Petrophysical interpretation of 1H NMR relaxation responses from saturated rocks is complicated by paramagnetic species present in fluids. Oxygen dissolved in liquids is one common example. Dipolar interactions of oxygen’s unpaired electron spins with the magnetic moment of fluid nuclei provide a strong relaxation mechanism known as paramagnetic relaxation enhancement (PRE). As a result even low concentrations of dioxygen in its common triplet ground state significantly shorten longitudinal and transverse relaxation times of host fluids. This effect may be employed similarly to any standard tracer technique to study pore connectivity in porous media by detecting a change of oxygen concentration due to diffusion resolved in time and space. Since relaxation enhancement effect is likely stronger in non-wetting phase than in wetting one (where surface relaxation process dominates) this difference can be utilized to study wettability in immiscible multiphase systems. We use a relaxation time contrast between air-saturated and oxygen-free fluids to evaluate oxygen concentration change within two fluid phases saturating rock, to estimate time required to establish equilibrium concentration and to calculate a mutual diffusion coefficient of oxygen. A spatially- and time-resolved T2(z,t) experiment provides the time-dependent oxygen concentration change along the fully- and partially-saturated carbonate core plug exposed to air saturated oil at its inlet. We derive an effective mutual diffusion coefficient of oxygen and accordingly a tortuosity estimate as a function of position along the core and rock saturation. The spatially resolved oxygen diffusion-based tortuosity is compared to simulated conductivitybased tortuosity. The latter is calculated on a high-resolution micro-tomographic image of Mount Gambier limestone by solving the Laplace equation for conductivity.

Multiphase flow in porous media is important in a wide range of industrial and environmental processes. It is well-known that the fluids’ relative affinity to the porous media (i.e., wettability) is a crucial factor controlling multiphase flow in porous media. Despite having a good understanding of multiphase flow in porous media under uniform wettability conditions, our knowledge of how fluids flow in mixed-wet porous media is more limited. Mixed-wet porous media (i.e., porous media with spatially heterogeneous wettability) is prevalent in nature, from groundwater aquifers to oil-bearing rocks. This Thesis aims to better understand the complexities of multiphase flow in mixed-wet porous media. The study begins with investigating fluid-fluid displacement in mixed-wet microfluidic flow cells. We performed experiments over a range of capillary numbers and mixed-wettability conditions, and our results show that the fluid-fluid interface in mixed-wet pores resembles an S shaped saddle with very low capillary pressure. In the next step, we derive analytical expressions for fluid-fluid interface evolution through mixed-wet pore throats. These analytical expressions are incorporated into a dynamic pore network model, which enables us to develop a numerical framework capable of simulating fluid-fluid displacement in mixed-wet porous media. Next, we leverage our model to simulate multiphase flow in simple mixed-wet porous micro-models consisting of distinct water-wet and oil-wet regions whose fractions are systematically varied to yield a variety of displacement patterns over a wide range of capillary numbers. Our simulations reveal that mixed-wettability impacts are most prominent at low capillary numbers, and it depends on the complex interplay between the wettability fraction and the intrinsic contact angle of the water-wet regions. We also investigate the dynamics of multiphase flow in mixed-wet porous media under quasi-static conditions and discover that it exhibits self-organized criticality (SOC). Finally, we determine the correlation between spatial and temporal aspects of this dynamical system. / Thesis / Doctor of Science (PhD)

Yes / The paper reports an investigation on the mechanical durability of textured thermoplastic surfaces together with their respective wetting properties. A range of laser-induced topographies with different aspect ratios from micro to nanoscale were fabricated on tool steel inserts using an ultrashort pulsed near infrared laser. Then, through micro-injection moulding the topographies were replicated onto polypropylene surfaces and their durability was studied systematically. In particular, the evolution of topographies on textured thermoplastic surfaces together with their wetting properties were investigated after undergoing a controlled mechanical abrasion, i.e. reciprocating dry and wet cleaning cycles. The obtained empirical data was used both to study the effects of cleaning cycles and also to identify cleaning procedures with a minimal impact on textured thermoplastic surfaces and their respective wetting properties. In addition, the use of 3D areal parameters that are standardised and could be obtained readily with any state-of-the-art surface characterisation system are discussed for monitoring the surfaces' functional response. / European Commission H2020 ITN programme “European ESRs Network on Short Pulsed Laser Micro/Nanostructuring of Surfaces for Improved Functional Applications” (Laser4Fun) under the Marie Skłodowska-Curie grant agreement No. 675063 (www.laser4fun.eu) and the UKIERI DST programme “Surface functionalisation for food, packaging, and healthcare applications”. In addition, the work was supported by three other H2020 programmes, i.e. the projects on “Modular laser based additive manufacturing platform for large scale industrial applications” (MAESTRO), “High-Impact Injection Moulding Platform for mass-production of 3D and/or large micro-structured surfaces with Antimicrobial, Self-cleaning, Anti-scratch, Anti-squeak and Aesthetic functionalities” (HIMALAIA) and “Process Fingerprint for Zero-defect Net-shape Micromanufacturing” (MICROMAN).

Yes / The paper reports an investigation on the mechanical durability of textured thermoplastic surfaces together with their respective wetting properties. A range of laser-induced topographies with different aspect ratios from micro to nanoscale were fabricated on tool steel inserts using an ultrashort pulsed near infrared laser. Then, through micro-injection moulding the topographies were replicated onto polypropylene surfaces and their durability was studied systematically. In particular, the evolution of topographies on textured thermoplastic surfaces together with their wetting properties were investigated after undergoing a controlled mechanical abrasion, i.e. reciprocating dry and wet cleaning cycles. The obtained empirical data was used both to study the effects of cleaning cycles and also to identify cleaning procedures with a minimal impact on textured thermoplastic surfaces and their respective wetting properties. In addition, the use of 3D areal parameters that are standardised and could be obtained readily with any state-of-the-art surface characterisation system are discussed for monitoring the surfaces' functional response.

