Device and method for quantitatively predicting different occurrence states during the production process of deep coalbed methane

Abstract

The present invention relates to a device and method for quantitatively predicting different occurrence states during the production process of deep coalbed methane, including: a detection box and a nuclear magnetic resonance device. The detection box includes a metal frame and a detachable plastic cover plate, and the plastic cover plate 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; both 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, where a standard sample or a coal sample is placed; during 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. Nuclear magnetic resonance detection is performed on the standard sample to obtain a standard curve of the nuclear magnetic signal amount of methane production of the standard sample and the actual gas volume of methane production; then the coal sample is detected, the nuclear magnetic signal amount of methane production at different relaxation times is recorded, and according to the standard curve, the methane gas volume corresponding to the nuclear magnetic signal amount of different occurrence states is obtained.

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 Technique

[0002] Coalbed methane is an unconventional natural gas that comes from underground coal seams. With the increasing development and utilization of a large number 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 the requirements for equipment and operation are also high. 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;

[0005] During 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.

[0006] Optionally, the detection box is a cube with a hollow interior, and plastic covers cover the upper and lower sides of the detection box;

[0007] 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 respectively provided on 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.

[0008] Further optionally, one installation port is connected to an inlet pipe, and the other installation port is connected to an outlet pipe. The inlet pipe is connected to a gas source cylinder and a regulating valve to input inert gas into the detection box and provide the confining pressure required for the experiment in the detection box. The outlet pipe is connected to an exhaust gas collection device;

[0009] 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.

[0010] 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 outwardly protruding fastening edges are provided at one end of the support tube close to the heat-sealed bag for installing and supporting the heat-sealed bag.

[0011] Optionally, two heating tubes are provided in the detection box. Hot fluorinated liquid is passed through 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;

[0012] 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 coiled pipe, 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 coiled pipes of the two heating tubes converge into one outlet pipe, and the outlet pipe passes through the detection box from any one installation port.

[0013] 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 coiled pipe and a second coiled pipe. 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 coiled pipe, and the second branch pipe is connected to the inlet of the second coiled pipe to provide hot fluorinated liquid for the two coiled pipes. The first coiled pipe and the second coiled pipe are respectively arranged on the front and rear sides of the sample area;

[0014] One end of the first coil pipe, which is close to the corresponding support pipe and at the top, is the inlet, and one end, which is far from the corresponding support pipe and at the bottom, is the outlet; one end of the second coil pipe, which is close to the corresponding support pipe and at the bottom, is the inlet, and one end, which is far from the corresponding support pipe and at the top, is the outlet, so that the flow directions of the coil pipes on both sides of the sample area are different.

[0015] There is a gap between adjacent pipelines coiled by each coil 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 coil pipe is 1:(0.75 - 0.85), which can achieve a good heating effect and does not waste energy.

[0016] 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:

[0017] 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;

[0018] 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.

[0019] The present invention uses nuclear magnetic resonance technology to monitor in real time the dynamic process of methane gas release from the standard sample and the coal sample. 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, it uses nuclear magnetic resonance technology to detect an actual coal sample saturated with adsorbed methane. According to different relaxation times, the first detected nuclear magnetic resonance signal amount corresponds to adsorbed methane, forming an obvious adsorption peak, and the later detected nuclear magnetic resonance signal amount corresponds to 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 methane volume in the adsorbed state. 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 methane volume in the free state. Thus, the dynamic distribution of different occurrence states of coalbed methane is quantitatively predicted.

[0020] 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.

[0021] Optionally, in step S100, when detecting the standard sample,

[0022] S101: Fix the standard sample in a heat-sealed bag of the sample tube by heat-sealing, then install the sample tube in the detection box, close both the installation opening of the detection box and the plastic cover plate, and then place it into the nuclear magnetic resonance device;

[0023] S102: Only open the ventilation pipe connected to the vacuum pump to evacuate the sample tube, and the evacuation time is 12 - 24h;

[0024] S103: Close the ventilation 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 intake pipe and close the outlet pipe to input inert gas into the detection box, so that the detection box reaches the formation pressure required for the experiment;

[0025] S104: Open another ventilation pipe to introduce methane gas into the sample tube. The air 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 saturate it for more than 60h. If the nuclear magnetic signal amount of methane gas in the standard sample does not change, it means that the standard sample has been saturated with adsorbed methane, and stop inputting methane.

