Fluid activity and hydrocarbon accumulation period of Sinian Dengying Formation in northern Guizhou, South China

By taken the Sinian Dengying Formation in Northern Guizhou as an example, based on the data from homogenization temperature, salinity and density of fluid inclusions, and combined with the restoration of burial history and thermal history, this paper investigates hydrocarbonaceous fluid activity periods and restores the process of hydrocarbon accumulation and destruction. Four periods of hydrocarbonaceous fluid activity periods occurred in the research region, and they correspond to the homogenization temperature of fluid inclusions of 87.1–111.4 °C, 126.1–163.0 °C, 166.9–225.1 °C and 95.3–116.4 °C respectively, reflecting two stages of hydrocarbon charge, one stage of gas accumulation and gas reservoir destruction activity in Dengying Formation reservoir. Comprehensive analysis on observation of thin sections, cathodoluminescence and oxygen isotope show that, Dengying Formation reservoir developed six generations of cements, four stages of dolomite, and had four stages of dissolution, the organic acids from fluid activities in different buried environment produced multiphase dissolution on residual pores and fillings of the ancient karst. Dengying Formation in Northern Guizhou occurred three periods of petroleum accumulation which are, in order, Middle-Late Caledonian (470–428 Ma), Indo-Chinese epoch (252–228 Ma), Early Yanshanian period (177–145 Ma), and the ideal depth for the preservation of natural gas accumulation in Dengying Formation in Northern Guizhou is about 3 600 m.