The Role of Biostratigraphy in Exploration-Led Play Prediction: The Importance of Regional Subsurface Chrono-Sequence Stratigraphy in Rapid Basin Evaluation, Barmer Basin, Rajasthan, India

Sarah L. Bower, Jenna L. Brady, and Richard Frost
Cairn Energy, Edinburgh, United Kingdom

Cairn Energy is actively exploring in the Barmer Basin, Rajasthan with over 100 exploration and appraisal wells drilled to date, more than 12 discoveries including the billion barrel STOIIP Mangala discovery. The continuing challenge is to unlock the remaining potential of the area using predictive, adaptable, play evaluation techniques.

Cairn has applied a fast-track approach to developing and understanding the subsurface of a virgin basin by the early adoption of a biostratigraphically calibrated stratigraphy. The basic scheme was derived from the first 9 wells drilled in the Barmer Basin between 1999 and July 2003 recognising subtle marine influences and applied a genetic sequence stratigraphic approach.

Candidate maximum flooding events were identified from wireline facies and calibrated using cuttings based palynology, micro and nanno-palaeontology. These were correlated regionally and tested almost immediately as new wells were drilled. The scheme was designed from the outset to have internal flexibility, allowing for anticipated differences between hanging-wall and foot-wall settings and future refinement.

The framework was expanded to 16 wells by January 2005, and a further five wells added by October 2005 confirming much of the initial framework and reconciling existing outcrop stratigraphy with the subsurface dataset.

The framework has provided a firm foundation for the creation of gross depositional environment maps for play prediction, assisting in the direction of the on-going drilling campaign. Substantial parts of the basin remain to be explored and this will be the challenge to the stratigraphic scheme as new areas and more unconventional plays are appraised.