The Discoveries of the Barmer Basin, Rajasthan, India

Whiteley, Nicholas J.; Burley, Stuart; Ananthakrishnan, B.; Ginger, David
Cairn India, Gurgaon, India.

The RJ-ON-90/1 PSC in the Thar Desert of Rajasthan, North-West India, was signed in 1995. This remote & arid area had no modern seismic, no proven hydrocarbon system and only 3 Exploration wells, all dry. The only indications of the presence a possible basin were from surface outcrops, poor quality gravity data, and a Tertiary hydrocarbon rift basin (the Cambay Basin), 300km to the South.

Regional 2D seismic identified a possible basin, and was confirmed by the disappointing first exploration well (Guda-1). However the second well, Guda-2, encountered oil in the shallow syn-rift section demonstrating a working hydrocarbon system, although reservoir presence and quality remained major risks. New seismic & interpretation, and integration of outcrop studies with well data suggested that better reservoir quality might be present in the northern part of the basin.

A further four exploration wells validated the reservoir, trap, charging and seal in the Barmer Basin and proved that a mature and prolific lacustrine source rock existed. It was also recognised that the northern parts of the basin had been uplifted and that the source rock facies extended into this part of the basin and had been previously buried sufficiently to reach oil maturation.

Exploration focus then headed north where better reservoir was expected. The NB-1 well drilled in 2004 (16th well in the basin) targeted a large simple structure tilted fault block, some 60 kilometres north of the earlier discoveries, and encountered 2 pay zones. The basin changing reservoir was the Fatehgarh Formation, with a total net pay of about 85 metres and an average porosity of 25% and water saturation in the range of 10%. This discovery was renamed as Mangala and contains STOIIP of over a billion barrels.

This discovery unlocked the basin and subsequent exploration drilling resulted in over 25 discoveries at a success rate of ~50% in 7 reservoir intervals. This proved around 4 billion barrels of oil (STOIIP) and >1 trillion cubic feet (TCF) in the basin at a finding cost of less than 1 USD/bbl. This prolific basin has a significant undrilled portfolio with recognised additional risked potential of over 2.5 billion barrels (STOIIP).

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