Damage assessments at four Corpus Christi, Texas, area oil refineries were underway on Aug. 26, a first step toward resuming production at the plants with combined capacity of 836,000 barrels per day (bbl/d), according to Gulf Coast refining sources.

The four, owned by Citgo Petroleum Corp., Flint Hill Resources and Valero Energy Corp., halted operations on Aug 24 ahead of Hurricane Harvey, which struck the area with 130 miles per hour winds and heavy rains late Aug. 25.

Together, they account for about 4.4% of the nation's refining capacity.

Refineries in Texas City and Houston, well north of Corpus Christi, continued to operate normally through the storm, according to the sources. Houston and Texas City are home to refineries accounting for 12%, or 2.2 MMbbl/d, of national refining capacity.

Harvey dumped at least seven inches of rain in the Houston metro area by noon local time Aug. 26 and officials were predicting another 20 to 30 inches would fall in the region by Thursday.

A Citgo spokeswoman had no immediate comment about efforts underway at its 157,500 bbl/d Corpus Christi refinery. Refiners begin assessing damage as soon as it safe for crews who rode out the storm in hardened control rooms to venture outside.

A Flint Hills spokesman did not reply to a message seeking comment about recovery work at its 296,470 bbl/d Corpus Christi refinery.

Valero confirmed damage assessments were under way at its 293,000 bbl/d Corpus Christi and 89,000 bbl/d Three Rivers, Texas, refineries.

The company's other Gulf Coast refineries continue to operate, Valero spokeswoman Lillian Riojas said.

Royal Dutch Shell Plc said its 227,586 bbl/d Convent and 225,800 bbl/d Norco refineries in Louisiana and its 325,700 bbl/d joint-venture refinery in Deer Park, Texas, had not been impacted by the storm.

Marathon Petroleum Corp.'s 459,000 bbl/d Galveston Bay Refinery and 86,000 bbl/d Texas City, Texas refinery, remained in operation, according to the city's Emergency Management office. Marathon spokesman Jamal Kheiry declined to discuss operations at the two plants.

Valero's 225,000 bbl/d Texas City refinery has also remained in operation, Texas City emergency management said.

Return to production of a shut refinery following a hurricane varies depending on the damage sustained, the amount of water within a plant and the availability of the external power supply.

Restarts are an especially dangerous period when fires and explosions occur.

Harvey is stalled near the central Texas coast and forecast to dump as much as 40 in. of rain in some areas through Aug. 31, according the National Hurricane Center.