CN109813645B - System and method for measuring radial permeability of core plunger of low-permeability rock ore - Google Patents
System and method for measuring radial permeability of core plunger of low-permeability rock ore Download PDFInfo
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- CN109813645B CN109813645B CN201910210028.0A CN201910210028A CN109813645B CN 109813645 B CN109813645 B CN 109813645B CN 201910210028 A CN201910210028 A CN 201910210028A CN 109813645 B CN109813645 B CN 109813645B
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Abstract
The invention provides a system and a method for measuring the radial permeability of a core plunger of a low-permeability rock ore. The system comprises: a clamping device; the first reference cavity is connected with a high-pressure gas source device for supplying high-pressure gas; a second reference chamber connected to the first reference chamber and to the sample chamber; the pressure control system is used for filling high-pressure gas into the first reference cavity and the second reference cavity, enabling the high-pressure gas in the first reference cavity and the second reference cavity to enter the sample cavity after the pressure of the first reference cavity and the pressure of the second reference cavity are kept unchanged, and only enabling the high-pressure gas in the second reference cavity to enter the sample cavity after preset time; a differential pressure sensor for reading a differential pressure value between the second reference chamber and the sample chamber as a whole and the first reference chamber after a preset time; and the data processing system is used for recording a differential pressure attenuation curve of the differential pressure value read by the differential pressure sensor along with the change of time, and fitting and calculating the differential pressure attenuation curve to obtain the radial permeability of the core plunger.
Description
Technical Field
The invention relates to the technical field of rock and ore permeability measurement, in particular to a system and a method for measuring the radial permeability of a core plunger of a low-permeability rock and ore.
Background
Unconventional natural gas resources represented by dense gas, coal bed gas and shale gas are key exploration and development objects of natural gas industries of countries in the world at present. The permeability and the diffusion coefficient are important physical properties of the rock and ore porous medium, quantitatively represent the migration capacity of reservoir gas in rock and ore pores, and are key parameters for reservoir evaluation. Reservoir rock of unconventional natural gas reservoirs has extremely low porosity (usually less than 10%), wherein shale and coal have a large amount of micro-nano pores, the matrix permeability of the shale and coal is as low as the order of nano-darcy, and the shale and coal have high measurement and analysis difficulty. The measurement of permeability (or diffusion coefficient) based on actual rock samples obtained by drilling and coring is an essential link in exploration process and also a current technical difficulty.
The existing measuring method of permeability of low-permeability rock ore is mainly a pressure attenuation method, and the type of a sample to be measured comprises a core plunger formed by machining or manually fractured core particles. The method for testing the pressure attenuation permeability of the core plunger sample generally applies a pressure difference step on two end faces of the sample, and reflects the permeability of gas along the axial direction of the core plunger through the attenuation rate of the pressure difference step. However, the permeability of natural rock samples has significant anisotropy, and unidirectional permeability measurements do not fully characterize the percolation resistance properties of anisotropic materials. The anisotropic permeability tensor is completely characterized, coring and testing are needed along different directions, the sampling cost is high, and the test result is greatly influenced by sampling.
The measurement of the radial permeability of the core plug sample can provide permeability data perpendicular to the axial direction, which when combined with the axial permeability measurements, can fully characterize the anisotropic character of the rock sample seepage. The existing radial permeability measurement technology of the pressure attenuation method is to directly measure the pressure signal attenuation characteristic of the annular space of the clamping device caused by sample suction by using a pressure sensor. The main means of improving the pressure curve measurement accuracy of the measurement system, reducing the temperature fluctuation of the system and improving the radial permeability measurement accuracy. The main defects of the prior art are as follows:
1) the internal pore space of the sample is far smaller than the dead volume formed by the annular space of the holder and the volume of the pipeline, the pressure attenuation amplitude of the annular space of the holder caused by the inspiration of the sample is very small, and the requirement on the precision of the sensor is extremely high when the pressure sensor is directly used for measurement. The measurement accuracy of the pressure sensor is in direct proportion to the measurement range (for example, the measurement accuracy is 0.1% of the full measurement range), when the measured pressure working condition is close to the actual underground reservoir pressure, the measurement accuracy is 20kPa at the moment, the pressure change below 20kPa cannot be distinguished, and therefore, the measurement of the annular space pressure attenuation curve of the clamp cannot be met.
2) In order to apply a certain axial pressure to the core plunger, a set of oil bath confining pressure system is usually required to be arranged in the holder, and a confining pressure booster pump, a circulating pump and the like are arranged outside the measuring system, so that the complexity and the cost of the whole system are increased.
Disclosure of Invention
It is an object of the invention to improve the accuracy of the measurement of the pressure decay curve.
It is another object of the present invention to reduce the complexity and cost of the overall system.
