CN109826621B - Coal bed gas multilayer combined gas-water two-phase seepage experimental device and test method - Google Patents
Coal bed gas multilayer combined gas-water two-phase seepage experimental device and test method Download PDFInfo
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Abstract
The invention belongs to the technical field of coal bed gas geology and oil and gas reservoir engineering, particularly relates to a gas-water two-phase seepage experimental device under a coal bed gas multilayer combined mining condition, further discloses a testing method based on the experimental device, and solves the problem that the existing coal bed gas combined mining simulation experimental device cannot objectively simulate the gas-water two-phase seepage process of the coal bed gas multilayer combined mining under the stratum condition. The invention relates to a coal bed gas multilayer combined gas-water two-phase seepage experiment device which comprises a gas injection system, a vacuum pumping system, a model system and a metering system which are sequentially arranged along the gas flow direction in a pipeline. The experimental device can effectively simulate the gas-water two-phase flow of the multi-layer combined production of the coal bed gas under the real stratum condition, realize the real-time monitoring of the in-layer seepage, the interlayer channeling and the on-way pressure change, and better accord with the stratum condition and the actual production condition.
Description
Technical Field
The invention belongs to the technical field of coal bed gas geology and oil and gas reservoir engineering, particularly relates to a coal bed gas multilayer combined gas-water two-phase seepage experimental device, and further discloses a testing method based on the experimental device.
Background
Coal bed gas, commonly referred to as "gas," refers to hydrocarbon gas stored in a coal bed that is primarily methane, primarily adsorbed on the surface of coal-based particles, partially dissociated in coal pores, or dissolved in coal bed water. The coal bed gas is associated mineral resources of coal, belongs to unconventional natural gas, is clean and high-quality energy and chemical raw materials which rise internationally in nearly twenty years, and the development and utilization of the coal bed gas not only contributes to the development of clean energy, but also can generate great economic benefit.
The high-efficiency exploitation of the coal bed gas has multiple effects of safety, environmental protection, energy and the like, and China is also dedicated to continuously promoting the exploration and development of the coal bed gas. The coal-bed gas well development in China has the common characteristics of multiple coal beds and low pressure, low permeability and low gas saturation of the coal-bed gas reservoir, so that the conditions of low single-well yield and poor economic benefit exist in the coal-bed gas well development. If no production increasing measures are taken, not only the yield of the coal bed gas single well is low, but also the coal bed gas exploitation well loses the exploitation value.
The multi-layer commingled production of the coal bed gas is an important measure for improving the single well yield of the coal bed gas well, and the multi-layer commingled production technology is a mode of opening a plurality of gas layers simultaneously for commingled production by one well, and the mode is favorable for improving the single well yield of the coal bed gas. However, because of the lack of fluid communication among different coal seams and the development of an overlapped fluid pressure system, the problems of interlayer interference, unbalanced reservoir utilization degree and the like are easily caused during multi-layer combined mining, even a gas backflow phenomenon can be caused for serious people, the coal bed gas productivity is greatly reduced, and the coal bed gas industrialization progress of China is further seriously hindered.
The commingled mining physical simulation is an important method for revealing fluid transfer behavior in the coalbed methane commingled mining process, and is helpful for providing certain theoretical guidance for the coalbed methane commingled mining process. At present, the research on the coal bed gas multilayer commingled mining at home and abroad is mainly carried out through an empirical formula or a model obtained by basic geological theory research; or carrying out numerical simulation by using commercial software such as COMET3, FastCBM, CBMRS1.0, Eclipse and the like; alternatively, various experimental devices beneficial to simulating the interference between the multiple layers of coal bed methane commingled production have been developed in the prior art. However, whether based on theoretical studies or numerical simulations using commercial software, the results obtained are far from the actual production process and are difficult to integrate with field practices. The multi-layer commingled mining simulation mode based on the multi-layer commingled mining experimental device can give certain theoretical guidance to actual mining work to a certain extent, but most of the existing coal bed methane commingled mining simulation experimental devices generally have the problems that simulation conditions are obviously different from actual stratum conditions, and the reliability of simulation results is poor; or, the defects that simulation and measurement of gas-water two-phase seepage experiments cannot be completed, and interlayer cross flow phenomena possibly occurring cannot be simulated and monitored are overcome; or, although the interlayer interference phenomenon which may occur can be simulated and monitored, the content of the coal bed gas flowing backwards when the gas flows backwards cannot be accurately measured, and the defects of actual coal bed gas multilayer commingled production and the like are difficult to guide. The defects greatly restrict the scientificity of the coalbed methane multilayer commingled production evaluation and also influence the yield of the coalbed methane multilayer commingled production.
Disclosure of Invention
Therefore, the technical problem to be solved by the invention is to provide a coal bed methane multi-layer combined mining gas-water two-phase seepage experimental device, so as to solve the problem that the coal bed methane combined mining gas-water two-phase seepage process under the stratum condition cannot be objectively simulated by the coal bed methane combined mining simulation experimental device in the prior art, and particularly the problem that the content of the coal bed methane flowing backwards when the gas flowing backwards cannot be accurately measured is solved;
the second technical problem to be solved by the invention is to provide a two-phase seepage test method for coal bed methane multi-layer combined gas production water.
In order to solve the technical problems, the invention is realized by the following technical scheme:
on one hand, the invention discloses a two-phase seepage experimental device for gas and water of multi-layer combined production of coal bed gas, which comprises a gas injection system, a model system and a metering system which are sequentially arranged along the gas flow direction in a pipeline;
the gas injection system comprises a gas source and a gas pressure control assembly, wherein the gas source is used for providing medium gas for injecting a rock core experiment; the gas pressure control assembly comprises a gas booster pump, and medium gas injected by a gas source is boosted to a target pressure by the gas booster pump;
the model system comprises at least 2 groups of core simulation assemblies which are arranged in parallel and a pressure loading assembly for controlling the confining pressure and the axial pressure of the core inside each core simulation assembly, and is used for simulating the coalbed methane production process under the real formation condition;
the metering system comprises at least 2 groups of gas-liquid separation assemblies which are arranged in parallel and correspondingly connected with the core simulation assembly, gas-water two-phase fluid obtained through phase simulation of the core simulation assembly is respectively collected and detected after gas-liquid separation, and control over system back pressure or gas flow is realized through the system pressure control assembly so as to respectively simulate a constant pressure mining process or a constant flow mining process.
