Cambay Basin (Note)

Date of discovery:
Cambay basin was first discovered in 1958. First exploratory well was drilled in the same year in Lunej near Cambay. The same well turned out to be discovery well which produced oil and gas. The first oil well was discovered in 1960 in Ankleshwar. Then after the exploration started with full fledged.

Type of structure:
Intracratonic rift grabben

Location:
The basin is located at 21° to 25°N and 71°30' to 79°30'E. The grabben is flanked in the east by aravalli range and deccan trap and in the west by saurashtra plateau.

Area:
The basin has covered area of about 56,000 sq.km

Total wells drilled:
Upto now about 2318 number of exploratory wells are drilled and out of 244 prospects 97 are found to be oil-gas bearing wells.
So the success ratio of the basin is 4.185%
Success ratio = (Oil-gas bearing well / Total number of exploratory wells)

Major tectonic blocks:
• Patan - Sanchar
• Ahmedabad - Mehsana
• Bharuch - Jambusar
• Narmada - Tapti
• Tarapur - Cambay

Depositional environment:
•The basement of the cambay basin is covered by the Deccan trap that was witnessed during late cretaceous.
•During Paleocene the thick sandstone and conglomerate were deposited over the Deccan trap. The Olpad formation was then marked by the unconformity.
•The unconformity was resumed by the gradual transgrassion resulting into the deposition of thick and dark shale, deposited during Early Eocene which are called as the Cambay shales. Thenafter it wa again marked by unconformity.
•During Middle Eocene, regression occured and deltas were formed, Kalol-Vasu in north and Hazad in south. In between these two delta system there is a large accumulation of oil.
•The trangression was commenced during the Late Eocene to Early Oligocene with the deposition of Tarapur shales over a large area of northern Cambay basin.
•Again the transgressive phase is followed by the regressive phase by the deposition of thick sandstones, shale alterations, limestone and claystones which together form the unit of Dhadhar formation.
• The basin is mostly covered by the alluvium which were brought by the Sabarmati, Mahisagar, Tapti and Dadhar.

New technologies/discoveries:
•Discovery of conventional energy source - shale gas in Dholka field. The technology employed there was hydraulic fracturing.
•Discovery of oil by Reliance which is 130 km in south away from Ahmedabad.
•Exploratory drilling by AWEL(Adani welspun exploration limited- Joint venture by Adani group and Welspun group) in the block which is close to Bharuch.