BEIJING -- PetroChina Co, China's biggest oil and gas producer, said on Tuesday that it will sell 20 billion yuan ($3.17 billion) worth of bonds on Thursday.

The upcoming bond sale will be the first batch of the offering, and the proceeds will be used to repay bank loans and replenish the company's working capital, according to a PetroChina statement filed to the Shanghai Stock Exchange.

The oil firm will sell the bonds in three tranches, including 12 billion yuan of five-year paper, 4 billion yuan of 10-year paper and 4 billion yuan of 15-year paper, the statement said.

The 20-billion-yuan bonds are rated AAA, the highest level assigned by rating agencies, which means they carry the smallest degree of investment risk.

PetroChina's shares rose 0.35 percent to 8.59 yuan at 9:50 am Tuesday in Shanghai.