Preferably, the gas-liquid separation component comprises a gas-liquid separator, a gas-water extraction measurement component and a gas backflow measurement component, wherein the gas-water extraction measurement component and the gas backflow measurement component are respectively communicated with the gas-liquid separator;
the gas-water extraction measuring assembly comprises a measuring cylinder which is communicated with the outlet of the gas-liquid separator and is used for measuring the volume of the separated water phase and a first gas flowmeter used for measuring the flow of the separated gas phase; the inlet of the first gas flowmeter is provided with a first one-way valve to allow gas to flow into the first gas flowmeter in one way;
the gas backflow measuring assembly comprises a second gas flowmeter communicated with the inlet of the gas-liquid separator and is used for metering gas entering the gas-liquid separator after being subjected to gas-liquid separation by other gas-liquid separation assemblies arranged in parallel; a second one-way valve is arranged at the inlet of the second gas flowmeter to allow the gas which flows backwards to flow into the second gas flowmeter in a one-way manner;
in the metering system, the gas metered by the first gas flowmeter and the second gas flowmeter is metered by a total gas flowmeter.
Preferably, the system pressure control assembly comprises a back pressure valve for applying back pressure to the system and a flow controller for controlling the flow of gas; and simulating a constant pressure mining process or a constant flow mining process through the system pressure control assembly.
Preferably, the core simulating assembly comprises a core holder; the inner cavity of the rock core holder is provided with a rock core cavity for accommodating a rock core, axial pressure cavities arranged at two sides of the rock core cavity and confining pressure cavities arranged at the periphery of the rock core cavity; the pressure loading assembly comprises an axial pressure automatic loading system and a confining pressure automatic loading system which respectively control the pressure of the axial pressure cavity and the confining pressure cavity, so that the rock core obtains preset confining pressure and preset axial pressure.
Preferably, the core simulation assembly further comprises a thermostat arranged on the outer side of the core holder, and the formation temperature is simulated by controlling the temperature of the core cavity.
Preferably, the core simulation assembly further comprises a pressure sensor for collecting the internal pressure of the core holder, and a differential pressure sensor for detecting the differential pressure at two ends of the core holder.
Preferably, the gas pressure control assembly is also provided with a pressure reducing valve and/or a buffer tank; the pressure reducing valve is arranged in front of the gas booster pump and is used for carrying out pressure reduction treatment on the medium gas injected by the gas source; the buffer tank is arranged behind the gas booster pump and used for storing medium gas boosted to a target pressure so as to stabilize the high-pressure gas pressure.
Preferably, the experimental device further comprises a vacuum pumping system arranged in front of the model system, and the vacuum pumping system is used for pumping vacuum to the core sample in the model system, so that the medium gas is fully contacted and adsorbed with the core sample.
Preferably, a camera is also provided for observing and recording the volume of water in the measuring cylinder and its changes.
On the other hand, the invention also discloses a test method for the two-phase seepage experiment of the gas-water of the multi-layer commingled coal bed methane production, which is based on the two-phase seepage experiment device of the gas-water of the multi-layer commingled coal bed methane production and comprises the following steps:
s1, connecting a test pipeline, loading a core sample with a selected size into the core holder, opening the vacuumizing system, vacuumizing the model system, injecting medium gas through a gas injection system, filling and adsorbing the medium gas into cracks and pores of the core sample, and injecting formation water into the core holder to simulate the saturated water-containing environment of an underground reservoir;
s2, respectively applying set confining pressure and axial pressure to the core cavity in the core holder through the confining pressure automatic loading system and the axial pressure automatic loading system according to actual stratum conditions; heating the core cavity through the constant temperature box to simulate the actual reservoir temperature;
s3, setting the back pressure of the system through the back pressure valve in the metering system or setting the gas flow in the system through the flow controller so as to respectively simulate constant pressure attenuated production or constant flow attenuated production;
s4, injecting medium gas into the core holder of the model system according to a set pressure through the injection system; after gas is injected, water in the core cavities is displaced to flow, gas-water two-phase fluid is formed in each core, and the change of the gas-water flow along the process pressure is recorded through the pressure sensor and the differential pressure sensor;
s5, allowing the gas-water two-phase fluid to flow out of the core holder, allowing the gas-water two-phase fluid to enter the metering system, separating gas from water through the gas-liquid separator, allowing the separated water to enter the measuring cylinder, and recording the volume change of the water in the measuring cylinder through the camera to realize the metering of water flow; the separated gas enters a gas flowmeter to realize metering;
s6, ending the experiment until the water does not flow and the air flow is stable, and performing data processing to obtain a simulation experiment result;
in the step S5, the gas metering step includes a step of metering the gas separated by the gas-liquid separator with the first gas flow meter, a step of metering the gas separated by the other components and poured back into the gas-liquid separator with the second gas flow meter, and a step of metering the total amount of gas metered by the first gas flow meter and the second gas flow meter with the total gas flow meter;
in the step S5, after the mixed gas-water two-phase simulation fluid flows out of the core holder, the mixed gas-water two-phase simulation fluid enters the metering system, gas-water separation is realized through the gas-liquid separator, then the separated water enters the measuring cylinder, and the volume change of the water in the measuring cylinder is recorded through the camera, so that the water flow metering is realized; the gas from the gas-liquid separator is dried by a drying pipe and then enters a first flowmeter through a first one-way valve to realize metering; meanwhile, if gas from the core holders of other groups enters the circuit, the gas enters a second flowmeter through a second one-way valve to realize metering, namely the interlayer flow-crossing gas quantity, and the metered flow-crossing gas is merged into a pipeline node above the gas-liquid separator.
Preferably, before the gas separated by each group of gas-liquid separation components enters the corresponding gas flowmeter, the gas is dried by a drying pipe.
Preferably, the step S4 further includes a step of pressurizing the injected medium gas to a target pressure by a gas booster pump, and injecting the medium gas into the buffer tank to perform pressure stabilization processing.
