Papers by Panos Papanastasiou
Global NEST International Conference on Environmental Science & Technology
A quantitative microbial risk analysis of Ezousa (Cyprus) Managed Aquifer Recharge (MAR) site is ... more A quantitative microbial risk analysis of Ezousa (Cyprus) Managed Aquifer Recharge (MAR) site is presented herein to evaluate the health risks associated with the pathogenic fraction of three microorganisms: the bacterium Escherichia Coli (E. Coli), the Rotavirus and the protozoan Giardia duodenalis. At Ezousa, raw wastewater from the urban area is subject to wastewater treatment followed by soil-aquifer filtration prior reaching the end-users, who are mainly farmers. The removal efficiency standards of wastewater treatment processes are determined according to World Health Organization (WHO) reports, whereas two extreme end-user exposure scenarios are considered. The first scenario refers to a situation commonly encountered in industrialised countries, where farmers use tractors and associated farming equipment and are expected to wear protective gloves during their activities. The second scenario describes farming practices in developing countries, in which tractors and gloves are...
International Journal of Engineering Science, 2021
We analyse a problem of a hydraulic fracture driven by a non-Newtonian shear-thinning fluid. Flui... more We analyse a problem of a hydraulic fracture driven by a non-Newtonian shear-thinning fluid. Fluid viscosity is described by the four-parameter truncated power-law model. By varying the parameters of the rheological model we investigate spatial and temporal evolution of fluid flow inside the crack and the resulting fracture geometry. A detailed quantitative and qualitative analysis of the underlying physical phenomena is delivered. The results demonstrate that rheological properties of fluids significantly affect the process of hydraulic fracture not only by the values of viscosity, but also by the range of fluid shear rates over which variation of viscosity occurs.
2022 2nd International Conference on Energy Transition in the Mediterranean Area (SyNERGY MED)
All Days
ABSTRACT: In this paper we present a new mechanism that explains hydraulic fracture containment i... more ABSTRACT: In this paper we present a new mechanism that explains hydraulic fracture containment in the target zone. The study is based on the modelling of hydraulic fracture propagation in weak rocks and comparison of the results of propagation in the vertical direction with propagation in the horizontal direction. The modelling is based on both analytical modelling with a Mohr-Coulomb dislocation theory and on FEM modelling of hydraulic fracture propagation in weak formations described by Mohr-Coulomb elastoplastic material and a cohesive-type fracture propagation criterion. It was found that the resistance to fracturing, expressed in the dislocation model by the required force and in the FEM by an effective fracture toughness that increases with fracture extension tending to asymptotic value, depends strongly on the fracture propagation direction. A dominant parameter that quantifies these effects is a new brittleness index (BI) that depends both on rock strength and insitu stress...
Environmental Technology & Innovation, 2022
Journal of Environmental Chemical Engineering, 2021
ABSTRACT Biochar produced from organic waste feedstocks have lately been utilized as adsorbents f... more ABSTRACT Biochar produced from organic waste feedstocks have lately been utilized as adsorbents for the decontamination of antibiotics-contaminated environmental matrices. The aim of the present study is a) the assessment of the adsorption capacity of three distinct derived biochars [biosolids (BDΒ), cattle manure (MDB) and spent coffee grounds (SCGDB)], applied either at a low (1 g L-1) or high (10 g L-1) dose on seven antibiotics (tetracycline, TET; erythromycin, ERY; clarithromycin, CLA; ampicillin, AMP; ofloxacin, OFL; sulfamethoxazole, SMX; trimethoprim, TMP) spiked as mixture in environmentally relevant concentration (100 μg L-1) of an aqueous solution (8.27 85%) of AMP and TMP. However, the studied biochar failed to remove OFL and SMX. The adsorption results were best fitted to the Freundlich model with the sole exception of SMX. The main responsible mechanisms for the adsorption of antibiotics included surface complexation, H-bonding, π-π electron-donor-acceptor (EDA) interactions, pore-filling effects or the simultaneous occurrence of several of these mechanisms. Overall, the results highlighted the potential utilization of BDB, MDB and SCGDB for the decontamination of antibiotics-contaminated water bodies, while promoting the circular economy strategy.
