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Perched Water in the Barmer Basin, India - Recognition and Implications

O'Sullivan, Timothy; De, Manidipa; Arora, Khushboo; Whiteley, Nicholas J.; Guttormsen, Joel; Dolson, John
Cairn India, Gurgaon, India.

The Barmer Basin is an Indian Tertiary rift basin. Economic hydrocarbons have been found identified in a number of geological facies, ranging from low sinuosity fluvial sandstones to lacustrine turbidites. It is within the turbidite mound complexes that perched water has been identified within the basin. In the petroleum context, perched water is "free water" that is contained within the hydrocarbon column and this water was unable to escape from the reservoir during the time when hydrocarbons were filling the trap. Typically, water moves downwards out of the trap as the more bouyant hydrocarbons displace it. If a very good basal and lateral seal is present, then water from cannot be expelled from the reservoir. Turbidite channels within slope/fan deposits are the units in which perched water often occurs. The turbidite channels are often encased in deep water muds which restrict the downward and lateral movement of the free water. This paper highlights examples of perched water in the turbidite facies of the Vijaya/Vandana fields within the Barmer Basin. The steps in the identification of perched water are presented in detail. Using a combination of wireline pressure interpretation and saturation height modelling, perched water can be correctly identified and distinguished from the water in transition zones and paleo oil-columns. Areas in which all three high water saturation types are present, a)perched water, b)transition zones and c)paleo oil-columns are often very difficult to unravel and the correct identification of each water type is fundamental to the assessment of a field. If unrecognised, perched water may lead to the incorrect interpretation of the geology and petroleum system of an area. Often the various hydrocarbon/water contacts are interpreted as isolated pressure systems which leads to an erroneous interpretation of compartmentalization with the ensuing downgrading of reserves and the reduction in economic viability of a field. With perched water, it is the various hydrocarbon/water contacts that are the anomaly and the whole complex is within one pressure system. Once perched water is recognized the economic viability of an area can be enhanced. This paper outlines the process of accurate identification of perched water so that the full potential of the areas involved could be realized.

 

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

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