EXPERIMENT OF ADSORPTION-DESORPTION HYSTERSIS OF GAS IN COAL SHALE BY USING NUCLEAR MAGNETIC RESONANCE SPECTRUMS

Coal shale gas was mainly composed of adsorbed and porous medium-confined gas. The desorption of coal shale gas generally lagged behind the adsorption, therefore, it was significance to quantitatively study the adsorption and desorption hysteresis law from the micro perspective for stable production and stimulation of shale gas wells in the later stage. Based on a large number of fruitful previous studies and the theory of nuclear magnetic resonance spectrums, an improved micro evaluation model for the accurate characterization of the adsorption and desorption hysteresis effect of coal shale gas was deduced. In order to simulate the whole process of adsorption and desorption hysteresis of gas in coal shale, the nuclear magnetic resonance spectrum technique was applied for the experimental research on adsorption and desorption hysteresis of gas in coal shale from coal floor of No. 36 coal seam in No. 3 mining area of Dongbaowei Mine in Shuangyashan Basin. And on such bases, the micro quantitative research on adsorption and desorption hysteresis law of the adsorbed gas, porous medium-confined gas, macro gas measurement by micro method in coal shale was carried out, the mechanism of adsorption and desorption hysteresis and its influence on shale gas mining in deep coal measures were preliminarily explored. Results indicated that in the process of adsorption and desorption under stress state, both adsorbed and porous medium-confined gas had obvious hysteresis; the relationship between macroscopic hysteresis coefficient of gas and the average effective stress was power function; while the relationship between hysteresis coefficient and average effective stress caused by adsorbed gas could be fitted by quadratic polynomial, and it was the same with porous medium-confined gas. The coupling of stress damage and gas diffusion in the pore fracture structure of coal series shale might be one of the fundamental reasons for the gas adsorption and desorption hysteresis of coal shale.