CN112881259A - Visualization device and method for measuring gas-water relative permeability of joint network based on steady state method - Google Patents
Visualization device and method for measuring gas-water relative permeability of joint network based on steady state method Download PDFInfo
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
- G01N15/082—Investigating permeability by forcing a fluid through a sample
- G01N15/0826—Investigating permeability by forcing a fluid through a sample and measuring fluid flow rate, i.e. permeation rate or pressure change
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
- G01N15/08—Investigating permeability, pore-volume, or surface area of porous materials
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Abstract
The invention relates to a visualization device and a visualization method for measuring gas-water relative permeability of a joint network based on a steady state method, which belong to the field of multiphase fluid flow in porous media and comprise a visualization autoclave, a microscope and a high-speed camera; the invention is based on the latest laboratory chip technology to visually research the flow state change of gas-liquid two phases under the microscale, does not use coal and rock cores directly to test, utilizes the digital image technology to extract the internal joint structure to be etched on the chip, and further tests the flow change of the two phases in the joint network. The device meets the acquisition function of multiple physical parameters in the multi-scale micro two-phase flow process, provides reliable experimental data for understanding the coal rock micro-scale flow characteristics and establishes the phenomenological relationship of coal (rock) -gas-liquid interaction.
Description
Technical Field
The invention relates to a visualization device and a visualization method for measuring gas-water relative permeability of a joint network based on a steady state method, and belongs to the technical field of multiphase fluid flow in porous media.
Background
Unconventional gas is high-quality clean energy existing in a reservoir, joints and cracks with different development degrees generally exist in the reservoir, and a complex joint network is formed. These networks become the main pathways for gas and water transport during gas production. The migration capacity of two-phase fluid in the gas-water relative permeability is generally characterized by gas-water relative permeability, and the laboratory usually adopts a steady-state method and an unsteady-state method to measure the coal (rock) core relative permeability, for details, see GB/T28912-2012. However, the assumptions of both methods are more stringent: in the unsteady state method, (i) because the coal sample has strong heterogeneity, the assumed condition of the homogeneity of the test piece is not satisfied, and the fluid is easy to break through prematurely; (ii) the water yield at the outlet is very little after the experiment begins, a large amount of water is produced quickly after breakthrough, the short-time flow change error is large after the tail end water break-through is measured by the current technical means, and (iii) the post-processing of the experimental data needs to carry out complex operation by integration. In the steady state method, (i) the clamp cannot rotate in real time after the experiment begins due to the limitation of experiment conditions to ensure that the gas and the water are injected simultaneously according to the proportion, and (ii) the method belongs to a black box experiment, and it is difficult to judge that each measuring point in the test piece reaches a stable state. (iii) It takes long time, and the experimental period is up to several weeks. In conclusion, the relative permeability laboratory measurement results influenced by the model hypothesis and the calculation method have great discreteness and do not have universal applicability.
Therefore, the conventional experimental method is difficult to achieve the above standards at the same time, and even if the assumed conditions are satisfied, various problems exist in the experimental test: it is difficult to achieve a steady state for flow determination as in steady state method testing. In the unsteady state method test, the water yield is very little after the experiment begins, then the output is very fast, it is difficult to the accurate measurement water yield, the data processing error is also great, and the experiment has very strong contingency, and different relative permeability can be measured to the same test piece under different conditions. Compared with the steady-state method, the method has more accurate relative permeability, but has large operation difficulty coefficient.
The characteristics of gas-liquid two-phase flow in the micro-channel are greatly different from the conditions in the macro-scale channel, and the influence of interfacial phenomena (such as surface tension, wettability and the like) caused by the micro-scale effect in the micro-channel is obvious, so that the two-phase flow characteristics and the conversion criterion between fluids are changed. The actual flow condition of the two-phase flow in the coal rock microscale is not verified by direct experimental data at present, and the flow characteristics are still based on numerical simulation. Aiming at the characteristics of the coal rock pore structure, the interaction of liquid-gas two-phase fluids under different joint networks is considered, so that the analysis of coal bed gas, shale gas exploitation, geothermal development and the like is of great importance.
Disclosure of Invention
In order to efficiently and accurately test the relative permeability of the complex microstructure of the coal rock mass and change the conventional macroscopic scale 'black box' experimental method, the invention provides a visualized device and method for measuring the gas-water relative permeability of a joint network based on a steady state method, aiming at solving the problem that the flow characteristics of the gas-water two phases in a coal (rock) core can only be tested by using a 'statistical' means at present, and the invention can represent the interaction of the two phases in a microchannel by visualizing the flow inside the joint so as to represent the gas-water relative permeability of the joint.
The invention adopts the following technical scheme:
a visualization device for measuring gas-water relative permeability of a joint network based on a steady state method comprises a visualization autoclave, a microscope and a high-speed camera;
a microscopic system is placed in the visual autoclave, the microscopic system comprises a microfluidic chip and a chip holder, a joint network reconstruction area is etched in the microfluidic chip to simulate a real joint network of a certain surface of a sample, the visual autoclave provides a controllable high-pressure environment for the microfluidic chip to ensure that the internal pressure meets a set pressure value, and transparent pressure-bearing glass is arranged above the visual autoclave;
the inlet end of the joint network reconstruction area is respectively connected with a liquid phase inlet hole and a gas phase inlet hole, the junction area of the liquid phase inlet hole and the gas phase inlet hole is an inlet observation section, the inlet observation section is connected with the inlet end of the joint network reconstruction area and is used for observing the mixing condition of two phases; the outlet end of the joint network reconstruction area is connected with an outlet hole through a micro-channel, and the micro-channel is an outlet observation section;
the visual autoclave is provided with an inlet sealing channel and an outlet sealing channel, the liquid-phase inlet hole and the gas-phase inlet hole are respectively connected with a pipeline A and a pipeline B through the inlet sealing channel, the pipeline A is connected with a liquid-phase micro-injection pump, the pipeline A is provided with a filter and a liquid pressure sensor, the pipeline B is connected with a gas-phase micro-injection pump, the pipeline B is provided with a gas pressure sensor, and the liquid pressure sensor and the gas pressure sensor are both connected to a computer and used for collecting pressure; the visual high-pressure kettle is also connected with a pressure adjusting system for adjusting the pressure environment of the micro-fluidic chip;
the micro-channel at the outlet end of the joint network reconstruction area is connected with a waste liquid recovery bottle through an outlet sealing channel by a pipeline C, a pressure sensor A is arranged on the pipeline C and used for recording the pressure at the outlet end, and the waste liquid recovery bottle is communicated with the atmosphere;
the microscope is used for amplifying a joint network reconstruction area through pressure-bearing glass of a visual high-pressure kettle, the high-speed camera is positioned above an ocular lens of the microscope, the whole flowing process is recorded, and a picture is transmitted to a computer in real time.
