Experimental study on unblocking of coalbed with single-slit filling by pulse hydraulic fracturing
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Abstract: During the process of coalbed methane extraction, a large amount of coal powder is produced. And coal powder accumulates in the fissure, which is one of the important factors to affect the permeability of coalbed methane. The unblocking test of coalbed under different frequency conditions is carried out by using the self-developed hydraulic fracturing system with adjustable frequency pulsation and the prefabricated samples with single-slit filling, to study the evolution process of the unblocking pressure and the unblocking effect under the pulse action. The results show that the evolution process of unblocking pressure can be divided into three stages: pressure rise phase, decline phase and pressure fluctuation stability phase; And compared to steady flow the pressure threshold under the pulse action is lower, the pressure drop duration is shorter, and the pressure drop amplitude is smaller. The coal powder has been transported in the pressure drop stage and the pressure fluctuation stable stage under the pulsating flow, while coal migration is concentrated in the pressure drop stage under the steady flow, and the total migration volume of coal powder in the two condition is equivalent ; The fluid infiltration along the radial direction mainly occurs the duration of the pressure rise to the peak pressure, the filtrate penetration radius is smaller due to shorter unblocking time under the pulsating flow, and the reservoir damage is small.Under the condition of 3 Hz, the unblocking effect is the best, and the plugging pressure threshold is lower, the unblocking path is the most straight, and the fracturing fluid seepage radius is the smallest.