Low permeability coal seams, especially if they contain CO2, can be difficult to drain sufficiently using in-seam drainage holes. Sand propped hydraulic fractures have been shown to be effective in stimulating gas drainage boreholes, allowing sufficient gas content reduction to occur to reach minable seam gas content limits. SCT has partnered with CSIRO on several projects that demonstrated the effectiveness of sand propped fractures. CSIRO’s Sand Adder provides a method of adding proppant sand on the output side of a high-pressure pump, allowing a normal explosion proof longwall support pump to be used to place sand-propped fractures. SCT offers in situ stress measurement and hydraulic fracture design advice in this area.
The propped fractures provide a large surface area in contact with the coal and a conductive channel connected to the borehole. Thus, the drainage of gas from the coal is accelerated and occurs typically more than 10 times faster than the rate from unfractured in-seam boreholes.