Assoc Prof Mahshid Firouzi

Coal seam gas (CSG) well operators typically follow an industry rule of thumb 0.5 ft/s liquid velocity to prevent the onset of gas carryover during CSG dewatering operations. However, there is very little experimental data to validate this rule of thumb with only a publication by Sutton, Christiansen, Skinner and Wilson [1] available in the open literature. A review of more general studies on two-phase gas-water flows in vertical pipes and annuli revealed that experimental conditions, especially pipe and annuli diameters, can have a significant impact on development of two-phase flow phenomena. As such, the limited available data may not be applicable due to differences in experimental conditions. This study experimentally investigates the onset of gas carryover using an experimental setup intended specifically for the study of CSG wells. The University of Queensland Well Simulation Flow Facilities were designed to replicate as closely as possible the production zone of a typical vertical CSG well in Queensland, Australia in transparent acrylic pipes to observe two-phase flow behavior in simulated downhole conditions. The annular test section in the rig was constructed of a 7-in casing and 2¾-in tubing. Modification of the experimental setup to include a vertical separator allowed for the detection of gas carryover. Conceptual demonstrations of gas carryover were captured and have been illustrated. The experiments in this study validate the industry rule of thumb of 0.5 ft/s liquid velocity as an appropriate guideline for onset of gas carryover in a casing-tubing annulus dimension similar to a typical CSG well in Queensland.

Salts can negatively affect the froth flotation process by increasing the recovery of unwanted gangue particles. This study investigated the effect of salt on gangue recovery and evaluated the effectiveness of counter-current washing using unique system hydrodynamics distinct from conventional flotation cells, to mitigate this issue in saline water environments. Experiments were conducted using a Reflux flotation cell (RFC¿) with fine hydrophilic silica particles (with a D90 of 68 µm) as a model for gangue particles at two solid concentrations of 3 wt.% and 12 wt.% and using sodium chloride 1 M reflecting the predominant salt composition in plant water. A single-mineral flotation approach was employed to isolate the effect of system hydrodynamics on gangue recovery, minimizing interference from ion-particle-collector interactions in saline environments. Key parameters such as yield and system hydrodynamics including bubble size and gas holdup were analyzed across a range of gas and wash water fluxes in the presence and absence of salt. In the absence of salt and counter-current washing, silica recovery (yield) reached 13.8%±0.21. This value increased by approximately 6.5% of the initial recovery when 1 M NaCl was introduced, attributed to salt-induced aggregation of fine silica particles through electrostatic double-layer screening. The application of counter-current washing in the presence of salt reduced silica recovery by 90%, resulting in a final recovery of less than 1.5%. This significant reduction is attributed to the formation of salt-induced agglomerates that are more effectively removed through washing. This trend was observed for both 12 wt.% solid concentration and the relatively dilute feed (3 wt.%). To investigate the potential hydrophobizing effect of salt on silica, surface wettability was measured with and without salt, showing minimal or no change in wettability. These findings highlight the potential of the RFC in mitigating the adverse effects of salts on gangue recovery, offering a promising approach for improving flotation performance in saline water.

Gangue particles, which are typically hydrophilic, impede the efficient recovery of valuable hydrophobic particles in flotation cells, and in turn lower the grade of the final concentrate. The system hydrodynamics, including the gas and liquid fluxes, and bubble segregation, plays a key role in the efficient separation of the valuable and gangue mineral particles. In conventional flotation cells, an increase in the gas flux leads to increased entrainment of the gangue minerals, due to an increase in water recovery. This new work investigates the effects of the gas flux and liquid fluxes on gangue entrainment in a Reflux Flotation Cell (RFC), a novel system that incorporates parallel inclined channels to prevent bubble losses to tailings. The study focused exclusively on fine hydrophilic silica as the model gangue mineral in the feed, completely excluding hydrophobic particles. Rigorous, continuous, steady state experiments produced an accurate measure of the particle transport into the concentrate. It was concluded that the wash water addition removed the bulk entrainment. Hence, the observed entrainment was primarily due to bubble surface entrainment. Interestingly, the silica entrainment decreased with increasing the gas flux and wash water flux. The system hydrodynamics was quantified through measurement of the gas hold-up and the bubble size distribution. Drift flux theory was applied to these accurate datasets, confirming the significant role of enhanced segregation of the bubbles due to the presence of the inclined channels, an effect known as the Boycott Effect.

