HOW STRAY GAS ESCAPED DURING CONSTRUCTION OF AN OIL/GAS WELL, INVADED A WATER-SUPPLY AQUIFER, AND CAUSED AN IN-HOUSE EXPLOSION (Invited Presentation)

On December 17, 2007, stray gas from construction of the English ^#1 gas well in Bainbridge Township, Ohio, caused an explosion in a residential home and triggered a nearby water well to spout 15 feet above land surface. The Ohio Department of Natural Resources (ODNR) routinely measured methane concentrations (lower explosive limits) for the next two years in basements of homes and in the headspace of residential wells. A subsequent lawsuit centered on interpretation of how the stray gas traveled from the 3700-ft deep oil/gas well into shallow residential wells at nearby properties. In an effort to settle the lawsuit by arbitration, ODNR, which was not a party in the lawsuit, set-up a panel of experts to review existing data and to identify additional types of data they needed to determine how the methane migrated to the residential properties. The expert panel consisted of faculty from three different universities in Ohio: a petroleum engineer, an aqueous geochemist, and a hydrogeologist.

Construction of a structure-contour map on the top of the Berea Sandstone, the major aquifer tapped by residential wells, indicated that stray gas from the English ^#1 well would migrate northward in the sandstone, which is overlain by a highly-jointed shale, along a sloping surface into a dome-like structure that has a spillover point on its eastern edge. The temporal methane measurements made in residential wells confirmed this migration pattern. Borehole videos taken in several residential wells directly after the in-house explosion were repeated in 2008 and 2009. Comparison of videos made in the same wells showed the bottom of the (stray) gas cap migrated vertically out of the sandstone into the Cuyahoga Shale. Overpumping 16 nearby residential wells for up to 7 months augmented this natural attenuation of the stray gas. The upward movement of the gas cap indicated accidental overpressurizing of the annular space following a substandard cement job in the English ^#1 well did not create multiple networks of fractures connecting the Clinton Sandstone production zone with the Berea Sandstone aquifer, as alleged in the lawsuit. The upward movement of the gas cap also indicated that natural gas from the production zone would not act as a perpetual source of hazardous gas that could invade homes and water wells forever, as also alleged in the lawsuit.