Lithologic and lithofacies sequences of volcanic rocks in Xushen gas field

Due to the rapid change of volcanic lithofacies,a large variation of physical properties and the strong heterogeneity of reservoirs,it is essential for the highly efficient development of volcanic reservoirs to make clear the lithologic and lithofacies sequence.Therefore,we performed a detailed outcrop observation and analyses of many well data in the wellblocks like Xushen-1 and Shengshen2-1,etc.According to outcrop and core data analysis,we presented a comprehensive naming method for the volcanic rocks in the Xushen gas field,Sonliao Basin.Upon the study of the lithologic and lithofacies sequence characteristics and correlation of well data with seismic data,we established the lithologic and lithofacies sequences for the volcanic rocks in the Lower Cretaceous Yingcheng Formation in the Xushen gas field,and revealed the characteristics of their distribution.The lithologic sequence consists of 4 cyclic sequences including,from bottom to top,①intermediate-basic-volcaniclastic-acidic rocks,②sedimentary rocks,③volcaniclastic-basic rocks-acidic rocks,and ④sedimentary rocks.The lithofacies mainly include the upper and lower subfacies of the effusive facies and the pyroclastic-bearing lava flow subfacies of the eruptive facies.This naming method can be used as a reference for the study of lithologic and lithofacies sequences in similar volcanic gas reservoirs.