Device and method for quantitatively predicting different occurrence states in deep coal bed gas output process

Abstract

The invention relates to a device and method for quantitatively predicting different occurrence states in the deep coal bed gas output process, the device comprises a detection box and a nuclear magnetic resonance device, the detection box comprises a metal frame and a detachable plastic cover plate, and the plastic cover plate corresponds to an upper magnet and a lower magnet of the nuclear magnetic resonance device; a sample tube is placed in the detection box, and the sample tube comprises supporting tubes at two ends and a flexible heat-sealing bag in the middle; the two ends of the heat-sealing bag are correspondingly sleeved with the supporting pipes on the two sides, the middle of the heat-sealing bag is a sample area, and a standard sample or a coal sample is placed in the sample area; when in use, a standard sample is put into the heat-sealing bag and is fixed by heat sealing, and then the sample tube is mounted in the detection box. Performing nuclear magnetic resonance detection on the standard sample to obtain a standard curve of the methane production nuclear magnetic semaphore of the standard sample and the actual methane production gas quantity; and detecting the coal sample, recording the nuclear magnetic semaphores generated by the methane at different relaxation times, and obtaining the methane quantity corresponding to the nuclear magnetic semaphores in different occurrence states according to the standard curve.

Description

Technical Field

[0001] The present invention belongs to the technical field of coalbed methane dynamic prediction, and particularly relates to a device and method for quantitatively predicting different occurrence states during the production process of deep coalbed methane. Background Art

[0002] Coalbed methane is an unconventional natural gas that comes from underground coal seams. With the increasing large-scale development and utilization of shallow underground coal seams, the development of coalbed methane in deep underground coal seams has great economic value. Due to the characteristics of high formation temperature, high in-situ stress, and high reservoir pressure in deep coalbed methane, its occurrence state is significantly different from that of shallow coalbed methane, especially in the desorption process and seepage process, there are complex dynamic changes. At present, conventional experimental techniques are difficult to accurately describe the desorption, diffusion, and seepage processes of deep coalbed methane, which makes it difficult to predict the gas production of deep coalbed methane wells, affecting the formulation of a reasonable production system and the optimization of the development plan.

[0003] In this field, it is relatively important to quantitatively analyze the production laws of adsorbed gas and free gas in coal samples. Commonly used methods for identifying the occurrence state of methane mainly include gas geochemical analysis method, core experiment method, geophysical method, thermodynamic simulation and numerical simulation method, and microscopic pore structure analysis method. The gas geochemical analysis method is easily interfered by sample contamination and other chemical reactions, and it is difficult to directly distinguish the occurrence state of methane. The core experiment method takes a long time, has a high cost, and the experimental conditions are not completely consistent with the actual formation conditions. In the geophysical method, the data resolution of the logging method is not high, the accuracy of the interpretation model is limited, and it can only provide an indirect judgment. The thermodynamic simulation and numerical simulation method depends on the accuracy of model assumptions and input parameters, and lacks stable reliability. The microscopic pore structure analysis method can only reflect the local characteristics of the sample, this method has a high cost, and also has high requirements for equipment and operation. Therefore, finding an accurate, fast, and stable method for analyzing the occurrence state of coalbed methane is a difficult problem in this field. Summary of the Invention

[0004] In view of the above problems, the present invention provides a device and method for quantitatively predicting different occurrence states during the production process of deep coalbed methane. The device for quantitatively predicting different occurrence states during the production process of deep coalbed methane includes a detection box and a nuclear magnetic resonance device. The detection box includes a metal frame and a detachable plastic cover plate. The plastic cover plate corresponds to the upper and lower magnets of the nuclear magnetic resonance device, and the plastic cover plate does not generate nuclear magnetic signals. A sample tube is placed in the detection box. The sample tube includes support tubes at both ends and a flexible heat-sealed bag in the middle. Neither the support tubes nor the heat-sealed bag generates nuclear magnetic signals. The two ends of the heat-sealed bag are correspondingly sleeved on the support tubes on both sides, and the middle part of the heat-sealed bag is the sample area. A standard sample or a coal sample is placed in the sample area; When in use, the standard sample is placed in the heat-sealed bag, heat-sealed and fixed, and then the sample tube is installed in the detection box.

[0005] Optionally, the detection box is a cube with a hollow interior, and plastic covers cover the upper and lower sides of the detection box; The other sides of the detection box are made of metal. Heating components are respectively provided on the inner walls of the front and rear sides of the detection box to supply heat to the interior of the detection box. One installation port is provided on each of the left and right sides of the detection box for installing the sample tube and inputting gas into the sample tube and the detection box.

[0006] Further optionally, one installation port is connected to the inlet pipe, and the other installation port is connected to the outlet pipe. The inlet pipe is connected to the gas source cylinder and the regulating valve to input inert gas into the detection box to provide the confining pressure required for the experiment in the detection box. The outlet pipe is connected to the waste gas collection device; The temperature sensor real-time monitors the temperature in the area near the installation port in the detection box. One pressure gauge detects the air pressure (confining pressure) in the detection box, and the other pressure gauge detects the air pressure (reservoir pressure) in the sample tube.

[0007] Optionally, both ends of the sample tube are respectively butted against one installation port. The support tube has a hollow interior, and an air vent pipe is provided at one end close to the corresponding installation port. The air vent pipe passes through the detection box through the installation port. Several fastening ridges protruding outwards are provided at one end of the support tube close to the heat-sealed bag for installing and supporting the heat-sealed bag.

[0008] Optionally, two heating tubes are provided in the detection box. Hot fluorinated liquid is introduced into the heating tubes to heat the standard sample or coal sample so that the standard sample or coal sample reaches the temperature required for the experiment. Neither the heating tubes nor the fluorinated liquid generates nuclear magnetic signals; The inlet pipe of the heating tube passes through the detection box from the installation port close to it and is connected to an external liquid supply device. The part of the heating tube corresponding to the sample area of the heat-sealed bag is divided into two parts, and each part is in the form of a meandering coil, that is, it is coiled layer by layer from top to bottom in the vertical direction and is on the same vertical plane. The outlets of the four coils of the two heating tubes converge into one outlet pipe, and the outlet pipe passes through the detection box from any installation port.

