New Delhi, April 12: ONGC has failed to discover oil and gas in the offshore region south of the Sundarbans. The company has transferred the rig it hired to drill in the region to the Mahanadi basin where there is a better chance of discovering hydrocarbons.

An ONGC official told The Telegraph that the well drilled near Sagar Island, about 150 km from Calcutta, had not thrown up any worthwhile discovery, forcing the company to abandon operations for now.

The official said the terrain was not conducive to drilling. ?The water depth is hardly 10 metres and there is a lot of sediment which makes the ground very slushy? it becomes difficult to move equipment and material in the area,? he explained.

The rig tends to sink in the mud which makes it very difficult to undertake exploration. However, ONGC may come back to drill later, the official said.

He said drilling costs were also very high as the rig, Transocean Nordic, was hired on a time-charter basis. More drilling can be undertaken in the same time in blocks where it is easier to operate.

He said the environmental conditions in the exploration block on the Bengal coast were different from other onland and offshore blocks in the country.

In the initial stages, ONGC encountered high gas pressure, and company chairman Subir Raha was mildly optimistic about a discovery.

After drilling for 4,000 metres, the rig encountered a high pressure gas zone which posed a technical difficulty in continuing the operations to a greater depth.

Inclined drilling was then taken up to bypass the zone and reach a depth of 5,000 metres.

ONGC officials observed that the geological structure of the block in Bengal was similar to Myanmar, where huge quantities of gas were discovered, encouraging the company to undertake exploratory drilling. However, the results of the first well have turned out to be a disappointment.

ONGC has hired three foreign drilling rigs, including Transocean Nordic. The company also owns some rigs.

In March last year, ONGC made a significant gas discovery in the Krishna Godavri basin in the deep sea KG- OS-DW-IV block off the Andhra coast, using the hired rig Discoverer Seven Seas.

More wells are now being drilled to ascertain the quantity of in-place reserves.