Isaac, now a tropical depression, continued to threaten the lower Mississippi valley with heavy rain and flash floods as it moved north after forcing offshore energy producers and coastal refiners to shut operations.

Energy companies have begun assessing the damage caused by the storm, which made landfall as a Category 1 hurricane on Tuesday. Some will be resuming operations on Friday.

Phillips 66 said floodwater at the Alliance refinery in Belle Chasse, Louisiana did not reach more than 2 feet in depth, although it did not say which parts of the refinery were flooded. The refinery remains shut with no timeline given for a restart.

Valero Energy Corp is ramping up rates at its 180,000 barrels-per-day refinery in Memphis, Tennessee after Royal Dutch Shell started its Capline pipeline system.

Shell said Friday that Motiva Enterprises' 233,500 bpd refinery in Norco, Louisiana will restart some units after it was shut during the storm because of power loss and wind damage.

Exxon Mobil Corp was conducting checks at its 192,500 bpd Chalmettte, Louisiana joint-venture refinery, it said Friday.

The U.S. Department of Energy will loan 1 million barrels of sweet crude to Marathon Petroleum Corp, which was operating its 490,000 bpd Garyville, Louisiana refinery at reduced rates after Isaac hit the Gulf Coast. Sources said the department received only one request for crude oil loans from the reserves.

The department estimated some 878,000 barrels per day of oil refining capacity remains offline on the Gulf Coast.

Anadarko Petroleum Corp will restaff five Gulf of Mexico platforms Friday and production will start once inspections are done and third-party pipelines ramp back up.

BP Plc, the largest oil producer in the Gulf of Mexico, said the company was restaffing its shut oil and gas platforms and would restart production "in coming days" once it was deemed safe.

ATP Oil and Gas said it is restaffing and restarting its Titan and Innovator platforms in the Gulf of Mexico on Friday.

Murphy Oil said it will begin restaffing Gulf of Mexico operations on Friday.

Oil firm Anadarko Petroleum Corp said it would start restaffing its shut Gulf of Mexico platforms on Friday.

Chevron started deploying personnel to its offshore facilities on Thursday but said its 330,000 barrel-per-day (bpd) Pascagoula, Mississippi refinery and is still operating at reduced rates.

The U.S. Bureau of Safety and Environmental Enforcement said 94.81 percent of oil and 68.34 percent of natural gas production was disrupted by the storm in the Gulf.

The Gulf of Mexico accounts for about 23 percent of U.S. oil production and 7 percent of natural gas output, according to the U.S. Energy Information Administration. About 30 percent of U.S. natural gas processing plant capacity and 44 percent of the country's oil refining capacity lies along the Gulf Coast, the EIA said.

The Port of New Orleans and a stretch of the Lower Mississippi River were opened with restrictions on Thursday night, the U.S. Coast Guard said. The port of Morgan City in Louisiana was opened at 7 p.m. CDT.

The Louisiana Offshore Oil Port (LOOP), which handles about 13 percent of foreign crude shipped to the United States, deliveries from its onshore storage facilities at Clovelly, Louisiana, and expects to restart offshore crude tanker offloadings as soon as possible.

Chevron Corp Subsidiary Sabine Pipeline LLC said its natural gas pipeline and interconnections to the Henry distribution hub in Louisiana were not affected by Isaac. The Henry Hub natural gas delivery point was operating normally Thursday.

Oil output shut: 1.31 million bpd nearly unchanged from Thursday.

Natural gas output shut: 3.07 bcf/d, down from 3.263 bcf/d Thursday.

(Source: U.S. Bureau of Safety and Environmental Enforcement)

OIL/GAS Company Asset Capacity oil/gas Date Shut Restarting

Anadarko Independence Hub 1 bcf/d Aug 26 N/A

Marco Polo 120,000 bpd/300 mmcf/d Aug 26 N/A

Constitution 70,000 bpd/200 mmcf/d Aug 26 N/A

Gunnison 40,000 bpd/200 mmcf/d Aug 26 N/A

Red Hawk 120 mmcf/d Aug 26 N/A

Neptune 14,000 bpd/ 23 mmcf/d Aug 26 N/A

ATP ATP Innovator 20,000 bpd/100 mmcf/d N/A Aug 31

ATP Titan 25,000 bpd/ 50 mmcf/d N/A Aug 31

BHP Billiton Shenzi 120,000 bpd/ 50 mmcf/d Aug 27 N/A

Neptune 50,000 bpd 50 mmcf/d Aug 27 N/A

BP Thunder Horse 250,000 bpd/ 200 mmcf/d Aug 24 N/A

Atlantis 200,000 bpd/ 180 mmcf/d Aug 26 N/A

Na Kika 110,000 bpd/ 500 mmcf/d Aug 25 N/A

Mad Dog 80,000 bpd/ 60 mmcf/d Aug 26 N/A

Holstein 110,000 bpd/

Horn Mountain 65,000 bpd/ 68 mmcf/d Aug 25 N/A

Marlin 60,000 bpd/ 250 mmcf/d Aug 25 N/A

Chevron Tahiti 120,000 bpd/ 70 mmcf/d Aug 29 N/A

Blind Faith 65,000 bpd/ 55 mmcf/d Aug 28 N/A

Genesis 55,000 bpd/ 72 mmcf/d Aug 29 N/A

Petronius 40,000 bpd/ 35 mmcf/d Aug 29 N/A

ConocoPhillips Magnolia 8,000 bpd/ 16 mmcf/d* Aug 26 N/A * (as of June 2011) ENI Devil's Tower 60,000 bpd 110 mmcf/d Aug 28 N/A

