LACUSTRINE SYN-RIFT FACIES ASSOCIATIONS AND RESERVOIR QUALITY FROM CORE: SHAHEJIE AND DONGYING FORMATIONS (EOCENE-OLIGOCENE), BOHAI BAY, PEOPLE’S REPUBLIC OF CHINA

Kuykendall, Michael D.
ConocoPhillips, Houston, Texas, USA

Sedimentological and petrographic evaluation of conventional whole cores (120 meter net) from syn-rift deposits of the Eocene – Oligocene Shahejie and Dongying formations in an exploration well in Bohai Bay, People’s Republic of China, has shown that the facies succession was deposited in a saline paralic lake environment. The 200 meter (gross) stratigraphic section cored can be subdivided in ascending order into: 1) a lower late-Eocene unit (Shahejie Formation) of mixed bioclastic limestone, sandstone, and shale deposited in shallow lake shoreline environments, 2) a middle early-Oligocene unit (lower Dongying formation) of stacked prograding shoreface sandstones; and 3) an upper middle-Oligocene unit (upper Dongying formation) of deltaic sandstones and prodelta to offshore shales. The middle and upper cored intervals consist of a series of coarsening-upward parasequences bounded by flooding surfaces. The upper shoreface reservoir sandstones are the “cleanest” and coarsest-grained and correspondingly have the best reservoir quality; whereas the bioclastic limestones at the base of the cored interval often have good secondary porosity due to effects of subaerial leaching, but have relatively low permeability resulting from the isolated nature of intrapartical pores and other associated diagenetic effects.