Nakhla Oil Field, Concession 97, LibyaDevelopment Strategy and Improved Oil Recovery

This paper presents the development strategy and the improved oil recovery potential of the Nakhla field. The Nakhla oil field is located in Concession 97 (G.S.P.L.A.J.) and is producing from the heterogeneous and compartmentalized Upper Sarir Sandstone since June 1995. Total production of the existing eight (8) vertical wells and one (1) horizontal well is approx. 22 MMSTB as of year end 2002. Seven vertical wells are hydraulic fractured and three wells are dry holes due to volcanics or technical problems.
Within the next development phase (II) six (6) additional producers are planned. Based on the good experience all new wells will be drilled vertically and post hydraulic fractured. Updated static and dynamic simulation models have been used to optimize the development concept. Through natural depletion ultimate recovery estimates currently stand at 12.0% or 112 MMSTB.

Further development (Phase III) is planned, but ongoing PreSDM and seismic interpretation has to be implemented to re-evaluate the geological and dynamic reservoir model. Ultimate recovery including Phase III estimates stand at 152 MMSTB or 16.3% of oil initially in place (OIIP).

To increase the ultimate recovery even further the ‘Improved Oil Recovery (IOR)’ potential is currently under investigation. Available input data was reviewed and new SCAL and PVT including special IOR/EOR data was requested. Laboratory results will be available by end of year 2003 and will be implemented into a new compositional reservoir simulation. In the meantime a preliminary analytical screening was performed to identify viable IOR/EOR techniques and to estimate ‘Performance Indicators’ of the West and East field regions.

Estimated ‘Performance Indicators’ vary between 13% - 19% for immiscible injection gas and 17% - 19% in case of miscible injection gas. In addition to improving oil recovery, the re-injection of produced gas would avoid gas flaring and confirm Wintershall’s policy to protect the environment. Water flooding is predicted to give good recoveries, too. However, low permeabilities may prevent or restrict injectivity into the reservoir. Further investigations are necessary and will be performed on a full-field compositional model.