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Maceral Distribution, Thermal Maturity, Palynomorph Assemblages and Coal Facies of Loa Janan District, Kutai Basin: Hydrocarbon Generation - Implications for Cbm Exploration

Tanjung, Heri 1; Siregar, Ben 1; Pramudhita, Bayu 1; Satrio, Satrio 1; Faris, Mangku 1; Indrajaya, Rian 1; Reyby Warren2
1 Geology, Padjadjaran University, Bandung, Indonesia.
2 Student Chapter, Padjadjaran University, Bandung, Indonesia.

The coal deposits of Loa Janan occur in the Balikpapan Group and Pulaubalang Formation of Miocene age. The coal bearing formation is considered to have been deposited in transitional environments. Based on field data, the facies of coal bearing strata are deposited in upper delta to the lower delta plain with different thickness and characteristic. Graphic log from the field observation shows the differences between the upper delta with lower delta plain.

Coal petrography shows that the samples are vitrinite rich varied from 60.6 % to 79,2 %, and they consist mainly of telocollinite and desmocollinite, followed by corpocollinite, vitrodetrinite, and to a lesser extent, telinite. The inertinite group varies between 2.6 % and 15.0 %, which consist of fusinite, semifusinite, sclerotinite, macrinite, micrinite, and inertodetrinite. The last maceral group is exinite (varied between 11.4 % and 18.5 %), which consist mainly of resinite.

For mire paleoenvironment analysis, all of maceral composition were put into several petrographic indices such as wood ratio, level of oxidation, Tissue Preservation Index, Gelification Index ranging, Ground Water Index ranging from, and Vegetation Index.

Vitrinite reflectance values (Rv), varied from 0,401 - 0,508 %, and spore colour index (SCI) showing yellow colour to orange. Calorific value range from 5347 to 6857 cal/g.

Based on palynology analysis, there are four main palynomorph assemblages which are associated with hinterland, mangrove, backmangrove and freshwater environment.

On the basis of maceral content, which was put into petrographic indices, the coal of Pulaubalang was deposited in wet forest swamp with limno-telmatic condition, medium density of tree and high microbial activity. The type of mire is bog which having ombrotrophic character (solely rain-fed). The coal rank is considered to be sub-bituminous, with thermal maturity varies from immature to early mature or oil window.

However, the reflectance suppression and occurrence of exsudatinite indicates possibility of hydrocarbon generation. The low vitrinite reflectance suggested that perhydrous vitrinites absorbed mobile hydrocarbon generated in-situ from the thermally mature liptinite macerals while the associated exsudatinite represents the residual, higher molecular weight by-product. The result of this research could give an insight for CBM exploration in Loa Janan, especially due to the abundance of liptinitic maceral like exsudatinite.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009