Theory and Application of Pseudo-Reservoir Hydraulic Stimulation for Coalbed Methane Indirect Extraction in Horizontal Well: Part 2—Application

Abstract

This paper provides details of the application of pseudo-reservoir stimulation technique to a U-shaped coalbed methane (CBM) well (i.e., Well ZU-01) in Jiaozuo mining area. Multistage hydrojet fracturing and channel fracturing were adopted to promote fracture network forming and fracture vertical propagation in pseudo-reservoir. The results of the pseudo-reservoir stimulation indicate that influenced by the reservoir lithology and coal structure between the horizontal well and coal seam, the fractures at the first stimulation stage only propagated in the pseudo-reservoir. However, the stimulations at the second, third and fourth stages achieved integrated stimulation of pseudo-reservoir and coal seam. The gas production rate of Well ZU-01 was only 1000 m3/d in the stable production stage. However, through negative-pressure extraction in the mine roadway, the joint gas extraction rate from the underground roadway and Well ZU-01 reached 6000 m3/d. After 450 days of extraction, the cumulative gas production was 15.55 × 105 m3, and the CBM extraction rate reached approximately 50%, indicating that good pseudo-reservoir stimulation and gas pre-extraction effects were achieved. The results of the adsorption/desorption and wettability tests show that water blocking damage caused by the slickwater fracturing fluid severely hindered the gas desorption and production processes, which was the main reason for the low gas production of the well. However, the water blocking damage was mitigated through negative-pressure extraction, resulting in a significant increase in CBM production.