Experimental study of CO2 injectivity impairment in sandstone due to salt precipitation and fines migration

Re-injection of carbon dioxide (CO2) in deep saline formation is a promising approach to allow high CO2 gas fields to be developed in the Southeast Asia region. However, the solubility between CO2 and formation water could cause injectivity problems such as salt precipitation and fines migration. Although both mechanisms have been widely investigated individually, the coupled effect of both mechanisms has not been studied experimentally. This research work aims to quantify CO2 injectivity alteration induced by both mechanisms through core-flooding experiments. The quantification injectivity impairment induced by both mechanisms were achieved by varying parameters such as brine salinity (6000–100,000 ppm) and size of fine particles (0–0.015 µm) while keeping other parameters constant, flow rate (2 cm3/min), fines concentration (0.3 wt%) and salt type (Sodium chloride). The core-flooding experiments were carried out on quartz-rich sister sandstone cores under a two-step sequence. In order to simulate the actual sequestration process while also controlling the amount and sizes of fines, mono-dispersed silicon dioxide in CO2-saturated brine was first injected prior to supercritical CO2 (scCO2) injection. The CO2 injectivity alteration was calculated using the ratio between the permeability change and the initial permeability. Results showed that there is a direct correlation between salinity and severity of injectivity alteration due to salt precipitation. CO2 injectivity impairment increased from 6 to 26.7% when the salinity of brine was raised from 6000 to 100,000 ppm. The findings also suggest that fines migration during CO2 injection would escalate the injectivity impairment. The addition of 0.3 wt% of 0.005 µm fine particles in the CO2-saturated brine augmented the injectivity alteration by 1% to 10%, increasing with salt concentration. Furthermore, at similar fines concentration and brine salinity, larger fines size of 0.015 µm in the pore fluid further induced up to three-fold injectivity alteration compared to the damage induced by salt precipitation. At high brine salinity, injectivity reduction was highest as more precipitated salts reduced the pore spaces, increasing the jamming ratio. Therefore, more particles were blocked and plugged at the slimmer pore throats. The findings are the first experimental work conducted to validate theoretical modelling results reported on the combined effect of salt precipitation and fines mobilisation on CO2 injectivity. These pioneering results could improve understanding of CO2 injectivity impairment in deep saline reservoirs and serve as a foundation to develop a more robust numerical study in field scale.

Coexistence and tuning of spin-singlet and triplet transport in spin-filter Josephson junctions

The increased capabilities of coupling more and more materials through functional interfaces are paving the way to a series of exciting experiments and extremely advanced devices. Here we focus on the capability of magnetically inhomogeneous superconductor/ferromagnet (S/F) interfaces to generate spin-polarized triplet pairs. We build on previous achievements on spin-filter ferromagnetic Josephson junctions (JJs) and find direct correspondence between neat experimental benchmarks in the temperature behavior of the critical current and theoretical modelling based on microscopic calculations, which allow to determine a posteriori spin-singlet and triplet correlation functions. This kind of combined analysis provides an accurate proof of the coexistence and tunability of singlet and triplet transport. This turns to be a powerful way to model disorder and spin-mixing effects in a JJ to enlarge the space of parameters, which regulate the phenomenology of the Josephson effect and could be applied to a variety of hybrid JJs.

Three-dimensional convective dissolution of carbon dioxide into brine

The sequestration of carbon dioxide (CO2) through storage into deep saline aquifers represents an indispensable support technology to achieve the zero-carbon target necessary to mitigate the impact of CO2 on climate change. The effectiveness of the sequestration process, partly driven by the convective dissolution of CO2 in brine, is nowadays well characterized for two-dimensional geometries, low permeabilities, and small pressures of injection of CO2. However, reliable predictions of process-efficiency are missing because of the lack of full understanding of the three-dimensional (3D) spatio-temporal behaviour of CO2-rich convective fingers in brine over a large range of injection pressures. Here, we show that the convective dissolution is determined by the instability of the boundary layer formed at the interface between the two phases and is totally independent of the overall vertical size. Experiments were conducted over a broad range of injection pressures, close to process-relevant conditions. The results show the formation of complex 3D structures, including interconnecting stream tubes at the CO2-liquid interface, which could not be detected in previous 2D Hele-Shaw studies, and fingerings. A scale-free theoretical modelling of the convective process allows us to remap our laboratory results to length-scales of relevance for geological reservoirs. The experiments and the model show that the times needed for the onset of convection and the convective flux are independent of the system size.

