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Smart waterflooding (SWF), an emerging EOR technique, was first investigated in sandstone reservoirs. However in recent years, the effect of smart water on carbonate reservoirs has gained wide interest. Despite the increasing number of research and publications in this area, the mechanism enhancing the recovery is still not fully understood. Wettability alteration and reduction in interfacial tension (IFT) have been identified as the two most dominant mechanisms. Divalent ions such as sulfate (SO42-) are found by many investigators to show promising results during SWF. However, limited research has been carried out to investigate the effect of trivalent ions. The objective of this study was to investigate the potential of phosphate (PO43-) spiked brines as a viable EOR technique in tight carbonate reservoirs. Seawater with different dilution factors and varying concentration of phosphate ions were investigated against non-phosphate brines. Impact of these brines on wettability alteration was qualitatively monitored by tracking the rate of contact angle change on several aged-carbonate core samples subjected to varying aging periods. Various designed phosphate brines were tested at elevated temperature of 90 °C, and IFT was also measured at both ambient and elevated temperature (90 °C) to complement our findings. To identify the impact of phosphate ions on wettability alteration due to brine/crude oil/rock interactions, carbonate core samples were prepared having initial contact angle ranging from 130° to 160°. The rate of contact angle change observed ranged from 9° to 36° as a function of varying composition of smart brines. A slight decrease in IFT was observed when lower salinity brines were used without phosphate. Phosphate spiked brines show a near surfactant reduction in IFT, compared to the low salinity brines. Smart brines with higher concentration of phosphate achieved better results than those with lower concentration.

Hydraulic fracturing of shale reservoirs often requires millions of gallons of water, but only a fraction of the injected water returns to the surface. Shale gas production has been demonstrated to be positively correlated with the amount of water imbibed by the shale. In this study, neutron radiography is used to evaluate the effect of two commonly used surfactants in hydraulic fracturing fluids on the rate of capillary water uptake in shale fractures. Cationic n-octadecyl trimethylammonium chloride (OTAC) and anionic ammonium dodecyl sulfate (ADS) were added to deionized water at a 1:1 molar ratio at different concentrations and imbibed into a 200 μm Marcellus shale saw-cut fracture. The correlations between the surfactant concentration and fracture aperture with the capillary pressure and water uptake were examined in detail to understand water imbibition during hydraulic fracturing. The effect of wettability alteration during aging of the reservoir on the water uptake rate was studied by comparing water imbibition rates into shale fractures pre-exposed to the surfactant solutions to those of unexposed shale fractures. A 51% reduction in the rate of water uptake into the unexposed shale fracture was observed when the 1:1 mixed ADS/OTAC surfactant concentration was increased from 0.1 to 0.9 mM. This decrease in imbibition rate is attributed to changes in interfacial tension and not wettability alteration of the fracture surface. For the pre-exposed sample, surfactants have sufficient time to adsorb to the shale and alter the surface wettability. The rate of water uptake for pre-exposed shale fractures was reduced by 96% compared to that of unexposed shale fractures for 0.1 mM ADS/OTAC mixture. These experimental observations suggest that natural gas production may be improved after a well shut-in period when mixed-charge surfactants are included in hydraulic fracturing fluid formulations and have sufficient time to alter shale wettability toward a more oil-wet state.

Abstract-Thermal energy storage (TES) for concentrated solar power (CSP) is gaining popularity because it has the potential to increase the hours of electricity production from the CSP technology. In this Study, we conducted a comparative life cycle assessment (LCA) of two TES technologies (concrete and molten salt) for Shams-1 CSP plant in United Arab Emirates. Eco-Indicator 99 was employed to model the environmental impact per 800MWhe produced. Results obtained show that concrete TES has a greater environmental impact than molten salt TES, with fossil fuel being the largest impact contributor in both cases. A sensitivity analysis in which different scenarios were considered showed a reduction in environmental impact when waste recycling and transportation changes are incorporated. Based on the results obtained, incorporating molten salt TES in Shams 1 will have a lower environmental impact than the use of concrete TES.Index Terms-Concentrated solar power plant, concrete storage, life cycle assessment, molten salt storage, thermal energy storage. I. INTRODUCTIONSince the beginning of the industrial revolution, the atmospheric concentration of carbon dioxide has increased alarmingly by about 30%, due to human activities such as combustion of fossil fuels [1]. In Australia for example, electricity generation accounts for 45% of the carbon dioxide emission [2]. There is a need to reduce the quantity of CO 2 emission in order to mitigate its global warming effect. Hence, the development of renewable sources of electricity becomes relevant as the global requirement for electricity increases.Electricity generation using Concentrated Solar Power (CSP) is a relatively new technology that utilizes solar thermal energy to produce electricity. In this system, highly reflective mirrors are employed to concentrate the Direct Normal Irradiance (DNI) of sunlight on receivers, through which Heat Transfer Fluid (HTF) is pumped. Afterwards, the HTF transfers the acquired heat to a steam generator to produce steam, which is used in a Rankine Cycle Steam Turbine for electricity generation [3].Since the HTF is thermally stable and suitable for operations up to 400 o C [4], the temperature of the generated steam cannot exceed 380 o C. In order to increase the efficiency of the Rankine thermal cycle, CSP-natural gas hybridization can be used (Fig. 1). In this process, a booster heater is used to superheat the steam from 380 o C to 540 o C [5]. Fig. 1. Schematics of the hybrid CSP-natural gas plant [13] The four configurations employed in CSP plants are Parabolic Trough, Solar Fresnel, Stand Alone Solar Dish, and Central Tower [3]. CSP mirrors are usually installed with a solar tracking system to ensure optimal capture of solar radiation [6]. Currently, the United States is the world leader in solar thermal power development, with 63% of the market share [7].One disadvantage of CSP technology is that thermal energy generation is subject to daily fluctuations in solar radiation. In order to mitigate the effect of these fluctuations, th...