CO2 foams often suffer from poor stability due to high coarsening and coalescence rates, limiting their effectiveness in various applications. While it is well-established that small amounts of insoluble vapours such as alkane or fluorocarbon vapours can impede coarsening and recent studies have demonstrated their impact on coalescence, their specific effect on the CO2 foams has not been studied. This research provides a comprehensive examination of stabilising effect of hexane on CO2 foams in the presence of sodium dodecylbenzenesulfonate (SDBS). We investigated the foam stability of CO2 foams, benchmarking them against N2 foams by analysing foam lifetime, liquid drainage rate, and the evolution of bubble size. Additionally, we quantified the stabilising impact of hexane by calculating the coarsening rate. To gain insights into the adsorption mechanism of surfactants in the presence of hexane, we conducted surface tension and interfacial dilational rheology measurements, which demonstrated an increased adsorption of surfactant molecules at the interface and increased dilational viscoelasticity of interface when n-hexane was present. The introduction of hexane significantly improved foam stability, reducing coarsening rates by more than an order of magnitude. This improvement in foam stability is attributed to inhibited CO2 diffusion from the bubbles, as well as enhanced surfactant adsorption and surface elasticity, resulting in an approximate 3.6-fold increase in foam half-life.

Declining ore grades have been addressed through exponentially higher cell residence times. With cell sizes approaching 1000 m3, improved kinetics is crucial. Downcomers, which increase shear rates for improved recovery of fine hydrophobic particles, may also cause a strong deposition flux of ultrafine hydrophilic particles close to the bubble surface, via lubrication forces. Model feeds of varying silica-to-chalcopyrite mass ratios up to 80 were processed using a REFLUX¿ Flotation Cell (RFC¿). Equivalent hydrodynamic conditions were applied, including a low solids concentration of 1 wt% to prevent kinetic limitations due to limited bubble surface area. The hydrophobic particle recovery declined significantly as the silica content increased, with clear evidence the ultrafine hydrophilic silica hindered the adhesion kinetics of the hydrophobic chalcopyrite.

Frothers play a key role in froth flotation by stabilising bubbles, which serve as a platform for separation of minerals of interest. This paper presents D-a-Tocopherol Polyethylene Glycol 6000 Succinate (VitE_PEG6000), an eco-friendly green frother. VitE_PEG6000's frothing performance was evaluated and benchmarked against MIBC using metrics such as the dynamic and static foam stability index (DFI, SFI), decay rate index (DRI), and critical coalescence concentration (CCC). The results show VitE_PEG6000 offers relatively high DFI of ~ 405 s/mM and low CCC of ~ 0.008 mM, classifying it as a powerful frother. Furthermore, NaCl enhances the foaming properties of VitE_PEG6000 by further lowering the surface tension and increasing dilational viscoelasticity. The outcome from this work suggests VitE_PEG6000 as a viable green frother, minimising environmental impact and hazards. Moreover, the compatibility of VitE_PEG6000 with NaCl, as the most dominant salt in groundwater and seawater allows the use of this novel frother with various water sources, thus reducing ecological footprints and fresh water usage.

Polymer composites are increasingly used in applications where they are subjected to abrasive wear. The bulk of prior research has focused on the performance of polymers under sliding wear conditions and in some cases resulted in a contradiction, particularly when it comes to the effect of reinforcing fibers on the wear performance. Another omission is the absence of pre-conditioning or accelerated aging which is clearly an important factor from an application standpoint. This work aims to highlight the influence of hydrothermal aging on the tribological and mechanical performance of polyamide 6 (PA6) and glass fiber-reinforced polyamide 6 (PA6-GF). The friction and abrasion wear behavior of unconditioned and conditioned PA6 and PA6-GF composites are measured against silicon carbide grinding paper on a pin-on-disk tribometer in a demineralized water medium at 60 °C. Specimens are conditioned in demineralized water at room temperature (RT) 25, 40, and 60 °C to investigate the effects of moisture and temperature. The presence of up to 25 wt.% glass fiber (GF) in PA6-based composites exhibits an increasing trend in abrasion wear mass loss and a reduction in coefficient of friction (COF). Interestingly, the mass loss of specimens conditioned to saturation does not increase compared to that of unconditioned samples. The FTIR spectroscopy is used to study the polymer degradation during hydrothermal aging.

