An ONGC Ltd.-led consortium is chasing hydrocarbon leads in the shallow waters of the MB-OSN-2005/1 Block, located in the Mumbai Offshore Basin near Saurashtra, after two exploration wells hit oil and gas.

A plan calls for drilling four more wells in north and northeastern part of the concession to assess the quantity of extractable oil and gas reserves.

“The future impetus of exploration in [the] MB-OSN-2005/1 Block is toward the north and northeast of [the] MBS051NAA structure,” ONGC said in a proposal. The “identified four prospects, which are to be evaluated in this project, will be upside to [the] MBS051NBA-1 and MBS051NAA-1 development schemes.”

The second phase exploration project is estimated to cost about $40 million.

The operator identified the drilling locations based on detailed interpretation of 3-D seismic data. The wells will be drilled to a target depth of between 2,600 m (8,530.1 ft) and 3,000 m (9,842.5 ft) in a water depth ranging from 17 m (55.77 ft) to 37 m (121.39 ft).

ONGC will target hydrocarbon prospects in the Daman Formation of upper Oligocene age.

The operator found gas and condensate in two of the four exploration wells drilled during the first phase. “Out of the four, two wells—MBS051NBA-1 and MBS051NAA-1—had commercial gas discoveries from Daman sands of Late Oligocene age,” the report said.

The first discovery well, MBSO51NBA-1, was drilled to 4,181 m (13,717 ft) in the shallow waters of the western part of the concession. The interval, between 2,596.5 m (8,518.7 ft) and 2,599.5 m (8,528 ft) in Daman Formation of upper Oligocene age on conventional testing, produced gas at 171,630 cu. m/d (6.06 MMcf/d) and condensate at 93 bbl/d through an ½-in. choke.

The second well, MBOS51NAA-1, was drilled to a depth of 3,385 m (11,105 ft) and produced gas at 250,107 cu. m/d (8.8 MMcf/d) and condensate at 255 bbl/d through 3/8-in. choke from interval between 2,549.5 m (8,364.5 ft) and 2,555 m (8,382 ft) in Tertiary Daman Formation on testing. Another interval, between 2,515.5 m (8,252 ft) and 2,526.5 m (8,289 ft) and also in Tertiary Daman formation, produced gas at 209,734 cu. m/d (7.4 MMcf/d) and condensate at 180 bbl/d through an 3/8-in. choke.

The MBS051NAA-2 well drilled to appraise the MBS051NAA-1 gas find discovered a new gas pool in Daman sandstone of Late Oligocene age. This well, drilled to a depth of 2,504 m (8215.2 ft), flowed gas at 95,275 cu. m/d (3.4 MMcf/d) with condensate at 72 bbl/day through a 3/8-in. choke from an interval of 2,462 m (8,077.4 ft) to 2,465.5 m (8,088.9 ft) in Daman Sands of Oligocene age.

The Directorate General of Hydrocarbons (DGH), the country’s upstream regulator, has approved the two discoveries in the Saurashtra concession. “The successful testing result in this [MB-OSN-2005/1] block has opened up more area for exploration of Daman plays and will help in early monetization of the discoveries of the block,” the DGH said.

The “commercial gas discoveries” made by the two exploration wells in the MB-OSN-2005/1 Block alone are considered to be enough to launch a field development plan. A senior ONGC official said that these prospects could be developed with the company’s discovered fields in neighboring acreage, such as B-9 and B-12, in a cluster method by sharing the offshore infrastructure.

A field development plan is expected to be finalized later this year after assessment of prospects in four additional wells.

The MB-OSN-2005/1 Block is located in the Surat Depression, which is known to be one of the major hydrocarbon kitchens in the Mumbai Offshore Basin. It lies on the northwestern rising flank of the Surat Depression in the southwest part of the prolific South Tapti gas field, where gas-bearing sandstone reservoirs occur within the Oligocene and Daman formations.

The offshore acreage spans 1,250 sq km (482.62 sq miles) in Saurashtra waters. The bathymetry within the block ranges from 17 m (55.77 ft) to 37 m (121.39 ft).

ONGC is the operator of the concession with an 80% participating interest and Gujarat State Petroleum Corp. Ltd. owns the remaining 20%.