Characteristics and distribution patterns of the Lower Cambrian Niutitang Shale reservoirs in Guizhou, China

In order to evaluate the shale gas potential of the Lower Cambrian Niutitang Fm in Guizhou, various data including field geologic survey, shale gas exploration achievements, core sample test, well-site desorption and isotherm adsorption experiment results were integrated to study the characteristics and distribution patterns of the Niutitang Shale reservoirs. The following conclusions were obtained. (1) The Niutitang Shale is mainly distributed in the northern, central and southern-southeastern parts of Guizhou province and its dominant lithologies are silt shale-silty and carbonaceous shales. (2) The organic matters are dominated by kerogens of I- and II1-type with a relatively strong hydrocarbon generation capacity, TOC content of 0.7 - 14. 6% and relatively high maturity (Ro mostly > 2.5%), indicating a over mature evolutionary stage. (3) The content of brittle minerals are relatively high. The clay minerals are dominated by illites and mixed illite-smectites. Its porosity is moderate but the permeability is very low and they are in a negative linear correlation. (4) In western North Guizhou and Central Guizhou, the play fairways of Niutitang Shale are mainly located in Bijie - Dafang - Western Guizhou, where the gas content is in the range of 1.5 - 2.5 m3/t. In eastern North Guizhou and Eastern Guizhou, the desorption gas content is relatively high as a whole. In South and Southeast Guizhou, the play fairways of the Niutitang Shale occur in Danzhai - Majiang - Huangping areas, where the shale gas content is in the range of 0.01 - 1.13 m3/t.