Time-lapse magnetotelluric monitoring of an enhanced geothermal system

Geophysics ◽  
2013 ◽  
Vol 78 (3) ◽  
pp. B121-B130 ◽  
Author(s):  
Jared R. Peacock ◽  
Stephan Thiel ◽  
Graham S. Heinson ◽  
Peter Reid
Keyword(s):  
South Australia ◽  
Time Lapse ◽  
Fault System ◽  
Fluid Distribution ◽  
Geothermal System ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Hydraulic Stimulation ◽  
Microseismic Data ◽  
Before And After

Realization of enhanced geothermal systems (EGSs) prescribes the need for novel methods to monitor subsurface fracture connectivity and fluid distribution. Magnetotellurics (MT) is a passive electromagnetic (EM) method sensitive to electrical conductivity contrasts as a function of depth, specifically hot saline fluids in a resistive porous media. In July 2011, an EGS fluid injection at 3.6-km depth near Paralana, South Australia, was monitored by comparing repeated MT surveys before and after hydraulic stimulation. An observable coherent change above measurement error in the MT response was present and causal, in that variations in phase predict variations in apparent resistivity. Phase tensor residuals proved the most useful representation for characterizing alterations in subsurface resistivity structure, whereas resistivity tensor residuals aided in determining the sign and amplitude of resistivity variations. These two tensor representations of the residual MT response suggested fluids migrated toward the northeast of the injection well along an existing fault system trending north-northeast. Forward modeling and concurrent microseismic data support these results, although microseismic data suggest fractures opened along two existing fracture networks trending north-northeast and northeast. This exemplifies the need to use EM methods for monitoring fluid injections due to their sensitivity to conductivity contrasts.

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.

A numerical study of the mechanism of injection-induced and triggered seismicity at the Pohang Enhanced Geothermal Systems project, South Korea

2021 ◽  
Author(s):  
Kwang-Il Kim ◽  
Hwajung Yoo ◽  
Seheok Park ◽  
Juhyi Yim ◽  
Linmao Xie ◽  
...  
Keyword(s):  
South Korea ◽  
Numerical Study ◽  
Geothermal System ◽  
Enhanced Geothermal Systems ◽  
Hydraulic Stimulation ◽  
Triggered Seismicity ◽  
Induced Stress ◽  
Shear Slip ◽  
Stress Dependent ◽  
The Impact

<p>Hydraulic stimulation for the creation of an Enhanced Geothermal System (EGS) reservoir could potentially reactivate a nearby fault and result in man-made earthquakes. In November 15, 2017, an M<sub>w</sub> 5.5 earthquake, the second largest after the initiation of the South Korean national instrumental monitoring system, occurred near an EGS project in Pohang, South Korea. The earthquake occurred on a previously unmapped fault, that is here denoted the M<sub>w</sub> 5.5 Fault. A number of previous studies to model the hydraulic stimulation in the Pohang EGS project have been carried out to identify the mechanism of seismic events. Those previous studies focused on coupled hydro-mechanical processes without the consideration of pre-existing fractures and thermal effects. This study presents an investigation of the mechanisms of induced and triggered seismicity in the Pohang EGS project through three-dimensional coupled thermo-hydro-mechanical numerical simulations. Fractures intersecting the open-hole sections of two deep boreholes, PX-1 and PX-2, clearly indicated by field observations are modeled along with the M<sub>w</sub> 5.5 Fault. Models of stress-dependent permeability models are calibrated based on the numerical reproduction of the pressure-time evolution during the field hydraulic stimulations. The Coulomb failure stress change at the M<sub>w</sub> 5.5 Fault is calculated to quantify the impact of five hydraulic stimulations. In the case of PX-2 stimulations, the pore pressure buildup results in a volumetric expansion of the reservoir and thereby the perturbation of stresses is transferred to the M<sub>w</sub> 5.5 Fault. The volumetric contraction of the reservoir by the temperature reduction could slightly perturb the stress distribution at the M<sub>w</sub> 5.5 Fault. In the case of PX-1 stimulations, shear slip of the PX-1 fracture is explicitly modeled. The modeling shows that transfer of the shear stress drop by the shear slip stabilizes the M<sub>w</sub> 5.5 Fault, which is consistent with the field observation that the seismicity was not induced at the M<sub>w</sub> 5.5 Fault by the PX-1 stimulations. The cooling-induced thermal stress additionally reduces the effective normal stress of PX-1 fracture. Thus, some additional shear slip of the PX-1 fracture is induced by the thermal effect. However, the modeling shows that for both PX-1 and PX-2 stimulations, thermally-induced stress perturbations are very small compared to pressure-induced stress perturbations.</p>

Microseismic monitoring of the hydraulic stimulation at the Paralana enhanced geothermal system, South Australia

First Break ◽  
2012 ◽  
Vol 30 (7) ◽  
Author(s):  
V. Oye ◽  
N. Langet ◽  
M. Hasting ◽  
I. Lecomte ◽  
M. Messeiller ◽  
...  
Keyword(s):  
South Australia ◽  
Microseismic Monitoring ◽  
Geothermal System ◽  
Enhanced Geothermal System ◽  
Hydraulic Stimulation

Modeling fluid flow through complex fracture network in geological media by using hierarchical hydraulic properties

2020 ◽  
Author(s):  
Kyung Won Chang ◽  
Gungor Beskardes ◽  
Chester Weiss
Keyword(s):  
Fluid Flow ◽  
Surrounding Medium ◽  
Computational Cost ◽  
Energy Resource ◽  
Fracture Network ◽  
Fractured Media ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Hydraulic Stimulation ◽  
Complex Fracture

