Experimental study of the effect of static water on imbibition gas recovery in coalbed methane reservoirs

Abstract

Imbibition gas recovery is a new method to strengthen the diffusion capacity of coalbed methane (CBM) under the coexistence of water and methane. To study the effect of imbibition gas recovery in CBM reservoirs, the imbibition process of static water in CBM reservoirs was stimulated through a self-designed experimental device. The results indicate that static water can not only improve the water saturation of coal samples via capillary force but also promote imbibition gas recovery. With increases in the initial absorption balanced pressure and water absorption rate, imbibition gas recovery has an increasing trend. At the same time the imbibition speed rapidly increases to the maximum value and then decreases, which matches a logarithmic function law. Under the same initial absorption balanced pressure, the imbibition rate gradually increases with increasing water absorption rate, which matches a negative exponential formula. Moreover, the imbibition rate increases with increasing absorption balanced pressure under the same water absorption rate. However, the influence of the water absorption rate is greater than that of the initial balanced absorption pressure on the imbibition gas recovery and imbibition rate. This study verifies the imbibition mechanism in CBM reservoirs with both water and gas, which is helpful for research to enhance CBM recovery.