Abstract
Acidizing is widely used to improve well productivity, but contact between hydrochloric acid (HCl) and heavy and polar components of heavy crude oils, including asphaltene molecules, can cause strong emulsions and fluid-fluid sludge that damage the heavy oil reservoir. This study investigates how combining HCl with different smart-water formulations (seawater, diluted seawater, and ion-enriched brines containing Ca²⁺, Mg²⁺, and SO₄²⁻) affects the interfacial behavior of heavy oil. In this regard, a novel series of bottle tests was conducted at 80 °C for 48 h, and the resulting oil, emulsion, and interfacial layers were analyzed. Emulsion stability, sludge mass, droplet size, viscosity, interfacial tension (IFT), SARA (saturates, aromatics, resins, asphaltenes) fractions, FTIR (Fourier transform infrared spectroscopy)-ATR (Attenuated total reflection), elemental analysis, and zeta potential were measured to link changes in asphaltene chemistry to the macroscopic oil properties. The results show that acid prepared with deionized water produced the most stable emulsion, the smallest droplets, and the highest sludge mass. Low-salinity and Ca²⁺-rich brines also promoted strong sludge formation, confirming that insufficient ionic strength allows HCl to protonate polar oil components strongly. On the other hand, Mg²⁺- and especially SO₄²⁻-rich brines greatly suppressed sludge formation (about 0.67 g), produced larger droplets, lowered IFT (29.9 mN/m), and kept more polar and heteroatom-rich asphaltenes inside the oil. FTIR-ATR and elemental analyses show that ion-rich brines preserve oxygen- and sulfur-containing functional groups within the oil phase, limiting their migration toward the oil–acid interface. In contrast, low-salinity and calcium-rich systems promote the removal and aggregation of these groups. Zeta potential measurements further support this trend, as sulfate-rich systems develop more negative surface charges and exhibit a reduced tendency for sludge-related damage. Collectively, these observations indicate that sludge formation during acidizing is governed by the ability of brine ionic composition to regulate asphaltene surface activity and interfacial charge balance. Accordingly, ion tuning, particularly through sulfate and magnesium enrichment, stabilizes asphaltenes in the oil phase and suppresses sludge generation even under strongly acidic conditions. Conversely, low-salinity and calcium-dominated fluids intensify acid–oil incompatibility by promoting asphaltene protonation and interfacial precipitation. This mechanistic insight establishes a clear scientific foundation for designing acidizing fluids that minimize formation damage, enabling a transition from empirical approaches to chemistry-driven optimization.
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The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request.
Refrences
Rogner, H.-H. An assessment of world hydrocarbon resources. Annu. Rev. Energy Environ. 22(1), 217–262 (1997).
Caineng, Z. et al. Formation, distribution, potential and prediction of global conventional and unconventional hydrocarbon resources. Pet. Explor. Dev. 42(1), 14–28 (2015).
Asif, M. & Muneer, T. Energy supply, its demand and security issues for developed and emerging economies. Renew. Sustain. Energy Rev. 11 (7), 1388–1413 (2007).
Portier, S., André, L. & Vuataz, F.-D. Review on chemical stimulation techniques in oil industry and applications to geothermal systems. Engine, work package 4, 32 (2007).
Mirkhoshhal, S. M., Mahani, H., Ayatollahi, S. & Shirazi, M. M. Pore-scale insights into sludge formation damage during acid stimulation and its underlying mechanisms. J. Pet. Sci. Eng. 196, 107679 (2021).
Khamehchi, E., Khaleghi, M. R., Abbasi, A. & Mahdavi Kalatehno, J. Basic Objectives and Concepts of Matrix Acidizing, in Applied Matrix Acidizing of Carbonate Reservoir: Springer, 1–43. (2024).
Li, N. et al. Application status and research progress of shale reservoirs acid treatment technology. Nat. Gas Ind. B 3(2), 165–172 (2016).
McLeod, H. O. Matrix acidizing. J. Pet. Technol. 36(12), 2055–2069 (1984).
Sayed, M., Chang, F. & Luce, T. Chemical Solution Mitigates Stuck Inflow Control Devices (ICDs) in Horizontal Completion, in Offshore Technology Conference, : OTC, p. D031S030R004. (2024).