<p>Hydraulic stimulation is the process of initiating fractures in a target reservoir for subsurface energy resource management with applications in unconventional oil/gas and enhanced geothermal systems. The fracture characteristics (i.e., number, size and orientation with respect to the wellbore) determines the modified permeability field of the host rock and thus, numerical simulations of flow in fractured media are essential for estimating the anticipated change in reservoir productivity. However, numerical modeling of fluid flow in highly fractured media is challenging due to the explosive computational cost imposed by the explicit discretization of fractures at multiple length scales. A common strategy for mitigating this extreme cost is to crudely simplify the geometry of fracture network, thereby neglecting the important contributions made by all elements of the complex fracture system.</p><p>The proposed “Hierarchical Finite Element Method” (Hi-FEM; Weiss, Geophysics, 2017) reduces the comparatively insignificant dimensions of planar- and curvilinear-like features by translating them into integrated hydraulic conductivities, thus enabling cost-effective simulations with requisite solutions at material discontinuities without defining ad-hoc, heuristic, or empirically-estimated boundary conditions between fractures and the surrounding formation. By representing geometrical and geostatistical features of a given fracture network through the Hi-FEM computational framework, geometrically- and geomechanically-dependent fluid flow properly can now be modeled economically both within fractures as well as the surrounding medium, with a natural “physics-informed” coupling between the two.</p><p>SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.</p>

scholarly journals Deep learning for extracting micro-fracture: Pixel-level detection by convolutional neural network

2020 ◽  
Vol 205 ◽  
pp. 03007
Author(s):  
Yejin Kim ◽  
Seong Jun Ha ◽  
Tae sup Yun
Keyword(s):  
Neural Network ◽  
Deep Learning ◽  
Convolutional Neural Network ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Frequency Noise ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Hydraulic Stimulation ◽  
Roughness Analysis

Hydraulic stimulation has been a key technique in enhanced geothermal systems (EGS) and the recovery of unconventional hydrocarbon resources to artificially generate fractures in a rock formation. Previous experimental studies present that the pattern and aperture of generated fractures vary as the fracking pressure propagation. The recent development of three-dimensional X-ray computed tomography allows visualizing the fractures for further analysing the morphological features of fractures. However, the generated fracture consists of a few pixels (e.g., 1-3 pixels) so that the accurate and quantitative extract of micro-fracture is highly challenging. Also, the high-frequency noise around the fracture and the weak contrast across the fracture makes the application of conventional segmentation methods limited. In this study, we adopted an encoder-decoder network with a convolutional neural network (CNN) based on deep learning method for the fast and precise detection of micro-fractures. The conventional image processing methods fail to extract the continuous fractures and overestimate the fracture thickness and aperture values while the CNN-based approach successfully detects the barely seen fractures. The reconstruction of the 3D fracture surface and quantitative roughness analysis of fracture surfaces extracted by different methods enables comparison of sensitivity (or robustness) to noise between each method.

Heat Flux to Fluids Within a Rock Fracture in a Geothermal System

2010 ◽  
Author(s):  
Dustin Crandall ◽  
Goodarz Ahmadi ◽  
Grant Bromhal
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Rate ◽  
Numerical Study ◽  
Rock Fracture ◽  
Working Fluid ◽  
Geothermal System ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Ct Scanner

Fractures in rocks enable the motion of fluids through the large, hot geologic formations of geothermal reservoirs. The heat transfer from the surrounding rock mass to the fluid flowing through a fracture depends on the geometry of the fracture, the fluid/solid properties, and the flow rate through the fracture. A numerical study was conducted to evaluate the changes in heat transfer to the fluid flowing through a rock fracture with changes in the flow rate. The aperture distribution of the rock fracture, originally created within Berea sandstone and imaged using a CT-scanner, is well described by a Gaussian distribution and has a mean aperture of approximately 0.6 mm. Water was used as the working fluid, enabling an evaluation of the efficiency of heat flux to the fluid along the flow path of a hot dry geothermal system. As the flow through the fracture was increased to a Reynolds number greater than 2300 the effect of channeling through large aperture regions within the fracture were observed to become increasingly important. For the fastest flows modeled the heat flux to the working fluids was reduced due to a shorter residence time of the fluid in the fracture. Understanding what conditions can maximize the amount of energy obtained from fractures within a hot dry geologic field can improve the operation and long-term viability of enhanced geothermal systems.

scholarly journals Analysis of Hydraulic Fracturing and Reservoir Performance in Enhanced Geothermal Systems

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Mengying Li ◽  
Noam Lior
Keyword(s):  
Hydraulic Fracturing ◽  
Flow Direction ◽  
Fractured Reservoirs ◽  
Geothermal System ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems ◽  
Fracture Width ◽  
Reservoir Performance ◽  
Flow And Heat Transfer ◽  
Engineered Geothermal System

Analyses of fracturing and thermal performance of fractured reservoirs in engineered geothermal system (EGS) are extended from a depth of 5 km to 10 km, and models for flow and heat transfer in EGS are improved. Effects of the geofluid flow direction choice, distance between fractures, fracture width, permeability, radius, and number of fractures, on reservoir heat drawdown time are computed. The number of fractures and fracture radius for desired reservoir thermal drawdown rates are recommended. A simplified model for reservoir hydraulic fracturing energy consumption is developed, indicating it to be 51.8–99.6 MJ per m3 fracture for depths of 5–10 km.

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.

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