Depositional environments and petrofacies of X\u2013XII sand groups of K2qn3 Formation, Daqingzijing area, Songliao Basin, China

Abstract

Integration of the geological context, core analysis, and petrographic investigation, together with data from wireline logs, resulted in the recognition of petrofacies types and the representation of facies models characterizing the X–XII sand groups of the K2qn3 Formation in the Daqingzijing area of the Songliao Basin, China. The results show that the lithology of the reservoir’s X–XII sand groups includes shale calcium-bearing siltstone and sandstone, calcareous siltstone and silty sandstone. The petrofacies consist mainly of quartz, feldspar and rock fragments cemented by clay, and some samples include calcite. The studied interval was deposited onto a delta front. Four types of petrofacies were recognized: subaqueous distributary channel, mouth bar, distal bar and subaqueous interdistributary bay. According to background investigation, the study area’s X–XII sand groups have experienced a large-scale decline in lake level. There are many subaqueous distributary channels in layers 36–40, while other layers were mainly deposited in a subaqueous interdistributary bay.