* Transocean says Marianas rig stable, no injuries
* Rig working 46 miles off Ghana for Eni for $450,000/day
* Marianas drilled first well at Macondo in Gulf of Mexico
* Rig maintenance flagged internally in early 2010--report (Adds more on Eni in Ghana, background on rig)
SAN FRANCISCO/NEW YORK, July 6 (Reuters) - Transocean Ltd (RIGN.VX)(RIG.N) evacuated 108 nonessential personnel from a deepwater rig working off Ghana for Eni SpA (ENI.MI) after it took on water on Wednesday.
Fears for the rig's safety, with memories of the Deepwater Horizon disaster still fresh, sent Transocean shares down more than 3 percent and weighed down the stocks of competitors.
The company said the situation was under control on the Transocean Marianas, which is working 46 miles (74 km) off Ghana's bustling port of Takoradi.
"The rig is stable at this time. There are no injuries," spokesman Guy Cantwell said.
After the evacuations by helicopter, 13 staff remained on the rig, he said. The company was conducting an investigation and looking into ways to fix the problem.
Cantwell declined to comment on the amount of water on board the Marianas. A U.S.-based official at Eni declined to comment and a spokesman in Milan was not immediately available for comment.
Eni announced a successful appraisal and testing of the Sankofa discovery off Ghana in April. [ID:nLDE73B0PF]
The Marianas, a semisubmersible that entered service in 1979 and was updated in 1998, is on a contract with Eni at a rate of $450,000 per day. It is capable of drilling in 7,000 feet of water (2,100 meters) to depths of 25,000 feet.
The shares of Transocean, the world's largest offshore drilling contractor, fell as much as 5 percent when the news emerged and closed 3.2 percent lower at $62.23. The shares of rival Noble Corp (NE.N) shed 3.4 percent, while Diamond Offshore Drilling Inc (DO.N) ended 1.2 percent down.
The shares of Switzerland-based Transocean have risen more than 50 percent off their lows last summer after BP Plc's (BP.L) Macondo well blowout in the Gulf of Mexico destroyed Transocean's Deepwater Horizon rig.
The Marianas, which moved out of the Gulf of Mexico last year due to the U.S. deepwater drilling moratorium that followed, happened to drill the first well at the Macondo prospect in 2009, before the rig was damaged by Hurricane Ida.
The Marianas was also one of four rigs examined in a confidential Transocean report on U.S. safety conducted prior to the Macondo blow-out, as reported by the New York Times last August, in which some workers expressed concern about both maintenance and safety procedures. (Reporting by Braden Reddall and Jennifer Ablan; editing by Richard Chang, Tim Dobbyn, Matthew Lewis and Andre Grenon)