Abstract
Nanofluids and low-salinity water (LSW) flooding are two novel techniques for enhanced oil recovery. Despite some efforts on investigating benefits of each method, the pros and cons of their combined application need to be evaluated. This work sheds light on performance of LSW augmented with nanoparticles through examining wettability alteration and the amount of incremental oil recovery during the displacement process. To this end, nanofluids were prepared by dispersing silica nanoparticles (0.1 wt%, 0.25 wt%, 0.5 wt% and 0.75 wt%) in 2, 10, 20 and 100 times diluted samples of Persian Gulf seawater. Contact angle measurements revealed a crucial role of temperature, where no wettability alteration occurred up to 80 °C. Also, an optimum wettability state (with contact angle 22°) was detected with a 20 times diluted sample of seawater augmented with 0.25 wt% silica nanoparticles. Also, extreme dilution (herein 100 times) will be of no significance. Throughout micromodel flooding, it was found that in an oil-wet condition, a combination of silica nanoparticles dispersed in 20 times diluted brine had the highest displacement efficiency compared to silica nanofluids prepared with deionized water. Finally, by comparing oil recoveries in both water- and oil-wet micromodels, it was concluded that nanoparticles could enhance applicability of LSW via strengthening wettability alteration toward a favorable state and improving the sweep efficiency.
Highlights
Despite advances with different enhanced oil recovery (EOR) methods, it is well understood that a great amount of petroleum remains unrecovered in underground reservoirs (Bera and Belhaj 2016)
We discuss the results of oil–water contact angle measurements, stability of nanofluids and oil recovery during injection of the nanofluids at varying salinities
The reflection of a light beam shone through fluid records its stability and is recorded in nephelometric turbidity units (NTU)
Summary
Despite advances with different enhanced oil recovery (EOR) methods, it is well understood that a great amount of petroleum remains unrecovered in underground reservoirs (Bera and Belhaj 2016). Researchers have unanimously regarded wettability alteration as the main reason for applying LSW to bring about additional oil recovery (Jalili and Tabrizy 2014; Kafili Kasmaei and Rao 2015; Mahani et al 2015; Shabib-Asl et al 2014; Shaddel et al 2014; Yang et al 2015) In this respect, various mechanisms have been proposed to explain the low-salinity effect (LSE) as follows: (1) osmotic pressure (Buckley and Morrow 2010), (2) IFT reduction in response to an increase in reservoir fluid pH (McGuire et al 2005), (3) multicomponent ion exchange (MIE) (Lager et al 2008), (4) double-layer expansion (Ligthelm et al 2009), (5) dissolution of heavy oil components by the salting in effect (RezaeiDoust et al 2009), (6) saponification (McGuire et al 2005) and (7) elasticity of water films lying on pore walls (Buckley and Morrow 2010). The two approaches that reveal the controlling factors behind the wettability alteration are (a) double-layer expansion between fine particles and limited fines release (LFR) between oil/rock contact areas (Nasralla and Nasr-El-Din 2014; Tang and Morrow 1999a; Xie et al 2016) and (b) surface complexation modeling (Brady and Krumhansl 2012; Brady and Thyne 2016; Brady et al 2015; Mahani et al 2017; Xie et al 2017)
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