Preferably, the microsystem further comprises a cold light source and a reflector, wherein the cold light source illuminates the field of view of the chip, and the reflector is used for increasing the brightness of the field of view.
Preferably, the visual autoclave is further provided with a pressure adjusting channel A and a pressure adjusting channel B, the pressure adjusting system comprises a gas source, the gas source is connected with the pressure adjusting channel A through a pipeline D, the pipeline D is provided with a one-way valve and a pressure reducing valve, the pressure adjusting channel B is connected with a waste gas bottle through a pipeline E, and the pipeline E is provided with a one-way pressure reducing valve;
the pressure sensor B, the one-way valve and the one-way pressure reducing valve are all connected with a pressure regulator, and the pressure regulator is connected with a computer.
Preferably, the gas source is a high-pressure gas cylinder, the gas in the high-pressure gas cylinder is preferably inert gas, the gas in the high-pressure gas cylinder is injected into the visual autoclave through a one-way pressure reducing valve, a one-way valve and a pressure adjusting channel, confining pressure is applied to the microfluidic chip, and the pressure regulator can regulate the pressure in the visual autoclave according to the set pressure value of the computer and the pressure sensor B in the visual autoclave through feedback adjustment of the one-way valve and the one-way pressure reducing valve so as to ensure that the internal pressure meets the set pressure value.
Preferably, the bottom of the visual autoclave is provided with a base, and a reflector clamping groove is formed in the visual autoclave and used for embedding a reflector.
Preferably, the pipelines A, B, C, D and E are polytetrafluoroethylene pipes, preferably 1/16 polytetrafluoroethylene (ptfe) pipes, which are hard and can ignore errors caused by pipeline deformation.
Preferably, the joint of the polytetrafluoroethylene tube and the liquid-phase micro-injection pump and the joint of the polytetrafluoroethylene tube and the gas-phase micro-injection pump are firstly sealed by hot melt adhesive, the joint is sealed again by shadowless adhesive after curing, and ultraviolet irradiation is used for accelerating sealing;
the joints of the polytetrafluoroethylene tube, the liquid pressure sensor and the gas pressure sensor are connected and sealed by silica gel hoses with the inner diameter of 1.6mm to prevent fluid leakage.
A visualization method for measuring gas-water relative permeability of a joint network based on a steady-state method comprises the following steps:
the method comprises the following steps: the wettability of coal (rock) and the gas-water-rock three-phase contact angle are tested.
Step two: and scanning the test piece through a CT three-dimensional microscope to obtain an internal pore and fracture network structure.
Step three: adjusting the picture threshold value by utilizing avizo software to distinguish the areas of joints and matrixes, selecting the area of the facial joint network to be researched to outline in CAD software to be used as a design drawing, and then transferring the design drawing in the CAD software to a mask plate;
step four: transferring the joint network structure in the mask to a microfluidic chip by using a microfluidic chip technology (the transfer process belongs to the prior art and is not described herein again), and modifying the microchannel wall in the microfluidic chip manufacturing process to make the microchannel wall conform to the coal (rock) core wetting characteristics measured in the step one (the modification of the wettability of the chip belongs to the prior art and is not described herein again);
step five: in the steady-state method test, in order to facilitate the gas and water to be fully mixed at the inlet end and directly observe whether the steady state is achieved at the outlet end, the inlet and outlet positions of the joint network reconstruction area need to be slightly modified, namely an inlet observation section and an outlet observation section are arranged;
step six: continuously injecting water into the microfluidic chip for 3 hours at a high flow rate (preferably 5-10 mu L/min, and can be properly adjusted according to the joint scale), wherein the inlet end initial pressure is increased when the flow rate is increased, the whole pore space is filled, so that the later measurement of the saturation of the bound water is facilitated, in order to distinguish gas and water phases in a visual field, methylene blue with the mass fraction of 0.1% is added into the water phase, and the ratio of the non-dyeing area to the total area, namely the saturation of the residual gas, is calculated at the moment;
the condition for measuring the relative permeability by the steady-state method is that gas-water is simultaneously injected into a test piece filled with saturated water, the high-flow-rate continuous injection is used for displacing a water phase out of a gas phase in a joint network under a larger inlet pressure, and the part which is not injected with the water phase is a dead hole and is also a position occupied by residual gas;
step seven: injecting a test liquid phase into the microfluidic chip at a low flow rate (preferably 0.5-1 mu L/min), and continuously measuring the water phase permeability for three times after the pressure difference between an inlet and an outlet is stable (namely the pressure difference between the liquid pressure sensor, the gas pressure sensor and the pressure sensor A is stable), wherein the relative error is less than 3% and meets the experimental conditions;
Sg0indicates residual gas saturation, AwRepresenting the water phase area in the chip joint network after the steady state is reached; a represents the total area of the joint network, qwDenotes the flow rate of the aqueous phase, ml/s, uwDenotes the liquid phase viscosity, p1Represents the inlet pressure, MPa, which is the sum of the readings of the liquid pressure sensor and the gas pressure sensor; p is a radical of2Represents the outlet pressure, MPa, which can be read from the pressure sensor a; kw(Sg0) Is the water phase permeability.
