A subsidiary of Exxon Mobil Corp. has moved an ultra-deepwater drillship into Nigerian waters to begin drilling work aimed at adding as much as 40,000 barrels a day of oil production from an ageing offshore field, part of a $1 billion push by the operator and its partners to squeeze more output from existing infrastructure rather than sink capital into discoveries.

Esso Exploration and Production Nigeria (Offshore East) Ltd., the Exxon unit that operates the Usan field in Oil Mining Lease 138, said the Noble Gerry de Souza has arrived offshore to launch what it’s calling the Usan Infill Project.

The drilling campaign is designed to be a short-cycle investment, with the company targeting the incremental barrels within 18 months — a relatively fast turnaround for deepwater work, where projects often take years to move from sanction to first oil.

The move adds to a string of bets by international oil majors that Nigeria’s fiscal and regulatory climate has improved enough to justify fresh capital, after years in which companies including Exxon, Shell Plc and TotalEnergies SE either scaled back onshore exposure or sold assets amid security concerns, pipeline theft and disputes over contract terms in the West African nation’s oil-rich Niger Delta and offshore blocks.