[0009] Further optionally, a first heating tube and a second heating tube are provided in the detection box. The first heating tube includes a first inlet pipe, a first coil and a second coil. After the first inlet pipe enters the detection box, it extends along the corresponding support tube to one end of the heat-sealed bag. The outlet of the first inlet pipe is connected in parallel with a first branch pipe and a second branch pipe. The first branch pipe is connected to the inlet of the first coil, and the second branch pipe is connected to the inlet of the second coil to provide hot fluorinated liquid for the two coils. The first coil and the second coil are respectively arranged on the front and rear sides of the sample area; One end of the first coiled pipe, which is on the top side close to the corresponding support pipe, is the inlet, and one end on the bottom side far from the corresponding support pipe is the outlet; one end of the second coiled pipe, which is on the bottom side close to the corresponding support pipe, is the inlet, and one end on the top side far from the corresponding support pipe is the outlet, so that the flow directions of the coiled pipes on both sides of the sample area are different.

[0010] There is a gap between adjacent pipelines coiled by each coiled pipe. Further optionally, the ratio of the longitudinal sectional area of the standard sample to the sum of the longitudinal sectional areas of the pipelines of the first coiled pipe is 1:(0.75 - 0.85), which can achieve a good heating effect and does not waste energy.

[0011] The present invention also provides a method for quantitatively predicting different occurrence states during the production process of deep coalbed methane, including the following steps: S100: Perform nuclear magnetic resonance detection on a standard sample saturated with adsorbed methane to obtain a standard curve of the nuclear magnetic resonance signal amount of methane production and the actual gas volume of methane production of the standard sample; S200: Perform nuclear magnetic resonance detection on a coal sample saturated with adsorbed methane, record the nuclear magnetic resonance signal amount of methane generated at different relaxation times of the coal sample, and the nuclear magnetic resonance signal amount corresponding to methane in different occurrence states. According to the standard curve, obtain the methane gas volume corresponding to the nuclear magnetic resonance signal amount in different occurrence states.

[0012] The present invention uses nuclear magnetic resonance technology to monitor the dynamic process of methane gas release from the standard sample and the coal sample in real time. Nuclear magnetic resonance is non-destructive to the sample and can provide nuclear magnetic resonance signals of the dynamic changes of coalbed methane in different states (adsorbed state and free state), with few interference factors and high accuracy. The present invention first uses nuclear magnetic resonance technology to detect a standard sample saturated with adsorbed methane, fits the total methane signal amount of the detected standard sample with the methane gas volume data to obtain a standard curve. Then, use nuclear magnetic resonance technology to detect an actual coal sample saturated with adsorbed methane. According to different relaxation times, the nuclear magnetic resonance signal amount detected first corresponds to the adsorbed methane, forming an obvious adsorption peak, and the nuclear magnetic resonance signal amount detected later corresponds to the free methane, forming one or more lower free peaks. The peak area of the adsorption peak is used as the nuclear magnetic resonance signal amount and substituted into the standard curve to calculate the volume of adsorbed methane. The peak area of the free peak is used as the nuclear magnetic resonance signal amount and substituted into the standard curve to calculate the volume of free methane. Thus, the dynamic distribution of different occurrence states of coalbed methane is quantitatively predicted.

[0013] The formation pressure is the pressure of the overlying formation where the deep coal reservoir is located, that is, the confining pressure. The reservoir pressure refers to the fluid pressure (including water pressure and air pressure) acting on the coal pore - fracture space, that is, the pore fluid pressure.

[0014] Optionally, in step S100, when detecting the standard sample, S101: Place the standard sample in a heat-sealed bag of the sample tube and heat-seal it for fixation. Then install the sample tube in the detection box, seal both the installation opening of the detection box and the plastic cover plate, and then place it in the nuclear magnetic resonance device. S102: Only open the air pipe connected to the vacuum pump to evacuate the sample tube. The evacuation time is 12 - 24h. S103: Close the air pipe for evacuation, turn on the heating plate, start the circulation of the fluorinated liquid in the heating tube, so that the standard sample reaches the formation temperature required for the experiment; open the air inlet pipe and close the air outlet pipe to input inert gas into the detection box, so that the pressure in the detection box reaches the formation pressure required for the experiment. S104: Open another air pipe to introduce methane gas into the sample tube. The pressure in the sample tube gradually increases until it reaches the reservoir pressure required for the experiment. Turn on the nuclear magnetic resonance device and fully saturate it for more than 60h. If the nuclear magnetic signal amount of methane gas in the standard sample does not change, it indicates that the standard sample has been saturated with adsorbed methane, and stop inputting methane.

[0015] Optionally, in step S100, the method for determining the standard curve is as follows: S105: Determine the volume of methane in the sample tube at the reservoir pressure in step S104 according to the real gas state equation. S106: Open the air pipe connected to the gas analysis device so that the methane released from the standard sample can be discharged from the sample tube; the nuclear magnetic resonance device continuously records the nuclear magnetic signal of the standard sample, and the nuclear magnetic resonance device analyzes the 1 H nuclear signal amounts at different relaxation times, and accumulate these signals to obtain the total methane signal amount of the standard sample. S107: Turn off the heating plate, drain the fluorinated liquid in the heating tube, open the air outlet pipe, drain the inert gas in the detection box, take out the sample tube, and take out and clean the standard sample. Repeat steps S101 to S107, each time using a different reservoir pressure to obtain the methane volume and the corresponding total methane signal amount at different reservoir pressures. S108: Use the total methane signal amount as the abscissa and the methane volume as the ordinate to fit the above data to obtain the equation of the standard curve.