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Yes / The mass production of polymeric parts with functional surfaces requires economically viable manufacturing routes. Injection moulding is a very attractive option however wear and surface damage can be detrimental to the lifespan of replication masters. In this research, the replication of superhydrophobic surfaces is investigated by employing a process chain that integrates surface hardening, laser texturing and injection moulding. Austenitic stainless steel inserts were hardened by low temperature plasma carburising and three different micro and nano scale surface textures were laser fabricated, i.e. submicron triangular LaserInduced Periodic Surface Structures (LIPSS), micro grooves and Lotus-leaf like topographies. Then, a commonly available talc-loaded polypropylene was used to produce 5000 replicas to investigate the evolution of surface textures on both inserts and replicas together with their functional response. Any wear orsurface damage progressively built up on the inserts during the injection moulding process had a clear impact on surface roughness and peak-to-peak topographies of the replicas. In general, the polymer replicas produced with the carburised inserts retained the wetting properties of their textured surfaces for longer periods compared with those produced with untreated replication masters. / European Union’s H2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 675063 (www.laser4fun.eu). The work was also supported by three other H2020 projects, i.e. “HighImpact Injection Moulding Platform for mass-production of 3D and/or large micro-structured surfaces with Antimicrobial, Self-cleaning, Anti-scratch, Anti-squeak and Aesthetic functionalities” (HIMALAIA, No. 766871), “Process Fingerprint for Zero-defect Net-shape Micromanufacturing” (MICROMAN, No. 674801) and “Modular laser based additive manufacturing platform for large scale industrial applications” (MAESTRO, No. 723826). Further support was provided by the UKIERI DST programme “Surface functionalisation for 18/20 Accepted in the journal Tribology – Materials, Surfaces & Interfaces. food, packaging, and healthcare applications”

Yes / Inspired from the low wetting properties of Lotus leaves, the fabrication of dual micro/nano-scale topographies is of interest to many applications. In this research, superhydrophobic surfaces are fabricated by a process chain combining ultrashort pulsed laser texturing of steel inserts and injection moulding to produce textured polypropylene parts. This manufacturing route is very promising and could be economically viable for mass production of polymeric parts with superhydrophobic properties. However, surface damages, such as wear and abrasion phenomena, can be detrimental to the attractive wetting properties of replicated textured surfaces. Therefore, the final product lifespan is investigated by employing mechanical cleaning of textured polypropylene surfaces with multipurpose cloths following the ASTM D3450 standard. Secondly, the surface damage of replication masters after 350 injection moulding cycles with glass-fiber reinforced polypropylene, especially to intensify mould wear, was investigated. In both cases, the degradation of the dual-scale surface textures had a clear impact on surface topography of the replicas and thus on their wetting properties, too. / Europe Union H2020 research and innovation programme.

As easy target reservoirs are depleted around the world, the need for intelligent enhanced oil recovery (EOR) methods increases. The first part of this work is focused on modeling aspects of novel chemical EOR methods for naturally fractured reservoirs (NFR) involving wettability modification towards more water wet conditions. The wettability of preferentially oil wet carbonates can be modified to more water wet conditions using alkali and/or surfactant solutions. This helps the oil production by increasing the rate of spontaneous imbibition of water from fractures into the matrix. This novel method cannot be successfully implemented in the field unless all of the mechanisms involved in this process are fully understood. A wettability alteration model is developed and implemented in the chemical flooding simulator, UTCHEM. A combination of laboratory experimental results and modeling is then used to understand the mechanisms involved in this process and their relative importance. The second part of this work is focused on modeling surfactant/polymer floods using a fully implicit scheme. A fully implicit chemical flooding module with comprehensive oil/brine/surfactant phase behavior is developed and implemented in general purpose adaptive simulator, GPAS. GPAS is a fully implicit, parallel EOS compositional reservoir simulator developed at The University of Texas at Austin. The developed chemical flooding module is then validated against UTCHEM. / text

Condensate blockage negatively impacts large natural gas condensate reservoirs all over the world; examples include Arun Field in Indonesia, Karachaganak Field in Kazakhstan, Cupiagua Field in Colombia,Shtokmanovskoye Field in Russian Barents Sea, and North Field in Qatar. The main focus of this thesis is to evaluate condensate blockage problems in the North Field, Qatar, and then propose solutions to increase well productivity in these gas condensate wells. The first step of the study involved gathering North Field reservoir data from previously published papers. A commercial simulator was then used to carry out numerical reservoir simulation of fluid flow in the North Field. Once an accurate model was obtained, the following three solutions to increasing productivity in the North Field are presented; namely wettability alteration, horizontal wells, and reduced Non Darcy flow. Results of this study show that wettability alteration can increase well productivity in the North Field by adding significant value to a single well. Horizontal wells can successfully increase well productivity in the North Field because they have a smaller pressure drawdown (compared to vertical wells). Horizontal wells delay condensate formation, and increase the well productivity index by reducing condensate blockage in the near wellbore region. Non Darcy flow effects were found to be negligible in multilateral wells due to a decrease in fluid velocity. Therefore, drilling multilateral wells decreases gas velocity around the wellbore, decreases Non Darcy flow effects to a negligible level, and increases well productivity in the North Field.