Lithology Effect on Total Organic Content, Maturity Level and Depositional Environment of Pemaluan Formation as a Shale Gas Bearing Formation, Kutai Basin, East Kalimantan

Abstract

Organic material content (TOC) and maturity level is very important in the analysis of shale gas. The organic material is more easily preserved in fine grain sediment such as in shale or clay, so that shale or clay is commonly used to determine TOC value and maturity levels. The organic material will become an oil and gas through the complex transformation and migrated from the source rock to sandstone reservoir, so that the organic material content in sandstone reservoir preferably will represent TOC in shale, however the shale or claystone is commonly used to determine TOC value. This study aims to understand lithology effect on organic material content, maturity level and the depositional environment of sandstone and shale (claystone) of Pemaluan Formation in the Kutai Basin, East Kalimantan. Rock-eval pyrolysis, vitrinite reflectance and GC-GCMS performed on 90 outcrops shale samples and as comparison were one sandstone sample from Rasamala-1 well. Shale samples showed an average TOC value of 1.68 wt% (kerogen type III) and confirmed as a gas bearing formation, while sandstone samples had TOC values of 0.31 wt% which is lower than the shales samples. The maturity level on the shale sample varies from immature to mature, while the sandstone sample is in the mature phase. The organic material from both samples are generated from higher plant material which is strong by terrestrial influence and deposited in transitional environment such as estuarin or fluvio-deltaic setting.