Ophir Energy, the London-based company heading the Fortuna development, and Golar LNG, which operates floating LNG facilities, said Schlumberger had decided to withdraw due to problems with the project's financing.

Schlumberger was not immediately available for comment.

The Fortuna development would be west Africa's first deepwater LNG project and includes a pioneering design for the infrastructure in the form of a floating terminal that liquefies gas offshore, not onshore as usual.

Reuters reported earlier this month the growing frustration of Equatorial Guinea's government at the delays and its ultimatum to take the project off Ophir or scrap it altogether.

Golar LNG participated in Fortuna as part of the OneLNG joint venture it had established with Schlumberger.

"Despite an agreed development plan and extensive efforts over the last 12 months by OneLNG and Ophir management, it has not been possible to finalise an attractive debt financing package," Golar said in a statement.

"This, together with other capital and resource priorities, has resulted in a decision from Schlumberger to end their participation in the project," it said.

Ophir said it and Golar were both actively engaged in talks on financing the project. Ophir also suggested it was close to finding a new partner to replace Schlumberger.

"Ophir has already held informal discussions with other, well-capitalised, potential partners for our Fortuna project," it said. "Following (Golar's) announcement ... we have now formalised discussions and are actively moving forward with them."

Ophir replaced its chief executive, Nicholas Cooper, this month in a bid to get its strategy back on track. Its shares were down almost 10 percent at 56.9 pounds each at 1345 GMT while Golar's shares fell 18 percent to $28.35.

(Reporting by Sabina Zawadzki and Shadia Nasralla; Editing by Edmund Blair and Adrian Croft)