May 14 (Bloomberg) -- PetroChina Co. and China Petroleum & Chemical Corp., the nation's largest oil companies, said some gas wells in Sichuan province remain shut after the country's biggest earthquake in 58 years struck the area.

PetroChina has cut daily gas output from Sichuan by about 14 percent, or 5.6 million cubic meters, as a safety measure, parent China National Petroleum Corp. said today. China Petroleum, or Sinopec, won't reopen its Western Sichuan gas wells ``too soon'' on transportation disruptions, after-shocks and shutdowns by customers, spokesman Huang Wensheng said today.

China yesterday ordered coal mines, chemical plants and oil and gas wells affected by the 7.9-magnitude quake to halt operations to avoid further casualties. The May 12 temblor has killed more than 12,000 people in Sichuan province, which holds about 40 percent of China's natural gas reserves.

``The demand for natural gas demand could decline as the province consumes about 19 percent of China's entire natural gas demand,'' Cheng Khoo, a Hong Kong-based Lehman Brothers Holdings Inc. analyst, said in a note yesterday. ``At this point, the impact from the quake to 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 today. The Beijing-based oil producer sent 100,000 metric tons of emergency fuel supplies to Sichuan after the earthquake, it said.

Shares Drop

The state-owned company's oil and gas fields, refinery and sales units in the area were ``affected to a differing extent,'' China National said.

PetroChina fell as much as 2.7 percent to HK$10.66 in Hong Kong and traded at HK$10.76 at the midday break. Sinopec fell as much as 4.7 percent to HK$7.30 and last traded at HK$7.34.

Sinopec's Dianqiangui oilfield was closed after the earthquake, spokesman Huang said today. The Sichuan field has annual production of 200,000 metric tons, or about 4,000 barrels a day. The company's pipelines in the area weren't affected. The shut gas field is relatively ``small,'' he said.

Puguang, Sinopec's largest gas field, is in the northeastern part of Sichuan and was unaffected by the earthquake, Huang said yesterday.

No casualties were reported at Sinopec facilities in quake- affected areas, parent China Petrochemical Corp. said in its online newsletter Sinopecnews today.

Pipeline Restarted

PetroChina said no major accidents had been reported at its operations after the quake. Precautionary measures taken to ensure safety at plants and fields won't have any effect on full-year production targets, spokesman Mao Zefeng said by telephone today.

PetroChina restarted a fuel pipeline from its Lanzhou refinery in northwestern Gansu province to Sichuan yesterday. The pipeline was shut for 22 hours and the current volume is 600 cubic meters an hour, China National Petroleum said today.

Twenty 20 coal miners have been killed and 132 are trapped after the quake affected pits in three provinces, the country's top economic planner said today. Twenty-two coal mines in Sichuan, Chongqing and Gansu had been affected by 4 p.m. yesterday, the National Development and Reform Commission said. Eleven miners were reported injured.

State Grid Corp. of China, the nation's largest electricity distributor, said it has restored 40 percent of the power supply in Sichuan that was disrupted by the earthquake.

Thirty-nine of its workers in the province died as a result of the quake and 11 were injured, State Grid said today. China Power Investment Corp. said 18 of its workers were missing at a Sichuan hydropower site. China Huaneng Group Corp. said it had lost contact with its Taipingyi power plant.