Non-Flattening Delta Front Sheet Sand – Evidence from Outcrops and Subsurface

Zhang Changmin, Yin Taiju, Wang Zhenqi, and Xu Long
Yangtze University, Jingzhou, Hubei, China

Delta front sheet sand on Yanchang profiles in Ordos Basin,China, a sand-shale interlayer vertically, is a sheet on a plane.. Sandstone lenticular bodies of different sizes in distributary channels can be seen on the profiles. It is found by dissecting the delta front sheet sands in Daqing Oilfield that though it is at outer front facies belt, there exists obvious characteristics of water courses in sheet sands. Because lake basin delta is slightly influenced by waves and tides, and is strongly influenced by rivers, thus the distributary channel is extended forword to the front end of delta, it looks like a flattening sheet sand, but actually different sizes of distributary channels are arranged on it. Delta front sheet sands superposed by symmetric or non-symmetric lenticular units with great wide-thick ratio are formed by the migration of the channels. The architectural heterogeneous body, the heterogeneous changes of reservoir physical properties are controlled by the architectural structures of sandbodies with obvious hierarchical rules. Key Words: delta, sheet sand, reservoir sedimentation, hierarchical analysis.