Eo-Oligocene Oil Shales of the Talawi, Lubuktaruk, and Kiliranjao Areas, West Sumatra: Are they potential source rocks?

Abstract

To anticipate the increasing energy demand, additional data and information covering unconventional fossil fuels such as oil shale must be acquired to promote the usage of alternative energy sources to crude oil. The Talawi and Lubuktaruk regions situated within intra-montane Ombilin Basin, and the Kiliranjao area assumed to be located in a small intra montane Kiliranjao Sub-basin are occupied by Eo-Oligocene sediments of Sangkarewang and Kiliran Formations, respectively. Field activity, geochemical screening techniques, and organic petrographic analysis, supported by SEM mode, are methods used. Most of the oil shale sequence is typically of an organically rich-succession comprising predominantly well-bedded, laminated and fissile, brownish to dark grey organic-rich shales and mudstones. The exinite macerals within oil shale comprise mainly Pediastrum-lamalginite with minor cutinite, resinite, liptodetrinite, sporinite, bituminite, and rare Botryococcus-telalginite. Therefore, the oil shale deposits can be described as "lamosites". Minor vitrinite maceral is also recognized. TOC analysis on selected shale samples corresponds to a fair up to excellent category of source rock characterization. The kerogen is suggested to be of mixed Type II and Type I autochthonous materials such as alginite, with minor allochthonous substances. Oil samples collected appear to be positioned within more oil prone rather than gas prone. Thermal maturity of the oil shales tends to show an immature to marginally/early mature stage. By evaluating all the results of geochemical and organic petrological analyses conducted on shale lithologies (shale and mudstone), it can be concluded that the oil shales in those areas are effective source rocks having a favourable potential for generating shale oil or gas to be included as alternative energy resources in the future.

Climatic control on primary productivity changes during development of the Late Eocene Kiliran Jao lake, Central Sumatra Basin, Indonesia

“…K, Mg and Na account only in minor amount (b1%). The high amount of Ca in the shale confirms that Paleogene source rocks in the most depocenters of the basin are typically calcareous as previously reported by Iqbal et al (2014), Sunardi (2015). The occurrence of carbonates in the lacustrine Kiliran Jao oil shale is interesting and will be discussed elsewhere.…”

“…The general sediment succession of the Kiliran Jao Sub-basin is presented in Fig. 2b based on Iqbal et al (2014), Sunardi (2015) and the references therein. The pregraben paleosol most probably corresponds to the Lower Red Beds Fm.…”

Mechanical properties of Indonesian organic-rich shales from the Central Sumatra and North Sumatra Basin, and comparison with US shales

“…The quarry samples belong to the Kiliran Jao/Pematang Formation of the Kiliran Jao Sub-basin (e.g., Iqbal et al, 2014;Sunardi, 2015;Widayat et al, 2016) and the Sumatran highway samples belong to the Sangkarewang Formation of the Ombilin Sub-basin (e.g., Koesoemadinata and Matasak, 1981). We classify samples of the Kiliran Jao Formation based on their lithofacies into mudstone (MDS), massive mudstone (MAS), papery laminated shale (PAP; Widayat et al, 2016), sandy mudstone (SDM), and sandstone (SST).…”

The Lithofacies Association of Brown Shales In Kiliran Jao Subbasin, West Sumatra Indonesia

“…Several researchers, i.e. Carnell et al (1998), Aswan et al (2009), Widayat et al (2013), and Iqbal et al (2014 concluded that the Eocene-Oligocene sediments in Kiliran Jao Subbasin was deposited in lacustrine to brackish environments associated with a coal deposition.…”