* Transocean ban could remove seven rigs from Petrobras
* Ban would make Brazil drill-rig shortage more acute -ANP
* Transocean operates 13 pct of Brazil drill-rig fleet
RIO DE JANEIRO, Sept 17 (Reuters) - Brazil's petroleum regulator ANP appealed an injunction on Monday banning Transocean Ltd and Chevron Corp from operating in Brazil on the grounds the ban would harm oil exploration in the country, ANP chief Magda Chambriard said.
Among the repercussions of a ban, which could take effect in less than a month, would be preventing state-led oil company Petrobras from drilling eight new wells in its massive Marlim field northeast of Rio de Janeiro, Chambriard told reporters on the sidelines of the Rio Oil & Gas conference.
Asked if the ban would cause a serious reduction in drilling and exploration in Brazil, Chambriard replied "absolutely."
The ban is part of a civil lawsuit brought by independent federal prosecutors seeking about $20 billion in damages from Chevron and its drilling contractor Transocean over a 3,600 barrel oil spill in the offshore Frade field in November.
Chevron stopped operations in Frade in March as it explored the causes of the spill. Transocean has 10 deep-water drill rigs in Brazil, which accounts for 13 percent of Brazil's total. Seven of the 10 are under contract to Petrobras.
"The ban is totally ridiculous as are the amounts that the prosecutors are seeking; there was no ecological damage," a Brazilian government oil official with knowledge of the appeal told Reuters. "If it is not overturned, this ban and lawsuit will have serious negative consequences for the industry."
An ANP report on the spill in July said Transocean was not to blame for the leak. The ANP has levied 35.1 million reais (US$17.3 million) in fines on Chevron.
The ANP wants the judicial ban lifted on both companies and for Chevron to resume production at Frade.
The appeal of the ban to Brazil's Supreme Justice Tribunal, a federal appeals court one step below the Supreme Court, comes after judges in Rio de Janeiro denied similar motions by the ANP, Chevron and Transocean in late August and early September.
The lower court judges said the ANP's failure to properly regulate Chevron may have led to the spill, a situation that forced them to abrogate the agency's legal right to decide who can and cannot work in Brazil's oil industry.
Petrobras chief executive officer Maria das Gracas Foster has said that a lack of drill rigs is one of the main reasons production is falling despite the discovery of new reserves and a $237 billion five-year investment plan, the world's largest corporate spending program.
Petrobras is responsible for about 90 percent of Brazilian output. Besides Petrobras, Transocean has Brazilian rig leases with BP Plc and Vanco, a privately held U.S. oil company that has some Russian investment.
The Frade Field is 53 percent owned by Chevron, the No. 2 U.S. oil company. Petrobras owns 30 percent and the remaining stake belongs to Frade Japao, a group owned by Japanese trading houses Sojitz Corp and Inpex Corp.