MarkWest Energy plans to expand its natural gas processing capacity by adding two new facilities to the two already at the Bluestone site of the Keystone complex in Jackson Township. The Bluestone III plant is expected to be operational in the fourth quarter of 2015, while Bluestone IV will follow in the second quarter of 2016.

JACKSON TWP — MarkWest Energy has announced an expansion project that would nearly triple the natural gas processing at its Keystone complex on Hartmann Road.

Kevin Hawkins, the manager of investor relations for MarkWest, said Tuesday the company will build two facilities for natural gas processing and fractionation.

The Keystone complex 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.

The two new facilities at the Bluestone site, which currently includes Bluestone I and Bluestone II facilities, each will be able to process 200 million cubic feet per day.

The Bluestone III plant is expected to be operational in the fourth quarter of 2015, while Bluestone IV will follow in the second quarter of 2016.

Hawkins said the processing facilities gather natural gas from wells in the area and separate it into wet and dry gas.

The dry gas is methane, which is then piped to utility companies.

The liquid gas continues its processing in the fractionation facilities, where it is separated into ethane and propane. MarkWest also will install additional fractionation facilities at the Keystone complex during the project.

Hawkins said the project will increase employment, but he did not know by how much.

Rex Energy is the main client at the plant. The additional facilities will increase Rex Energy’s capacity in its Butler Operated Area to 405 million cubic feet per day.

The Butler Operated Area includes Butler County and the surrounding counties where it has acreage.

Tom Stabley, CEO of Rex Energy, said in a statement Tuesday that the recent purchase of gas leases of 208,000 acres of Royal Dutch Shell land will require the additional processing facilities.

“The recently announced Shell transaction will significantly expand our Butler Operated Area, and we are excited to partner with MarkWest to support our growth with this increased processing and fractionation capacity,” the statement said.

Stabley added the purchase of Shell leases and the expansion at MarkWest will “firmly” position the company to develop its plans in the Butler Operated Area.

Rex Energy has about 76,000 acres leased in the county and about 90 wells, primarily in southwestern Butler County. Its purchase from Shell will add another 90,825 acres leased in the county.

EdgeMarc Energy also will use the complex. EdgeMarc has about 23,000 acres leased in the county. That company is constructing a 22-mile long pipeline from the Bluestone II facility up through northeastern Butler County.

Frank Semple, the CEO for MarkWest, said in a statement the expansion of Rex’s leased land and the building of the new MarkWest facility will help development of natural gas resources in the area.

“Since our acquisition of the Keystone assets over two years ago, volumes continue to increase significantly and we are leading the development of full-service midstream services in the highly prospective rich-gas areas of Northwest Marcellus,” he said.

MarkWest Energy Partners bought the Bluestone I and Sarsen facilities from Keystone Midstream in 2011 for $512 million to boost its operations in the Marcellus Shale natural gas region.

The 80,000-square-foot Bluestone II facility was completed earlier this year. The complex is on 30 acres of former farmland.

MarkWest officials last year said they planned to invest up to $500 million over the next five years to support Rex Energy’s drilling program in the region.