Residual gas and oil saturations and relative permeabilities have been quantified in the Maui Field. Additional Special Core Analysis (SCAL) laboratory data was acquired using decane/brine and oil/brine centrifuge experiments. Such measurements are considered most representative of water influx into gas and oil reservoirs respectively. In the case of oil, ageing of the samples to restore wettability is shown to be essential. Relative permeability curves were obtained by history matching the raw experimental production data via numerical simulation. This process corrects for experimental artefacts and limitations, resulting in a significant reduction in residual hydrocarbon saturations compared to typical analytical interpretations. A correlation using a form originally proposed by Land has been used to relate the residual hydrocarbon saturations to the initial water saturations. In-situ field measurements of hydrocarbon saturations using pulsed neutron logs in water-flooded zones are shown to support the SCAL data.

The work described represents the state-of-the-art in quantification of residual hydrocarbons. In particular, the combination of the sampling methodology, the experiment design, the advanced numerical interpretation and the in-situ measurements is material previously unpublished in technical literature. The results are significant in that they show lower residual saturations than commonly expected, while adding to the limited published data on residual hydrocarbons. Use of lower residual hydrocarbon saturations together with the appropriate relative permeabilities in reservoir simulation has resulted in improved reservoir history matches and has had a positive influence on Maui Field reserves. Application of these state-of-the-art techniques to other water-drive fields is likely to have a similar impact.

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