[0026] Optionally, in step S100, the method for determining the standard curve is as follows:

[0027] S105: Determine the volume of methane in the sample tube under the reservoir pressure in step S104 according to the real gas state equation;

[0028] S106: Open the ventilation 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, and accumulates this signal to obtain the total methane signal amount of the standard sample;

[0029] S107: Turn off the heating plate, drain the fluorinated liquid in the heating tube, open the outlet pipe, discharge the inert gas in the detection box, take out the sample tube, and take out and clean the standard sample;

[0030] 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;

[0031] 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.

[0032] Optionally, step S200 is specifically as follows:

[0033] S201: First, dry the actual coal sample in an oven at 110 °C for 24 h to eliminate the influence of free water in the coal sample; then perform the above steps S101 to S103.

[0034] 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 eliminate the influence of substances containing 1 H nuclei in the original coal sample on the nuclear magnetic resonance detection result.

[0035] S203: Perform the above steps S104 and S106. The difference is 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 several subsequent weak signal peaks correspond to free methane.

[0036] Subtract the base signal from the nuclear magnetic resonance signal amount corresponding to adsorbed methane to obtain the corrected signal amount of adsorbed methane. Subtract the base signal from the nuclear magnetic resonance 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 to obtain the volumes of adsorbed methane and free methane under the reservoir pressure respectively.

[0037] 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.

[0038] 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 several subsequent weak signal peaks correspond to the substance containing 1 H nuclei in the free state.

[0039] In step S203, subtract the nuclear magnetic resonance signal amount (peak area) corresponding to the substance containing 1 H nuclei in the adsorbed state in the base signal from the nuclear magnetic resonance signal amount (peak area) corresponding to adsorbed methane to obtain the corrected signal amount of adsorbed methane.

[0040] Subtract the nuclear magnetic resonance 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 resonance signal amount (sum of several small peak areas) corresponding to free methane to obtain the corrected signal amount of free methane.

[0041] 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.

[0042] 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic structural diagram of the detection box;

[0044] Figure 2 It is a schematic diagram of the sample tube;

[0045] Figure 3 It is a schematic diagram of the heating tube;

[0046] Figure 4 It is a nuclear magnetic resonance signal curve diagram of standard samples under different reservoir pressures;

[0047] Figure 5 It is the standard curve obtained by fitting;

[0048] Figure 6 It is the T2 spectrum diagram of the coal sample base;

[0049] Figure 7 It is a nuclear magnetic resonance signal curve diagram of coal samples under different reservoir pressures;

[0050] Figure 8 It is a diagram of the dynamic distribution of different occurrence states during the release and production process of coalbed methane.

[0051] In the drawings, 1 - detection box, 2 - plastic cover plate, 3 - sixth branch pipe, 4 - installation port, 5 - sample tube, 6 - support tube, 7 - heat-sealed bag, 8 - heating tube, 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 coil pipe, 18 - second coil pipe, 19 - third coil pipe, 20 - fourth coil 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 DESCRIPTION OF THE INVENTION

[0052] Example 1

[0053] The device for quantitatively predicting different occurrence states during the production of deep coalbed methane in this embodiment 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 signals. A sample tube is placed inside 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.

[0054] During use, place the standard sample into the heat-sealed bag, seal it by heat, and then install the sample tube in the detection box.

[0055] 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 signals.

[0056] 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. One 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.

[0057] Horizontal edges made of metal are respectively provided on the top and bottom surfaces of the detection box 1. 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.

[0058] 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 sides of the detection box 1 are made of metal, which can provide sufficient strength, but the 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 sides 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 installation of the sample tube 5 into the detection box 1 and other maintenance inside the detection box 1.

[0059] 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 through the installation port and out of the detection box 1 to connect to an external power supply.

