Geochemical and petrophysical characterization of potential gas shale reservoirs in the Lishu depression, southern Songliao Basin, northeastern China

The Lower Cretaceous shales of the Shahezi Formation (K(1)sh) and Yingcheng Formation (K(1)y) 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 K(1)sh and K(1)y 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 K(1)sh and K(1)y 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 similar to 10(-19) to 10(-17) m(2) and from similar to 0.89% to 16.6%, respectively, and are higher for the K(1)y shale. Moderate correlations are found between porosity and depth as well as surface area versus TOC content. The K(1)y shale has greater thickness and in situ gas content (average 3.45 m(3)/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 K(1)y shale is more suitable for gas shale exploration and K(1)sh 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.