Abstract

Oil was found in the late 30's in the Bintuni basin located in western Irian Jaya and limited production obtained from the New Guinea limestones in the Wasian and Mogoi fields. Since then, although many wells were drilled in the Bintuni basin, only a modest discovery was made in 1981 at Wiriagar.

A geochemical review, including recent laboratory studies, has been carried out on rock samples from wells, or collected in the field on the northern edge of the Bintuni basin. This geochemical review led to the questioning of previous models of Tertiary source rocks sourcing the New Guinea limestones.

It was found that the source potential of the late Tertiary Steenkool and Klasafet formations was marginal (low T.O.C., humic type of Kerogen). Moreover, sufficient maturity is not reached, except maybe in the deeper part of the basin, implying unlikely long distance horizontal mirgration. In contrast the oils of Wasian, Mogoi and Wiriagar fields are thermally mature and therefore have already undergone high temperatures during their geological history, a fact inconsistent with a Tertiary source.

Sediments having good source rock potential were recorded in middle Jurassic upper Tipuma shales and paralic uppermost Permian Ainim formation within numerous coal seams and carbonaceous shales rich in plant debris. These sediments are thought to lie in the oil window and to have reached maturity.

An attempt at oil to source rock correlation suggests that the Mogoi and Wasian oils could have been sourced by the Permian Aifat formation while the Wiriagar oil is of a different origin, tentatively correlated with the upper Tipuma source rock.

The existence of such pre-Tertiary source rocks is of interest for hydrocarbon exploration in the Bintuni basin. This underlines the role of geochemistry in exploration.