Characterization of marine-terrigenous transitional Taiyuan formation shale reservoirs in Hedong coal field, China

To better understand the basic characteristics of Marine-terrigenous Transitional Taiyuan formation shale (TYS) reservoirs in Hedong coal field, a series of reservoir evaluation experiments were conducted on 33 core samples, which were collected from an exploration shale gas well (SL-1). The results show that organic matters in TYS are Type III gas prone kerogen and are in the high-maturity stage with an average Ro value of 1.87% (ranging from 1.71 to 2.10%). The total organic carbon (TOC) is ranging from 0.29% to 11.87% with an average value of 2.91% and gas content is from 0.41 to 2.96 ml/g, which indicates that TYS still has certain hydrocarbon generation potential despite a mass generation of hydrocarbons occurred during the geological history. XRD analysis shows that TYS is composed mainly of quartz minerals and clay minerals with an average brittleness index of 46.5%, which is relatively favorable for hydraulic fracture. Pore size of TYS ranges from a few nanometers to hundreds of nanometers. The permeability is irrelevant with porosity and its values are all lower than 0.1 md. The average value of BET surface area and BJH volumes are 8.57 m2/g and 1.84 cm3/100g, respectively. Similar to previous studies, TOC content is a decisive control on gas adsorption capacity in this study.