Oil quality and drilling-pad constraints for a viscous-oil field defined a development scheme that consisted of a waterflood line drive with horizontal producers and water-injection (WINJ) wells side by side. Different well designs for producer wells were implemented: a single horizontal trajectory undulating between the two sand bodies in counterphase with the related water injectors, a fishbone design with the main borehole in the lower sand and multiple branches in the upper sand, and a multilateral (ML) counterphase design with extended-reach undulating dual laterals. As a result of the ML campaign, well productivity doubled.
Introduction
The field is located on the North Slope of Alaska in the Beaufort Sea in water depth less than 20 ft. The reservoir consists of four zones hydraulically communicating, named OA1, OA2, OA3, and OA4. The differentiation is mainly sedimentological; OA1 and OA3 are associated with a more-proximal depositional system, while OA2 and OA4 are characterized by a predominance of thin laminated silty sandstones because of a more-distal depositional system.
The crude quality and drill-pad constraints (one offshore, one onshore) drove a development concept that consisted of a waterflood line drive with alternating horizontal producers and WINJ wells with a 1,200-ft spacing.