Step eight: establishing the saturation of the bound water of the joint network, performing a gas drive experiment by using low flow rate (generally 0.5 mu L/min, and properly adjusting different joint scales), gradually increasing the displacement flow rate until water does not flow out, and measuring the effective permeability of a gas phase in a bound water state;
irreducible water saturation:
gas phase effective permeability in bound water state:
wherein S isw0Indicating irreducible water saturation;
Aw0representing the water phase area in the conditioning network after the tail end does not discharge water;
a represents the total area of the joint network;
Kg(Sw0) A value representing the effective permeability of the gas phase in the water-bound state in millidarcy (mD);
qgrepresenting the gas phase flow, ml/s, typically 0.5. mu.L/min;
p1represents the inlet pressure, MPa, which is the sum of the readings of the liquid pressure sensor and the gas pressure sensor;
parepresents atmospheric pressure, MPa;
μgthe gas phase viscosity is shown, and L represents the distance between an inlet and an outlet of the microfluidic chip;
step nine: the pressure is adjusted, and the pressure adjusting system automatically adjusts the pressure in the kettle to keep the pressure in the kettle at a set value all the time;
when the pressure is automatically adjusted, the pressure reducing valve is opened, the gas in the gas source is injected into the visual high-pressure kettle through the one-way valve, and the pressure regulator automatically adjusts the one-way valve and the one-way pressure reducing valve through the pressure sensor B to control the pressure in the visual high-pressure kettle;
the principle of testing the relative permeability of gas-water two phases by using a steady state method is utilized, and gas and water are respectively injected into a gas phase inlet hole and a liquid phase inlet hole at different proportions and constant speeds through a gas phase micro-injection pump and a liquid phase micro-injection pump;
step ten: when each gas and water flow ratio is injected, each phase is injected with at least 3 times of the volume of the joint network, a pressure curve is stable and fixed or shows periodic change (the pressure curve refers to a curve that the pressure displayed by a liquid pressure sensor and a gas pressure sensor changes along with time), meanwhile, when an inlet observation section shows Taylor flow with uniform gas and water and an outlet observation section shows a stable layered flow state, the flow is judged to reach a stable state, the pressure and the flow of the fluid at the inlet end are recorded, and a flow picture in the joint network structure is shot to calculate the saturation;
step eleven: calculating the effective permeability by using a Darcy formula according to the flow, the pressure and the geometric characteristics of the joint structure, and further obtaining the relative permeability:
in equation (3):
Kewirepresenting the relative water-phase permeability md under the ith gas-water ratio condition;
Kegirepresents the relative gas phase permeability, md;
qwirepresenting the water phase flow under the ith gas-water ratio condition, ml/s;
μwthe dynamic viscosity of the liquid phase is shown, and L represents the distance between an inlet and an outlet of the microfluidic chip;
qgirepresenting the water phase flow under the ith gas-water ratio condition, ml/s;
μgrepresents gas phase dynamic viscosity;
a represents the total area of the joint network;
p1represents the inlet pressure, MPa, which is the sum of the readings of the liquid pressure sensor and the gas pressure sensor;
p2represents the outlet pressure, MPa, which can be read from the pressure sensor a;
parepresents atmospheric pressure, MPa;
step twelve: calculating the water phase saturation through the area of the stabilized gas-water two phases, and defining the water saturation according to the difference of the gas phase and the water phase colors in the picture shot by the high-speed camera to the joint network reconstruction area:
Swirepresenting the water saturation after the i gas-water flow ratios are stabilized under the injection condition;
Awirepresenting the water phase area in the joint network after the ith gas-water ratio injection condition is stable;
a represents the total area of the joint network;
step thirteen: changing the gas-water injection ratio at the inlet end, and repeating the steps eight to twelve;
fourteen steps: drawing a relation curve of the gas-water relative permeability and the water saturation according to the calculation result:
Krgrepresents the relative permeability of the gas phase;
Krwrepresenting the relative permeability of the aqueous phase.
Preferably, in the fourth step, the modification treatment process is as follows:
injecting mixed solution of octamethyltetrasiloxane dichloride and pentane into a chip medium, continuously injecting for 30min at a low flow rate (1 mu L/min) after fully mixing to ensure that the mixed solution is fully contacted with the wall surface of a micro-channel in the chip, then placing the chip in a vacuum environment, volatilizing pentane to leave octamethyltetrasiloxane dichloride silicide solution to cover the surface of the wall of the micro-channel, and controlling different ratios of the concentrations of the two liquids to complete the hydrophilic/hydrophobic performance of the micro-channel of the chip.
In the present invention,
(1) setting two-phase injection numerical values of a liquid-phase micro-injection pump and a gas-phase micro-injection pump by adopting a principle of measuring relative permeability by a steady state method, and removing micro particles from liquid flow through a filter to prevent a micro channel from being blocked;
(2) the liquid pressure sensor detects the water phase pressure of a flowing point, and the gas pressure sensor detects the gas phase pressure of the flowing point and is connected with the computer to realize real-time data acquisition;
(3) the two phases enter the inlet observation section through the liquid phase inlet hole and the gas phase inlet hole respectively to be mixed;
(4) the micro-fluidic chip is fixed by the chip holder to prevent micro movement, the cold light source illuminates the chip field of view, the field of view brightness is increased by the aid of the reflector, the microscope amplifies the joint network reconstruction area, the high-speed camera records the whole flow process, and the picture is transmitted to the computer in real time;
(5) recording the pressure at the outlet end by using a pressure sensor A, wherein a waste liquid recovery bottle is communicated with the atmosphere;
(6) the steady state was reached throughout the experiment as the inlet observation period continued to appear as in fig. 3 and the computer 13 showed that the two-phase pressure tended to stabilize;
(7) the outlet end pressure is read by the tail end pressure sensor a.