[0060] One mounting port is connected to the intake pipe, and the other mounting port is connected to the exhaust pipe. The intake 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 exhaust pipe is connected to the waste gas collection device.

[0061] The mounting ports are provided with flanges to facilitate sealing the detection box 1. The flanges are provided with several through holes for allowing the circuits of the heating components, the vent pipes of the sample tube 5, the temperature sensor, the two pressure gauges, the heating tube, the intake pipe, and the exhaust pipe to penetrate into the detection box 1.

[0062] The temperature sensor monitors the temperature in the area near the mounting port in the detection box 1 in real time. One pressure gauge detects the air pressure (confining pressure) in the detection box 1, and the other pressure gauge detects the air pressure (reservoir pressure) in the sample tube 5.

[0063] 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 provided above and below the cavity respectively. The detection box 1 is placed in the cavity. The left and right sides of the cavity are open, and sliding grooves are provided on the front and rear sides respectively. Sliding ways 11 are provided on the outer sides of the front and rear sides of the detection box 1. The sliding ways 11 cooperate with the corresponding sliding grooves to facilitate the pushing and pulling installation of the detection box 1.

[0064] Both ends of the sample tube 5 are respectively butted with a mounting port. The sample tube 5 includes the support tubes 6 at both ends and the 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 a vent pipe 12 is provided at one end close to the corresponding mounting port. The vent pipe 12 penetrates out of the detection box 1 through the mounting port. Several outwardly protruding fastening edges 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. The two 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 the sample area 14, and standard samples or coal samples are contained in the sample area 14.

[0065] The vent pipe of one support tube is connected to the methane gas source outside the detection box 1 to input methane gas into the sample tube 5 so that the standard sample or coal sample can be saturated with methane adsorption. The vent pipe of the other support tube is connected in parallel with the gas analysis device and the vacuum pump outside the detection box 1 to detect the component content of the gas output from the sample tube 5. When the vent pipe is connected to the vacuum pump, the sample tube 5 can be evacuated.

[0066] When loading a standard sample or a 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. One end of each of the two support tubes on both sides with fastening ridges is sleeved at both ends of the heat-sealed bag 7, and the openings of the heat-sealed bag 7 are sleeved outside the fastening ridges 13 to support the openings of the heat-sealed bag 7. Then, use the hot air of a hair dryer to blow across the entire heat-sealed bag 7, so that the heat-sealed bag 7 tightly wraps around the outer surfaces of the standard sample or the coal sample and the outer surfaces of the support tube openings, thereby fixing the standard sample or the coal sample.

[0067] In the present invention, the sample tube 5 is used to hold the standard sample and the coal sample. The material of the sample tube 5 does not affect nuclear magnetic detection. The two 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 passes through the middle part inside the detection box 1, making it easier 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 packed in the heat-sealed bag 7 to prevent the confining pressure gas from directly contacting the sample. After the heat-sealed bag 7 shrinks due to heat, it clings to the sample surface to form an effective package. There is very little residual gas in the heat-sealed bag 7, which avoids the gas in the heat-sealed bag 7 resisting the external confining pressure and also avoids the heat-sealed bag 7 being broken by the external confining pressure. When the standard sample or the coal sample is subjected to methane saturation adsorption, only methane needs to be introduced into the sample tube 5, saving the amount of methane used. The space of the detection box outside the sample tube 5 facilitates the setting of heating components and provides a suitable temperature environment for the heat-sealed bag 7.

[0068] Two heating tubes 8 are provided inside the detection box 1. Hot fluorinated liquid is introduced into the heating tubes 8 to heat the standard sample or the coal sample so that the standard sample or the coal sample reaches the temperature required for the experiment; neither the heating tubes 8 nor the fluorinated liquid generates nuclear magnetic signals;

[0069] The liquid inlet pipes of the heating tubes pass through the detection box 1 from the nearby installation ports and are connected to the external liquid supply device. The part of the heating tubes 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 one liquid outlet pipe 25, and the liquid outlet pipe 25 passes through the detection box 1 from any one of the installation ports.

