Functional compounds of crude oil during low salinity water injection
Graphical abstract
Introduction
Enhanced Oil Recovery (EOR) by injection of Low Salinity Water (LSW) into the deep subsurface sandstone and carbonate geological layers containing crude oil has attracted a great attention in the past decade. Despite the list of mechanisms being proposed in the literature, to date, the microscopic interactions between rock, crude oil, and brine leading to further oil recovery remain poorly known. Low Salinity Water Injection (LSWI) was first reported to be effective in sandstones cores [1] which was subsequently confirmed by more researchers [2], [3], [4], [5], [6], [7]. Most of the early works emphasized on the predominant role of clay minerals during LSWI in sandstone rocks [8], [9], a factor that was absent in carbonate rocks. Surprisingly in 2011, LSWI were reported with positive results in carbonate rocks [10]. The reported extra oil recovery from the tertiary LSWI in carbonate cores was substantial (7–8.5% IOIP for two times diluted seawater and 9–10% IOIP for 10 times diluted seawater). While the previously proposed clay-related mechanisms could not predict and explain the reported extra oil recovery in carbonate rocks, other mechanisms were proposed for LSWI in carbonate rocks.
Despite the discrepancy on the role of clay and rock type in low salinity water effect (LSE), the consensus on the mechanism of LSWI centres around the wettability alteration toward more water-wet or less oil-wet state (mixed-wet state) [2], [6], [8], [11], [12], [13], [14]. Mixed wettability conditions mean that the larger pores within a rock are preferably oil-wet and water phase paths through smaller pores [15]. This is in turn allows the water drainage (waterflooding) to continue until the residual oil saturation reaches a small value (very low residual oil saturation is achievable in mixed-wet rocks). However, wettability alteration is a macroscopic definition that arises from the more-fundamental interactions that need to be defined themselves. Several mechanisms have been introduced for explaining the wettability alteration during LSWI [1], [8], [14], [16], [17], [18] which are all concentrated around the possible role of rock/fluid (i.e., rock/brine) interactions [19], [20], [21], [22], [23], [24] and the possible role of fluid/fluid (i.e., oil/brine) interactions were thoroughly overlooked. However, there are some refutations in the literature challenging the proposed mechanisms [25], [26], [27].
In 2013, a new mechanism [28] was introduced which revealed the paramount importance of fluid/fluid (i.e., crude oil/brine) interactions during LSWI. It was articulated through visual evidence that formation of water microdispersion within the crude oil is the main mechanism of LSWI, something that could explain the reported additional oil recovery from both sandstone and carbonate rocks. It was after the introduction of this mechanism that even the inability of LSWI in producing additional oil in some oil reservoirs was clarified [29], [30]. In recent years, the water microdispersion mechanism has been progressively reported as the main mechanism of LSWI [30], [31], [32], [33], [34], [35], [36], [37], [38], [39] for different systems by several researchers encouraging the oil industry to put more time and efforts into determining the key components within the crude oil that are important for LSWI to optimize this EOR tool.
Asphaltenes are the polar aromatic species in crude oil constituting a high sulphur, oxygen, and nitrogen contents with a trace of heavy metals such as Nickel and Vanadium [40], [41]. Also, they are defined to be a fraction insoluble in paraffinic solvents (i.e., n-hexane and n-heptane) and soluble in aromatic solvents (i.e., benzene and toluene) [42], [43]. Asphaltenes have been reported to be the most surface-active material with the ability to diffuse into the oil/water interface and decrease the oil–water interfacial tension [44], [45], [46]. They have been extensively analysed through mass spectroscopy by Fourier Transform Ions Cyclotron Resonance (FT-ICR MS) in both positive and negative electrospray ionization modes (+ESI and −ESI) [47], [48], [49], [50], [51], [52], [53] generating precise and valuable information.