[0016] Optionally, step S200 is specifically as follows: S201: First dry the actual coal sample in an oven at 110°C for 24h to exclude the influence of free water in the coal sample; then perform the above steps S101 to S103. S202: Turn on the nuclear magnetic resonance device, use the CPMG pulse sequence to perform nuclear magnetic resonance measurement on the coal sample, and invert to obtain the T2 spectrum of the coal sample, which is used as the base signal to exclude the influence of substances containing 1 H nuclei in the original coal sample on the nuclear magnetic resonance detection result. S203: Perform the above steps S104 and S106, with the difference that the nuclear magnetic resonance device analyzes the 1 amounts of H nuclear signals at different relaxation times. The first complete strong signal peak corresponds to adsorbed methane, and the subsequent several weak signal peaks correspond to free methane. Subtract the base signal from the nuclear magnetic signal amount corresponding to adsorbed methane to obtain the corrected signal amount of adsorbed methane. Subtract the base signal from the nuclear magnetic signal amount corresponding to free methane to obtain the corrected signal amount of free methane. Substitute the corrected signal amounts of adsorbed methane and free methane into the equation of the standard curve respectively to obtain the volume of adsorbed methane and the volume of free methane under the reservoir pressure. Repeat steps S201 to S203, each time using a different reservoir pressure, to obtain the dynamic distribution of methane in different occurrence states during the actual coalbed methane release process.

[0017] Further optionally, in step S202, the first complete strong signal peak in the base signal corresponds to the substance containing 1 H nuclei in the adsorbed state, and the subsequent several weak signal peaks correspond to the substance containing 1 H nuclei in the free state; In step S203, subtract the nuclear magnetic signal amount (peak area) corresponding to the substance containing 1 H nuclei in the adsorbed state in the base signal from the nuclear magnetic signal amount (peak area) corresponding to adsorbed methane to obtain the corrected signal amount of adsorbed methane; Subtract the nuclear magnetic signal amount (sum of several small peak areas) corresponding to the substance containing 1 H nuclei in the free state in the base signal from the nuclear magnetic signal amount (sum of several small peak areas) corresponding to free methane to obtain the corrected signal amount of free methane; Substitute the corrected signal amount of adsorbed methane into the equation of the standard curve to obtain the volume of adsorbed methane, and substitute the corrected signal amount of free methane into the equation of the standard curve to obtain the volume of free methane; During the actual coalbed methane release, under the action of the drainage medium, as the mining time extends, the reservoir pressure gradually decreases. The volumes of adsorbed methane and free methane under different reservoir pressures reflect the dynamic distribution of methane in different occurrence states during the release and production process of the coalbed methane well. Description of the Drawings

[0018] Figure 1 It is a schematic structural diagram of the detection box; Figure 2 It is a schematic diagram of the sample tube; Figure 3 It is a schematic diagram of the heating tube; Figure 4Nuclear magnetic resonance signal curve diagram of standard samples under different reservoir pressures; Figure 5 Standard curve obtained by fitting; Figure 6 T2 spectrum diagram of coal sample substrate; Figure 7 Nuclear magnetic resonance signal curve diagram of coal samples under different reservoir pressures; Figure 8 Diagram of the dynamic distribution of different occurrence states during the release and production of coalbed methane.

[0019] In the attached drawings, 1 - detection box, 2 - plastic cover plate, 3 - sixth branch pipe, 4 - installation port, 5 - sample tube, 6 - support pipe, 7 - heat-sealed bag, 8 - heating pipe, 9 - metal frame, 10 - magnet, 11 - slideway, 12 - ventilation pipe, 13 - fastening edge, 14 - sample area, 15 - first liquid inlet pipe, 16 - second liquid inlet pipe, 17 - first coiled pipe, 18 - second coiled pipe, 19 - third coiled pipe, 20 - fourth coiled pipe, 21 - first branch pipe, 22 - second branch pipe, 23 - third branch pipe, 24 - fourth branch pipe, 25 - liquid outlet pipe, 26 - fifth branch pipe. Detailed implementation method

[0020] Example 1 The device for quantitatively predicting different occurrence states during the production of deep coalbed methane in this example includes a detection box and a nuclear magnetic resonance device. The detection box used for detection includes a metal frame and a detachable plastic cover plate. The plastic cover plate corresponds to the upper and lower magnets of the nuclear magnetic resonance device, and the plastic cover plate does not generate nuclear magnetic resonance signals; a sample tube is placed inside the detection box. The sample tube includes support pipes at both ends and a flexible heat-sealed bag in the middle. Neither the support pipes nor the heat-sealed bag generates nuclear magnetic resonance signals; both ends of the heat-sealed bag are correspondingly sleeved on the support pipes on both sides, and the middle part of the heat-sealed bag is the sample area, where standard samples or coal samples are placed. During use, place the standard sample into the heat-sealed bag, heat-seal and fix it, and then install the sample tube into the detection box.

[0021] As Figures 1 - 3 shown, the detection box 1 is a cube with a hollow interior, including a metal frame 9 and a detachable plastic cover plate 2. The plastic cover plate 2 covers the upper and lower sides of the detection box 1 and corresponds to the upper and lower magnets 10 of the nuclear magnetic resonance device. The plastic cover plate 2 does not generate nuclear magnetic resonance signals; The other sides of the detection box 1 are made of metal. Heating components are respectively provided on the inner walls of the front and rear sides of the detection box 1 to supply heat to the inside of the detection box 1; an installation port 4 is respectively provided on the left and right sides of the detection box 1 for installing the sample tube 5 and inputting gas into the sample tube 5 and the detection box 1.

[0022] The top and bottom surfaces of the detection box 1 are respectively provided with horizontal edges made of metal. The plastic cover plate 2 is detachably connected to the horizontal edges by screws, and a gasket is provided between the plastic cover plate 2 and the horizontal edges to ensure the airtightness of the detection box 1. The cross-sectional area of the plastic cover plate 2 is not less than the cross-sectional area of the magnet 10 of the corresponding nuclear magnetic resonance device.

[0023] The detection box 1 simulates the geological environment of the actual deep coal seam and needs to withstand a certain temperature and formation pressure. The four side surfaces of the detection box 1 are made of metal, which can provide sufficient strength, but metal cannot withstand nuclear magnetic detection. The nuclear magnetic resonance device is provided with two magnets 10. The detection box 1 is located between the two magnets. The upper and lower side surfaces of the detection box 1 facing the magnets are plastic cover plates 2, which allow nuclear magnetic rays to pass through the detection box 1. The plastic cover plate 2 only needs to be sealed with the detection box 1, and the detachable plastic cover plate 2 also facilitates the loading of the sample tube 5 into the detection box 1 and other maintenance inside the detection box 1.

