Dynamic Evolution of the Fluid Effect of Multiple Reservoirs Due to CBM Coproduction: An Experimental Investigation

Coalbed methane (CBM) coproduction in areas with multiple reservoirs has been an important means of improving gas production. The dynamic evolution of the fluid effect is not considered, which is a key factor leading to low production. To study coproduction mechanisms further and understand the evolution of the spatiotemporal characteristics of the dynamic fluid effect, a large-scale vertical well coproduction device was designed and the coproduction process was simulated. The results are as follows: (1) in the early stage of CBM coproduction, a dynamic pressure balance leads to an increase in the reservoir pressure of a low fluid energy reservoir, wherein the pressure rise gradually decreases with the increasing distance of the measurement point from the wellbore. The rate of pressure increase in the low-pressure reservoir is higher than that in the high-pressure reservoir; (2) under the equilibrium effect of dynamic pressure, reversed gas flow would inhibit gas production in the low fluid energy reservoir. The dynamic pressure balance effect has a weak influence on gas production in the relatively high fluid energy reservoir; with an increase in reservoir fluid energy, the effect of gas production inhibition is weakened; (3) in the early stage of CBM coproduction, the reversed gas flow is injected into the low-pressure reservoir. The closer a measurement point is to the wellbore, the greater the deflection angle at that point. Over time, the reversed gas flow caused by interlayer interference on the reservoir is weakened, and the longer the coproduction time, the smaller the influence range of the reversed gas flow.