UPDATE 1-Chevron's Brazil output seen halved if restarted-ANP

* Chevron output reached 78,000 bpd before spill

* Petrobras, Japan's Sojitz, Inpex will also lose output

* Chevron asking to restart output without water injection

* Transocean ban could hurt Brazil oil industry -ANP chief

By Leila Coimbra

RIO DE JANEIRO, Sept 14 (Reuters) - Chevron's output in Brazil will be less than half the production levels it had before a November oil spill if the courts allow the company to restart operations, Magda Chambriard, head of Brazil's petroleum regulator ANP, said Friday.

Production from the offshore Frade field, owned in partnership with Petrobras and Japanese trading companies Sojitz and Inpex, reached a maximum of 78,000 barrels per day shortly before a November oil spill, Chambriard told reporters in Rio de Janeiro.

Based on Chambriard's estimate, the field, which was shut in March after unexplained oil residue was found in the area, would now produce less than 39,000 bpd of a heavy grade of crude.

At current market prices for Maya crude , a benchmark for heavy oil, the cut represents a loss of revenue compared to pre-spill levels of as much as $4 million a day.

Chevron, the No. 2 U.S. oil company, owns 52 percent of Frade and operates the field. Brazil's state-run Petrobras owns 30 percent and Sojitz and Inpex's Frade Japao Group owns 18 percent.

Production would be lower because Chevron's request to restart output in Frade seeks to produce without water injection into the reservoir. Companies frequently inject water or unused natural gas back into wells to increase pressure and force oil to the surface.

Chevron and its drilling contractor Transocean, the world's largest operator of offshore drilling rigs, face an injunction banning them from operating in the country until lawsuits by federal prosecutors seeking nearly $20 billion in damages over the November spill are resolved.

While the suspension of Chevron would not change the situation facing the company and its partners in Frade where production is already stopped, the suspension of Transocean could have serious consequences for Brazilian oil operations, Chambriard said.

"We cannot loose Transocean's 10 rigs at this moment of decline in oil production," said Chambriard. "The ANP believes that Transocean did nothing wrong."

She said she believes the courts will strike down the injunction and does not expect Chevron and Transocean to be permanently prohibited from operating in Brazil.

Transocean has 10 rigs operating in Brazil, seven for Petrobras. The Petrobras rigs are drilling some of the company's most promising offshore prospects.

Petrobras is responsible for more than 90 percent of Brazilian oil and natural gas output of nearly 2.5 million bpd.

An ANP petition to quash the injunction banning Chevron and Transocean was twice denied by Brazilian courts in recent weeks.

The ANP plans to appeal the injunction next week, Chambriard said.

The 3,400-barrel November oil spill, less than 1/1000 of the Deepwater Horizon disaster in the Gulf of Mexico in 2010, never reached shore and caused no discernable damage to wildlife, the ANP said earlier this year.

OIL AUCTIONS DELAYED

Chambriard also said the country will run out of active exploration areas in 2016 unless new oil rights concessions are sold. The country has not held any oil rights auctions in four years.

Brazil halted the sale of exploration areas in the most promising offshore areas after Petrobras and its partners, Britain's BG Group Plc. and Portugal's Galp Energia SGPS announced in October 2007 the discovery of the first in a series of giant offshore "subsalt" fields.

A move to rewrite the country's oil legislation to give the government and state-controlled Petrobras more power regarding resources has prevented all auctions except a 2008 sale of risky on-shore frontier areas.

The changes in the law also opened up a dispute over oil royalties that must be solved before new rights sales can take place.

Chambriard does not believe Brazil's congress will approve the new law this year.