Biomass Conversion and Biorefinery, 2020
A laboratory analysis is presented in this study that evaluates the impact of three different bio... more A laboratory analysis is presented in this study that evaluates the impact of three different biochars, derived from biowastes of sludge (SDB), manure (MDB) and spent coffee grounds (SCGDB), on the physical properties of a loamy sand soil. Column experiments are conducted to measure the hydraulic conductivity and water content of these biochars when mixed with soil at a fixed concentration (5% with respect to (w.r.t) reference soil) under saturated conditions. The results show a substantial increase of the hydraulic conductivity for the biochars derived from SCGDB and SDB, whereas no changes were observed for MDB. The saturated water content is increased with the addition of SCGDB and trivial changes are observed for the remaining treatments. Numerical computations using HYDRUS-1D are conducted for a hypothetical scenario, revealing the different impact that each biochar has on the reference soil.
We employed a higher order continuum based on Mohr-Coulomb Cosserat elastoplasticity in a non-lin... more We employed a higher order continuum based on Mohr-Coulomb Cosserat elastoplasticity in a non-linear finite element analysis capable of modelling the localization of deformation in shear bands that leads to failure near underground openings. The model is used to investigate the stability of wellbore multilateral junctions. The obtained results show a progressive failure mechanism and the computed failure modes are in a good qualitative agreement with laboratory observations. We found that the multilateral junction of a lateral wellbore drilled to the direction parallel to the maximum insitu stress is more stable than in the case of a lateral wellbore drilled to the direction perpendicular to the maximum insitu stress.
Soil Dynamics and Earthquake Engineering, 2021
Abstract Offshore pipelines often cross large areas with geomorphological, geological, and tecton... more Abstract Offshore pipelines often cross large areas with geomorphological, geological, and tectonic conditions that may pose a variety of geohazards, one of which is the co-seismic slippage of active tectonic faults. Ground movement induced by fault slippage imposes substantial straining on the pipelines, threatening their integrity. This paper presents the results of a series of large-deformation parametric finite element simulations of a partially embedded pipeline resting on a fine-grained seabed and subjected to the differential movement of an active strike-slip tectonic fault. Parametric computations were performed for different values of the angle between fault strike and the pipeline axis, shear strength at the seabed surface, and different contact conditions at the soil-pipeline interface. The pipeline is examined for both pressurized and non-pressurized conditions and for different values of wall thickness and pipeline embedment. The developed strains in the pipeline with the application of fault displacement are determined and compared with appropriate performance criteria for steel pipelines. It was found that the angle at which the pipeline crosses the fault trace is an important parameter. For a range of oblique intersection angles for which the pipeline is subjected to overall compression, pipeline buckling occurs at relatively small fault displacements. For other intersection angle values, local buckling is unlikely due to the pipeline stretching with the fault movement that reduces the compressive stresses. Pipeline safety against strike-slip fault rupture may be substantially improved by simply adjusting the routing at the location of fault crossing.
Energies
Hybrid photovoltaic–regenerative hydrogen fuel cell (PV-RHFC) microgrid systems are considered to... more Hybrid photovoltaic–regenerative hydrogen fuel cell (PV-RHFC) microgrid systems are considered to have a high future potential in the effort to increase the renewable energy share in the form of solar PV technology with hydrogen generation, storage, and reutilization. The current study provides a comprehensive review of the recent research progress of hybrid PV-RHFC microgrid systems to extract conclusions on their characteristics and future prospects. The different components that can be integrated (PV modules, electrolyzer and fuel cell stacks, energy storage units, power electronics, and controllers) are analyzed in terms of available technology options. The main modeling and optimization methods, and control strategies are discussed. Additionally, various application options are provided, which differentiate in terms of scale, purpose, and further integration with other power generating and energy storage technologies. Finally, critical analysis and discussion of hybrid PV-RHFC ...
In this paper the problem of a plane strain hydraulic fracture propagating in elasto-plastic mate... more In this paper the problem of a plane strain hydraulic fracture propagating in elasto-plastic material is analyzed. The Finite Element Method computations are employed in the framework of ELFEN package to simulate the Mini-Frac test. The basic trends of fracture evolution are identified for both, the propagation and the closure stage. Pressure decline analysis is conducted. The results show that the standard techniques of the pressure decline analysis can be adopted also for the case where the fractured material deforms inelastically.
