PetroChina (PTR.NYSE, 601857.SH, 0857.HK) announced that it would pay US$5.4 billion for a 50% stake in a natural gas shale field in Canada owned by EnCana (ECA.NYSE), the Financial Times reported. Under the deal, EnCana will continue to operate the field while PetroChina funds half of all future capital costs. The purchase constitutes the largest investment in Canada’s energy resources by a Chinese firm. Analysts say that PetroChina is investing in shale gas specifically to master the relatively difficult technology and expertise necessary to extract the gas. China is estimated to have spent around US$10 billion on such unconventional gas deals over the past six months. The bid is still pending regulatory approval under the Investment Canada Act, which requires the deal to demonstrate "net benefit" to Canada.