Keynote Address: A Speleologist's View of the High-Yielding Wells in Ohio's Newburg Zone

Construction of geothermal wells on the Ohio State campus in Columbus provided unprecedented insight into the character and origin of the Newburg Zone. In 2010, several 550-foot deep wells were drilled on 20-foot centers using air-rotary rigs. The boreholes were open-hole completions below 100 feet of surface casing. Drillers consistently encountered void zones at depths of 280 to 350 feet that produced geysers in previously drilled wells. This foreseeable calamity would continue to bedevil the project until another drilling method was used. Borehole videotapes taken in several wells, thin sections of core and geophysical logs taken in wells constructed by Ohio DNR subsequent to the benchmark work of Norris and Fidler in the 1970’s showed that the void zones occur from near the top of the Salina Group down into the top of the Lockport Dolomite. From campus, these units were traced northwestward to Toledo where they crop out in several quarries. Unusual caves, known as flank-margin caves, can be seen at one or more horizons in the walls of these quarries. Flank-margin caves form from the mixing of fresh groundwater with seawater, which can produce highly undersaturated conditions around the rims of carbonate islands and peninsulas such as exist today in the Bahamas and other tropical areas. These caves, which formed 400 million years ago when the North American continental plate was 30 degrees south of the equator, comprise the Newburg Zone. The origin of flank-margin caves is consistent with the areal extent, multiple levels, and sporadic occurrence of the Newburg Zone. All of which should serve as a warning to anyone contemplating construction of geothermal wells in west-central Ohio.