It is worth noting that:
1. when the liquid phase flow is injected, tiny particles are removed through a filter to prevent the tiny particles from blocking a micro channel;
2. the micro-injection pump is a micro-rigid injector, and deformation errors generated by the wall of the rigid injector can be completely ignored in the micro-injection pump;
3. the calculation of the saturation degree is different from the calculation method of the traditional laboratory core weighing method, the water phase saturation degree can be calculated visually, after the flowing is stable, the picture captured by the camera is a dynamic balance picture, the gas and water continuously flow but the occupied area of the gas and water in the joint network is not changed, the picture is led into ImageJ software, and the area occupied by the gas and water is distinguished by adjusting the threshold value, namely the phase saturation degree in the joint network.
The invention is not described in detail in the prior art.
The invention has the beneficial effects that:
in order to efficiently and accurately test the permeability of the complex microstructure of the coal rock mass and change the conventional black box experiment method for solving the problem macroscopically, the invention visually researches the change of gas-liquid two-phase flow state under the microscale based on the latest laboratory chip technology, does not use the coal and rock core for testing directly like the prior art, extracts an internal joint structure by using a digital image technology and etches the internal joint structure on the chip, and further tests the change of two-phase flow in a joint network. The device meets the acquisition function of multiple physical parameters in the multi-scale micro two-phase flow process, provides reliable experimental data for understanding the coal rock micro-scale flow characteristics and establishes the phenomenological relationship of coal (rock) -gas-liquid interaction;
the invention provides a new direction for researching relative permeability, expands from a core scale to a microcosmic fracture scale, changes the traditional 'black box' experiment, visualizes the whole flowing process, can visually display the interaction of gas and water in a porous medium, visualizes the phenomena of water lock and air lock caused by the change of the fracture opening, and can quantitatively research the influence of the fracture opening on the relative permeability under different conditions.
Drawings
FIG. 1 is a schematic overall structure diagram of a visualization device for measuring gas-water relative permeability of a joint network based on a steady-state method;
FIG. 2 is a schematic diagram of a visual autoclave configuration of the present invention;
FIG. 3 is a schematic diagram of the construction of the microsystem of the present invention;
FIG. 4a is a schematic representation of the two-phase flow regime of the inlet observation stage at experimental stability according to the present invention;
FIG. 4b is a schematic diagram of the two-phase flow regime of the outlet observation stage at experimental stability according to the present invention;
FIG. 5 is a graph of gas-water relative permeability versus water saturation for an example.
In the figure, 1-liquid phase micro injection pump, 2-gas phase micro injection pump, 3-pipeline C, 4-filter, 5-liquid pressure sensor, 6-gas pressure sensor, 7-visual high pressure kettle, 8-microscope, 9-cold light source, 10-high speed camera, 11-pressure sensor A, 12-waste liquid recovery bottle, 13-computer, 14-pressure regulator, 15-one-way pressure reducing valve, 16-pressure reducing valve, 17-gas source, 18-waste gas bottle, 19-inlet sealing channel, 20-stainless steel shell, 21-pressure-bearing glass, 22-outlet sealing channel, 23-pressure sensor B, 24-base, 25-reflector clamping groove, 26-pressure regulating channel A, 27-a reflector, 28-a chip holder, 29-a microfluidic chip, 30-a liquid-phase inlet hole, 31-a gas-phase inlet hole, 32-an inlet observation section, 33-a joint network reconstruction region, 34-an outlet observation section, 35-an outlet hole, 36-a pipeline A, 37-a pipeline B, 38-a pressure regulation channel B, 39-a pipeline D, 40-a one-way valve and 41-a pipeline E.
The specific implementation mode is as follows:
in order to make the technical problems, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings and specific examples, but not limited thereto, and the present invention is not described in detail and is in accordance with the conventional techniques in the art.
Example 1:
the structure of the visualization device for measuring the gas-water relative permeability of the joint network based on the steady state method is shown in figures 1-3 and comprises a visualization autoclave 7, a microscope 8 and a high-speed camera 10;
a microscopic system is placed in the visualized autoclave 7, as shown in fig. 3, the microscopic system comprises a microfluidic chip 29 and a chip holder 28, a joint network reconstruction area 33 is etched in the microfluidic chip 29, a joint network structure of a sample is formed in the microfluidic chip to simulate a real certain joint network of the sample, the visualized autoclave 7 is used for providing a controllable high-pressure environment for the microfluidic chip to ensure that the internal pressure meets a set pressure value, and transparent pressure-bearing glass 21 is arranged above the visualized autoclave 7;
the inlet end of the joint network reconstruction region 33 is respectively connected with the liquid phase inlet hole 30 and the gas phase inlet hole 31, the junction region of the liquid phase inlet hole 30 and the gas phase inlet hole 31 is an inlet observation section 32, the inlet observation section 32 is connected with the inlet end of the joint network reconstruction region, and the inlet observation section 32 is used for observing the mixing condition of two phases; the outlet end of the joint network reconstruction region 33 is connected with an outlet hole 35 through a micro-channel, which is an outlet observation section 34;
the visual high-pressure kettle 7 is provided with an inlet sealing channel 19 and an outlet sealing channel 22, the liquid-phase inlet hole 30 and the gas-phase inlet hole 31 are respectively connected with a pipeline A36 and a pipeline B37 through the inlet sealing channel 19, the pipeline A36 is connected with the liquid-phase micro-injection pump 1, the pipeline A36 is provided with a filter 4 and a liquid pressure sensor 5, the pipeline B36 is connected with the gas-phase micro-injection pump 2, the pipeline B37 is provided with a gas pressure sensor 6, and the liquid pressure sensor 5 and the gas pressure sensor 6 are connected to the computer 13 and used for achieving pressure collection; the visualized autoclave 7 is also connected with a pressure adjusting system for adjusting the pressure environment of the microfluidic chip;
the micro-channel at the outlet end of the joint network reconstruction area is connected with a waste liquid recovery bottle 12 through an outlet sealing channel 22 and a pipeline C3, a pressure sensor A11 is arranged on the pipeline C3 and used for recording the pressure at the outlet end, and the waste liquid recovery bottle 12 is communicated with the atmosphere;
the microscope 8 is used for amplifying the joint network reconstruction area 33 through the pressure-bearing glass 21 of the visual autoclave, the high-speed camera 10 is positioned above an ocular lens of the microscope, the whole flowing process is recorded, and the picture is transmitted to a computer in real time.