In particular, the invention provides a radial permeability measurement system for a core plunger of a hypotonic rock ore, comprising:
the clamping device is provided with a sample cavity for placing a core plunger and two clamping ends for clamping the core plunger;
a first reference chamber connected to a high pressure gas supply means for supplying high pressure gas through a first isolation valve;
a second reference chamber connected to the first reference chamber through an automatic balancing valve and to the sample chamber through a second isolation valve;
the pressure control system is used for controlling the opening and closing of the first isolation valve, the automatic balance valve and the second isolation valve so as to enable the first reference cavity and the second reference cavity to be filled with the high-pressure gas, enabling the high-pressure gas in the first reference cavity and the second reference cavity to enter the sample cavity after the pressure of the first reference cavity and the pressure of the second reference cavity are kept unchanged, and enabling only the high-pressure gas in the second reference cavity to enter the sample cavity after a preset time;
a differential pressure sensor connected between said first reference chamber and said second reference chamber for reading a differential pressure value between said second reference chamber and said sample chamber as a whole and said first reference chamber after said preset time;
and the data processing system is used for recording a differential pressure attenuation curve of the differential pressure value read by the differential pressure sensor along with the change of time, and fitting and calculating the differential pressure attenuation curve to obtain the radial permeability of the core plunger.
Optionally, the data processing system performs fitting calculation on the differential pressure attenuation curve according to the following formula to obtain the radial permeability of the core plunger:
wherein Δ p (t) is the differential pressure sensor reading at time t in Pa;
Δpfis the reading of the differential pressure sensor at the end of the gas permeation process of the sample chamber, and has the unit of Pa;
p0iis the pressure at which the gas pressures in the second reference chamber and the sample chamber reach equilibrium, in Pa;
p1ithe pressure in the sample cavity is Pa before the second reference cavity is communicated with the sample cavity;
gamma is the time constant of the differential pressure attenuation curve;
c is the intercept of the linear fit;
k is the radial permeability of the core plunger in m2；
a1As Bessel function J0(r0an) The smallest positive root, 0, whose size is determined by the core radius, is given in m-1；
M is the molar mass of the high-pressure gas and has the unit of kg/kmol;
rho is the density of the high-pressure gas and has the unit of kg/m3；
μ is the viscosity of the high pressure gas in Pa · s;
z is the true gas compression factor in m3/m3；
R is a gas constant 8.314 with the unit of kJ/kmol.K;
t is the thermodynamic temperature in K;
Optionally, the second reference chamber and the sample chamber except for the part occupied by the core plunger are filled with steel balls.
Optionally, one of the clamping ends of the clamping device has a cavity facing the sample chamber;
the clamping device further comprises a metal plate arranged between the sample cavity and the clamping end where the concave cavity is located, and a confining pressure air chamber is formed between the metal plate and the concave cavity.
Optionally, the radial permeability measurement system further comprises:
the pressure reducer is communicated with the high-pressure air source device through a high-pressure air source valve and is communicated with the confining pressure air chamber;
the pressure control system is also used for controlling the opening and closing of the high-pressure gas source valve, adjusting the pressure of the high-pressure gas through the high-pressure gas source valve, and stabilizing the pressure of the confining pressure gas chamber at the required pressure when the pressure reducer is opened, so that the axial confining pressure of the clamping device is controlled.
Optionally, the radial permeability measurement system further comprises an incubator, the first reference cavity, the second reference cavity, and the holder being disposed within the incubator;
and a temperature controller and a convection fan are also arranged in the constant temperature box and used for providing constant measurement temperature.
Particularly, the invention also provides a radial permeability measuring method based on the radial permeability measuring system of the core plunger of the hypotonic rock ore, which comprises the following steps:
placing a core plunger in a sample cavity of a clamping device, clamping the core plunger through two clamping ends of the clamping device, and vacuumizing;
filling high-pressure gas into the first reference cavity and the second reference cavity;
stopping filling the high-pressure gas into the first reference chamber and the second reference chamber, and waiting for the gas flow to be balanced with heat until the pressure of the first reference chamber and the second reference chamber is kept unchanged;
communicating the second reference chamber with the sample chamber, and setting an automatic balance valve for communicating the first reference chamber with the second reference chamber to be closed after a preset time;
after the automatic balance valve is closed, recording a differential pressure attenuation curve of the pressure difference value, which is read by a differential pressure sensor connected between the first reference cavity and the second reference cavity and changes along with time, and stopping recording until the pressure difference value does not change any more;
and fitting and calculating the differential pressure attenuation curve to obtain the radial permeability of the core plunger.
Optionally, the radial permeability of the core plug is obtained by fitting and calculating the differential pressure attenuation curve according to the following formula:
wherein Δ p (t) is the differential pressure sensor reading at time t in Pa;
Δpfis the reading of the differential pressure sensor at the end of the gas permeation process of the sample chamber, and has the unit of Pa; p is a radical of0iIs the pressure at which the gas pressures in the second reference chamber and the sample chamber reach equilibrium, in Pa;
p1ithe pressure in the sample cavity is Pa before the second reference cavity is communicated with the sample cavity;
gamma is the time constant of the differential pressure attenuation curve;
c is the intercept of the linear fit;
k is the radial permeability of the core plunger in m2；
a1As Bessel function J0(r0an) The smallest positive root, 0, whose size is determined by the core radius, is given in m-1；
M is the molar mass of the high-pressure gas and has the unit of kg/kmol;
rho is the density of the high-pressure gas and has the unit of kg/m3；
μ is the viscosity of the high pressure gas in Pa · s;
z is the true gas compression factor in m3/m3；
R is a gas constant 8.314 with the unit of kJ/kmol.K;
t is the thermodynamic temperature in K;
Optionally, after the filling of the high-pressure gas into the first reference chamber and the second reference chamber and before the stopping of the filling of the high-pressure gas into the first reference chamber and the second reference chamber, the method further includes:
and filling the high-pressure gas into a confining pressure gas chamber at one end of the clamping device to control the pressure of the confining pressure gas chamber to be at the required pressure so as to apply the required axial confining pressure to the clamping device.