[0024] The heating component is a heating plate, which is closely attached to the corresponding side wall of the detection box 1. The circuit of the heating plate passes out of the detection box 1 through the installation opening and is connected to an external power supply.

[0025] One installation opening is connected to the inlet pipe, and the other installation opening is connected to the outlet pipe. The inlet pipe is connected to the gas source cylinder and the regulating valve to input inert gas into the detection box 1 and provide the confining pressure required for the experiment in the detection box 1. The outlet pipe is connected to the waste gas collection device.

[0026] The installation opening is provided with a flange to facilitate the sealing of the detection box 1. The flange is provided with a number of through holes to allow the circuits of the heating components, the ventilation pipes of the sample tube 5, the temperature sensor, the two pressure gauges, the heating pipe, the inlet pipe, and the outlet pipe to penetrate into the detection box 1. The temperature sensor real-time monitors the temperature in the area near the installation opening inside the detection box 1. One pressure gauge detects the air pressure (confining pressure) inside the detection box 1, and the other pressure gauge detects the air pressure (reservoir pressure) inside the sample tube 5.

[0027] The nuclear magnetic resonance device is a conventional nuclear magnetic detection and analysis device. The inside of the device has a cavity. A magnet 10 is respectively provided above and below the cavity. The cavity is used to place the detection box 1. The left and right side surfaces of the cavity are open, and the front and back side surfaces are respectively provided with chutes. The outer sides of the front and back side surfaces of the detection box 1 are respectively provided with slideways 11, and the slideways 11 cooperate with the corresponding chutes to facilitate the pushing and pulling installation of the detection box 1.

[0028] Both ends of the sample tube 5 are respectively butted with an installation port. The sample tube 5 includes support tubes 6 at both ends and a flexible heat-sealed bag 7 in the middle. Neither the support tubes 6 nor the heat-sealed bag 7 generates nuclear magnetic signals. The inside of the support tube 6 is hollow, and an air vent pipe 12 is provided at one end close to the corresponding installation port. The air vent pipe 12 passes through the detection box 1 through the installation port. Several outwardly protruding fastening ridges 13 are provided at one end of the support tube close to the heat-sealed bag 7 for installing and supporting the heat-sealed bag 7. Both ends of the heat-sealed bag 7 are correspondingly sleeved on the support tubes on both sides. The middle part of the heat-sealed bag 7 is a sample area 14, and a standard sample or a coal sample is contained in the sample area 14.

[0029] The air vent pipe of one support tube is connected to a methane gas source outside the detection box 1 for inputting methane gas into the sample tube 5 so that the standard sample or the coal sample can be saturated with adsorbed methane. The air vent pipe of the other support tube is connected in parallel with a gas analysis device and a vacuum pump outside the detection box 1 for detecting the component content of the gas output from the sample tube 5. When this air vent pipe is connected to the vacuum pump, the sample tube 5 can be evacuated.

[0030] When loading the standard sample or the coal sample into the sample tube 5, first load the standard sample or the coal sample into the sample area 14 in the middle of the heat-sealed bag 7. Both ends of the heat-sealed bag 7 are respectively sleeved on the openings at one end of the support tubes on both sides with fastening ridges. The opening of the heat-sealed bag 7 is sleeved outside the fastening ridges 13 to support the opening of the heat-sealed bag 7. Then, use the hot air of a hair dryer to blow the entire heat-sealed bag 7 so that the heat-sealed bag 7 tightly wraps the outer surface of the standard sample or the coal sample and the outer surface of the support tube opening, thereby fixing the standard sample or the coal sample.

[0031] The present invention uses the sample tube 5 to hold the standard sample and the coal sample. The material of the sample tube 5 does not affect nuclear magnetic detection. Both ends of the sample tube 5 are respectively connected to two installation ports. The flange surface at the installation port is provided with an installation groove for the part inside the detection box 1. One end of the support tube is fixedly clamped in the corresponding installation groove, so that the sample tube 5 crosses the middle part inside the detection box 1 and is more likely to receive nuclear magnetic detection. Confining pressure gas is introduced between the detection box 1 and the sample tube 5 to provide confining pressure for the standard sample and the coal sample to simulate the formation pressure of the real deep coal seam. The standard sample or the coal sample is contained in the heat-sealed bag 7 to avoid the confining pressure gas directly contacting the sample. After the heat-sealed bag 7 shrinks due to heat, it closely adheres to the sample surface to form an effective package. There is very little residual gas in the heat-sealed bag 7, avoiding the gas in the heat-sealed bag 7 resisting the external confining pressure and also avoiding the heat-sealed bag 7 being broken by the external confining pressure. When the standard sample or the coal sample is saturated with adsorbed methane, only methane needs to be introduced into the sample tube 5, saving the amount of methane used. The detection box space outside the sample tube 5 facilitates the setting of heating components and provides a suitable temperature environment for the heat-sealed bag 7.

[0032] Inside the detection box 1, there are two heating tubes 8. Hot fluorinated liquid is passed through the heating tubes 8 to heat the standard sample or coal sample so that the standard sample or coal sample reaches the temperature required for the experiment. Neither the heating tubes 8 nor the fluorinated liquid generates nuclear magnetic signals. The liquid inlet pipe of the heating tube passes through the detection box 1 from the adjacent installation opening and is connected to an external liquid supply device. The part of the heating tube corresponding to the sample area 14 of the heat-sealed bag 7 is divided into two parts, and each part is in the form of a meandering coil, that is, it is coiled layer by layer from top to bottom in the vertical direction and is on the same vertical plane. The outlets of the four coils of the two heating tubes converge into a liquid outlet pipe 25, and the liquid outlet pipe 25 passes through the detection box 1 from any installation opening.

[0033] An external constant temperature device is provided outside the detection box 1 to heat the fluorinated liquid at a constant temperature. The liquid inlet pipe and the liquid outlet pipe 25 are both connected to the constant temperature device.

