Royal Dutch Shell plc, which earlier this month launched a review of its entire North American portfolio, is selling some of its operations in northwestern Colorado’s Niobrara formation, according to a spokeswoman.

In May company officials had said that Shell planned this year to drill about 17 wells in Routt and Moffat counties, the land now for sale. However, Shell took a huge loss on some of its unconventional leaseholds in the second quarter, areas that it didn’t disclose, and CEO Peter Voser said early this month as much as half of the company’s main nine unconventional oil and natural gas assets in North America were being reviewed for possible sale (see Shale Daily, Aug. 2).

Shell put the Colorado properties on the market following a “periodic” portfolio review, said a spokeswoman, “which assesses which assets we want to focus on, and [to] commercialize those that don’t have as much growth potential.”

However, until the sale is completed, Shell plans to “continue safe operations, maintenance and drilling activities while the asset is marketed, so we are not ‘abandoning’ or ‘walking away.’ We will continue to work with the communities during the transition.”

The mineral leases were included in Shell’s $4.7 billion takeover of East Resources Inc. in May 2010, which handed the company, among other things, an opening in the Marcellus and Eagle Ford shales. East had kept some of its Niobrara leasehold in the sale.