Abstract
AbstractHydrofracturing is a routine industrial technique whose safety depends on fractures remaining confined within the target rock volume. Both observations and theoretical models show that, if the fluid volume is larger than a critical value, pockets of fluid can propagate large distances in the Earth's crust in a self‐sustained, uncontrolled manner. Existing models for such critical volumes are unsatisfactory; most are two‐dimensional and depend on poorly constrained parameters (typically the fracture length). Here we derive both analytically and numerically in three‐dimensional scale‐independent critical volumes as a function of only rock and fluid properties. We apply our model to gas, water, and magma injections in laboratory, industrial, and natural settings, showing that our critical volumes are consistent with observations and can be used as conservative estimates. We discuss competing mechanisms promoting fracture arrest, whose quantitative study could help to assess more comprehensively the safety of hydrofracturing operations.
Highlights
Official guidelines for hydraulic fracturing (e.g., EPA, 2016; Mair et al, 2012) outline safe operational practices for regulators
Both observations and theoretical models show that, if the fluid volume is larger than a critical value, pockets of fluid can propagate large distances in the Earth's crust in a self‐sustained, uncontrolled manner
We apply our model to gas, water, and magma injections in laboratory, industrial, and natural settings, showing that our critical volumes are consistent with observations and can be used as conservative estimates
Summary
Official guidelines for hydraulic fracturing (e.g., EPA, 2016; Mair et al, 2012) outline safe operational practices for regulators. Such reports often state that during routine operations, fractures are unlikely to grow out of the target rock formation, as typical injection pressures are too low for this to occur. These claims are substantiated with empirical observations from closed access microseismic data of scarce vertical fracture growth following injection (Fisher & Warpinski, 2012). After deriving a theoretical model and validating it with numerical simulations, we apply this to cracks filled with air, water, oil, and magma in solids of varying stiffness and toughness, across a wide range of length scales
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