Marathon Oil Ewing Bank 9,700 bpd/ 8.2 mmcf/d Aug 27 N/A

Murphy Oil Thunder Hawk 60,000 bpd/ 70 mmcf/d Aug 26 N/A

FrontRunner 60,000 bpd/ 110 mmcf/d Aug 27 N/A

Medusa 35,000 bpd/ 35 mmcf/d Aug 27 N/A

Petrobras Cascade/Chinook 80,000 bpd/ 16 mmcf/d Aug 28 N/A

Shell Mars 160,000 bpd/ 121 mmcf/d Aug 28 N/A

Ursa 150,000 bpd/ 400 mmcf/d Aug 28 N/A

Auger 101,000 bpd/ 415 mmcf/d Aug 28 N/A

Brutus 100,000 bpd/ 150 mmcf/d Aug 28 N/A

Ram-Powell 70,000 bpd/ 260 mmcf/d Aug 28 N/A

Company Location Capacity Status

(1,000 bpd) Alon Krotz Springs LA 80 Reduced rates Citgo Lake Charles, LA 427.8 Normal Ops Chevron Pascagoula MS 330 Reduced rates Exxon Chalmette LA 192.5 Shut

Baton Rouge LA 502.5 Reduced rates Marathon Garyville LA 490 Reduced rates Motiva Norco LA 233.5 Shut, to restart units Friday

Convent LA 235 Will restart Phillips66 Belle Chasse 247 Water receding Valero Norco LA 205 Shut

Meraux LA 125 Shut

Memphis, TN 180 Reduced rates

* Anadarko Petroleum Corp -- Restaffing five shut Gulf of Mexico platforms on Friday.

* Apache Corp -- began sending crews to its Gulf of Mexico operations on Friday.

* ATP Oil and Gas Corp -- Restaffing and soon restarting two Gulf Coast platform

* BHP Billiton Ltd -- Restarting two platforms, production to resume "as soon as possible."

* BP Plc -- Restaffing platforms, production to start in coming days.

* Chevron Corp -- Has begun to deploy staff to offshore platforms

* ConocoPhillips -- No damage on Magnolia platform, remanning to continue over the weekend.

* DCP Midstream Partners LP -- Shut natural gas plant at Mobile bay, Alabama ahead of Isaac's landfall.

* Enbridge Inc -- Stingray natural gas pipeline will begin accepting nominations for flows of natural gas as of Thursday night.

* Entergy Corp -- preparing to restart

* Enterprise Products Partners LP -- Shut all platforms except for Mustang Island and shuttered two fractionators in Baton Rouge and Norco, Louisiana. All gas processing plants were shut down while the Neptune plant operated at reduced rates.

* Exxon Mobil Corp -- conducting assessments of impacted offshore facilities.

* Kinder Morgan Energy Partners LP -- Tennessee Gas Pipeline has 435 million cubic feet per day of gas offline due to Tropical Storm Isaac. Some 400 million also remains offline on the Southern Natural Gas Pipeline.

* Marathon Oil -- Evacuated all personnel, shut in production at Ewing Bank oil and gas platform.

* Marathon Petroleum -- Requested and got approval for 1 million barrels of crude oil from the Strategic Petroleum Reserve (SPR) after Isaac.

* Murphy Oil Corp -- Shut and evacuated Thunder Hawk platform, will shut and evacuate Medusa and FrontRunner on Monday.

* Petrobras -- Shut production at its Cascade and Chinook fields in the Gulf of Mexico but staff remained onboard the offloading tanker at the site.

* Shell -- Expects to begin restarting and restaffing Gulf of Mexico platforms on Friday. Platforms are shut and evacuated.

* Williams Cos Inc -- post-Tropical Storm Isaac inspections of the Chevron Corp-operated Blind Faith and the ENI-operated Devil's Tower oil and gas platforms to begin Thursday afternoon.

* Port of Morgan City open, Port of New Orleans and Mobile Bay closed.

* Louisiana Offshore Oil Port -- restarted deliveries from its onshore storage facilities at Clovelly, Louisiana, and expects to restart offshore crude tanker offloadings "as soon as we can."

* Nustar's St. James terminal to start full operations Saturday.

* Shell's Convent, Louisiana and Collins, Mississippi terminals reopened while Kenner, Louisiana terminal shut.

* Chevron subsidiary Sabine Pipe Line LLC shut the Sea Robin/Henry Hub interconnection due to Isaac.

* Colonial Pipeline -- Operations continue normally, no power losses.

* Enbridge Inc -- Natural gas flows to restart on Enbridge's Stingray Pipeline Co LLC. Soon will start assessing the status of onshore platforms.

* Kinder Morgan Energy Partners -- Southern Natural Gas pipeline to determine if site visits are necessary.

* Magellan Midstream Partners LP -- Resumed normal operations at Gibson, Louisiana terminal, operations at Marrero, Louisiana, terminal remain suspended.

* Nustar Energy LP -- Operations at St. James, Louisiana hub to resume Saturday.

* Southern Union Co -- Subsidiary Panhandle Energy shut the Sea Robin Natural Gas Pipeline System.

* Spectra Energy -- No significant damage seen in onshore natural gas facilities.

* Shell says Capline pipeline system restarted.

* Shell says its offshore Gulf of Mexico pipeline network and its Houma-Houston pipeline remain, may conduct aerial inspections of those facilities on Friday if weather permits.

* Williams Cos Inc -- The Mobile Bay lateral of Transco natural gas pipeline has been shut due to storm Isaac.

* Enbridge's U.S. operating units Mississippi Canyon Gas Pipeline LLC and Nautilus Pipeline Co both declared force majeure over the weekend because of severe weather conditions

* Destin Pipeline Co LLC, majority owner BP, still under force majeure due to the storm.

* Targa Resources Partners LP's Venice natural gas gathering system declared a force majeure and has shut down operations.