UPDATE 2-Oil and gas firms work to restore output after Isaac
* Most oil and natgas output in U.S. Gulf still shut
* Marathon Petroleum refinery to receive SPR crude loan
* Some Gulf Coast crude import hubs resume operations
* Phillips 66 assesses flooding damage at Alliance plant
HOUSTON, Aug 31 (Reuters) - Energy firms worked on Friday to resume oil, gas and refining operations in the U.S. Gulf region following Hurricane Isaac, with most offshore production still shut and several refineries offline.
Nearly 95 percent of oil and 68 percent of natural gas production in the U.S. Gulf of Mexico remained shut as of Friday, little changed from Thursday, according to government figures.
Four refineries representing 878,000 barrels-per-day (bpd) of capacity remained shut, government figures showed. Several other refineries continued to operate at reduced rates.
The idled refineries represented 5 percent of total U.S. capacity. Offshore production from the U.S. Gulf of Mexico -- most of which remained shut -- typically makes up 23 percent of U.S. oil production and 7 percent of U.S. natural gas output.
Energy companies had started to shut down their facilities a week ago as Isaac cut a path through the Gulf before making landfall on Tuesday in Louisiana. The slow-moving storm had made it difficult to assess damages or to restart facilities.
Major offshore producers including Royal Dutch Shell and Chevron Corp were working to restaff and restart platforms on Friday. That process could take several days, energy experts said.
To bring refining throughput levels along the Gulf Coast back to near pre-storm rates could take at least five to 10 days since plants will restart slowly for safety reasons, according to a source at a major Gulf Coast refiner, who asked not to be named.
For a factbox on energy infrastructure affected by Isaac, click here:
ALLIANCE REFINERY FLOODING
Uncertainty remained about one refinery's prospects for restarting. Phillips 66 said that parts of its 247,000-bpd Alliance refinery in Belle Chasse, Louisiana were inundated with two feet (60 cm) of water after Isaac-related flooding. Phillips was working to assess any damage and pump out the water, but offered no timeline for a restart.
A Reuters reporter near the Alliance plant said water was visible within the facility but it was not clear if any processing units had been flooded.
Trucks were able to enter and exit the plant site. Dozens of loose cattle were standing in water up to their bellies in front of the refinery, along the Route 23 highway.
Oil futures rose on Friday by 2 percent to settle at $96.47 a barrel. Gasoline futures and natural gas also rose.
Shell said Motiva Enterprises expects to restart some units at its 233,500-bpd refinery in Norco, Louisiana, on Friday.
SPR CRUDE LOAN
Marathon Petroleum Corp said its 490,000-bpd refinery in Garyville, Louisiana, was operating at reduced rates. The U.S. Department of Energy (DOE) said Marathon will receive a loan of 1 million barrels of crude from the U.S. Strategic Petroleum Reserve (SPR) to supply the refinery with crude it needs to ramp up to normal processing rates.
"This is a small, limited time swap in response to Isaac and should not have a major impact on crude prices," said Bob McNally, head of the Washington-based consulting firm The Rapidan Group.
The DOE said it continues to analyze a broader release of crude from its SPR in response to any crude supply disruptions.
The DOE will "keep all options on the table to address additional or sustained oil supply issues," it said in a Friday statement.
CRUDE IMPORT TERMINALS, GAS AND POWER
Facilities that receive U.S. crude imports were re-opening on Friday from Isaac-related shutdowns this week.
The Louisiana Offshore Oil Port (LOOP), which receives up to 13 percent of U.S. crude imports, has restarted deliveries from its onshore storage facilities at Clovelly, Louisiana and expects to restart offshore crude tanker offloadings as soon as possible, a spokeswoman said.
The U.S. Coast Guard said the Port of Morgan City in Louisiana had reopened late on Thursday.
Power utilities were working to restore electricity to hundreds of thousands of homes and businesses along the Gulf Coast.
Henry Hub, the Louisiana delivery point for U.S. natural gas futures, and most of the pipeline connections to it were operating normally and weren't affected by Isaac, Sabine Pipe Line LLC said.