Biosketch

Luke P. Frash is a staff scientist at Los Alamos National Laboratory with more than 11 years experience in the topic area of rock fractures and fluid flow. His work includes triaxial experiments to characterize rock fracture strength, permeability, and geometry at in-situ stress and temperature conditions. This work has also included hydraulic fracture studies in rock blocks at elevated stress and temperature conditions. Most recently, he has been focusing on scaling theory to predict natural and stimulated fracture properties at in-situ conditions. Learnings from this work is currently being combined with laboratory and field experience to develop a fast simplified-physics rock fracture, fluid flow, and power prediction discrete fracture network model named “GeoDT”. Applications include fundamental geosciences, hydrology, CO2 sequestration and utilization, geothermal energy, oil and gas, and nuclear waste repositories.

Introduction of the Lecture

Enhanced Geothermal Systems (EGS) bring together complex multi-physics and subsurface uncertainty while at the same time demanding useful quantitative predictions. For this application, fractures with apertures that can be less than 1 mm and lengths that can exceed 100 m are used to extract heat from three-dimensional reservoirs at the greater than 1 km scale for hopefully more than 20 years. Adding to the prediction challenge, the properties of pre-existing natural fractures and yet-to-be stimulated fractures are unknown and change over time. However, even with uncertainties that can span orders of magnitudes, it should be possible to optimize the design of enhanced geothermal systems using statistical analysis. In this talk, I will present an overview of our work to predict EGS performance using an open-source Geothermal Design Tool that we developed (GeoDT). This tool uses empirical power-law scaling to estimate fracture and flow properties that are supported by measurements from lab and field. The tool also leverages the concept of ‘fracture caging’ to shift the engineering challenge away from predicting fracture behavior and towards imposing the desired fracture behavior. Such a capability is vital to overcoming thermal ‘short circuiting’ where pre-mature cooling shortens the useful life of an EGS project. Our work here is still in progress, but the results so far are indicating that EGS could be made more viable by bringing together directional drilling, zonal-isolation, high-rate high-pressure pumping, and fracture caging technology. By this approach, we have a feasible path forward to decrease capital costs, decrease or eliminate the risk of damaging induced seismicity, and improve the efficiency and predictability of geothermal wells.

Biosketch

Cyprien Soulaine is an Associate Scientist at CNRS, the French National Centre for Scientific Research, working at the Institute of Earth Sciences of Orléans, France. He develop hybrid-scale models for coupled processes in porous and fractured media. He considers a wide variety of scales ranging from nanometers to kilometers. Cyprien’s interest in pore-scale physics led to the development of computational microfluidics for geosciences. His research is very broad and applications include carbon dioxide storage in the subsurface, hydrogen production, water resources management, and superfluid quantum turbulence in porous media. Before, joining CNRS, Cyprien spent 5 years at Stanford University in Energy Resources Engineering department as a Research Associate in the group of Prof. Tchelepi. He has a PhD in Fluid Dynamics from Institut Polytechnique de Toulouse, France.

Introduction of the Lecture

Naturally occurring porous media involve a wide range of spatial scales.  Image-based simulations offer an appealing framework to investigate fracture-matrix interactions in reactive environments. However, the large contrast of characteristic length-scales involved in fractured porous media – the typical pore sizes of the rock matrix and the fracture aperture differ by several orders of magnitude – limits the use of very high-resolution images that fully resolve both the fracture and the matrix microstructure. Nevertheless, the presence of the surrounding porous matrix can impact the evolution of the fracture aperture by the development of a weathered zone at the vicinity of the fracture-matrix interface and must be included in the modeling. Here, we use micro-continuum simulations to compare the evolution of a fracture geometry under various conditions.

Micro-continuum models are a versatile and powerful approach to simulate multi-scale coupled processes in porous media [1,2]. The governing equations are rooted in the elementary physical principles and combined with appropriate sub-grid models for describing processes in the unresolved porosity [3]. Micro-continuum approaches are intrinsically two-scale allowing simulations in fractures (Stokes flow) surrounded by a porous matrix (Darcy’s law) [4]. Conditions at the interface between the two domains are included in the partial differential equations and automatically satisfied. The technique is also powerful to move fluid / solid boundaries in the presence of geochemical processes.

