EK
Entela Kane
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1
Carbonate rocks exhibit a span of clast and grain size in fault zones. However, the effect of grain size distribution on the frictional behavior of carbonate faults and its implications for natural and induced seismicity remain poorly understood. This study elucidates the effect of grain size distribution on the frictional behavior of Lower Carboniferous (Dinantian) simulated fault gouge, relevant to geothermal energy exploitation in Northwest Europe. We tested samples in a rotary shear apparatus under air dry and drained conditions using deionized (DI) water or geothermal brine. In each experiment, we stepped the normal stress from 1 to 10 (Formula presented.) and back, in 1 (Formula presented.) intervals. At each interval, we performed a slide-hold-slide procedure with 10 (Formula presented.) slide time, 10-100-1000 (Formula presented.) hold times, and shear velocity of 20 (Formula presented.). Our results demonstrated that the presence of fluids in carbonate gouges increased the creep coefficient of internal friction, healing, and relaxation (absolute values and rates), consistent with the effects of pressure solution and corroborated by the CNS microphysical modeling. Additionally, frictional sliding facilitated by water films along grain boundaries controlled the peak and steady-state coefficients of friction. Healing was independent of the initial grain size distribution and occurred in the PSZ. Relaxation occurred both in the PSZ and bulk gouge and was governed by PSZ thickness, which positively correlated with the initial mean grain size.
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Carbonate rocks exhibit a span of clast and grain size in fault zones. However, the effect of grain size distribution on the frictional behavior of carbonate faults and its implications for natural and induced seismicity remain poorly understood. This study elucidates the effect of grain size distribution on the frictional behavior of Lower Carboniferous (Dinantian) simulated fault gouge, relevant to geothermal energy exploitation in Northwest Europe. We tested samples in a rotary shear apparatus under air dry and drained conditions using deionized (DI) water or geothermal brine. In each experiment, we stepped the normal stress from 1 to 10 (Formula presented.) and back, in 1 (Formula presented.) intervals. At each interval, we performed a slide-hold-slide procedure with 10 (Formula presented.) slide time, 10-100-1000 (Formula presented.) hold times, and shear velocity of 20 (Formula presented.). Our results demonstrated that the presence of fluids in carbonate gouges increased the creep coefficient of internal friction, healing, and relaxation (absolute values and rates), consistent with the effects of pressure solution and corroborated by the CNS microphysical modeling. Additionally, frictional sliding facilitated by water films along grain boundaries controlled the peak and steady-state coefficients of friction. Healing was independent of the initial grain size distribution and occurred in the PSZ. Relaxation occurred both in the PSZ and bulk gouge and was governed by PSZ thickness, which positively correlated with the initial mean grain size.
Steel-Reinforced Resin (SRR) is a particulate material originally developed as an injectant for anchoring applications. More recently, it has been proposed as a filler material for cavities embedding mechanical connectors in FRP–steel hybrid bridges. In this context, the compressive behaviour of SRR becomes critical due to the multiaxial stress states and fatigue demands at a joint scale. This paper presents a comprehensive experimental and numerical investigation of SRR under monotonic, incremental cyclic, and fatigue compressive loading in unconfined conditions. A custom triaxial setup is also used to evaluate pressure sensitivity and strength enhancement due to confinement under monotonic loading. In parallel, micromechanical finite element models are developed to simulate the interactions between the resin matrix and the steel balls at the microscale, incorporating interface damage, friction, and cohesive failure. The models reproduce the observed nonlinear behaviour and reveal distinct Poisson's ratio responses in tension and compression, offering deeper insight into the mechanisms governing stiffness degradation, strain softening, and plateau behaviour.
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Steel-Reinforced Resin (SRR) is a particulate material originally developed as an injectant for anchoring applications. More recently, it has been proposed as a filler material for cavities embedding mechanical connectors in FRP–steel hybrid bridges. In this context, the compressive behaviour of SRR becomes critical due to the multiaxial stress states and fatigue demands at a joint scale. This paper presents a comprehensive experimental and numerical investigation of SRR under monotonic, incremental cyclic, and fatigue compressive loading in unconfined conditions. A custom triaxial setup is also used to evaluate pressure sensitivity and strength enhancement due to confinement under monotonic loading. In parallel, micromechanical finite element models are developed to simulate the interactions between the resin matrix and the steel balls at the microscale, incorporating interface damage, friction, and cohesive failure. The models reproduce the observed nonlinear behaviour and reveal distinct Poisson's ratio responses in tension and compression, offering deeper insight into the mechanisms governing stiffness degradation, strain softening, and plateau behaviour.