Compared with the prior art, the invention can realize at least one of the following beneficial effects:
a) the coal bed gas multilayer combined production gas-water two-phase seepage experiment device provided by the invention is provided with a gas injection system, a vacuum pumping system, a model system and a metering system, has a simple structure and is convenient to operate, the gas-water two-phase flow of the coal bed gas multilayer combined production under the real formation condition can be effectively simulated, the real-time monitoring of the in-layer seepage, the interlayer channeling and the on-way pressure change is realized, the actual formation confining pressure, the axial pressure and the temperature condition are fully considered, and the core simulation assembly is provided with an axial pressure automatic loading system, a confining pressure automatic loading system and a constant temperature box, so that the core obtains the preset confining pressure, the axial pressure and the temperature, the simulation condition is more in line with the actual formation condition, the reliability of the experiment result is obviously improved, and the simulation result is more close to the actual production condition;
b) the invention provides a gas-water two-phase seepage experimental device for multi-layer combined production of coal bed gas, which is particularly designed with a two-way metering mode, namely, a gas-liquid separation component comprises a gas-liquid separator, a gas-water production measurement component and a gas backflow measurement component which are respectively communicated with the gas-liquid separator, and the gas separated by the gas-liquid separator and the gas which is poured into the gas-liquid separator after other components are separated are respectively metered;
when interlayer interference occurs in the experimental process, forward gas from the clamp holder is metered through the first gas flowmeter; reverse gas from other core holders is metered by the second gas flowmeter, and the experimental device with the bidirectional metering component can monitor and accurately meter interlayer channeling in the multi-layer commingled production process;
c) the invention provides a test method for a coal bed gas multilayer combined gas-water two-phase seepage experiment, which comprises the steps of firstly placing core saturated water in a core cavity of a core holder, setting confining pressure, axial pressure and temperature, then injecting gas at different gas injection pressures, developing a gas-water flooding experiment, simulating the combined gas-water two-phase seepage and pressure transmission process by respectively measuring gas and water output and along-the-way pressure change, and ending the experiment after no water flows out of an outlet and gas flow is stable, wherein the whole experiment process is simple to operate and easy to control, and the actual formation confining pressure, axial pressure and temperature conditions are fully considered, so that the simulation conditions are more in line with the actual formation conditions, and the experiment result is more reliable; by utilizing the designed bidirectional metering mode, the interlayer channeling in the multilayer commingled production process is monitored and accurately metered, the stratum condition and the actual production condition are better met, a way is provided for objectively revealing the dynamic behavior of the commingled production fluid and the interlayer interference, and the method has important significance for the research and the actual exploration and development of the multilayer commingled production of the coal bed gas.
Drawings
In order that the present disclosure may be more readily and clearly understood, the following detailed description of the present disclosure is provided in connection with specific embodiments thereof and the accompanying drawings, in which,
FIG. 1 is a schematic structural diagram of a gas-water two-phase seepage experimental apparatus for multi-layer commingled coal bed methane production in the first embodiment;
FIG. 2 is an enlarged view of a portion of the mold system of FIG. 1;
fig. 3 is an enlarged view of a portion of the metering system of fig. 1.
The reference numbers in the figures denote: 1-a gas injection system, 11-a gas source, 12-a gas booster pump, 13-an air compressor, 14-a high-pressure buffer tank, 15-a gas pressure regulating valve, 16-a pressure instrument, 2-a vacuum system, 21-a vacuum pump, 22-a valve, 3-a model system, 31-a thermostat, 32-a rock core holder, 33-a confining pressure automatic loading system, 34-an axial pressure automatic loading system, 35-a pressure sensor, 36-a differential pressure sensor, 37-a pressure regulating valve, 321-a rock core cavity, 322-an axial pressure cavity, 323-a confining pressure cavity, 4-a metering system, 41-a gas-liquid separator, 42-a camera, 43-a measuring cylinder, 44-a drying pipe, 45-0-a total gas flowmeter, 45-1-a first gas flowmeter, 45-2-second gas flow meter, 46-1-first check valve, 46-2-second check valve, 47-back pressure valve, 48-flow controller.
Detailed Description
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate preferred embodiments of the invention and together with the description, serve to explain the principles of the invention and not to limit the scope of the invention.
Example one
As shown in fig. 1 to 3, the experimental apparatus for coal bed methane multi-layer commingled mining gas-water two-phase seepage flow in this embodiment is a triaxial gas-water two-phase seepage flow experimental apparatus, and the commingled mining is performed by simulating a multi-layer coal bed, so as to discuss the interference characteristics between coal beds. The coal bed gas multilayer commingled production gas-water two-phase seepage experiment device provided by the embodiment is mainly used for conducting a multilayer commingled production simulation experiment in a mode that three layers of coal core samples are connected in parallel, researching the influence of conditions such as interlayer permeability difference and reservoir pressure difference on the flow behavior of the commingled production gas, and realizing real-time monitoring and metering of gas-water two-phase fluid output, backflow and on-way pressure.
As shown in fig. 1-3, the experimental apparatus for two-phase seepage of gas and water in multi-layer commingled coal seam gas production according to the present embodiment includes a gas injection system 1, a model system 3, and a metering system 4, which are sequentially disposed along a gas flow direction in a pipeline, and a vacuum pumping system 2 is disposed in front of the model system 3; wherein,
the gas injection system 1 comprises a gas source 11 and a gas pressure control assembly and is used for providing medium gas for core injection experiments, wherein the medium gas is pure methane or gas which mainly contains methane and can be adsorbed on a coal bed, and gas CH with different components can be configured according to research purposes4+N2+CO2Etc.;
the vacuum-pumping system 2 comprises a vacuum pump 21 for pumping air inside the model system 3 to form and simulate a vacuum environment;
the model system 3 comprises a rock core simulation assembly and a pressure loading assembly for controlling the pressure of a rock core in the rock core simulation assembly, and is used for simulating the coalbed methane production process under the real formation condition;
the metering system 4 comprises a gas-liquid separation component, gas-water two-phase fluid is respectively collected and detected after gas-liquid separation, the control of system back pressure or gas flow is realized through a system pressure control component, and a constant pressure mining process or a constant flow mining process is respectively simulated.
In the experimental apparatus shown in fig. 1, in the experimental apparatus of this embodiment, in the gas injection system 1, the gas pressure control assembly includes a gas booster pump 12, and the medium gas injected from the gas source 11 may be boosted to a target pressure by the gas booster pump 12 and continuously injected into the model system 3 for gas-water flow simulation.
