Effects of Asperity Distribution on Fluid Flow and Induced Seismicity During Deep Geothermal Exploitation

AbstractThis work investigates the injection-induced seismic response of a heterogeneous fault plane, featuring low-permeability asperities embedded into a high-permeability damage zone. We simulate the pressure evolution with a hydrogeological simulator, accounting for the heterogeneous fault plane. Seismicity occurs then on the asperities, represented as unstable patches reactivating by means of the Mohr-Coulomb criterion. The hydrological and seismic modules are implicitly coupled to account for effects of asperity reactivation on the permeability. Results show that permeability changes may cause at a later time a change in seismicity propagation. We also investigated such effects by varying the density of asperities

Full three-dimensional relocation and tomographic inversion of the 1977-2008 earthquakes in north-eastern Italy: a feasibility study

In a regional seismological network, the estimation of the epicenter is usually robust, especially for events inside or close to the network boundaries. In contrast, the hypocentral depth is very sensitive to the assumed velocity field. In this study, we compare the hypocenter estimates obtained by a classical algorithm in a simple one-dimensional (1D) model with a recently developed full 3D model that is based on shrinking grids. This study is preliminary, as the 3D Earth model is based on limited data from the literature; however, it demonstrates that different patterns show up when a more representative geological model is adopted. This encourages further studies, based on fully integrated 3D models from active surface seismic, well data and other geophysical measurements. Such an integrated approach has been successfully adopted by the oil and gas industries for decades, which has increased the exploration success rate and the production of hydrocarbon reservoirs

Fault reactivation induced by tunneling activity in clay material: Hints from numerical modeling

ISSN:0886-7798ISSN:1878-436

Effects of asperity distribution on fluid flow and induced seismicity during deep geothermal exploitation

This work investigates the injection-induced seismic response of a heterogeneous fault plane, featuring low-permeability asperities embedded into a high-permeability damage zone. We simulate the pressure evolution with a hydrogeological simulator, accounting for the heterogeneous fault plane. Seismicity occurs then on the asperities, represented as unstable patches reactivating by means of the Mohr-Coulomb criterion. The hydrological and seismic modules are implicitly coupled to account for effects of asperity reactivation on the permeability. Results show that permeability changes may cause at a later time a change in seismicity propagation. We also investigated such effects by varying the density of asperities.ISSN:1876-610

Effects of asperities distribution on induced seismicity and permeability during deep underground exploitation

International audienc

Fault Stability Perturbation by Thermal Pressurization and Stress Transfer Around a Deep Geological Repository in a Clay Formation

ISSN:2169-9313ISSN:0148-0227ISSN:2169-935

On the physics-based processes behind production-induced seismicity in natural gas fields

Induced seismicity due to natural gas production is observed at different sites worldwide. Common understanding states that the pressure drop caused by gas production leads to compaction, which affects the stress field in the reservoir and the surrounding rock formations and hence reactivates preexisting faults and induces earthquakes. In this study, we show that the multiphase fluid flow involved in natural gas extraction activities should be included. We use a fully coupled fluid flow and geomechanics simulator, which accounts for stress-dependent permeability and linear poroelasticity, to better determine the conditions leading to fault reactivation. In our model setup, gas is produced from a porous reservoir, divided into two compartments that are offset by a normal fault. Results show that fluid flow plays a major role in pore pressure and stress evolution within the fault. Fault strength is significantly reduced due to fluid flow into the fault zone from the neighboring reservoir compartment and other formations. We also analyze scenarios for minimizing seismicity after a period of production, such as (i) well shut-in and (ii) gas reinjection. In the case of well shut-in, a highly stressed fault zone can still be reactivated several decades after production has ceased, although on average the shut-in results in a reduction in seismicity. In the case of gas reinjection, fault reactivation can be avoided if gas is injected directly into the compartment under depletion. However, gas reinjection into a neighboring compartment does not stop the fault from being reactivated.ISSN:2169-9313ISSN:0148-0227ISSN:2169-935

Hydro-mechanical fault reactivation modeling based on elasto-plasticity with embedded weakness planes

In this paper, an elasto-plastic constitutive model is employed to capture the shear failure that may occur in a rock mass presenting mechanical discontinuities, such as faults, fractures, bedding planes or other planar weak structures. The failure may occur in two modes: a sliding failure on the weak plane or an intrinsic failure of the rock mass. The rock matrix is expected to behave elastically or fail in a brittle manner, being represented by a non-associated Mohr-Coulomb behavior, while the sliding failure is represented by the evaluation of the Coulomb criterion on an explicitly defined plane. Failure may furthermore affect the hydraulic properties of the rock mass: the shearing of the weakness plane may create a transmissive fluid pathway. Verification of the mechanical submodel is conducted by comparison with an analytical solution, while the coupled hydro-mechanical behavior is validated with field data and will be applied within a model and code validation initiative. The work presented here aims at documenting the progress in code development, while accurate match of the field data with the numerical results is current work in progress.ISSN:1674-7755ISSN:2589-041

Combined approach of poroelastic and earthquake nucleation applied to the reservoir-induced seismic activity in the Val d’Agri area, Italy

In this work, an approach is developed to study the seismicity associated with the impoundment and level changes of a water reservoir (reservoir induced seismicity – RIS). The proposed methodology features a combination of a semi-analytical poroelastic model with an earthquake nucleation approach based on rate-and-state frictional law. The combined approach was applied to the case of the Pertusillo Lake, located in the Val d’Agri area (Italy), whose large seasonal water level changes are believed to induce protracted micro-seismicity (local magnitude ML < 3). Results show that the lake impoundment in 1962 could have produced up to 0.5 bar (1 bar = 100 kPa) changes in Coulomb failure stress (ΔCFS), while the seasonal water level variation is responsible for variation up to 0.05 bar. Modeling results of the seismicity rates in 2001−2014 show that the observed earthquakes are well correlated with the modeled ΔCFS. Finally, the reason that the seismicity is only observed at southwest of the Pertusillo Lake is provided, which is likely attributed to different rock lithologies and depletion caused by significant hydrocarbon exploitation in the northeastern sector of the lake.ISSN:1674-7755ISSN:2589-041