The Use of Detailed Reservoir Description And Simulation Studies in Investigating Completion Strategies, Cormorant – UK North Sea

Abstract

ABSTRACT A portion of the Cormorant field in the U.K. North Sea is being developed using a subsea production system. All layers in the stratified reservoir section are being waterflooded concurrently by perforating the entire interval in both producers and injectors. The permeability contrast among the layers is such that there is potential for severe imbalance in the movement of the waterflood fronts, resulting in large volumes of early water production from high permeability layers and incomplete displacement of oil from less permeable layers. With the high cost of expanding platform facilities or performing workovers on subsea wells to re-distribute production and/or injection, there is considerable incentive to optimise the completions in new wells. This paper describes studies undertaken by Esso Exploration and Production U.K. to evaluate various completion strategies for new subsea wells. These studies were done to complement work done by the operator, Shell U.K. Exploration and Production. The studies included detailed reservoir description work to define the oil-in-place and permeability distribution, followed by simulation of the waterflood for a representative reservoir cross-section. Wellbore, flowline and pipeline hydraulics for the complex production and injection system were included to more accurately model well rates. The results provide general insight into the nature of the displacement when waterflooding a stratified section with a limited number of wells. They also provide specific guidance on: (1) dual vs. single completions, (2) perforating, testing and stimulation sequence and (3) the benefits of partially perforating high permeability sands.