Naphthenic acids are another type of surface-active materials within the crude oil which are defined as the carboxylic acids with at least one naphthenic ring [54]. The term can be used to refer to all organic acids in crude oil [55], [56]. Also, the carboxylic acids can be identified by the general chemical formula of R-COOH [57]. They can diffuse into the oil/water interface and partition into the aqueous phase through formation of organic-soaps with cations such as sodium, calcium, and magnesium [56], [58]. In addition, they have been reported to be strongly encouraging in stabilizing the water in oil (W/O) emulsions [59], [60], [61], [62] and decrease the oil–water interfacial tension [63], [64]. The surface activity of naphthenic acids has been estimated to be strongly pH-dependent as they are strongly active at the oil/water interface at neutral pH values [56], [65]. The heavier acids or asphaltene-like acids (i.e., heavy aromatic acids inside the crude oil) can contribute to the oil/water interface and enhance the stability of W/O emulsions under all conditions [66]. Stearic acid is believed to be the most reactive linear carboxylic acid within the crude oil and has been reported to have a synergic effect with asphaltenes at the oil/water interface [64]. Using electrospray ionisation mode (ESI) is believed to be the most suitable method for characterizing the naphthenic acids in crude oil [67], [68]. However, this technique has been reported to be selective [69] as in −ESI mode, the deprotonated species (with negative charges) such as carboxylic acids, carbazoles, and phenols can be detected [70], [71]. In contrast, the protonated species (positively charged compounds) such as basic materials, and positively charged asphaltene molecules can be studied through +ESI mode [72], [73]. Also, the highest offered mass resolution, mass accuracy, and mass resolving power are achievable by using this technique, and the analysis the complicated petroleum mixtures in molecular level is possible [74], [75], [76], [77], [78] as well. Taking the benefit of ionization technique (i.e., +ESI and −ESI modes) with the highest mass resolution, the discrimination of different complex compounds within the crude oil is possible appreciating the different ionization efficiencies [79], [80], [81].
In the current study, different crude oil samples were contacted with HSW and LSW. The samples were taken from the oil/water interface, then they were analysed by a Karl Fischer Titrator to quantify the amount of water microdispersion within the crude oil. The most potent crude oil toward formation of water microdispersion was chose for further analysis by FT-ICR MS. The collected crude oils from the oil/water interface of corresponding crude oil were analysed through +ESI and −ESI modes of FT-ICR MS in order to get an insight into the structure of oil/water interface during waterflooding. Another purpose of this study is to characterize the surface-active materials contributing to LSE and the interactions at the interface. Detecting the most responsible compounds of crude oil for additional oil recovery during LSWI will resolve the inconsistencies around the underlying mechanism of this EOR method. Likewise, this can lead to achieve the most reliable screening method for recognising the crude oils of suitable composition for LSWI based on the physicochemical properties of the resident oil. The interfacial crude oil samples were also investigated with Fourier Transform Infrared (FT-IR) spectroscopy to detect the compositional changes, in particular, any possible change in the intensity of functional groups.
Section snippets
Fluids preparation
The ionic aqueous solutions of LSW and high salinity water (HSW) were made by adding pure grade salts [BioXtra grade salts, 99.5 (AT), supplied by Sigma-Aldrich chemicals Co. Inc] to deionized water [molecular biology reagent grade, with a conductivity of approximately 0.05 , supplied by Sigma-Aldrich chemicals Co. Inc]. The ionic composition of the brines used in the study are demonstrated in Table 1. The synthetic HSW brine was made based on the formation water composition of an oil
Water content measurements
Eight crude oil samples with different physicochemical properties were analysed after contact with brines. The crude oil samples were taken from the oil/water interface and investigated by KFT method to measure the amount of spontaneously formed water-in-oil microdispersion. The water content of interfacial crude oil samples was measured and converted into the water microdispersion ratio. As illustrated in Fig. 1, the ratio is higher at the oil/LSW interface indicating the stronger water-in-oil
Conclusion
The results of this study systematically demonstrate that the chemical composition of crude oil contacted by water can be thoroughly different depending on the salinity of injection water. These compositional changes provide us with important clues about the mechanism of LSWI through which further oil recovery may be achieved. It was revealed through FT-IR analysis that conjugated acidic materials or acidic asphaltenes promote the spontaneous formation of water-in-oil microdispersion at the
CRediT authorship contribution statement
Mohammad Fattahi Mehraban: Conceptualization, Formal analysis, Investigation, Writing - original draft, Writing - review & editing, Visualization. Seyed Amir Farzaneh: Resources, Supervision. Mehran Sohrabi: Supervision, Project administration.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work was performed as a part of the Low Salinity Water Injection joint industry project (JIP) in the Centre for Enhanced Oil Recovery (EOR) and CO2 Solutions at Heriot-Watt University, Edinburgh, Scotland, UK. The project is equally funded by ADNOC, BP, the UK Oil and Gas Authority, Total E&P, Wintershall Dea GmbH, Woodside Energy, and ConocoPhillips which is gratefully acknowledged.
References (98)
- et al.
