located at the upper part of the space ①. The outlet and inlet are located on both sides of the reactor to achieve the overall flow of the drilling fluid in the entire reactor space ①.

[0100] The natural gas injection module is mainly used for the injection and release of high-pressure natural gas in the reactor. It is composed of a natural gas storage cylinder 31, a buffer tank 32, a third valve 33, a second pressure regulating pump 34, a gas flow meter 35, a fourth valve 36, a first pressure sensor 37, a fifth venting valve 38 and a high-pressure manifold connected in sequence. The natural gas storage cylinder is a storage device for natural gas, and can also store other gases such as carbon dioxide and nitrogen according to experimental needs; the buffer tank is a natural gas pressure buffer device, which provides the required gas for the pressure regulating pump; the pressure regulating pump is a regulating device for the pressure required for the experiment, which pressurizes the gas to the required experimental pressure; the gas flow meter adopts an ultrasonic gas flow meter with an accuracy of 1.5% mv. The pressure sensor is used to measure the pressure in the injection manifold. The fifth venting valve 38 is used to release the gas in the reactor 1 at the end of the experiment or according to experimental needs. The released natural gas should be led out of the room or recycled to avoid harm.

[0101] The needle penetration strength test module is mainly used for the determination of the needle penetration strength of the natural gas hydrate formation, and then the mechanical parameters such as the uniaxial compressive strength and tensile strength of the formation can be calculated, which is used for the evaluation and analysis of the stability performance of the well wall. The module is mainly composed of a liquid storage tank 41, a high-precision plunger pump 42, a second pressure sensor 43, the sixth to tenth valves 44-48 in sequence, the first to fourth needle penetration strength gauges 49-52 in sequence, the eleventh pressure relief valve 57 and an auxiliary hydraulic manifold connection. The liquid storage tank 41 has a volume of 1000ml, and the stored fluid medium is deionized water or other fluids with extremely low compression ratios. The high-precision plunger pump 42 can continuously and stably supply fluid at a constant flow rate, and the module controls the probe penetration by pumping out the volume of the fluid medium through the high-precision plunger pump; the high-precision plunger pump has a flow control accuracy of 0.002ml / min, a fluid delivery capacity of 0.02-80ml / min, and a maximum working pressure of 45MPa. The second pressure sensor 43 is used to measure the pressure changes in the manifold during the operation of the high-precision plunger pump. The valves 44-48 are used to control the operation of different needle penetration strength meters, such as opening the sixth valve 44 and the seventh valve 45, closing the eighth valve 46, the ninth valve 47 and the tenth valve 48, and making the first needle penetration strength meter 49 work alone. The needle penetration strength meter consists of a rear cover 61, a shell 62, an inner piston 63 and a probe 64; the rear cover 61 is connected to the shell 62 by a threaded connection, and is connected to the hydraulic manifold to guide the fluid medium into the shell 62; the shell 62 is threadedly connected to the top cover of the reactor 1, and the built-in inner piston 63 divides the shell into two parts, the upper part is the hydraulic fluid medium, and the lower part is the probe stroke space. Under the action of hydraulic pressure, the inner piston 63 moves downward and drives the probe 64 installed on the inner piston 63 to move downward and penetrate into the hydrate. The shell has an inner diameter of 15 mm, an outer diameter of 20 mm, a height of 25 mm, and is made of hard alloy steel. The probe has a diameter of 1.2 mm, a length of 50 mm, and is made of hard alloy steel. The first to fourth penetration strength gauges 49-52 in the sequence can be used to measure the strength of natural gas hydrate formations at different times to monitor their changes. The eleventh pressure relief valve 57 is used to release the hydraulic pressure in the penetration strength test module. The penetration strength value can be obtained by multiplying the maximum value recorded by the pressure sensor by the area coefficient; the area coefficient is the ratio of the inner diameter area of ​​the shell to the cross-sectional area of ​​the probe.

[0102] The temperature and pressure test module is used to measure the temperature and pressure of the hydrate formation ② and the upper circulation space ① inside the reactor 1. It is mainly composed of a third temperature sensor 55 and a fourth temperature sensor 56, a third pressure sensor 53 and a fourth pressure sensor 54; wherein the third temperature sensor 55 and the fourth pressure sensor 54 are used to measure the temperature and pressure conditions inside the natural gas hydrate; the fourth temperature sensor 56 and the third pressure sensor 53 are used to measure the temperature and pressure conditions of the upper circulation space; the pressure sensor has an accuracy of 0.05% FS and a test range of 0.05 to 50 MPa; the pressure sensor has an accuracy of ±0.1°C and a test range of -20°C to 100°C.

