Hydro-thermo-mechanical analysis during injection of cold fluid into a geologic formation

doi:10.1016/j.ijrmms.2015.04.010

International Journal of Rock Mechanics and Mining Sciences

Volume 77, July 2015, Pages 220-236

https://doi.org/10.1016/j.ijrmms.2015.04.010 Get rights and content

Highlights

•
We investigate geomechanical responses when isothermal or cold fluid is injected.
•
We also investigate a hypothetical stepwise injection to explore its advantages.
•
The stepwise injection method alleviates thermal drop in the injection zone.
•
The stepwise injection improves mechanical stability at a site for both stress regimes.
•
We suggest dimensionless parameters to compare poro- and thermo-elastic stresses.

Abstract

We conducted in-depth investigations of pore-pressure buildup, temperature, and stress changes under isothermal or nonisothermal injection scenarios, using numerical simulations. The numerical simulation method combines fluid flow, poroelasticity, thermal diffusion, and thermal stress, and is based on the single-phase fluid flow condition. We also examined temporal evolutions of stress states and mobilized friction angles across base, injection zone, and caprock layers for two different stress regimes, normal-faulting and reverse-faulting. Results show that injecting cold fluid shifts an area in which the mobilized friction angle becomes maximum, which is where induced-seismic events are likely to be triggered first, for both stress regimes. We also tested a hypothetical stepwise injection of cold fluid; results show that this injection helps to improve the stability of the injection zone to some extent. Finally, we suggest using dimensionless parameters to determine a prevalence of the thermal-stress effect in the injection zone, and discuss the impact of the initial stress regime and implications of using the single-phase fluid flow condition.

Introduction

Extracting petroleum and natural gas during the era of fossil-fuel dominance has been a major operation that artificially disturbs stress states in geological formations that are generally deeper than ~500 m. In the meantime, efforts—such as CO₂ geologic sequestration, enhanced geothermal system (EGS), and wastewater injection—to diversify the energy portfolio and to alleviate the greenhouse gas effect are rendering fluid injection as important as fluid extraction. Injecting fluid into a geological formation could be more complex than extracting fluid for these primary reasons: first, injected fluid, whether similar to an original formation fluid (single-phase fluid flow such as wastewater injection and EGS) or a different one (two-phase flow such as CO₂ geologic sequestration and EGS with CO₂), causes pore-pressure buildup and poroelastic effects. Second, injected fluid (nonisothermal fluid flow such as CO₂ geologic sequestration, wastewater injection, and EGS) could retain a different temperature. Poroelastic and thermal stress effects can increase or oppose each other, depending on the condition of the injection/extraction and the bottom-hole temperature of fluids. In particular, injecting fluid colder than an original fluid will cause thermal contraction and corresponding decreases in stresses, which yield an effect opposite of what volume expansion and increases in stresses driven by isothermal fluid injection do. This study focuses on this phenomenon as it can occur in various operations deep under the surface.

These hydro-thermo-mechanical effects have drawn a great deal of attention for the last couple of decades, particularly in regard to energy and/or environmental applications. Salient examples include single-phase isothermal fluid flow [1], [2], [3], [4], two-phase isothermal fluid flow [5], [6], single-phase nonisothermal fluid flow [7], [8], [9], two-phase nonisothermal fluid flow [10], [11], [12], and wellbore heat-transfer problems [13].

In this study, we attempt an in-depth investigation of pore-pressure buildup, thermal diffusion, and stress changes for an isothermal and a nonisothermal cold fluid injection, using numerical simulations. We use the single-phase fluid flow condition to simplify a computation model and thus facilitate a focus on mechanical responses [14]. After the simulations, we examine stress states and mobilized friction angles to determine which layer—bottom, injection, or caprock—approaches most closely a failure criterion under different stress regimes. We also explore a stepwise injection of nonisothermal cold fluid as an alternative to nonisothermal fluid injection with a constant rate. Lastly, we provide discussions on the implications for various energy/environmental applications based on observations from this study.

