Keita Yoshioka

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• PhD
• Professor (Full) at Montanuniversität Leoben

Rigorous coupling of fracture-porous medium fluid flow and topologically complex fracture propagation is of great scientific interest in geotechnical and biomechanical applications. In this paper, we derive a unified fracture-porous medium hydraulic fracturing model, leveraging the inherent ability of the variational phase-field approach to fractur...

This paper proposes a diffused approach to approximate failure at interfaces that physically occupy negligible space compared to the bulk material. For an interface diffused over a certain length, we derive an effective interface fracture toughness based on the diffused length and the fracture toughness of the bulk and the interface. Our derivation...

Plain Language Summary Hydraulic fractures may form complex patterns as they grow outward from a wellbore by turning or deflecting when they interact with preexisting discontinuities in rocks. Because complex fractures enhance the permeability of rock formations more effectively than planar fractures, many studies have investigated how a fracture i...

Though a number of formulations have been proposed for phase-field models for hydraulic fracture in a fully saturated porous medium, the definition of the degraded poroelastic strain energy varies from one model to another. This study explores previously proposed forms of the poroelastic strain energy with diffused fracture and assesses their abili...

Significant volumes of water are injected into the subsurface for purposes such as maintaining reservoir pressure, enhancing production efficiency, or water disposal. In these operations, injection pressures are typically kept low to prevent the formation from fracturing. However, fractures may still be induced even at low injection pressures if th...

We present a comprehensive model to simulate fracture nucleation and propagation in porous media, incorporating chemical reactions. This model integrates three main processes: fluid flow in porous media, reactive transport, and the mechanical deformation of fractured porous media using a variational phase‐field approach. To account for chemical rea...

Many hydraulic fracturing experiments suggest that low-viscosity fluid tends to generate a complex fracture network, which may be beneficial for geo-energy production. However, the precise impacts of low-viscosity fluid on the fracture nucleation and propagation are unknown. This study focuses on the stress jump at weak interfaces (e.g., grain boun...

The Strategic Research Agenda (SRA; https://www.ejp-eurad.eu/publications/eurad-sra ) of the European Joint Programme on Radioactive Waste Management (EURAD; https://www.ejp-eurad.eu/ ) describes the scientific and technical domains and sub-domains and knowledge management needs of common interest between EURAD participant organizations. Theme numb...

Hydraulic fracturing experimental studies suggest that low viscous fluid injection leads to complex fracture morphology. A complex fracture network is more desirable for producing geoenergy more effectively. However, the precise impacts of low viscous fluid on the fracture nucleation and evolution are unknown. Here, we focused on the local variatio...

Many hydraulic fracturing experiments suggest that low viscous fluid tends to generate a complex fracture network, which may be beneficial for geo-energy production. However, the precise impacts of low viscous fluid on the fracture nucleation and propagation are unknown. This study focuses on the local stress jump caused by spatial variation in Bio...

Geological materials such as Opalinus Clay show complex coupled hydro-mechanical behavior at laboratory and field scales. In the context of radioactive waste disposal, in-situ excavations might remain open for ventilation and operation for decades and, consequently, be susceptible to environmental changes such as desaturation. The saturation change...

Numerical simulations become a necessity when experimental approaches cannot cover the required physical and time scale of interest. One of such area is a simulation of long-term host rock behaviors for nuclear waste disposal and simulation tools involved in the assessment must go through rigorous validation tests. The DECOVALEX project (Developmen...

Understanding complex systems, such as radioactive waste repositories, involves the study of cross-scale coupled processes. We discuss some important concepts and their mutual interactions for interpreting such systems based on complementary model-based analyses at various scales (Fig. 1). These points are linked with practical examples that pertai...

We present a fully coupled chemo-hydro-mechanical variational phase field model for simulating fracture initiation and propagation including chemical reactions in cementitious systems.

GeomInt2 is the follow-up project to the joint project “Geomechanical Integrity of Host and Barrier Rocks—Experiment, Modelling and Analysis of Discontinuities (GeomInt)”. The results of GeomInt made essential contributions to the analysis of the origin and development of discontinuities in clay, salt and crystalline rocks. Discontinuities are cons...