Example 2:
a visualization device structure for measuring gas-water relative permeability of a joint network based on a steady state method is disclosed, as shown in embodiment 1, except that a microscopic system further comprises a cold light source 9 and a reflector 27, wherein the cold light source 9 illuminates the field of view of a chip, and the reflector 27 is used for increasing the brightness of the field of view.
Example 3:
the structure of the visualization device for measuring the gas-water relative permeability of the joint network based on the steady state method is different from that of embodiment 1 in that a pressure adjusting channel A26 and a pressure adjusting channel B38 are further arranged on a visualization high-pressure autoclave 7, a pressure adjusting system comprises a gas source 17, the gas source 17 is connected with the pressure adjusting channel A26 through a pipeline D39, a one-way valve 40 and a pressure reducing valve 16 are arranged on the pipeline D39, the pressure adjusting channel B38 is connected with a waste gas bottle 18 through a pipeline E41, and a one-way pressure reducing valve 15 is arranged on the pipeline E41;
the outside of the visualized autoclave 7 is a stainless steel shell 20, the inside of the visualized autoclave is provided with a pressure sensor B23 for real-time sensing and transmitting the pressure in the visualized autoclave 7, the pressure sensor B23, the one-way valve 40 and the one-way reducing valve 15 are all connected with a pressure regulator 14, and the pressure regulator 14 is connected with a computer 13.
Example 4:
the structure of the visualization device for measuring the gas-water relative permeability of the joint network based on the steady state method is as shown in embodiment 1, except that a gas source 17 is a high-pressure gas cylinder, the gas in the high-pressure gas cylinder is preferably inert gas, the gas in the high-pressure gas cylinder is injected into a visualization autoclave through a one-way pressure reducing valve 15, a one-way valve 40 and a pressure adjusting channel A/B, confining pressure is applied to a microfluidic chip, and a pressure regulator 14 can perform feedback adjustment on the one-way valve 40 and the one-way pressure reducing valve 15 according to a set pressure value of a computer and a pressure sensor B23 in the visualization autoclave to adjust the pressure in the visualization autoclave so as to ensure that the internal pressure in the visualization autoclave.
Example 5:
the structure of the visualization device for measuring the gas-water relative permeability of the joint network based on the steady state method is different from that in embodiment 1, a base 24 is arranged at the bottom of a visualization autoclave 7, and a reflector clamping groove 25 is arranged in the visualization autoclave 7 and used for embedding a reflector 27.
Example 6:
a visualization device for measuring gas-water relative permeability of a joint network based on a steady-state method is disclosed in example 1, except that a pipeline A36, a pipeline B37, a pipeline C3, a pipeline D39 and a pipeline E41 are all made of polytetrafluoroethylene tubes, and errors caused by pipeline deformation can be ignored due to the fact that the pipeline is hard in texture.
Example 7:
a structure of a visualization device for measuring gas-water relative permeability of a joint network based on a steady-state method is different from that of embodiment 1 in that a joint of a polytetrafluoroethylene tube and a liquid-phase micro-injection pump and a joint of a polytetrafluoroethylene tube and a gas-phase micro-injection pump are firstly sealed by hot melt adhesive, the joints are sealed again by shadowless adhesive after curing, and ultraviolet irradiation is used for accelerating sealing;
the joints of the polytetrafluoroethylene tube, the liquid pressure sensor and the gas pressure sensor are connected and sealed by silica gel hoses with the inner diameter of 1.6mm to prevent fluid leakage.
Example 8:
a visualization method for measuring gas-water relative permeability of a joint network based on a steady-state method comprises the following steps:
the method comprises the following steps: testing the wettability of coal (rock) and testing a gas-water-rock three-phase contact angle;
step two: scanning a test piece through a CT three-dimensional microscope to obtain an internal pore and fracture network structure;
step three: adjusting the picture threshold value by utilizing avizo software to distinguish the areas of joints and matrixes, selecting the area of the facial joint network to be researched to outline in CAD software to be used as a design drawing, and then transferring the design drawing in the CAD software to a mask plate;
step four: transferring the joint network structure in the mask to a microfluidic chip by using a microfluidic chip technology (the transfer process belongs to the prior art and is not described herein again), and modifying the wall of the microchannel in the manufacturing process of the microfluidic chip to make the wall of the microchannel conform to the wetting characteristic of the coal (rock) core measured in the step one;
step five: in the steady-state method test, in order to facilitate the gas and water to be fully mixed at the inlet end and directly observe whether the steady state is achieved at the outlet end, the inlet and outlet positions of the reconstruction area 33 of the rational network need to be slightly modified, namely an inlet observation section 32 and an outlet observation section 34 are arranged;
step six: continuously injecting water into the microfluidic chip 29 at a high flow rate of 10 mu L/min for 3 hours, wherein the inlet end has larger initial pressure when the flow rate is larger, the whole pore space is filled, and the saturation of the bound water is convenient to measure in the later period;
the condition for measuring the relative permeability by the steady-state method is that gas-water is simultaneously injected into a test piece filled with saturated water, the high-flow-rate continuous injection is used for displacing a water phase out of a gas phase in a joint network under a larger inlet pressure, and the part which is not injected with the water phase is a dead hole and is also a position occupied by residual gas;
step seven: injecting the test liquid phase into the microfluidic chip 29 at a low flow rate of 1 μ L/min, continuously measuring the three-time water phase permeability after the pressure difference between the inlet and the outlet is stable (namely the pressure difference between the liquid pressure sensor 5, the gas pressure sensor 6 and the pressure sensor A11 is stable), wherein the relative error is less than 3%, and calculating the average value of the three-time water phase permeability;
Sg0indicates residual gas saturation, AwRepresenting the water phase area in the chip joint network after the steady state is reached; a represents the total area of the joint network, qwDenotes the flow rate of the aqueous phase, ml/s, uwDenotes the dynamic viscosity of the liquid phase, p1Represents the inlet pressure, MPa, which is the sum of the readings of the liquid pressure sensor and the gas pressure sensor; p is a radical of2Represents the outlet pressure, MPa, which can be read from the pressure sensor a; kw(Sg0) Is the water phase permeability.
