As India’s petroleum ministry prepares to announce the country’s shale gas policy, state-run ONGC Ltd. is firming up plans to explore shale gas prospects in four basins – Damodar, Cambay, Krishna Godavari (KG), and Cauvery – in India.

“The deeper formations in all these basins, which are known to possess high organic richness and maturity to gas window level, are considered potential for shale gas exploration and exploitation,” said Sudhir Vasudeva, ONGC chairman and managing director.

ONGC has established the Centre of Delivery of Shale Gas to pursue business opportunities in shale gas sector in India. The company also has partnered with ConocoPhillips. The two have entered an agreement for shale gas projects in India and North America.

“India has a lot of potential in shale gas. We want to exploit that with the technical expertise of ConocoPhillips," ONGC's Vasudeva said.

After the discovery of shale gas in Damodar basin, ONGC began working with ConocoPhillips on the plans to launch exploration activities in the Damodar, Cambay, Krishna Godavari, and Cauvery basins. The four basins are considered to be the most prospective shale gas zones with estimated reserves of about 63 Tcf.

Pilot project

ONGC, in collaboration with global technology provider Schlumberger, carried out a pilot project which produced shale gas from the Permina-age Barren Measure shale formation in the Damodar basin. The first well (RNSG-1) of the two, drilled to a depth of 2,000 m (6,562 ft) at Icchapur village in Raniganj zone, encountered Barren Measure shale from 985 m (3,232 ft) to 1,843 m (6,047 ft). Gas flowed from an interval at a depth of around 1,700 m (5,577 ft) in Barren Measure shale after hydrofracturing.

A company official claimed the gross thickness of more than 800 m (2,600 ft) of gas indicates the presence of significant shale gas reserves in the Raniganj area. The shale gas flowed from RNSG-1 well is believed to have total organic compound (TOC) and thermal maturity higher than the initial estimate of 4.5% and 1.20%, respectively.

Based on the two wells’ data and its integration with the available geological and geophysical data, Schlumberger estimated a total of 48 Tcf of gas resources in the Barren Measure shale. The other two wells drilled in North Karanpura are not found to be encouraging, as only absorbed gas has been shown to exist.

“Integrated study suggests risked shale gas resource of about 48 Tcf in Damodar basin, of which about 10 Tcf could be technically recoverable against the EIA (Energy Information Administration) estimate of 7 Tcf,” Vasudeva said.

The EIA’s estimate of shale gas reserves in Damodar basin was based on available conventional data not on actual shale specific data, he said.

The prospective area for Barren Measure shale in the Damodar basin is spread across an area of 2,797 sq km (1,080 sq miles) in the Raniganj, Bokaro and Karanpura sub-basins. The prospective area in Raniganj covers an estimated 1,683 sq km (650 sq miles), 285 sq km (110 sq miles) in Bokaro, and 829 sq km (320 sq miles) in Karanpura.

Prospective basins

With encouraging results from the Damodar basin pilot study, ONGC is planning to launch exploration activities in three other prospective basins – Cambay, Krishna Godavari, and Cauvery.

The company’s exploration teams already have identified potential exploration sites in these basins. The Cambay basin in Gujarat is the largest basin in the country, spread across 51,800 sq km (20,000 sq miles), with a prospective area of 2,435 sq km (940 sq miles). As per the initial studies, around 20 Tcf of gas is estimated as technically recoverable reserves in the basin. The average depth of occurrence of shale in the Cambay basin is about 42,651 m (13,000 ft). The thickness varies from 5,249 m (1,600 ft) to 16,076 m (4,900 ft) with average TOC of 3% and thermal maturity of 1.10%.

Krishna Godavari basin, located in eastern India, is considered to hold the largest shale gas reserves in the country. It extends across 20,202 sq km (7,800 sq miles), with a prospective area of around 11,241 sq km (4,340 sq miles). The basin is estimated to have around 27 Tcf of technically recoverable gas. The average depth of occurrence of Raghavapuram shale is 37,730 m (11,500 ft) with average TOC of 6% and thermal maturity of 1.60%.

The Cauvery basin in Tamil Nadu state, spread across 23,569 sq km (9,100 sq miles), has prospective area of 2,603 sq km (1,005 sq miles). It is estimated to have recoverable shale gas reserves of 7 Tcf. The average depth of occurrence of Andimadam shale is 32,808 m (10,000 ft) with average TOC of 2% and thermal maturity of 1.15%.

Other basins, including Assam Arakan, Pranhita Godavari, Satpura, Son Mahanadi, Vindhyan, and Rajasthan, also are considered to have potential shale gas reserves. Largely unexplored,their reserve estimates are not known.

The EIA estimates that Damodar, KG, Cambay, and Cauvery have total shale gas resources of 290 Tcf, of which 63 Tcf is considered technically recoverable.

The Cambay, Cauvery, and Krishna Godavari frontier basins have technically recoverable shale gas resources of 6.1 Tcf, the US Geological Survey (USGS) said in a 2011 study.

However, Vasudeva disputes the EIA and USGS estimates, saying the numbers are higher. “There is a huge scope of upward revision of the EIA estimates of 63 Tcf for the country, which are merely based on the available conventional data from these basins.”

Schlumberger has indicated a shale gas resource base of between 600 Tcf and 2,000 Tcf in seven hydrocarbon-producing sedimentary basins in India. This puts India in the list of shale gas prospective regions in the world.

New policy norms

ONGC is waiting for Indian authorities to release policy regulating shale gas exploration and development. The petroleum and natural gas ministry already has prepared the policy and moved it to the Cabinet for approval.

“We are ready with our shale policy and can announce it any time,” said Petroleum Minister Veerappa Moily. “The shale gas policy will provide necessary impetus to the exploration activities and eventually pave the way for increased domestic supplies of natural gas.”

A petroleum ministry official said the new policy would allow state-run oil and gas companies to look for shale gas in blocks allocated before the exploration licensing policy changes took effect in 1999. New blocks, however, will be awarded by competitive bidding.

The regulator, the directorate general of hydrocarbons, has identified more than 70 blocks with potential shale gas reserves for exploration and development. They are located in the Cambay, Assam Arakan, Gondwana, Krishna Godavari, Cauvery, and Indo-Gangetic basins.

The petroleum ministry says there is a need to vigorously explore for unconventional or alternate hydrocarbon resources like shale gas and CBM to bridge the increasing shortage of gas supplies in the country, which is expected reach 232 MMcm/d by March 2017 from around 143 MMcm/d in 2013.