In this paper a problem of numerical simulation of hydraulic fractures is considered. An efficien... more In this paper a problem of numerical simulation of hydraulic fractures is considered. An efficient algorithm of solution, based on the universal scheme introduced earlier by the authors for the fractures propagating in elastic solids, is proposed. The algorithm utilizes a FEM based subroutine to compute deformation of the fractured material. Consequently, the computational scheme retains the relative simplicity of its original version and simultaneously enables one to deal with more advanced cases of the fractured material properties and configurations. In particular, the problems of poroelasticity, plasticity and spatially varying properties of the fractured material can be analyzed. The accuracy and efficiency of the proposed algorithm are verified against analytical benchmark solutions. The algorithm capabilities are demonstrated using the example of the hydraulic fracture propagating in complex geological settings.
Soil Dynamics and Earthquake Engineering, 2020
Abstract This paper presents the results of a series of parametric finite element analyses of a p... more Abstract This paper presents the results of a series of parametric finite element analyses of a partially embedded (unburied) pipeline resting on a soft fine-grained seabed and subjected to the differential movement of an active tectonic fault. Three-dimensional elastoplastic simulations are carried out for normal and reverse faults with the objective of assessing the vulnerability of pipeline infrastructure to a fault rupture. Geometrical non-linearity is considered in order to be able to capture possible pipeline-wall buckling under compressive loads. The effects of fault slip magnitude, fault dip angle, shear strength at the seabed surface, pipeline thickness and pressurization of the pipeline on the developing stress and deformation state of the pipeline are monitored and compared with appropriate performance criteria of steel pipelines. It is found that the rupture of a normal fault does not impose a severe risk on the pipeline, even for a large earthquake, whereas in reverse fault conditions severe risk is generated due to compressive local buckling.
International Journal of Engineering Science, 2021
We analyse a problem of a hydraulic fracture driven by a non-Newtonian shear-thinning fluid. Flui... more We analyse a problem of a hydraulic fracture driven by a non-Newtonian shear-thinning fluid. Fluid viscosity is described by the four-parameter truncated power-law model. By varying the parameters of the rheological model we investigate spatial and temporal evolution of fluid flow inside the crack and the resulting fracture geometry. A detailed quantitative and qualitative analysis of the underlying physical phenomena is delivered. The results demonstrate that rheological properties of fluids significantly affect the process of hydraulic fracture not only by the values of viscosity, but also by the range of fluid shear rates over which variation of viscosity occurs.
SPE Annual Technical Conference and Exhibition, 2020
This paper presents an optimum way to produce down to depletion a compartmentalized reservoir in ... more This paper presents an optimum way to produce down to depletion a compartmentalized reservoir in offshore deep environment by considering geomechanical stress-deformation mechanisms and associated problems. The case study is for a faulted reservoir zone of the Aphrodite field, located in the Eastern Mediterranean. The study is based on finite element modelling using 2D plane strain analysis that incorporates pore pressure and elastoplastic deformation of reservoir and overburden rock formations using the Drucker-Prager plasticity model. The mechanical properties of the reservoir sandstones were derived from calibration of data obtained from triaxial tests and for the overburden shale layers from acoustic velocities and correlation functions. The compartmentalized geometry was constructed based on seismic data and logging data obtained at the exploration and appraisal phases. The estimated insitu stress field was transformed and applied on the boundaries of the model blocky geometry. Four different initial and equilibrium depletion scenarios were examined and the obtained results in terms of deformation and effective stresses are compared. The first scenario reflects the initial stress state, the next two intermediate scenarios present non-uniform depletion cases for each fault block, and the fourth scenario presents the case of a uniform depletion. It was found that the uniform depletion of the reservoir compartments creates the least stress contrast in the field and consequently, ensures better control of stress-related impacts during the production. The analysis highlights the local regions of a fault blocks system that potentially suffer by high shear strains that can cause fault reactivation or induced fractured zones but the over-all risk remains low. Furthermore, the analysis establishes relationships between the mean effective stress, volumetric strain, and permeability changes in order to predict the regions with improved transmissibility characteristics or the less permeable compacted rock regions of the reservoir. Overall, the analysis can provide an appreciation of the stress/strain-driven characteristics of the reservoir showing the area of rock compaction tendencies of the faulted blocks and the further deformation in depletion conditions. The presented work demonstrates clearly that a properly calibrated reservoir geomechanical model can be used as a screening tool for examining depletion scenarios of compartmentalized reservoirs, highlighting areas of potential problems such as fault activation, wellbore shearing, reservoir compaction, permeability changes and fault sealing.
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Papers by Panos Papanastasiou