Step eight: establishing the saturation of the bound water of the joint network, performing a gas flooding experiment by using a flow rate of 0.5 mu L/min, gradually increasing the displacement flow rate until the water does not flow out, and measuring the effective permeability of the gas phase in the bound water state;
irreducible water saturation:
gas phase effective permeability in bound water state:
wherein S isw0Indicating irreducible water saturation;
Aw0representing the water phase area in the conditioning network after the tail end does not discharge water;
a represents the total area of the joint network;
Kg(Sw0) A value representing the effective permeability of the gas phase in the water-bound state in millidarcy (mD);
qgrepresenting the gas phase flow, ml/s, typically 0.5. mu.L/min;
p1represents the inlet pressure, MPa, which is the sum of the readings of the liquid pressure sensor and the gas pressure sensor;
parepresents atmospheric pressure, MPa;
μgthe gas phase viscosity is shown, and L represents the distance between an inlet and an outlet of the microfluidic chip;
step nine: the pressure is adjusted, and the pressure adjusting system automatically adjusts the pressure in the kettle to keep the pressure in the kettle at a set value all the time;
when the pressure is automatically adjusted, the pressure reducing valve 16 is opened, the gas in the gas source 17 is injected into the visual autoclave 7 through the one-way valve 40, and the pressure regulator 14 automatically adjusts the one-way valve 40 and the one-way pressure reducing valve 15 through the pressure sensor B23 to control the pressure in the visual autoclave;
the principle of testing the relative permeability of gas-water two phases by using a steady state method is utilized, and gas and water are respectively injected into a gas phase inlet hole and a liquid phase inlet hole at different proportions and constant speeds through a gas phase micro-injection pump and a liquid phase micro-injection pump;
step ten: when each gas-water flow ratio is injected, each phase is injected with at least 3 times of the volume of the joint network, a pressure curve is stable and fixed or shows periodic change (the pressure curve refers to a curve that the pressure displayed by a liquid pressure sensor and a gas pressure sensor changes along with time), meanwhile, when an inlet observation section shows Taylor flow with uniform gas and water (as shown in a state of figure 4 a) and an outlet observation section shows a stable layered flow state (as shown in a state of figure 4 b), the flow is judged to reach a stable state, the pressure and the flow of the fluid at the inlet end are recorded, and a flow picture in the joint network structure is shot to calculate the saturation;
step eleven: calculating the effective permeability by using a Darcy formula according to the flow, the pressure and the geometric characteristics of the joint structure, and further obtaining the relative permeability:
in equation (3):
Kewirepresenting the relative water-phase permeability md under the ith gas-water ratio condition;
Kegirepresenting the gas-phase relative permeability md under the ith gas-water ratio condition;
qwirepresenting the water phase flow under the ith gas-water ratio condition, ml/s;
μwindicating dynamic viscosity of liquid phase, L indicating micro-fluidic chipThe distance between the port and the outlet;
qgirepresenting the water phase flow under the ith gas-water ratio condition, ml/s;
μgrepresents gas phase dynamic viscosity;
a represents the total area of the joint network;
p1represents the inlet pressure, MPa, which is the sum of the readings of the liquid pressure sensor and the gas pressure sensor;
p2represents the outlet pressure, MPa, which can be read from the pressure sensor a;
parepresents atmospheric pressure, MPa;
step twelve: calculating the water phase saturation through the area of the stabilized gas-water two phases, and defining the water saturation according to the difference of the gas phase and the water phase colors in the picture shot by the high-speed camera to the joint network reconstruction area:
Swirepresenting the water saturation after the i gas-water flow ratios are stabilized under the injection condition;
Awirepresenting the water phase area in the joint network after the ith gas-water ratio injection condition is stable;
a represents the total area of the joint network;
step thirteen: changing the gas-water injection ratio at the inlet end, and repeating the steps eight to twelve;
fourteen steps: drawing a relation curve of the gas-water relative permeability and the water saturation according to the calculation result:
Krgrepresents the relative permeability of the gas phase;
Krwrepresenting the relative permeability of the aqueous phase.
The abscissa of the curve relating gas-water relative permeability to water saturation is SwOrdinate is Krw，Krg。
Example 9:
a visualization method for measuring gas-water relative permeability of a joint network based on a steady-state method is described by a specific example:
1) fixing the designed microfluidic chip 29 on a chip holder 28, placing the microfluidic chip and the reflector 27 on a high-pressure kettle base and fixing the microfluidic chip and the reflector by using a reflector clamping groove 25;
2) the silicone tube is sequentially connected with the liquid phase micro-injection pump 1/the gas phase micro-injection pump 2, each pressure sensor, the micro-fluidic chip and the like, and the sealing of the inlet sealing channel 19 and the outlet sealing channel 22 of the visual high-pressure kettle is required after the connection is finished;
3) inputting a set pressure of 3MPa into the computer 13, opening the gas source 17 and the pressure reducing valve 16 to inject inert gas into the visual autoclave 7 for pressurization, and carrying out an experiment after the pressure reading is stable for 30 min;
4) injecting deionized water into the inlet end of the chip at a rate of 5 μ L/min by a liquid phase micro-injection pump 1/a gas phase micro-injection pump 2, and continuously injecting for 30min after the pressure difference between the inlet and the outlet is stable to ensure that water is filled in the process as much as possible;
5) adjusting the injection phase micro-injection pump 1/gas phase micro-injection pump 2 to 0.5 muL/min, continuously measuring the relative permeability of the water phase for three times after the inlet and outlet pressure is stable, wherein the relative error is less than 0.5 percent, and calculating the average value;
in the above formula, PmIs P1Denotes the inlet pressure, PoutIs P2Expressing the outlet pressure, calculated as Kw＝4.46×103mD；
6) Filling gas into a chip filled with water at a rate of 0.5 mu L/min by a liquid phase micro-injection pump 1/a gas phase micro-injection pump 2, recording pressure values after the pressure of an inlet and an outlet is stable, collecting the gas and water distribution state of the whole joint network by a high-speed camera, and calculating the total joint area and the dyeing water area by adjusting a picture threshold value to obtain the bound water saturation and the effective gas phase permeability under the bound water state:
Kg(Sws)＝3.75×103mD
7) injecting gas and water into the chip according to a certain proportion, when the inlet water pressure and the air pressure are kept unchanged or the pressure is changed regularly, the gas and the water at the outlet section uniformly flow out and can flow stably, measuring the stable inlet water pressure and air pressure and the outlet back pressure, acquiring the gas and water distribution of the joint of the whole chip by using a high-speed camera, calculating the ratio of the area of dyeing water to the total area of the joint, namely the saturation by adjusting the picture threshold, and filling the data into an original recording table;
8) calculating the relative permeability and water saturation of the gas phase and the water phase according to a formula;
9) and drawing a relation curve of the relative permeability of the gas and the water and the saturation of the water according to the calculation result, and showing in a figure 5.
