The acquisition includes Keystone’s assets in Butler County, Pennsylvania, including Sarsen and Bluestone cryogenic gas processing plants with a total capacity of 90 million cubic feet per day (MMcf/d), a gas gathering system and associated field compression.

The Bluestone plant has a processing capacity of 50 MMcf/d and is currently in the final stage of commissioning.

As per the deal, the partners, Rex Energy and Sumitomo Corporation, have allocated an 895 square mile area to MarkWest, where it will gather and process natural gas, and fractionate the natural gas liquids.

MarkWest engages in midstream services under long-term agreements that include acreage dedications from key producers.

MarkWest noted the transaction would augment the partnership’s foothold in the liquids-rich Marcellus Shale area into northwest Pennsylvania and eastern Ohio.

Stonehenge holds a 60% stake in Keystone, while the remaining 40% is held by the units of Rex Energy Corporation and Sumitomo.