Despite its early age micro-continuum approach for pore-scale processes has already demonstrated its strength in image-based simulations and coupled physics. State-of-the-art micro-continuum models handle hydro-bio-geochemical processes [4,5,6], two-phase flow [7,8], and poromechanics [9]. In this talk, we give an overview of micro-continuum models applied to fracture-matrix interactions and we discuss our most recent developments.

References

[1] Soulaine and Tchelepi, Micro-continuum approach for pore-scale simulation of subsurface processes, Transport In Porous Media, 2016, 113, 431-456

[2] Steefel, Beckingham, Landrot “Micro-continuum approaches for modeling pore-scale geochemical processes” Rev Mineral Geochem 80, 217-246 (2015)

[3] Soulaine, Gjetvaj, Garing, Roman, Russian, Gouze, Tchelepi, The impact of sub-resolution porosity of X-ray microtomography images on the permeability, Transport in Porous Media, 2016, 113(1), 227-243

[4] Noiriel and Soulaine “Pore-scale imaging and modelling of reactive flow in evolving porous media: tracking the dynamics of the fluid-rock interface” Transport in Porous Media 140, 181-213 (2021)

[5] Soulaine, Roman, Kovscek, Hamdi, Mineral dissolution and wormholing from a pore-scale perspective, Journal of Fluid Mechanics, 2017, 827, 457–483

[6] Soulaine, Pavuluri, Claret, Tournassat “porousMedia4Foam: Multi-scale open-source platform for hydro-geochemical simulations with OpenFOAM®” Environmental Modelling and Software 145, 105199 (2021)

[7] Soulaine, Creux, Tchelepi, Micro-Continuum Framework for Pore-Scale Multiphase Fluid Transport in Shale Formations, Transport in Porous Media, 2019

[8] Carrillo, Bourg, Soulaine “Multiphase Flow Modeling in Multiscale Porous Media: An Open-Source Micro-Continuum Approach” Journal of Computational Physics (2020), 8, 100073

[9] Carrillo and Bourg, A Darcy-Brinkman-Biot Approach to Modeling the Hydrology and Mechanics of Porous Media Containing Macropores and Deformable Microporous Regions, Water Resources Research, 2019

Biosketch

Yi Fang is an assistant professor of Geological Engineering at South Dakota School of Mines and Technology. He studies flow and deformation in both hard and soft rocks. His research goal is first to understand the coupled multi-physical processes occurring in these rocks, and then address the associated challenges in geoengineering activities. Yi has a multidisciplinary background. He was a research associate in the Institute for Geophysics at the University of Texas at Austin, focusing on laboratory characterization of methane hydrate systems in the deepwater Gulf of Mexico. He earned his Ph.D. degree in Energy and Mineral Engineering from Pennsylvania State University in late 2017, focusing on fluid flow and induced seismicity in fractured rocks. Before that, he received his M.Sc. in Geology from California State University, Long Beach in 2013, working on stable isotope analysis for fluid-rock interactions. He received his B.E. in Civil Engineering from China University of Geosciences (Wuhan) in 2011. Yi is the recipient of 2020 Rocha Medal Runner-up Certificate from ISRM, and he serves as the future leader (2018 class) of the American Rock Mechanics Association (ARMA).

