Abstract

Intra-platform shoal reservoirs are widely developed in the Ordovician of the Tarim Basin, western China and are prospective for hydrocarbon exploration. Early Paleozoic tectonic evolution of the Tarim Basin was one of extension and followed by compression. The dynamic transformation of the regional plate margins caused differentiation of the intra-platform paleogeomorphology, which imposed changes on the development of sedimentary facies contemporaneous with the development of intra-platform shoals. An integrated model for recognition of intra-platform shoal reservoirs was established through outcrop investigation, core observation, logging analysis and seismic data interpretation. Ordovician intra-platform shoals in the Tarim Basin occur as ‘shoal deposits containing small reefs’, ‘shoal deposits covering large reefs’, as well as ‘reef-dominated shoal deposits’. Each of these types tend to dominate at different stratigraphic levels. Few but large intra-platform shoals are developed in the Penglaiba Formation. Large numbers of small-scale intra-platform shoals are widely developed in the lower member of the Yingshan Formation, whereas larger and thicker intra-platform shoals are widely developed in the upper member of the Yingshan Formation. This study indicates that the development of intra-platform shoals is controlled by many factors such as platform structure, sea-level change, paleodepth, and paleogeomorphology, among which the sea-level changes and micro-paleogeomorphology play the most significant role. The shoals are found mainly in highstand system tracts of high-frequency depositional cycles. The ideal locations for the development of intra-platform shoals are over micro-uplifts and facing windward paleoslopes.

You do not currently have access to this article.