Abstract:

The lower Cambrian Qiongzhusi Formation in southern Sichuan is one of the important strata for marine shale gas exploration. In the early stage, the exploration of black shale in Qiongzhusi Formation has achieved certain results, but the thin thickness of black shale restricts the breakthrough of commercial productivity. Silt-shale of Qiongzhusi Formation's gas logging shows high. Therefore, it is necessary to strengthen the systematic research of this new type of shale reservoir and widen the exploration field of unconventional shale gas. Based on the experimental data such asTOC, X-ray diffraction, thin section, SEM, Helium porosity, pulse permeability, Nitrogen adsorption, and mercury intrusion porosimetry, the studies of the geochemical characteristics, petrological characteristics, reservoir space types, physical properties and pore structure of this new type of reservoir have been carried out. The study shows that the new type of shale reservoir is mainly composed of silty shale, which has the property of low TOC, high brittleness, high porosity, good pore connectivity and high gas bearing. The main types of reservoir space are brittle mineral intergranular pores, carbonate minerals and feldspar dissolution intrapores, with only a small amount of organic pores. The support of silty brittle minerals is the key factor for pore preservation. It is generally considered that the new strata of shale reservoirs in Qiongzhusi Formation of southern Sichuan have good reservoir conditions for shale gas exploration.

Key words: southern Sichuan, Qiongzhusi Formation, shale, siltstone, reservoir characteristics