CO 2 -Enhanced Gas Recovery in Shale: Lessons Learned in the Devonian Ohio Shale of Eastern Kentucky

The Kentucky Geological Survey tested CO2-enhanced gas recovery in the Devonian shale in Johnson County, in response to a directive from the Kentucky General Assembly in 2007; the study site included a fracture-stimulated shale-gas well. To supplement a standard suite of open-hole logs acquired when the well was drilled, a well-logging program was designed to identify open perforations, construct a flow profile, and acquire pre-injection baseline data to characterize the Devonian Ohio Shale for a pressure falloff test. Tubing and packer were installed, with gel and brine filling the annulus between the tubing and packer to block flow-through perforations identified above the packer. From Sept. 6–10, 2012, 87 tons of CO2 was injected in three phases, with at least 12 hr between phases to allow for pressure decline. On the last day of injection, the pressure of the annulus between the casing and injection tubing approached the injection pressure, indicating CO2 had leaked out of the test zone. Therefore, the test was terminated before a planned injection of 300 tons of CO2 was completed. Following injection, the well was closed for 2 weeks to allow a “soak. ” A meter run was constructed to monitor flowback, and during the flowback a second flow profile and post-injection production log were acquired. Analysis indicates the leak was likely the result of communication through induced fractures (from the original completion) from the Ohio Shale to the overlying Berea Sandstone. The Ohio Shale likely retained some of the CO2, thus confirming the potential to displace additional natural gas, but the small volume of CO2 and escape of an unknown amount of CO2 from the zone of interest severely constrained anything but a qualitative assessment. Introduction The Intergovernmental Panel on Climate Change (2014) and others have identified an increase in manmade emissions of greenhouse gases, particularly CO2 emitted from industrial sources such as electric utilities, as contributing to climate change. The concerns identified by the Panel have driven research to develop carbon-management strategies, including storing CO2 in deep geologic structures and formations. Geologic storage of carbon has been identified as an essential strategy for mitigating manmade carbon and reducing the effects of greenhouse-gas emissions (Pacala and Socolow, 2004; Metz and others, 2005; National Energy Technology Laboratory–Office of Fossil Energy, 2015; Koperna and others, 2016), and often the beneficial reuse of that stored CO2 is cited as being a valuable offset for the cost of capture and storage. Since the 1970s, CO2 has been injected for enhanced oil recovery in deep reservoirs in Texas, Louisiana, and Mississippi, among other states. CO2-enhanced gas recovery and sequestration have been tested in coal; the advantage in coal is that CO2 becomes immobile by adsorbing onto organic matter in the coal (Reznik and others, 1984; Gunter and others, 1997, 2005; Reeves, 2002). With the emergence of the “shale revolution,” organic-rich shales across the United States are being recognized as self-sourced