Kankaria, S., Nasr-El-Din, H. A. & Rimassa, S. Matrix acidizing of carbonate rocks using new mixtures of HCl/methanesulfonic acid, in SPE International Conference on Oilfield Chemistry? : SPE, p. D021S007R007. (2017).
Mahdavi Kalatehno, J. et al. A successful case study of using HCl and viscoelastic diverting acid systems for carbonate matrix acidizing in an oil well with optimized predictive model. J. Pet. Explor. Prod. Technol. 15(1), 1. (2025).
Abbasi, A., Malayeri, M. R. & Shirazi, M. M. Stability of spent HCl acid-crude oil emulsion. J. Mol. Liq. 383, 122116 (2023).
K. I.-I. I. & Eshiet Production from Unconventional Petroleum Reservoirs: Précis of Stimulation Techniques and Fluid Systems, in Emerging Technologies in Hydraulic Fracturing and Gas Flow Modelling: IntechOpen, (2022).
Mahmoud, M. A., Nasr-El-Din, H. A. & de Wolf, C. A. High-temperature laboratory testing of illitic sandstone outcrop cores with HCl-alternative fluids. SPE Prod. Oper. 30(01), 43–51 (2015).
Yousufi, M. M., Mohyaldinn Elhaj, M. E. & Dzulkarnain, I. B. A review on use of emulsified acids for matrix acidizing in carbonate reservoirs. ACS Omega 9(10), 11027–11049 (2024).
Shirazi, M. M., Ayatollahi, S. & Ghotbi, C. Damage evaluation of acid-oil emulsion and asphaltic sludge formation caused by acidizing of asphaltenic oil reservoir. J. Pet. Sci. Eng. 174, 880–890 (2019).
Ramy, C. et al. Advanced delayed acid system for stimulation of ultra-tight carbonate reservoirs: A field study on single-phase, polymer-free delayed acid system performance under extreme sour and high-temperature conditions. Processes 13(8), 2547 (2025).
Mahdavi, S. & Mousavi Moghadam, A. Critical review of underlying mechanisms of interactions of asphaltenes with oil and aqueous phases in the presence of ions. Energy Fuels. 35 (23), 19211–19247 (2021).
Kalhori, P., Abbasi, A., Malayeri, M. R. & Shirazi, M. M. Impact of crude oil components on acid sludge formation during well acidizing. J. Pet. Sci. Eng. 215, 110698 (2022).
Mahdavi, M. S., Tajikmansori, A., Saeedi Dehaghani, A. H. & Seyed Mousavi, S. A. H. The synergic effect of brine salinity and dispersed clay particles on water-in-heavy oil emulsion: Insight into asphaltene structure and emulsion stability. SPE J. https://doi.org/10.2118/223598-pa (2024).
Amiri-Ramsheh, B., Sahebalzamani, S., Zabihi, R. & Hemmati-Sarapardeh, A. Predicting asphaltene precipitation during natural depletion of oil reservoirs by integrating SARA fractions with advanced intelligent models. Sci. Rep. 15(1), 26214. (2025).
Thomas, A. W. A review of the literature of emulsions. J. Ind. Eng. Chem. 12(2), 177–181 (1920).
Kharazi, M. & Saien, J. Mechanism responsible altering in interfacial tension and emulsification of the crude oil-water system with nano Gemini surface active ionic liquids, salts and pH. J. Pet. Sci. Eng. 219, 111090 (2022).
Kilpatrick, P. K. Water-in-crude oil emulsion stabilization: Review and unanswered questions. Energy Fuels 26(7), 4017–4026 (2012).
Raya, S. A., Mohd Saaid, I., Abbas Ahmed, A. & Abubakar Umar, A. A critical review of development and demulsification mechanisms of crude oil emulsion in the petroleum industry. J. Petroleum Explor. Prod. Technol. 10 (4), 1711–1728 (2020).
Ghorbani-Bavariani, M., Rezaei, A., Ahmadi, M., Vatanparast, H. & Hemmati-Sarapardeh, A. Experimental study and geochemical modeling of the effect of asphaltene during smart water flooding in carbonate reservoirs. Sci. Rep. 15(1), 37404. (2025).
