A MAP OF RECOMMENDED SURFACE CASING DEPTHS FOR OIL AND GAS WELL CONSTRUCTION IN A REGION OF THE MARCELLUS AND UTICA SHALES

Domestic shale gas usage is expected to reduce U.S. spending on foreign hydrocarbons, create new jobs, and add to both federal and state revenue streams. However, localized environmental impacts can occur if improperly cased wells do not seal off freshwater aquifer zones. A geographic information system (GIS) was used to combine several geologic map layers and perform raster analysis to produce a map of minimum surface casing depths that meet state regulations for oil and gas well construction. Mapped casing depths range from 20-200 m feet below ground surface. Three different hydrogeologic areas were identified based on the presence or absence of the Cussewago Sandstone, assumed to be the deepest bedrock aquifer. Each area required a different approach to spatial analysis and data set for mapping purposes. Areas without the Cussewago Sandstone (55% of the region) used the depth to bedrock as the base of the freshwater zone and had the largest casing depths. Areas with Cussewago Sandstone in the subsurface (39% of the region) and outcrops of the Cussewago Sandstone (6% of the region) had much smaller casing depths. The result is a regional map (1,325 km2 area) that provides recommended outer casing depths based on ground surface elevation, elevation of the base of the deepest freshwater aquifer, and state regulations. This represents a novel mapping effort based on published datasets that provides a timely resource for well drillers, regulators, and/or property owners to effectively manage regional groundwater resources.