Reservoir Characteristics And Metallogenic Conditions Of Oil Sands Of Silurian Wengxiang Group In Southeastern Guizhou Province

This paper focuses on the study of the oil sands of the Wengxiang Group of Silurian in Majiang-Kaili area,southeastern Guizhou Province.Based on outcrop and shallow well core investigation and by means of thin section observation, scanning electron microscope, fluorescence analysis,porosity and permeability test and oil content test of the samples,studying the oil sandstone characteristics of sedimentary facies, reservoir characteristics, reservoir space types and features, physical characteristics, diagenesis and oil content of oil sands.The result shows that the oil sands mainly developed in the second and third members of the Wengxiang Group. The reservoir dominantly consists of Medium-fine grained(including) calcareous or lithic quartz sandstone and quartz sandstone. There are obvious differences in the type of cement: Kaili area calcite cement with the content of 6-22%,which is based on the sparry calcite cement,the siliceous cement is 1-10%, and emented primarily by calcite and quartz in the Majiang area is 1-7%.The main pore type of the reservoir is primary intergranular porosity. With porosity between 0.3% and 7% and permeability between 0.006 ×10-3?m 2 and 6.21×10-3?m 2, the sandstone reservoirs are classified as low-porosity and low-permeability reservoirs. Although the corrected data shows an average oil content of 3.73%,the oil content of sandstones in Kaili area is higher than that of Majiang area. The diagenesis types in the study area are compaction, dissolution, cementation and fracture, and cementation is the main destructive diageneses.Based on the extraction of oil sands and the analysis of the GC?GC-MS of saturated hydrocarbons and metallogenic conditions, combined with previous information,the results show that the oil sand has high saturated hydrocarbons, high ratio of saturate to aromatic hydrocarbon, and the oil is in the mature stage.Abundant biomarkers,including n-alkanes,isoprenoid,steranes and terpanes,have been detected by GC and GC-MS.The result shows that The n-alkanes are composed of C13-C36 with nC17,nC18 as the main peaks, CPI and OEP values are close to 1. Pr/Ph values range between 0.67 and 1.28,In the m/z191 GC-MS,C30 hopane is the most abundant in the terpanes,Ts/Tm values range between 0.65 and 1.53.In the m/z=217 GC-MS,the regular steranes C27~C28~C29 distributed with Anti “L” and “V” shape,C2920S/(20S+20R)values range between 0.36 to 0.50,C29 ? ? /( ? ? + ??)values is 0.38~0.56.The carbon isotope ?13C between-32.5‰ and-27.9‰, the average is-30.8%.Through the comparative analysis of oil sources, oil sands crude oil mainly originated from the Niutitang Formation of Cambrian. According to oil sands development of different geotectonic location, tectonic evolution and source reservoir cap rock assembla, Majiang Kaili area of oil and gas into accumulation model is a low produce up reservoir and Paleo oil reservoir.