A north Indonesian basin: geo, thermal and hydrocarbon generation histories

Abstract

Geohistory, thermal history, oil generation and accumulation have been examined in an Early Pliocene basin which is located offshore north of Indonesia. The basinal sediments are 4500 m thick and were deposited in about 5 million years, leading to development of high excess fluid pressures (up to 170 atm at 2000 m), mainly due to strong undercompaction. The successive deltaic platforms in the basin are controlled by a major growth fault system, which is probably related to a large overpressured shale diapir. A one dimensional study of two wells was undertaken using an inverse non-linear scheme to determine dynamic and thermal parameters and then to reconstruct the geohistories and thermal histories at the well sites. The two thermal histories suggest a major heating event about 4 million years before present, probably tied to revewed volcanism, which boosted the maturation of organic matter so that the development of hydrocarbons was massively enhanced. Without the heating event, hydrocarbon generation would have been very unlikely in such a young basin.