In order to better control the pressure condition of the gas medium provided by the gas injection system 1, the gas pressure control assembly of the gas injection system 1 of the present embodiment further includes a pressure reducing valve 17 and/or a buffer tank 14; the pressure reducing valve 17 is arranged in front of the gas booster pump 12 and is used for reducing the pressure of the medium gas injected from the gas source 11; the buffer tank 14 is disposed behind the gas booster pump 12, and is configured to store the medium gas boosted to a target pressure to stabilize a high pressure. After being output from the gas source 11, the medium gas is decompressed through the decompression valve 17, is then boosted to a target pressure through the booster pump 12, is then injected into the buffer tank 14 to stabilize the pressure of the high-pressure gas, and the medium gas after being stabilized by the buffer tank 14 is injected into the model system 3 through the gas pressure regulating valve 15 to stabilize the pressure of the medium gas, and is collected by the pressure instrument 16 to be subjected to real-time adjustment. The gas injection system 1 of the present embodiment is further provided with an air compressor 13 for providing a power source for the gas booster pump 12 and the gas pressure regulating valve 15.
As shown in the experimental apparatus shown in fig. 1, in the experimental apparatus of this embodiment, the vacuum pumping system 2 mainly includes a vacuum pump 21 and a valve 22 for pumping air inside the model system 3 to form a vacuum environment.
In the structure shown in fig. 1-2, in the experimental apparatus according to this embodiment, the model system 3 simulates a coalbed methane production process under a real formation condition by controlling the core simulation module, and is a core part of the entire apparatus.
The core simulation assembly comprises a core holder 32, wherein a core cavity 321 for accommodating a core with a selected size, an axial compression cavity 322 arranged on two sides of the core cavity 321, and a confining pressure cavity 323 arranged on the periphery of the core cavity 321 are arranged in an inner cavity of the core holder 32. The pressure loading assembly comprises an axial pressure automatic loading system 34 and a confining pressure automatic loading system 33 which respectively control the pressure of the axial pressure cavity 322 and the confining pressure cavity 323. According to the target confining pressure, confining pressure is applied to the inner core of the core holder 32 through the confining pressure automatic loading system 33; and according to the target axial pressure, applying axial pressure to the core inside the core holder 32 through the automatic axial pressure loading system 34, so that the core obtains preset confining pressure and axial pressure.
In order to monitor the pressure transfer difference of different coal seams in the combined mining process, the experimental device in this embodiment designs a pressure acquisition scheme combining pressure acquisition inside the core holder 32 and differential pressure acquisition at two ends of the core holder, that is, a plurality of pressure sensors 35 for acquiring the pressure inside the core holder 32 are arranged at the core holder 32 to acquire differential pressure sensors 36 for acquiring the differential pressure at two ends of the core holder 32. After the pressure of the medium gas entering the model system 3 through the gas injection system 1 is further regulated and stabilized by the pressure regulating valve 37, the medium gas is further injected into the core holder 32 for simulation experiment.
In order to control the temperature of the core in the core cavity 321 to simulate the formation temperature, in the experimental apparatus of this embodiment, a temperature controllable incubator 31 is disposed at the periphery of the core holder 32, and the incubator 31 is mainly used for heating the core cavity of the core holder 32 to simulate the formation temperature (room temperature-200 ℃).
In the experimental apparatus shown in fig. 1-2, the core simulation modules are arranged into 3 parallel lines, the medium gas entering the model system 3 through the gas injection system 1 is distributed to the 3 parallel gas passages, and forms a gas-water two-phase fluid with the cores arranged in the core holders 32 on the respective lines, and the subsequent experimental measurement is performed.
As shown in fig. 1-3, in the experimental apparatus of this embodiment, the metering system 4 includes a gas-liquid separation module, the gas-water two-phase simulation fluid formed by the model system 3 enters the gas-liquid separation module to perform gas-liquid separation, and the separated gas and liquid are collected and detected respectively. The experimental device also realizes the control of the system back pressure or the gas flow through the arranged system pressure control assembly, and respectively simulates the constant pressure mining process or the constant flow mining process.
In the experimental apparatus shown in fig. 1 to 3, the gas-liquid separation modules are designed as a total of 3 groups of parallel lines which are arranged in one-to-one correspondence with the core simulation modules, that is, each group of core simulation modules is respectively and correspondingly connected with one group of gas-liquid separation modules.
As shown in fig. 1-3, the gas-liquid separation assembly includes a gas-liquid separator 41, and in order to simulate a gas backflow phenomenon in a coalbed methane combined production process and accurately obtain coalbed methane content data with gas backflow, the apparatus of this embodiment is specially designed with a gas-water production measurement assembly and a gas backflow measurement assembly, which are respectively connected to the gas-liquid separator 41.
The gas-water extraction measuring component comprises a measuring cylinder 43 which is communicated with the outlet of the gas-liquid separator 41 and is used for measuring the volume of the separated water phase and a first gas flowmeter 45-1 for metering the flow of the separated gas phase; the liquid separated by the gas-liquid separator 41 enters the measuring cylinder 43 for collection, and the volume and the change of the water in the measuring cylinder are observed and recorded by a camera 42; and the separated gas is further dried by a drying pipe 44 and then enters a first gas flow meter 45-1 through a first one-way valve 46-1 for metering.
The gas backflow measuring assembly comprises a second gas flowmeter 45-2 communicated with the inlet of the gas-liquid separator 41 and used for metering gas entering the gas-liquid separator 41 after being subjected to gas-liquid separation by other gas-liquid separation assemblies arranged in parallel; if the gas separated in the gas-liquid separation assembly of the second group and/or the third group is poured into the gas-liquid separator 41 of the first group, the poured gas needs to enter a second gas flowmeter 45-2 through a second one-way valve 46-2 for metering, so that the total amount of the gas poured into the core simulation assembly of the first group is obtained;
if the gas in the first group of core simulating assemblies is filled into the second group of core simulating assemblies and the third group of core simulating assemblies simultaneously, the gas separated from the first group of gas-liquid separating assemblies enters a second gas flow meter 45-2 through second one-way valves 46-2 of the second group and the third group respectively for metering, and the gas amount filled into the second group and the third group is obtained respectively.