Section snippets

Numerical simulations

Accounting for both poroelastic and thermal effects during fluid flow in a porous medium greatly increases the complexity of the problem. If this type of problem were to be solved analytically, initial and boundary conditions and geometry should be limited to a simple setting. In this regard, we conducted numerical simulations to investigate spatio-temporal evolutions of poroelastic and thermally-induced stresses and corresponding changes in stability when imposing isothermal or nonisothermal

Analyses: mechanical stability

Initial effective stress σ′ can be assessed simply as a function of initial total stress σ₀, initial pore pressure p_f0, and Biot׳s coefficient α: σ′=σ₀−αp_f0. Vertical and horizontal effective stresses, σ_v′ and σ_h′, are updated in response to the poroelastic and thermal-stress effects $σ_{v}^{'} = σ_{v 0} + Δ σ_{v}^{P} + Δ σ_{v}^{T} - α p_{f}$ $σ_{h}^{'} = K σ_{v 0} + Δ σ_{h}^{P} + Δ σ_{h}^{T} - α p_{f}$ where K represents the initial total stress ratio K=σ_h0/σ_v0, ∆σ^P denotes contribution from the poroelastic effect, and ∆σ^T represents thermally induced stress. We recorded (

Results and discussion: thermo-poroelastic behavior

We present numerical simulation results that shed light on geomechanical responses at a site across a base, an injection, and a caprock layer when isothermal or nonisothermal cold fluid is injected. We focus analysis on three lines of interest: the middle line of the injection zone, the interface between the injection zone and the caprock, and the vertical line located 10 m away from the injection well. When presenting results, compression is regarded as positive for stress changes.

Results and discussion: stepwise injection

The fluid injection rate affects the bottom-hole temperature at the injection well. When a cold fluid is injected from the surface, the fluid gets warmer because of the heat exchange with ambient rock before arriving at the bottom hole. Therefore, the slower the injection rate, the more heat the fluid gains from the ambient geothermal [13]. In this regard, we can hypothesize that if the injection rate of cold fluid jumps up stepwise, then the bottom-hole temperature of the fluid would

Discussion

In this section we discuss dimensionless numbers related to poroelastic and thermoelastic stresses, impact of the initial stress regime, and implications when the two-phase flow condition prevails.

Conclusions

We investigated geomechanical responses at an ideally designed site when isothermal or nonisothermal cold fluid is injected into it, using the numerical simulation method that is based on the single-phase fluid flow condition and combines poroelasticity and thermal stress equations. We also attempted a hypothetical stepwise injection method to explore its possible advantages.

The injection of cold fluid causes thermal contraction to be added to the overpressure-driven compression in the lower

Acknowledgments

This work was funded by the Gulf Coast Carbon Center at the Bureau of Economic Geology (BEG) and the U.S. Department of Energy, NETL, under Contract number DE-FE0009301.

References (32)

J.B. Altmann et al.
Poroelastic contribution to the reservoir stress path
Int J Rock Mech Min Sci
(2010)
V. Vilarrasa et al.
Hydromechanical characterization of CO₂ injection sites
Int J Greenh Gas Control
(2013)
J. Rutqvist et al.
Estimating maximum sustainable injection pressure during geological sequestration of CO₂ using coupled fluid flow and geomechanical fault-slip analysis
Energy Convers Manag
(2007)
J. Rutqvist et al.
Coupled reservoir–geomechanical analysis of the potential for tensile and shear failure associated with CO₂ injection in multilayered reservoir–caprock systems
Int J Rock Mech Min Sci
(2008)
S. De Simone et al.
Thermal coupling may control mechanical stability of geothermal reservoirs during cold water injection
Phys Chem Earth Parts A/B/C
(2013)
M. Preisig et al.
Coupled multi-phase thermo-poromechanical effects. Case study: CO₂ injection at In Salah, Algeria
Int J Greenh Gas Control
(2011)
V. Vilarrasa et al.
Long term impacts of cold CO₂ injection on the caprock integrity
Int J Greenh Gas Control
(2014)
V. Vilarrasa et al.
Liquid CO₂ injection for geological storage in deep saline aquifers
Int J Greenh Gas Control
(2013)
R.W. Zimmerman
Thermal conductivity of fluid-saturated rocks
J Pet Sci Eng
(1989)
F. Tong et al.
An effective thermal conductivity model of geological porous media for coupled thermo-hydro-mechanical systems with multiphase flow
Int J Rock Mech Min Sci
(2009)

P. Segall et al.

A note on induced stress changes in hydrocarbon and geothermal reservoirs

Tectonophysics

(1998)

A.V. Newman et al.