Optionally, the radial permeability measurement method further comprises the steps of:
and closing the second isolation valve, and opening the first isolation valve and the automatic balance valve to charge high-pressure gas into the first reference cavity and the second reference cavity again, and adjusting the output pressure of the high-pressure gas until the pressure is close to the pressure of the next test working condition.
Compared with the prior art that the pressure value of the annular space of the holder (the sample cavity except the residual part occupied by the core plunger sample) caused by sample suction is directly measured by using a pressure sensor, the pressure measurement method has the advantage that the measurement accuracy of the pressure attenuation curve caused by the core plunger sample suction is greatly improved by measuring the pressure difference between the pressure value of the annular space of the holder (the sample cavity except the residual part occupied by the core plunger sample) caused by the core plunger sample suction and the first reference cavity.
The automatic balance valves connected to two ends of the differential pressure sensor are arranged, so that the differential pressure attenuation amplitude is not more than the measuring range of the differential pressure sensor, on the premise, the measurement accuracy of the pressure attenuation curve is in direct proportion to the measuring range of the differential pressure sensor, taking a sensor with the measuring range of 500kPa and the accuracy of 0.1% as an example, the discrimination of the pressure attenuation curve can reach 500Pa, the measurement accuracy of the sensor is improved by several times to ten times compared with that of the pressure sensor adopting the same accuracy, and the measurement accuracy of the pressure is not changed along with the increase of the absolute pressure of a system, so that the measurement accuracy of the pressure attenuation curve measured from the pressure attenuation curve is greatly improved.
The above and other objects, advantages and features of the present invention will become more apparent to those skilled in the art from the following detailed description of specific embodiments thereof, taken in conjunction with the accompanying drawings.
Drawings
Some specific embodiments of the invention will be described in detail hereinafter, by way of illustration and not limitation, with reference to the accompanying drawings. The same reference numbers in the drawings identify the same or similar elements or components. Those skilled in the art will appreciate that the drawings are not necessarily drawn to scale. In the drawings:
FIG. 1 is a schematic block diagram of a radial permeability measurement system for a hypotonic rock core plunger according to one embodiment of the present invention;
FIG. 2 is a schematic flow chart diagram of a method of measuring radial permeability of a core plug of a hypotonic rock ore according to one embodiment of the present disclosure;
FIG. 3 is a schematic diagram of a method of measuring radial permeability of a core plug of a hypotonic rock core according to one embodiment of the invention;
FIG. 4 is a schematic view of the gas flow when the automatic balancing valve is closed in step S400 of FIG. 2;
FIG. 5 is a schematic diagram of the gas flow when the gas in the second reference chamber and the sample chamber reaches equilibrium in step S400 of FIG. 2;
FIG. 6 is a graph of pressure changes in the first and second reference chambers and differential pressure sensor readings when the delay time is zero in step S400 of FIG. 2;
FIG. 7 is a graph of pressure changes in the first and second reference chambers and differential pressure sensor readings at a time delay of non-zero in step S400 of FIG. 2;
in the figure: 1-clamping device, 101-clamping end, 102-sample cavity, 103-clamp annular space, 104-concave cavity, 105-metal plate, 106-sealing piece, 107-sealing ring, 2-first reference cavity, 3-second reference cavity, 4-core plunger, 5-first isolation valve, 6-automatic balance valve, 7-second isolation valve, 8-differential pressure sensor, 9-pressure reducer, 10-first relief valve, 11-confining pressure air chamber, 12-high pressure air source valve, 13-pressure sensor, 14-constant temperature box, 15-temperature controller, 16-convection fan, 17-steel ball, 18-vacuum valve and 19-second relief valve.
Detailed Description
FIG. 1 shows a schematic block diagram of a radial permeability measurement system for a hypotonic core plunger according to one embodiment of the present invention. As shown in fig. 1, the radial permeability measurement system comprises a holding device 1, a first reference chamber 2, a second reference chamber 3, a pressure control system (not shown), a differential pressure sensor 8 and a data processing system (not shown).
The holding device 1 has two holding ends 101 and a sample chamber 102 located between the two holding ends 101 and used for placing the core plunger 4, and applying pressure to the sample chamber 102 can make high-pressure gas flow in the radial direction of the core plunger 4, so that the pressure of the sample chamber 102 can be gradually attenuated.
A first isolating valve 5 is arranged on a pipeline between the first reference cavity 2 and a high-pressure gas source device for supplying high-pressure gas, and the first reference cavity 2 is communicated with the high-pressure gas source device when the first isolating valve 5 is opened.
An automatic balance valve 6 is arranged on a pipeline between the second reference cavity 3 and the first reference cavity 2, and the second reference cavity 3 is communicated with the first reference cavity 2 when the automatic balance valve 6 is opened. A second isolation valve 7 is arranged on a pipeline between the second reference cavity 3 and the sample cavity 102, and the second reference cavity 3 is communicated with the sample cavity 102 when the second isolation valve 7 is opened.
