Dr. Mahmoud Hefny
Geothermal Energy & Geofluids
Institute of Geophysics
NO F 61
CH-8092 Zurich Switzerland
|Phone||+41 44 633 2751|
|Dominique Ballarin Dolfin|
|Phone||+41 44 632 3465|
Underlined names are links to current or past GEG members
REFEREED PUBLICATIONS IN JOURNALS
Qin, C.-Z., X. Wang, H. Zhang, M. Hefny, W. Deng, and H. Jiang, Numerical studies of spontaneous imbibition in porous media: Model development and pore-scale perspectives, Journal of Petroleum Science and Engineering, 2022. https://doi.org/htt10.1016/j.petrol.2022.110961 [Download] [View Abstract]Spontaneous imbibition is a crucial two-phase flow process in a variety of subsurface and industrial applications. Due to the lack of an efficient and reliable pore-scale model, however, how pore-filling events in spontaneous imbibition influence average transport properties (i.e., capillary pressure and relative permeability curves) and entrapment of the nonwetting fluid has not been fully understood. In this work, we first experimentally verify an image-based dynamic pore-network model of spontaneous imbibition that is computationally efficient. Then, case studies of a Nubian sandstone are conducted. We demonstrate that average capillary pressure in cocurrent spontaneous imbibition is significantly overestimated by the widely used Young-Laplace equation. This is because the effects of dynamic pore-filling and air entrapment on average capillary pressure are not parameterized in the equation. Based on our pore-scale numerical results, we elaborate on the competition of pore-filling events under different viscosity ratios of the wetting to the nonwetting fluids. It is found that the filling mode evolves from the co-filling of neighboring pores to the preferential filling of small pores as the nonwetting viscosity increases. Our model will be a useful numerical tool for quantitatively predicting spontaneous imbibition in geological formations. Our findings will help us bridge the gap between pore-scale flow dynamics and the Darcy theory of spontaneous imbibition.
Qin, C.-Z., X. Wang, M. Hefny, J. Zhao, S. Chen, and B. Guo, Wetting Dynamics of Spontaneous Imbibition in Porous Media: from Pore Scale to Darcy Scale, Geophysical Research Letters , 2022. https://doi.org/10.1029/2021GL097269 [Download] [View Abstract]Spontaneous imbibition is an important fundamental process due to its significance in many subsurface and industrial applications. Unveiling pore-scale wetting dynamics, and particularly its upscaling to the Darcy model, are still unresolved. We conduct image-based pore-network modeling of cocurrent spontaneous imbibition and the corresponding quasi-static imbibition, in homogeneous sintered glass beads and heterogeneous Estaillades carbonate. We show the influence of pore-scale heterogeneity on wetting dynamics and nonwetting entrapment. We illustrate the influence of wetting dynamics on capillary pressure and relative permeability curves. More importantly, we propose a non-equilibrium model for the wetting relative permeability that incorporates flow dynamics. We further implement the non-equilibrium model into two-phase Darcy modeling of spontaneous imbibition in a 10 cm long medium. Sharp wetting fronts are numerically predicted, which are in good agreement with experimental observations. Our studies provide insights into developing two-phase imbibition models with measurable material properties of capillary pressure and relative permeability.
Osman, A., N. Mehta, A. Elgarahy, M. Hefny, A. Al-Hinai, A. Al-Muhtaseb, and D. Rooney , Hydrogen production, storage, utilisation and environmental impacts: a review , Environmental Chemistry Letters, 2021. https://doi.org/10.1007/s10311-021-01322-8 [Download] [View Abstract]Dihydrogen (H2), commonly named ‘hydrogen’, is increasingly recognised as a clean and reliable energy vector for decarbonisation and defossilisation by various sectors. The global hydrogen demand is projected to increase from 70 million tonnes in 2019 to 120 million tonnes by 2024. Hydrogen development should also meet the seventh goal of ‘affordable and clean energy’ of the United Nations. Here we review hydrogen production and life cycle analysis, hydrogen geological storage and hydrogen utilisation. Hydrogen is produced by water electrolysis, steam methane reforming, methane pyrolysis and coal gasification. We compare the environmental impact of hydrogen production routes by life cycle analysis. Hydrogen is used in power systems, transportation, hydrocarbon and ammonia production, and metallugical industries. Overall, combining electrolysis-generated hydrogen with hydrogen storage in underground porous media such as geological reservoirs and salt caverns is well suited for shifting excess off-peak energy to meet dispatchable on-peak demand.