PFAS are biologically recalcitrant compounds that are persistent in the environment and have subsequently contaminated groundwater, landfill leachate and surface water. Due to their persistence and toxicity, there are environmental concentration limits imposed on some PFAS compounds that extend down to a few nanograms per litre and even proposals for reducing these to picogram per litre levels. Since PFAS concentrates at water-air interfaces as a result of their amphiphilic nature, this characteristic is important for the successful modelling and prediction of transport behaviour of PFAS through various systems. Here we present a procedure for using a foam fractionation method to experimentally determine the PFAS adsorption behaviour at ng/L and µg/L concentrations in the presence of salts. The equilibrium air-water adsorption coefficients for PFHxS and PFOA at different salinities and concentrations are experimentally shown to be constant across the range of PFAS concentrations investigated (approx. 0.1¿100 µg/L). The adsorption isotherms may consequently be modelled by Henry or Langmuir style equations at these low concentrations.

Per- and poly-fluoroalkyl substances (PFAS) are recalcitrant, synthetic chemicals that are ubiquitous in the environment because of their widespread use in a variety of consumer and industrial products. PFAS contamination has become an increasing issue in recent years, which needs to be urgently addressed. Foam fractionation is emerging as a potential remediation option that removes PFAS by adsorption to the surface of rising air bubbles which are removed from the system as a foam. PFAS concentrations in the environment are often not sufficient to allow for formation of a foam by itself and often a co-foaming agent is required to be added to enhance the foamability of the solution. In this study, the effect of different classes of co-foaming agents, anionic, non-ionic, zwitterionic and cationic surfactants on the removal of PFAS with varying fluorocarbon chain length from 3 to 8 in a foam fractionation process have been investigated. Evaluation of the air-water interface partitioning coefficient (k') in addition with surface tension and PFAS removal results support the contention that using a co-foaming agent with the opposite charge to the PFAS in question significantly facilitates the adsorption of PFAS to the air-water interface, enhancing the efficiency of the process. Using the non-ionic surfactant (no headgroup electrostatic interaction with PFAS), as a reference, it was observed, in terms of PFAS separation and rate of PFAS removal, that anionic co-surfactant performed worst, zwitterionic was better, and cationic co-surfactant performed best. All of the PFAS species were able to be removed below the limit of detection (0.05 µg/L) after 45 minutes of foaming time with the cationic surfactant.

Pickering foams are available in many applications and have been continually gaining interest in the last two decades. Pickering foams are multifaceted, and their characteristics are highly dependent on many factors, such as particle size, charge, hydrophobicity and concentration as well as the charge and concentration of surfactants and salts available in the system. A literature review of these individual studies at first might seem confusing and somewhat contradictory, particularly in multi-component systems with particles and surfactants with different charges in the presence of salts. This paper provides a comprehensive overview of particle-stabilized foams, also known as Pickering foams and froths. Underlying mechanisms of foam stabilization by particles with different morphology, surface chemistry, size and type are reviewed and clarified. This paper also outlines the role of salts and different factors such as pH, temperature and gas type on Pickering foams. Further, we highlight recent developments in Pickering foams in different applications such as food, mining, oil and gas, and wastewater treatment industries, where Pickering foams are abundant. We conclude this overview by presenting important research avenues based on the gaps identified here. The focus of this review is limited to Pickering foams of surfactants with added salts and does not include studies on polymers, proteins, or other macromolecules.

Prediction of the flowing bottom hole pressure (FBHP) of gas¿water two-phase flows is of great importance in optimising the production of gas and reducing down-time in unconventional gas wells. Unlike the case for conventional gas wells, prediction of FBHP for unconventional gas wells, particularly coal seam gas (CSG) wells, has not been studied. Monitoring of FBHP typically is done using a downhole pressure sensor placed close to the bottom of the well. Replacing a failed pressure sensor or recalibration of a pressure gauge, which is required frequently throughout the life of a well for reliable measurement of FBHP, requires interruption of the gas production at a high cost. A low-cost and reliable model for continuous prediction of FBHP, would enable smooth operation of CSG wells in the event a pressure gauge fails, without interrupting the well production. This work presents predictive models for real-time and reliable prediction of FBHP using surface and subsurface data, acquired from 91 CSG wells in Australia over 5¿19 month production periods. Two sets of models are developed; one for specific wells using data from that individual well and another one for a group of wells. Three different modelling approaches, multiple linear regression, linear mixed-effects and gradient boosting regression tree (XGBoost) are implemented. The XGBoost modelling outcomes show promising results with the best mean absolute percentage error (MAPE) of 10% and 11.7% for specific well models and multiple well models, respectively.

