PROPERTIES OF RESERVOIR QUALITY ROCKS OF THE BELAIT AND LAMBIR FORMATIONS, NORTH EAST SARAWAK

This studywas conducted to evaluate the field characteristics, mineralogical, physical
and geochemical properties of the Early to Late Miocene Belait Formation in Marudi
and the Early to Middle Miocene Lambir Formation in Miri, Sarawak at various
scales of observations and to provide a key differentiation between these two
formations. Representative samples were collected at Marudi, Northern Sarawak
(Belait Formation) and nearby Miri, Sarawak (Lambir Formation). Field observations
suggested that there are at least four differentiating characteristics between these
Formations. The four major differentiating characteristics are; microfabric analysis
revealed that the Belait Formation consists of angular to sub-angular grains whereas
the Lambir Formation has sub-rounded grains. Presence of mudclasts in the Belait
Formation suggests deposition in a low energy, muddy environment with short
transportation. Extensive fracturing of the quartz grains in the Belait Formation
suggests variations in the degree of compaction resulting from differences in
thickness or rates of diagenesis.