Rafalscky, L. et al. Composition and stabilization mechanisms of interfacial material in petroleum Emulsions: a systematic review. Fuel 408, 137763 (2026).
Hou, B., Jia, R., Fu, M., Huang, Y. & Wang, Y. Mechanism of wettability alteration of an oil-wet sandstone surface by a novel cationic gemini surfactant. Energy Fuels. 33 (5), 4062–4069 (2019).
Yang, F. et al. Asphaltene subfractions responsible for stabilizing water-in-crude oil emulsions. Part 2: Molecular representations and molecular dynamics simulations. Energy Fuels 29(8), 4783–4794 (2015).
Yang, F. et al. Asphaltene subfractions responsible for stabilizing water-in-crude oil emulsions. Part 1: Interfacial behaviors. Energy Fuels 28(11), 6897–6904 (2014).
Ganeeva, Y. et al. The composition of acid/oil interface in acid oil emulsions. Pet. Sci. 17, 1345 (2019).
Hou, B. et al. A novel high temperature tolerant and high salinity resistant gemini surfactant for enhanced oil recovery. J. Mol. Liq. 296, 112114 (2019).
Hou, B. et al. Wettability alteration of an oil-wet sandstone surface by synergistic adsorption/desorption of cationic/nonionic surfactant mixtures. Energy Fuels. 32 (12), 12462–12468 (2018).
O’Neil, B., Maley, D. & Lalchan, C. Prevention of acid-induced asphaltene precipitation: A comparison of anionic vs. cationic surfactants. J. Can. Pet. Technol. 54(01), 49–62 (2015).
Poteau, S., Argillier, J. F., Langevin, D., Pincet, F. & Perez, E. Influence of pH on stability and dynamic properties of asphaltenes and other amphiphilic molecules at the oil– water interface. Energy Fuels. 19 (4), 1337–1341 (2005).
Sun, J. et al. Influencing factors and predictive models of oil–water emulsions: A comprehensive review and future outlook. Ann. N. Y. Acad. Sci. 1552(1), 94–116 (2025).
Mansouri, A. T., Mahdavi, M. S. & Dehaghani, A. H. S. Experimental investigation of divalent ions and CTAB effects on heavy oil emulsion stability in carbonate reservoirs. Sci. Rep. 15(1), 43462 (2025).
Hou, B. et al. Wettability alteration of oil-wet carbonate surface induced by self-dispersing silica nanoparticles: Mechanism and monovalent metal ion’s effect. J. Mol. Liq. 294, 111601 (2019).
Macedo, E. A. M. et al. Interfacial stability of acid–crude oil emulsions in matrix acidizing of carbonate reservoirs. ACS. Omega 10(44), 53407–53416 (2025).
Ismail, I. et al. Formation and stability of W/O emulsions in presence of asphaltene at reservoir thermodynamic conditions. J. Mol. Liq. 299, 112125 (2020).
Hedayati, E., Mohammadzadeh-Shirazi, M., Abbasi, A. & Malayeri, M. R. Experimental investigation of the acid-oil emulsion stability influenced by operational conditions and oil properties. J. Mol. Liq. 390, 123132 (2023).
AlMubarak, T. et al. Investigation of acid-induced emulsion and asphaltene precipitation in low permeability carbonate reservoirs, in SPE Kingdom of Saudi Arabia Annual Technical Symposium and Exhibition, : SPE, pp. SPE-178034-MS. (2015).
Abbasi, A. & Malayeri, M. R. Impact of crude oil properties on stability of HCl-crude oil emulsion using XDLVO theory,. Fuel 338, 127315 (2023).
Abbasi, A., Mohammadzadeh-Shirazi, M. & Malayeri, M. R. Functionality of chemical additives and experimental conditions during formation of acid-induced emulsion and sludge. J. Mol. Liq. 398, 124257 (2024).
Behera, U. S., Sangwai, J. S., Baskaran, D. & Byun, H.-S. A comprehensive review on low salinity water injection for enhanced oil recovery: Fundamental insights, laboratory and field studies, and economic aspects. Energy Fuels 39(1), 72–103 (2024).