Qin, C.-Z., H. van Brummelen, M. Hefny, and J. Zhao, Image-based modeling of spontaneous imbibition in porous media by a dynamic pore network model, Advances in Water Resources, pp. 103932, 2021. https://doi.org/https://doi.org/10.1016/j.advwatres.2021.103932 [Download] [View Abstract]The dynamic pore-network modeling, as an efficient pore-scale tool, has been used to understand spontaneous imbibition in porous media, which plays an important role in many subsurface applications. In this work, we aim to compare a dynamic pore-network model of spontaneous imbibition with the VOF (volume of fluid) model. The μCT scanning of a porous medium of sintered glass beads is selected as our study domain. We extract its pore network by using an open-source software of PoreSpy, and further project the extracted information of individual watersheds into multiform idealized pore elements. A number of case studies of primary spontaneous imbibition have been conducted by using both the pore-network and the VOF models under different wettability values and viscosity ratios. We compare those model predictions in terms of imbibition rates and temporal saturation profiles along the flow direction. We show that the pore-network model can reproduce the VOF model results for an air-water system, in which water is the wetting phase. For a more viscous nonwetting phase such as oil, however, the pore-network model predicts a slower imbibition process and a rougher wetting front, in comparison to the predictions by the VOF model.
Osman, A. , M. Hefny, M. Abdel Maksoud, A. Elgarahy, and D. Rooney, Recent advances in carbon capture storage and utilisation technologies: a review, Environmental Chemistry Letters, 2020. https://doi.org/10.1007/s10311-020-01133-3 [Download] [View Abstract]Human activities have led to a massive increase in CO2 emissions as a primary greenhouse gas that is contributing to climate change with >1°C global warming than that of the pre-industrial level. The three main technologies that are utilised in carbon capture; pre-combustion, post-combustion and oxy-fuel combustion, have been evaluated. We critically reviewed the advances in carbon capture, storage and utilisation in the recent literature. In this review, the affirmed carbon uptake technologies with techniques of carbon dioxide separation, as well as listing all the disadvantages and advantages of each technology, have been addressed. Monoethanolamine is the most common carbon sorbent; however, it requires high regeneration energy of 3.5 GJ per tonne of CO2, while recent advances in the sorbent technology showed novel solvent (Modulated Amine Blend) with lower regeneration energy of 2.17 GJ per tonne of CO2. Graphene type materials showed CO2 adsorption capacity of 0.07 mol/g, which is 10 times higher than that of specific types of activated carbon, zeolites and metal-organic frameworks. CO2 geosequestration provides an efficient and long-term strategy for storing the captured CO2 in geological formations with a global storage capacity factor at a Gt-scale within operational timescales. Regarding the utilisation route, currently, the gross global utilisation of CO2 is < 200 million tonnes/year, which is roughly negligible compared with the extent of global anthropogenic CO2 emissions (> 32,000 million tonnes/year). Herein, we reviewed different CO2 utilisation methods such as direct routes (i.e. beverage carbonation, food packaging and oil/gas recovery), material/chemical industries (i.e. acrylates, carbamates, carbonates, polyurethanes, polycarbonates, formaldehyde and urea) and fuels (i.e. biofuels, dimethyl ether, tertiary butyl methyl ether and methanol). Moreover, we investigated additional CO2 utilisation for base-load power generation, seasonal energy storage, and district cooling and/or cryogenic direct air CO2 capture using geothermal energy. Through bibliometric mapping, we identified the research gap in the literature within this field which requires future investigations, for instance, designing new and stable ionic liquids, pore size and selectivity of metal-organic frameworks and enhancing the adsorption capacity of novel solvents. Moreover, areas such as techno-economic evaluation of novel solvents, process design and dynamic simulation require further effort as well as research and development before pilot and commercial-scale trials.
