Well Infrastructure and Geologic Setting at NETL's Marcellus Shale Test Site in Greene County, Pennsylvania

Hammack, Richard W.

Research at NETL's Marcellus Shale Test Site in Greene County, PA will evaluate three key aspects of unconventional gas development: 1) fracture height growth during hydraulic fracturing; 2) preservation of zonal isolation after hydraulic fracturing; and 3) air quality during hydraulic fracturing and flowback. The geology and existing well infrastructure at the Greene County Test Site provided an optimum location for this research.

The Marcellus Shale Test Site comprises eight Marcellus Shale wells (six horizontal wells and two vertical wells) in the Middle Devonian (at 8100-8200 ft total vertical depth) that are below seven vertical wells completed in Upper Devonian gas sands (completions at multiple depths between 2400 ft and 4800 ft). When NETL began monitoring at the site in March 2012, the six horizontal Marcellus Shale wells had been drilled but not completed. Microseismic geophones were placed in the two vertical Marcellus Shale wells to monitor fracture height growth above the six horizontal Marcellus Shale wells during hydraulic fracturing. Hydraulic fracturing occurred during two time intervals: April 24-May 6, 2012 and June 4-11, 2012.

Industry acquired 3-D surface seismic revealed that Middle Devonian strata at the Greene County site are offset by multiple northeast trending reverse faults. These faults extend upwards through the Tully Limestone but terminate below the Elk Sands in the Upper Devonian. The well pad for the six horizontal Marcellus Shale wells was constructed directly above the known fault zone in the Middle Devonian, in order to maximize lateral length. From there, the wells descended through unbroken strata above the top of the fault zone and were landed in the Marcellus Shale between faults. Three of six horizontal wells extend northwest away from the fault zone; the other three horizontal wells extend southeast and end near a second fault zone.

This study looked for evidence that fluids and gas from hydraulically fractured areas of the Marcellus Shale were migrating upward and being produced from the wells in the Upper Devonian gas field. The gas and water produced from the Upper Devonian wells were monitored for: 1) pressure increases; 2) presence of man-made tracer injected with hydraulic fracturing fluids in an underlying Marcellus Shale well; and 3) natural isotopic tracers that might indicate the presence of gas and fluids from the Marcellus Shale.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013