# Interfacial Stability of Acid–Crude Oil Emulsions in Matrix Acidizing of Carbonate Reservoirs

## TL;DR

This study examines how acid and crude oil mixtures form stable emulsions during oil recovery in carbonate reservoirs and identifies conditions and additives that reduce emulsion stability.

## Contribution

The study introduces a systematic evaluation of the Emulsion Stability Index (ESI) under controlled conditions to guide safer acidizing operations in carbonate reservoirs.

## Key findings

- Lower acid-to-oil ratios (e.g., 0.2) significantly reduce emulsion stability.
- Elevated temperatures and FeCl3 concentrations enhance the reduction of emulsion stability.
- Additives at 3–5 vol % concentration effectively reduce emulsion formation when combined with optimal acid-to-oil ratios.

## Abstract

Matrix acidizing is a fundamental technique for enhancing
oil recovery
in carbonate reservoirs by injecting acidic solutions, typically 15%
(w/w) HCl, to promote wormhole formation and bypass damaged zones.
However, acid–crude oil interactions frequently result in stable
emulsions, leading to formation damage, reduced hydrocarbon mobility,
and excessive acid consumption. This study presents a systematic investigation
of the Emulsion Stability Index (ESI) in acid–oil systems under
carefully controlled laboratory conditions designed to simulate potential
field scenarios, assessing the effects of temperature (30–80
°C), acid-to-oil volumetric ratio (0.2–0.8), and FeCl3 concentration (0–3000 ppm). The experiments were conducted
in triplicate to ensure reproducibility with no significant differences
observed among replicates. The acid-to-oil ratio was identified as
the most influential factor in mitigating emulsion formation. Lower
ratios (e.g., 0.2) significantly reduced ESI values, particularly
when combined with elevated temperatures and ferric ion concentrations.
In addition, commercial additivesa demulsifier and a corrosion
inhibitor, both characterized by high hydrophilic–lipophilic
balance (HLB) and applied at concentrations of 1, 3, and 5 vol %were
evaluated for their performance. The main findings indicate that lower
acid-to-oil ratios combined with elevated temperatures, FeCl3, and the presence of 3–5 vol % of these additives significantly
reduce emulsion stability, enabling safer and more effective acidizing
operations in carbonate reservoirs.