U-Shaped Re-Entry Drilling Revitalizes Depleted Reservoirs Offshore Congo

摘要

Against the background of a low-oil-price environment,a redevelopment project was launched to give a second life to a shallow,depleted,mature offshore Congo oil field with viscous oil(22 “API)in a cost-effective manner.The solution selected was to drill U-shaped side tracks(inclination at total depth=115°)from the original boreholes on an existing platform at a water depth of 60 m.The objective was to create a second drainage area.The project team used innovative,low-cost techniques to overcome many challenges.Under 27 platforms(four to five wellheads each),an accumulation of heavy,viscous oil is trapped in three reservoir layers.The field was produced with a combination of cold mode followed by a period of hot mode from steam injection.The consequence is a depleted(0.3-sg)and highly steam-fractured reservoir where fluid loss presents one of the primary challenges for infill development.The pilot project consists of reentering the current producers and then deepening them in a U shape to access the same shallow reservoirs more than 200 m away from the initial production leg.All reservoirs share the same water table identified below an impermeable formation underneath the target layers.To avoid water breakthrough,the trajectories were planned with up to i8°/30 m to prevent the well from entering the water-bearing layer,with minimum 30-m true vertical depth standoff from the oil/water contact.