Inga Berre is Professor at the Department of Mathematics, University of Bergen. Her main research interests are mathematical modelling, partial differential equations and numerical methods, in particular motivated by simulation of coupled thermal-hydraulic-mechanical processes in fractured geothermal systems. Related to these topics, she has led several research projects and graduated many PhD and master students. Since 2018, Inga Berre has chaired the Joint Program Geothermal, European Energy Research Alliance and since 2019 she has been co-chair of the SET-Plan Deep Geothermal Implementation Working Group. She is Associate Editor of Geothermal Energy (Springer). Inga Berre is member of the Norwegian Academy of Technological Sciences.
Title: Mathematical and numerical modeling of coupled subsurface dynamics due to fluid injection in fractured formations Abstract
Fluid injection in the subsurface effects the thermal, hydraulic, mechanical and chemical (THMC) state at depth, resulting in strongly coupled processes that lead to significant structural deformation of the subsurface, for example fracture reactivation and slip. This talk focus on mathematical and numerical modeling of coupled dynamics in fractured formations as a consequence of fluid injection. A main challenge is in properly capturing the interaction between the fractured structure and coupled THMC processes; how the processes results in deformation and propagation of fractures and how the fractured structures strongly affect the processes. The talk will discuss modeling approaches, numerical solution strategies and provide results from a recent case study.
Emily E. Brodsky (U. of California, Santa Cruz)Profile
Emily Brodsky is a professor and earthquake physicist at the University of California, Santa Cruz. Her research focuses on connecting empirical observations of earthquakes with fundamental physical processes. Prof. Brodsky earned her A.B. from Harvard in 1995 and Ph.D. from Caltech in 2001. She is the recipient of the inaugural 2005 Charles Richter Early Career award from the Seismological Society of America, the 2008 James Macelwane Medal from the American Geophysical Union (AGU), the 2019 Woolard Award from the Geological Society of America (GSA) and the 2019 Gutenberg Lectureship and is a Fellow of both AGU and GSA. She was selected as a Distinguished Lecturer for the NSF Earthscope program, the Geo-Prisms program, International Ocean Discovery Program (IODP) and the National Science Board. She has served on the Board of Directors of the Southern California Earthquake Center (SCEC) and Incorporated Research Institutes for Seismology (IRIS). She has published over 100 peer-reviewed articles, has an h-index of 50 and presented over 150 invited lectures talks in 30 states and 13 countries. Her work was been featured in major press outlets such as the BBC, NPR, Time Magazine, NY Times, Nature, Reuters, LA Times and The Wall Street Journal.
Title: Permeability that Changes over Time Abstract
Earthquakes can increase permeability in fractured rocks. In the farfield, such permeability increases are attributed to seismic waves and can last for months after the initial earthquake. Laboratory studies suggest that unclogging of fractures by the transient flow driven by seismic waves is a viable mechanism. Permeability enhancement by seismic waves could potentially be engineered and the experiments suggest the process will be most effective at a preferred frequency.
We have observed similar processes inside active fault zones after major earthquakes. A borehole observatory in the fault that generated the M9.0 2011 Tohoku earthquake revealed a sequence of temperature pulses during the secondary aftershock sequence of an M7.3 aftershock. The pulses are attributed to fluid advection by a flow through a zone of transiently increased permeability. Directly after the M7.3 earthquake, the fault zone was damaged and highly susceptible to further permeability enhancement, but ultimately heals within a month and becomes no longer as sensitive. Longer term healing was seen in the fault zone of the 2008 M7.9 Wenchuan earthquake.
The competition between damage and healing (or clogging and unclogging) results in dynamically controlled permeability, storage and hydraulic diffusivity. Recent measurements of in situ fault zone architecture at the 1-10 meter scale suggest that active fault zones often have hydraulic diffusivities near 10-2 m2/s. This uniformity is true even within the damage zone of the San Andreas fault where permeability and storage increases balance each other to achieve this value of diffusivity over a ~400 m wide region. Fault zones may evolve to a preferred diffusivity in a dynamic equilibrium.