Biyouki, A. A. et al. Comprehensive experimental study of multivariable oil–brine–rock interactions: Impact of brine–rock chemistry and crude oil polarity on enhanced oil recovery in carbonate reservoirs,. Sci. Rep. 15(1), 25605 (2025).
Bigdeli, A. Wettability alteration or wettability improvement? A fundamental question toward a deeper understanding of low salinity water flooding (LSWF), (2025).
Mumbere, W., Sagala, F., Gupta, U. & Bbosa, D. Reservoir potential unlocked: Synergies between low-salinity water flooding, nanoparticles and surfactants in enhanced oil recovery a review. ACS Omega 10(29), 31216–31261 (2025).
Mahdavi, M. S. & Dehaghani, A. H. S. Experimental study on the simultaneous effect of smart water and clay particles on the stability of asphaltene molecule and emulsion phase. Sci. Rep. 15(1), 3393. (2025).
Balavi, A., Ayatollahi, S. & Mahani, H. The simultaneous effect of brine salinity and dispersed carbonate particles on asphaltene and emulsion stability. Energy Fuels 37(8), 5827–5840 (2023).
Zhou, Q. et al. Synergistic effects of asphaltenes, kaolinite, and water chemistry on oil-water emulsion stability,. Sep. Purif. Technol. https://doi.org/10.1016/j.seppur.2025.133461 (2025).
Wang, Y. et al. Surfactant induced reservoir wettability alteration: Recent theoretical and experimental advances in enhanced oil recovery. Pet. Sci. 8(4), 463–476 (2011).
Cheng, Z. et al. Experimental investigation on the interfacial characteristics of tight oil rocks induced by tuning brine chemistry. ACS Omega 9(28), 30654–30664 (2024).
Mahdavi, M. S., Mansouri, A. T. & Dehaghani, A. H. S. Experimental investigation of CTAB modified clay on oil recovery and emulsion behavior in low salinity water flooding. Sci. Rep. 15(1), 21471. (2025).
Taheri-Shakib, J., Esfandiarian, A., Rajabi-Kochi, M., Kazemzadeh, E. & Afkhami Karaei, M. Evaluation of rock and fluid intermolecular interaction between asphaltene and sand minerals using electrochemical, analytical spectroscopy and microscopy techniques. Sci. Rep. 14(1), 670 (2024).
Taheri-Shakib, J., Saadati, N., Esfandiarian, A., Hosseini, S. A. & Rajabi-Kochi, M. Characterizing the wax-asphaltene interaction and surface morphology using analytical spectroscopy and microscopy techniques. Journal of Molecular Liquids 302, 112506 (2020).
Zojaji, I., Esfandiarian, A. & Taheri-Shakib, J. Toward molecular characterization of asphaltene from different origins under different conditions by means of FT-IR spectroscopy. Advances in Colloid and Interface Science 289, 102314 (2021).
Sui, Y. et al. Application, progress, and trend of thickened acid fracturing in carbonate rock reservoir development,. Processes 12(10), 2269 (2024).
Badizad, M. H. et al. Ion-specific interactions at calcite–brine interfaces: A nano-scale study of the surface charge development and preferential binding of polar hydrocarbons. Physical Chemistry Chemical Physics 22(48), 27999–28011 (2020).
Farhadi, H., Ayatollahi, S. & Fatemi, M. The effect of brine salinity and oil components on dynamic IFT behavior of oil-brine during low salinity water flooding: Diffusion coefficient, EDL establishment time, and IFT reduction rate. Journal of Petroleum Science and Engineering 196, 107862 (2021).
Wang, G.-D. et al. Structural determinants of asphaltenes behavior: Heteroatom-driven aggregation dynamics and viscosity enhancement in heavy oil systems,. Pet. Sci. https://doi.org/10.1016/j.petsci.2025.07.025 (2025).
Joonaki, E., Buckman, J., Burgass, R. & Tohidi, B. Water versus asphaltenes; liquid–liquid and solid–liquid molecular interactions unravel the mechanisms behind an improved oil recovery methodology. Sci. Rep. 9 (1), 11369 (2019).