MIXED CLASS TEACHING AS AN EMERGING TREND ACCELERATED BY COVID-19

The COVID-19 pandemic has essentially accelerated the pace of the teaching transformation. Mixed (also hyflex) class teaching has become indispensable in medical, engineering, teacher and other fields of education when only online teaching is not enough to ensure the continuity of the instruction. The research aim is to identify scenarios of mixed class teaching underpinning the elaboration of implications for higher education. The present research used both - theoretical and empirical methods. The theoretical methods included the analysis of scientific literature, theoretical modelling, systematisation, synthesis, comparison, and generalisation. The empirical study carried out in June 2021 was exploratory. Data were collected through the analysis of published studies. The collected data were processed via content analysis. The present research allows concluding that teaching has undergone significant changes in different historical periods. The findings of the empirical study facilitate the conclusion on the existence of two scenarios of mixed class teaching, namely HOT (Here or There) and COIL (Collaborative Online International Learning). Both scenarios are oriented to students’ learning, teaching in these scenarios is neither segmented nor structured. The novel contribution of the research is revealed in the implications on mixed class teaching for higher education. Future research work was proposed.

On Modelling Approaches to the Influence of Mechanical Deformation on the Micromagnetic Activity in a Mild Steel

In this study an attempt is made to develop a theoretical modelling by which the influence of certain mechanical deformation factors on the micromagnetic emission behavior of a low-carbon steel can reasonably be described and estimated. This modelling consists of a simple kinetics – kinematics – aided approach of the pinning state – controlled domain wall motion by which appropriate specific parameters are introduced. In this aspect the basic notion of specific micromagnetic activity (s.m.a.) is introduced by which the energetic strength of the activity is reflected. In this way, the synergetic effect of the quantitative (count rate) and qualitative (voltage) the detected micromagnetic Barkhausen emission (MBE) is taken into consideration. Thus it is possible, theoretically, to give a prediction of the general trend of changes in the s.m.a. under the influence of the tensile elastic as well as plastic deformation. For instance, one can demonstrate that tensile elastic deformation cannot influence the s.m.a. whereas plastic one leads to an increase in this. Furthermore, one can also predict that increasing permanent (residual) plastic deformation, obtained after unloading from prior tensile loading, leads to an obvious decrease in the s.m.a. Similar decrease in the s.m.a. can also be predicted for increasing rolling deformation by means of the same modelling approach used for the permanent tensile plastic deformation. Owing to the good agreement with the experimental results and the simplicity of the proposed theoretical approaches that can be seen as a promising valuable tool for further similar studies.

Topological phonons and electronic structure of Li2BaSi class of semimetals

Extension of the topological concepts to the Bosonic systems has led to the prediction of topological phonons in materials. Here we discuss the topological phonons and electronic structure of Li2BaX (X = Si, Ge, Sn, and Pb) materials using first-principles theoretical modelling. A careful analysis of the phonon spectrum of Li2BaX reveals an optical mode inversion with the formation of nodal line states in the Brillouin zone. Our electronic structure results reveal a double band inversion at the Γ point with the formation of inner nodal-chain states in the absence of spin-orbit coupling (SOC). Inclusion of the SOC opens a materials-dependent gap at the band crossing points and transitions the system into a trivial insulator state. We also discuss the lattice thermal conductivity and transport properties of Li2BaX materials. Our results show that coexisting phonon and electron nontrivial topology with robust transport properties would make Li2BaX materials appealing for device applications.

Solar thermal energy application to dry reforming of methane on the open-cell foam to enhance the energy storage efficiency of a thermochemical fluidized bed membrane reformer: modelling and simulation

The hydrodynamic characterization of the solar-driven CO2 reforming of methane through b-SiC open-cell foam in a fluidized bed configuration is performed by reacting Methane (CH4) with carbon dioxide (CO2). The mathematical modelling is important to design and optimize the reforming methods. Usually, the reforming methods's application through b-SiC foam bed improves the heat transfer and mass transfer due to high porosity and surface area of the b-SiC foam. Fluidized Bed Membrane (FBM) Reformers can be substantially studied as a promising equipment to investigate the thermochemical conversion of CH4 using CO2 to produce solar hydrogen. This work has as main objective a theoretical modelling to describe the process variables of the solar-driven CO2 reforming of methane in the FBM reformer. The FBM reformer is filled with b-SiC open-cell foam where the thermochemical conversion is carried out. The model variables describe the specific aims of work and these objectives can be identified from each equation of the developed mathematical model. The present work has been proposed to study two specific aims as (i) The effective thermal conductivity's effect of the solid phase and (ii) molar flows of chemical components. The endothermic reaction temperature's profiles are notably increased as the numeral value of the effective thermal conductivity's effect of the solid phase. is rised. The solar-driven CO2 reforming method is suggested to improve the Production Rate (PR) of H2 regarding the PR of CO.