Tomasz Hueckel is a Professor at Duke University, in Durham, NC, USA. He obtained his PhD in Applied Mechanics from Polish Academy of Sciences, Warsaw, Poland and D.Sc. in Physical Sciences from University and Polytechnical Institute of Grenoble, France. He started his career at the Institute of Fundamental Technological Research, Warsaw, Poland, after which he worked 5 years in energy industry in Italy, before joining Duke University. He was a visiting professor in Belgium, France, Switzerland, Spain and Poland. Has been one of early pioneers in multi-physics geomechanics, of application to underground energy resource and environmental geomechanics. His most impactful work concerns constitutive modeling of soils with elasto-plastic coupling in 1970s, thermo-plasticity of soils and shales, in 1980s, and chemo-plasticity of soils and rocks, in 1990s, criteria of instability and cyclic loading of soils, evaporation of capillary bridges, drying shrinkage and cracking of soils, intergranular chemo-mechanical contact effects, as well as development of specialized equipment for soil testing.
Title: Phenomenological versus Mechanism Modeling of Multiphysics Coupling in Fracturing Geomaterials Abstract
This presentation addresses modeling of coupling of physico-chemical -hydraulic-processes and mechanical properties of geomaterials undergoing fracturing. The context of the modeling are applications to enhanced geothermal technology, shale fracking, as well as cracking due to drying of exposed rock surfaces and potential of cracking in CO2 sequestration technology. The technological objectives may be opposite in the above cases: either to form/enhance or prevent/contain fracturation of rocks. The main question though remains the same, which is modeling of conditions at which cracks form and propagate in geomaterials under complex induced physico-chemical environment. There are two (at least) ways of addressing coupled processes involved in fracturing of geomaterials: one phenomenological, and another one is through hypothetical mechanisms developing at different scales. The choice of the approach is linked to the level of understanding of the phenomena involved as well as to the availability of their numerical characterization. The outcome of the different modeling approach may result in a different level of controllability of the processes involved. Two examples are discussed: one of a phenomenological coupling of chemical effect of acidification on mechanical processes in crack propagation in rock, and another one of crack generation as a result of drying of rock either through natural or forced ventilation, or gas injection into saturated medium.
Takatoshi Ito is now Professor of Geomechanics, Institute of Fluid Science, Tohoku University, Japan, since January 2010. He received a Dr. Eng. from Tohoku University in 1993, and served as an Associate Professor at the institute from 1993 to 2008. Within that period, he stayed temporarily at Stanford University as a Visiting Associate Professor to work with Professor Zoback in the SRB group from 1997 to 1998. He was involved in the National project of methane hydrate development in Japan since 2006. His current research interests include sand production, fracturing in unconsolidated sands, CO2 geological storage, geomechanical approach to geothermal energy development, and in-situ stress measurements.
Title: A breakthrough in rock stress measurement applicable deep and high temperature environment Abstract
By releasing anisotropic compressive strains of rock mass, the core samples expand radially in anisotropic manner at core drilling, and as a result, they become to have a very slight elliptical cross section. This phenomenon allows us to measure the rock stress state from cross sectional shape of the retrieved core as presented in Funato and Ito, IJRMMS (2017). However, the method can measure only the difference between the maximum and minimum horizontal stresses, Smax and Smin, in a plane perpendicular to the borehole but not each one of those stress components separately. The reason for the limitation is come from the difficulty to measure the original core diameter before expansion. To overcome this problem, we proposed a new concept to modify the way of core drilling so that a partial section of a core sample expands to have elliptical cross section due to stress relief but the other section maintains circular cross section before expansion. From the core samples obtained in that way, we can measure how much the core expands in any direction, and the measured amount of expansion allows us to estimate the in-situ stress magnitude. Since this method does not require any in-situ test, it should be applicable to deep depth and high temperature environment in geothermal field, as long as the core samples can be obtained.
