Reservoir Characteristics Of Volcanic Rocks And Petroleum Geological Significance In The Upper Paleozoic Of Santanghu Basin

Based on the analyses of experimental data and the microscope observation of core slices,the reservoir characteristics of volcanic rocks in carboniferous of Santnaghu Basin are studied by the theory of petrology as the main object of this study. Through these methods, the petrologic characteristics and reservoir characteristics of volcanic rocks in this area are analyzed, and the relationship between volcanic activity and reservoir formation are studied in detail. The lithologic characters of the study area are mainly intermediate-basic rocks, including basalt, andesite, trachyandesite, etc. and the main mineral components are quartz, plagioclase, pyroxene and hornblende. The volcanic facies in the study area were classified into four types, which are respectively volcanogenic sedimentary facies, explosive facies, effusive facies and volcanic conduit. The reservoir space are composed by original stomata, dissolved pore, structural seam, etc. and on the basis of which the combination types of this area are divided into five types. According to the statistical results, some meaningful conclusions are summarized, firstly, breccia in the explosive facie has primary pores and the porosity of volcanic tuff is the smallest one. The porosity weathered is doubled than the original one in the group of Kalagang, which has been the main spaces for oil and gas to accumulate into, though the number of them is smaller than the original ones. The dissolution process can enlarge pores, while the cementation and filling can decrease porosity. The favorable effects of volcanic activities for oil and gas accumulating contain some aspects as followed: Thermal effect can accelerate organic matter evolution, volcanic breccia have better reservoir quality and oiliness, weathered and corroded volcanic reservoir are better than others, structural fracture is the one of the most shapping factors for oil and gas reservoir forming in the Santanghu Basin. Volcanic rocks in the group of Kalagang are compact, thick and have good sealing property, which can be the local seal. On the basis of characteristics of volcanic reservoir, two types of traps are summarized as followed: lithological traps and lithologic -fault traps. The destructive action of volcanic activity for oil-gas reservoir forming is mainly the blocking of reservoir spaces by authigenic minerals which is impeled by high temperature and hydrothermal fluids in the volcanic activities.