In the experimental apparatus shown in fig. 1-3, the gas-water two-phase fluid formed by simulation of the first group of core simulation modules enters the first group of gas-liquid separation modules correspondingly connected with the first group of core simulation modules, the liquid separated by the gas-liquid separator 41 enters the measuring cylinder 43 for collection, and the volume of water in the measuring cylinder is observed and recorded by the camera 42; and the separated gas is further dried by a drying pipe 44 and then enters a first gas flow meter 45-1 through a first one-way valve 46-1 for metering. If the gas separated in the second group and the third group of gas-liquid separation assemblies is poured into the first group of core simulation assemblies, the gas separated in the second group and the third group of gas-liquid separation assemblies enters a second gas flowmeter 45-2 through a second one-way valve 46-2 in the first group for metering, and therefore the total amount of the gas poured into the first group of core simulation assemblies is obtained; if the gas in the first group of core simulating assemblies is filled into the second group of core simulating assemblies and the third group of core simulating assemblies simultaneously, the gas separated from the first group of gas-liquid separating assemblies enters a second gas flow meter 45-2 through second one-way valves 46-2 of the second group and the third group respectively for metering, and the gas amount filled into the second group and the third group is obtained respectively. Accordingly, the operation of the second and third sets of gas-liquid separation modules as shown in FIG. 1 is the same as described above. In the metering system 4, the gas metered by the first gas flow meter 45-1 and the second gas flow meter 45-2 is metered by the total gas flow meter 45-0 to obtain the total data of the gas flow.
The experimental device provided by the embodiment is particularly designed with the bidirectional metering mode, and the forward gas (produced gas) from the clamp is metered by a first gas flow rate 45-1 meter; and reverse gas (namely, backward flowing gas) from other core holders 32 is metered by the second gas flow meter 45-2, so that interlayer channeling in the multi-layer commingling production process is monitored and accurately metered, the stratum condition and the actual production condition are better met, a way is provided for objectively revealing the dynamic behavior of commingling production fluid and interlayer interference, and the method has important significance for research and actual exploration and development of multi-layer commingling production of coal bed gas.
In the experimental device shown in fig. 1-3, the total gas flow meter 45-0 is arranged on the bus of the gas-liquid separation assembly to realize the metering of the gas flow of the bus, and the back pressure valve 47 arranged on the bus can be used for applying back pressure to the system to simulate the constant pressure mining process; or by controlling the bus gas flow through a flow controller 48 also provided on the bus to simulate a fixed flow mining process.
In this embodiment, the two-phase seepage flow experimental apparatus for gas and water in multi-layer combined coal bed methane production can increase or decrease the number of rock core simulation assemblies arranged in parallel and the number of gas-liquid separation assemblies correspondingly connected in series according to the number of actually produced coal bed layers, and the gas-liquid separation assemblies are also incorporated into a bus to perform gas flow detection and control, so that multi-layer combined coal production of different coal bed layers can be simulated.
In the embodiment, the gas injection system 1 is provided with a plurality of gas outlet valves, and the simulated pressure of the corresponding core simulation assembly is adjusted by controlling the gas outlet valves connected with different core simulation assemblies; of course, a single set of gas injection system 1 may be provided for each set of core simulating assemblies.
The experimental device provided by the embodiment can be used for prediction before multilayer combined mining by scientific research and production units, and can also be used for experimental teaching. In order to research the process and mechanism of the coal bed gas output from the core sample, the core holder 32 and the incubator 31 in the embodiment are made of transparent materials, preferably made of toughened glass, so that the process of analyzing the coal bed gas from the core sample can be observed by naked eyes during experiments, the process of analyzing the coal bed gas from the core sample can be recorded by a camera, and the camera is used for follow-up research and teaching demonstration through playback.
In this embodiment, the metering system 4 may further include an element analyzer, the element analyzer is disposed in a bus and/or a gas measurement pipeline of the metering system 4, and is configured to test the content of trace elements in produced water and real-time change data thereof during a multi-layer commingled production process, and trace elements that are the same as or similar to actual formation water are added in advance into core sample saturated water, so that a trace element change rule curve of produced water in a multi-layer commingled production coal seam is obtained, which is of great significance to theoretical research and actual production of multi-layer commingled production of coal bed methane.
In this embodiment, the core simulation module may be connected to the formation water injection module to simulate the real environmental state of water content in the underground coal bed methane reservoir, and may also be connected to the bottom water simulation module to simulate the process of water content in the bottom formation of the coal reservoir and flooding into the coal reservoir with the coal bed methane bottom water. In this embodiment, the model system 3 is vacuumized by the vacuum pumping system 2, then the medium gas is injected by the gas injection system 1 to fill and adsorb the medium gas in the fractures and pores of the core sample, and then the formation water is injected into the core holder 32 to simulate the saturated water-containing environment of the underground reservoir, so that the environment of the underground coal bed methane reservoir is simulated to the maximum extent, and the reliability of the simulation result is improved.
Example two
The test method for the two-phase seepage experiment of the gas and water in the multi-layer combined coal bed methane production is based on simulation and experiment of the experimental device in the first embodiment, and specifically comprises the following steps:
s1, preparing, connecting a test pipeline, respectively loading equal-size core samples into the core holder 32, and controlling the sample size to be 25mm in diameter and 50-200mm in length; then opening a valve 22 and a vacuum pump 21 of a vacuum system 2, vacuumizing the model system 3, injecting medium gas through a gas injection system 1, filling and adsorbing the medium gas in cracks and pores of a core sample, and then injecting formation water into the core holder 32 to simulate the saturated water-containing environment of an underground reservoir;
s2, respectively applying a set confining pressure and a set axial pressure to a core cavity 321 in a core holder 32 through the confining pressure automatic loading system 33 and the axial pressure automatic loading system 34 in the model system 3 according to actual formation stress and temperature conditions, preferably setting the confining pressure to be 0-70 MPa and the axial pressure to be 0-70 MPa; heating the core cavity 321 of the core holder 32 through the thermostat 31 with controllable temperature to simulate the actual reservoir temperature, wherein the heating temperature is preferably 0-200 ℃;
s3, in the embodiment, the back pressure of the system is set through the back pressure valve 47 in the metering system 4, and preferably, the back pressure is set to be 0-50 MPa so as to simulate a constant-pressure attenuated mining mode;
s4, injecting gas into the 3 groups of parallel rock core holders 32 of the model system 3 according to a set pressure through the gas injection system 1; the gas pressure at the inlet end of the core holder 32 is adjusted through a preposed pressure adjusting valve 37 in the model system 3, and each group of core holders 32 can be adjusted to different gas injection pressures but cannot be larger than the gas injection pressure of the gas injection system 1; after gas is injected into the core holder 32, water in the displacement core flows, gas-water two-phase flow is formed inside each core, and gas-water flow along-way pressure changes are respectively recorded through the pressure sensors 35 at the core cavity 321 and the differential pressure sensors 36 arranged at two ends of the core holder 32;
s5, after the mixed gas-water two-phase simulation fluid flows out of the core holder 32, the mixed gas-water two-phase simulation fluid leaves the model system 3 and then enters the metering system 4; the two-phase fluid entering the metering system 4 firstly passes through the gas-liquid separator 41 to realize gas-water separation, and then the separated water further enters the measuring cylinder 43, and the volume change of the water in the measuring cylinder 43 is recorded through the camera 42, so as to realize the metering of the water flow; the gas from the gas-liquid separator 41 is dried by the drying pipe 44 and then enters the first flowmeter 45-1 through the first one-way valve 46-1 to realize metering; meanwhile, 3 groups of core holders 32 are arranged in parallel, gas from the core holders 32 of other groups possibly enters the circuit, if the gas enters the circuit, the gas firstly enters a second flow meter 45-2 through a second one-way valve 46-2 to realize metering, namely the interlayer cross flow gas quantity, and the metered cross flow gas is merged into a pipeline node above the gas-liquid separator 41;
and S6, after the branching gas and water flow are measured, the gas is finally merged into the bus, the gas flow of the bus is measured through a total gas flow meter 45-0 on the bus until the water does not flow, the experiment is ended after the gas flow is stable, and data processing is carried out to obtain a simulation experiment result.