Per- and poly-fluoroalkyl substances (PFAS) are a group of recalcitrant compounds whose widespread use in a variety of consumer products has led to contamination of groundwater and surface water systems. Foam fractionation is a potential remediation technology for treatment of PFAS contaminated water, which takes advantage of the high surface activity imparted by the fluorocarbon chain to remove them from solution by adsorption to the surface of air bubbles. In this study, the effect of mono- and di-valent cations on the performance of a PFAS foam fractionation process where sodium dodecyl sulphate (SDS) is used as a co-foaming agent has been evaluated. The results indicated that the separation of PFAS was improved in an order that followed the charge density of the salts with Mg2+ > Na+ > K+. It was also observed that at salt concentrations above 100 mM for Na+, above 10 mM for K+ and Mg2+ but between 0.1 and 10 mM for Ca2+ in the presence of greater than 4 ppm of SDS, the cations can complex with the SDS in the system and suppress foam formation due to the surfactant precipitation. Foam fractionation was able to remove perfluorohexane sulphonic acid (PFHxS), perfluorooctanoic acid (PFOA) and perfluorooctane sulphonic acid (PFOS) from a sample of Australian groundwater to below the analytical detection limit of 0.1 ppb within 60 min with SDS being used as the co-foaming agent, but was unable to remove the short chain perfluorobutanoic acid (PFBA).

Surfactant-stabilized foams have been at the centre of scientific research for over a century due to their ubiquitous applications in different industries. Many of these applications involve inorganic salts either due to their natural presence (e.g. use of seawater in froth floatation) or their addition (e.g. in cosmetics) to manipulate foam characteristics for the best outcomes. This paper provides a clear understanding of the effect of salts on surfactant-stabilized foams through a critical literature survey of this topic. Available literature shows a double effect of salts (LiCl, NaCl and KCl) on foam characteristics in the presence of surfactants. To elucidate the underlying mechanisms of the stabilizing effect of salts on foams, the effect of salts on surfactant-free thin liquid films is first discussed, followed by a discussion on the effect of salts on surfactant-stabilized foams with the focus on anionic surfactants. We discuss two distinctive salt concentrations, salt transition concentration in surfactant-free solutions and salt critical concentration in surfactant-laden systems to explain their effects. Using the available data in literature supported by dedicated experiments, we demonstrate the destabilizing effect of salts on foams at and above their critical concentrations in the presence of anionic surfactants. This effect is attributed to retarding the adsorption of the surfactant molecules at the interface due to the formation of nano and micro-scale aggregates.

Foam fractionation is a well-developed technology used to separate surface-active compounds from solution by exploiting their affinity for the air¿water interface. The technology was founded in the 1940s and has since evolved into a key technology for treatment of many different pollutants from a variety of different industries such as textiles and dyes, heavy metals, proteins in food processing waste and even per- and poly-fluoroalkyl substances (PFAS). The technology has even progressed from a standard batch process to a continuous process with an applied reflux to being presently used as an in-situ groundwater remediation and soil remediation process. This review provides a snapshot of the historical evolution of foam fractionation, a discussion of the mechanism behind foam fractionation, the effect of key operating variables on the performance parameters, identification of the key transport processes that take place within a foam fractionation system, a review of the modeling of foam fractionation as a water treatment technology and a review of the applications of foam fractionation as a water treatment technology.

