An Integrated Study of Reservoir Compartmentalization at Ewing Bank 873, Offshore Gulf of Mexico

Abstract

Abstract Ewing Bank 873 is an offshore Gulf of Mexico field discovered in 1991 in 775 ft of water. The discovery well was drilled on a seismic amplitude anomaly on the flank of a salt withdrawal mini-basin. Field development began in 1994, and in mid 1998 daily production from the Bulminella 1 reservoir averaged 40,000 BOPD and 32 × 106 ft3/D of gas. The Bul 1 reservoir in this combination structural-stratigraphic trap consists of six stacked and overlapping Pliocene turbidite sand lobes. In turn, integration of seismic, well log, geochemical and pressure data indicates these six turbidite lobes comprise three compartments. All of the various data types give constraints on different aspects of compartmentalization, but at the stratigraphically complex Ewing Bank 873 field, geochemical analyses provided key information unavailable through any other means. These geochemical analyses were performed as individual wells in the field went on production and immediately provided information regarding fluid communication and reservoir connectivity that was missing from earlier interpretations based solely on seismic and log data. Early recognition of three reservoir compartments using geochemical data also helped constrain preliminary stratigraphic interpretations and provided initial input for flow units and reservoir simulation models. The geochemical information further provided advance notice of economically significant oil quality variations in the three compartments. These fluid variabilities were later substantiated by PVT analyses and include notable differences in oil gravity, weight percent sulfur, viscosity and solution gas. Integrating all available data shows there are three compartments at EW 873 and each compartment comprises different turbidite sand lobes and exhibits its own characteristic pressure regime and fluid properties. The early indications of both compartmentalization and variation in fluid properties by the geochemical analyses contributed significantly to improved field recovery and economics by allowing fewer and better placed wells to be drilled. P. 653