As in fig. 5, the abscissa is SwOrdinate is Krw，KrgRespectively representing the relative permeability of the water phase and the relative permeability of the gas phase;
it should be noted that in the present invention, the effective permeability is calculated by equation (3), where i represents the relative permeability value at the time of injecting the 1 st, 2 nd, and 3 rd gas-water ratio, and represents a corresponding point at a certain saturation, and the gas-phase relative permeability and the water-phase relative permeability are calculated by equations (5) and (6), respectively, and the relationship therebetween is:
while the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (9)
1. A visualization device for measuring gas-water relative permeability of a joint network based on a steady state method is characterized by comprising a visualization autoclave, a microscope and a high-speed camera;
a microscopic system is placed in the visual autoclave, the microscopic system comprises a microfluidic chip and a chip holder, a joint network reconstruction area is etched in the microfluidic chip to simulate a real joint network of a certain surface of a sample, the visual autoclave provides a controllable high-pressure environment for the microfluidic chip to ensure that the internal pressure meets a set pressure value, and transparent pressure-bearing glass is arranged above the visual autoclave;
the inlet end of the joint network reconstruction area is respectively connected with a liquid phase inlet hole and a gas phase inlet hole, the junction area of the liquid phase inlet hole and the gas phase inlet hole is an inlet observation section, the inlet observation section is connected with the inlet end of the joint network reconstruction area and is used for observing the mixing condition of two phases; the outlet end of the joint network reconstruction area is connected with an outlet hole through a micro-channel, and the micro-channel is an outlet observation section;
the visual autoclave is provided with an inlet sealing channel and an outlet sealing channel, the liquid-phase inlet hole and the gas-phase inlet hole are respectively connected with a pipeline A and a pipeline B through the inlet sealing channel, the pipeline A is connected with a liquid-phase micro-injection pump, the pipeline A is provided with a filter and a liquid pressure sensor, the pipeline B is connected with a gas-phase micro-injection pump, the pipeline B is provided with a gas pressure sensor, and the liquid pressure sensor and the gas pressure sensor are both connected to a computer and used for collecting pressure; the visual high-pressure kettle is also connected with a pressure adjusting system for adjusting the pressure environment of the micro-fluidic chip;
the micro-channel at the outlet end of the joint network reconstruction area is connected with a waste liquid recovery bottle through an outlet sealing channel by a pipeline C, a pressure sensor A is arranged on the pipeline C and used for recording the pressure at the outlet end, and the waste liquid recovery bottle is communicated with the atmosphere;
the microscope is used for amplifying a joint network reconstruction area through pressure-bearing glass of a visual high-pressure kettle, the high-speed camera is positioned above an ocular lens of the microscope, the whole flowing process is recorded, and a picture is transmitted to a computer in real time.
2. The device for visualizing gas-water relative permeability of joint network based on steady state method as claimed in claim 1, wherein said microsystem further comprises a cold light source and a reflector.
3. The visualization device for measuring the gas-water relative permeability of the joint network based on the steady-state method according to claim 1, wherein a pressure regulation channel A and a pressure regulation channel B are further arranged on the visualization autoclave, the pressure regulation system comprises a gas source, the gas source is connected with the pressure regulation channel A through a pipeline D, a one-way valve and a pressure reducing valve are arranged on the pipeline D, the pressure regulation channel B is connected with a waste gas bottle through a pipeline E, and a one-way pressure reducing valve is arranged on the pipeline E;
the pressure sensor B, the one-way valve and the one-way pressure reducing valve are all connected with a pressure regulator, and the pressure regulator is connected with a computer.
4. The visualization device for measuring the gas-water relative permeability of the joint network based on the steady-state method as claimed in claim 3, wherein the gas source is a high-pressure gas cylinder, and the gas in the high-pressure gas cylinder is inert gas.
5. The visualization device for measuring the gas-water relative permeability of the joint network based on the steady-state method as claimed in claim 3, wherein the bottom of the visualization autoclave is provided with a base, and the inside of the visualization autoclave is provided with a reflector slot for embedding a reflector.
6. The visualization device for measuring the gas-water relative permeability of the joint network based on the steady-state method according to claim 3, wherein the pipeline A, the pipeline B, the pipeline C, the pipeline D and the pipeline E are all polytetrafluoroethylene pipes.
7. The visualization device for measuring the gas-water relative permeability of the joint network based on the steady-state method according to claim 6, wherein the joint of the polytetrafluoroethylene tube and the liquid-phase micro-injection pump and the joint of the polytetrafluoroethylene tube and the gas-phase micro-injection pump are firstly sealed by hot melt adhesive, the joint is sealed again by shadowless adhesive after curing, and the ultraviolet irradiation is accelerated to seal;
the joints of the polytetrafluoroethylene tube, the liquid pressure sensor and the gas pressure sensor are connected and sealed by silica gel hoses with the inner diameter of 1.6mm to prevent fluid leakage.