The principal interest of the GeomInt project consists of the investigation of effects on barrier integrity of three host rock formations: clay, salt and crystalline. The project focuses on distinct physical processes that can influence barrier integrity in these rocks, particularly those related to swelling and shrinkage, pressure-driven percolati...

In this chapter we briefly describe information methods and technologies supporting geotechnical systems analyses of to large extend, i.e. using virtual reality methods for data and model integration (Sect. 5.1) and improving computational efficiency by using high-performance-computing techniques (Sect. 5.2).

In this chapter, we investigate hydro-mechanical effects in the Opalinus Clay, especially those leading to cracking. We present a methodology comprising laboratory and field scale experiments, as well as the development and application of numerical approaches.

Though a number of formulations have been proposed for phase--field models for hydraulic fracture, the definition of the degraded poroelastic strain energy varies from one model to another. This study explores previously proposed forms of the poroelastic strain energy with diffused fracture and assesses their ability to recover the explicit fractur...

At the interface between the steel canister and the bentonite in a nuclear waste repository, we expect generation of hydrogen gas because of corrosion processes. The pressurized gas might fracture the engineered or natural clay barrier system, enhancing radionuclide transport into the geosphere. To assess the long-term integrity of the clay host ro...

We propose a decomposition of constitutive relations into crack-driving and persistent portions, specifically designed for materials with anisotropic/orthotropic behavior in the phase field approach to fracture to account for the tension-compression asymmetry. This decomposition follows a variational framework, satisfying the orthogonality conditio...

Experimental studies suggest that the fracture toughness of rocks increases with the confining pressure. Among many methods to quantify this dependency, a so-called burst experiment (Abou-Sayed, 1978) may be the most widely applied in practice. Its thick wall cylinder geometry leads to a stress state resembling the subsurface condition of a pressur...

The engineered barrier concept typically includes a range of sub-systems or components, such as waste form (i.e., spent fuel), canisters, buffers (i.e., bentonite), backfills, seals, and plugs. We expect a significant amount of hydrogen gas generation at the interface between the canister and the bentonite due to the long disposal times and anaerob...

Hydraulic fracturing is a widely used technique applied in unconventional reservoirs to generate large fracture networks. Interactions between hydraulic fracture (HF) and natural fracture (NF) can impact the fracture topology and thus the subsequent productivity. Despite a large number of studies on HF–NF interactions, the HF propagation path is no...

OpenGeoSys (OGS) is a scientific open-source initiative for the numerical simulation of thermo-hydro-mechanical/chemical (THMC) processes in porous and fractured media. OGS provides a flexible numerical framework using primarily the Finite Element Method (FEM) for solving multi-field coupled processes with application in different scientific and tech...

We propose a decomposition of constitutive relations into crack-driving and persistent portions, specifically designed for materials with anisotropic/orthotropic behavior in the phase field approach to fracture to account for the tension-compression asymmetry. This decomposition follows a variational framework, satisfying the orthogonality conditio...

Fracking, or hydraulic fracturing, is a ubiquitous technique for generating fracture networks in rocks for enhanced geothermal systems or hydrocarbon extraction from shales. For decades, models, numerical simulation tools, and practical guidelines have been based on the assumption that this process generates networks of self-similar parallel cracks...

Supercritical/superhot geothermal success depends on successful drilling. However, wellbore stability in supercritical environments has not been investigated because imposing sufficient stress on high-temperature granite with true triaxial loading is difficult. We conducted wellbore failure experiments on 200–450 °C granite under true triaxial stre...

Success of our ongoing energy transition largely depends on subsurface exploitation. The subsurface can act as a “battery” to store energy dense fluids such as hydrogen, or a “host” to sequester unwanted substances such as carbon dioxide or radioactive waste. On the other hand, these operations cause the subsurface pressure and/or temperature to ch...

Developing high-enthalpy geothermal systems requires a sufficiently permeable formation to extract energy through fluid circulation. Injection experiments above water’s critical point have shown that fluid flow can generate a network of highly conductive tensile cracks. However, what remains unclear is the role played by fluid and solid rheology on...

