Experimental Investigation of Reservoir Fluid Interlayer Crossflow Through Fracture During the Drainage Stage of Coal Measure Gas Well

Coal measure gas (CMG) development is effective to increase gas production of coalbed methane wells. However, the reservoir fluid migration law during CMG development is different from that of single-layer development and it remains to be identified. In this work, self-developed devices were used to study fluid interlayer crossflow (IC) law through fractures in the single-phase liquid flow and gas-liquid two-phase flow stages during CMG well drainage. The results showed that, in the single-phase flow stage, liquid flowed from the medium- and low-permeability samples to the high-permeability sample, changing the fluid pressure and flow rate of each sample, and promoting total liquid production. In the two-phase flow stage, the gas IC caused total gas production capacity to increase, but the liquid IC was inhibited, which made the liquid production capacity to increase firstly and then decrease. Also, the irreducible liquid saturation of the medium- and low-permeability samples increased, aggravating the water blocking damage. However, by adding the surfactant AN, the liquid surface tension and pore capillary pressure were decreased, and the irreducible liquid saturation of each sample before and after the fluid IC was reduced. Thus, the water blocking damage of each sample was mitigated, including the damage aggravated by the fluid IC, promoting the desorption and migration of coalbed methane, as well as the CMG efficient development. This study is helpful to clarify the CMG migration law, and provides fundamental supports for the optimization of CMG development technology.