Optimization and Field Application of Hydraulic Fracturing Techniques in Deep Shale Reservoirs

Hydraulic fracturing of deep shale reveals that high injection pressure, low fracture conductivity, limited stimulated reservoir volume, and unsatisfactory primary production are mainly due to deep burial, variable lithology and high in-situ stresses. Based on the comprehensive evaluation of geological characteristics and fracturing potential of deep shale reservoirs, technical difficulties in volumetric stimulation were discussed and relevant countermeasures were proposed. Then, a fracturing optimization method for deep shales was proposed, and it combined a numerical simulation of the gas reservoir, a calculation of induced stress and fracturing simulation. Fracturing segment/cluster, perforation and stimulation treatment parameters were analyzed. Taking Well Dingye 2HF as an example, the implementation and control of deep shale fracturing techniques were discussed, and the responses of stimulation pressure in field application were identified. Through stage-by-stage optimization and fine adjustment of parameters in aspects of pad volume, fracture initiation by gel, and initial sand and fluid ratio. Finally, a composite fracturing treatment procedure was formed, i.e. pre acid+moderate viscosity gel+slick water+low viscosity gel+moderate viscosity gel. The fracturing of deep shales has been improved successfully through the application of the proposed procedure. In field application of Well Dingye 2HF, 12 stages of fracturing stimulation were completed with initial gas production of 10.5×104 m3/d after the treatment. This procedure will provide technical reference for hydraulic fracturing in similar deep shale gas reservoirs in the future.