Depositional characteristics of fan delta deposits and their impacts to reservoir development-An example from Liaohe Basin

The Yulou oil bearing sets from one of the experimental areas in the south end of western slope of the West Depression of the Liaohe Basin is selected in this paper as a case to study the depositional characteristics of a fan delta and their impacts to reservoir development. Core and slice data, geochemical data of seven wells and logging data for 400 wells in addition to seismic data are collected for interpretation. On the basis of the high resolution stratigraphic framework, sedimentary facies are identified and described. At the same times, the influences of sedimentary facies to reservoir development are analyzed. The target layer is divided into 29 single sublayers according to well data and seismic data. The conclusion of facies analysis of the target layer is further confirmed as a fan delta front by lithology, beddings, colour of mudstone, fossil assemblage and grain size distribution patterns. Sediments came from NW and north. Five types of sedimentary facies, i.e. the underwater distributary and channel sands, river mouth bar, underwater distributary channel mudstone and delta front sheet-like sand are well developed in the study area. In general, underwater distributary channel and underwater distributary channel sand dominate the sequence with the river mouth bar and delta front sheet-like sand as the next. From the bottom single layer of yII36b to the top single layer of yI11a, the target layer shows an inversed cyclic characteristic and becomes coarsening up from bottom to top. Effected by frequent rechannelization of underwater distributaries, sandstone deposits become more heterogeneous. Distribution pattern and composition of depositional facies should be sufficiently considered in thermal recovery of oil with steam.