Abstract:

The 5th- 6th interval, of the upper part of Xujiahe Formation, in Central Sichuan Basin, is the main studying stratum in this paper. Based on many outcrops, cores, logging and seismic data, Xujiahe Formation is one typical kind of shallow-water delta. According to the characteristics of coal rocks, plant stems, leaves, channel scouring, lags, and the stratification, shallow-water delta could be divided into four kinds of subfacies. They are upper delta plain，lower delta plain，delta front and prodelta. Two types of models for shallow-water deltas are summarized in this paper. The first is of low supply, i.e. the 5th interval. The second is of high supply, i.e. the 6th interval. Coal rocks on the lower delta plain of the delta with low supply are good source rocks. Sandstones of distributary channel and crevasse splay on the lower delta plain of delta with high supply are the favorite reservoirs. Favorable generating-reserving assemblages could be found on the lower delta plain of shallow-water delta, which is the major exploration zone for lithological reservoirs.

Key words:  shallow-water delta, braided river, depositional model, Sichuan Basin, Xujiahe Formation