The results of two experiments using the experimental set-up and test method described above are given below.
The first test: 3 groups of parallel core holders 32 are arranged, the confining pressure is 3MPa, 4MPa and 5MPa, the axial pressure is 2MPa, 3MPa and 4MPa, the temperature is 20 ℃, 30 ℃ and 40 ℃, the system back pressure is 0.5MPa, the gas injection pressure is 4, 5 and 6MPa respectively from top to bottom, and the core sample is a standard coal sample (with the diameter of 25mm and the length of 50mm) with the permeability of 1mD, so that the multi-layer combined gas-water two-phase seepage experiment is carried out. After the experiment lasted for 12 minutes and 45 seconds, no liquid was produced and the airflow was stable. The cumulative liquid production of each layer from top to bottom was 0.22mL, 0.31mL, 0.35mL, and the cumulative gas production was 7.66mL, 9.95mL, 11.14 mL. The pressure sensors 35 are distributed at the positions of 12.5 mm, 25.0 mm and 37.5mm along the sample length, and the variation of the pressure along the path at the stable state is as follows: the uppermost layer is 3.1MPa, 1.9MPa and 1.0 MPa; an intermediate layer, 3.7MPa, 2.3MPa, 1.1 MPa; the lowest layer, 4.8MPa, 3.3MPa, 1.1 MPa. When the sample is stable, the pressure difference between two ends of the sample displayed by the pressure difference sensor 36 is 3.3MPa, 4.1MPa and 5.2MPa from top to bottom in sequence. It can be seen that the pressure difference at two ends of the sample increases layer by layer when the gas injection pressure is stable along with the increase of the gas injection pressure from top to bottom, the gas and liquid flow is correspondingly increased, the displacement effect is better and better, and the phenomenon of interlayer fluid channeling is avoided.
And (3) carrying out a second experiment: 3 groups of parallel rock core holders 32 are arranged, the confining pressure is 3MPa, 4MPa and 5MPa sequentially from top to bottom, the axial pressure is 2MPa, 3MPa and 4MPa, the temperature is 20 ℃, 30 ℃ and 40 ℃, the system back pressure is 0.5MPa, the three layers of gas injection pressure are 5MPa, the rock core sample is a standard coal sample (with the permeability of 5mD, 1mD and 0.5 mD) (with the diameter of 25mm and the length of 50mm), and the rock core holders are arranged sequentially from top to bottom, so that a multi-layer combined production gas-water two-phase seepage experiment is carried out. After the experiment lasted for 10 minutes and 02 seconds, no liquid was produced and the airflow was stable. The cumulative liquid production of each layer from top to bottom was 0.78mL, 0.28mL, 0.07mL, and the cumulative gas production was 19.33mL, 8.81mL, 1.25 mL. The pressure sensors 35 are distributed at the positions of 12.5 mm, 25.0 mm and 37.5mm along the sample length, and the variation of the pressure along the path at the stable state is as follows: the uppermost layer is 3.5MPa, 2.2MPa and 1.0 MPa; intermediate layer, 3.9MPa, 2.7MPa, 1.3 MPa; the lowest layer, 4.3MPa, 3.4MPa, 2.6 MPa. When the sample is stable, the pressure difference between two ends of the sample displayed by the pressure difference sensor 36 is 4.3MPa, 3.9MPa and 3.2MPa from top to bottom in sequence. It can be seen that with the decrease of permeability from top to bottom, the pressure difference at two ends of the sample is decreased layer by layer when the sample is stable, the gas and liquid flow is correspondingly decreased, the displacement effect is increasingly poor, and the phenomenon of interlayer channeling is not seen.
