Experimental study on the permeability features of long flame gas water phase

Abstract

There is a large amount of CBM in the long flame coal. With the continuous increase of mining depth, it is necessary to explore the complex permeability features between CBM and groundwater in the coal reservoir to reduce the difficulty of CBM mining and improve the efficiency of CBM mining. Taking the long flame coal in the Weijiamao mining area of Zhungeer Banner, Ordos, Inner Mongolia as the experimental object, the TCXS-II coal rock gas water relative permeability tester is used to conduct the long flame gas water phase permeability experiment. The non steady state method is used to obtain the gas water phase permeability features of long flame coal under different effective stresses, pore pressures, and temperatures during the gas water drive process. The results show the following points. ① When the effective stress increases from 3.7 MPa to 7.7 MPa, the increase in gas phase relative permeability decreases, while the decrease in water phase relative permeability slightly increases. The increase of effective stress will have an inhibitory effect on the permeability of the fluid, and the inhibitory effect on water phase seepage is greater than that on gas phase seepage. The residual water saturation increases with the increase of effective stress. ② When the pore pressure increases from 2 MPa to 6 MPa, the decrease in the relative permeability curve of the water phase slows down, and the increase in the relative permeability curve of the gas phase becomes more obvious. The range of gas water co-permeation becomes wider, the saturation of the isotonic point increases, and the residual water saturation decreases. ③ When the temperature rises from 20 ℃ to 80 ℃, the increase in gas phase relative permeability and the decrease in water phase relative permeability gradually increase. The range of gas water co-permeation becomes wider, the residual water saturation shows a decreasing trend, and the gas phase permeability flow rate shows an increasing trend. The research results can provide theoretical basis and experimental reference for the research of CBM extraction technologies such as hydraulic fracturing and thermal injection in long flame coal reservoirs.

Keywords

• long flame coal
• gas water relative permeability
• relative permeability
• effective stress
• pore pressure
• temperature
• residual water saturation