Coal rock permeability experiment system with adjustable outlet pressure as well as method

Abstract

A coal rock permeability experiment system with adjustable outlet pressure comprises a methane gas tank, a confining pressure loading pump, an axial compression loading pump, a first three-way valve, a second three-way valve, a third three-way valve, a coal sample holder, a display, a pressure tracker and a computer, wherein the methane gas tank is connected with an inlet of the first three-way valve through a first gas pipe, one outlet of the first three-way valve is connected with a gas inlet of the coal sample holder through a second gas pipe, and a gas outlet of the coal sample holder is connected with a gas inlet of the pressure tracker through a third gas pipe; a first pressure sensor is in sealed connection at another outlet of the first three-way valve; a pressure reducing valve is arranged on the first gas pipe, and a mass flowmeter is arranged on the third gas pipe. A method is simple in process and convenient to operate, the pressure difference between a gas inlet and a gas outlet can be reduced when a higher-pressure permeability experiment is performed with the method, and a model error is reduced; according to the method, experiment parameters are acquired with an electronic technology, the precision of the acquired experiment parameters is high, and an observation error is reduced greatly.

Description

technical field [0001] The invention relates to a coal rock seepage experiment system and method with adjustable outlet pressure. Background technique [0002] In the fields of coalbed methane and natural gas, the permeability of coal rock is an extremely important technical parameter, which is related to the mining value of coal reservoirs and the estimation of production. However, the permeability of coal rock is affected by many factors, such as stress, gas adsorption, Temperature, disturbance of drainage engineering, etc. make it very difficult to measure the permeability of coal and rock. How to accurately measure the permeability of coal and rock is of great significance. [0003] At present, the method for testing the permeability of coal samples in the laboratory is mainly to fill a certain pressure gas at one end of the clamped coal rock sample, that is, the inlet end, and collect the permeability at the other end of the coal rock sample, that is, the gas outlet end...

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Problems solved by technology

[0004] (1) In the past, the outlet end of the coal-rock gas permeability measurement was atmospheric pressure, but during the extraction of coalbed methane and natural gas, the extraction end was in a negative pressure environment, and the seepage outlet was in a negative pressure state. The traditional outlet The end is atmospheric pressure, which cannot simulate the negative pressure environment during extraction well, and is inconsistent with the actual situation;

[0005] (2) The adsorption of coal and rock to gas is one of the main factors affecting the permeability. During the permeability test, because the coal and rock samples are under a certain pressure gradient, the adsorption pressure is often replaced by the average adsorption pressure: , where p is the adsorption pressure, The outlet pressure is the atmospheric pressure, is the inlet pressure, changing the adsorption pressure is by adjusting the inlet It is realized by the pressure of the inlet end, but the greater the pressure difference between the inlet and outlet ends, the greater the error caused by replacing the adsorption pressure with the average adsorption pressure, and when the pressure difference between the two ends is large, the permeation flow rate increases , the error of collecting gas flow rate will also increase, so there is a large error in the measured permeability;

[0006] (3) The loaded gas pressure, axial pressure, and confining pressure are all read manually through the indication of the pressure gauge at this stage, and the obtained pressure parameters have large errors

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