Abstract

A regional oil generation/migration model developed from an integrated geochemical/geological study explains the current distribution of oilfields in the Kampar Block, Central Sumatra. It can be used as a quantitative predictive model for future exploration.

The study indicates 3 genetic oil types in the block. The majority of oils, which includes oilfields along the Merbau Trend, Lirik Trend plus the Pekan and Binio Fields, are sourced from deep lacustrine, non-marine algal Kelesa shales. The Panduk and North Merbau Fields are probably sourced from lake edge, mainly terrestrial/minor algal Kelesa shales. The Parum Field is probably sourced from Kelesa or, less probably Lakat terrestrial rich marsh/swamp coals and coaly shales. Generation of the oils has occurred over a narrow maturity range at an Ro = 0.55 - 0.64%.

The major lacustrine Kelesa shale source rock is present in the deepest parts of the sourthern Bengkalis half graben. It's lateral extent was mapped by reconstructing the palaeogeography of the pre-29 mybp sequence. The source rock is currently mature and in the main to late phase of oil generation. Onset of major oil generation in the block occurred in the Plio-Pleistocene, probably due to an increase in heat flow at this time.

Distribution of the oilfields is largely fault controlled. The oil has migrated vertically out of Kelesa shales and laterally up the flanks of the graben, generally in a westward and southward direction, and thence up major faults to fill younger Tualang and Lakat reservoirs. Migration distance is generally small, ranging from 2-10 km.

Quantification of oil charge to prospects/Fields along the Lirik and Merbau Trends indicate the Kelesa source rocks can easily account for the amount of oil found in the Block to date and suggests considerable future potential.