Experimental investigation of hydraulic sand fracturing on fracture propagation under the influence of coal macrolithotypes in Hancheng block, China

Abstract

The mechanical properties, brittleness and micro-fracture development of different coal macrolithotypes (bright coal, semi-bright coal, semi-dull coal and dull coal) are different, and these differences have an impact on the propagation of hydraulic fractures. To understand the influence of coal macrolithotypes on fractures propagation, several hydraulic sand fracturing experiments considering the classification of coal macrolithotypes were carried out by taking No. 11 coal seam of the Taiyuan formation in Hancheng block, China. We mainly investigated the influence of coal macrolithotypes and perforation location on the propagation of hydraulic fractures. Combined with observation results of mining excavation, the experimental results are verified. The research finds that fractures morphology and proppants distribution in bright-type coal is better than dull-type coal. Thus, bright-type coal is the fracturing sweet-spot section in coal seam. We also find that hydraulic fractures are prone to propagate along the stratigraphic interfaces or lithologic interfaces to form horizontal major-fractures, and the overall stimulation effect of coal seam is dependent on the fractures morphology and proppants placement of these horizontal major-fractures. The stimulation effect of horizontal major-fractures for coal seam is better when perforation location is selected near the weak planes instead of the middle of coal seam. The research results provide theoretical guidance for efficient fracturing of coal seam.