[0103] The tomography scanning module is mainly composed of high-precision industrial CT. During the experiment, the reactor 1 is placed on the high-precision industrial CT test platform and fixed in position; after setting the scanning parameters, the container is fixed on the scanning bed to scan the original rock sample; after the scanning is completed, the CT image is processed by computer on the main console to obtain the ideal image effect; the CT image is reconstructed into two-dimensional and three-dimensional photos for observation, comparison and analysis. The maximum resolution of the high-precision industrial CT is less than 1μm, the test sample diameter is 300mm, the length is 400mm, and the maximum weight of the test sample is 20kg.

[0104] Method for evaluating the stability of wellbore wall of hydrate formation using the above device

[0105] Example 1

[0106] The synthetic natural gas hydrate formation and its performance evaluation, the specific operation method includes the following steps:

[0107] (1) Check the air tightness of reactor 1 and each module and prepare for the experiment;

[0108] (2) Fill the inner space ② of the reactor 1 with a porous medium up to the dividing line, and inject the prepared formation water into the porous medium until all the air is discharged;

[0109] (3) Open the first valve 12, turn on the cooling / heating device 11, and adjust the temperature of the reactor 1 to the experimental temperature of 2°C;

[0110] (4) Open the natural gas storage cylinder 31, the third valve 33, and the fourth valve 36, start the second pressure regulating pump 34, open the fifth pressure release valve 38, and inject natural gas into the upper space ① of the reactor 1 until all the air inside is discharged;

[0111] (5) After (4) is completed, close the fifth pressure relief valve 38, adjust the second pressure regulating pump 34, and increase the pressure of the upper space ① of the kettle to the required pressure of 9 MPa for the experiment;

[0112] (6) Natural gas hydrate is gradually formed in space ② of reactor 1. During this process, the third temperature sensor 55 and the fourth temperature sensor 56, the third pressure sensor 53 and the fourth pressure sensor 54 are used to record the temperature and pressure changes during the reaction process for subsequent analysis;

[0113] (7) Use high-precision industrial CT to quickly scan the formed natural gas hydrate, obtain the two-dimensional and three-dimensional microstructure of the internal structure, and analyze the spatial distribution characteristics of its voids, pores, and fillings, such as Figure 4 As shown in;

[0114] (8) Open the high-precision plunger pump 42, the sixth to seventh valves 44 and 45, close the eighth to tenth valves 46, 47, 48 and the pressure relief valve 57, and use the needle penetration strength meter 49 to test the strength of the synthesized natural gas hydrate. The compressive strength of the synthesized natural gas hydrate is 63.3 MPa;

[0115] (9) After the test is completed, close and open the high-precision plunger pump 42, open the pressure relief valve 57, release the pressure in the manifold, close the sixth and seventh valves 44 and 45, and close the pressure relief valve 57.

[0116] Example 2

[0117] The specific operation method of simulating the natural gas hydrate formation in the drilling fluid circulation and the performance evaluation thereof may include continuing the following steps after the steps in Example 1 are completed:

[0118] (1) Close the natural gas storage cylinder 31, the third valve 33, the fourth valve 36, and the pressure regulating pump, open the fifth pressure relief valve 38, and release the pressure of the upper space ① of the reactor 1 to 6 MPa;

[0119] (2) Turn on the temperature regulating device in the drilling fluid storage tank 21 to adjust the temperature of the drilling fluid to the experimental set temperature of 2°C;

[0120] (3) Open the plunger pump 22 and the second valve 24 to inject drilling fluid into the upper space ① of the reactor 1. After all the natural gas is discharged, close the fifth valve 38 to establish a circulation of the drilling fluid; adjust the pressure regulating valve 23 to 6 MPa to simulate the pressure conditions during the actual drilling process;

[0121] (4) After 3 hours of circulation, the formed natural gas hydrate was quickly scanned using a high-precision industrial CT 7 to obtain the two-dimensional and three-dimensional microstructures of the internal structure and the changes in the internal microstructure of the natural gas hydrate under the coupling conditions with the drilling fluid. Figure 6 It can be seen that part of the gas hydrate has disappeared and the pores have expanded;

[0122] (5) The high-precision plunger pump 42, the sixth valve 44 and the eighth valve 46 are turned on, and the seventh valve 45, the ninth valve 47, the tenth valve 48 and the pressure relief valve 57 are closed. The strength of the natural gas hydrate under the drilling fluid coupling condition is tested using a needle penetration strength meter 50, and the tested natural gas hydrate strength is 55.1 MPa;

[0123] (6) After the test is completed, the high-precision plunger pump 42 is turned off and on, and the pressure relief valve 57 is opened to release the pressure in the manifold. Then, the sixth valve 44 and the eighth valve 46 are closed, and the pressure relief valve 57 is closed.

