Latest research progresses in network fracturing theories and technologies for shale gas reservoirs

In view of the bottleneck of shale gas development technologies, the latest progresses in such theories on the fields like fracture network fracability evaluation, fracture network propagation mechanism, stimulated reservoir volume (SRV) evaluation and fracturing fluid research & development were analyzed comprehensively in reference to the existing achievements and experiences in North American shale gas reservoir development and based on the probes, practices and cognitions of shale gas development technologies in China since 2005. First, the study on the shale brittleness develops from the definition of mineral and mechanical semi-quantitative threshold measurement to a comprehensive evaluation which integrates rock constituents, elastic mechanics and development characteristics of natural fractures together. Second, the study on the fracture network development develops from the directional extension theory to the simulation of fracture network formation in the stochastic distribution pattern of natural fractures. Third, the study on SRV develops from the micro-seismic monitoring based instrument and technology to the mathematical theory evaluation method dependent on the discrete fracture network and extended finite element. And fourth, the study on fracturing fluids develops from the wide application of slick water (drag reducing water) and a linear gel fracturing fluid system to the development and application of novel fracturing fluids with little or no water. Then, the theoretical and technological challenges were pointed out, including the comprehensive fracability evaluation of reservoir fracture networks, the deep seated shale gas fracturing, the operation curve diagnosis of shale gas fracturing, the shale gas refracturing theory, and the research & development and flowback control of novel fracturing fluids. Finally, the development trend of related technologies was predicted so as to provide a theoretical and technical guidance for the efficient shale gas development in China in the future.