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Seismic Evaluation of the Mangala Field Through High Density 3-D - Barmer Basin, Rajasthan, North West India

Shiju C. Joseph, Graham Bowyer, and Michael Micenko
Reservoir Development, Cairn India Limited, Gurgaon, India

The world class Mangala Oil Field was discovered in the northern Barmer Basin of Rajasthan in January 2004. Following the drilling of appraisal wells, 3D seismic acquisition and major data gathering efforts, Mangala was confirmed as the largest oil discovery in India since 1985.

The Mangala structure is one of a series of simple, tilted fault blocks, bounded to the north and west by intersecting faults with strong dip closure to the south east. Although the structure is relatively simple the current PSTM seismic dataset using conventional acquisition and processing parameters provided relatively poor imaging at the crest due to shallow geological variations.

A high density 2D test acquired in 2005 over the crest with 8m acquisition station spacing provided non-aliased spatial sampling of much of the noise, which facilitates the use of better digital noise suppression filters. A shallow, thick low velocity layer below a high velocity layer was discovered on the western part of the main bounding fault during the deep uphole campaign. The combination of the closer trace spacing and the better static model gave encouraging results in imaging the main bounding fault, thereby reducing the uncertainty on the fault positioning and improving the vertical resolution at the reservoir level.

Subsequent to the test line, a 120 sq. km high density 3D survey was acquired to obtain a fully migrated, full fold image of the reservoir with a short shot and receiver interval and high trace density. Currently the volume is under the final stage of state-of-art PSTM processing. This volume will be used for reservoir characterisation for the optimal placement of development wells and will also be the baseline survey for future time lapse studies.

Presentation GEO India Expo XXI, Noida, New Delhi, India 2008©AAPG Search and Discovery