Acidic fluid flow in geologic formations leads to mineral dissolution and, under certain circumstances, to localized dissolution forming a dendritic pattern, known as wormhole. Such patterns of conduits and caves are often observed in karstic aquifer and deliberately engineered in oil and gas well stimulation with acid injection. Two different kind...

Because of the long disposal times and the anaerobic corrosion of the steel-canister, we expect a considerable amount of hydrogen gas generation at the interface between the canister and the bentonite. Even though we expect the gas production to be slow (H2 ux of 5 �g=m2y), gas generation at higher rates could pressurize the engineered barrier syst...

The present paper gives an overview of the GeomInt project “Geomechanical integrity of host and barrier rocks—experiment, modelling and analysis of discontinuities” which has been conducted from 2017–2020 within the framework of the “Geo:N Geosciences for Sustainability” program. The research concept of the collaborative project is briefly introduc...

Upscaling of mineral precipitation and dissolution processes in porous media affecting the pore structure and subsequently the flow and transport properties in the continuum scale is a challenging task to be considered in mathematical models. To accurately model such processes, one needs conservation laws for mass and momentum in time-dependent dom...

The presence of heterogeneously distributed mineral grain boundaries introduces a characteristic length-scale leading to a size-dependent strength and toughness of brittle rocks. This study focuses on fracture nucleation and quasi-static propagation in three-point bending experiments in notched beams. We employed a variational approach to fracture...

The basic idea of Model-Experiment-Exercises (MEX) is to link modelling and experimental works from the very beginning i.e. in the conceptual phase. Due to the complexity of each part in the systems analysis, this combination is sometimes lost. Moreover, both models and experiments require highly sophisticated tools and equipment as well as highly...

Data management includes the development and use of architectures, guidelines, practices and procedures for accurate managing of data during the entire data lifecycle of an institutional unit or a research project. Data are defined as different information units such as numbers, alphabetic characters, and symbols that are particularly formatted and...

An essential scientific goal of the GeomInt project is the analysis of potentials and limitations of different numerical approaches for the modelling of discontinuities in the rocks under consideration in order to improve the understanding of methods and their synergies with regard to theoretical and numerical fundamentals. As numerical methods, th...

TheFFS Forces on Fracture Surfaces FFS method (see Sect. 3.2.1) was developed to simulate direct shear tests. To provide a tool for the project work and get things easier done a graphical user interface (GUI) was also created. The GUI simply calls all necessary functions by letting the user either fill form fields or choose input files from the wor...

Superhot geothermal environments with temperatures of approximately 400–500 °C at depths of approximately 2–4 km are attracting attention as new kind of geothermal resource. In order to effectively exploit the superhot geothermal resource through the creation of enhanced geothermal systems (superhot EGSs), hydraulic fracturing is a promising techni...

Development and Improvement Of NUmerical methods and Tools for modelling coupled processes (DONUT) Workpackage in the European Joint Programme on Radioactive Waste Management (EURAD)

OpenGeoSys (OGS) is a scientific open-source initiative for the numerical simulation of thermo-hydro-mechanical/chemical (THMC) processes in porous and fractured media. The basic concept of OGS consist on providing a flexible numerical framework, using primarily the Finite Element Method (FEM) for solving multi-field coupled processes with applicat...

Due to a stress redistribution after the excavation of an underground tunnel for radioactive waste disposal, an Ed/DZ (excavation disturbed/damaged zone) will be generated in the near field of the opening, resulting in significant changes in the hydraulic and mechanical properties of the rock mass in the zone. Initially more or less randomly distri...

Plain Language Summary At Acoculco, Mexico, the temperature of the rock at 2 km depth is approximately 300°C, which can be potentially exploited for the production of geothermal energy. To produce deep geothermal energy, water must be extracted from the rock, which is currently not possible in Acoculco because the host rock, a granite, is practical...