A four-dimensional viscoelastic deformation model for Long Valley Caldera, California, between 1995 and 2000

J Volcanol Geotherm Res

(2006)

R.T. Okwen et al.

Temporal variations in near-wellbore pressures during CO₂ injection in saline aquifers

Int J Greenh Gas Control

(2011)

S. Kim et al.

Above-zone pressure monitoring and geomechanical analyses for a field-scale CO₂ injection project in Cranfield

MS. Greenhouse Gases: Science and Technology

(2014)

M. Schoenball et al.

Fluid-induced microseismicity in pre-stressed rock masses

Geophys J Int

(2010)

Goodarzi S, Settari A, Zoback MD, Keith D. Thermal aspects of geomechanics and induced fracturing in CO2 injection with...

Cited by (64)

Thermo-poroelastodynamic response of a borehole in a saturated porous medium subjected to a non-hydrostatic stress field
2023, International Journal of Rock Mechanics and Mining Sciences
A thermo-poroelastodynamic (TPED) model incorporating the thermo-osmosis and thermal-filtration phenomena is used to analyze the transient response of a borehole subject to a non-hydrostatic stress field. The coupled TPED model is developed on the basis of equations of motion, fluid flow, heat transfer and constitutive equations so as to couple the stress wave, pressure wave and thermal wave in early times. Poroelastodynamics (PED) and thermo-elastodynamics (TED) models correspond two particular cases of the current model. The borehole problem is decomposed into the superposition of an axisymmetric mode and an asymmetric mode, corresponding to axisymmetric and deviatoric loadings, respectively. The semi-analytical solutions in the Laplace transform space are inverted numerically to obtain time-dependent displacement, pore pressure, temperature and stresses. Comparisons are performed among different sub-models to examine the influence of thermal effect on the response of pore pressure and stresses as well as the influence of pore water on the response of stress components. A direct comparison among the dynamic, quasi-static and static models shows that inertial effect is very important in the early times and it contributes to the early-time wave behavior.
Thermal-hydraulic-mechanical analysis of enhanced geothermal reservoirs with hybrid fracture patterns using a combined XFEM and EDFM-MINC model
2023, Geoenergy Science and Engineering
The long-term fluid circulation of Enhanced Geothermal Systems (EGS) involves complex coupled Thermal-Hydrological-Mechanical (THM) processes dominated by both hydraulic and activated natural fractures. The simulation of such multiphysical processes is known to be a challenging problem. In this work, we have developed an integrated numerical approach to advance the multiphysical simulation of EGS. In our model, the hydraulic fractures of arbitrary shapes in response to pressure changes and thermal strains are handled by the three-dimensional (3D) eXtended Finite Element Method (XFEM). The induced/natural fractures are incorporated into the model and treated as one continuum of the Multiple INteracting Continua (MINC) for the investigation of their impacts. A TOUGH -based program, TOUGH2-EGS, is utilized to simulate the Thermal-Hydrological processes. The 3D Embedded Discrete Fracture Method (EDFM), compatible with the 3D XFEM, is adopted to model the hydraulic fractures. Sensitivity analyses are performed for this model in terms of injection temperature and thermal expansivity. The hybrid EDFM and MINC model is established and analyzed for an EGS with both hydraulic and induced/natural fractures. The convergence performance of the single-fracture model shows that an appropriate stiffness coefficient is essential for this model and different choices of the coefficient values result in distinct behaviors. Our numerical results illustrate that the fracture aperture is opened by the cold fluid injection and the reservoir performance is dominated by the thermal stress/strain, which highlights the necessity of multiphysical simulation. In the hybrid model, the enhancement of the natural fracture permeability notably delays the thermal breakthrough by allowing injected fluid to contact more hot reservoirs. The novelties of this work lie in three aspects. Firstly, the combined 3D XFEM and EDFM is capable of handling arbitrary fracture shapes in a 3D EGS model. Secondly, the hybrid hydraulic and induced/natural fracture model enables us to establish the stimulated reservoir volume of the EGS and investigate the operational and geological parameters. Thirdly, the introduction of fracture stiffness stabilizes the numerical solution.
Seismicity induced by geological CO<inf>2</inf> storage: A review
2023, Earth-Science Reviews