Lashkarbolooki, M. & Ayatollahi, S. Effect of asphaltene and resin on interfacial tension of acidic crude oil/sulfate aqueous solution: Experimental study. Fluid. Phase. Equilibria. 414, 149–155 (2016).
Lashkarbolooki, M., Riazi, M., Ayatollahi, S. & Hezave, A. Z. Synergy effects of ions, resin, and asphaltene on interfacial tension of acidic crude oil and low–high salinity brines,. Fuel 165, 75–85 (2016).
Lashkarbolooki, M., Riazi, M., Hajibagheri, F. & Ayatollahi, S. Low salinity injection into asphaltenic-carbonate oil reservoir, mechanistical study. J. Mol. Liq. 216, 377–386 (2016).
Liu, D. et al. Synergetic effect of resins and asphaltenes on water/oil interfacial properties and emulsion stability. Fuel 252, 581–588 (2019).
Shi, Q. et al. Characterization of heteroatom compounds in a crude oil and its saturates, aromatics, resins, and asphaltenes (SARA) and non-basic nitrogen fractions analyzed by negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Energy Fuels. 24 (4), 2545–2553 (2010).
Tajikmansori, A., Dehaghani, A. H. S., Sadeghnejad, S. & Haghighi, M. New insights into effect of the electrostatic properties on the interfacial behavior of asphaltene and resin: An experimental study of molecular structure. J. Mol. Liq. 377, 121526 (2023).
Chukwudeme, E. & Hamouda, A. Oil recovery from polar components (asphaltene and SA) treated chalk rocks by low salinity water and water containing SO42 – and Mg2 + at different temperatures. Colloids Surf., A. 336, 1–3 (2009).
Ilyin, S. et al. Asphaltenes in heavy crude oil: Designation, precipitation, solutions, and effects on viscosity. J. Petrol. Sci. Eng. 147, 211–217 (2016).
Wang, Q. et al. Microstructure of heavy oil components and mechanism of influence on viscosity of heavy oil. ACS. Omega 8(12), 10980–10990 (2023).
Mohammadi, A. & Keradeh, M. P. Exploring the effect of relaxation time, natural surfactant, and potential determining ions (Ca2+, Mg2+, and SO42−) on the dynamic interfacial tension behavior of model oil-brine systems. Heliyon https://doi.org/10.1016/j.heliyon.2024.e29247 (2024).
Acknowledgements
The authors extend their appreciation to the Deanship of Scientific Research at Imam Mohammad Ibn Saud Islamic University (IMSIU) for funding this research work (grant number IMSIU-DDRSP2603).
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This work was supported and funded by the Deanship of Scientific Research at Imam Mohammad Ibn Saud Islamic University (IMSIU) (grant number IMSIU-DDRSP2603).
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Z. A: Conceptualization, Formal Analysis, Investigation, Funding Acquisition, Writing – Original Draft, Writing – Review & EditingA. B. M. A: Conceptualization, Software, Investigation, Validation, Writing – Original Draft, Writing – Review & EditingZ. K: Formal Analysis, Resources, Validation, Methodology, Writing – Original Draft, Writing – Review & EditingP. K. S: Conceptualization, Methodology, Investigation, Writing – original draft, Writing – Review & EditingO. J. A: Formal Analysis, Resources, Investigation, Visualization, Writing – Original Draft, Writing – Review & EditingK. K: Methodology, Software, Investigation, Visualization, Writing – Original Draft, Writing – Review & EditingI. M: Resources, Data Curation, Supervision, Project Administration, Writing – Original Draft, Writing – Review & EditingM. D: Resources, Methodology, Supervision, Project Administration, Writing – Original Draft, Writing – Review & Editing.
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Ahmed, Z., Ali, A.B.M., Khan, Z. et al. Control of sludge formation during acidizing through the investigation of acid and oil interactions and emulsion behavior in heavy oils using low salinity water. Sci Rep (2026). https://doi.org/10.1038/s41598-026-44381-z
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DOI: https://doi.org/10.1038/s41598-026-44381-z
