Addax has been operating two onshore fields in Gabon since 2005, in addition to non-operated partnerships in several other onshore and offshore fields. The main reservoir rock in these fields is the Gamba Formation, which is comprised of shallow marine post-rift sands and dolomites. The sandstones are excellent, multi-darcy, reservoir rocks, however production implies that they are not homogenous. Thin dolomite layers within the sand are interpreted to be either shallow marine or lagoonal in origin. These dolomitic layers appear to significantly influence the vertical flow behavior of reservoir fluids. The dolomites are often unrecognizable on logs but identifiable in samples, as well, their limited areal extent makes them difficult to correlate. The presence of these dolomite layers can be inferred from water and/or gas breakthrough in production wells. The use of reservoir models together with historical production data is one way to quantify the distribution of these features. This paper presents lessons learned and the improvements to modeling workflows that take advantage of linking field performance with geological understanding of the depositional system.


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