scholarly journals Towards understanding earthquake triggering due to enhanced geothermal systems

2021 ◽  
Author(s):  
Saumik Dana
Keyword(s):  
Wave Propagation ◽  
Fracture Propagation ◽  
Friction Model ◽  
Fault Slip ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Earthquake Triggering ◽  
Fault Interaction ◽  
Poroelastic Media ◽  
Fracture Interaction

The effect of fluid pulse driven fractures (FPDF) propagating in poroelastic media on fault slip in the presence of natural fractures is a complicated interplay between fracture propagation, fracture-fracture interaction, fracture-fault interaction, friction model governing fault slip and wave propagation associated with pulsing injection. Furthermore, the problem is stochastic due to the uncertainty associated with the existing fracture-fault topology.

scholarly journals Comparing poroelastostatics and poroelastodynamics: Numerics, solvers and algorithms

2021 ◽  
Author(s):  
Saumik Dana
Keyword(s):  
Seismic Design ◽  
Fault Slip ◽  
Climate Mitigation ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Underground Structures ◽  
Wastewater Disposal ◽  
Energy Technologies ◽  
Time Marching ◽  
Mitigation Projects

Understanding the causality between the events leading upto and post fault slip and the earthquake recording is important for seismic design and monitoring of underground structures, bridges and reinforced concrete buildings as well as climate mitigation projects like carbon sequestration and energy technologies like enhanced geothermal systems or oilfield wastewater disposal. While the events leading upto fault slip are typically governed by poroelastostatics, the events post fault slip can easily transition into poroelastodynamics territory due to runaway fault slip velocities. There are marked differences in the numerics of poroelastostatics and poroelastodynamics, and a simple switch from one algorithm to another based on fault slip velocities is not trivial. In fact, an understanding of expected fault slip velocities is critical apriori, as an algorithm which can seamlessly transition from time marching in poroelastostatics realm to poroelastodynamics realm and vice-versa is extremely difficult to achieve. We present the numerics of both physics and point out the differences between the two in this work.

scholarly journals Fault slip potential induced by fluid injection in the Matouying EGS field, Tangshan seismic region, North China

2022 ◽  
Author(s):  
Chengjun Feng ◽  
Guangliang Gao ◽  
Shihuai Zhang ◽  
Dongsheng Sun ◽  
Siyu Zhu ◽  
...  
Keyword(s):  
Stress Field ◽  
North China ◽  
Active Faults ◽  
Fault Slip ◽  
Quantitative Risk Assessment ◽  
Fluid Injection ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Seismic Region ◽  
Hydraulic Stimulation

Abstract. The Tangshan region is one of the most seismically active areas in the North China, and the 1976 M 7.8 earthquake occurred on July 28th near the Tangshan fault zone. The Matouying Enhanced Geothermal Systems (EGS) field is located ~90 km away from Tangshan City. Since the late 2020, preliminary hydraulic stimulation tests have been conducted at depths of ~3965–4000 m. Fluid injection into geothermal reservoir facilitates heat exchanger system. However, fluid injection may also induce earthquakes. In anticipation of the EGS operation at the Matouying uplift, it is essential to assess how the fault slip potential of the nearby active and quiescent faults will change in the presence of fluid injection. In this study, we first characterize the ambient stress field in the Tangshan region by performing stress tensor inversions using 98 focal mechanism data (ML ≥ 2.5). Then, we estimate the principal stress magnitudes near the Matouying EGS field by analyzing in situ stress measurements at shallow depths (~600–1000 m). According to these data, we perform a quantitative risk assessment using the Mohr-Coulomb framework in order to evaluate how the main active faults might respond to hypothetical injected-related pore pressure increases due to the upcoming EGS production. Our results mainly show that most earthquakes in the Tangshan seismic region have occurred on the faults that have relatively high fault slip potential in the present ambient stress field. At well distances of less than 15 km, the probabilistic fault slip potential on most of the boundary faults increase with continuing fluid injection over time, especially on these faults with well distances of ~6–10 km. The probabilistic fault slip potential increases linearly with the fluid injection rate. However, the FSP values decrease exponentially with increased unit permeability. The case study of the Matouying EGS field has important implications for the deep geothermal exploitation in China, especially for Gonghe EGS (in Qinghai province) and Xiong’an New Area (in Hebei province) geothermal reservoirs that are close to the Quaternary active faults. Ongoing injection operations in the regions should be conducted with these understandings in mind.