In this study, we investigate the effect of liquid viscosity (lL) on the slug/churn transition in gas/liquid flows in vertical pipes. A total of 80 experimental churn-flow data points from two different sources are compiled as a data set, covering liquid viscosities from 17.23 to 586 mPa·s. Air was used in these studies as a gas phase with two different liquids, aqueous glycerol and a commercial synthetic mineral oil, flowing in vertical pipes of 0.0192- and 0.0508-m inner diameter (ID). The data set is used to examine the existing slug/churn-flow-transition models and provide further insights into the effect of lL on the transition. The existing models are categorized into two groups according to their response of the slug/churn transition to the increase in liquid superficial velocity (Vsl) on the Vsg/Vsl flow map. The first category exhibits a decrease in superficial gas velocity (Vsg) with the increase in Vsl at slug/churn (the transition concave to the left). The other one predicts an increase in Vsg with increasing of Vsl (the transition concave to the right). Analysis of the data set reveals that on the Vsg/Vsl flow map, the slug/churn transition moves toward lower superficial gas velocities as liquid viscosity increases and occurs approximately at a constant Vsg for low to medium Vsl. The predictions of these models were tested against the data set and poor results were shown by most models. The best performance is given by the Abdul-Majeed (1997) model. A dimensional analysis is applied in the present study to develop a new slug/churn-transition model. This analysis indicates that the transition is related to three dimensionless numbers, namely gas- and liquid-phase Froude numbers, in addition to the inverse liquid-viscosity number. An improved revision to the Abdul-Majeed model is achieved using these three dimensionless numbers. The revision enables the model to predict the transition for low, medium, and high liquid viscosity. The revised model clearly outperforms all the existing models for the present data and viscous data from independent studies. Furthermore, the revised model exhibits the expected trend against changes in pipe diameter and gas density.

Interfacial rheology of adsorbed layers of surfactants, demonstrating the response of the interface to interfacial deformations, plays a key role in formation and stability of foams and emulsions. It also provides insights into complex surfactant systems in different applications, in particular, medical treatments and diagnostics. The response of the interface is mainly determined by the composition of a surfactant system, the equilibrium and kinetic adsorption properties of the included surface-active compounds and their interaction within the adsorption layer. The subject of ongoing investigations is interfacial rheology of surfactant layers in the presence of inorganic ions. Although these ions have no surface activity, they can strongly influence the interfacial rheological properties owing to their interaction with the surface-active molecules. This work aims to present recent developments in the interfacial rheology of surfactant adsorbed layers at liquid¿fluid interfaces in the presence and absence of salts, highlighting the state of the art of experimental and theoretical works in this area. We highlight drawbacks of recently developed techniques for measuring dilational interfacial properties of surfactant layers, compared with previous techniques. Moreover, this review shows the dearth of research on the ion-specific effect on the interfacial rheology of surfactant layers. This demonstrates the necessity of further investigation of the effect of ion specificity on interfacial viscoelasticity.

The demand for natural gas in Queensland, Australia has historically been supplied from conventional reservoirs. However, depletion in conventional sources has led producers to turn to extensive supplies in Queensland's coal resources. These coal seam gas (CSG) developments not only represent new supplies for the domestic market in eastern Australia, they are also the first time that CSG (aka coal bed methane or CBM) has been liquefied to serve the expanding world LNG market. In order to make this development occur, considerable infrastructure had to be installed, with field developments still on-going. This AUD$60 billion investment precipitated a major overhaul of state regulations to provide not only a safe and clean operating environment, but also to allay the concerns of certain stakeholders.The gas is primarily produced from thin high permeability coals in the Jurassic-age Walloon Coal Measures in the Surat Basin and from several relatively thick Permian-age coal seams in the Bowen Basin, of which the Baralaba Coal Measures and the Bandanna formation are the most important. There are numerous technical challenges with this production, such as fines production from the inter-burden clays, which can form a thick paste that is difficult to pump. Salt extraction by reverse osmosis, from associated water produced to depressurise the coal seams and enable the flow of gas, allows for the beneficial use of the water. Technical challenges also include mathematical modelling of the counter-current two-phase flow (gas and water) in the well annuli because conventional models in simulators only handle co-current two-phase flow in the well-bores. Also, the subject of on-going investigations is decommissioning of the large number of shallow wells over the next few decades in a safe and cost effective manner, with compressed bentonite being a promising option for well plugging.As with any major commercial development, in addition to the technical challenges there have been social challenges as well. These include interaction and coexistence of extensive surface operations with an established agricultural sector, interactions between gas production and ground water aquifers in water-stressed areas, and the cumulative social and economic impacts of 3 large projects on a rural area.Ultimately, the State of Queensland expects to produce more than 1800 BCF/annum, of which about 1400 BCF/annum will be exported as LNG. Depending on the demand and well productivity, up to 1000 CSG wells may be drilled per year for the next thirty years. A review of CSG resources, development, and challenges is presented in this paper to provide context for a stream of research findings that are emerging on the Queensland CSG experience.