[0070] A 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.

[0071] Inside the detection box 1, there are a first heating pipe and a second heating pipe. The first heating pipe includes a first liquid inlet pipe 15, a first coil pipe 17, and a second coil pipe 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-sealing 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 pipe 17, and the second branch pipe 22 is connected to the inlet of the second coil pipe 18, providing hot fluorinated liquid for the two coil pipes. The first coil pipe 17 and the second coil pipe 18 are respectively arranged on the front and back sides of the sample area 14.

[0072] One end at the top on the side of the first coil pipe 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 pipe 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 coil pipes on both sides of the sample area 14 are different.

[0073] The structure of the second heating pipe is the same as that of the first heating pipe. The second heating pipe includes a second liquid inlet pipe 16, a third coil pipe 19, and a fourth coil pipe 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-sealing 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 pipe 19, and the fourth branch pipe 24 is connected to the inlet of the fourth coil pipe 20, providing hot fluorinated liquid for the two coil pipes. The third coil pipe 19 and the fourth coil pipe 20 are respectively arranged on the front and back sides of the sample area 14, that is, the first coil pipe 17 and the third coil pipe 19 are on the same side of the sample area 14, and the second coil pipe 18 and the fourth coil pipe 20 are on the other side of the sample area 14.

[0074] One end at the bottom on the side of the third coil pipe 19 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. One end at the top on the side of the fourth coil pipe 20 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, so that the flow directions of the coil pipes on both sides of the sample area 14 are different.

[0075] The outlet of the third coil pipe 19 is connected to the outlet of the first coil pipe 17, and then connected to a fifth branch pipe 26. The outlet of the second coil pipe 18 is connected to the outlet of the fourth coil pipe 20, and then connected to a 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 are combined into an outlet pipe 25, which extends along the support pipe to the outside of the detection box 1.

[0076] In the present invention, a heating plate is provided inside the detection box 1 to play a basic heating role, so that the temperature inside 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 inside 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 around the sample. The present invention adopts a method combining a heating plate and a heating tube, and selects a heating tube without nuclear magnetic signal and a fluorinated liquid to be close to the sample for auxiliary heating to ensure that the sample can reach the temperature required by the experiment.

[0077] Specifically, four coiled pipes are placed on the front and rear sides of the sample area 14, and the magnet is located above and below the sample area 14. 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 receive the heat supply of one coiled pipe. The fluorinated liquid of the first coiled pipe 17 flows from top to bottom, and the fluorinated liquid of 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 of the second coiled pipe 18 flows from bottom to top, and the fluorinated liquid of 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.

[0078] 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.

[0079] Example 2

[0080] The method for quantitatively predicting different occurrence states during the production process of deep coalbed methane in this embodiment includes the following steps:

[0081] S100: Perform nuclear magnetic resonance detection on a standard sample saturated with adsorbed methane to obtain a standard curve of the nuclear magnetic signal amount of methane production and the actual gas amount of methane production of the standard sample;

[0082] S200: Perform nuclear magnetic resonance detection on a coal sample saturated with adsorbed methane, record the nuclear magnetic signal amount of methane generated at different relaxation times of the coal sample, corresponding to the nuclear magnetic signal amounts of methane in different occurrence states, and according to the standard curve, obtain the methane gas amounts corresponding to the nuclear magnetic signal amounts in different occurrence states;

[0083] The method for quantitatively predicting different occurrence states during the production process of deep coalbed methane is specifically:

[0084] (1)Collect coal samples in deep coal seams, record the formation pressure and temperature of the deep coal seams, and make the collected coal samples into the same style as the standard sample size.

[0085] (2)Fix the standard sample in the sample tube, then install the sample tube in the detection box, then seal the detection box, then place the detection box in the nuclear magnetic resonance device. After evacuating the inside of the sample tube, provide the same formation pressure and temperature as the deep coal seam for the detection box; introduce methane gas, turn on the nuclear magnetic resonance device, and stop introducing methane gas after the standard sample is saturated with methane adsorption.