Influence of brine composition and fines migration on crude oil/brine/rock interactions and oil recovery
J Petrol Sci Eng
(1999) - et al.
Enhanced oil recovery of low salinity water flooding in sandstone and the role of clay
Pet Explor Dev
(2018) - et al.
A multi-scale experimental study of crude oil-brine-rock interactions and wettability alteration during low-salinity waterflooding
Fuel
(2019) - et al.
Interfacial rheological insights of sulfate-enriched smart-water at low and high-salinity in carbonates
Fuel
(2017) - et al.
Fundamental investigation of underlying mechanisms behind improved oil recovery by low salinity water injection in carbonate rocks
Fuel
(2018) - et al.
The diffusion of water through oil contributes to spontaneous emulsification during low salinity waterflooding
J Petrol Sci Eng
(2019) - et al.
Direct insights into the pore-scale mechanism of low-salinity waterflooding in carbonates using a novel calcite microfluidic chip
Fuel
(2020) - et al.
Characterization of Algerian Hassi-Messaoud asphaltene structure using Raman spectrometry and X-ray diffraction
Fuel
(2007) - et al.
Improving compositional space accessibility in (+) APPI FT-ICR mass spectrometric analysis of crude oils by extrography and column chromatography fractionation
Fuel
(2016) - et al.
Emulsion stabilization by means of combined surfactant multilayer (D-phase) and asphaltene particles
Colloids Surf A
(2003)
Liquid crystals in aqueous solutions of sodium naphthenates
J Colloid Interface Sci
Phase behavior of sodium naphthenates, toluene, and water
J Colloid Interface Sci
Mesomorphous phases, a factor of importance for the properties of emulsions
J Colloid Interface Sci
Fatty acid-asphaltene interactions at oil/water interface
Colloids Surf A
Molecular characterization of naphthenic acids from heavy crude oils using MALDI FT-ICR mass spectrometry
Fuel
Laser desorption ionization FT-ICR mass spectrometry and CARSPLS for predicting basic nitrogen and aromatics contents in crude oils
Fuel
Monitoring the liquid/liquid extraction of naphthenic acids in Brazilian crude oil using electrospray ionization FT-ICR mass spectrometry (ESI FT-ICR MS)
Fuel
Characterization of naphthenic acids in crude oils and naphthenates by electrospray ionization FT-ICR mass spectrometry
Int J Mass Spectrom
FT-ICR MS analysis of asphaltenes: asphaltenes go in, fullerenes come out
Fuel
Effect of injection brine composition on wettability and oil recovery in sandstone reservoirs
Fuel
Identification of acidic NSO compounds in crude oils of different geochemical origins by negative ion electrospray Fourier transform ion cyclotron resonance mass spectrometry
Org Geochem
Interfacial behavior of asphaltenes
Adv Colloid Interface Sci
Interfacial and electrokinetic properties of asphaltenes and alkali/surfactant/polymer in produced water system
J Petrol Sci Eng
Salinity, temperature, oil composition, and oil recovery by waterflooding
SPE Reservoir Eng
Low salinity oil recovery-log-inject-log
Low salinity oil recovery–The role of reservoir condition corefloods
IOR 2005–13th European Symposium on Improved Oil Recovery.
