Publications

The Malacca Strait Contract Area comprises some 12,000 km2 of offshore and island acreage located between the eastern Sumatra coastline and the Malaysia - Indonesia international boundary. A total of 14 wells had been drilled in the Contract Area up to the end of 1981, these include 2 discovery wells (for the Mengkapan and Lalang oilfields), 4 successful delineation wells and 8 exploratory dry holes.Geologically, the Contract Area represents the northeastern margin of the Tertiary Central Sumatra Basin, characterized by a relatively thin wedge of Tertiary sediments onlapping the core of the Sundaland Craton. An area of thicker sedimentation in the far western portion of the block is related to the faultcontrolled Bengkalis Depression. Both the Mengkapan and Lalang Fields are located within this depocentre.The oil in the Mengkapan and Lalang Fields is reservoired in coarse clastics of the Miocene Sihapas Group. This sandy sequence was deposited in fluviatile to marginal marine environments, and marks the onset of the regional Early Miocene marine transgression. It is demonstrated that the upper boundary of the Sihapas Group is strongly diachronous, varying in age from Lower Miocene (NN2) in the south to Middle Mocene (NN5) in the north. Geochemical data indicate that the best potential source rocks in this part of the basin are shales interbedded within the Sihapas Group. The progressive younging and thinning of marine Upper Tertiary sediments is, therefore, a serious downgrading factor for hydrocarbon exploration along the basin margin, since regionally maturity of source rocks has only been achieved by virtue of very high geothermal gradients.