Hefny, M., C.-Z. Qin, M.O. Saar, and A. Ebigbo, Synchrotron-based pore-network modeling of two-phase flow in Nubian Sandstone and implications for capillary trapping of carbon dioxide, International Journal of Greenhouse Gas Control, 103/1031642, 2020. https://doi.org/10.1016/j.ijggc.2020.103164 [Download] [View Abstract]Depleted oil fields in the Gulf of Suez (Egypt) can serve as geothermal reservoirs for power production using a CO2-Plume Geothermal (CPG) system, while geologically sequestering CO2. This entails the injection of a substantial amount of CO2 into the highly permeable brine-saturated Nubian Sandstone. Numerical models of two-phase flow processes are indispensable for predicting the CO2-plume migration at a representative geological scale. Such models require reliable constitutive relationships, including relative permeability and capillary pressure curves. In this study, quasi-static pore-network modeling has been used to simulate the equilibrium positions of fluid-fluid interfaces, and thus determine the capillary pressure and relative permeability curves. Three-dimensional images with a voxel size of 0.65 μm3 of a Nubian Sandstone rock sample have been obtained using Synchrotron Radiation X-ray Tomographic Microscopy. From the images, topological properties of pores/throats were constructed. Using a pore-network model, we performed a sequential primary drainage–main imbibition cycle of quasi-static invasion in order to quantify (1) the CO2 and brine relative permeability curves, (2) the effect of initial wetting-phase saturation (i.e. the saturation at the point of reversal from drainage to imbibition) on the residual–trapping potential, and (3) study the relative permeability–saturation hysteresis. The results illustrate the sensitivity of the pore-scale fluid-displacement and trapping processes on some key parameters (i.e. advancing contact angle, pore-body-to-throat aspect ratio, and initial wetting-phase saturation) and improve our understanding of the potential magnitude of capillary trapping in Nubian Sandstone.
Hefny, M., A. Zappone, Y. Makhloufi, A. de Haller, and A. Moscariello, A laboratory approach for the calibration of seismic data in the western part of the Swiss Molasse Basin: the case history of well Humilly-2 (France) in the Geneva area , Swiss Journal of Geosciences , 113/11, 2020. https://doi.org/https://doi.org/10.1186/s00015-020-00364-4 [Download] [View Abstract]A collection of 81 plugs were obtained from the Humilly-2 borehole (France), that reached the Permo-Carboniferous sediments at a depth of 3051 m. Experimental measurements of physical parameters and mineralogical analysis were performed to explore the links between sedimentary facies and seismic characteristics and provide a key tool in the interpretation of seismic field data in terms of geological formations. The plugs, cylinders of 22.5 mm in diameter and ~30 mm in length were collected parallel and perpendicular to the bedding in order to explore their anisotropy. Ultrasound wave propagation was measured at increasing confining pressure conditions up to 260 MPa, a pressure where all micro-fractures are considered closed. The derivatives of velocities with pressure were established, allowing the simulation of lithological transitions at in-situ conditions. At room conditions, measured grain densities [kg/m3] range from 2630 to 2948 and velocities vary from 4339 to 6771 m/s and 2460 to 3975m/s for P- and S-waves propagation modes, respectively. The largest seismic-reflections coefficients were calculated for the interface between the evaporitic facies of the Keuper (Lettenkohle) and the underlying Muschelkalk carbonates (Rc= 0.3). The effective porosity has a range of 0.23% to 16.65%, while the maximum fluid permeability [m2] is 9.1e-16. A positive correlation between porosity and ultrasound velocity has been observed for P- and S-waves. The link between velocities and modal content of quartz, dolomite, calcite, and micas has been explored. This paper presents a unique set of seismic parameters potentially useful for the calibration of seismic data in the Geneva Molasse Basin.
