Extended Reach U-Shape Re-Entry Drilling in Shallow Depleted Fractured Reservoirs in Congo Offshore Oldest Oilfield

Abstract

Congo has been an oil producing country since the 70's, it is in this context of aging oilfield and low oil price environment that a redevelopment project was launched to give a second life to a shallow, depleted, mature, offshore oilfield with viscous oil (22° API) in a cost-effective manner. The solution selected was to drill "U-shape" side tracks (inclination at TD 115deg) from the original boreholes on an existing platform (60m WD). The objective was to create a second drainage area of up to 500m, ~200m away from the original producing zone. Five re-entries U-shape wells were delivered with measured to vertical depth ratios up to 2.5 in shallow heavily depleted reservoirs (270m TVD). The team selected innovative and low cost techniques to overcome many challenges, from high DLS in unconsolidated formations using simple mud motor BHA, to running 4-1/2" liner up to 115deg inclination and implementing a thixotropic mixed metal oxide mud system to mitigate losses. The project has been successful both from a budget and production standpoint.