Geochemical and petrophysical characterization of potential gas shale reservoirs in the Lishu depression, southern Songliao Basin, northeastern China摘要
The Lower Cretaceous shales of the Shahezi Formation (K1sh) and Yingcheng Formation (K1y) in the Lishu depression have been an excellent source of oil and gas for plays in the Songliao Basin. However, there is little published work about shale gas potential, storage, and transport properties to assess the reservoir quality. This paper comprises geochemical and petrophysical data and other significant aspects of potentially economic terrestrial shale. The K1sh and K1y are orderly generated under anoxic–suboxic lacustrine depositional conditions, which are indicated as the abundant vitrinite, bordered pits, and cormophyte spores. The organic matter of K1sh and K1y is characterized as type II and III kerogen and has almost low peaks of Rock-Eval free hydrocarbon (mg HC/g rock) and potential hydrocarbon (mg CO2/g rock) peaks. Most samples are in the gas window and hence have already lost half of their initial total organic carbon (TOC). Permeability and porosity range from ∼10−19 to 10−17 m2 and from ∼0.89% to 16.6%, respectively, and are higher for the K1y shale. Moderate correlations are found between porosity and depth as well as surface area versus TOC content. The K1y shale has greater thickness and in situ gas content (average 3.45 m3/t), and significant similarity in terms of porosity, maturity, and brittleness with known gas shale in global. However, differences with respect to organic richness and tectonic activity play an essential role on gas in place and fracturing performance. The K1y shale is more suitable for gas shale exploration and K1sh shale is a secondary target. This observation suggests there may be a prolific shale gas play in the depression that has been overlooked in the past. The findings from integrated hydrocarbon potential and gas storage capacity studies provide a database and some insights into the reservoir quality of the terrestrial gas shales.
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