Generation conditions of shale gas in Carboniferous Keluke Formation, northern Qaidam Basin

Based on outcrop geological survey in the northern Qaidam Basin and integrated with other data of drillings, outcrops and previous research results, the Carboniferous Keluke Formation shale gas accumulation conditions and core area selection were investigated by delineating regional distribution of gas shale, organic geochemical features, mineral compositions, pore system and gas content in gas shale. Shale in the Keluke Formation is rich in organic matter. The TOC value ranges from 0.28% to 11.93%, and is over 2% in average. The thermal maturity value (R_o) ranges from 0.9% to 1.44%, and is 1.12% in average, indicating for the mature stage of organic matter thermal evolution. The available thickness of shale in the Keluke Formation is 30-150 m. The content of brittle minerals is greater than 40%. Pore systems of micro and nano scales are well-developed. Gas content ranges from 1.01 to 2.85 m³/t, and is 1.87 m³/t in average. The Gaqiu Sag, Ounan Sag and Delingha Fault Depression are favorable for the generation and accumulation of shale gas, hence are the targets for shale gas exploration in the Keluke Formation.