Clean up water blocking damage in coalbed methane reservoirs by microwave heating: Laboratory studies

Abstract Water blocking damage is one of the most serious formation damages that restricts the development of low-permeability coalbed methane (CBM) reservoirs. Characterized by the conversion of the electromagnetic energy into heat, microwave heating may be a promising method to remove water blocking damage. In this study, contact angle tests and permeability tests were performed to investigate the effects of microwave heating on water blocking damage in CBM reservoirs. The results indicate that microwave heating can lead to hydrophobization of coal. The permeability of coal first decreases after water intrusion and then increases after microwave heating. The permeability sensitivity of the moist coal to microwave heating is much greater than that of the dry coal. Furthermore, the increase in the water content of coal promotes the microwave recovery effect of permeability. Theoretical analysis shows that the petrophysical evolution of coal during microwave heating involves gas desorption, dehydration, pore damage, fracturing and decomposition. Outcome of this study implies that microwave heating can be used as a supplemental measure of hydraulic fracturing to enhance CBM recovery by removing the water blocking damage.