Geological storage is a valuable strategy for reducing CO₂ emissions to the atmosphere, although seismicity induced by CO₂ injection can be a serious hazard that also becomes an obstacle to the development of CO₂ geological storage. The most important challenge in this field is fault systems that are difficult to detect and that have complex activation mechanisms, making the evaluation, prediction and control of CO₂ injection induced seismicity extremely difficult. It is also challenging to determine the triggering mechanism of injection induced seismicity. To promote the solution of these problems, we first review the experience and lessons learned from recent induced seismicity monitored in CO₂ geological storage (CGS) projects, and summarize the mechanisms that can be used to analyze CO₂ injection induced seismicity, including critical pressure theory, Biot's incremental strain theory, rate- and state-dependent frictional theory and fracture potential theory. We then discuss the theory and modeling of thermo-hydro-mechanical-chemical (THMC) coupling in CGS-induced seismicity. Knowledge of THMC coupling is an efficient way to improve the prediction of fault activation and seismic activity and enables characterization of pore pressure perturbation, temperature changes, and stress and geochemical effects. Through THMC simulation, we can more accurately characterize the change process of stress field, analyze and speculate the triggering and spatio-temporal evolution of induced earthquakes. We also summarize the advantages and disadvantages of maximum magnitude prediction based on statistical and physical models. The statistical method is easy to use, but ignores the physical characteristics of the reservoir. Although physical method overcomes this deficiency, obtaining sufficient modeling input parameters is always an challenging work. Finally, we analyze the challenges involved in the seismicity forecasting, including the quantification of stress state, the identification and characterization of complex fault system, the seismic mitigation injection scheme design, and reasonable seismic risk analysis model selection. This paper focuses on the scientific function of THMC coupling in the studies of CO₂ injection induced seismicity, so as to provide reference and guidance for the researches on the mechanism analysis and forecasting of such induced seismicity.
Numerical modeling of injection-induced earthquakes based on fully coupled thermo-poroelastic boundary element method
2022, Geothermics
In recent years, there has been a substantial increase in the induced seismicity associated with geothermal systems. However, understanding and modeling of injection-induced seismicity have still remained as a challenge. This paper presents a two-dimensional fully thermo-hydro-mechanical (THM) coupled boundary element approach to characterize the fault response to forced fluid injection and assess the effect of different injection protocols on seismic risk mitigation as well as permeability enhancement. The laboratory-derived rate-and-state friction law was used to capture the frictional paradigm observed in mature faults produced in granite rocks. All phases of stick-slip cycles, including aseismic slip, propagation of dynamic rupture, and interseismic periods, were simulated. The modeling results showed that the residual values of effective normal stress and static shear stress after a particular event completely dominate the constitutive behavior of fault friction during the next seismic event. The seismic energy analyses indicated that there is a negative correlation between the seismic magnitude and the total injected volume, such that a prolonged monotonic injection eventually results in the steady slip, rather than the seismic slip. Several fluid injection protocols were designed based on a volume-controlled (VC) approach and traffic light systems (TLS) to explore their effectiveness on the seismic risk mitigation and permeability enhancement. The results showed that cyclic injection based on TLS is the most effective approach for irreversible permeability enhancement of faults through promoting slow and steady slips. Our numerical simulations also revealed that fluid extraction (backflow-fixing bottom hole pressure at atmospheric pressure), regardless of the injection style, can considerably reduce the seismicity-related risks by preventing the fast-accelerated fracture slip during the post-injection stage. This study presents novel insights into modeling the rate-and-state governed faults exposed to forced fluid injection, and provides useful approaches for shear stimulation of faults with reduced seismic risks.