[0124] (7) Using the above steps, the changes in the internal structure and mechanical properties of natural gas hydrate after 6 hours can be measured. Figure 8 From the perspective of the mesostructure and microstructure, the area occupied by natural gas hydrates continued to decrease on the basis of 3 hours, and the black holes continued to expand, indicating that the hydrates were further reduced at this time, resulting in weakening of the formation cementation and reduced strength. At this time, the compressive strength of natural gas hydrates was measured to be 46MPa.

[0125] Through the steps of the above-mentioned embodiments, the instability of the formation can be clearly characterized by tomography and changes in mechanical properties. The above embodiments are only used to illustrate the technical solutions of the present invention. The technical solutions in the above-mentioned embodiments can also be used to determine the internal conditions of the hydrate formation under other conditions. For example, by using the above-mentioned steps, the changes in the internal structure and mechanical properties of the natural gas hydrate after circulation for 9 hours or longer can be determined; by using the above-mentioned steps, the changes in the internal structure and mechanical properties of the natural gas hydrate caused by different drilling fluid temperatures can also be determined; by using the above-mentioned steps, the changes in the internal structure and mechanical properties of the natural gas hydrate caused by different drilling fluid wellbore pressures can also be determined. Therefore, through the device and method for evaluating the stability of the wellbore of the hydrate formation during simulated drilling provided by this application, it is possible to clearly observe the changes in the internal microstructure and mechanical properties of the hydrate formation under the conditions of coupling with the drilling fluid during the drilling process, and provide a basis and support for the future drilling and development and production of natural gas hydrate formations.

Claims

1. A device for evaluating the stability of a natural gas hydrate formation well wall, comprising a simulation reaction module, a gas injection module, a temperature and pressure test module, a needle penetration strength test module, a chromatography scanning module, and an optional drilling fluid circulation module, wherein the reaction module is placed on a test platform of the chromatography scanning module and connected to the drilling fluid circulation module by a hydraulic pipeline, a temperature and pressure test module is arranged inside the reaction module, the gas injection module is connected to the reaction module by a high-pressure pipeline, and a probe of the needle penetration strength test module is placed in the reaction module; the needle penetration strength test module comprises a liquid storage tank, a plunger pump, a pressure sensor, a valve, a needle penetration strength meter, a pressure relief valve, and a hydraulic pipe connected in sequence by a hydraulic pipe, the needle penetration strength test module comprises at least 2 groups of needle penetration strength meters, the needle penetration strength meter comprises a shell, a rear cover, an inner piston, and a probe, the shell is connected to the top cover of the reactor by a thread, the rear cover is connected to the shell by a threaded connection, the inner piston divides the shell into a hydraulic fluid medium space and a probe stroke space, and the probe is mounted on the inner piston.

2. The device according to claim 1, characterized in that The reaction module comprises a reaction kettle and a constant temperature system; and / or, The device also includes a data acquisition and control module.

3. The device according to claim 2, characterized in that The reactor comprises a top cover and a reactor body, and a pressure sensor and a temperature sensor are arranged on the top cover; and / or, The reactor body is divided into a space for storing circulating drilling fluid and gas, and a space for storing porous media and formation water. The upper part of the space for storing circulating drilling fluid and gas is provided with a drilling fluid outlet of a drilling fluid circulation module, and the lower part of the other side of the space for storing circulating drilling fluid and gas is provided with a drilling fluid inlet of the drilling fluid circulation module; and / or, The constant temperature system comprises a temperature control device, a valve, a temperature sensor, and a constant temperature box which are sequentially connected by connecting pipes; and / or, The temperature of the constant temperature system is -30 to 120°C; and / or, The data acquisition and control module is connected with the gas injection module, the temperature and pressure test module, and the needle penetration strength test module through a circuit.

4. The device according to claim 3, characterized in that The temperature of the constant temperature system is -10 to 90°C.

5. The device according to claim 1, characterized in that The drilling fluid circulation module comprises a drilling fluid storage tank, a plunger pump, a pressure regulating valve, a valve, and a temperature sensor which are sequentially connected by a connecting pipe; and / or, The gas injection module comprises a gas storage bottle, a buffer tank, a valve, a pressure regulating pump, a gas flow meter, and a pressure sensor connected in sequence by a connecting pipe; and / or, The gas in the gas injection module is selected from one of natural gas, carbon dioxide and nitrogen; and / or, The temperature and pressure test module includes at least two groups of temperature sensors and pressure sensors.

