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Source Rock Potential and Evolution of Tertiary Strata, Pattani Basin,
Gulf of Thailand1
R. M. Bustin and A. Chonchawalit2,3
The Pattani Basin in the Gulf of Thailand
contains a 10-km-thick succession of synrift upper Eocene-lower Miocene,
mainly nonmarine clastics and lower Miocene-Holocene postrift marine and
nonmarine clastics. Rock-Eval® pyrolysis, organic petrography,
and thermal history analyses are used to evaluate the petroleum source
rock potential and generative history of the strata. The organic matter
is dispersed, terrestrially derived, type III kerogen with minor type II
kerogen, and consists primarily of vitrinite. The average total organic
carbon (TOC) contents are generally low to moderate (0.2-1.4 wt. %). The
hydrogen index (HI) averages 100 mg HC/g TOC, the hydrocarbon potential
ranges from 0.01 to 2.5 mg HC/g rock, and the quality of the organic matter
ranges from 0.13 to 1.9 mg HC/g TOC. Abundance and character of organic
matter vary both laterally and vertically across stratigraphic units. Within
stratigraphic units, the lowest TOC and HI values occur in high-energy
sediments, such as alluvial-fan and braided-stream deposits, likely reflecting
both low organic input and a low degree of preservation. Higher TOC and
HI values occur in low-energy flood plain, interdistributary bay, and shallow-marine
deposits due to the proximity of these sediments to marshes and swamps
containing abundant organic matter, and to a greater degree of preservation.
Negative correlation between TOC and sedimentation rate in some units reflects
the effect of clastic dilution.
1997. The American Association of Petroleum Geologists. All rights reserved.
received July 17, 1996; revised manuscript received December 10, 1996;
final acceptance July 17, 1997.
of Earth and Ocean Sciences, University of British Columbia, Vancouver,
BC, Canada V6T 1Z4.
Address: 39/98 Moo Baan Suanthong, Lad Plakhao Road, Bang Khen, Bangkok,
thank UNOCAL Thailand for providing access to samples, well logs, and seismic
data. This study was supported financially by the Canadian International
Development Agency and a Natural Sciences and Engineering Research Grant
(Canada) to Bustin. We thank Michelle Lamberson for her comments on an
earlier copy of this paper and Matt Bustin for his editorial assistance.
Journal reviewers B. J. Katz and L. Snowdon are thanked for their constructive
critique of the manuscript.
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