[0034] Inside the detection box 1, there are a first heating tube and a second heating tube. The first heating tube includes a first liquid inlet pipe 15, a first coil 17, and a second coil 18. After the first liquid inlet pipe 15 enters the detection box 1, it extends along the corresponding support pipe to one end of the heat-sealed bag 7. The outlet of the first liquid inlet pipe 15 is connected in parallel with a first branch pipe 21 and a second branch pipe 22. The first branch pipe 21 is connected to the inlet of the first coil 17, and the second branch pipe 22 is connected to the inlet of the second coil 18 to provide hot fluorinated liquid for the two coils. The first coil 17 and the second coil 18 are respectively arranged on the front and back sides of the sample area 14. One end at the top on the side of the first coil 17 close to the corresponding support pipe is the inlet, and one end at the bottom on the side away from the corresponding support pipe is the outlet. One end at the bottom on the side of the second coil 18 close to the corresponding support pipe is the inlet, and one end at the top on the side away from the corresponding support pipe is the outlet, so that the flow directions of the coils on both sides of the sample area 14 are different.

[0035] The structure of the second heating tube is the same as that of the first heating tube. The second heating tube includes a second liquid inlet pipe 16, a third coil 19, and a fourth coil 20. After the second liquid inlet pipe 16 enters the detection box 1, it extends along the corresponding support pipe to the other end of the heat-sealed bag 7. The outlet of the second liquid inlet pipe 16 is connected in parallel with a third branch pipe 23 and a fourth branch pipe 24. The third branch pipe 23 is connected to the inlet of the third coil 19, and the fourth branch pipe 24 is connected to the inlet of the fourth coil 20 to provide hot fluorinated liquid for the two coils. The third coil 19 and the fourth coil 20 are respectively arranged on the front and back sides of the sample area 14, that is, the first coil 17 and the third coil 19 are on the same side of the sample area 14, and the second coil 18 and the fourth coil 20 are on the other side of the sample area 14. One end of the third coiled pipe 19, which is on the side close to the corresponding support pipe and at the bottom, is the inlet, and one end on the side away from the corresponding support pipe and at the top is the outlet; one end of the fourth coiled pipe 20, which is on the side close to the corresponding support pipe and at the top, is the inlet, and one end on the side away from the corresponding support pipe and at the bottom is the outlet, so that the flow directions of the coiled pipes on both sides of the sample area 14 are different.

[0036] The outlet of the third coiled pipe 19 is connected to the outlet of the first coiled pipe 17, and then to the fifth branch pipe 26; the outlet of the second coiled pipe 18 is connected to the outlet of the fourth coiled pipe 20, and then to the sixth branch pipe 3. The fifth branch pipe 26 and the sixth branch pipe 3 extend horizontally to any one of the support pipes and then merge into a liquid outlet pipe 25, which extends along the support pipe to the outside of the detection box 1.

[0037] In the present invention, a heating plate is arranged in the detection box 1 to play a basic heating role, so that the internal temperature of the detection box 1 is close to the temperature required by the experiment. However, there is still a gas space between the heating plate and the sample tube 5, and the thermal conductivity of the gas is poor, resulting in a higher temperature near the heating plate than the temperature of the sample in the heat-sealed bag 7. Ordinary heating plates, heating wires, etc. are made of metal materials, which will affect nuclear magnetic detection and can only supply heat outside the sample. The present invention adopts a method of combining a heating plate and a heating tube, and selects a heating tube without nuclear magnetic signal and a fluorinated liquid close to the sample for auxiliary heating to ensure that the sample can reach the temperature required by the experiment.

[0038] Specifically, the four coiled pipes are placed on the front and rear sides of the sample area 14, while the magnets are above and below the sample area 14, and the coiled pipes do not block the nuclear magnetic rays. The coiled pipes can extend the residence time of the fluorinated liquid in the sample area 14. The total height of the coiled pipes is not less than the actual height of the standard sample. On one side of the sample area 14, one coiled pipe corresponds to half of the length of the sample area 14, so that each half of the sample area 14 can be heated by one coiled pipe. The fluorinated liquid in the first coiled pipe 17 flows from top to bottom, and the fluorinated liquid in the opposite third coiled pipe 19 flows from bottom to top, that is, on this side of the sample area 14, the high-temperature fluorinated liquid is injected in a diagonal manner and then flows out in a diagonal manner; it is similar on the other side of the sample area 14, the fluorinated liquid in the second coiled pipe 18 flows from bottom to top, and the fluorinated liquid in the opposite fourth coiled pipe 20 flows from top to bottom; moreover, on the same end of the sample area 14, for example, the first coiled pipe 17 and the second coiled pipe 18, the flow directions of the fluorinated liquid are opposite. The above design makes the sample area 14 heated more evenly and has a better heat preservation effect.

[0039] There is a gap between adjacent pipelines coiled by each coiled pipe itself, and the ratio of the longitudinal sectional area of the standard sample to the sum of the longitudinal sectional areas of the pipelines of the first coiled pipe is 1:0.75.

[0040] Embodiment 2 The method for quantitatively predicting different occurrence states during the production process of deep coalbed methane in this embodiment includes the following steps: S100: Perform nuclear magnetic resonance (NMR) detection on a standard sample saturated with adsorbed methane to obtain a standard curve of the NMR signal amount of methane production in the standard sample and the actual gas volume of methane production. S200: Perform NMR detection on a coal sample saturated with adsorbed methane, record the NMR signal amounts of methane generated at different relaxation times of the coal sample, corresponding to the NMR signal amounts of methane in different occurrence states, and obtain the methane gas volumes corresponding to the NMR signal amounts of different occurrence states according to the standard curve. The method for quantitatively predicting different occurrence states during the production of deep coalbed methane is specifically as follows: (1) Collect a coal sample in a deep coal seam, record the formation pressure and temperature of the deep coal seam, and make the collected coal sample into a style with the same size as the standard sample. (2) Fix the standard sample in a sample tube, then install the sample tube in a detection box, then seal the detection box, then place the detection box in an NMR device, evacuate the inside of the sample tube, and provide the detection box with the same formation pressure and temperature as the deep coal seam. Introduce methane gas, turn on the NMR device, and stop introducing methane gas after the standard sample is saturated with adsorbed methane. (3) Record the total NMR signal amount of methane generated in the sample tube, and obtain a standard curve of the total methane signal amount in the sample tube and the methane gas volume of the standard sample according to the actual gas volume of methane in the standard sample. (4) Take out the standard sample, perform the operation of step S2 using the actual coal sample, then turn on the NMR device, record the NMR signal amounts of methane generated at different relaxation times in the sample tube, corresponding to the NMR signal amounts of methane in different occurrence states, and obtain the methane gas volumes corresponding to the NMR signal amounts of different occurrence states according to the standard curve.