In the context of geotechnical and geological barriers, a thorough analysis of uncertainty and sensitivity is a crucial aspect of any physics-based performance assessment. While experimental data are scarce in actual waste repositories, large-scale experiments in underground research laboratories (URLs) provide such data that can be used to not onl...

Phase-field models for fracture have gained exceptional popularity in the last couple of decades and have been extended into areas well beyond brittle quasi-static fracture propagation to ductile, dynamic, or hydraulic fracturing. Despite the significant theoretical advancements in these more complex physical settings, little attention has been pai...

In every tight formation reservoir, natural fractures play an important role for mass and energy transport and stress distribution. Enhanced Geothermal Systems (EGS) make no exception, and stimulation aims at increasing the reservoir permeability to enhance fluid circulation and heat transport. EGS development relies upon the complex task of predic...

Awi 18-1 is an injection well drilled in the Cianten Caldera, near the western margin of the Salak (Awibengkok) reservoir in west Java, Indonesia. As the initial well injectivity was low, a long-term hydraulic stimulation was conducted to improve the permeability and establish a better connection to existing natural fractures. A geologic model of t...

The numerical treatment of propagating fractures as embedded discontinuities is a challenging task for which an analyst has to select a suitable numerical method from a range of options. Since their inception in the mid-80s, smeared approaches for fracture simulation such as non-local damage, gradient damage or more lately phase-field modelling hav...

Hydraulic fracture containment in layered reservoirs is simulated using a numerical model that couples fluid flow with a lattice representation of the solid with quasi-random distributed nodes connected by springs. We consider the influence of horizontal stress contrasts between layers, vertical stress, material fracture toughness, and the presence...

Decades of research have led to numerous insights for in modeling the impact of stresses and rock properties on hydraulic fracture height growth. However, the conditions under which weak horizontal interface are expected to impede height growth remains for the most part unknown. We presents an experimental study of the impact of weak horizontal dis...

The tip behavior of hydraulic fractures is characterized by a rich nesting of asymptotic solutions, comprising a formidable challenge for the development of efficient and accurate numerical simulators. We present experimental validation of several theoretically-predicted asymptotic behaviors, namely for hydraulic fracture growth under conditions of...

A variational fracture model coupled to an external reservoir simulator through variable exchange is presented. While convergence is not optimal without Jacobian matrices with which fully coupling can provide, the presented coupling scheme is versatile enough that the reservoir simulator could be easily replaced with any other simulator. A variatio...

Robust understanding of natural fracture distribution and connectivity is crucial in hydrocarbon and geothermal energy development. Unfortunately, such characterization of the fractured formation remains a major challenge to the industry. We propose the variational approach to fracture modelling, which provides a unified framework for studying frac...

Layer flow contributions are increasingly being quantified through the analysis of measured sandface flowing temperatures. It is commonly known that the maximum temperature change is affected by the magnitude of the drawdown and the Joule-Thomson expansion coefficient of the fluid. Another parameter that strongly impacts layer sandface flowing temp...

Most hydraulic fracturing simulation approaches ap-ply propagation criteria to an individual fracture along prescribed path(s). In practice, however, the modeling of hydraulic fracturing in reservoir stimula-tion requires handling interactions between multiple natural or induced fractures growing along unknown paths, and changes in fracture pattern...

Geothermal reservoirs are usually relatively impermeable matrix rocks from which heat is extracted by water flow through natural fractures. Fractured reservoirs are usually modeled using dual-porosity models. However, the coupled heat transfer and fluid flow in geothermal reservoirs require multiple porosity models because the dual-porosity represe...

One of the most critical capabilities of realistic hydraulic fracture simulation is the prediction of complex (turning, bifurcating, or merging) fracture paths. In most classical models, complex fracture simulation is difficult due to the need for a priori knowledge of propagation path and initiation points and the complexity associated with stress...

Enhanced Geothermal Systems (EGS) rely on the creation a connected fracture system or the enhancement of existing (natural) fractures by hydraulic and chemical treatments. EGS studies at Fenton Hill (New Mexico, USA) and Hijiori (Japan) have revealed that only a limited number of fractures contribute to the effective heat transfer surface area. Thu...

