Modeling of methane migration from gas wellbores into shallow groundwater at basin scale
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ORIGINAL ARTICLE
Modeling of methane migration from gas wellbores into shallow groundwater at basin scale Reza Taherdangkoo1 · Alexandru Tatomir1,2 · Martin Sauter1 Received: 10 March 2020 / Accepted: 3 September 2020 © The Author(s) 2020
Abstract Methane contamination of drinking water resources is one of the major concerns associated with unconventional gas development. This study assesses the potential contamination of shallow groundwater via methane migration from a leaky natural gas well through overburden rocks, following hydraulic fracturing. A two-dimensional, two-phase, two-component numerical model is employed to simulate methane and brine upward migration toward shallow groundwater in a generic sedimentary basin. A sensitivity analysis is conducted to examine the influence of methane solubility, capillary pressure–saturation relationship parameters and residual water saturation of overburden rocks, gas leakage rate from the well, tilted formations, and low-permeability sediments (i.e., claystones) on the transport of fluids. Results show that the presence of lithological barriers is the most important factor controlling the temporal–spatial distribution of methane in the subsurface and the arrival time to shallow groundwater. A pulse of high leakage rate is required for early manifestation of methane in groundwater wells. Simulations reveal that the presence of tilted features could further explain fast-growing methane contamination and extensive lateral spreading reported in field studies. Keywords Hydraulic fracturing · Methane leakage · Groundwater monitoring · Unconventional gas development · Numerical modeling
Introduction The global demand for energy is continuously increasing around the world and the International Energy Agency (IEA) anticipated more than 25% of growth by 2040 (IEA 2018). Natural gas production from unconventional resources is considered as a promising future source for energy supply as a bridge fuel toward a low-carbon energy system (Brown et al. 2009; McGlade et al. 2013). The surge for unconventional gas development has been projected to have impact on drinking water resources (Osborn et al. 2011; Sauter et al. 2012; Vengosh et al. 2014). The most frequent and severest threats are likely associated with (1) water acquisition in dry areas, (2) leaks and spills of fracturing fluids and wastewater * Reza Taherdangkoo [email protected]‑goettingen.de 1
Department of Applied Geology, Geosciences Center, University of Göttingen, Goldschmidtstr. 3, 37077 Göttingen, Germany
Department of Earth Sciences, Uppsala University, Villavägen 16, 75236 Uppsala, Sweden
2
(i.e., flowback and produced water) at the surface, (3) discharge of inadequately treated wastewater to the environment, and (4) migration of liquids (i.e., fracturing fluids and brine) and gas from deep hydrocarbon reservoirs into shallow aquifers (Melchers 2009; Rudolph et al. 2010; Sauter et al. 2012; Kissinger et al. 2013; U.S. EPA 2015; Rice et al. 2018a; Schout et al. 2020). Of the potential mechanis
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