USE OF REMOTE SENSING TECHNOLOGIES TO DETECT SURFACE AND NEAR-SURFACE STRAY GAS OCCURRENCE AND POTENTIAL MIGRATION PATHWAYS IN TIOGA CO., PA (Invited Presentation)

Shell has an active program of Marcellus Shale gas development in NE Pennsylvania. Ongoing gas production in Pennsylvania depends on industry's ability to drill and complete gas wells in a safe and environmentally responsible manner. Key to protection of fresh groundwater resources is avoidance of pre-existing natural and man-made conduits of methane coupled with proper drilling and well construction techniques to ensure zonal isolation.

In Tioga County, Pennsylvania, Upper Devonian gas-bearing sandstones of the Catskills Formation occur at or near the surface across most of Tioga County. In addition to naturally occurring methane surface seeps seen across this region, historical oil / gas and water well construction practices have in some cases resulted in vertical conduits for methane migration from shallow gas-bearing sandstones into freshwater aquifers. Methane injected into the Oriskany Sandstone for storage has also been detected by USGS researchers in freshwater aquifers. Finally, imperfect zonal isolation by the surface and intermediate casing and cement intervals can result in a potential conduit for methane getting into groundwater.

In August 2011, Shell contracted with NEOS GeoSolutions to conduct a remote sensing survey of our Tioga County operating area in Pennsylvania. A fixed-wing aircraft was used to collect band-specific hyperspectral, magnetic, gravity, electromagnetic and radiometric data over all of Tioga County. In addition, a helicopter system was used to collect high-resolution band-specific hyperspectral, magnetic, electromagnetic and radiometric data over a project specific area. Key project objectives were:

• Detection of surface hydrocarbon seeps and potential indirect hydrocarbon indicators.
• Detection of abandoned / derelict oil and gas wells not found in state agency or commercial databases.Mapping of resistivity anomalies in the near-surface to provide an indication of potential aquifer salinity variations and locations of shallow gas sands in the Upper Devonian Bradford Group.
• Definition of surface lineaments and fracture corridors, and identification of fault networks that can be extended from the surface into the subsurface when integrated with 3D and 2D seismic.
• Developing a hyperspectral-derived image of surface geo-hazards and geo-botanical variations.