Ophir said Schlumberger had been considering taking part in the Fortuna scheme off the coast of Equatorial Guinea and had satisfactorily completed due diligence on the project.
But it added: "Ophir and Schlumberger have been unable to complete the transaction on the terms agreed. As such, discussions between the parties have terminated."
Shares in Ophir dropped 16.5% to 76.75p.
Under the deal, Ophir would have sold half its 80% stake in Fortuna for pro-rata back costs amounting to US$300mln, which would have covered its residual 40% share of capital spending to first gas production.
Ophir said the scheme remained attractive and the Schlumberger partnership was one of several development options being considered.
It vowed to continue developing Fortuna and said the capital costs of progressing to first gas production had been further reduced to US$450-500mln gross from US$600mln.
Chief executive Nick Cooper said: "Our discussions continue with other quality counterparties that can offer an attractive source of funding."
Mirabaud Securities said Ophir needed either to find another partner or to reduce costs enough to enable it to carry out the project alone.
The broker said the reduced costs to first gas should make the "go-it-alone" option more viable, but it added: "Securing a partner seems the best bet from a risk-management perspective."