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Hefny, M., M.B. Setiawan, M. Hammed, C.-Z. Qin, E. Ebigbo, and M.O. Saar, Optimizing fluid(s) circulation in a CO2-based geothermal system for cost-effective electricity generation , European Geothermal Congress 2022, 2022. https://doi.org/10.3929/ethz-b-000584323 [Download] [View Abstract]Carbon Capture and permanent geologic Storage (CCS) can be utilized (U) to generate electrical power from low- to medium-enthalpy geothermal systems in so-called CO2-Plume Geothermal (CPG) power plants. The process of electrical power generation entails a closed circulation of the captured CO2 between the deep underground geological formation (where the CO2 is naturally geothermally heated) and the surface power plant (where the CO2 is expanded in a turbine to generate electricity, cooled, compressed, and then combined with the CO2 stream, from a CO2 emitter, before it is reinjected into the subsurface reservoir). In this research, initially a comprehensive techno-economic method (Adams et al., 2021), which coupled the surface power plant and the subsurface reservoirs, supplies the curves for CO2-based geothermal power potential and its Levelized Cost of Electricity (LCOE) as a function of the mass flowrate. This way, the optimal mass flowrate can be determined, which depends on the wellbore configuration and reservoir properties. However, the method does not account for the possibility of unwanted water accumulation in the production wells (liquid loading). In order to account for this in the optimization process, a wellbore-reservoir coupling is necessary. In this research, flow of fluids from the geological formation into the production wellbores has been analysed by optimizing the reservoir modelling. The optimization method has been extended to a set of representative geological realizations (500+). The optimal CO2 mass flowrate provided using genGEO, which maximizes net-electrical power output while minimizing LCOE, can now be related to the risk of liquid loading occurring. Additionally, the resultant reservoir model can forecast the CO2-plume migration, the reservoir pressure streamlines among the wellbores, and the CO2 saturation around the production wellbore(s).
Hefny, M., C.-Z. Qin, A. Ebigbo, J. Gostick, M.O. Saar, and M. Hammed, CO2-Brine flow in Nubian Sandstone (Egypt): Pore-Network Modeling using Computerized Tomography Imaging, European Geothermal Congress (EGC), 2019. https://doi.org/10.3929/ethz-b-000445810 [Download] [View Abstract]The injection of CO2 into the highly permeable Nubian Sandstone of a depleted oil field in the central Gulf of Suez Basin (Egypt) is an effective way to extract enthalpy from deep sedimentary basins while sequestering CO2, forming a so-called CO2-Plume Geothermal (CPG) system. Subsurface flow models require constitutive relationships, including relative permeability and capillary pressure curves, to determine the CO2-plume migration at a representative geological scale. Based on the fluid-displacement mechanisms, quasi-static pore-network modeling has been used to simulate the equilibrium positions of fluid-fluid interfaces, and thus determine the capillary pressure and relative permeability curves. 3D images with a voxel size of 650 nm3 of a Nubian Sandstone rock sample have been obtained using Synchrotron Radiation X-ray Tomographic Microscopy. From the images, topological properties of pores/throats were constructed. Using a pore-network model, we performed a cycle of primary drainage of quasi-static invasion to quantify the saturation of scCO2 at the point of a breakthrough with emphasis on the relative permeability–saturation relationship. We compare the quasi-static flow simulation results from the pore-network model with experimental observations. It shows that the Pc-Sw curve is very similar to those observed experimentally.
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Hefny, M., Rock Physics and Heterogeneities Characterization Controlling Fluid flow in Reservoir Rocks, Dissertation, pp., 2020. https://doi.org/10.3929/ethz-b-000445518 [Download] [View Abstract]Integrating geothermal energy production with CO2 capture and sequestration (CCS) in deep saline aquifers or oil/gas reservoirs is a promising approach in order to stabilize atmospheric CO2 concentrations while producing a reliable net-zero energy supply. The underlying base energy system is a so-called CO2-Plume Geothermal (CPG) power plant, where the captured CO2 is circulated in geological reservoirs. Within these reservoirs, the CO2 is naturally geothermally heated, produced to the surface, where it is expanded in a turbine for generating electricity. It is then cooled and finally combined with any CO2 additional stream, from any CO2 emitter, before being re-injected into the subsurface reservoir. The CO2 re-injection along with the continued supply of captured CO2 results in the continued growth of the subsurface CO2 plume. To ensure that 100% of the subsurface-injected CO2 is eventually permanently stored underground, it is essential to predict the migration and distribution of the CO2 in the subsurface reservoir. In this way, injection and flow can be maximized through the reservoir while keeping the risk of leakage through the sealing caprock at a minimum. In