The pressure control system is used for controlling the opening and closing of the first isolation valve 5, the automatic balance valve 6 and the second isolation valve 7, so that high-pressure gas is filled in the first reference cavity 2 and the second reference cavity 3, the high-pressure gas in the first reference cavity 2 and the second reference cavity 3 enters the sample cavity 102 after the pressure of the first reference cavity 2 and the pressure of the second reference cavity 3 are kept unchanged, and only the high-pressure gas in the second reference cavity 3 enters the sample cavity 102 after preset time.
The differential pressure sensor 8 is connected between the first reference chamber 2 and the second reference chamber 3, and is used for reading a differential pressure value between the second reference chamber 3 and the sample chamber 102 as a whole and the first reference chamber 2 after a preset time. Wherein, automatic balance valve 6 is connected simultaneously at differential pressure sensor 8's both ends, so, can adjust the numerical range of differential pressure sensor 8 reading through the time delay closure time that sets up automatic balance valve 6, ensure that differential pressure attenuation amplitude does not exceed differential pressure sensor 8's range to prevent that differential pressure sensor 8 from damaging.
The data processing system is used for recording a differential pressure attenuation curve of the differential pressure value read by the differential pressure sensor 8 along with the change of time, and fitting and calculating the differential pressure attenuation curve to obtain the radial permeability of the core plunger 4.
Compared with the prior art that the pressure sensor 13 is used for directly measuring the pressure value of the annular space of the holder (the sample cavity except the residual part occupied by the core) caused by sample suction, the pressure sensor provided by the invention has the advantage that the measurement accuracy of the pressure attenuation curve caused by the sample suction of the core plunger 4 is greatly improved by measuring the pressure difference between the pressure value of the annular space 103 of the holder (the sample cavity 102 except the residual part occupied by the core plunger 4) caused by the sample suction of the core plunger 4 and the first reference cavity.
Through setting up the automatic balance valve 6 of connecting at differential pressure sensor 8 both ends, can ensure that differential pressure attenuation range does not exceed its range, under this prerequisite, pressure attenuation curve measurement accuracy is directly proportional to differential pressure sensor 8's range, use the range to be 500kPa, the sensor that the precision is 0.1% is for example, its degree of distinction to pressure attenuation can reach 500Pa, this sensor's measurement accuracy compares and adopts pressure sensor 13 of equal precision to have the promotion of several times to several tens of times, and this pressure measurement accuracy does not produce the change along with the absolute pressure increase of system, consequently, the pressure attenuation curve measurement accuracy of measurement obtains very big improvement from this.
The data processing system performs linear fitting calculation on the differential pressure attenuation curve according to the following formula to obtain the radial permeability of the core plunger 4:
wherein Δ p (t) is the differential pressure sensor reading at time t in Pa;
Δpfis the reading of the differential pressure sensor at the end of the gas permeation process in the sample chamber, and has the unit of Pa;
p0iis the pressure at which the gas pressures in the second reference chamber and the sample chamber reach equilibrium, in Pa;
p1ithe pressure in the sample cavity is Pa before the second reference cavity is communicated with the sample cavity; is the time constant of the differential pressure decay curve;
c is the intercept of the linear fit;
k is the radial permeability of the core plunger in m2；
a1As Bessel function J0(r0an) The smallest positive root, 0, whose size is determined by the core radius, is given in m-1；
M is the molar mass of the high-pressure gas and has the unit of kg/kmol;
rho is the density of the high-pressure gas and has the unit of kg/m3；
μ is the viscosity of the high pressure gas in Pa · s;
z is the true gas compression factor in m3/m3；
R is a gas constant 8.314 with the unit of kJ/kmol.K;
t is the thermodynamic temperature in K;
In one embodiment, the steel ball 17 fills the remaining portion (holder annular space 103) of the second reference chamber 3 and the sample chamber 102 occupied by the coring plunger 4. The steel ball 17 may be a stainless steel ball. By filling stainless steel balls in the second reference cavity 3 and the holder annular space 103, the variation range of the pressure attenuation process can be improved, and the measurement accuracy of the pressure attenuation curve can be further improved. Meanwhile, the interference of the external temperature disturbance on the pressure attenuation process can be shielded by utilizing the specific heat capacity of the stainless steel ball.
In order to apply a certain axial pressure to the core plunger, a set of oil bath confining pressure system is usually arranged in the holder in the prior art, and a new confining pressure system which is small in size, low in cost, simple and ingenious in structure is creatively developed in the application. The confining pressure system comprises a pressure reducer 9, a first vent valve 10 and a confining pressure air chamber 11.
One of the clamping ends 101 of the clamping device 1 has a cavity 104 facing the sample chamber 102. The clamping device 1 further comprises a metal plate 105 arranged between the sample chamber 102 and the clamping end 101 of the cavity 104, the metal plate 105 and the cavity 104 forming an enclosure 11 between them. The metal plate 105 may be, for example, a metal blind plate. The metal blind plate can be a stainless steel flat plate with extremely low surface roughness. A seal 106 is arranged between the metal blind plate and one end of the core plunger 4 sample, and a seal 106 is also arranged between the other clamping end 101 and the other end of the core plunger 4 sample. The seal 106 may be a gasket, and may be made of an elastic material such as polytetrafluoroethylene. In one embodiment, the two clamping ends 101 of the clamping device 1 are a clamp flange and a clamp end cap, respectively. The cavity 104 is located in the holder flange. The joints of the holder flange, the holder end cap and the sample chamber 102 are sealed by sealing rings 107, and the sealing rings 107 may be rubber O-rings adapted to high-pressure gas.