[0041] In step (1), the material of the standard sample is polyetheretherketone, which does not generate NMR signals, is not easily deformed, has a weak adsorption capacity for methane gas, and is suitable for NMR detection. The standard sample is cylindrical and has a number of through holes that penetrate the standard sample along the axial direction of the standard sample, making the standard sample in a ventilated state; the structure, shape, and size of the coal sample are the same as those of the standard sample, except that it does not include through holes.

[0042] In step S100, when detecting the standard sample, step (2) is specifically as follows: S101: Heat-seal and fix the standard sample in a heat-sealable bag of the sample tube, then install the sample tube in the detection box, seal both the installation port and the plastic cover plate of the detection box, and then install it in the NMR device. S102: Only open the ventilation pipe connected to the vacuum pump to evacuate the inside of the sample tube, and the evacuation time is 24 hours. S103: Close the vent pipe for evacuation, turn on the heating plate, start the circulation of the fluorinated liquid in the heating pipe, so that the standard sample reaches the formation temperature of 70 °C required for the experiment; turn on the inlet pipe and close the outlet pipe, and input inert gas into the detection chamber so that the formation pressure in the detection chamber reaches 25 MPa required for the experiment; S104: Open another vent pipe, introduce methane gas into the sample tube, the air pressure in the sample tube gradually increases until it reaches the reservoir pressure of 20 MPa required for the experiment, turn on the nuclear magnetic resonance device, fully saturate for 60 h, and detect that the nuclear magnetic signal amount of methane gas in the standard sample does not change, indicating that the standard sample has been saturated with adsorbed methane, and stop inputting methane.

[0043] In step S100, the method for determining the standard curve (i.e., step (3)) is as follows: S105: Determine the volume of methane in the sample tube under the reservoir pressure in step S104 according to the real gas state equation; S106: Open the vent pipe connected to the gas analysis device so that the methane released from the standard sample can be discharged from the sample tube; the nuclear magnetic resonance device continuously records the nuclear magnetic signal of the standard sample, and the nuclear magnetic resonance device analyzes the 1 H nuclear signal amount at different relaxation times, accumulate this signal, and obtain the total methane signal amount of the standard sample; S107: Turn off the heating plate, drain the fluorinated liquid in the heating pipe, open the outlet pipe, drain the inert gas in the detection chamber, take out the sample tube, take out and clean the standard sample; Repeat steps S101 to S107, each time using a different reservoir pressure, to obtain the methane volume and the corresponding total methane signal amount under different reservoir pressures. As Figure 4 shown, the reservoir pressures corresponding to the curve from front to back are 0.1, 5, 10, 13, 15, 20 MPa respectively; S108: Use the total methane signal amount as the abscissa and the methane volume as the ordinate to fit the above data to obtain the equation of the standard curve.

[0044] In step S105, the volume of methane in the sample tube is determined by the following formula: V = n × V m × 1000 where V is the volume of methane gas injected into the sample tube, cm 3 ; V m is the molar volume of gas, 22.4 L / mol; n is determined by the real gas state equation, and n is: ; where P is the reservoir pressure, MPa; V 标 is the pore volume of the standard sample, which is taken as 2.6 cm 3; Z is the methane gas compressibility factor, dimensionless; R is the universal gas constant, 8.314 cm 3 ·MPa / (mol·K); T is the experimental temperature, 70 °C = 344.15 K.

[0045] Z is determined by the following formula: ; where P is the reservoir pressure, MPa; T is the experimental temperature, 70 °C = 344.15 K.

[0046] In step S108, linear fitting is performed, and the obtained standard curve is a straight line, as Figure 5 shown. The equation of the standard curve is: ; where Q is the methane volume, in mL; T is the total methane signal amount, in p.u.; the determination coefficient R 2 obtained by fitting is 0.99.

[0047] Step S200 is specifically as follows (i.e., step (4)): S201: First, dry the actual coal sample in an oven at 110 °C for 24 h to exclude the influence of free water in the coal sample; then perform the above steps S101 to S103; S202: Turn on the nuclear magnetic resonance device, use the CPMG pulse sequence to perform nuclear magnetic resonance measurement on the coal sample, and invert to obtain the T2 spectrum of the coal sample, as Figure 6 shown, and use it as the base signal to exclude the influence of substances containing 1 H nuclei originally in the coal sample on the nuclear magnetic resonance detection result; S203: Perform the above steps S104 and S106. The difference is that the nuclear magnetic resonance device analyzes the 1 H nucleus signal amounts at different relaxation times. The first complete strong signal peak corresponds to adsorbed methane, and several subsequent weak signal peaks correspond to free methane. The nuclear magnetic resonance signal amount corresponding to adsorbed methane minus the base signal is the corrected signal amount of adsorbed methane, and the nuclear magnetic resonance signal amount corresponding to free methane minus the base signal is the corrected signal amount of free methane. Substitute the corrected signal amounts of adsorbed methane and free methane into the equation of the standard curve respectively to obtain the volumes of adsorbed methane and free methane at this reservoir pressure; Repeat steps S201 to S203, each time using a different reservoir pressure, to obtain the dynamic distribution of methane in different occurrence states during the actual coalbed methane release process, as Figure 7As shown, the reservoir pressures corresponding to the curve from front to back are 1.22, 2.22, 3.77, 4.35, 6.33, 8.41, 9.48, 10.00, 11.49, 12.06, 13.12, 14.32, 16.30, 17.26, 18.53, 19.10 MPa respectively.

[0048] In steps S103 and S201, the heating plate is powered on for heating, and the heating tube is filled with hot fluorinated liquid, so that the temperature in the detection box reaches the experimental requirements. The temperature measured by the temperature sensor is 1 - 3 °C lower than the experimental requirements, and the temperature of the hot fluorinated liquid is 3 - 5 °C higher than the experimental requirements. The manometer is used to judge whether the confining pressure in the detection box reaches the formation pressure required by the experiment, and during the subsequent experiment process, the manometer is observed in real time to facilitate pressure supplementation for the detection box to maintain its confining pressure.