Introduction of the Lecture

Methane hydrate is potentially a source of high energy density fuel. It is a crystalline solid composed of methane molecules trapped in cages of water molecules, stable at low temperatures and/or high pressures. The experimental characterization of the petrophysical and hydromechanical properties of hydrate-bearing core samples are essential for the engineering development of this energy resource. However, the laboratory measurements are incredibly challenging because sub-sampling, sample preparation, and testing must be conducted at high pressure and low temperature. This work develops experimental protocols to accurately and systematically characterize the relationship among porosity, permeability, compressibility, and the ratio of horizontal to vertical effective stress (K₀) in hydrate-bearing sandy silts from Green Canyon Block 955 (GC 955) in the deepwater Gulf of Mexico. The samples have an in-situ porosity of 0.38 to 0.40 and in-situ effective permeability (k_eff) ranges from 0.1 md (1.0×10^-16 m²) to 2.4 md (2.4×10^-15 m²) in these natural sandy silts cores with hydrate occupying 83% to 93% of the pore space. The hydrate-bearing sediments are stiffer than the equivalent hydrate-free sediments; the K₀ stress ratio is greater for hydrate-bearing core samples relative to the hydrate-free core samples. The porosity decreases by 0.01 to 0.02 when the hydrate is dissociated at the in-situ stress. The hydrate in the sediment pores is interpreted to be a viscoelastic material that behaves like a fluid over experimental timescales, yet cannot escape the sediment skeleton. It carries a fraction of the vertical load and transfers the applied stress laterally. This work provides insight into the gas hydrate reservoir formation. It also aids in predicting gas production potential and stress state evolution of hydrate reservoirs in the deepwater Gulf of Mexico.

Biosketch

Anna Suzuki is an associate professor in the Institute of Fluid Science (IFS) at Tohoku University. She graduated from Mechanical Engineering and completed Master’s and Doctor’s degrees in Environmental Studies at Tohoku University. After receiving her Ph.D. in 2014, and she was a postdoctoral researcher in Energy Resources Engineering at Stanford University between 2014 and 2016. She was a tenure-track assistant professor for five years in the IFS and became the current position in November 2021. Her research mainly focuses on geothermal reservoir modeling. She works on mathematical modeling of fluid and heat flows, numerical simulations, and structure-controlled flow experiments. Recently, she is also working on co-creation with citizens and social marketing to use local energy resources.

Introduction of the Lecture

Models representing complex fracture structures in a large number of parameters have high uncertainty, but data that can be measured from reservoirs are limited in estimating the structures. In this study, we focus on interwell structures and flow characteristics in fractured rocks. Topological data analysis was applied to evaluate and detect structures of flow paths from the image data. We could estimate the flow characteristics based on the new topological descriptions. We also estimated the structure of fractured rock masses using thermal responses and particle-tracer rsposes. Flow experiments were conducted with 3D-printed fracture models, and we evaluated each method of interwell structures.

Biosketch

Dr. Xuhai Tang is professor at Wuhan University. He obtained PhD degree at Imperial College London, and has been a research assistant at Princeton University. He is the editorial board member of the “International Journal of Rock Mechanics and Mining Sciences”. His group developed the AiFrac-TOUGH simulator and microscale Rock Mechanics Experiment (micro-RME) system, in order to understand, predict and control the behavior of fractured rocks with Hydraulic-Mechanical-Thermal coupling process. The micro-RME system, including nanoindentation testing and AFM testing, is developed to investigate the micro-cracking and mechanical property of rock-forming minerals. The AiFrac-TOUGH is developed for modelling the three-dimensional fracturing, which contributes to the smarter unconventional petroleum production, thermal energy exploitation and space exploitation.

Introduction of the Lecture

The future human activities beyond Earth definitely need the development of geotechnical engineering. Understanding the cracking of rocks on asteroids is not only helpful for the optimizing of drilling, but also helpful for the investigation of impact history happened beyond Earth. In this work, the shock-induced melt veins in Hammadah al Hamra 346 asteroid meteorites are investigated numerically and experimentally, which records the impact history of their parent bodies. Firstly, the microstructure of minerals and shock-induced melt veins are achieved using TESCAN Integrated Mineral Analyzer (TIMA). Then, the physical and mechanical properties of minerals and shock-induced melt veins are measured using nanoindentation testing and Atomic Force Microscope (AFM) testing. Secondly, based on these experimental results, grain-based digital rocks can be generated for the meteorites. Thirdly, the AiFrac-TOUGH is extended to model the propagation of shock-induced melt veins. The evolutions of very high shock pressures, heat diffusion and impact heating induced by the impact between two asteroids are simulated, which leads to the cracking, melting and deformation of rocks. Meanwhile, the influence of different impact velocities on the propagation path of shock-induced melt veins is discussed.