India’s ONGC Ltd. is evaluating hydrocarbon prospects located beyond the continental shelf of Mumbai High in the Arabian Sea after the discovery of gas.
The state-run explorer has lined up a plan to drill five appraisal wells in the shallow-water MB-OSN-2005/3 Block, located southwest of the Mumbai High-Deep Continental Shelf platform in the Mumbai Offshore Basin.
This also will be the company’s first exploration play in the Shelf Margin area of the Mumbai Offshore Basin.
The plan involves drilling five appraisal wells, with a target depth of up to 1,300 m (4,265 ft), at identified locations in the block over the next 24 months. They are: MBS053NAB-A with a target depth (TD) of 1,750 m (5,741 ft), MBS053NAC-A with a TD of 1,900 m (6,234 ft), MBS053NAD-A with a TD of 1,750 m (5,741 ft), MBS053NAE-A with a TD of 1,650 m (5,413 ft) and MBS053NAF-A with a TD of 2,300 m (7,546 ft).
“[The] drilling depth will be 1,650 m to 2,300 m [5,413 ft to 7,546 ft]. Water-based/SOBM [synthetic oil-based mud] will be used as a drilling fluid,” ONGC said in a report. The estimated cost of each well will be Rs 1.40 billion (US$20.3 million).
These wells will be drilled in water depths ranging from 102 m to 107 m (335 ft to 351 ft).
Drilling locations were identified based on interpretation studies of 2-D and 3-D seismic data collected by the operator in 2015.
In February ONGC made a gas discovery in the first exploratory well, MBSO53NAA1, in Block MB-OSN- 2005/3. Testing of object-I in the interval between 932 m and 938 m (3,058 ft and 3,077 ft) and object-II in the interval between 581 m and 583 m (1,906 m and 1,912 m) as well as between 585 m and 589 m (1,919 ft and 1,932 ft) flowed gas at 47,128 cu. m/d (1.6 MMcf/d) and gas at 21,282 cu. m/d (751,567 cf/d), respectively, through a 1⁄2-in. choke from the Chinchini Formation of Pliocene age.
This marked the first discovery beyond the shelf margin and in the Pliocene Formation of the Mumbai Offshore Basin.
The discovery is significant geologically because it’s the first on the west coast in the Pliocene formation, with reservoir depths at about 1,000 m (3,280 ft). The presence of gas at a shallower depth could significantly bring down both costs and time needed to commercialize the discovered oil and gas, thereby ensuring quicker access to potential gas reserves.
The reservoirs in Mumbai Basin are generally located at a depth of 2,000 m to 2,500 m (6,562 ft to 8,202 ft).
If the discovery is deemed commercial, the operator said it would consider using existing infrastructure to transport extracted oil and gas from these fields.
The initial estimate of total resources is between 9.9 Bcm and 14 Bcm (350 Bcf and 500 Bcf).
MB-OSN-2005/3, spread across an area of 1,685 sq km (650.5 sq miles), falls in the Shelf Margin Block of the Mumbai Offshore Basin. It is bounded to its west by the Kori-Comorin ridge and on the east by the Paleocene hinge. The NW-SE trending local depression of the Eocene and Oligocene age within the Shelf Margin Block has accommodated good quality, potentially matured source rock deposited under restricted marine environment.
In the Shelf Margin Basin, gravity driven tectonic activity has deformed sedimentary sequences resulting in episodic folding, faulting and shale diapirism during the period from Oligocene to Pliocene thus forming a thick sequence of ponded sediments that represent a wide range of depositional processes.
Hydrocarbons discovered in the five other blocks of the Mumbai Offshore Basin are related to the L-III limestone reservoir of Miocene age (Mumbai High), early Oligocene (Mukta), middle Eocene (Bassein), Paleocene to early Eocene reservoirs (Panna) and early Miocene-late Oligocene (Daman).
ONGC as the operator holds a 70 % participating interest in the MB-OSN-2005/3 Block, which was awarded in 2008. Essar Exploration Ltd. holds the remaining 30% interest.
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