Braided river delta outcrop architecture: A case study of Triassic Huangshanjie Formation in Kuche depression, Tarim Basin, NW China

Abstract

Guided by the theory of reservoir architecture, the architecture of braided river delta of Triassic Huangshanjie Formation in Kuche Depression of Tarim Basin was studied using cycle constraints and hierarchical dissection analysis method. According to sedimentary cycle and lithofacies assemblage characteristics, two types (distributary channel and distributary bar) of fourth level architectural units and their boundaries were identified on outcrops. Vertically, the reservoir sand bodies overlay in the three patterns, distributary channel-distributary bar, distributary bar-distributary bar, and distributary channel-distributary channel. Laterally, the architecture units stitching in four patterns, distributary channel-distributary channel intersecting and stacking, distributary channel-distributary bar intersecting and stacking, distributary bar-distributary bar and distributary bar-distributary channel intersecting and stacking. The fourth level units overlay and joint together, forming complex fifth level architectural units of channel filling divided by architectural boundaries of different levels. The fourth and fifth level boundaries reduce the vertical connectivity and enhance the heterogeneity of the reservoir. Through field measurement, profile architecture element database, was established and the quantitative relationship among the parameters was characterized. The research results provide a geological basis for the characterization of fine reservoir architecture of the similar sedimentary conditions in the Tarim Basin. Key words: Tarim Basin, Kuche depression, Triassic Huangshanjie Formation, braided river delta, outcrop dissection, architectural analysis