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In the last years, numerous seismological evidences have shown a strict correlation between fluid injection and seismicity. An important topic that is currently under discussion in the scientific community concerns the prediction of the earthquake magnitude that may be triggered by fluid injection activities. Coupled fluid flow and geomechanical de...
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This paper examines the impact of the effective stresses that develop during depletion of a faulted reservoir. The study is based on finite element modeling using 2D plane strain deformation analysis with pore pressure and elastoplastic deformation of the reservoir and sealing shale layers governed by the Drucker–Prager plasticity model. The mechan...
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... Therefore, the existing studies potentially do not capture the full range of fluid-solid interactions. Furthermore, some studies choose to implement Biot poroelasticity via commercial tools, either by using default options (e.g., Schoenball et al., 2010;Vadacca et al., 2018) or through parameter tuning (e.g., Altmann et al., 2010;Fan et al., 2016), although it is yet to be understood how the underlying governing equations of these tools relate to Biot poroelasticity (Jin, 2023). The limitation in model complexity also constrains the scope of postmodeling analysis, leaving several critical issues largely unaddressed. ...
Knowledge of subsurface coupled pore pressure and stress perturbations due to saltwater disposal (SWD) is crucial for understanding and managing induced seismicity. Current studies choose Biot poroelasticity to implement fluid-rock coupling and perform numerical modeling in relatively simple settings. In this study, we first introduce a general poromechanical framework to capture a broader range of hydro-mechanical coupling and then apply it to model real-world SWD problems with geological and operational complexities. We demonstrate a viable workflow through the case study of a 2500 km2, layered, faulted, and recently seismically awaken area that has undergone multi-decadal multi-zone injection by nearly 200 SWD wells in the Midland basin. The example provides a unique opportunity to study the respective impact of shallow and deep injections across depths and the roles of inter-zone interactions, among others. Our modeling shows over 500 and 250 psi increases in the pore pressure and the Coulomb stress, respectively, in the deep disposal zone in the last decade, which were 5 to 10 times greater than their counterparts accumulated over the last four decades in shallower zones. Vertically, shallower injections impacted mostly shallower zones, whereas the deep injection produced changes across depths and dominated especially in the deep zone and the upper segment of the basement. Towards the mid-segment of the basement, changes due to shallow and deep injections were comparable, with the latter 2– 5 times higher. Laterally, in-zone changes were dominated by pore pressure diffusion in the near field and poroelastic stressing in the far field in shallower zones but were dominated by pore pressure diffusion everywhere in the deep zone, owing to their different hydraulic diffusivities. Faults acted as pore pressure and Coulomb stress sinks for a disposal zone and sources otherwise, and fault-zone structure led to a minor impact. Finally, seismological modeling suggests that the seismicity in the area was driven most likely by the deep injection.
... Another degree of complexity is more rarely considered when modelling geological contacts and fault slip: the possible anisotropy in their frictional properties. Morphological anisotropy is a known feature of faults, notably impacting the seismic waves velocity in their vicinity [16][17][18] or the mobility of natural and injected fluids [19] in the subsurface. Frictional anisotropy, interest- * vincentdospitalt@unistra.fr † renaud.toussaint@unistra.fr ...
The surface morphology of faults controls the spatial anisotropy of their frictional properties and hence their mechanical stability. Such anisotropy is only rarely studied in seismology models of fault slip, although it might be paramount to understand the seismic rupture in particular areas, notably where slip occurs in a direction different from that of the main striations of the fault. To quantify how the anisotropy of fault surfaces affects the friction coefficient during sliding, we sheared synthetic fault planes made of plaster of Paris. These fault planes were produced by 3D-printing real striated fault surfaces whose 3D roughness was measured in the field at spatial scales from millimeters to meters. Here, we show how the 3D-printing technology can help for the study of frictional slip. The results show that fault anisotropy controls the coefficient of static friction, with μ S / / , the friction coefficient along the striations being three to four times smaller than μ S ⊥ , the friction coefficient along the orientation perpendicular to the striations. This is true both at the meter and the millimeter scales. The anisotropy in friction and the average coefficient of static friction are also shown to decrease with the normal stress applied to the faults, as a result of the increased surface wear under increased loading.
... The slip tendency indicates if a fault is in a stable or unstable state of stress: if ST < μ s the state of stress is stable and no slip occurs along the fault plane. Otherwise, if ST ≥ μ s the strength of the fault is overcome and slip starts to propagate along the fault plane (Collettini & Trippetta, 2007;Lisle & Srivastava, 2004;Moeck et al., 2009;Morris et al., 1996;Vadacca et al., 2018). We use a static friction constitutive model where μ s is constant and equal to 0.6, which is a typical value for faults within carbonate rocks (Scuderi & Collettini, 2016). ...
... The volume is meshed by 3.3 million of tetrahedral elements with characteristic length varying from 100 m in the storage aquifer to 500 m away from it. The nodes along the fault surfaces are split in two following the split-node technique as described in Vadacca et al. (2018). This condition is necessary in order to model the deformation along the faults via frictional contacts. ...
