Environmental Life Cycle Analysis of Water and CO₂-Based Fracturing Fluids Used in Unconventional Gas Production

Abstract

Many of the environmental impacts associated with hydraulic fracturing of unconventional gas wells are tied to the large volumes of water that such operations require. Efforts to develop nonaqueous alternatives have focused on carbon dioxide as a tunable working fluid even though the full environmental and production impacts of a switch away from water have yet to be quantified. Here we report on a life cycle analysis of using either water or CO for gas production in the Marcellus shale. The results show that CO-based fluids, as currently conceived, could reduce greenhouse gas emissions by 400% (with sequestration credit) and water consumption by 80% when compared to conventional water-based fluids. These benefits are offset by a 44% increase in net energy use when compared to slickwater fracturing as well as logistical barriers resulting from the need to move and store large volumes of CO. Scenario analyses explore the outlook for CO, which under best-case conditions could eventually reduce life cycle energy, water, and greenhouse gas (GHG) burdens associated with fracturing. To achieve these benefits, it will be necessary to reduce CO sourcing and transport burdens and to realize opportunities for improved energy recovery, averted water quality impacts, and carbon storage.

Role of Cations in the Methane/Carbon Dioxide Partitioning in Nano- and Mesopores of Illite Using Constant Reservoir Composition Molecular Dynamics Simulation

“…A modified version of the PLUMED 2.3.0 plugin was used to apply the bias forces to maintain the fluid composition in the control regions. 69 The target CO 2 and CH 4 densities in the control regions were set to two CO 2 and two CH 4 molecules/ nm 3 . At the simulated temperature of 323 K, the reference target densities of fluid species in the control regions correspond to a total fluid pressure of 124 bar, based on the Peng−Robinson equation of state.…”

An Investigation of the Underlying Evolution of Shale Gas Research’s Domain Based on the Co-Word Network

“…Sustainability 2018, 10, 164 2 of 23 economic research of considering the potential application of SG [7,25,[33][34][35][36], the environmental impact assessment in SG exploitation [21,[37][38][39][40][41][42][43][44][45][46][47][48] and many others. Anyway, with the evolution from initial exploitation to the more and more complicated development of SG, the diverse research of SG can be found in available literature during past decades.…”

“…SG has complex characteristics such as large reserves, long production cycle, somewhat expensive exploration costs compared with other unconventional types of gas reservoirs and so on. The complexity of SG brings that the fields of SGR during the past years are diverse, which include theoretical SGR of analyzing the foundation of SG exploration [1,2,10,[24][25][26], model investigation in SG [24,[27][28][29][30][31][32][33], technical and economic research of considering the potential application of SG [7,25,[33][34][35][36], the environmental impact assessment in SG exploitation [21,[37][38][39][40][41][42][43][44][45][46][47][48] and many others. Anyway, with the evolution from initial exploitation to the more and more complicated development of SG, the diverse research of SG can be found in available literature during past decades.…”

Collapse of Reacted Fracture Surface Decreases Permeability and Frictional Strength

“…• Flow of acidic brine through fractures in mineralogically heterogeneous rocks selectively dissolves calcite and creates a porous layer • Calcite-depleted porous layer collapses under normal stresses, filling the fracture with fine particles, decreasing permeability • Layer of fine particles lowers fracture frictional strength because it prevents the formation of interlocking microasperities 2013; Fang et al, 2016;Majer et al, 2007;Moeck et al, 2009;Rinaldi et al, 2015;Segall & Fitzgerald, 1998;Talwani, 1997;Walsh & Zoback, 2016;Zoback & Gorelick, 2012). Concurrently, the injection of fluids into the subsurface can create reactive fluids, such as the injection of CO 2 which dissolves in water and forms carbonic acid (Benson & Cole, 2008;Bielicki et al, 2018;Borgia et al, 2012;Gaus, 2010;Pearce & Dawson, 2018;Wilkins et al, 2016). Such reactive brines can enter and alter flow pathways by dissolving reactive minerals and increasing fracture permeability (e.g., Hawkes et al, 2005).…”