# Pore-Scale Analysis and Visualization of Tertiary Cationic Surfactant Flooding in a Complex Carbonate

## TL;DR

This study uses advanced imaging to show how a cationic surfactant improves oil recovery in complex carbonate rocks by altering wettability and reducing interfacial tension.

## Contribution

The study demonstrates that DTAB flooding enhances oil recovery in carbonates without requiring ultralow interfacial tension, offering a cost-effective EOR method.

## Key findings

- DTAB flooding reduced interfacial tension and altered wettability, increasing oil recovery from small pores.
- Switching from brine to surfactant injection caused a transition from oil-wet to mixed-wet states.
- DTAB flooding was more effective than brine in displacing oil trapped in complex carbonate structures.

## Abstract

We investigate the
pore-scale mechanisms of displacement using
cationic surfactant dodecyltrimethylammonium bromide (DTAB) flooding
as a tertiary enhanced oil recovery (EOR) technique in a complex carbonate
rock using high-resolution X-ray microcomputed tomography (micro-CT).
A carbonate sample was initially altered to be oil-wet through contact
with crude oil, followed by sequential brine and surfactant injection
to evaluate the impact on oil displacement and investigate oil recovery
mechanisms. We used a concentration of DTAB above the critical micelle
concentration, CMC, with no cosolvent. Image-based pore-scale analysis
of fluid occupancy, wettability alteration, contact angles, interfacial
areas, capillary pressure, and fluid connectivity was performed. The
contact angles, mean curvatures, and capillary pressures indicated
a transition from oil-wet to a mixed-wet state when we switch from
brine to surfactant injection. The results indicate that DTAB flooding
reduced interfacial tension and altered wettability, leading to increased
oil recovery, particularly from small pores and throats, where brine
flooding was ineffective. The results were compared to those of a
previous study of secondary DTAB flooding. We hypothesize that wettability
alteration was caused by competitive adsorption and hydrophobic interactions,
promoting oil detachment from the rock surface. This study demonstrates
that DTAB can enhance oil recovery in carbonate formations without
requiring ultralow interfacial tension, making it a cost-effective
alternative for complex reservoirs.