Experimental Study on Hydraulic Fracturing of Laminated Sandstone Combined with Industrial CT and L-NMR

Hydraulic fracturing in the immediate roof is a suitable method to increase the permeability of soft outburst coal seam. In this work, the propagation law of hydraulic fractures in laminated virgin sandstone and the change of microstructure after hydraulic fracturing were revealed. The results show that the hydraulic fracturing pressure of sandstone with different bedding angles is 15.69 similar to 22.17 MPa. In the experiments, the hydraulic fractures extend through the bedding planes when the bedding angle is 45 degrees. When the bedding angle is 0 degrees, 15 degrees, 30 degrees, or 60 degrees, the hydraulic fracture is prone to extend along a bedding plane. The hydraulic fracture in sandstone is jointly determined by the internal fractures and the cementation strengths of the bedding planes. The internal fractures may not necessarily guide the extension of the hydraulic fractures. The hydraulic fracturing pressures of the samples affected by the bedding plane and internal fractures are significantly lower than that of samples with uniform strength. Besides, hydraulic fracturing cannot change the connectivity between pores. The hydraulic fractures are the main channel for gas migration. The results can provide some guidance for the design and application of hydraulic fracturing in the immediate roof of the soft outburst coal seam.

Automated summary

This study reveals the propagation law of hydraulic fractures in the immediate roof of soft outburst coal seam and the changes in microstructure after hydraulic fracturing. Experimental results show that the bedding angle significantly affects the extension of hydraulic fractures, which are determined by both internal fractures and the cementation strengths of the bedding planes. The findings provide guidance for the design and application of hydraulic fracturing in the immediate roof of soft outburst coal seam.