The Val d'Agri basin hosts an oil‐field, the largest in onshore Europe, and it is one of the areas of highest seismic hazard in Italy. In an unproductive marginal portion of the reservoir, wastewater is re‐injected by a high‐rate well. Since the beginning of re‐injection in June 2006, a spatio‐temporal correlation between microseismicity (ML ≤ 2.0) and wastewater injection has been observed (suggesting induced seismicity). In this study, we perform a slip‐tendency analysis on the fault system involved in the induced seismicity through a coupled fluid‐flow and geomechanical numerical model simulating the stress partitioning due to the tectonic forces and to the fluid injection. The model results show that the fluid diffusion is strongly dependent on the active stress field and the geological structure in which fluids are injected, which conditioned the occurrence of seismicity that aligned on a small portion of a NE‐dipping fault. However, another fault located closer to the injection well and where no seismicity was detected, is the better well‐oriented fault with the active stress field and, also, the one more susceptible to the pore pressure increase. These results suggest different types of fault deformation acting in the Val d'Agri oilfield as response to the fluid injection (i.e., a mixed‐mode fault slip behavior). Understanding the stress partitioning in tectonically active regions where underground activities such as fluid injection are ongoing is fundamental to give strong constraints for the discrimination between natural and induced seismicity, and finally for a more reliable and robust definition of seismic hazard.
... The mesh nodes on Γ are split, this means that the nodes along the fault surfaces are duplicated, new node-IDs are assigned to the new nodes, and the mesh connectivity is updated. In this way, each fault is characterized by two surfaces that are geometrically coincident but distinct from the numerical point of view: one surface belongs to the hanging-wall block and the second one to the foot-wall block (Vadacca et al. 2018). The nodes on the perimeter of the fault are instead merged, as it is assumed that no crack propagation phenomena occur. ...
Induced seismicity as an effect of injection of fluids in a geological basin is a widely observed phenomenon which is nowadays under public scrutiny. In most cases, the numerical simulation and interpretation of these phenomena requires models with a high degree of realism. In turn, this requires accounting for complex interactions between the fluid and solid components, as well as a detailed description of geometry and a high degree of heterogeneity in the material properties. Also, issues related to the uncertainty of parameters, to an incorrect modeling of sub-scale or multiscale effects and to a limited knowledge of initial conditions are unavoidable and can be detrimental to the reliability of the results. In this work, a statistical analysis including uncertainty quantification and sensitivity analysis on variances has been applied as a post-processing to data coming from a set of numerical simulations of a real world setting (the Val D’Agri oilfield), with the aim of studying the stability of a fault that is known to have experienced a good amount of microseismicity during the modeled period. The uncertainty quantification targeted the effects of fault surface local orientation and pore pressure fluctuations, as well as variability in the friction coefficient of the fault. The analysis of variances focused on the effects of varying the permeability of the fault damage zones (the area enveloping the faults) and the geometrical orientation of the fault as well. The model shows that the zone where the microseismicity has been measured is included in a wider region of moderate instability, which is higher the lower the permeability of the fault damage zone. From the model results the fault seems to be far from a critical state, but the analysis offers, nevertheless, some useful information on the relationship of slip tendency with geometrical and flow quantities in the system, and suggests some improvements in the dynamical model assumptions and settings.
... Another degree of complexity is sometimes considered when modelling geological contacts and fault slip: the fault roughness and the possible anisotropy in their frictional properties. Morphological anisotropy is a known feature of faults, notably impacting the seismic waves velocity in their vicinity [14][15][16] or the mobility of natural and injected fluids [17] in the subsurface. Frictional anisotropy, interestingly, is also regularly studied in other fields than seismology, for instance the tribology of rubber tires [18,19], the strength of advanced adhesives [20], or the mitigation of water condensation [21]. ...
The surface morphology of faults controls the spatial anisotropy of their frictional properties, and hence their mechanical stability. Such anisotropy is only rarely studied in seismology models of fault slip, although it might be paramount to understand the seismic rupture in particular areas, notably where slip occurs in a direction different from that of the main striations of the fault. To quantify how the anisotropy of fault surfaces affects the friction coefficient during sliding, we sheared synthetic fault planes made of plaster of Paris. These fault planes were produced by 3D-printing real striated fault surfaces whose 3D roughness was measured in the field at spatial scales from millimeters to meters. Here, we show how the 3D-printing technology can help for the study of frictional slip. Results show that fault anisotropy controls the coefficient of static friction, with the friction coefficient along the striations being three to four times smaller than the friction coefficient along the direction perpendicular to the striations. This is true both at the meter and the millimeter scales. The anisotropy in friction and the average coefficient of static friction are also shown to decrease with the normal stress applied to the faults, as a result of the increased surface wear under increased loading.
... The volume is meshed by 3,673,141 tetrahedral elements. The nodes along the fault surfaces are split in two following the split-node technique described in [26] to allow fault slip. The crust is characterized entirely by a frictional-elastic rheology. ...
