PetroChina Co and China Petroleum & Chemical Corp (Sinopec), the nation's largest oil companies, said some gas wells in Sichuan province remain shut after the country's biggest earthquake in 32 years struck the area.

PetroChina has cut its daily gas output from Sichuan by about 14 percent, or 5.6 million cubic meters, as a safety measure, parent company China National Petroleum said yesterday.

Sinopec won't reopen its Western Sichuan gas wells "too soon" due to transport disruptions, after-shocks and shutdowns by customers, spokesman Huang Wensheng said yesterday.

The nation's two oil giants, PetroChina and Sinopec, saw their

shares drop yesterday as a result of Monday's earthquake. Bloomberg

China ordered coal mines, chemical plants and oil and gas wells affected by the 7.8-magnitude earthquake to halt operations to avoid further casualties.

The quake has killed more than 12,000 people in Sichuan, which holds about 40 percent of China's natural gas reserves.

"The demand for natural gas could decline as the province consumes about 19 percent of China's entire natural gas usage," said Cheng Khoo, a Hong Kong-based Lehman Brothers Holdings analyst. "At this point, the impact from the quake on the companies seems minimal."

China National has shut its refinery in the Sichuan city of Nanchong, it said in its company newsletter, China Oil News.

The plant can process one million tons of crude a year, Deputy Board Secretary Jiang Lixin said by phone from Beijing.

The newsletter also said the oil producer has sent 100,000 metric tons of emergency fuel supplies to the inland province.

The State-owned company's oil and gas fields, refinery and sales units in the area were "affected to differing extents", China National said.