New York (AP)- Encana Corporation said Wednesday that a subsidiary plans to sell part of it's natural gas pipeline business for $590 million. Encana, based in Calgary, Canada, didn't say who was buying the pipelines. The sale includes 260 miles of pipeline and compression facilities that serve fields near Rifle, Colorado, about 180 miles west of Denver. The pipeline gathers and transports about 500 million cubic feet per day of natural gas. The Colorado pipeline sale must be approved by regulators. It's expected to close in the fourth quarter of 2011. Encana said it plans to sell up to $1.4 billion in additional assets by the end of the year. It may sell even more to balance any future acquisitions this year. Part of the sale will include some Canadian assets, the company said.