Causes and mitigation strategies of surface hydrocarbon leaks at heavy-oil fields: examples from Alberta and California

Schultz, R. A.

doi:10.1144/petgeo2016-070

Cited by 6 publications

(5 citation statements)

References 34 publications

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Section: Applicationsmentioning

confidence: 99%

“…Few observations attest to the fact that industrial operations can cause ascent of fluids in fractures. One such example is the spectacular surface fissures created due to steam injection documented in Schultz (2016); additional examples can be found in Schultz et al (2016). Geochemical data from aquifers above fracking operation sites have shown some evidence of the contamination of overlying units, which is attributed to poor well casing design, rather than fracture ascent (Vidic et al, 2013).…”

Section: Water Injection Into Stiff Rockmentioning

confidence: 99%

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Critical Fluid Injection Volumes for Uncontrolled Fracture Ascent

Davis

Rivalta

Dahm

2020

Geophysical Research Letters

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Hydrofracturing 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.

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Section: Applicationsmentioning

confidence: 99%

Section: Water Injection Into Stiff Rockmentioning

confidence: 99%

Critical Fluid Injection Volumes for Uncontrolled Fracture Ascent

Davis

Rivalta

Dahm

2020

Geophysical Research Letters

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show abstract

“…Few observations attest to the fact that industrial operations can cause ascent of fluids in fractures. One such example, are the spectacular surface fissures created due to steam injection documented in Schultz (2016); additional examples can be found in Schultz et al (2016). Geochemical data from aquifers above fracking operation sites has shown some evidence of the contamination of overlying units, which is attributed to poor well casing design, rather than fracture ascent (Vidic et al, 2013).…”

Section: Water Injection Into Stiff Rockmentioning

confidence: 99%

Critical fluid injection volumes for uncontrolled fracture ascent

Davis¹,

Rivalta²,

Dahm³

2020

Preprint

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Hydro-fracturing is a routine industrial technique whose safety depends on fractures remaining confined within the target rock volume. Both observations and theoretical models show that pockets of fluid can propagate large distances in the Earth's crust, in a self-sustained, uncontrolled manner, providing that the fluid volume is large enough. Existing models that describe when self-sustaining ascent starts are difficult to use for predictions, as they are mostly twodimensional (2D) and depend on parameters (typically the fracture length) that are hard to assess, even a posteriori.Here we constrain, both analytically and numerically in three-dimensions (3D), scale-independent critical volumes as a function of only rock and fluid properties. We apply our model to laboratory, industrial and natural settings, showing that our critical volumes are consistent with observations and can be used as a conservative estimate in geological applications. We find typical injection volumes exceed the limit we define for the start of self-sustaining fracture ascent. We describe a number of other processes that may work to arrest fractures with volumes exceeding this limit.This appears to have resulted in a false sense of operational safety when working with large injection volumes. In Non-peer reviewed EarthArXiv preprint the context of our findings we outline the quantitative work that would be required to better elucidate the processes causing fracture arrest, which could help to assess more comprehensively the safety of such operations.

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“…Observations of supraglacial lakes suddenly draining through growing crevasses indicate similar propagation rates (Das et al 2008;Stevens et al 2015). Although there is evidence that water-and gas-filled fractures can ascend through the crust (Schultz 2016;Cartwright et al 2021), this process has not been observed directly. Estimates based on geochemical analysis give ascent rates of ∼0.01-0.1 m s −1 (one kilometre per day) (Okamoto & Tsuchiya 2009).…”

Section: Motivationmentioning

confidence: 99%

Ascent rates of 3-D fractures driven by a finite batch of buoyant fluid

et al. 2022

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Propagation of fluid-filled fractures by fluid buoyancy is important in a variety of settings, from magmatic dykes and veins to water-filled crevasses in glaciers. Industrial hydro-fracturing utilises fluid-driven fractures to increase the permeability of rock formations, but few studies have quantified the effect of buoyancy on fracture pathways in this context. Analytical approximations for the buoyant ascent rate facilitate observation-based inference of buoyant effects in natural and engineered systems. Such analysis exists for two-dimensional fractures, but real fractures are three-dimensional (3-D). Here we present novel analysis to predict the buoyant ascent speed of 3-D fractures containing a fixed-volume batch of fluid. We provide two estimates of the ascent rate: an upper limit applicable at early time, and an asymptotic estimate (proportional to $t^{-2/3}$ ) describing how the speed decays at late time. We infer and verify these predictions by comparison with numerical experiments across a range of scales and analogue experiments on liquid oil in solid gelatine. We find the ascent speed is a function of the fluid volume, density, viscosity and the elastic parameters of the host medium. Our approximate solutions predict the ascent rate of fluid-driven fractures across a broad parameter space, including cases of water injection in shale and magmatic dykes. Our results demonstrate that in the absence of barriers or fluid loss, both dykes and industrial hydro-fractures can ascend by buoyancy over a kilometre within a day. We infer that barriers and fluid loss must cause the arrest of ascending fractures in industrial settings.

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Causes and mitigation strategies of surface hydrocarbon leaks at heavy-oil fields: examples from Alberta and California

Cited by 6 publications

References 34 publications

Critical Fluid Injection Volumes for Uncontrolled Fracture Ascent

Critical Fluid Injection Volumes for Uncontrolled Fracture Ascent

Critical fluid injection volumes for uncontrolled fracture ascent

Ascent rates of 3-D fractures driven by a finite batch of buoyant fluid

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