The first air release valve 10 is connected with the confining pressure air chamber 11, and when the first air release valve 10 is opened, the pressure in the confining pressure air chamber 11 can be kept consistent with the atmospheric pressure.
A high-pressure air source valve 12 is arranged on a pipeline between the pressure reducer 9 and the high-pressure air source device, and when the high-pressure air source valve 12 is opened, the high-pressure air source device is connected with the pressure reducer 9. When the high-pressure air source valve 12 and the pressure reducer 9 are both opened and the first emptying valve 10 is closed, the pressure reduced by the pressure reducer 9 can be applied to the confining pressure air chamber 11. The axial confining pressure of the clamping device 1 can be controlled by adjusting the opening degree of the pressure reducer 9, namely, a determined axial clamping force is applied to the core plunger 4 sample.
Through the ingenious design of the sample cavity 102 and the clamp holder flange, an adjustable confining pressure is directly supplied to the confining pressure air chamber 11 from a high-pressure air source through the pressure reducer 9, so that the core plunger 4 can be reliably clamped and properly applied, and the axial sealing of the core plunger is ensured. The confining pressure system replaces a confining pressure oil bath system which is conventionally used in the industry, and the complexity and the cost of the system are reduced.
As shown in fig. 1, the radial permeability measurement system further includes a vacuum valve 18 and a second vent valve 19. The specific form of the high-pressure air source valve 12, the vacuum valve 18, the first emptying valve 10 and the second emptying valve 19 can be ball valves or stop valves. The first isolation valve 5, the second isolation valve 7, and the automatic balancing valve 6 are shut valves having excellent sealing performance, such as a diaphragm-sealed valve, a bellows-sealed valve, and the like. The radial permeability measurement system further comprises a pressure sensor 13 and an incubator 14. The pressure sensor 13 is connected to the second reference chamber 3. The first reference cavity 2, the second reference cavity 3, the clamp, the first isolation valve 5, the second isolation valve 7, the automatic balance valve 6, the differential pressure sensor 8 and the pressure sensor 13 are all arranged in an incubator 14. Also disposed within oven 14 are a temperature controller 15 and a convection fan 16 for providing a constant measured temperature within oven 14. The temperature controller 15 and the convection fan 16 can stabilize the temperature change in the oven 14 to 0.1 ℃ or less.
The changes in first reference chamber 2, second reference chamber 3, and sample chamber 102 caused by the opening and closing of the respective valves above are:
the system can be sufficiently evacuated by closing the high pressure gas source valve 12, the first vent valve 10 and the second vent valve 19, and opening the vacuum valve 18 and all other valves in the radial permeability measurement system.
And closing the vacuum valve 18, the first isolation valve 5, the first vent valve 10 and the second vent valve 19, adjusting the pressure of the high-pressure gas source to fill high-pressure gas into the first reference cavity 2 and the second reference cavity 3, and opening the pressure reducer 9, so that the pressure of the confining pressure gas chamber 11 can be controlled to be stabilized at a required pressure, and a determined axial clamping force is applied to the core plunger 4 sample.
Second isolation valve 7 is opened and automatic balancing valve 6 is set to close automatically after a preset time, allowing the high pressure gas in first reference chamber 2 and second reference chamber 3 to enter sample chamber 102, and allowing only the high pressure gas in second reference chamber 3 to enter sample chamber 102 after the preset time. After automatic equalization valve 6 is closed, the gas pressures in second reference chamber 3 and sample chamber 102 remain the same, and a pressure difference develops between second reference chamber 3 and sample chamber 102 and first reference chamber 2.
FIG. 2 shows a schematic flow diagram of a method of measuring radial permeability of a hypotonic core plunger as measured using the radial permeability measurement system described above, according to one embodiment of the present invention. As shown in fig. 2, the radial permeability measurement method includes:
step S100, placing a core plunger in a sample cavity of a clamping device, clamping the core plunger through two clamping ends of the clamping device, and vacuumizing;
step S200, filling high-pressure gas into the first reference cavity and the second reference cavity;
step S300, stopping filling high-pressure gas into the first reference cavity and the second reference cavity, and waiting for gas flow and heat balance until the pressure of the first reference cavity and the pressure of the second reference cavity are kept unchanged;
step S400, communicating a second reference cavity with the sample cavity, and setting an automatic balance valve for communicating the first reference cavity with the second reference cavity to be closed after a preset time;
step S500, after the automatic balance valve is closed, recording a differential pressure attenuation curve of the pressure difference value, which is read by a differential pressure sensor connected between the first reference cavity and the second reference cavity and changes along with time, and stopping recording until the pressure difference value does not change any more;
and step S600, fitting the differential pressure attenuation curve to obtain the radial permeability of the core plunger.
According to the method, the pressure difference between the pressure value of the annular space (the sample cavity except the residual part occupied by the core plunger sample) of the holder caused by the air suction of the core plunger sample and the first reference cavity is measured, so that the measurement accuracy of the pressure attenuation curve caused by the air suction of the core plunger sample is greatly improved. And the pressure measurement precision adopting the scheme does not change along with the increase of the absolute pressure of the system.
