Abstract: A complete analysis was conducted of the reservoir characteristics of the organic-rich mudstone of the Niutitang Formation in Northern Guizhou, China. The rock core of seven shale-gas survey wells and four geology shallow wells was sampled and various experimental tests, such as mineral and geochemical analyses, porosity and permeability measurements, and hydrocarbon content analysis were carried out. The results show that the organic-rich mudstone of the Niutitang Formation develops mainly in a deep-water shelf facies. The rocks are mainly silty carboniferous and silty carbonaceous mudstone. The brittle minerals are mainly quartz-feldspar combinations. The content of other authigenic brittle minerals, such as calcite, dolomite, and pyrite is generally low. The clay mineral content, mainly illite, is low but the variation range is large. The overall organic carbon content is high (1.5%～15.7%), and the organic matter has a high level of maturity (1.74%～3.40%), with a higher evolution level. The average density of the reservoir rock is 2.52 g/cm³, and the BET specific surface area is 0.33～33.76 m²/g. The main reservoir spaces are interparticle pores and intraparticle pores. The development of the organic holes is inferior and there is a lack of micro-fractures. The characteristics of the reservoir point to low porosity and low permeability, as well as low porosity and ultra-low permeability. The total gas content is 0.02～2.05 m³/t. Field gas-component analysis shows the N₂ and H₂ content is higher than is the CH₄ content.

Key words: organic-rich mudstone, Niutitang Formation, reservoir characteristics, Lower Cambrian, Northern Guizhou