Simulation testing method for discharging and mining pressure-reduction control under different coal reservoir conditions

Abstract

A simulation testing method for discharging and mining pressure-reduction control under different coal reservoir conditions comprises the following steps that (1) samples are prepared and clamped; (2)pipelines are connected, and airtightness detection is conducted; (3) a discharging and mining control simulation system is adjusted; (4) axial pressure, confining pressure and water pressure are loaded by turns; (5) a coal sample starting pressure gradient test is conducted; (6) a dynamic pressure spreading speed test is conducted, specifically, the time of reading change of all pressure monitoring points and the corresponding pressure reduction amplitude are analyzed, and if the corresponding pressure reduction amplitude is larger than the starting pressure of the pressure monitoring points, the pressure reduction speed is over high; (7) a discharging and mining work mechanism is determined, the pressure reduction speed is continuously adjusted, and operation of the step (6) is repeatedtill the pressure reduction speed can exactly maintain stable spreading of the pressure; and (8) after the test is finished, pressure relief, unloading and coal sample recovery are conducted. According to the simulation testing method for discharging and mining pressure-reduction control under the different coal reservoir conditions, the discharging and mining process can be reasonably evaluatedand simulated, and the reasonable discharging and mining work mechanisms of the single-phase-flow stage under the different coal reservoir conditions are obtained.

Description

technical field [0001] The invention belongs to the technical field of coal bed gas extraction and relates to a pressure drop control simulation test method for extraction under different coal reservoir conditions. Background technique [0002] Surface coalbed methane wells are mainly produced by desorbing coalbed methane through "drainage-depressurization". During vertical well drainage of coalbed methane, with the production of water in the coal reservoir, the effective stress on the coal matrix increases, resulting in the narrowing and even partial closure of the cracks in the coal seam. The macroscopic manifestation is the decrease of the permeability of the coal seam. With the development of drainage, the water pressure continues to spread from near the wellbore to far away, forming a certain pressure gradient. The drainage during the period before the gas desorption pressure is reached is called the single-phase water flow stage. [0003] During single-phase flow sta...

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Problems solved by technology

Coal reservoir pressure, critical desorption pressure, coal reservoir permeability, coal seam stress, coal seam water content, coal rock mechanical properties, etc. all have an impact on the change of permeability in the process of coalbed methane well drainage. When these conditions change , will have an impact on the water pressure transmission distance in the single-phase flow stage. What kind of drainage rate is reasonable for the vertical coalbed methane well in the single-phase flow stage? At present, th

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