CALGARY, Canada /HONG KONG - PetroChina is purchasing half of a prolific shale gas project from Canada's Encana Corp for C$5.4 billion ($5.4 billion), marking the largest Chinese investment yet in a foreign natural gas asset.

Chinese companies such as PetroChina and CNOOC have been scouring globally for unconventional gas assets to reduce reliance on coal and satisfy its energy hunger to fuel its economy, now the world's second-largest.

In January, CNOOC struck a $570 million shale deal with US natural gas company Chesapeake Energy Corp, its second such deal with the American company in about four months.