Depositional Facies architecture of an off-shore river-dominated Shallow-water Delta : a case study from Member 3 Eocene Shahejie Formation, Kenli10-1 Oilfield, Bohai Bay Basin, China

Shallow-water delta reservoirs have become major offshore hydrocarbon exploration targets for Bohai Bay Basin, one of the most petroliferous basin located in east China. Located in northern sag of Laizhouwan Depress, south of... [ view full abstract ]

Shallow-water delta reservoirs have become major offshore hydrocarbon exploration targets for Bohai Bay Basin, one of the most petroliferous basin located in east China. Located in northern sag of Laizhouwan Depress, south of Bohaibay Basin, Kenli10-1 Oilfield was discovered in 2008 when the first prospecting well Kenli A1 got a well test production of 400 BOPD(barrel oil per day) from Member 3 Eocene Shahejie Formation.The goal of this paper is to identify facies architecture of Member 3 Eocene Shahejie Formation, Kenli10-1 Oilfield with the new acquired 150km2 of high resolution 3D seismic data and wireline-logs of 12 wells sparsely located within the Block, which is of great importance to calculate the original volume of hydrocarbon and determine the optimal well locations of the offshore oilfield.
Core and log data were used to study the stratigraphic architecture and depositional settings of the study area. Member 3 Eocene Shahejie Formation was subdivided into 15 sub-zones according to depositional cycles and each got a thickness of 10-15 meters. 8 main lithofacies were identified by core observation and wireline log interpretation which belonged to river-dominated shallow water delta complexities. Single net sandstones ranged from 3-6 meters and were determined as distributary channel and distributary mouth-bar facies. Distributary channel exhibited a serrate, upward-fining log patterns while distributary mouth-bar showed a blocky, subtly upward-coarsening log character. Distributary mouth-bar and Distributary channel sandstones could stack vertically to thicknesses as much as 15-20 meters and made the pay formation of the oilfield. Then strata slices of seismic attributes picked from the 3D seismic volume were utilized to delineate the shallow water delta lobes and detect the individual distributary channels and mouth bars distribution between and beyond wells of the 15 subzones. We could see from these slices that individual distributary channels were separated laterally by muddy floodplains and in the down current direction, the channels bifurcated and formed distributary mouth-bars. Above 80 percent of the channels and mouth-bars recognized from the seismic slice attributes were confirmed by available well data, and furthermore, five new recently drilled infill wells targeted several of these channels and mouth-bars all got a high oil production, which demonstrated that the methodology presented here was suitable for the facies architecture characterization of offshore thin-bedded shallow-water delta reservoirs.