In step S100, the convection fan and the temperature controller may be turned on, so that the temperature change in the incubator is stabilized to 0.1 ℃. And when the vacuum pumping is carried out, the high-pressure air source valve, the first vent valve and the second vent valve are closed, and the vacuum valve and all other valves in the radial permeability measuring system are opened.
In step S200, the vacuum valve and the isolation valve 1 are closed, and the pressure of the high-pressure air source is adjusted to pHThe first reference cavity and the second reference cavity are filled with high-pressure gas, the pressure reducer is opened, and the pressure of the confining pressure gas chamber is controlled to be stabilized at pzApplying a determined axial clamping force to the plunger sample;
in step S300, the first isolation valve is closed, waiting for the gas flow to thermally equilibrate until the pressures of the first and second reference chambers remain constant.
In step S400, the second isolation valve is opened and the automatic balancing valve is openedSetting the time delay to be off, and recording the time delay as tw。
In step S500, the data processing system is turned on and the pressures of the first reference chamber and the second reference chamber are rapidly reduced and equalized with the sample chamber pressure. When the automatic balance valve is closed, the gas pressure of the second reference cavity and the sample cavity is further reduced along with the permeation of high-pressure gas along the radial direction of the core plunger. And the data processing system records the change curves delta p (t) and p (t) of the pressure difference and the pressure reading along with the time until the pressure difference delta p does not change along with the time, and the data recording is completed.
Flexible adjustment of delay time twThe numerical range of the differential pressure sensor reading can be adjusted to ensure that the delta p (t) does not exceed the range of the sensor, and the differential pressure sensor is prevented from being damaged.
In step S600, based on the Δ p (t) curve measurement result output by the differential pressure sensor, Δ p (t) data points that are verified to have been performed for a sufficiently long time (preferably, the second half time point of the differential pressure decay curve) are taken, and the differential pressure decay curve is fitted by using the following formula:
wherein Δ p (t) is the differential pressure sensor reading at time t in Pa, Δ pfIs the reading of the differential pressure sensor at the end of the gas permeation process in the sample chamber, and has the unit of Pa; p is a radical of0iIs the pressure at which the gas pressures in the second reference chamber and the sample chamber reach equilibrium, in Pa; p is a radical of1iThe pressure in the sample cavity is Pa before the second reference cavity is communicated with the sample cavity; . Gamma is the time constant of the differential pressure decay curve and C is the intercept of the linear fit.
According to the analytic solution of gas unsteady flow under the cylindrical coordinates, the radial permeability k and the pressure decay time constant gamma of the rock core satisfy the relationship shown in the formula (2):
wherein k is the radial permeability of the core plunger and is in m2，a1As Bessel function J0(r0an) The smallest positive root, 0, whose size is determined by the core radius, is given in m-1Rho is the density of the high-pressure gas, and M is the molar mass of the high-pressure gas and has the unit of kg/kmol; unit is kg/m3Mu is the viscosity of the high-pressure gas in Pa.s, Z is the real gas compression factor in m3/m3R is the gas constant 8.314 in kJ/kmol.K, T is the thermodynamic temperature in K,
core porosity.
FIG. 3 shows a measurement schematic of a method of measuring radial permeability of a hypotonic core plunger according to one embodiment of the present invention. Fig. 4 is a schematic view showing the gas flow when the automatic balancing valve is closed in step S400 shown in fig. 2, wherein the direction indicated by the hollow arrow is the gas flow direction. FIG. 5 is a schematic diagram of the gas flow when the gas in the second reference chamber and the sample chamber reaches equilibrium in step S400 of FIG. 2. As can be seen from fig. 3 to 5, after the automatic balance valve is closed, the high-pressure gas in the annular space of the holder flows in along the radial direction of the core plunger, the pressure of the second reference chamber and the pressure of the sample chamber are gradually reduced along with the suction of the sample until the balance is finally achieved, the gas does not flow any more, and the pressure in the second reference chamber and the pressure in the sample chamber does not change any more.
FIG. 6 shows the pressure change in the first and second reference chambers and the differential pressure sensor reading when the delay time is zero in step S400 of FIG. 2. As shown in FIG. 6, when the delay time is zero, the pressure of the first reference cavity is kept constant after the second isolation valve is opened and is always maintained at pHThe pressure of the second reference chamber is also p when the second isolation valve is openHAfter the second isolation valve opens, the pressure in the second reference chamber decreases gradually over time, first reaching equilibrium with the pressure in the sample chamber, at a value p0iThen the pressure in the second reference chamber and the sample chamber is reduced synchronouslyAnd finishing the gas permeation process.
FIG. 7 shows the pressure changes in the first and second reference chambers and the differential pressure sensor readings when the delay time is not zero in step S400 of FIG. 2. As shown in FIG. 7, when the delay time is not zero, after the second isolation valve is opened, the pressures of the first reference chamber and the second reference chamber are both rapidly reduced and gradually approach to the pressure of the sample chamber before the automatic balance valve is closed, and the pressures of the second reference chamber and the sample chamber are balanced, wherein the value of the pressure is p0i. The pressure of the first reference chamber is maintained at p after the auto-balance valve is closed0iWithout change, the pressure in the second reference chamber gradually decreases over time until the gas permeation process is complete.
