Whiting Petroleum Corp. has agreed to sell mostly nonoperated Bakken Shale assets to a subsidiary of upstart producer RimRock Oil and Gas Inc. for $500 million.

The sale,expected to close Sept. 1., includes Whiting’s Fort Berthold Indian Reservation area assets that span 29,637 acres in Dunn and McLean Counties, ND. They produced 7,785 boe/d and accounted for 7% of second quarter production.

RimRock was formed last year by former Talisman Energy Inc. executives with a $500 million investment from the private equity firm Warburg Pincus LLC. Talisman was sold to Repsol SA in 2014 for $13 billion. All of RimRock’s executive management team worked for Talisman.

The company is led by CEO James Fraser and Managing Director Bob Rooney. Fraser previously served as senior vice president of Talisman’s North American Shale Division and as vice president of Chesapeake Energy Corp.’s Southern Division, which includes Texas, New Mexico and Louisiana. Rooney served as executive vice president at Talisman.

Headquartered in Calgary, RimRock is primarily focused on the Rockies and the Alberta Deep Basin.

Whiting’s sale follows another earlier this year in which it sold its North Dakota midstream assets for $375 million. The company also sold its North Ward Estes acreage in Texas for $300 million a year ago. The company has reduced its debt significantly over the last year or so and said Tuesday it would use the proceeds from the Fort Berthold sale to pay down $550 million in debt.

Whiting is one of the largest oil producers in North Dakota’s Bakken. The company held 449,857 net acres in the Williston Basin at the end of 2Q2017.