Chun’an Tang (Dalain U. of Technology)Profile
Chun'an TANG, as a chair Professor, is the Director of the Center for Rock Instability and Seismicity Research (CRISR) and the Deep Underground Research Center (DURC) of Dalian University of Technology. He is also the Vice President of the Chinese Society of Rock Mechanics and Engineering CSRME, and was the China National Group Chairman of International Society of Rock Mechanics. In 1988, he got his Ph.D at Northeastern University, China, and continued his post-doctoral work in Imperial College, London, UK. He leads several major research projects in rock mechanics, especially on rock failure process analysis and monitoring in civil engineering. He proposed a damage model using continuum mechanics and the linear method for numerically processing non-linear and discontinuum mechanics problems in rock failure which is fulfilled in numerical code Realistic Failure Process Analysis (RFPA). He is the chief scientist of a National 973 program for fundamental research. His work was funded by the "Trans-Century Training Programme Foundation for Outstanding Young Scholars in China" from the State Education Ministry and by the "Special Natural Science Foundation for Outstanding Young Scholars in China" from National Nature Science Foundation. So far, he has published more than 400 technical papers on rock failure mechanisms and civil engineering, and is the author of five Chinese books of rock mechanics and the principle author of "Rock Failure Mechanism" published by CRC (Taylor & Francis Group, 2010, UK).
Title: TOUGH-RFPA: A Coupled Thermal-Hydro-Mechanical Rock Failure Process Analysis Simulator Abstract
Coupled processes are vital in reservoir engineering during both reservoir stimulation and subsequent energy production (e.g., geothermal, oil and gas reservoirs). Complex thermal-hydro-mechanical (THM) processes including heat transfer, fluid flow, and rock deformations occur simultaneously and are affected by many non-linear processes. In this work, the multiphase, multicomponent fluid flow, and heat transport simulator TOUGH2 is linked with the geomechanics analysis software Realistic Failure Process Analysis (RFPA). The linked simulator TOUGH-RFPA takes advantage of the capability of calculating multiphase and multicomponent flow using TOUGH, and the ability to analyzing damage processes of rocks using RFPA. TOUGH accounts for the transition of components between the available phases and internally calculate the thermophysical properties of specific fluid mixtures, which change dynamically and should be considered in deep underground engineering. RFPA can simulate the failure process of heterogenous rock without special fracture elements or predefined fracture paths. Reproducing the process of rock failure and the growth of discrete fractures is required in the mechanical calculation, because rock failures and fractures influence the fluid flow transmissivity and heat transfer. Moreover, mechanical properties and thermophysical properties may be spatially heterogeneous according to the Weibull distribution initially and evolve with system temperature, pressure, and mechanical stress. The TOUGH-RFPA combination is ideal for investigation such spatial heterogeneity impact in reservoir managements, from wellbore, stimulation volume to the large-scale reservoirs. For geothermal and hydrocarbon reservoir management, both coupled THM processes, and the phase change and thermophysical property variations of fluid are necessary to be considered as usually a high-pressure and high-temperature systems. At last, the applicability of TOUGH-RFPA was demonstrated for modeling cooling-induced damage around a very deep geothermal well with micro-scale heterogenous properties, which indicated unexpectedly complex damage evolution during well cooling.
Ki-Bok Min (Seoul National University)Profile
Prof Min is currently a professor at the department of energy resources engineering in Seoul National University. His research interest is coupled thermal, hydraulic and mechanical processes in fractured rock applied to various Geo-Energy applications. Numerical modeling of coupled process, stress- and temperature-mediated change of fracture hydraulics and integrated in situ stress estimations are the focus of his recent research. Prof Min received BSc and MSc from Seoul National University and PhD from the Royal Institute of Technology (KTH) in Sweden, and is currently an associate editor of International Journal of Rock Mechanics and Mining Sciences
Ove Stephansson memorial lecture *
Title: Outstanding Issues in Coupled Process for Engineering Fractured Rock Mass at Depth
* This memorial lecture is in memory of professor Ove Stephansson who passed away on February 19, 2020. Abstract
Fractured rock mass has been engineered for various geological applications for a long time. While the applications in shallow depths such as tunnels and underground caverns are established, there are great challenges in deeper formation, e.g., > ~500 m. This talk will present outstanding issues in engineering fractured rock mass at depth by focusing on coupled thermal, hydraulic and mechanical processes with recent and historical examples. Grand challenges include, but not limited to, characterization of fractures, estimation of in situ stress, enhancing or suppressing permeability, management of induced seismicity and numerical modeling of coupled process. This keynote lecture is dedicated to Prof Ove Stephansson who passed away in Feb, 2020.