EQT Midstream Partners LP said it would buy parent EQT Corp.'s Northern West Virginia Marcellus Gathering System and a preferred interest in an EQT subsidiary for about $1.05 billion.

EQT shares were down 1.5 percent in after-hours trading on Tuesday, while EQT Midstream shares were flat at $80.46.

EQT formed EQT Midstream in 2012 to own, operate, acquire and develop midstream assets in the Appalachian Basin. EQT has a 34.4 percent limited partner interest and a 2 percent general partner interest in EQT Midstream, according to the company's website.

EQT Midstream said it would pay $997.5 million in cash and $52.5 million in common and general partner units for the assets, which are expected to immediately add to the partnership's distributable cash flow per unit.

The company said separately that it would offer nearly 8.3 million common units representing limited partner interests to help fund the deal.

The system includes about 70 miles of natural gas gathering pipeline and nine compressor units with 25,000 horsepower of compression.

EQT Midstream said it expected to invest about $370 million over the next several years to install about 100 miles of gathering pipeline and five compressor units.

The partnership forecast ongoing maintenance capital expenditure of less than $5 million per year for the system.

Evercore Group LLC is EQT Midstream's financial adviser on the deal, while its legal adviser is Richards, Layton & Finger P.A.