The Captain Field is situated in the outer Moray Firth in approximately 340ft water depth. The reservoirs are shallow sandstone, either sheet turbidite or channel sands. The oil is relatively viscous and is drained using long horizontal wells. The reservoir is sub hydrostatic and uses either electrical or hydraulic submersiblepumps for artificial lift.
Produced water re-injection supplemented by the field aquifer is used for voidage replacement and to maintain reservoir pressure above bubble point. The water injectors are long horizontal wells with one injector supporting a number of producers. The sand is unconsolidated and injectors are generally completed with stand-alone screens.
Since drilling the first injector well in 1995 there has been an evolution in drilling and completion practices and while the original wells were drilled with non-aqueous drilling fluids, current wells are drilled with water based fluids that have been optimized over the years. This has been an iterative process with the aim of reducing formation damage and increasing baseline injectivity.
Screen type and stimulation techniques have also changed over time and later platform wells have also been flowed back to surface which tends to greatly improve the initial injectivity. This improved injectivity is critical for the success of future field development and enhanced oil recovery deployment, which initially requires drilling of new subsea injectors. However flowing a subsea injector back to a semisubmersible rig involves significant safety and operational issues, thus new methods of increasing injectivity are being sought.
This paper will present the history of the Captain Field's injectors, explain the lessons learned over time and describe the ongoing studies that are being performed to better understand the damage mechanisms to ultimately eliminate the requirement for flowing back injector wells.