Pore-scale imaging and analysis of surfactant flooding in carbonate reservoirs using micro-computed tomography
File(s)
Author(s)
Alzahrani, Hussain Mohammad A
Type
Thesis
Abstract
Cationic surfactant flooding improves oil recovery from oil-wet carbonate rocks by shifting wettability toward more water-wet conditions while moderately reducing interfacial tension (IFT). This study combines high-resolution X-ray micro-CT imaging with high-pressure/high-temperature flow experiments to directly visualize pore-scale displacement mechanisms and compare secondary and tertiary flooding strategies at surfactant concentrations near and above the critical micelle concentration (CMC).
In secondary mode, DTAB injected above the CMC reduced IFT to 6.3 mN/m and achieved 91% oil recovery. Imaging showed preferential displacement of oil from medium and large pores, with limited access to the smallest pores. Contact angle and curvature analyses indicated a transition from weakly oil-wet to mixed-wet conditions, confirming that recovery resulted from the combined effects of wettability alteration and moderate IFT reduction.
In tertiary mode, surfactant injection after brine flooding mobilized oil trapped in smaller pores and throats, further reducing contact angles and shifting curvature and capillary pressure toward neutral or positive values. However, ultimate recovery (80%) remained lower than secondary flooding, indicating reduced efficiency when surfactant is injected later.
Concentration effects showed that above-CMC flooding outperformed near-CMC injection, particularly during early pore volumes. Across all cases, contact angles decreased, curvature changed sign, and capillary pressure evolved from negative to positive, demonstrating systematic wettability alteration.
Overall, this work provides new pore-scale evidence that surfactant enhanced recovery in carbonates is governed by the synergistic effects of wettability alteration and moderate interfacial tension reduction, rather than by ultralow IFT alone in case of adding a co-solvent. The integration of in situ X-ray imaging, quantitative image analysis, and curvature-based wettability metrics establishes a framework linking interfacial geometry to macroscopic oil recovery. The results demonstrate that early surfactant injection in secondary mode and the use of concentrations above the CMC optimise displacement efficiency and ultimate recovery.
In secondary mode, DTAB injected above the CMC reduced IFT to 6.3 mN/m and achieved 91% oil recovery. Imaging showed preferential displacement of oil from medium and large pores, with limited access to the smallest pores. Contact angle and curvature analyses indicated a transition from weakly oil-wet to mixed-wet conditions, confirming that recovery resulted from the combined effects of wettability alteration and moderate IFT reduction.
In tertiary mode, surfactant injection after brine flooding mobilized oil trapped in smaller pores and throats, further reducing contact angles and shifting curvature and capillary pressure toward neutral or positive values. However, ultimate recovery (80%) remained lower than secondary flooding, indicating reduced efficiency when surfactant is injected later.
Concentration effects showed that above-CMC flooding outperformed near-CMC injection, particularly during early pore volumes. Across all cases, contact angles decreased, curvature changed sign, and capillary pressure evolved from negative to positive, demonstrating systematic wettability alteration.
Overall, this work provides new pore-scale evidence that surfactant enhanced recovery in carbonates is governed by the synergistic effects of wettability alteration and moderate interfacial tension reduction, rather than by ultralow IFT alone in case of adding a co-solvent. The integration of in situ X-ray imaging, quantitative image analysis, and curvature-based wettability metrics establishes a framework linking interfacial geometry to macroscopic oil recovery. The results demonstrate that early surfactant injection in secondary mode and the use of concentrations above the CMC optimise displacement efficiency and ultimate recovery.
Version
Open Access
Date Issued
2025-11-26
Date Awarded
2026-03-01
Copyright Statement
Attribution-NonCommercial 4.0 International Licence (CC BY-NC)
License URL
Advisor
Blunt, Martin J.
Bijeljic, Branko
Sponsor
None
Grant Number
None
Publisher Department
Department of Earth Science & Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)