this study, we combine laboratory experiments and numerical techniques to understand characteristic features of subsurface fluid migration/entrapment of CO2 occurring within deep geological formations. The results cover three main topics at different scales: Calibration of seismic data Seismic reflection imaging within the earth's upper crust may be greatly distorted due to the attenuation in seismic waves, particularly the high-frequency waves, passing through fluid-bearing rocks. Our approach is to understand the origin of seismic reflectors at the microscopic scale. Experimental measurements at ultrasonic frequencies and under high confining pressures were performed to explore the link between the intrinsic rock properties (i.e. mineralogy, porosity, grain density, permeability) and the characteristics seismic response. We provide a unique set of seismic parameters necessary to calibrate seismic surveys in the Swiss Molasse Basin. This calibration of the seismic data provides a starting point for generating a synthetic seismic trace, based on the calculated reflection coefficients. The synthetic trace then correlates with both the seismic field data and the well logs in order to dynamically simulate wave propagation in the porous (and saturated) media. Our results improve the seismic interpretations of the geological reservoir and caprock geometries. CPG reservoir flow impedance Petrophysical properties of subsurface reservoirs are generally poorly understood, which increases the uncertainty related to the CO2 potential and storage security as well as the potential to use the CO2, stored in the reservoir, to produce geothermal energy. To this end, we investigate whether the Nubian Sandstone (a common reservoir rock found in the Gulf of Suez at depths of 2.5 to 4.4 km, with a geothermal gradient of 35.7 oC/km, confined by multiple aquitards) can serve as a CCS/CPG subsurface target. We combine field permeability estimates with laboratory measurements to provide constraints for reservoir modelling to estimate the power generation potential of the Nubian Sandstone reservoir. The reservoir geometry is constrained by seismic surveys, which show that the region of interest has several extensional faults with an accumulative dip-slip displacement of 810 m. We estimate the reservoir flow impedance [kPa.s/kg] for each compartmentalized block using a 1D analytical Darcy solution, developed for a single-phase fluid in an inverted 5-spot well-pattern configuration. With this flow impedance, we determine a potential net electric power of 1137 kWe for the deepest fault block (depth: 4.0 km, surface area: 1.0 km2, pressure: 40 MPa, well diameter: 0.41 m). This potential net power decreases by 47% for a smaller well diameter of 0.17 m, and 88% for over-pressurized zones (pressure: 62 MPa). Overall, we estimate a potential net electric power generation capacity for the entire field (with a reservoir footprint of 15 km2) of 12 MWe and a Levelized Cost Of Electricity (LCOE) of less than 150 $/MWh (0.15 $/kWh), depending on the availability of infrastructure and other resources (i.e. CO2 sources, geophysical exploration, and the existence of a well network). These results substantially reduce uncertainties in assessing the geothermal prospect in the Hammam Faraun hot spring region, Sinai Peninsula, Egypt. Capillary trapping: Implication for CCS This study describes how digital rock physics investigations compare with laboratory experiments to quantify two-phase fluid flow properties. Three-dimensional images, with a voxel size of 0.65 m3 of a Nubian Sandstone sample, have been obtained using Synchrotron Radiation X-ray Tomographic Microscopy. From the images, topological properties of pores/throats were constructed. Using a pore-network model, we perform sequential primary drainage--main imbibition cycle of quasi-static invasion to quantify: (1) the CO2 and brine relative permeability curves, (2) the effect of initial wetting-phase saturation (i.e. the saturation at the point of reversal from drainage to imbibition) on the residual–trapping potential, and (3) study the relative permeability–saturation hysteresis. The results illustrate the sensitivity of the pore-scale fluid-displacement and trapping processes on some key parameters (i.e. advancing contact angle, pore-body-to-throat aspect ratio, and initial wetting-phase saturation) and improve our understanding of the potential magnitude of capillary trapping in Nubian Sandstone. Finally, we are developing a numerical model in MOOSE (Multiphysics Object Oriented Simulation Environment) to (1) quantify the CO2 saturation profiles at the reservoir-scale and (2) simulate the reservoir behaviour under different physical processes and different well pattern configurations. We base our reservoir simulations on a well-established static geological model from an offshore oilfield in the Gulf of Suez (the model that has been developed under CPG reservoir flow impedance part; Chapter 3), utilizing the physical properties and two-phase fluid flow behavior properties that we have obtained from the Capillary trapping part (Chapter 4). The first results of the reservoir simulations show how the CO2-plume evolves over time and predict a heat extraction potential for the heterogeneous reservoirs.