Conference paper
(2025)
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Entela Kane, Milad Naderloo, Annemarie Muntendam-Bos, Auke Barnhoorn, André R. Niemeijer, Matsen Broothaers, Anne M.H. Pluymakers
Carbonate rocks, which often serve as geo-energy reservoirs, are prone to fluid-assisted deformation, which is susceptible to fluid chemistry. Acknowledging the impact of fluids and fluid chemistry on the mechanical behaviour of rocks substantiates the safety of exploiting the geo-energy reservoirs. We saturated Dinantian carbonate samples overnight at a similar fluid mass with 4 different fluids: deionised water, calcium carbonate saturated solution, sulfuric acid, and a sodium chloride-rich geothermal brine, which cover a range of redox potentials, pH, and ionic strength. After saturation, we conducted Brazilian Disc and uniaxial compressive tests from which we obtained tensile strength, Young's modulus, Poisson’s ratio and Uniaxial Compressive Strength (UCS). The tensile strength of the sample depends on both sample porosity and fluid chemistry, and tensile strength decreases with decreasing fluid ionic strength. In contrast, Young’s modulus doesn’t exhibit a clear dependence on pH, and instead correlates with the ionic strength of the fluids used, just as UCS. Poisson’s ratio is affected by pH, redox potential and ionic strength. This correlation implies that the ionic strength induces more deformation and lowers UCS. Additionally, given the differences in the effect on Young’s modulus and Poisson’s ratio, the magnitude and direction of the local stress field determine if further fluid complexity affects elastic deformation and hence local stress transfer.
...
Carbonate rocks, which often serve as geo-energy reservoirs, are prone to fluid-assisted deformation, which is susceptible to fluid chemistry. Acknowledging the impact of fluids and fluid chemistry on the mechanical behaviour of rocks substantiates the safety of exploiting the geo-energy reservoirs. We saturated Dinantian carbonate samples overnight at a similar fluid mass with 4 different fluids: deionised water, calcium carbonate saturated solution, sulfuric acid, and a sodium chloride-rich geothermal brine, which cover a range of redox potentials, pH, and ionic strength. After saturation, we conducted Brazilian Disc and uniaxial compressive tests from which we obtained tensile strength, Young's modulus, Poisson’s ratio and Uniaxial Compressive Strength (UCS). The tensile strength of the sample depends on both sample porosity and fluid chemistry, and tensile strength decreases with decreasing fluid ionic strength. In contrast, Young’s modulus doesn’t exhibit a clear dependence on pH, and instead correlates with the ionic strength of the fluids used, just as UCS. Poisson’s ratio is affected by pH, redox potential and ionic strength. This correlation implies that the ionic strength induces more deformation and lowers UCS. Additionally, given the differences in the effect on Young’s modulus and Poisson’s ratio, the magnitude and direction of the local stress field determine if further fluid complexity affects elastic deformation and hence local stress transfer.
Journal article
(2025)
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Entela Kane, Olwijn Leeuwenburgh, Gerard Joosten, Alexandros Daniilidis, David Bruhn
The Netherlands aims to be CO2 neutral by 2050, aligning with the Paris Agreement. To achieve this, it is crucial to increase the contribution of geothermal energy to renewable energy sources, necessitating large-scale exploitation to speed up the energy transition. Only small-scale (1–2 km) geothermal field developments exist in the Netherlands primarily for heating. Expanding to extensive geothermal fields (10 km length) requires a strategic approach to well placement and consideration of the economic constraints associated with geothermal projects. The heterogeneity of the subsurface is a critical factor in developing large-scale geothermal reservoirs. This study introduces an innovative approach to optimising well placement based on geological trends, using a well-density function as a proof of concept. Implementing and optimising flexible well patterns for large-scale geothermal developments significantly enhances profitability compared to conventional oil and gas industry methods. Optimised flexible well patterns favour a long-term utilisation of energy recovered, minimise pressure extrema in the reservoir, and improve sweep efficiency. However, their application depends on reservoir operational decisions. The optimisation process ensures economic viability, even with lower heat prices. Broadly, this methodology could be key to scaling up geothermal developments to meet the objectives of the Paris Agreement.
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The Netherlands aims to be CO2 neutral by 2050, aligning with the Paris Agreement. To achieve this, it is crucial to increase the contribution of geothermal energy to renewable energy sources, necessitating large-scale exploitation to speed up the energy transition. Only small-scale (1–2 km) geothermal field developments exist in the Netherlands primarily for heating. Expanding to extensive geothermal fields (10 km length) requires a strategic approach to well placement and consideration of the economic constraints associated with geothermal projects. The heterogeneity of the subsurface is a critical factor in developing large-scale geothermal reservoirs. This study introduces an innovative approach to optimising well placement based on geological trends, using a well-density function as a proof of concept. Implementing and optimising flexible well patterns for large-scale geothermal developments significantly enhances profitability compared to conventional oil and gas industry methods. Optimised flexible well patterns favour a long-term utilisation of energy recovered, minimise pressure extrema in the reservoir, and improve sweep efficiency. However, their application depends on reservoir operational decisions. The optimisation process ensures economic viability, even with lower heat prices. Broadly, this methodology could be key to scaling up geothermal developments to meet the objectives of the Paris Agreement.