Pre-Cenozoic Petroleum System Evaluation from the Aruah Islands Outcrops
Abstract
A geological field work in Aruah Islands as part of JointStudy in Rupat Area was conducted in 2020 for an evaluation of Greater Central Sumatra Basin hydrocarbon potential. The island is located about 68 kilometers from port of Bagan Siapiapi, situated at the border of Indonesia’s territory and Malaysia in Malacca Strait.
Field observation and rock samples collection were done to provide new data set. The geological field work visited three islands, they are Jemur, Sarang Elang, and Labuhan Bilik Islands. Stratigraphic measured section, structural geology measurement, and sample collection were the main geological field works and conducted at the Jemur Island. The islands lithology is sedimentary assemblage, no granite or crystalline limestone found as originally expected. The sedimentary lithology is dominated by amalgamated quartz sandstone beddings succession with (black) shale interbeds. It is interpreted as dominantly deep-water mass-transport deposits. The outcrop’s total measured thickness is approximately 360m thick of stratigraphic record with total of 18 hand specimens were collected. Homoclinal folding structure with general dip above 45o was observed as the result of tilted (compressional) tectonic regime. High degree of fractures density is dominated by pure shear (extensional) tectonic regime. Field interpretation suggested a lithology of PreCenozoic basement, as part of Sibumasu Terrane (fragment of Gondwana Supercontinent, Metcalfe, 2014) that becoming microplate basement of northeastern part of Central Sumatra Basin. Laboratory analyses are included geochemistry, biostratigraphy, petrography, and mineralogy examinations.
Pre-Cenozoic basement lithology implies an opportunity for presence of reservoir and source rock that potentially becomes a possible secondary petroleum system in the Rupat Area (Greater Central Sumatra Basin).
(+) Presence of sandstones as poor to medium quality reservoir.
(+) Presence of black shale as possible source rock type lithology.
(-) Geochemistry analyses so far do not support capability of the black shale as productive source rock. Further data acquisition is required to provide more comprehensive geochemistry analysis.