EXAMPLE III
The test method for the two-phase seepage experiment of the multi-layer coal bed methane gas recovery water is based on simulation and experiment of the experimental device in the first embodiment, and specifically comprises the following steps:
s1, preparing, connecting a test pipeline, respectively loading equal-size core samples into the core holder 32, and controlling the sample size to be 25mm in diameter and 50-200mm in length; then opening a valve 22 and a vacuum pump 21 of a vacuum system 2, vacuumizing the model system 3, injecting medium gas through a gas injection system 1, filling and adsorbing the medium gas in cracks and pores of a core sample, and then injecting formation water into the core holder 32 to simulate the saturated water-containing environment of an underground reservoir;
s2, respectively applying a set confining pressure and a set axial pressure to a core cavity 321 in a core holder 32 through the confining pressure automatic loading system 33 and the axial pressure automatic loading system 34 in the model system 3 according to actual formation stress and temperature conditions, preferably setting the confining pressure to 0-70 MPa and the axial pressure to 0-70 MPa; heating the core cavity 321 of the core holder 32 through the thermostat 31 with controllable temperature to simulate the actual reservoir temperature, preferably, the heating temperature is 0-200 ℃;
s3, in the embodiment, the flow of the bus gas of the system is set through the flow controller 48 in the metering system 4, and preferably, the flow is set to be 0-5L/min so as to simulate a constant flow attenuated mining mode;
s4, injecting gas into the 3 groups of parallel core holders 32 of the model system 3 according to a set pressure through the gas injection system 1; the gas pressure at the inlet end of the core holder 32 is adjusted through a preposed pressure adjusting valve 37 in the model system 3, and each group of core holders 32 can be adjusted to different gas injection pressures but cannot be larger than the gas injection pressure of the gas injection system 1; after gas is injected into the core holder 32, water in the displacement core flows, gas-water two-phase flow is formed inside each core, and gas-water flow along-way pressure changes are respectively recorded through the pressure sensors 35 at the core cavity 321 and the differential pressure sensors 36 arranged at two ends of the core holder 32;
s5, after the mixed gas-water two-phase simulation fluid flows out of the core holder 32, the mixed gas-water two-phase simulation fluid leaves the model system 3 and then enters the metering system 4; the two-phase fluid entering the metering system 4 firstly passes through the gas-liquid separator 41 to realize gas-water separation, then the separated water further enters the measuring cylinder 43, and the volume change of the water in the measuring cylinder 43 is recorded through the camera 42 so as to realize the metering of water flow; the gas from the gas-liquid separator 41 is dried by the drying pipe 44 and then enters the first flowmeter 45-1 through the first one-way valve 46-1 to realize metering; meanwhile, as 3 groups of core holders 32 are arranged in parallel, gas from the core holders 32 of other groups possibly enters the circuit, if the gas enters the circuit, the gas firstly enters a second flow meter 45-2 through a second one-way valve 46-2 to realize metering, namely the interlayer blow-by gas quantity, and the metered blow-by gas enters a pipeline node above a gas-liquid separator 41;
and S6, after the branching gas and water flow are measured, the gas is finally merged into the bus, the gas flow of the bus is measured through a total gas flow meter 45-0 on the bus until the water does not flow, the experiment is ended after the gas flow is stable, and data processing is carried out to obtain a simulation experiment result.
In this embodiment, in order to simulate the interlayer interference phenomenon generated by multi-layer commingled mining and accurately measure the content of the coal bed gas which flows backwards, 3 sets of parallel core holders 32 are arranged, the confining pressure is 3MPa, 4MPa and 5MPa from top to bottom, the axial pressure is 2MPa, 3MPa and 4MPa, the temperature is 20 ℃, 30 ℃ and 40 ℃, the flow controller 48 is set to be 5mL/min, the gas injection pressure is 4MPa, 10MPa and 6MPa, the core sample is selected from standard coal samples (diameter is 25mm, length is 50mm) with permeability of 0.5mD, 10mD and 1mD, and the two-phase seepage experiment of gas water of multi-layer commingled mining is performed according to the above.
And after 9 seconds of the start of the experiment, the gas backflow phenomenon occurs, the gas in the second group of core simulation assemblies flows back to the other two groups of core simulation assemblies, namely, the gas separated in the second group of gas-liquid separation assemblies enters the second gas flow meter 45-2 through the second one-way valves 46-2 of the first group and the third group respectively, and the second gas flow meters 45-2 of the first group and the third group are displayed at the moment, which indicates that the gas flows in. In this case, the second group cumulative fluid production amount was 0.46mL, the first group cumulative fluid production amount was 0.01mL, and the third group cumulative fluid production amount was 0.05 mL.
After the experiment lasted 8 minutes and 28 seconds, no liquid was produced and the airflow was stable. The accumulated liquid production of the layers from top to bottom is 0.06mL, 0.77mL, 0.21mL, the accumulated gas production is 0.9mL, 35.75mL, 5.7mL, the gas quantity filled into the first group and the third group in the experiment process finally flows out completely, the backflow phenomenon occurs in the initial stage of the experiment, the maximum gas filling quantity of the first group in the process is 9.23mL, and the maximum gas filling quantity of the second group in the process is 6.75 mL. The cumulative gas production rate of each layer is obtained by subtracting the cumulative value of the second gas flowmeter 45-2 from the cumulative value of the first gas flowmeter 45-1. The pressure sensors 35 are distributed at the positions of 12.5 mm, 25.0 mm and 37.5mm along the sample length, and the variation of the pressure along the path at the stable state is as follows: the uppermost layer is 3.6MPa, 2.5MPa and 1.9 MPa; an intermediate layer of 8.3MPa, 5.6MPa, 3.0 MPa; the lowest layer, 5.1MPa, 3.4MPa, 1.8 MPa. When the sample is stable, the pressure difference between two ends of the sample displayed by the pressure difference sensor 36 is 2.3MPa, 8.3MPa and 4.4MPa from top to bottom in sequence. In the experimental process, the whole interlayer interference process can be recorded by a camera, and the method can be used for subsequent research analysis and teaching demonstration.
It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications derived therefrom are intended to be within the scope of the invention.
Claims (8)
1. A coal bed gas multilayer combined gas-water two-phase seepage experiment device is characterized by comprising a gas injection system (1), a model system (3) and a metering system (4) which are sequentially arranged along the gas flow direction in a pipeline;
the gas injection system (1) comprises a gas source (11) and a gas pressure control assembly, wherein the gas source (11) is used for providing medium gas for injecting a core experiment; the gas pressure control assembly comprises a gas booster pump (12), and medium gas injected by a gas source (11) is boosted to a target pressure by the gas booster pump (12);
the model system (3) comprises at least 2 groups of core simulation assemblies which are arranged in parallel and a pressure loading assembly for controlling cores in the core simulation assemblies, and the model system (3) is used for simulating a coalbed methane production process under a real stratum condition;
the metering system (4) comprises at least 2 groups of gas-liquid separation assemblies which are arranged in parallel and correspondingly connected with the core simulation assembly, gas-water two-phase fluid obtained by phase simulation of the core simulation assembly is respectively collected and detected after gas-liquid separation, and the control of system back pressure or gas flow is realized through a system pressure control assembly so as to respectively simulate a constant pressure mining process or a constant flow mining process;
the gas-liquid separation assembly comprises a gas-liquid separator (41), a gas-water extraction measuring assembly and a gas backflow measuring assembly, wherein the gas-water extraction measuring assembly and the gas backflow measuring assembly are respectively communicated with the gas-liquid separator (41);
the gas-water extraction measuring assembly comprises a measuring cylinder (43) which is communicated with an outlet of the gas-liquid separator (41) and is used for measuring the volume of the separated water phase and a first gas flowmeter (45-1) which is used for metering the flow of the separated gas phase; the inlet of the first gas flowmeter (45-1) is provided with a first one-way valve (46-1);
the gas backflow measuring assembly comprises a second gas flowmeter (45-2) communicated with an inlet of the gas-liquid separator (41) and used for metering gas entering the gas-liquid separator (41) after being subjected to gas-liquid separation by other gas-liquid separation assemblies arranged in parallel; the inlet of the second gas flowmeter (45-2) is provided with a second one-way valve (46-2);
in the metering system (4), the gas metered by the first gas flowmeter (45-1) and the second gas flowmeter (45-2) is metered by a total gas flowmeter (45-0).
