* Coast guard fires warning shots over Greenpeace vessel
* Similar protest action last year delayed operations
* Greenpeace says Russia cannot guarantee safety of rig
* Companies have become more hesittant to invest acrossArctic
By Vladimir Soldatkin
MOSCOW, Sept 18 (Reuters) - Russian coast guards firedwarning shots and arrested two Greenpeace activists who scaledthe Prirazlomnaya Arctic oil platform in a protest over thepotential threat to the environment from operations slated tostart this year.
Production at the rig, owned by state group Gazprom and Russia's first such project in the Barents Sea,was delayed last year after similar actions. Gazprom said thedelay was down to "technical reasons".
The Arctic holds 13 percent of the world's undiscovered oiland 30 percent of its undiscovered gas according to industryestimates. However, its economic viability, as well as itsenvironmental safety credentials, remain a matter of debate.
The arrested activists were from the Greenpeace icebreakerArctic Sunrise. After they scaled the platform, a coast guardboat fired the warning shots to force the ship to withdraw fromthe base of the rig.
Before the withdrawal, Greenpeace photographs of the sceneshowed a group of boats - both coast guard vessels andinflatables from the Arctic Sunrise - jostling for position atthe base of the rig.
"Due to the refusal of the Arctic Sunrise captain to haltthe unlawful activity, the administration took a decision tostop the ship. The coast guard was forced to fire warning shotsfour times from an artillery cannon on board a vessel," Russia'sFederal Security Service said in a statement.
Greenpeace said it received a threat that the ship itselfwould be fired at if it did not leave the area immediately.
The group said it had sent five boats to the Prirazlomnayarig. It was unclear where the four other boats were located.
"Despite massive financing for Prirazlomnaya, it is not ableto guarantee safe production of Arctic oil," Greenpeace said.
Gazprom Neft, the oil arm of state gas exportmonopoly Gazprom, and Gazprom declined immediate comment.
INFANCY
Onshore drilling is well established, but significantoffshore work is in its infancy despite numerous attempts tomake it work and relatively shallow waters.
A decade of high oil prices, scarcity of opportunitieselsewhere, relatively low political risk and a shrinking ice caphas led companies to look to unexploited parts of the Arctic inrecent years
Global majors including ExxonMobil, Eni andStatoil have agreed deals with Russia's state-ownedRosneft to enter Russia's Arctic offshore waters.
Most of these projects are due to begin extracting in the2020s, and are seen as crucial to maintaining the 10 millionbarrels a day of oil flow from the world No. 1 producing nation.
Environmental campaigners, worried about the impact on afragile ecosystem and about how a spill clean-up could work insuch remote places, have stepped up their campaigns to match theincreasing business interest.
There is now greater hesitation among companies as highcosts, mishaps, a weaker oil price outlook and determinedanti-drilling campaigns take their toll.
Offshore safety concerns have grown after BP's Deepwater Horizon oil rig exploded in 2010, killing 11 workersand spewing millions barrels of oil into the Mexican Gulf.
LICENCES
An incident at the end of last year, where Royal DutchShell's offshore Alaska rig Kulluk broke free in astorm from the vessel towing it and ran aground became thelatest slip for its drilling programme and has been seenindustry wide as a turning point for Arctic.
Shell later shelved its plans for this year and looksincreasingly unlikely to put a 2014 drilling season in place.
"The reality is that going forward, the obviousdemonstration of climate change in the Arctic will affectpolicymakers and boardrooms for years to come, and I see thatmore clearly now than five years ago or three years ago," Harald Norvik, a former CEO of Statoil and an Arcticpioneer, told Reuters in an interview earlier this year.
Plans are not entirely on hold though. As well as theRussian projects, in August Norway invited bids for licences todrill in its eastern Arctic waters after settling a borderdispute with Russia.
Prirazlomnoye is the first Arctic offshore oil deposit to bedeveloped by Russia and is located in the Pechora Sea, a part ofthe Barents Sea, 60 km (40 miles) from the northern coast.
Its operations are slated to start by the end of 2013 isexpected to reach peak production of 6 million tonnes per year(120,000 barrels per day) in 2019.
Gazprom Neft is expected to obtain a licence from Gazprom todevelop the field. It expects investment in the project to bearound 200 billion roubles ($6 billion), of which half has beenspent.