As can be seen from the combination of FIGS. 6 and 7, the delay time twThe shorter Δ p (t) and Δ pfThe larger the value. Preferably, the delay time can be shortened as much as practical while ensuring that the range of the differential pressure sensor is not exceeded, but at the same time should be ensured to be greater than the time required from the opening of the second isolation valve to the pressure equalization of the second reference chamber with the sample chamber.
In another embodiment, step S400 may be followed by closing the second isolation valve, opening the first isolation valve and the automatic balancing valve, adjusting the output pressure of the high-pressure air source until the reading of the pressure sensor approaches the next test condition pressure, and proceeding to step S300 to start the next condition test. In this embodiment, it can be understood that the final pressure of the sample chamber in the previous working condition is the initial sample pressure p in the new working condition1i(in the first operating regime, p1i0), the permeability of which is a function of pressure can be obtained by measuring the permeation process of the sample under different initial pressure conditions.
The following examples are used to illustrate the process of measuring radial permeability using the radial permeability measuring system and method of the present invention.
Example 1:
in the embodiment, a Yokogawa differential pressure transmitter with the range of 100kPa and the precision of 0.065% is used as a core measurement sensor, and the sample clamping pressure is 2.0 MPa. Firstly, the sample is vacuumized for 8 hoursAt the initial pressure p of the sample chamber1iAt 10Pa, the second isolation valve was then closed, the rest of the system was pressurized to 1.0MPa with helium, the first isolation valve was shut off, and the thermostatted system was set at 27.0 ℃ for 30 minutes. Setting the automatic balancing valve to delay 15s for closing, opening the second isolating valve and starting to record the pressure difference and pressure curve. Through the observation of the differential pressure curve, the pressure curve is found to be 0 in the reading of the differential pressure of about 12s, and the pressure curve is maintained basically after rapidly reducing to 0.572MPa, so that the p of the test is determined0iIs 0.572 MPa. After the experiment is carried out for 2 hours, the pressure difference curve basically does not change, and delta pfThe final value was 74.125 KPa. The time constant of the current differential pressure curve obtained by fitting according to the formula (1) is 3.495 multiplied by 10-4s-1. The radial permeability k of the sample is calculated to be 2.73 multiplied by 10 by taking the physical property data of the sample and the helium gas into the formula (2)-5mD。
Example 2: immediately following the final state of example 1, the second isolation valve was closed, at which time the sample chamber initial pressure was 0.498 MPa. Adjusting the clamping pressure of the sample to be 2.5MPa, opening the first isolation valve and the automatic balance valve, pressurizing the system to 1.5MPa by using helium, cutting off the first isolation valve, and keeping the temperature for 10 minutes. Setting the automatic balance valve to close with a delay of 15s, repeating the operation, measurement and calculation in example 1, and measuring p0iIs 1.083MPa, Δ pf67.479KPa, k is 2.21 × 10-5And (mD). This indicates that the radial permeability of the sample decreases with increasing pore pressure, a phenomenon related to the slip flow of gas in the pores.
Thus, it should be appreciated by those skilled in the art that while a number of exemplary embodiments of the invention have been illustrated and described in detail herein, many other variations or modifications consistent with the principles of the invention may be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Accordingly, the scope of the invention should be understood and interpreted to cover all such other variations or modifications.
Claims (9)
1. A radial permeability measurement system of a core plunger of a hypotonic rock ore is characterized by comprising:
the clamping device is provided with a sample cavity for placing a core plunger and two clamping ends for clamping the core plunger;
a first reference chamber connected to a high pressure gas supply means for supplying high pressure gas through a first isolation valve;
a second reference chamber connected to the first reference chamber through an automatic balancing valve and to the sample chamber through a second isolation valve;
the pressure control system is used for controlling the opening and closing of the first isolation valve, the automatic balance valve and the second isolation valve so as to enable the first reference cavity and the second reference cavity to be filled with the high-pressure gas, enabling the high-pressure gas in the first reference cavity and the second reference cavity to enter the sample cavity after the pressure of the first reference cavity and the pressure of the second reference cavity are kept unchanged, and enabling only the high-pressure gas in the second reference cavity to enter the sample cavity after a preset time;
a differential pressure sensor connected between said first reference chamber and said second reference chamber for reading a differential pressure value between said second reference chamber and said sample chamber as a whole and said first reference chamber after said preset time;
the data processing system is used for recording a differential pressure attenuation curve of the differential pressure value read by the differential pressure sensor along with the change of time, and fitting and calculating the differential pressure attenuation curve to obtain the radial permeability of the core plunger;
and steel balls are filled in the second reference cavity and the sample cavity except for the part occupied by the core plunger.
