In response to requests from Appalachian producers, MarkWest Energy Partners LP on Tuesday said it would add another 400 MMcf/d of rich gas processing capacity by building two cryogenic plants at existing facilities serving Marcellus Shale production in West Virginia.

MarkWest already has 17 major processing and fractionation projects under development at nine locations in Ohio, West Virginia and Pennsylvania, 11 of which it expects to complete this year that would bring its Northeast capacity to 4 Bcf/d and 250,000 b/d.

At its Sherwood complex in Doddridge County, WV, MarkWest said it would construct another 200 MMcf/d processing plant at the request of Antero Resources Corp., which anchors the facility. Antero would support the new plant with a long-term, fee-based contract. The addition would expand Sherwood’s capacity to 1.2 Bcf/d with completion by 2Q2015.

At its Mobley Complex in Wetzel County, WV, MarkWest also would add a 200 MMcf/d processing plant at the request of EQT Corp. to be operational also in 2Q2015. The facility currently consists of three plants with 520 MMcf/d of processing capacity, and MarkWest plans to bring online a fourth at the end of this year to boost capacity to 720 MMcf/d. The Mobley Complex also serves Magnum Hunter Resources Corp., Stone Energy Corp., Consol Energy Inc. and Noble Energy Inc.

MarkWest is the Appalachian Basin’s largest processor and fractionator. Management has said for the last couple of years that it cannot build processing facilities fast enough to match the rate of production in the region, where the company says it has spent about two-thirds of its budget since 2002 when it was founded (see Shale Daily, Feb 3).

EQT and Antero have been steadily increasing their production. Last year, EQT said the Marcellus accounted for 73% of the company’s total sales volumes of 378.2 Bcfe, a 43% increase from 2012, while it said last week that 1Q2014 production increased 30% year/year (see Shale Daily, April 25; Feb. 13). Pure-play Appalachian operator Antero saw its production grow 119% last year, compared to 2012. It will report 1Q2014 results tomorrow.