Geology of Sikuati, Kudat with Emphasis on the Existence of Hydrocarbon Leakage Zone

Oil seepage at Kampung Minyak, Sikuati was discovered in 1881 and the occurrence of the oil seep can still be observed until present day. This study aims to investigate the relation of oil seepage at Sikuati area with the stratigraphic, structural and petroleum system of Kudat Peninsula. Eight localities including the oil seepage were visited and observed during geological excursion at the beginning of this study. The abundance of highly carbonaceous rocks with presence of lamination in the Sikuati Member outcrop at Kudat Peninsula may give an idea on the presence of oil seepage in this area. Petrography analysis shows Sikuati area is dominated with detrital quartz, feldspar arkose and lithic arkose. A detailed geochemical analysis of source rock sample and oil seepage from Sikuati area was carried out for their characterization and correlation. Hydrocarbon prospectivity of Sikuati Member source rock is poor to good with Total Organic Carbon (TOC) value of 0.11% to 1.48%. and also categorized as immature to early mature oil window with Vitrinite Reflectance (VRo) value of 0.43% to 0.50 %Ro. Based on biomarker distribution, from Gas Chromatography (GC) and Gas Chromatography-Mass Spectrometry (GC-MS) analysis, source rock sample from Main Road (Sample 5.1) shows Pr/Ph, CPI and WI of 2.22 to 2.68, 2.17 to 2.19 and 2.46 to 2.74 respectively indicates the source rock is immature and coming from terrestrial environment. Steranes and diasteranes distribution interpreted shows that the source rock evolved from planktonic/land plant organic matter with clastic-clay rich influence occurred at distributive fluvial system or lacustrine environment. Meanwhile, oil seepage from Pool 1 shows Pr/Ph, CPI and WI of 5.63, 1.04 and 2.18 respectively indicate that the oil is coming from mature and oxidizing environment. The source rock might be rich in carbonaceous material organic matter resulting from planktonic/bacterial activity which occurs at fluvial to fluvio-deltaic environment. Overall, the source rock from outcrop level of Kudat Peninsula is moderately prolific in term of prospectivity and maturity. However, as go far deeper beneath the surface, we can expect more activity of mature source rock that generate and expulse hydrocarbon from the subsurface then migrating through deep-seated fault beneath the Sikuati area.