China National Petroleum Corp, the country's biggest oil and gas company, said recently that it will ramp up clean energy production capacity and ensure that domestic natural gas accounts for more than 50 percent of its primary energy output at home by 2020.

Domestic natural gas output accounted for 50 percent of its primary energy output at home last year and is expected to reach 55 percent by 2025, said Zhou Aiguo, deputy director of its quality health safety and environment department.

The company, also known as PetroChina, said its natural gas production reached 138.02 billion cubic meters in 2018, of which 109.37 billion cubic meters were domestic output, a year-on-year increase of 5.9 percent and which accounted for 70.2 percent of the domestic natural gas production last year, according to the 2018 Environmental Protection Communique 2018.

The company has also increased imports of overseas pipeline natural gas and LNG last year while striving to further improve its production capacity in the upcoming years.

The company said shale gas production in Sichuan reached 4.27 billion cubic meters in 2018, up 40 percent compared with the previous year and helped ensure national energy security.

The daily output of PetroChina's shale gas in southern Sichuan reached 20.11 million cubic meters, with a year-on-year increase of 119.3 percent, it said.

It has also released 300,000 metric tons of national VI standard gasoline and diesel to the market every day since January this year.

According to Wang Yilin, chairman of CNPC, chemical oxygen demand and ammonia nitrogen emissions, sulfur dioxide and nitrogen oxides decreased by 7.9 percent, 7 percent, 7.6 percent and 7.2 percent respectively year-on-year in 2018.

The company said it would invest another 31.9 billion yuan ($4.6 billion) in the 2019-20 period to strengthen pollution prevention and boost low carbon transformation.

Li Li, energy research director at ICIS China, a think tank focusing on energy trends, said it has become a trend for national oil majors to increase their share of clean energy in the domestic primary energy production to optimize the country's energy structure, including China Petroleum and Chemical Corp, which earlier pledged to increase its share of clean energy production capacity by increasing its output of natural gas, shale gas and related facilities.

The resource and environment research center of Sinolink Securities said earlier that national oil and gas majors, including PetroChina, will have sufficient time to ensure gas supply for the heating season this year.