Life Cycle Implications of Using CO2-Based Fracturing Fluids As a Substitute for Slickwater

The rapid growth in the United States of unconventional oil and gas production from tight reservoirs has resulted in a variety of environmental impacts. At the regional scale these impacts are driven by the use of large volumes of water-based fracturing fluids, which create produced waste water and can impair fresh drinking water reservoirs. At the global scale, these fossil fuel reservoirs represent a major new source of previously inaccessible carbon, resulting in air emissions that negatively impact regional air quality and radiative forcing of the atmosphere. Many of these environmental impacts could be reduced by using non-aqueous CO₂-based fracturing fluids. Here we conducted a complete life cycle analysis of CO₂-based fracturing fluids to understand the costs and benefits associated with moving away from water. A stochastic life cycle model was built and tested using three fluids/scenarios: 1. Conventional slickwater-based fracturing fluids, 2. CO₂-based fracturing fluids as currently conceived, and 3. CO₂-based fracturing fluid using outlook parameters obtained from expert elicitation. The first scenario provides a benchmark in our process-based life cycle model. The second scenario evaluates the upstream and physicochemical processes that influence performance of CO₂-based fluids. The third scenario is based on near-term targets for CO₂ development. Water-based slickwater formations benefitted from several decades of technological refinement and improvements and the goal of this scenario was to understand how much technological investment could benefit CO₂ as a working fluid.

Our results suggest that even though CO₂-based fluids require more energy to deliver than water-based fluids, they have a lower GHG emission profile because much CO2 is buried during the fracturing process. More importantly, CO₂-based fluids also enable the production of considerably more natural gas from the same well. The capillary trapping that results from the use of water based fluids could be largely avoided by using non-aqueous fluids. Over the course of the full life cycle, this increase in production means CO₂-fracked wells have a lower impact on a per MJ natural gas produced basis. As expected, CO₂-based fracturing fluids lower the life cycle water demands of fracturing by a great deal.

These findings will then be framed in the context of regional-scale models of CO2 availability. Much of the United States exists in so-called “carbon deserts” wherein facilities can provide the large volumes of CO₂ that would be needed to complete an unconventional well. Pipeline infrastructure would need to be expanded to support these efforts, which would also support the development of other carbon management technologies. Using facility-scale models of CO₂-generating industries, we will compare the availability of CO₂ with the location of unconventional oil and gas fields to understand where opportunities exist for early adoption of this technology.