Laboratory investigation of hydraulic fracture networks in formations with continuous orthogonal fractures

Abstract

Researchers have recently realized that hydraulic fracture networks are significant for the exploitation of unconventional reservoirs (tight gas, shale gas, coalbed methane, etc.). Studies have shown that slickwater fracturing treatments can create complex fractures that increase the ‘stimulated reservoir volume’ in naturally fractured formations. However, the influence of the created hydraulic fracture network is not well understood. Laboratory experiments are proposed to study the evolution of hydraulic fracture networks in naturally fractured formations with specimens that contain two groups of orthogonal cemented fractures. The influence of dominating factors was studied and analyzed, with an emphasis on natural fracture density and injection rate. We concluded that hydraulic fracture networks are formed by the interactive process between the reopening and connecting of the natural fractures through slickwater fracturing in the specimens, indicated by frequent pressure fluctuations. The spatial envelope of the fracture network is an approximate ellipsoid with the major axis deviating from the orientation of the maximum horizontal stress. It is suggested from the pressure curve that great natural fracture density and high injection rates tend to raise the treatment pressure and the pressure profiles could reflect different characteristics of extending behaviors.