Induced seismicity in geologic carbon storage

Lyesse Laloui, Victor Vilarrasa Riano
Copernicus GmbH, 2019
Article

Résumé

Geologic carbon storage, as well as other geo-energy applications, such as geothermal energy, seasonal natural gas storage and subsurface energy storage imply fluid injection and/or extraction that causes changes in rock stress field and may induce (micro)seismicity. If felt, seismicity has a negative effect on public perception and may jeopardize wellbore stability and damage infrastructure. Thus, induced earthquakes should be minimized to successfully deploy geo-energies. However, numerous processes may trigger induced seismicity, which contribute to making it complex and translates into a limited forecast ability of current predictive models. We review the triggering mechanisms of induced seismicity. Specifically, we analyze (1) the impact of pore pressure evolution and the effect that properties of the injected fluid have on fracture and/or fault stability; (2) non-isothermal effects caused by the fact that the injected fluid usually reaches the injection formation at a lower temperature than that of the rock, inducing rock contraction, thermal stress reduction and stress redistribution around the cooled region; (3) local stress changes induced when low-permeability faults cross the injection formation, which may reduce their stability and eventually cause fault reactivation; (4) stress transfer caused by seismic or aseismic slip; and (5) geochemical effects, which may be especially relevant in carbonate-containing formations. We also review characterization techniques developed by the authors to reduce the uncertainty in rock properties and subsurface heterogeneity both for the screening of injection sites and for the operation of projects. Based on the review, we propose a methodology based on proper site characterization, monitoring and pressure management to minimize induced seismicity.

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https://infoscience.epfl.ch/record/267504?ln=fr

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Lyesse Laloui, Victor Vilarrasa Riano
Copernicus GmbH, 2019
Article

Résumé

Official source

https://infoscience.epfl.ch/record/267504?ln=fr

À propos de ce résultat

Concepts associés (11)

Concepts associés

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Publications associées (3)

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Fault reactivation during CO2 sequestration: Effects of well orientation on seismicity and leakage

Victor Vilarrasa Riano

Injection or withdrawal of fluid at depth may trigger felt seismicity. Such human-induced seismicity is a key environmental concern related to the exploitation of natural underground resources. Thus, understanding how to avoid triggering felt earthquakes plays a crucial role in the success of underground anthropogenic activities, such as CO2 geological storage. In this work, we conduct 3D simulations of injection-triggered fault reactivation, in order to investigate the effects of well geometry on seismic rupture and CO2 leakage. We analyze two different cases of injection, through (1) a vertical and (2) a horizontal well. Simulation results for the vertical well show the fault pressurizing faster and more locally than for the horizontal well, resulting in a smaller seismic event. For the horizontal well, the pressure is distributed over a wider area along the fault, which requires a longer time to reactivate, but results in a larger event. Fault reactivation also produces changes in damage-zone and fault-core permeability, allowing the CO2 to leak from the injection zone through overlying caprock, toward shallower depths. Although the calculated fault permeability enhancement is similar for the two cases, results show a slightly higher leakage rate for the vertical well in the region close to the well itself, while the leakage resulting from injection through the horizontal well is more widely distributed.Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

