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1 R&D Centre, Oil India Limited, Duliajan, Assam 786 602, India; rnd{at}oil.asm.nic.in
2 Directorate General of Hydrocarbons, HT House, K. G. Marg, New Delhi 110 001, India; srinivasan_raju{at}hotmail.com
3 R&D Centre, Oil India Limited, Duliajan, Assam 786 602, India; tgk{at}oil.asm.nic.in
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.
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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