[0049] In step S202, as Figure 6 shown, the first complete strong signal peak in the base signal corresponds to the adsorbed substance containing 1 H nuclei, and the subsequent weak signal peaks correspond to the free substance containing 1 H nuclei; In step S203, the nuclear magnetic signal quantity (peak area) corresponding to adsorbed methane, after deducting the nuclear magnetic signal quantity (peak area) corresponding to the adsorbed substance containing 1 H nuclei in the base signal, obtains the corrected signal quantity of adsorbed methane; The nuclear magnetic signal quantity (sum of several small peak areas) corresponding to free methane, after deducting the nuclear magnetic signal quantity (sum of several small peak areas) corresponding to the free substance containing 1 H nuclei in the base signal, obtains the corrected signal quantity of free methane; Substituting the corrected signal quantity of adsorbed methane into the equation of the standard curve to obtain the volume of adsorbed methane, and substituting the corrected signal quantity of free methane into the equation of the standard curve to obtain the volume of free methane; The production of coalbed methane is a comprehensive process of drainage - pressure reduction - desorption - diffusion - seepage - gas production. Its core process is to continuously drain and reduce pressure to lower the reservoir pressure below the methane desorption pressure, so that methane desorbs and is produced. As Figure 8 shown, during the actual release of coalbed methane, under the action of the drainage medium, as the mining time extends, the reservoir pressure gradually decreases. The volumes of adsorbed methane and free methane under different reservoir pressures reflect the dynamic distribution of methane in different occurrence states during the release and production process of coalbed methane wells.

[0050] Example 3 The device for quantitatively predicting different occurrence states during the production of deep coalbed methane provided in this embodiment is the same as that in Embodiment 1, except that no heating tube is provided in the detection box, and only the heating plate is used for heating.

[0051] Embodiment 4 The device for quantitatively predicting different occurrence states during the production of deep coalbed methane provided in this embodiment is the same as that in Embodiment 1, except that the first coiled pipe and the third coiled pipe are combined into one coiled pipe, which has one inlet and one outlet. The inlet is close to and connected to the first branch pipe, and the outlet is close to and connected to the fifth branch pipe; the second coiled pipe and the fourth coiled pipe are combined into one coiled pipe, which has one inlet and one outlet. The inlet is close to and connected to the second branch pipe, and the outlet is close to and connected to the sixth branch pipe; the first liquid inlet pipe supplies liquid to the two coiled pipes. The inlets of the two coiled pipes are both arranged at the top, and the outlets are both arranged at the bottom. The second liquid inlet pipe, the third branch pipe and the fourth branch pipe are not provided, and the fifth branch pipe and the sixth branch pipe are parallel outlet pipes.

[0052] Embodiment 5 The device for quantitatively predicting different occurrence states during the production of deep coalbed methane provided in this embodiment is the same as that in Embodiment 1, except that there is a gap between adjacent pipelines coiled by each coiled pipe itself, and the ratio of the longitudinal sectional area of the standard sample to the sum of the longitudinal sectional areas of the pipelines of the first coiled pipe is 1:0.85.

[0053] Embodiment 6 The device for quantitatively predicting different occurrence states during the production of deep coalbed methane provided in this embodiment is the same as that in Embodiment 1, except that there is a gap between adjacent pipelines coiled by each coiled pipe itself, and the ratio of the longitudinal sectional area of the standard sample to the sum of the longitudinal sectional areas of the pipelines of the first coiled pipe is 1:0.74.

[0054] In the experimental devices of Embodiment 1 and Embodiments 3 - 6, the temperature sensor extends to closely adhere to the upper surface of the sample area, and can actually detect the temperature of the sample area. In Embodiment 1 and Embodiments 3 - 6, the standard sample, the sample tube and the detection box are installed according to the method of Embodiment 2. After closing the detection box, the intake pipe and one vent pipe are closed, and check valves are respectively installed on the outlet pipe and the other vent pipe, allowing the gas in the detection box and the sample tube to expand and discharge due to heating, and not allowing external gas to enter the detection box and the sample tube to bring in cold; the heating plate is started, and the preset temperature of the heating plate is 70°C; the temperature of the hot fluorinated liquid is 73°C, and the flow rates are the same. The target temperature of the sample area is 70°C. The temperature of the sample area of each preparation example and embodiment is detected by the temperature sensor, and the results are shown in the following table.

[0055] Table 1 Comparison of the sample area temperatures of Embodiment 1 and Embodiments 3 - 6 。

[0056] As can be seen from the above table, Example 1 and Example 5 are closest to the target temperature of 70°C. The heating effects of other preparation examples are not good, indicating that the heating tubes in the experimental device of the present invention are reasonably arranged, which helps the samples in the sample area reach the experimental required temperature, is closer to the simulation conditions, and has higher accuracy.

Claims

1. A device for quantitatively predicting different occurrence states of deep coalbed methane production, characterized in that: It includes a detection box and a nuclear magnetic resonance device. The detection box includes a metal frame and a detachable plastic cover, and the plastic cover corresponds to the upper and lower magnets of the nuclear magnetic resonance device. A sample tube is placed in the detection box, and the sample tube includes support tubes at both ends and a flexible heat-sealed bag in the middle. The two ends of the heat-sealed bag correspond to the support tubes at both sides, and the middle of the heat-sealed bag is a sample area, and the standard sample or coal sample is placed in the sample area. When in use, place the standard sample into a heat-sealed bag, heat-seal it, and then install the sample tube in the test box.

2. The device for quantitatively predicting different occurrence states in the production process of deep coalbed methane according to claim 1 is characterized in that: The detection box is a cube with a hollow interior, and a plastic cover covers the upper and lower sides of the detection box; the other sides of the detection box are made of metal, and the inner walls of the front and rear sides of the detection box are respectively provided with heating components to provide heat to the inside of the detection box; the left and right sides of the detection box are respectively provided with an installation port for installing a sample tube and inputting gas into the sample tube and the detection box.

