Polymer Injection in Deep Offshore Field: The Dalia Angola Case

Whereas on-shore polymer injection may be qualified as a mature EOR technique, considering the hundreds of operations that have been conducted all over the world, only one polymer pilot has been implemented offshore, and none in deep offshore conditions. A very thorough feasibility study of polymer injection has been made on the Dalia field in Angola, a typical deep-offshore high permeability (>1D as an average) sandstone reservoir containing medium viscosity oil (3 to 7cP under reservoir conditions). The study has demonstrated that high molecular weight hydrolyzed polyacrylamides could be used under a wide range of salinities covering sea water and a mixture of sea water and produced water. Additional recoveries in the range of 3 to 7 % can be expected in this particular context of large well-spacing development of a medium viscosity field. Powder polymer supply is achievable for deep offshore fields either with a specific bulk carrier or using standard international containers to transport big bags (750 kg). Although the on-deck option is simpler, even in the case where no room is left on the existing FPSO, marine options can be found to safely process the polymer on a barge connected to the FPSO (depending on the sea conditions), but the on-deck option is more simple. The need for an injectivity pilot is compulsory to demonstrate the operability of the facilities, and the injectivity of the polymer solution. A single well test has been designed and is planned fall 2008 in Luanda on one of the well of the Camelia reservoir. A skid dedicated to the injectivity test has been designed, assembled and constructed to prepare a mother solution of polymer from powder. Tested in France (no injection), the skid has been shipped to Luanda for installation on the FPSO during summer 2008. Future of the project will depend on the injectivity tests results and on-going studies on a phased approach.