8. A visualization method for measuring gas-water relative permeability of a joint network based on a steady state method based on the device of claim 1 is characterized by comprising the following steps:
the method comprises the following steps: testing the wettability of the coal core and testing the gas-water-rock three-phase contact angle;
step two: scanning a test piece through a CT three-dimensional microscope to obtain an internal pore and fracture network structure;
step three: adjusting the picture threshold value by utilizing avizo software to distinguish the areas of joints and matrixes, selecting the area of the facial joint network to be researched to outline in CAD software to be used as a design drawing, and then transferring the design drawing in the CAD software to a mask plate;
step four: transferring the joint network structure in the mask to a microfluidic chip by using a microfluidic chip technology, and modifying the wall of the microchannel in the manufacturing process of the microfluidic chip to enable the wall of the microchannel to meet the coal rock core wetting characteristic measured in the step one;
step five: in the steady state method test, in order to facilitate the gas and water to be fully mixed at the inlet end and directly observe whether the steady state is achieved at the outlet end, the inlet and outlet positions of the joint network reconstruction area need to be modified, namely an inlet observation section and an outlet observation section are arranged;
step six: continuously injecting water into the microfluidic chip at a high flow rate of 5-10 mu L/min for 3h, so as to facilitate later-stage measurement of the saturation of the bound water, adding methylene blue with a mass fraction of 0.1% into the water phase, and calculating the ratio of the non-dyeing area to the total area, namely the saturation of the residual gas;
step seven: injecting the test liquid phase into the microfluidic chip at a low flow rate of 0.5-1 mu L/min, continuously measuring the water phase permeability for three times after the pressure difference between an inlet and an outlet is stable, wherein the relative error of the water phase permeability is less than 3%, and taking the average value of the three times as the relative permeability of the water phase;
step eight: establishing the saturation of the bound water of the joint network, performing a gas drive experiment by using a low flow rate of 0.5 mu L/min, gradually increasing the displacement flow rate until the water does not flow out, and measuring the effective permeability of the gas phase in the state of the bound water;
irreducible water saturation:
gas phase effective permeability in bound water state:
wherein S isw0Indicating irreducible water saturation;
Aw0representing the water phase area in the conditioning network after the tail end does not discharge water;
a represents the total area of the joint network;
Kg(Sw0) A value representing the effective permeability of the gas phase in a water-bound state, in millidarcy;
qgrepresents the gas phase flow rate, ml/s;
p1represents the inlet pressure, MPa, which is the sum of the readings of the liquid pressure sensor and the gas pressure sensor;
parepresents atmospheric pressure, MPa;
μgthe gas phase viscosity is shown, and L represents the distance between an inlet and an outlet of the microfluidic chip;
step nine: the pressure is adjusted, and the pressure adjusting system automatically adjusts the pressure in the kettle to keep the pressure in the kettle at a set value all the time;
respectively injecting gas and water into a gas-phase inlet hole and a liquid-phase inlet hole at different proportions and constant speeds through a gas-phase micro injection pump and a liquid-phase micro injection pump;
step ten: when each gas-water flow ratio is injected, each phase is injected with at least 3 times of the joint network volume, a pressure curve is stable and does not move or shows periodic change, meanwhile, when an inlet observation section shows Taylor flow with uniform gas and water and an outlet observation section shows a stable layered flow state, the flow is judged to reach a stable state, the pressure and the flow of the fluid at the inlet end are recorded, and a flow picture in a joint network structure is shot to calculate the saturation;
step eleven: calculating the effective permeability by using a Darcy formula according to the flow, the pressure and the geometric characteristics of the joint structure, and further obtaining the relative permeability:
in equation (3):
Kewirepresenting the relative water-phase permeability md under the ith gas-water ratio condition;
Kegirepresenting the gas-phase relative permeability md under the ith gas-water ratio condition;
qwirepresenting the water phase flow under the ith gas-water ratio condition, ml/s;
μwexpressing dynamic viscosity of liquid phase, L expressing inlet and outlet of micro-fluidic chipThe distance between them;
qgirepresenting the water phase flow under the ith gas-water ratio condition, ml/s;
μgrepresents the gas phase viscosity;
a represents the total area of the joint network;
p1represents the inlet pressure, MPa, which is the sum of the readings of the liquid pressure sensor and the gas pressure sensor;
p2represents the outlet pressure, MPa, which can be read from the pressure sensor a;
parepresents atmospheric pressure, MPa;
step twelve: calculating the water phase saturation through the area of the stabilized gas-water two phases, and defining the water saturation according to the difference of the gas phase and the water phase colors in the picture shot by the high-speed camera to the joint network reconstruction area:
Swirepresenting the water saturation after the i gas-water flow ratios are stabilized under the injection condition;
Awirepresenting the water phase area in the joint network after the ith gas-water ratio injection condition is stable;
a represents the total area of the joint network;
step thirteen: changing the gas-water injection ratio at the inlet end, and repeating the steps eight to twelve;
fourteen steps: drawing a relation curve of the gas-water relative permeability and the water saturation according to the calculation result:
Krgindicating relative permeation of gas phaseRate;
Krwrepresenting the relative permeability of the aqueous phase.
9. The method for visualizing gas-water relative permeability of a joint network based on steady-state method according to claim 8, wherein in the fourth step, the modification treatment process comprises:
injecting a mixed solution of octamethyltetrasiloxane dichloride and pentane into a microfluidic chip, continuously injecting for 30min at a low flow rate of 1 mu L/min after the mixed solution is fully mixed, ensuring that the mixed solution is fully contacted with the wall surface of a microchannel in the microfluidic chip, then placing the microfluidic chip in a vacuum environment, volatilizing pentane to leave octamethyltetrasiloxane dichloride silicide solution to cover the surface of the wall of the microchannel, and controlling different ratios of the concentrations of two liquids to complete the hydrophilic/hydrophobic performance of the microchannel of the microfluidic chip.
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