Factors Affecting Shale Gas Accumulation in Overmature Shales Case Study from Lower Cambrian Shale in Western Sichuan Basin, South China

Abstract

A series of comprehensive and systematic experimental data and log data of lower Cambrian Qiongzhusi Formation, from the first successful Well Jin-1 in western Sichuan Basin, were analyzed to investigate the properties of lower Cambrian organic-rich shale and to illustrate its shale gas potential, so as to investigate the factors affecting shale gas potential in overmature and ultratight shale. Trace element ratios (V/Cr and Ni/Co) and the concentrations of Cu + Zn imply the lower Cambrian shale deposited under suboxic–anoxic bottom water with high primary productivity. The organic matter is enriched in Qiongzhusi Formation as sapropelic (type I) mainly, and Ro (2.65–2.97%) values indicate the organic matter is in the overmature stage. Pores are dominated by organic pores in lower organic-rich shale and by inorganic intragranular and intergranular pores in upper organic-rich shale. Generally, organic-rich shale was deposited in anoxic shelf (high ratios of V/Cr and Ni/Co) with high productivity (high conc...