EQT Corp. said late Tuesday it would bolt-on 90,000 net acres and associated midstream assets in West Virginia in a cash and stock transaction valued at $5.2 billion.

EQT, the nation’s largest natural gas producer, is acquiring upstream assets from THQ Appalachia I LLC and midstream assets from THQ XcL Holdings I LLC. Both companies are backed by funds managed by private equity firm Quantum Energy Partners, which is poised to become a core EQT shareholder when the deal closes.

The transaction would add 800 MMcfe/d of production from properties near EQT assets in the core of southwest Appalachia. It would provide 11 years of inventory in the Marcellus and Utica shales at current maintenance capital levels, EQT said. The transaction also includes 95 miles of midstream gathering...