JACKSON TWP — MarkWest Energy Partners, which has natural gas processing plants in the township, announced Monday it will become a subsidiary of a Marathon Petroleum Corp. pipeline company through a $15.8 billion deal.

The Denver-based MarkWest and MPLX LP of Findlay, Ohio, merged to create the fourth-largest master limited partnership, according to a joint announcement by the companies.

The deal is expected to close this year.

“This powerful combination provides MarkWest with an investment grade balance sheet and a significant expansion of growth projects driven by MPC’s significant pipeline and refinery operations in the upper Midwest and the Gulf Coast,” said Frank Semple, MarkWest’s chairman, president and chief executive officer, in a news release.

“Our best-in-class midstream platform will provide the combined company with an extraordinary portfolio of integrated services and long-term growth opportunities.”

MarkWest’s Keystone complex on Hartmann Road consists of two Bluestone processing and fractionation facilities and the Sarsen processing facility, which combined provide 210 million cubic feet per day of processing capacity and 26,500 barrels per day of fractionation capacity.

It has plans to expand the processing capacity at the facility by 400 million cubic feet per day.

MarkWest operates several other facilities in Pennsylvania, Ohio, West Virginia, Michigan and Kentucky that process gas and related liquids pulled from the Marcellus and Utica shales.

Under the merger, MarkWest stockholders will get 1.09 MPLX common stock units and a one-time cash payment of $3.37 per MarkWest unit, or the equivalent of $78.64 per unit.