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High Resolution Correlation of Facies between Closely Spaced Wells and its Impact on Water Injection and Oil Production: A Pilot Study for Chemical EOR in Fluvial Reservoirs from the Mangala Field, Barmer Basin, India

Singh, Amit P.¹; Sunder, Vatai R.¹; Raine, Robert J.²; Taylor, Andrew M.²; Gould, Thomas²
¹Cairn India Ltd., Gurgaon, India.
²Ichron UK, Chester, United Kingdom.

The Mangala Field is the largest discovered oilfield in the Barmer Basin of north western India containing over 1 billion barrels in place of moderately viscous crude oil. The base development plan is a hot waterflood, but due to the adverse mobility ratio between injected water and in situ oil, large volumes of water will be produced over the field life along with the oil. As a result, aqueous-based chemical Enhanced Oil Recovery (EOR) treatments are being evaluated which has the potential to significantly improve the Estimated Ultimate Recovery (EUR) by 15%.

The EOR pilot was executed by drilling nine wells in a quadrant with 40 to 100 m spacing to evaluate polymer and ASP floods. Five of these wells were cored (~393m recovery), with comprehensive core description, conventional core analysis and petrographic studies being undertaken. Cores acquired in these wells helped in building a facies association model to better understand the heterogeneity within low-sinuosity single storey fluvial channels. The test area was then subjected to dynamic testing, with hot water injection and resulting production monitored over time. The close spacing of the cores enabled the influence of channel incision and channel belt width to be assessed.

The depositional system was primarily controlled by water table fluctuations, which culminated with replacement of fluvial deposits by regional-scale lake deposits. Increasingly sheet-like sand bodies are present towards the top of the fluvial succession, where the high water table was likely to have promoted lateral channel migration or avulsion. Channels lower in the succession are more incised and mapping indicates vertical channel connectivity outside the pilot area. The close spacing of the cores has enabled the definition of reservoir quality and facies changes at the margins of the channels and their transition into crevasse deposits and floodplain muds. Primary controls on reservoir quality include grain size, sediment source, and silt/clay content. Secondary controls (post deposition) are also significant and include pedogenesis, grain dissolution and diagenetic history.

The close spacing of the study wells enabled the understanding of vertical pressure isolation between the sheet-like sand bodies towards the top of the fluvial succession and the underlying fluvial channel sands. Data from core analysis is being used to construct a high resolution geo-cellular model which will be extended to a field-wide model.

 

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012