One of the challenges that operating companies face during any oil field development project is to deal with the uncertainty associated with the data acquired in the exploration and appraisal phases, which can be ultimately used to forecast reservoir behaviour, hydrocarbon recovery, and production. This particularly applies to marginal fields where uncertainties such as geology (static information) and reservoir drive mechanism (dynamic information) may impact significantly the estimation of reserves and result in the termination of the project during the appraisal phase. The context of this case study is the appraisal phase in the development of two fields with heterogeneous, thin shaly sand sequences, where potential sand discontinuity exists. The fields are located in the Intra-Latrobe formations of the Gippsland Basin, offshore Australia. Accurate field description and reserves estimation was critical for the outcome of the full field development project. Logging-while- drilling logs, wireline logs and wireline formation tester pressure data, identified a number of potential hydraulically isolated hydrocarbon-bearing sands. During data acquisition, the degree of uncertainty associated with some of these intervals was perceived as significant for the estimation of oil in place and prediction of reservoir behaviour. This uncertainty was addressed by a comprehensive wireline downhole fluid analysis (DFA) program consisting of multiple pumping stations over the reservoir intervals. The program conclusively identified multiple independent hydrocarbon- bearing sand intervals and assisted critical interpretation of the sand continuity particularly the semi-continuous distribution of fluid composition and gas-oil ratio versus depth. The DFA data was pre-processed in real time, enabling more accurate preliminary hydrocarbon volume estimation, as well as establishing with more confidence the perforating strategy over the main producing intervals. For the first two wells of the field appraisal campaign, samples were recovered from all the hydrocarbon-bearing intervals and analyzed in the laboratory. The comparison between lab results and DFA provided a benchmark for optimizing the sampling programme with DFA for subsequent appraisal wells.
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