China Petrochemical Corporation (Sinopec) said on Saturday that it has completed the purchase of 50 percent of Chesapeake's share in its Mississippi Lime assets for $1.02 billion.

Chesapeake is the second-largest natural gas developer in the United States and its Mississippi Lime oil and natural gas assets are in northern Oklahoma.

Sinopec signed the agreement with Chesapeake on February 23 through its wholly-owned subsidiary Sinopec International Petroleum Exploration and Production Corporation.

The deal means Sinopec acquires 425,000 acres (171,991 hectares) in the Mississippi Lime shale formation, with estimated proven and probable (2P) oil equivalent of 245 million barrels.

Sinopec bought one-third of the Devon Energy Corporation's gas reserves for $2.5 billion in 2012.

Limestone gas, along with shale gas and coalbed methane, is considered to be a source of unconventional gas.