3. The device for quantitatively predicting different occurrence states in the production process of deep coalbed methane according to claim 2, characterized in that: One installation port is connected to the air inlet pipe, and the other installation port is connected to the air outlet pipe. The air inlet pipe is connected to the gas source cylinder and the regulating valve to input inert gas into the test box and provide the test box with the ambient pressure required by the experiment; the air outlet pipe is connected to the exhaust gas collection device; The temperature sensor monitors the temperature of the area near the installation port in the detection box in real time; a pressure gauge detects the air pressure in the detection box, and another pressure gauge detects the air pressure in the sample tube.

4. The device for quantitatively predicting different occurrence states in the production process of deep coalbed methane according to claim 3 is characterized in that: The two ends of the sample tube are respectively connected to a mounting port, the interior of the support tube is hollow, and a vent pipe is provided at one end close to the corresponding mounting port, and the vent pipe passes through the mounting port and out of the detection box.

5. The device for quantitatively predicting different occurrence states in the production process of deep coalbed methane according to claim 4, characterized in that: The detection box is provided with two heating tubes, and hot fluoride liquid is passed into the heating tubes to heat the standard sample or coal sample so that the standard sample or coal sample reaches the temperature required by the experiment; neither the heating tubes nor the fluoride liquid generate nuclear magnetic signals; The portion of the heating tube corresponding to the sample area of ​​the heat-sealed bag is divided into two parts, each of which is in the form of a circuitous coil, which is coiled layer by layer in the vertical direction and is located in the same vertical plane.

6. The device for quantitatively predicting different occurrence states in the production process of deep coalbed methane according to claim 5, characterized in that: The detection box is provided with a first heating tube and a second heating tube, the first heating tube includes a first liquid inlet tube, a first coil and a second coil, the first liquid inlet tube enters the detection box and extends along the corresponding support tube to one end of the heat-sealed bag, the outlet of the first liquid inlet tube is connected in parallel with the first branch tube and the second branch tube, the first branch tube is connected to the inlet of the first coil, and the second branch tube is connected to the inlet of the second coil, so as to provide hot fluorinated liquid for the two coils; the first coil and the second coil are respectively arranged at the front and rear sides of the sample area; The end of the first coil that is close to the corresponding support tube and at the top is the inlet, and the end that is away from the corresponding support tube and at the bottom is the outlet; the end of the second coil that is close to the corresponding support tube and at the bottom is the inlet, and the end that is away from the corresponding support tube and at the top is the outlet, so that the flow directions of the coils on both sides of the sample area are different.

7. A method for quantitatively predicting different occurrence states during deep coalbed methane production, characterized in that: The method is implemented by using the device for quantitatively predicting different occurrence states in the deep coalbed methane production process as described in claim 5, including the following steps: S100: Performing nuclear magnetic resonance detection on a standard sample saturated with methane adsorption to obtain a standard curve between the nuclear magnetic resonance signal amount of methane produced by the standard sample and the actual amount of methane produced; S200: Perform nuclear magnetic resonance detection on the coal sample saturated with adsorbed methane, record the nuclear magnetic resonance signal quantities of methane generated at different relaxation times of the coal sample, and the nuclear magnetic resonance signal quantities corresponding to methane in different occurrence states, and obtain the methane gas quantities corresponding to the nuclear magnetic resonance signal quantities in different occurrence states according to the standard curve.

8. The method for quantitatively predicting different occurrence states in the deep coalbed methane production process according to claim 7, characterized in that: In step S100, when testing the standard sample, S101: Put the standard sample into the heat-sealed bag of the sample tube and heat-seal it, then install the sample tube in the detection box, and install the detection box into the nuclear magnetic resonance device; S102: evacuate the sample tube; S103: starting the fluorinated liquid circulation of the heating tube so that the standard sample reaches the formation temperature required by the experiment; inputting inert gas into the detection box so that the formation pressure in the detection box reaches the formation pressure required by the experiment; S104: Introduce methane gas into the sample tube, turn on the nuclear magnetic resonance device, and allow the standard sample to be saturated with methane.

9. The method for quantitatively predicting different occurrence states in the deep coalbed methane production process according to claim 8, characterized in that: In step S100, the method for determining the standard curve is: S105: determining the volume of methane in the sample tube under the reservoir pressure of step S104 according to the real gas state equation; S106: The methane released by the standard sample is discharged from the sample tube, and the nuclear magnetic resonance device continuously records the nuclear magnetic signal of the standard sample. The nuclear magnetic resonance device analyzes and obtains the nuclear magnetic signals at different relaxation times. 1 H nuclear signal, accumulate the signal to obtain the total methane signal of the standard sample; S107: Exhaust the fluorinated liquid and the inert gas in the test box and take out the standard sample; Repeat steps S101 to S107, each time using a different reservoir pressure, to obtain the methane volume and the corresponding total methane signal at different reservoir pressures; S108 uses the total methane signal as the horizontal coordinate and the methane volume as the vertical coordinate, and fits the methane volume and the corresponding total methane signal under different reservoir pressures to obtain the equation of the standard curve.

10. The method for quantitatively predicting different occurrence states in the deep coalbed methane production process according to claim 9, characterized in that: Step S200 is specifically as follows: S201: Firstly dry the actual coal sample, and then perform the above steps S101 to S103; S202: Use CPMG pulse sequence to measure the coal sample by nuclear magnetic resonance, invert the T2 spectrum of the coal sample, and use it as a base signal to exclude the original presence of 1 The influence of H-nuclear substances on the results of NMR detection; S203: Perform the above steps S104 and S106, except that the NMR device analyzes the different relaxation times. 1 H nuclear signal, the first complete strong signal peak corresponds to adsorbed methane, and the subsequent several weak signal peaks correspond to free methane. The base signal is deducted from the NMR signal corresponding to the adsorbed methane to obtain the corrected signal of the adsorbed methane. The base signal is deducted from the NMR signal corresponding to the free methane to obtain the corrected signal of the free methane. The corrected signal of the adsorbed methane and the corrected signal of the free methane are substituted into the equation of the standard curve to obtain the volume of the adsorbed methane and the volume of the free methane under the reservoir pressure respectively. Repeat steps S201 to S203, using different reservoir pressures each time, to obtain the dynamic distribution of methane in different occurrence states during the actual coalbed methane release process.

Images