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ABSTRACT: Brunei Deepwater Exploration: Lateral prediction of the petrophysical attribute EHC in turbidites

van den Heuvel, Erik1 and Matthias Bruhl2
(1) Brunei Shell Petroleum, Seria, Brunei
(2) Nederlands Aardolie Maatschappij, Assen, Netherlands

Quantification of pre- and post-drill exploration volumes often relies independently on petrophysical evaluation of existing well penetrations and gross rock volumes determined from seismic. Ideally seismic information is used to constrain petrophysical attributes away from existing penetrations. BSP established a relation between seismic attributes and the petrophysical attribute net EHC (net pay * porosity * hydrocarbon saturation). This relation was used to quantify hydrocarbon volumes for deepwater turbidite prospects.

The main petrophysical challenge in a slope turbidite setting is the thin-bedded nature of some reservoirs. These thin-bedded reservoirs are typically below the normal tool resolution. As a result, conventional (shaly sand) resistivity-based saturation models fail. NMR was utilised to correctly identify all fluids present in an interval, independent of lithology and to accurately determine EHC. Thin-bed evaluation techniques calibrated to the NMR result were applied to remaining wells.

To calculate volumetrics from the petrophysical evaluation it is necessary to extrapolate results away from the wells. The most simple approach is to average the derived net EHC values and apply it over the whole area of the field. This however does not honour the seismic information available. A more sophisticated approach has been devised that uses the seismic data to calculate an attribute that can be linked to the petrophysical attribute EHC. A best-fit relation between the seismic and petrophysical attribute was established to generate a map of net EHC of the reservoir. Summation of such an EHC map over the entire area of interest results directly in in-situ hydrocarbon volumes.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia