Abstract
The Tembungo field located offshore Sabah is a highly faulted anticlinal structure where oil and gas accumulations occur in different fault blocks. This paper discusses source rock potential, characteristics of Tembungo oils, and oil- oil and oil- source rock correlations between oils and source rocks from Tembungo and adjacent fields. The shales of the Tembungo wells have poor to fair source rock potentials mainly of Type III gas-prone organic matter and minor contributions from Type II oil-prone organic matter. Maturity data show that the organic matter in the Tembungo well sections are immature. The Tembungo crude oils from the different fault blocks are genetically similar, paraffinic, contain low sulphur and wax, and have moderate API gravity. The presence of C24- tetracyclic terpanes, oleananes, C80- resin triterpanes and predominance ofC29- steranes in all the samples suggest that the oils are derived from source rocks of terrigenous origin containing different mixtures of land-plant organic matter including resins. GC and GeMS analyses indicate that the crude oils produced from the same fault block have similar biomarker distributions but some variations occur in oils from different fault blocks. These variations are interpreted as due to the effect of migration and biodegradation whereby each fault block has a separate fluid system and there is no or very little intermixing between them. Oil- oil correlation indicates that the oils in the study area have similar biomarker fingerprints and could have been generated from the same source rock type containing abundant terrigenous organic matter. Geochemical studies have so far failed to identify the exact source. rock which could have generated the commercial quantities of oils in the Sabah basin. The source rock intervals in the area are lean in organic matter but are sufficient in quantity. This study describes the application of geochemical approach particularly in the use of biomarkers in characterising crude oils and source rocks from the Sabah basin. It is hoped that the present study would be able to throw some light
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