Production Enhancement In Arctic Environment: The Multilateral Experience For Viscous Oil

Abstract

AbstractThe paper presents the experience of a multilateral well campaign for a viscous oil field and its benefits in terms of production.The field is located in the North Slope of Alaska. The production start up was in January 2011. The main hydrocarbon reservoir is a Cretaceous sedimentary series developed in a sand lobe environment within the Schrader Bluff formation. The structure is a monocline gently dipping to NE with a gross thickness of about 30–35 ft. The oil presents different characteristics due to the instauration of a biodegradation process. Oil densities vary between 16°-19° API with associated viscosities in the range of 50–200 cP at reservoir conditions.The crude quality and drill pad constraints (one offshore, one onshore) drove the development concept which consisted of a waterflood linedrive with horizontal producers and water injector wells located side by side. The lateral sections are 6,000′–10,000′ long through the reservoir with undulating counter-phase trajectories across the two main sand bodies. A challenging horizontal reach/depth step-out ratio around 6.5 has been achieved. The completion string was equipped to provide the capability of integrating a complex reservoir monitoring plan including distribute temperature surveys, inflow control devices and polymer tracers. The choice came out from the need of minimizing the cost and mitigating risk with the highest respect for the environment and the local communities.With the goal of increasing reservoir contact, the multilateral concept consisting of undulating counter-phase dual-laterals was tested in August 2013. This initial test was followed by a limited campaign. As a result, well production doubled with respect to the average before the intervention. Similar productivity improvements were also observed in the new producers. At the time production was sustained by 20 producers and 15 injectors. Since then, eight additional laterals were added to existing producers and three new development wells were drilled and completed. The fieldwide step-change was evident with an overall production enhancement around plus 82% in May 2014.After the first encouraging results, the multilateral campaign has been extended to all the producers and is now standard practice for the remaining development wells in this field.