[0086] (3)Record the total nuclear magnetic signal amount generated by methane in the sample tube, and obtain the standard curve of the total methane signal amount in the sample tube and the methane gas amount of the standard sample according to the actual methane gas amount of the standard sample.

[0087] (4)Take out the standard sample, perform the operations in step S2 with the actual coal sample, then turn on the nuclear magnetic resonance device, record the nuclear magnetic signal amount generated by methane at different relaxation times in the sample tube, corresponding to the nuclear magnetic signal amounts of methane in different occurrence states, and obtain the methane gas amounts corresponding to the nuclear magnetic signal amounts in different occurrence states according to the standard curve.

[0088] In step (1), the material of the standard sample is polyether ether ketone, which does not generate nuclear magnetic signals, is not easily deformed, has a weak methane gas adsorption capacity, and is suitable for nuclear magnetic resonance detection.

[0089] 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 ventilation 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.

[0090] In step S100, when detecting the standard sample, that is, step (2) is specifically:

[0091] S101: Fix the standard sample in the heat-sealed bag of the sample tube by heat-sealing, 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 nuclear magnetic resonance device.

[0092] S102: Only open the air pipe connected to the vacuum pump to evacuate the inside of the sample tube, and the evacuation time is 24h.

[0093] 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 experimental required formation temperature of 70°C; open the air inlet pipe and close the air outlet pipe to input inert gas into the detection box, so that the inside of the detection box reaches the experimental required formation pressure of 25MPa.

[0094] S104: Open another vent pipe, introduce methane gas into the sample tube, and the air pressure in the sample tube gradually increases until it reaches the reservoir pressure of 20 MPa required for the experiment. Then turn on the nuclear magnetic resonance device and fully saturate it for 60 h. If the nuclear magnetic signal amount of methane gas in the standard sample does not change, it indicates that the standard sample is saturated with adsorbed methane, and then stop inputting methane.

[0095] In step S100, the method for determining the standard curve (i.e., step (3)) is as follows:

[0096] S105: Determine the volume of methane in the sample tube under the reservoir pressure in step S104 according to the real gas state equation;

[0097] 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 amount of H nuclear signal at different relaxation times, and accumulate this signal to obtain the total methane signal amount of the standard sample;

[0098] S107: Turn off the heating plate, drain the fluorinated liquid in the heating tube, open the outlet pipe, drain the inert gas in the detection box, take out the sample tube, and take out and clean the standard sample;

[0099] 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, and 20 MPa respectively;

[0100] 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.

[0101] In step S105, the volume of methane in the sample tube is determined by the following formula:

[0102] V = n×V m ×1000

[0103] where V is the volume of methane gas injected into the sample tube, cm 3 ; V m is the molar volume of the gas, 22.4 L / mol; n is determined by the real gas state equation, and n is:

[0104] ;

[0105] 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 compression factor of methane gas, dimensionless; R is the universal gas constant, 8.314 cm 3 ·MPa / (mol·K); T is the experimental temperature, 70 °C = 344.15 K.

[0106] Z is determined by the following formula:

[0107] ;

[0108] where P is the reservoir pressure, in MPa; T is the experimental temperature, 70 °C = 344.15 K.

[0109] 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:

[0110] ;

[0111] where Q is the volume of methane, in mL; T is the total signal amount of methane, in p.u.; the determination coefficient R 2 obtained by fitting is 0.99.

[0112] Step S200 is specifically as follows (i.e., step (4)):

[0113] 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;

[0114] 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 in the original coal sample on the nuclear magnetic resonance detection result;

[0115] S203: Perform the above steps S104 and S106. The difference is that the nuclear magnetic resonance device analyzes the 1 H nuclear 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.

[0116] The nuclear magnetic signal amount corresponding to adsorbed methane minus the base signal is the corrected signal amount of adsorbed methane, and the nuclear magnetic 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 volume of adsorbed methane and the volume of free methane under this reservoir pressure;

[0117] 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, such as Figure 7 shown. The reservoir pressures corresponding to the curves 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.

[0118] In steps S103 and S201, the heating plate is powered on for heating, and the heating tube is filled with a hot fluorinated liquid to make the temperature in the detection box reach 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.

[0119] Judge whether the confining pressure in the detection box reaches the formation pressure required by the experiment through a pressure gauge, and observe the pressure gauge in real time during the subsequent experiment to facilitate pressure supplementation for the detection box to maintain its confining pressure.

[0120] 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;

[0121] In step S203, the nuclear magnetic signal quantity (peak area) corresponding to the adsorbed methane, after subtracting 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 the adsorbed methane;

[0122] The nuclear magnetic signal quantity (sum of several small peak areas) corresponding to the free methane, after subtracting 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 the free methane;

[0123] Substitute the corrected signal quantity of the adsorbed methane into the equation of the standard curve to obtain the volume of the adsorbed methane, and substitute the corrected signal quantity of the free methane into the equation of the standard curve to obtain the volume of the free methane;

[0124] 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 8As 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.

[0125] Example 3

[0126] The device for quantitatively predicting different occurrence states during the production of deep coalbed methane provided in this example is the same as that in Example 1, except that no heating tube is provided in the detection box, and only the heating plate is used for heating.

[0127] Example 4

[0128] The device for quantitatively predicting different occurrence states during the production of deep coalbed methane provided in this example is the same as that in Example 1, except that the first coil and the third coil are combined into one coil, 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 coil and the fourth coil are combined into one coil, 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 coils. The inlets of the two coils 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 connected in parallel to the liquid outlet pipe.

[0129] Example 5

[0130] The device for quantitatively predicting different occurrence states during the production of deep coalbed methane provided in this example is the same as that in Example 1, except that there is a gap between adjacent pipelines coiled by each coil, and the ratio of the longitudinal cross-sectional area of the standard sample to the sum of the longitudinal cross-sectional areas of the pipelines of the first coil is 1:0.85.

[0131] Example 6

[0132] The device for quantitatively predicting different occurrence states during the production of deep coalbed methane provided in this example is the same as that in Example 1, except that there is a gap between adjacent pipelines coiled by each coil, and the ratio of the longitudinal cross-sectional area of the standard sample to the sum of the longitudinal cross-sectional areas of the pipelines of the first coil is 1:0.74.

[0133] In the experimental devices of Example 1 and Examples 3 - 6, the temperature sensor extends to closely adhere to the upper surface of the sample area, capable of actually detecting the temperature of the sample area. In Example 1 and Examples 3 - 6, the standard sample, sample tube, and detection box are installed according to the method of Example 2. After closing the detection box, the intake pipe and one ventilation pipe are closed, and one-way air valves are respectively installed on the outlet pipe and the other ventilation pipe, allowing the gas in the detection box and the sample tube to expand and discharge due to heat, 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, and the temperature of the sample area of each preparation example and example is detected by the temperature sensor. The results are shown in the following table.

[0134] Table 1 Comparison of the sample area temperatures of Example 1 and Examples 3 - 6

[0135] 。

[0136] As can be seen from the above table, Example 1 and Example 5 are closest to the target 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 method for quantitatively predicting different occurrence states during the production process of deep coalbed methane, characterized in that It is implemented by using a device for quantitatively predicting different occurrence states during the production process of deep coalbed methane, including the following steps: S100: Conduct 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 amount of methane production; S200: Conduct NMR detection on a coal sample saturated with adsorbed methane, record the NMR signal amount of methane production 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 amounts corresponding to the NMR signal amounts of different occurrence states according to the standard curve; The device for quantitatively predicting different occurrence states during the production process of deep coalbed methane includes a detection box and an NMR device. The detection box includes a metal frame and a detachable plastic cover plate, and the plastic cover plate corresponds to the upper and lower magnets of the NMR device. 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. 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. The standard sample or coal sample is placed in the sample area; During use, place the standard sample in the heat-sealed bag, heat-seal and fix it, and then install the sample tube in the detection box.

2. The method for quantitatively predicting different occurrence states during the production process of deep coalbed methane according to claim 1, characterized in that, The detection box is a cube with a hollow interior. The plastic cover plate covers 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 inside 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.

