Jurassic structural evolution and oil & gas geology conditions for Washixia Depression in Tarim Basin

Based on geological outcrop sections,seismic data and drilling data,the Jurassic structural evolution history,structural sequence characteristics and oil gas geology conditions in Washixia Depression were analyzed in this paper,the following understanding was reached:the Jurassic structural evolution in Washixia Depression were divided into three stages,they were Early Jurassic fault depression stage,Middle Jurassic depression stage and late Jurassic shrinkage stage.Five important sequence boundaries were identified (including two of first class boundaries,one of second class boundary and two of third class boundaries),so the Jurassic was divided into one of first class sequence,two of second class sequence and four of third class sequence,among them the two of second class boundaries corresponded to the transformation tectonic movement boundary of the Early Jurassic fault depression stage,Middle Jurassic depression stage and late Jurassic shrinkage stage.Early Jurassic late stage to Middle Jurassic early stage was the main period of the source rock development in the basin,organic type of the source rock was mainly the humic type,Yangye Formation dark mudstone in Middle Jurassic had relatively high organic abundance,it was the major source rock in this area,Kangsu Formation dark mudstone was relatively poor gas source rock,the sandstone and glutenite of Jurassic episode and its overburden mudstone and coal-bearing strata acted as major reservoir and seal assemblage.Therefore Washixia Depression is the oil gas exploration frontier in Tarim Basin.