Wiley Periodicals, Inc2015

Chargement

Stress management in the context of induced seismicity in subsurface reservoirs

Barnaby Padraig Fryer

The stress state of the subsurface has been shown to have an influence on a number of key processes. For example, the criticality of the stress state indicates how large stress changes need to be before a fault begins to slip, the mean effective stress controls compaction and permeability loss in hydrocarbon reservoirs, the differential stress has been seen in seismology to have a strong influence on the size distribution of earthquake catalogues, with stress state further influencing the affinity of a fault to slip either seismically or aseismically, and the stress state strongly influences the propagation of a hydraulic fracture, with stress jumps being capable of completely halting a fracture's propagation. For reasons such as these, it has long been recognized that the state of stress is an important parameter for subsurface industrial operations such as hydrocarbon production, Enhanced Geothermal System (EGS) stimulation, carbon storage, and hydraulic fracturing. Generally, however, the state of stress does not remain constant during many of these operations. Decreasing effective stresses have led to induced seismicity during injection, fluid production has led to total stress changes which have induced seismicity, even in areas where pore pressure has decreased, temperature-induced stress changes have led to shear stimulation, and changes in total stress have led to so-called "frac-hits" where hydraulic fractures propagate towards depleted zones. These examples demonstrate an operator's ability to alter the state of stress, yet deliberate attempts to alter the stress state for the benefit of future operations have only been suggested a handful of times. Here, this idea of altering the state of stress is extended through a series of investigations. It is shown that, because production-induced seismicity is caused by total stress changes associated with the gradient of the produced fluid pressure, a hydraulic fracture which reduces the gradient required for production will also reduce the resulting seismicity. Conversely, compaction which leads to permeability loss will result in higher pore pressure gradients and therefore more induced seismicity. Both of these studies, which also have implications for optimal horizontal wellbore orientation, are investigated through the use of a poroelastic reservoir simulator developed during the thesis. In a following study, it is suggested that high stress path reservoirs are attractive targets for fluid injection, as total stress changes will result in an increased stability despite increasing pore pressure. Further, the concept of stress preconditioning is introduced, such that operators alter the stress state of an EGS reservoir to promote more favorable earthquake distributions. These concepts, which make up the first three chapters of the thesis, all are forms of reservoir management that reduce the risk associated with induced seismicity. Following this, in a numerical study, the idea of stress preconditioning is extended to allow for directed stimulation treatments in EGS's. Finally, the idea of inducing stress jumps through production such that hydraulic fractures do not propagate vertically is evaluated by means of scaling analyses and numerical simulation, with implications for carbon storage. More than the individual propositions, this thesis promotes the mindset that, where appropriate, attempts should be made to alter the state of stress for the benefit of future operations.

EPFL2020

Chargement

In the past 20 years, the growing interest in deep geo-reservoirs for purposes such as carbon storage, waste water disposal, or geothermal energy exploitation have led to large-volume fluid injections into the upper continental crust. These fluid injections have caused a massive increase in the seismicity rate in some normally âquietâ regions. Recent observations suggested that different injection strategies could produce different mechanical responses in these reservoirs. In this vein, cyclic fluid injections have been proposed as an alternative to conventional monotonic injections to mitigate induced earthquakes. Additionally, recent studies have suggested that injection into deeper geo-reservoirs, at the brittle-ductile transition, could reduce (or suppress) induced earthquakes. In this context, this research has aimed at bettering our understanding of reservoir deformation during different fluid injection strategies. Laboratory experiments were performed on porous reservoir rock under different reservoir conditions and fluid injection strategies. In the first section, it is demonstrated that water-saturated conditions, compared to dry conditions, cause a reduction in uniaxial compression strength in five sandstones. Additional experiments suggest that this water weakening of sandstones is due to the reduction of the fracture toughness and of the static friction of the materials. In the second section, it is shown that under drained conditions, pore fluid pressure oscillations affect the long-term mechanical behaviour of intact porous rocks. More than the amplitude of the oscillations, the period controls the time-to-failure, failure strength and dilatancy rate of the sample. Additionally, the pore fluid pressure oscillations control the AE events (a proxy for the seismicity): the AE events rate oscillates in-phase with the pore fluid pressure variations. Increasing the differential stress, the amplitude and the period of the oscillations accentuates this behaviour. In the third section, it is demonstrated that under drained conditions, pore fluid pressure oscillations strongly affect the mechanical behaviour of faults. The pore fluid pressure signal directly controls the instabilitiesâ (i.e., stick-slip and AE events) distribution, with an increase of events at elevated pore fluid pressure. For initially stable sliding faults, the pore fluid pressure oscillation signal controls the onset of unstable slip: the higher the pore fluid pressure oscillationâs amplitude, the lower the stress and displacement at the onset of a seismic event. In the fourth section, it is shown that under quasi-drained conditions, a pore fluid pressure increase within a rock undergoing ductile deformation causes instantaneous dilation of the system. Further increasing the pore fluid pressure leads to the development of localized deformations and the shear fracturing of the rock. The macroscopic shear fracturing is not instantaneous when the ductile to brittle transition is passed. Prior to this, a creeping phase is necessary. The time and strain length of this creeping phase are controlled by the rate of pore fluid pressure increase: the faster the injection, the longer the creeping phase. This work provides new insight into the mechanical behaviour of rock masses and faults under various crustal conditions during pore fluid pressure variations. It helps to constrain the mechanisms involved in deep geo-reservoirs submitted to different injection strategies.

EPFL2021

Chargement

EPFL2021

Stress management in the context of induced seismicity in subsurface reservoirs

Barnaby Padraig Fryer

EPFL2020