Oil-Prone Mangrove-Derived Tertiary Coals and Dispersed Organic Matter of Balingian Province, Sarawak, Malaysia

Abdullah, Wan H.¹; Abolins, Peter²
¹Geology Department, University of Malaya, Kuala Lumpur, Malaysia.
²Carigali Sdn Bhd, PETRONAS, Kuala Lumpur, Malaysia.

Tertiary coals of NW Borneo, and SE Asia in general, are known to be effective source rocks in the prolific gas- and oil-producing basins of the region. Based on geological and biomarker studies it has been established that much of the petroleum in the productive Balingian Province, was generated from organic matter of higher plant origin deposited within the paralic conditions of a lower delta plain to marine prodelta setting. Coal extracts of the Nyalau Formation, the onshore equivalents of offshore source rocks, are characterised by the presence of higher plant derived biomarkers such as oleanane and bicadinanes. Similar biomarker distributions are observed in the Balingian oils. These terrestrial markers have been widely associated with triterpenoids of angiosperm origin and resin-derived compounds. Sedimentary facies association and reported occurrence of a high abundance of mangrove pollen within intertidal successions are supportive evidence to a mangrove origin for these Sarawak Basin coals and their associated oils. In this study, the maceral suberinite and the associated macerals bituminite, liptodetrinite/fluorinite and phlobaphinite are shown to be the most oil-prone macerals of the Balingian province mangrove-derived coals and coaly sediments. The high abundance of these suberinitic constituents which are known to expel hydrocarbons within a narrow range of 0.45-0.75%Ro, consequently gives rise to a relatively lower onset of liquid petroleum generation compared to the commonly acceptable 0.6%Ro. These are considered important characteristics of mangrove-derived coals.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012