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Hydraulic fracturing and horizontal drilling has led to a shale gas energy boom in the United States. In addition to decreasing domestic energy costs, shale gas production has substantially reduced domestic CO2 emissions, largely due to natural gas displacing coal-fired electricity generation. Water is the principal component of working fluids used for commercial hydraulic fracturing, along with other constituent chemicals and substances to enhance fracture propagation/longevity and propping agent (e.g., sand) transport. Industry, policy makers, and other stakeholders are aware of potential disadvantages of aqueous fracturing fluids, including water scarcity, environmental impact from constituent chemicals, and poor fracture performance. To address these problems we are undertaking a study using supercritical CO2 as a replacement working fluid. Supercritical CO2 has many potential benefits and drawbacks compared with water as a fracturing fluid; it may increase gas production through several coupled processes including enhanced fracturing, reduced flow blocking, and miscibility with in-place hydrocarbons, as well as challenges such as economics, resource availability, and assurances that the CO2 is safely sequestered in the target formation. Through a combination of basic experiments, modelling, and historical research, we formally address these issues.
Middleton et al. (Wed,) studied this question.