Bulletin of the Geological Society of Malaysia, Volume 27, November 1990, pp. 27 – 55
Petroleum Research Institute, PETRONAS, Lot 1026, PKNS Industrial Area, 54200 Ulu Kelang, Selangor
Abstract: The reservoir interval in the Malong Field, offshore West Malaysia, consists of three main types of sand bodies which are interpreted as a) prograding shoreface, b) shallow marine (inner-shelf), and c) fluvial channel sequences.
The prograding shoreface sequence consists of upward coarsening units in which heterolithic sandstone-mudstone are overlain by ripple cross-laminated and parallel-laminated sandstone. The inner-shelf sequence is made up of upward-coarsening offshore bar sandstones encased in shelf muds. The shelf sandbodies show evidence for deposition by storms, and are characterized by the association of distal, low-energy heterolithic facies overlain by proximal, amalgamated high-energy sandstone units. The fluvial channel sequence consists mainly of trough cross-bedded sandstone, intercalated with minor floodplain mudstone.
The Malong sandstones are buried at depths of not more than 150 m, and are probably in the early stages of diagenesis, as shown by the well-preserved depositional (primary) porosity. The porosity and permeability of the sandstones are related to depositional environments. Poroperm values are highest (Ф = 25-36%, K = 100-800mD) in the channel and storm-deposited inner-shelf sandstones. Shoreface sandstones have slightly lower poroperm range (Ф = 24-35%, K = 10-100mD), but are still considered as high-quality reservoirs, permeability barriers (Ф = 10-22%, K<10mD) may be formed of lower shoreface and offshore mudstones.