Abstract

Abnormally high fluid pressures in the Baram Delta are the result of (a) undercompaction and (b) inflation of originally normally pressured reservoirs by injection (leakage) from an underlying indercompacted sequence.

Hydrocarbons are only found in overpressured reservoirs if the abnormal pressures are due to inflation, whereas the undercompacted sequence is barren.

The absence of hydrocarbon can be explained by assuming an early sealing of the now undercompacted sequence with the result that only little time was available for hydrocarbons to migrate into it.

In case of hydrocarbon generation within the undercompacted sequence it can be argued that vertical tension cracks, generated by the additional pressure created by the hydrocarbons, provided escape routes for these hydrocarbons. After release of the hydrocarbons these tension cracks would close again.

Ampte drilling data seem to confirm indeed that the undercompacted sequence in the Baram Delta forms an unfavourable habitat for hydrocarbons. These data further indicate that in the inflated sequence the chances of finding gas relative to oil increase with increasing pressure.