Evaluation of highly thermally mature shale-gas reservoirs in complex structural parts of the Sichuan Basin

Successful exploration and development of shale-gas in the United States and Canada suggest a new solution to the energy problem in China. The Longmaxi (龙马溪) Formation in the Sichuan (四川) Basin is regarded as a strong potential play for shale-gas with the following significant features: (1) complex structural types caused by multiphase tectonic superposition and reconstruction; (2) varied slippage processes that enhance porosity and permeability; (3) high thermal maturation of organic matter (Ro>2.5%); (4) high brittle mineral contents; (5) high and constant thicknesses of shale horizons within the formation. Evaluation of shale-gas prospects in this area should consider not only hydrocarbon parameters, but also preservation conditions and structural stability. Data from several new exploration wells in the Sichuan Basin indicate that tectonically induced net-shaped fractures effectively enhance shale reservoir properties. Structural types providing favorable storage conditions for shale-gas are described and evaluated. The high-yielding shale gas reservoir shares the same characteristics of conventional gas reservoirs except for its consubstantial source rock and reservoir in South China.