Correlation Problem in Miocene Sediments of Kumchai Oil & Gas Field of Upper Assam Basin (India) and a Unique Method of Correlation Adopted in Field Development Study Based on Heavy Mineral Assemblage — A Case Study

Deb, Sasanka S.¹; Barua, Indrajit ¹; Borgohain, Romem ¹
(1)Geology & Reservoir, Oil India Limited, Duliajan, India.

Subsurface correlation plays a vital role in field development and from a reservoir management point of view in a hydrocarbon bearing area. There are different methods of correlation used in present day Geoscientific studies viz lithostratigraphic, chronostratigraphic and biostratigraphic , highly resistive layer, palaeosol layer and high density rock layer correlation .However, in certain cases, particularly at the reservoir scale none of these methods are able to provide a practical solution in subsurface correlation, and very local factor/factors can play an important role in providing a workable solution in subsurface correlation. Such a local factor viz. ''Heavy mineral assembly'' has played an important role in subsurface correlation in a structure with hydrocarbon potential of Upper Assam Basin (India)

The study area comprises the Kumchai Structure, which is a deep seated domal anticline and located in the foot hill of eastern Himalaya. The majority of wells drilled in the area have shown multiple hydrocarbon prospects. Study indicates that the density of the sediments in the hydrocarbon bearing Girujan formation of Pliocene age vary from 2.05-2.35 gm/cc. However, a few discrete streaks/layers with more than 2.4 gm/cc density have been observed. Sedimentological analysis indicates that the heavy mineral assemblage is responsible for these high density streaks. Three such high density streaks have been utilized for correlation of reservoirs and sedimentary layering purpose.

A correlation scheme based on established methods is very difficult in the Kumchai structure. More than thousand meters of sediments with hydrocarbon bearing zones of less than hundred meters are distributed throughout the litho-column and this necessities the grouping of sediment for proper understanding of the fluid distribution pattern for field development purpose. Correlation based on high density spikes have very good resemblance with the prominent seismic horizons of the area. Hydrocarbon distribution pattern shows a very good match with the sand grouping based on these density streaks. Therefore, based on this study, reservoir management and future development strategy of the area can be planned.

This correlation scheme can be useful for strata correlation in other part of the globe in similar type of depositional setting.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.