Exploration of the induced fluid-disturbance effect in CBM co-production in a superimposed pressure system

Abstract

Fluid disturbance in coalbed methane co-production in a superimposed pressure system is universal. Two sets of tests were conducted with different constant outlet pressure values and reservoir pressure gradients to explore the fluid-disturbance characteristics. First, in the constant outlet pressure mode, reservoirs with large differences in the initial fluid energy are prone to fluid disturbance in the early stage of co-production, and the dynamic pressure balance drives part of the fluid from reservoirs with a high initial fluid energy to flow to reservoirs with a low initial fluid energy. Second, an increase in the constant outlet pressure value reduces the intensity of the fluid disturbance, and the reservoir pressure gradient has a positive effect on the fluid-disturbance effect. The design of a constant-pressure co-production must incorporate disturbance-reduction measures and appropriately increase the constant outlet pressure at the wellbore outlet. Alternatively, reservoirs with smaller reservoir pressures should be selected for co-production. Third, the gas-production mode of a single reservoir under the constant-pressure co-production can be separated into three major categories and seven subcategories: the conventional mode is applicable to reservoirs with a high initial fluid energy, the inhibition mode is primarily for reservoirs with a medium-low initial fluid energy, and the backflow mode is primarily for reservoirs with a low initial fluid energy.