6. The device according to claim 5, characterized in that The gas in the gas injection module is natural gas.

7. The device according to claim 5, characterized in that The drilling fluid storage tank is provided with a temperature regulating device; and / or, The gas flow meter is selected from one of an orifice plate type, a vortex type, a turbine type, and an ultrasonic type; and / or, The fluid medium in the liquid storage tank of the penetration strength test module is selected from hydraulic oil; and / or, The plunger pump has a flow control accuracy of 0.01 to 0.03 ml / min, a fluid delivery capacity of 0.02 to 80 ml / min, and a working pressure of 3 to 40 MPa; and / or, The pressure sensor of the temperature and pressure test module has an accuracy of 0.1-0.3% and a test range of 0.05-50 MPa; and / or, The temperature sensor of the temperature and pressure test module has an accuracy of ±0.1°C and a test range of -20 to 100°C.

8. A method for evaluating the wellbore stability of a hydrate formation using the device described in any one of claims 1 to 7, comprising synthesizing a hydrate formation and evaluating its performance, and simulating the hydrate formation in drilling fluid circulation and evaluating its performance.

9. The method according to claim 8, characterized in that The synthetic hydrate formation and its performance evaluation include the following steps: Step 1-1: Fill the reactor with porous media, inject formation water, and start the temperature control device; Step 1-2: Open the valve of the gas injection module, inject the stored gas into the reactor, and adjust the pressure of the gas storage space in the reactor body; Step 1-3 starts the synthesis reaction, and the temperature and pressure during the reaction are recorded by the temperature and pressure test module; Step 1-4 uses a chromatography scanning module to quickly scan and analyze the hydrate obtained after the reaction; Steps 1-5 use a needle penetration strength test module to test the strength of the synthesized hydrate.

10. The method according to claim 9, characterized in that The porous medium is selected from at least one of sand and ceramsite; and / or, The stored gas is selected from one of natural gas, carbon dioxide and nitrogen; and / or, The reaction temperature in step 1-3 is -20 to 100° C., the reaction time is 0 to 240 h, and the reaction pressure is 0 to 40 MPa.

11. The method according to claim 10, characterized in that The porous medium is selected from at least one of sand particles and ceramsite particles of different particle sizes; and / or, The stored gas is selected from natural gas; and / or, The reaction temperature in step 1-3 is 2-60° C., the reaction time is 1-48 h, and the reaction pressure is 2-30 MPa.

12. The method according to any one of claims 9 to 11, characterized in that: The hydrate formation and performance evaluation in the simulated drilling fluid circulation includes the steps 1-1 to 1-3, or includes the steps 1-1 to 1-5 and the following steps thereafter: Step 2-1: Turn on the temperature regulating device of the drilling fluid circulation module and set the experimental temperature; Step 2-2: injecting drilling fluid into the storage circulating drilling fluid in the reactor, establishing a drilling fluid circulation, and setting the pressure and circulation time; Step 2-3 uses a tomography scanning module to quickly scan and analyze hydrates under drilling fluid coupling conditions; Step 2-4 uses a needle penetration strength test module to test the hydrate strength under drilling fluid coupling conditions.

13. The method according to claim 12, characterized in that Before step 2-1, the gas storage module needs to be closed to release the pressure of the gas storage space of the reactor; and / or, The experimental temperature in step 2-1 is -10 to 80° C.; and / or, The pressure in step 2-2 is 0 to 60 MPa; and / or, The cycle time in step 2-2 is 0 to 480 hours.

14. The method according to claim 13, characterized in that The experimental temperature in step 2-1 is 0 to 60° C.; and / or, The pressure in step 2-2 is 6 to 40 MPa; and / or, The cycle time in step 2-2 is 2 to 240 hours.

15. An application of the device for evaluating the wellbore stability performance of a hydrate formation as described in any one of claims 1 to 7 or the method for evaluating the wellbore stability performance of a hydrate formation as described in any one of claims 8 to 14, for detecting and evaluating the wellbore stability performance of a hydrate formation.

16. The use according to claim 15, characterized in that The application is used to measure the changes in the internal structure and mechanical properties of hydrates; and / or, The application is used to determine the changes in the internal structure and mechanical properties of hydrates caused by different drilling fluid temperatures; and / or, The application is used to measure the changes in the internal structure and mechanical properties of hydrates caused by different drilling fluid circulation pressures.

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