CNOOC Petroleum North America

In July 2012, CNOOC Limited, a major subsidiary of CNOOC headquartered in Beijing, announced its intention to acquire Nexen for C$15.1 billion.[8] The proposal was accepted by shareholders in September under interim chief executive Kevin Reinhart,[9] but was a matter of significant public and political debate in Canada.[10][11] Prime Minister Stephen Harper approved the deal in December 2012 but simultaneously announced more stringent guidelines for foreign acquisitions of Canadian oil sands companies.[12]

The acquisition closed in February 2013, representing China's largest-ever foreign acquisition.[13] Nexen's common stock shareholders received cash proceeds of US$27.50, without interest, whereas preferred stock shareholders of Nexen received cash proceeds of CAD$26, plus accrued and unpaid dividends without interest.[4] In April 2014, Fang Zhi replaced Kevin Reinhart as the firm's chief executive.[14] Two years after the deal, in 2015, about 14% of the company's workforce (300 in Calgary and 40 in the field) was fired in a move the drew concern in relation to Chinese ownership, but which at the time was consistent with layoffs at other companies in the industry in response to global oil price depression.[14]

The Nexen name disappeared from both legal and practical perspectives on 31 December 2018, and it became known as CNOOC Petroleum North America ULC henceforth.[15] Simultaneously and with the same date of effectiveness, related Nexen subsidiaries and affiliates changed both their legal and branding names. Its American depository receipts remained concurrently traded on the TSX and its ultimate parent company, CNOOC Limited, remained a foreign reporting issuer in Canada.

As of 2019 the company had "shrunk considerably" since the CNOOC acquisition, having gone through multiple rounds of layoffs amid a difficult Canadian oil and gas industry as a whole.[16] In 2019 the company moved its headquarters within downtown Calgary from its former namesake Nexen Building to The Bow, subleasing 8 floors from Cenovus[17] and reducing its office space from approximately 620,000 sq ft to approximately 300,000 sq ft.[16]

The Long Lake project in the Athabasca Oil Sands was initiated in 2001, as a 50/50 partnership between Nexen and OPTI Canada. It was started in order to develop the Long Lake site using steam-assisted gravity drainage and OPTI's OrCrude process for on-site upgrading. Production capacity at Long Lake was estimated 72,000 barrels per day (11,400 m³/d) of bitumen per day which could be upgraded to 58,500 barrels per day (9,300 m³/d) of synthetic crude. The proved reserves at the Long Lake site are 310,000,000 bbls.[18] In 2017, the site produced approximately 41,000 barrels per day (6,500 m³/d) of bitumen.[19]

The Long Lake site has had a troubled history, including OPTI's near-bankruptcy in 2011 (with Nexen growing its ownership stake to 65% and eventually 100%),[20] a significant oil spill in 2015,[21] and an explosion in 2016 that resulted in two deaths and the permanent shutdown of the upgrader.[19][22]

In 2018, Nexen announced a $400 million expansion project, which is expected to begin production in late 2020.[19]