2. The radial permeability measurement system of claim 1, wherein the data processing system fits the differential pressure decay curve to obtain the radial permeability of the core plug according to the following equation:
wherein Δ p (t) is the differential pressure sensor reading at time t in Pa;
Δpfis the reading of the differential pressure sensor at the end of the gas permeation process in the sample chamber, and has the unit of Pa; p is a radical of0iIs the pressure at which the gas pressures in the second reference chamber and the sample chamber reach equilibrium, in Pa;
p1ithe pressure in the sample cavity is Pa before the second reference cavity is communicated with the sample cavity;
gamma is the time constant of the differential pressure attenuation curve;
c is the intercept of the linear fit;
k is the radial permeability of the core plunger in m2；
a1As Bessel function J0(r0an) The smallest positive root, 0, whose size is determined by the core radius, is given in m-1；
M is the relative mass of the high-pressure gas, and the unit is kg/kmol;
rho is the density of the high-pressure gas and has the unit of kg/m3；
μ is the viscosity of the high pressure gas in Pa · s;
z is the true gas compression factor in m3/m3；
R is a gas constant 8.314 with the unit of kJ/kmol.K;
t is the thermodynamic temperature in K;
3. The radial permeability measuring system of claim 1 or 2, wherein one of the clamping ends of the clamping device has a cavity facing the sample chamber;
the clamping device further comprises a metal plate arranged between the sample cavity and the clamping end where the concave cavity is located, and a confining pressure air chamber is formed between the metal plate and the concave cavity.
4. The radial permeability measurement system of claim 3, further comprising:
the pressure reducer is communicated with the high-pressure air source device through a high-pressure air source valve and is communicated with the confining pressure air chamber;
the pressure control system is also used for controlling the opening and closing of the high-pressure gas source valve, adjusting the pressure of the high-pressure gas through the high-pressure gas source valve, and stabilizing the pressure of the confining pressure gas chamber at the required pressure when the pressure reducer is opened, so that the axial confining pressure of the clamping device is controlled.
5. The radial permeability measurement system of claim 4, further comprising an incubator, the first reference cavity, the second reference cavity, and the clamping device being disposed within the incubator;
and a temperature controller and a convection fan are also arranged in the constant temperature box and used for providing constant measurement temperature.
6. A radial permeability measurement method based on the radial permeability measurement system of the core plunger of the hypotonic rock ore of any one of claims 1 to 5, characterized by comprising the following steps:
placing a core plunger in a sample cavity of a clamping device, clamping the core plunger through two clamping ends of the clamping device, and vacuumizing;
filling high-pressure gas into the first reference cavity and the second reference cavity;
stopping filling the high-pressure gas into the first reference chamber and the second reference chamber, and waiting for the gas flow to be balanced with heat until the pressure of the first reference chamber and the second reference chamber is kept unchanged;
communicating the second reference chamber with the sample chamber, and setting an automatic balance valve for communicating the first reference chamber with the second reference chamber to be closed after a preset time;
after the automatic balance valve is closed, recording a differential pressure attenuation curve of the pressure difference value, which is read by a differential pressure sensor connected between the first reference cavity and the second reference cavity and changes along with time, and stopping recording until the pressure difference value does not change any more;
fitting and calculating the differential pressure attenuation curve to obtain the radial permeability of the core plunger;
and steel balls are filled in the second reference cavity and the sample cavity except for the part occupied by the core plunger.
7. The method for measuring radial permeability according to claim 6, wherein the radial permeability of the core plug is obtained by fitting the differential pressure attenuation curve according to the following formula:
wherein Δ p (t) is the differential pressure sensor reading at time t in Pa;
Δpfis the reading of the differential pressure sensor at the end of the gas permeation process in the sample chamber, and has the unit of Pa;
p0iis the pressure at which the gas pressures in the second reference chamber and the sample chamber reach equilibrium, in Pa;
p1ibefore the second reference cavity is communicated with the sample cavity, the pressure in the sample cavityIn Pa;
gamma is the time constant of the differential pressure attenuation curve;
c is the intercept of the linear fit;
k is the radial permeability of the core plunger in m2；
a1As Bessel function J0(r0an) The smallest positive root, 0, whose size is determined by the core radius, is given in m-1；
M is the molar mass of the high-pressure gas and has the unit of kg/kmol;
rho is the density of the high-pressure gas and has the unit of kg/m3；
μ is the viscosity of the high pressure gas in Pa · s;
z is the true gas compression factor in m3/m3；
R is a gas constant 8.314 with the unit of kJ/kmol.K;
t is the thermodynamic temperature in K;
8. The radial permeability measurement method of claim 6 or 7, further comprising, after the charging of the high pressure gas into the first and second reference chambers and before stopping the charging of the high pressure gas into the first and second reference chambers:
and filling the high-pressure gas into a confining pressure gas chamber at one end of the clamping device to control the pressure of the confining pressure gas chamber to be at the required pressure so as to apply the required axial confining pressure to the clamping device.
9. The radial permeability measurement method of claim 8, further comprising the steps of:
and closing the second isolation valve, and opening the first isolation valve and the automatic balance valve to charge high-pressure gas into the first reference cavity and the second reference cavity again, and adjusting the output pressure of the high-pressure gas until the pressure is close to the pressure of the next test working condition.
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| CN112630118B (en) * | 2020-11-16 | 2022-07-26 | 苏州开洛泰克科学仪器科技有限公司 | Gas permeability measuring device and measuring method for compact material |
| CN112834405A (en) * | 2021-01-07 | 2021-05-25 | 中国科学院西北生态环境资源研究院 | Method and device for testing permeability of rock core overburden pressure matrix |
| CN114993916A (en) * | 2022-06-07 | 2022-09-02 | 中国科学院武汉岩土力学研究所 | Device and method for rapidly measuring permeability of low-permeability core |
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