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Implications of Lessons Learned from US Shale Plays to China Shale Reservoir Evaluation and Development

Abstract

The exploration and production of US shale plays reveal that shale reservoirs have a wide range of lithologies, facies, grain size, mineral composition, fabric, petrophysics, geochemical and geomechanics properties, etc. The lithologies of US producing shales include siliceous shale, carbonate rich shale, chalk, dolomite, etc. The best acreage and stratigraphic interval of shale plays have high resistivity, high gamma for organic rich shale reservoir or low gamma ray for calcite rich interval, high porosity, appropriate thermal maturity, overpressure, high young's modulus or high brittle mineral content. The open natural fractures and overpressure in liquids rich US shale plays are essential for shale oil production. Many above mentioned lessons learned from US shales have been applied to China shale reservoir evaluation and development. China shales also have various lithologies, e.g. Silurian siliceous marine Longmaxi shale in South China; Triassic clay rich lacustrine Yangchang7 shale in Ordos Basin; Jurassic carbonate rich lacustrine Dongyuemiao shale in Sichuan Basin; Paleogene dolomitic lacustrine Kongdian2 shale in Bohai Bay Basin, etc. The sample test of China shales shows the rough trend of quartz or brittle mineral content in shales of different depositional settings is Marine>lacustrine>transitional. For the gas potential marine shales in China, they are similar to Barnett shale in US with regard to mineralogy and organic richness and have shown promising production, but the complex tectonic activities could have caused the leaking of shale gas accumulation. For the clay rich lacustrine shale source rocks in China, even though the clay content is high due to proximity to sediment source, the detrital quart and feldspar can help contribute brittleness for hydraulic fracturing. The dolomite and sandstone interbeds within lacustrine shale source rock interval play significant role for oil and gas accumulation due to their better reservoir quality. This could mimic Bakken and Niobrara plays in terms of lithology association and hydrocarbon accumulation. These interbeds charged by their neighboring organic rich shale and the self-sourced shale reservoir are hybrid plays for future lacustrine basin exploration.