Investigation of injection-induced seismicity using a coupled fluid flow and rate/state friction model

Geophysics ◽  
2011 ◽  
Vol 76 (6) ◽  
pp. WC181-WC198 ◽  
Author(s):  
Mark W. McClure ◽  
Roland N. Horne
Keyword(s):  
Fluid Flow ◽  
Induced Seismicity ◽  
Large Scale ◽  
Injection Pressure ◽  
Friction Model ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Isolated Fracture ◽  
Lower Magnitude ◽  
Event Magnitude

We describe a numerical investigation of seismicity induced by injection into a single isolated fracture. Injection into a single isolated fracture is a simple analog for shear stimulation in enhanced geothermal systems (EGS) during which water is injected into fractured, low permeability rock, triggering slip on preexisting large scale fracture zones. A model was developed and used that couples (1) fluid flow, (2) rate and state friction, and (3) mechanical stress interaction between fracture elements. Based on the results of this model, we propose a mechanism to describe the process by which the stimulated region grows during shear stimulation, which we refer to as the sequential stimulation (SS) mechanism. If the SS mechanism is realistic, it would undermine assumptions that are made for the estimation of the minimum principal stress and unstimulated hydraulic diffusivity. We investigated the effect of injection pressure on induced seismicity. For injection at constant pressure, there was not a significant dependence of maximum event magnitude on injection pressure, but there were more relatively large events for higher injection pressure. Decreasing injection pressure over time significantly reduced the maximum event magnitude. Significant seismicity occurred after shut-in, which was consistent with observations from EGS stimulations. Production of fluid from the well immediately after injection inhibited shut-in seismic events. The results of the model in this study were found to be broadly consistent with results from prior work using a simpler treatment of friction that we refer to as static/dynamic. We investigated the effect of shear-induced pore volume dilation and the rate and state characteristic length scale, [Formula: see text]. Shear-induced pore dilation resulted in a larger number of lower magnitude events. A larger value of [Formula: see text] caused slip to occur aseismically.

scholarly journals Thermo-Poroelastic Analysis of Induced Seismicity at the Basel Enhanced Geothermal System

2019 ◽  
Vol 11 (24) ◽  
pp. 6904 ◽  
Author(s):  
Sandro Andrés ◽  
David Santillán ◽  
Juan Carlos Mosquera ◽  
Luis Cueto-Felgueroso
Keyword(s):  
Rock Fracture ◽  
Green Energy ◽  
Fault Reactivation ◽  
Geothermal System ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Earthquake Triggering ◽  
Hydraulic Stimulation ◽  
Frictional Contacts ◽  
Stimulation Of

Geothermal energy has emerged as an alternative to ensure a green energy supply while tackling climate change. Geothermal systems extract the heat stored in the Earth’s crust by warming up water, but the low rock permeability at exploitation depths may require the hydraulic stimulation of the rock fracture network. Enhanced Geothermal Systems (EGS) employ techniques such as hydro-shearing and hydro-fracturing for that purpose, but their use promotes anthropogenic earthquakes induced by the injection or extraction of fluids. This work addresses this problem through developing a computational 3D model to explore fault reactivation and evaluating the potential for earthquake triggering at preexisting geological faults. These are included in the model as frictional contacts that allow the relative displacement between both of its sides, governed by rate-and-state friction laws and fully coupled with thermo-hydro-mechanical equations. We apply our methodology to the Basel project, employing the on-site parameters and conditions. Our results demonstrate that earthquakes which occurred in December 2006 in Basel (Switzerland) are compatible with the geomechanical and frictional consequences of the hydraulic stimulation of the rock mass. The application of our model also shows that it can be useful for predicting fault reactivation and engineering injection protocols for managing the safe and sustainable operation of EGS.

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