The storm hit Louisiana early Thursday with 150 mile-per-hour (240 kph) winds, damaging buildings, knocking down trees and cutting power to more than 400,000 people in Louisiana and Texas. Its storm surge was less than predicted, sparing inland plants from feared flooding.

Laura passed over Lake Charles, Louisiana, and its oil refineries overnight and was moving quickly north toward Arkansas on Thursday.

Offshore operators were busy scheduling reconnaissance flights over the more than 300 offshore platforms and drilling rigs whose crews evacuated last week. Laura tore through the Gulf of Mexico’s prime oil production fields, with first assessments due Thursday for pipelines and platforms.

“This is closer to the more powerful storms of the prior decade,” said Ethan Bellamy, a managing director at consultants East Daley Capital Advisors, referring to Hurricanes Ike and Rita. Operators will need to vet underwater pipelines that bring oil and gas ashore, as well as platforms, he said.

Exxon Mobil Corp said it was contacting employees of its 369,000 barrel-per-day (bpd) oil refinery and chemical plant in Beaumont, Texas, and preparing a preliminary tally of damages. The large plant was one of six plants along the Gulf Coast’s refinery row that shut this week ahead of the storm.

Refiner Phillips 66 was unable early Thursday to send workers into its 260,000 bpd Lake Charles refinery but expects to run a thorough evaluation once it can access the plant, said spokesman Dennis Nuss.

Even with no or little damage, refineries take days to resume production from a cold shut and the widespread power outages in the region and evacuations could slow the process further.

Utilities reported more than 650,000 customers in Texas and Louisiana were without power on Thursday and at least one reconnaissance flight was canceled because of travel disruptions.

Oil producers were preparing to fly over evacuated offshore platforms on Thursday. Some 1.5 million barrels of oil, and or 1.65 billion cubic feet of natural gas output were halted by well closures on Wednesday.

Companies have regularly scheduled crew changes beginning on Saturday and could take the first steps to resuming production this weekend if conditions allow, said Lani Moneyhon, manager of Bristow Group’s Galliano heliport. The company provides transport to offshore producers.

Energy firms typically fly over platforms looking for damage, and later conduct walk-throughs by safety experts before crews can return. It can take several days to run reviews and schedule crew returns.