Abstract

The oils accumulated in the fields of Hudbay's Malacca Strait P.S.C. are believed to be sourced mainly from intraformational coals within the Sihapas Formation reservoir sequence. Several lines of evidence, including analytical studies and an analysis of the oil distribution of the region, indicate that significant oil expulsion commences from these coals at around 125°-130° C with most expulsion occurring in the range 130°-140°C.

Heat flow, source temperature and source rock thickness maps have been constructed over the region, and together with analytical studies of the source rock, enable a quantification of oil generation. A comparison with the amounts discovered, in structures that often appear to be not full to spill, indicates that migration losses are considerable, and approximate to 2 percent of the pore volume of the rock through which the oil flowed.

It is thus now possible to roughly quantify both oil generation and migration losses. It is estimated that in the Malacca Strait region, the portion of the drainage area of a prospect which is immature must not substantially exceed the portion that is mature, for that prospect to receive adequate oil charge. This general rule enables explanation of past drilling results and a more confident ranking of remaining prospects and leads.