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

4. The method for quantitatively predicting different occurrence states during the production process of deep coalbed methane according to claim 3, characterized in that, Both ends of the sample tube are respectively butted against one installation port. The inside of the support tube is hollow, and a ventilation pipe is provided at one end close to the corresponding installation port, and the ventilation pipe passes through the detection box through the installation port.

5. The method for quantitatively predicting different occurrence states during the production process of deep coalbed methane according to claim 4, characterized in that Two heating tubes are provided inside the detection box. Hot fluorinated liquid is passed through 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 NMR signals; The part of the heating tube corresponding to the sample area of the heat-sealed bag is divided into two parts, each part is in the form of a circuitous coiled pipe, coiled layer by layer in the vertical direction, and is on the same vertical plane.

6. The method for quantitatively predicting different occurrence states during the production process of deep coalbed methane according to claim 5, wherein A first heating tube and a second heating tube are provided inside the detection box. The first heating tube includes a first liquid inlet pipe, a first coiled pipe and a second coiled pipe. After the first liquid 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 liquid 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 coiled pipe, and the second branch pipe is connected to the inlet of the second coiled pipe to provide hot fluorinated liquid for the two coiled pipes. The first coiled pipe and the second coiled pipe are respectively arranged on the front and rear sides of the sample area; One end of the first coiled tube, which is on the side close to the corresponding support tube and at the top, is the inlet, and the other end, which is on the side far from the corresponding support tube and at the bottom, is the outlet; one end of the second coiled tube, which is on the side close to the corresponding support tube and at the bottom, is the inlet, and the other end, which is on the side far from the corresponding support tube and at the top, is the outlet, so that the flow directions of the coiled tubes on both sides of the sample area are different.

7. The method for quantitatively predicting different occurrence states during the production process of deep coalbed methane according to claim 6, characterized in that, In step S100, when detecting the standard sample, S101: Put the standard sample into the heat-sealed bag of the sample tube for heat-sealing and fixing, then install the sample tube in the detection box, and put the detection box into the nuclear magnetic resonance device. S102: Evacuate the sample tube. S103: Start the circulation of the fluorinated liquid in the heating tube so that the standard sample reaches the formation temperature required by the experiment; input inert gas into the detection box so that the formation pressure required by the experiment is reached in the detection box. S104: Introduce methane gas into the sample tube, turn on the nuclear magnetic resonance device, and saturate the standard sample with adsorbed methane.

8. The method for quantitatively predicting different occurrence states during the production process of deep coalbed methane according to claim 7, characterized in that In step S100, the method for determining the standard curve 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: Drain the methane released by the standard sample from the sample tube. The nuclear magnetic resonance device continuously records the nuclear magnetic signals of the standard sample, and the nuclear magnetic resonance device analyzes to obtain the 1 amount of H nuclear signals at different relaxation times, accumulate the signals, and obtain the total methane signal amount of the standard sample; S107: Drain the fluorinated liquid and the inert gas in the detection 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 amount under different reservoir pressures. S108: Use the total methane signal amount as the abscissa and the methane volume as the ordinate to fit the methane volume and the corresponding total methane signal amount under different reservoir pressures, and obtain the equation of the standard curve.

9. The method for quantitatively predicting different occurrence states during the production process of deep coalbed methane according to claim 8, characterized in that Step S200 is specifically as follows: S201: First dry the actual coal sample, and then perform steps S101 to S103 above. S202: 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 results; 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 several subsequent weak signal peaks correspond to free methane. Deduct the base signal from the nuclear magnetic signal amount corresponding to the adsorbed methane to obtain the corrected signal amount of the adsorbed methane, deduct the base signal from the nuclear magnetic signal amount corresponding to the free methane to obtain the corrected signal amount of the free methane, and substitute the corrected signal amounts of the adsorbed methane and the free methane into the equation of the standard curve respectively to obtain the volume of the adsorbed methane and the volume of the free methane under 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 release process of actual coalbed methane.

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