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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
(Begin page 309)
AAPG Bulletin, V.
Improved identification of pay zones through integration of geochemical
and log data: A case study from Upper Assam basin, India
N. Mathur,1 S. V. Raju,2 T. G. Kulkarni3
1R&D Centre, 
Oil
India Limited, Duliajan, Assam 786 602,
India; email: [email protected]
2Directorate General of Hydrocarbons, HT House, K. G. Marg, New Delhi 110
001, India; email: [email protected]
3R&D Centre, Oil India Limited, Duliajan, Assam 786 602, India; email: [email protected]
AUTHORS
Neeraj Mathur received his M.S. degree in chemistry from the
Indian Institute of Technology, Delhi, in 1984. Since 1985, he has been with the
Geochemistry Section of Oil India Limited and is presently working as a superintending
research scientist. His research interests include oil-oil correlation studies using light
hydrocarbon parameters, reservoir geochemistry, crude oil characterization, and source
rock evaluation. He is a member of the European Association of Organic Geochemists.
S. V. Raju is a deputy chief research scientist in the
Geochemistry Section of Oil India Limited and is presently on deputation to the
Directorate General of Hydrocarbons, New Delhi. He has been with Oil India Limited since
1983. He previously worked for three years as a scientist with the Department of Atomic
Energy. He also worked as a research fellow at Osmania University, Andhra Pradesh, India,
where he received his Ph.D. in geology. He is a member of the Geological Society of India,
European Association of Organic Geochemists, and Indian Society of Applied Geochemists.
His current research interests include application of geochemistry in petroleum
exploration
T. G. Kulkarni received his M. S. degree in chemical
and petroleum engineering from University of Calgary, Alberta, Canada, in 1983. He is
working as a deputy general manager (R&D) for Oil India Limited, and his research
interests are geochemical exploration techniques, production technologies for oil and
natural gas, oil field chemicals, and synfuels.
ACKNOWLEDGMENTS
We thank the management of Oil India Limited for permission to publish
this article. Constructive reviews by Mark McCaffrey and an anonymous reviewer helped us
greatly in improving the article.
ABSTRACT
The upper Paleocene-lower Eocene clastic reservoirs constitute one
of the most important hydrocarbon-producing horizons in the Upper Assam basin of northeast
India. These reservoirs are characterized by the presence of (1) normal gravity oil
(23-31° API), (2) low to intermediate gravity oil (13-23° API), and (3) gas and light
oil/condensate (> 31° API). The sandstone reservoirs show complex wire-line log
signatures, which are commonly misleading. The main impediments to understanding the
nature of reservoir fluid include (1) distinguishing low gravity, intermediate gravity,
and normal gravity oil-bearing zones and (2) resolving the problem of density
(RHOB)-neutron porosity (NPHI) crossover for gas-bearing, as well as oil-bearing,
reservoirs.
Geochemical analyses of sidewall core extracts by thin layer
chromatography with flame ionization detection (TLC-FID) and gas chromatography (GC)
provide valuable, cost-effective input for reservoir fluid characterization. The important
parameters needed to identify the nature and composition of the reservoir fluid include
(1) the bulk composition of the sidewall core extract (i.e., % saturated hydrocarbons, %
aromatic hydrocarbons, and % resins + asphaltenes), (2) amount of extract in mg/g of rock,
(3) GC fingerprint, and (4) the ratio of pristane to n-C17. These parameters,
integrated with geological and geophysical (wire-line logs) evidence, yield more accurate
and reliable formation evaluation criteria. The technique is simple and inexpensive and
may find application as an additional formation evaluation tool in any geological setting.
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