Experimental study on interlayer interference effect of CBM commingled production in a multi-pressure system under output control mode

Abstract

This research adopted the self-developed test device to conduct tests to understand the interlayer interference in a multi-pressure system under output control mode. It analyzed the reservoir response and gas production characteristics in coalbed methane (CBM)'s commingled production and discussed the interlayer interference mechanism. The results revealed that the CBM's commingled production at the initial stage would generate interlayer interference under the output control mode, causing the cross-fluids of interlayer fluids. The interlayer interference would form a gas-production state. That is, the gas production of reservoirs with high fluid energy would inhibit that of the reservoirs with low fluid energy. When the gas production of reservoirs with high fluid energy is attenuated, that of reservoirs with low fluid energy would start recovering to maintain stable production. The reservoir pressure gradients positively influence interlayer interference. The more significant the difference between the reservoir's fluid energies aggravates, the more severe this interlayer interference. The output control values negatively affect the interlayer interference, as their increase would weaken the severity of interlayer interference. Therefore, the output control design should appropriately increase the output value or rationally select the reservoirs with a slighter difference in fluid energies. The gas model can be divided into three: conventional type, inhibitory type, and reverse-flow type, and their production stage can be divided into five different phases: gas rise, gas inhibition, reverse flow, gas recovery, and gas attenuation.