MarkWest Energy Partners LP announced a major expansion of processing and fractionation infrastructure at its Keystone complex in Butler County, Pa., to support increasing rich-gas production from the Marcellus Shale and Upper Devonian formations.

The complex, which is anchored by Rex Energy Corp., includes the Bluestone processing and fractionation complex and the Sarsen processing facility, providing a total of 210 million cubic feet per day (MMcf/d) of processing capacity and 26,500 barrels per day (bbl/d) of fractionation capacity. In May, MarkWest began operations of the 120 MMcf/d Bluestone II plant and 10,000 bbl/d each of ethane and propane plus fractionation capacity.

The new expansion will consist of Bluestone III and IV, both of which are 200 MMcf/d plants. It will be supported by agreements with Rex Energy and EdgeMarc Energy. MarkWest will also build 40,000 bbl/d of additional de-ethanization capacity and more than 20,000 bbl/d of additional propane and heavier NGL fractionation capacity. Bluestone III is expected to begin operations in fourth-quarter 2015 and Bluestone IV is expected to be in operation in second-quarter 2016.