CO<inf>2</inf> plume and pressure monitoring through pressure sensors above the caprock
2022, International Journal of Greenhouse Gas Control
Commercial-scale development of CO₂ geological storage necessitates robust and real-time monitoring methods to track the injected CO₂ plume and provide assurance of CO₂ storage. Pressure monitoring above the injection zone is a method to detect potential CO₂ leaks into overlying formations. We present a generic CO₂ storage model with a single injector to predict pressure changes above the caprock due to both fast hydraulic communication and partially undrained loading, the latter often neglected in reservoir simulation. The simulation used a compositional simulator coupled with geomechanics to solve the poroelastic equations in the entire storage complex. The results show that changes of pore pressure above the caprock caused by partially undrained loading reach up to ∼15 kPa within ∼10 days followed by a gradual decay with time. This is about 1% of the pressure increase in the injection zone. Furthermore, the pressure changes above the caprock are closely related to the advance of the CO₂ plume. The results also include forward simulations considering the presence of: a fault either with high or low permeability, a poorly isolated abandoned well, a leaky injector, and a second injector. Fluid flow through high permeability paths across the caprock favors a ∼one order of magnitude higher, yet more gradual pressure increase than the base case with a fully covering caprock. Pressure monitoring above the caprock is a feasible technology to track the CO₂ plume, requires high precision pressure measurements, and must account for partially undrained poroelastic loading to interpret correctly measured pressure signals in the field.
Competition between cooling contraction and fluid overpressure on aperture evolution in a geothermal system
2022, Renewable Energy
Comprehensive understanding of aperture evolution of HDR (hot dry rock) fracture is critical for enhancing permeability in a geothermal system. Coupled HM (hydro-mechanical) and THM (thermo-hydro-mechanical) simulations are conducted to elucidate the competition between cooling contraction and fluid overpressure in fracture aperture enhancement during heat extraction. The effects of critical factors, including fracture geometry, reservoir properties, and injection settings on this competitive relationship, are systematically examined. We find that (1) fracture aperture is dominated by the competing effect of cooling contraction and fluid overpressure; the cooling-induced aperture grows as the injection time increases, declining the overpressure-induced aperture; (2) high thermal expansion coefficient and low fracture normal stiffness tremendously enlarge total and cooling-induced apertures and mildly shrink the overpressure-induced aperture; (3) decreasing fracture spacing and increasing fracture length remarkably improves the total aperture; the former increases the cooling-induced aperture while the latter enhances the overpressure-induced aperture; (4) the reduction of injection temperature increases the cooling-induced aperture and lowers the overpressure-induced aperture; the growth of flow rate expands both the cooling-induced and overpressure-induced apertures. We thus unveiled the mystery of the invisible aperture evolution during heat extraction. The findings largely benefit the optimization of mining parameters of a geothermal reservoir.

View all citing articles on Scopus

¹: Present address: Department of Civil and Environmental Engineering, Western New England University, 1215 Wilbraham Road, Springfield, MA 01119, USA.

View full text

Hydro-thermo-mechanical analysis during injection of cold fluid into a geologic formation

Highlights

Abstract

Introduction

Section snippets

Numerical simulations

Analyses: mechanical stability

Results and discussion: thermo-poroelastic behavior

Results and discussion: stepwise injection

Discussion

Conclusions

Acknowledgments

Int J Rock Mech Min Sci

Int J Greenh Gas Control

Energy Convers Manag

Int J Rock Mech Min Sci

Phys Chem Earth Parts A/B/C

Int J Greenh Gas Control

Int J Greenh Gas Control

Int J Greenh Gas Control

J Pet Sci Eng

Int J Rock Mech Min Sci

Tectonophysics

J Volcanol Geotherm Res

Int J Greenh Gas Control

Above-zone pressure monitoring and geomechanical analyses for a field-scale CO2 injection project in Cranfield

MS. Greenhouse Gases: Science and Technology

Fluid-induced microseismicity in pre-stressed rock masses

Geophys J Int

Above-zone pressure monitoring and geomechanical analyses for a field-scale CO₂ injection project in Cranfield