Petroleum systems analysis of the Paleocene play in the West of Shetland area

Abstract

The Lower Tertiary petroleum system in the West of Shetland area has been reconstructed by integrating sequence stratigraphical interpretation, pressure data analysis and basin modelling with hydrocarbon migration pathways prediction. Twelve sequences in the Paleocene–Early Eocene section can be grouped into three sequence sets. The lower two sequence sets are dominated by deep marine turbidite fan reservoir sandstones encased within hemipelagic shales. The youngest sequence set is dominated by a series of prograding delta facies rocks. A regionally extensive shale, deposited during a marine flooding event sits at the top of the oldest sequence set. This shale is an effective regional seal and pressure barrier. A study of well pressure data and sedimentary facies variations within the oldest sequence set has led to the identification of three pressure cells. Structural modelling, heat flow mapping, vitrinite reflectance and apatite fission track analysis were used to reconstruct the thermal history West of Shetland. From this dataset, the Kimmeridge Clay Formation source-rock maturity and hydrocarbon generation history were modelled for several time periods. These results were used to generate migration pathways at the Base Tertiary unconformity which sits stratigraphically below the reservoirs in the oldest Paleocene to Eocene sequence set. The resulting model predicts an oil-prone southern province and gas-prone central province which accords with the Foinaven and Schiehallion oil fields in Quadrant 204 and the gas discoveries in Quadrants 206 and 214. The model also suggests the possibility of further oil potential in Quadrant 208.