Characteristics of volcanic explosive facies and factors influencing reservoir performance in Dixi area,Junggar Basin

The explosive facies volcanic rock is a combination of different forms of pyroclastic materials.According to the classifications and the combinations of the pyroclastic materials,the explosive facies can be divided into airfall,thermal base surge,thermal debris flow and splash sub-facies.Each sub-facies has its own unique discrimination criteria.Studies show that the lithology is complex and the explosive facies volcanic rocks are mainly distributed in Dixi 10 and 14 well areas in Kelameili Dixi area,as evidenced by the observation of volcanic rocks core,ordinary thin section and casting thin section as well as the analysis of logging data.The lithology is dominated by volcanic tuff,volcanic breccia,ignimbrite and welded volcanic breccia.The reservoir space of explosive facies is characterized by matrix solution pores,intragranular solution pores,structural fractures and dissolution fissure.The ignimbrite-dominated thermal debris flow sub-facies and volcanic tuff-dominated airfall sub-facies are the high-quality well-developed reservoir sites among all sub-facies.The tectonism and the dissolution of fluid are the main factors for the reservoir.The results of the study will provide a reference for the judgement of a volcanic rock reservoir as to whether it is a valuable reservoir or not in the similar area.