Geological and geophysical evidence suggests that the Altotiberina low-angle (dip angle of 15–20 ° ) normal fault is active in the Umbria–Marche sector of the Northern Apennine thrust belt (Italy). The fault plane is 70 km long and 40 km wide, larger and hence potentially more destructive than the faults that generated the last major earthquakes in Italy. However, the seismic potential associated with the Altotiberina fault is strongly debated. In fact, the mechanical behavior of this fault is complex, characterized by locked fault patches with a potentially seismic behavior surrounded by aseismic creeping areas. No historical moderate (5 ≤ Mw ≤ 5.9) nor strong (6 ≤ Mw ≤ 6.9)-magnitude earthquakes are unambiguously associated with the Altotiberina fault; however, microseismicity is scattered below 5 km within the fault zone. Here we provide mechanical evidence for the potential activation of the Altotiberina fault in moderate-magnitude earthquakes due to stress transfer from creeping fault areas to locked fault patches. The tectonic extension in the Umbria–Marche crustal sector of the Northern Apennines is simulated by a geomechanical numerical model that includes slip events along the Altotiberina and its main seismic antithetic fault, the Gubbio fault. The seismic cycles on the fault planes are simulated by assuming rate-and-state friction. The spatial variation of the frictional parameters is obtained by combining the interseismic coupling degree of the Altotiberina fault with friction laboratory measurements on samples from the Zuccale low- angle normal fault located in the Elba island (Italy), considered an older exhumed analogue of Altotiberina fault. This work contributes a better estimate of the seismic potential associated with the Altotiberina fault and, more generally, to low-angle normal faults with mixed-mode slip behavior.
Knowledge of subsurface pore pressure and stress perturbations due to saltwater disposal (SWD) is crucial for understanding, forecasting, and managing induced seismicity. Current studies choose Biot poroelasticity, which postulates two constitutive relationships to achieve hydro-mechanical (HM) coupling, as the governing framework, and perform numerical modeling in relatively simple settings. In this study, we first introduce a new poromechanical framework that naturally gives rise to HM coupling without prerequisites. We then use it to perform complex three-dimensional numerical modeling of fully coupled transient pore pressure and quasi-static poroelastic stress changes from multi-decadal, multi-zone SWD by over 180 wells injecting in a 900 mile2 area in and near Martin County, TX in the Midland Basin. We characterize pore pressure and Coulomb stress changes in both disposal and non-disposal zones, and explore inter-zone interactions, as well as effects of hydromechanical properties, faults, and fault-zone structures. We also separately quantify contributions by shallow and deep disposal and illustrate where pore pressure effects and poroelastic effects dominate, respectively. Finally, we model depth-dependent seismicity rate changes based on a rate-and-state earthquake nucleation model while generating maps of the associated triggering mechanisms. This study sheds light on SWD-induced changes in the subsurface and can inform future injection strategy in the area and other similar areas.
The dynamics of cracks is of paramount importance in material sciences and in everyday engineering, to correctly grasp the toughness of matter and of structures. It is also rather central in geosciences, for instance in the instability of seismic faults.During the rupture of a brittle elastic medium, a portion of the external mechanical load, provided to the matrix, is dissipated in a plastic zone at the fracture tip. This irreversible dissipation, which can be characterized by a macroscopically measurable energy release rate, derives from various physical processes. In particular, a rise in temperature from the intermolecular friction, directly inside the plastic zone.More than a marker for the damage, such a thermal dissipation at the tip can lead to an increase in the fracture velocity, as understood by statistical physics. In the present thesis, we study this possibility and propose an activation law in which the fracture induced heat is reintroduced. We show that it allows a good reproduction of the actual rupture of several materials and can explain the brittle-ductile transition of matter.
Rock is a heterogeneous material with primary damage and defects, which can greatly affect the mechanical properties of the rock and the slip on a fault. Additionally, slip on a fault can generate secondary damage in the surrounding rock. Therefore, this paper focuses on investigating injection-induced seismicity considering the heterogeneity and secondary damage in surrounding rocks with the FEM-based numerical code COMSOL. First, a heterogeneous model was established using the digital image processing technique, and the elemental microscale parameters were determined through comparison with testing results from a homogeneous model. Subsequently, using the defined damage variable and the rate and state friction law, numerical modeling was performed with the established homogeneous and heterogeneous models while considering the heterogeneity, fluid pressure, and generated secondary damage. The results showed that fluid pressure and heterogeneity can significantly influence injection-induced earthquakes. With increasing fluid pressure, the initial time for shear stress drop decreases, both the stress drop and the area of secondary damage increase, and the probability of unstable slip increases in a homogeneous rock matrix. Compared with the homogeneous numerical model, the heterogeneous model has a reduced time, a higher stress drop, a higher probability of seismicity, and a larger area of secondary damage. In addition, secondary damage is generated at two ends of the fault. The area of the secondary damage zone increases when unstable slip is induced, and the rate increases with slip velocity. The findings in this paper could facilitate better understanding of the mechanisms of fluid injection-induced seismicity and hence may be helpful for predicting, evaluating, and controlling induced seismicity.