The Salak field is the largest developed geothermal resource in Indonesia operated by Chevron. Steam production levels in Salak have been successfully maintained at or above the rated power plant capacity since 1994. Infill drilling has been the primary tool to meet the steam supply target. Besides formulating steam supply strategy, formulating inj...

Awi 18-1 is an injection well drilled in the Cianten Caldera, near the western margin of the Salak (Awibengkok) reservoir in west Java, Indonesia. The initial well injectivity was low, so long-term hydraulic stimulation was conducted to improve the permeability and establish a better connection to existing natural fractures. A reservoir geologic mo...

The Salak field is the largest developed geothermal resource in Indonesia operated by Chevron. Steam production levels in Salak have been successfully maintained at or above the rated power plant capacity since 1994. Infill drilling has been the primary tool to meet the steam supply target. Besides formulating steam supply strategy, formulating inj...

The Earth's heat is an inexhaustible resource whose use creates almost no greenhouse gas emissions. Many of the geothermal wells feeding power plants have been constructed by oilfield workers using essentially traditional drilling and completion equipment and techniques. Engineered geothermal systems (EGS) is a system that can tap the widely availa...

The increasing deployment of distributed temperature- and pressure-measuring devices in intelligent-well completions is providing the means to monitor the inflow profiles of wells without any well intervention. If the profiles of pressure and/or temperature are affected by the inflow profiles of the various phases being produced, it is possible to...

The Salak field is the largest developed geothermal resource in Indonesia. Steam production levels have been maintained at or above the rated power plant capacity for 15 years through periodic infill drilling and injection realignment. The reservoir management strategy for Salak involves injecting separated brine into deep wells on the margins of t...

In the Salak geothermal field, a five well acid treatment campaign was conducted in 2008. The choice of candidate wells for stimulation was based on low production/injection capacity, flowing wellhead pressure below normal system operating pressure, and massive water-based mud losses while drilling the reservoir section. After the wells were select...

In the Salak geothermal field, a five well acid treatment campaign was conducted in 2008. The choice of candidate wells for stimulation was based on low production/injection capacity, flowing wellhead pressure below normal system operating pressure, and massive water-based mud losses while drilling the reservoir section. After the wells were select...

Conventional geothermal applications are limited to those with sufficient temperature, thermal gradient, and permeability. If these applications could be expanded to those with low or zero permeability, tremendous energy resources would suddenly be available. Thermal fracturing techniques are being looked at as potential methods of commercializing...

Conventional geothermal applications are limited to those with sufficient temperature, thermal gradient, and permeability. If these applications could be expanded to those with low or zero permeability, tremendous energy resources would suddenly be available. Thermal fracturing techniques are being looked at as potential methods of commercializing...

With the recent development of temperature measurement systems such as fiber-optic distributed temperature sensors, continuous temperature profiles in a horizontal well can be obtained with high precision. Small temperature changes with a resolution on the order of 0.1°F can be detected by modern temperature-measuring instruments in intelligent com...

With the recent development of temperature measurement systems, continuous wellbore temperature profiles can be obtained with high precision. Small temperature changes can be detected by modern temperature-measuring instruments, such as fiber optic distributed temperature sensors (DTS) in intelligent completions. Analyzing such changes will potenti...

The temperature profiles in a horizontal oil-producing well can be measured precisely with distributed temperature sensors, which are being increasingly installed in intelligent well completions. With temperature resolution on the order of 0.1 °F, modern temperature-measuring instruments can detect small temperature changes along the wellbore that...

Use of distributed temperature sensors is becoming increasingly common for monitoring producing sections of horizontal wells through a real-time measurement of a temperature profile. This information can potentially be inverted to infer the types and amounts of fluid entering along the wellbore. This information is essential for reservoir managemen...

This paper presents methods to interpret measurements in complex wells (horizontal, multilateral and multi-branching wells) to determine the inflow profiles of oil, gas and water. These methods are needed to take full advantage of intelligent well, a technology that is rapidly evolving to continuously and permanently monitor downhole temperature, p...