A laboratory study investigating methods for improving oil recovery in carbonates
International Petroleum Technology Conference
Low salinity oil recovery: An exciting new EOR opportunity for Alaska's North Slope
Comparison of secondary and tertiary recovery with change in injection brine composition for crude-oil/sandstone combinations
SPE/DOE symposium on improved oil recovery
Low salinity oil recovery-an experimental investigation1
Petrophysics
A proposed pore-scale mechanism for how low salinity waterflooding works
SPE improved oil recovery symposium
Laboratory investigation of the impact of injection-water salinity and ionic content on oil recovery from carbonate reservoirs
SPE Reservoir Eval Eng
Investigation of wettability alteration by low salinity water
Snorre low-salinity-water injection-coreflooding experiments and single-well field pilot
SPE Reservoir Eval Eng
Novel Waterflooding Strategy By Manipulation Of Injection Brine Composition
EUROPEC/EAGE conference and exhibition
Wettability literature survey-part 1: rock/oil/brine interactions and the effects of core handling on wettability
J Petrol Technol
Improved oil recovery by low salinity waterflooding: a mechanistic review
Smart water as wettability modifier in carbonate and sandstone: a discussion of similarities/differences in the chemical mechanisms
Energy Fuels
Chemical mechanism of low salinity water flooding in sandstone reservoirs
SPE improved oil recovery symposium
Novel insights into mechanisms of oil recovery by use of low-salinity-water injection
SPE J
Pore scale visualization of low salinity water flooding as an enhanced oil recovery method
Energy Fuels
Linking low salinity EOR effects in sandstone to pH, mineral properties and water composition
SPE Improved Oil Recovery Conference
Evaluation of EOR LS water flooding in sandstone: eliminate the role of clay
SPE Kingdom of Saudi Arabia Annual Technical Symposium and Exhibition
Oil recovery by low-salinity brine injection: laboratory results on outcrop and reservoir cores
SPE Annual Technical Conference and Exhibition
Effect of brine salinity and crude oil properties on relative permeabilities and residual saturations
SPE Annual Technical Conference and Exhibition
Visual investigation of oil recovery by low salinity water injection: formation of water micro-dispersions and wettability alteration
SPE annual technical conference and exhibition
Low salinity water flooding in carbonate: screening, laboratory quantification and field implementation
Society of Petroleum Engineers
November 13). A Case Study of Oil Recovery Improvement by Low Salinity Water Injection
Society of Petroleum Engineers
Cited by (10)
Fluid-fluid interfacial properties during low salinity waterflooding
2023, Journal of Molecular LiquidsSurface-active compounds induce time-dependent and non-monotonic fluid-fluid displacement during low-salinity water flooding
2023, Journal of Colloid and Interface ScienceCitation Excerpt :Contrarily, other studies, including our earlier research [39], show evidence that low salinity water can improve the displacement without the presence of clay [32–34]. In the subsurface, rock surfaces are naturally hydrophilic, but they usually appear to be hydrophobic where oil is present as the polar compounds in oil adsorb on the solid/oil interfaces [40–43]. Low salinity water is believed to cause changes in the interface properties to what are beneficial for increasing displacing efficiency, such as wettability alteration to a more water wet state [24,44–46].
Microfluidics experimental investigation of the mechanisms of enhanced oil recovery by low salinity water flooding in fractured porous media
2022, FuelCitation Excerpt :It should be mentioned that the contact angle (CA) measurement in the conventional sessile drop method (which is also implemented in this study) is based on the pure diffusion-controlled physics. In a separate study Farhadi et al. [25] showed that the difference of the measured contact angles for the cases based on pure diffusion-controlled (where the same oil droplet is tracked vs. time) and pure advection-controlled systems (where the contact angle of the oil droplets are investigated after different soaking times of the aged substrate in the desired brine) during LSWF. The results show that pure diffusion-controlled process for the oil drop is too much slow to efficiently cause the replacement of the high salinity water, flanked by the oil drop and the rock surface, with low salinity water.
Deformation and breakup mechanism of water droplet in acidic crude oil emulsion under uniform electric field: A molecular dynamics study
2022, Colloids and Surfaces A: Physicochemical and Engineering AspectsCitation Excerpt :Therefore, dissecting the effect of NA existence on droplet breakup under electric field would be helpful in revealing the electrodispersion mechanism of water droplets in acidic crude oil, and is conducive to improving electrocoalescence process to the occurrence of non-coalescence. The acidic component in crude oil is mainly naphthenic acid, and there have been many researches on how NA stabilizes emulsions [15–19]. The solubility of NA in aqueous solution increases by reducing the ionic concentration of brine, which significantly affects the interfacial tension (IFT) characteristics [20] between oil and water.
Experimental investigation on synergic effect of salinity and pH during low salinity water injection into carbonate oil reservoirs
2021, Journal of Petroleum Science and EngineeringCitation Excerpt :Geochemical modelling of Yousef experiments (Yousef et al., 2010) by Al-Shalabi et al. (2014) suggested electrical double layer expansion as the main mechanism of LSWI in carbonate oil reservoirs. Notwithstanding the rock/fluid interactions, fluid/fluid interactions have been also proposed to significantly affect the wettability of rock systems (Emadi and Sohrabi, 2013; Sohrabi et al., 2017; Mehraban et al., 1191). Mehraban et al. (2020) showed through visual microfluidic tests that formation of microdispeersion within the crude oil phase leads to wettability alteration and oil swelling.
Engineered Low Salinity Waterflood in Carbonate Reservoirs―Boosting Fluid-fluid Interaction and Oil Recovery by Cost Effective Additives
2024, International Petroleum Technology Conference, IPTC 2024