HOUSTON (Reuters) - Energy companies forged ahead restoring oil and natural gas production in the U.S.-regulated northern Gulf of Mexico on Monday, three days after Hurricane Delta made landfall, said the U.S. Bureau of Safety and Environmental Enforcement (BSEE). Shut offshore crude oil production fell to 69.4%, or 1.28 million barrels per day (bpd), on Monday from 91%, or 1.68 million barrels, on Sunday, the regulator said. BSEE also said 47%, or 1.28 billion cubic feet per day (bcfd), in offshore natural gas production remained shut as of midday on Monday. On Sunday, the agency said 62%, or 1.68 bcfd, was shut. Onshore, Total SA TOTF.PA completed restarting units at its 225,500 barrel-per-day (bpd) Port Arthur, Texas, refinery on Monday that were shut by a Friday night power outage caused by Delta, said sources familiar with plant operations. Total spokeswoman Marie Maitre declined comment. Phillips 66 PSX.N said on Monday that Delta did not disrupt the power supply at its Lake Charles, Louisiana, manufacturing complex, which includes a 260,000-bpd refinery that has been shut since Aug. 25 because of extensive damage to the electrical power infrastructure by Hurricane Laura. Phillips 66 plans to begin restart the Lake Charles refinery by the end of this week, the company said. Royal Dutch Shell Plc RDSa.L, Chevron Corp CVX.N and BP Plc BP.L were returning workers to offshore platforms and restarting production as pipelines to carry crude onshore come back. The Louisiana Offshore Oil (LOOP) said on Monday it resumed offloading tankers at its terminal in the Gulf, south of the Louisiana coast. The LOOP is the only U.S. port where the largest tankers can dock. Between Oct. 6 and Monday, a cumulative total of 10.1 million barrels of crude oil production and 9.6 billion cubic feet of natural gas output from the Gulf has been shut because of Hurricane Delta.