2. The two-phase seepage experimental apparatus for gas and water in coal bed methane multi-layer commingled production is characterized in that the system pressure control assembly comprises a back pressure valve (47) for applying back pressure to the system and a flow controller (48) for controlling the gas flow.
3. The two-phase seepage experimental device for gas and water of coalbed methane multi-layer commingled production according to claim 2, wherein the core simulation assembly comprises a core holder (32);
a rock core cavity (321) for accommodating a rock core, axial pressure cavities (322) arranged at two sides of the rock core cavity (321) and a confining pressure cavity (323) arranged at the periphery of the rock core cavity (321) are arranged in the inner cavity of the rock core holder (32);
the pressure loading assembly comprises an axial pressure automatic loading system (34) and a confining pressure automatic loading system (33) which respectively control the pressure of the axial pressure cavity (322) and the confining pressure cavity (323), so that the rock core obtains preset confining pressure and axial pressure.
4. The two-phase seepage experiment device of gas and water for coal bed methane multi-layer commingled production according to claim 3, wherein the core simulation assembly further comprises a constant temperature box (31) arranged at the outer side of the core holder (32), a pressure sensor (35) used for collecting the internal pressure of the core holder (32), and a differential pressure sensor (36) used for detecting the differential pressure at two ends of the core holder (32).
5. The two-phase seepage experimental device for gas and water of multi-layer commingled production of coal bed methane according to claim 4, wherein the gas pressure control assembly is further provided with a pressure reducing valve (17) and/or a buffer tank (14);
the pressure reducing valve (17) is arranged in front of the gas booster pump (12) and is used for reducing the pressure of the medium gas injected by the gas source (11);
the buffer tank (14) is arranged behind the gas booster pump (12) and is used for storing medium gas boosted to a target pressure so as to stabilize the high-pressure gas pressure.
6. The two-phase seepage experiment device for gas and water in coal bed methane multi-layer commingled production is characterized by further comprising a vacuumizing system (2) arranged in front of the model system (3) and used for vacuumizing a core sample in the model system (3) so that medium gas and the core sample are fully contacted and adsorbed.
7. A test method for two-phase seepage experiment of multi-layer coal bed gas-water mixture, which is characterized in that the two-phase seepage experiment device of multi-layer coal bed gas-water mixture based on claim 6 comprises the following steps:
s1, connecting a test pipeline, loading a core sample with a selected size into the core holder (32), opening the vacuumizing system (2), vacuumizing the model system (3), injecting medium gas through the gas injection system (1), filling and adsorbing the medium gas into cracks and pores of the core sample, and injecting formation water into the core holder (32) to simulate a saturated water-containing environment of an underground reservoir;
s2, respectively applying set confining pressure and axial pressure to the core cavity (321) in the core holder (32) through the confining pressure automatic loading system (33) and the axial pressure automatic loading system (34) according to actual formation conditions; and heating the core cavity (321) by the thermostat (31) to simulate the actual reservoir temperature;
s3, setting the back pressure of the system through the back pressure valve (47) in the system pressure control assembly or setting the gas flow in the system through the flow controller (48) to simulate constant pressure attenuated production or constant flow attenuated production respectively;
s4, injecting medium gas into the core holder (32) of the model system (3) according to a set pressure through the gas injection system (1); after gas is injected, water in the core cavity (321) is displaced to flow, gas-water two-phase fluid is formed in each core, and gas-water flow along-way pressure change is recorded through the pressure sensor (35) and the differential pressure sensor (36);
s5, allowing the gas-water two-phase fluid to flow out of the core holder (32), allowing the gas-water two-phase fluid to enter the metering system (4), realizing gas-water two-phase separation through the gas-liquid separator (41), and allowing the separated water to enter the measuring cylinder (43) to realize water flow metering; the separated gas enters a gas flowmeter to realize gas metering;
s6, ending the experiment until the water does not flow and the air flow is stable, and performing data processing to obtain a simulation experiment result;
in the step S5, the gas metering step includes a step of metering the gas separated by the gas-liquid separator (41) by the first gas flow meter (45-1), a step of metering the gas separated by the other components and poured back into the gas-liquid separator (41) by the second gas flow meter (45-2), and a step of metering the total amount of gas metered by the first gas flow meter (45-1) and the second gas flow meter (45-2) by the total gas flow meter (45-0);
in the step S5, after the mixed gas-water two-phase simulated fluid flows out of the core holder (32), the mixed gas-water two-phase simulated fluid enters the metering system (4), gas-water separation is realized through the gas-liquid separator (41), then the separated water enters the measuring cylinder (43), and the volume change of the water in the measuring cylinder (43) is recorded through the camera (42), so that the water flow metering is realized; the gas from the gas-liquid separator (41) is dried by a drying pipe (44) and then enters a first flowmeter (45-1) through a first one-way valve (46-1) to realize metering; meanwhile, if gas from the core holders (32) of other groups enters the circuit, the gas enters a second flow meter (45-2) through a second one-way valve (46-2) to realize metering, namely the interlayer flow-crossing gas volume, and the metered flow-crossing gas is merged into a pipeline node above a gas-liquid separator (41).
8. The test method for the two-phase seepage experiment of the gas and water in the multi-layer commingled production of coal bed methane according to claim 7, wherein the step S4 further comprises the step of pressurizing the injected medium gas to a target pressure by a gas booster pump (12), and injecting the medium gas into a buffer tank (14) for pressure stabilization.
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