# Effect of Additives on the Dissolution Rate of Different Carbonate Rocks by Hydrochloric Acid

## TL;DR

This study examines how additives affect how fast hydrochloric acid dissolves different carbonate rocks, finding that additives significantly slow down the process.

## Contribution

The novel contribution is quantifying how commercial additives, containing surfactants, reduce dissolution rates of carbonate rocks in acid treatments.

## Key findings

- Calcitic rocks dissolved faster than dolomitic rocks without additives.
- Additives slowed dissolution rates, especially in calcitic rocks, increasing dissolution time by over 18-fold.
- Surfactants in additives reduced H+ availability and caused foam formation, slowing reactions.

## Abstract

Matrix acidizing is a widely applied technique for stimulating
carbonate reservoirs by promoting mineral dissolution and restoring
well productivity. In this context, this study aimed to investigate
the effect of commercial additives, a corrosion inhibitor and an emulsion
preventer, both containing surfactants in their formulations, on the
dissolution rate of different carbonate rocks by hydrochloric acid
(HCl), comparing the performance of systems with and without additives.
Samples of Indiana Limestone, Mount Gambier Limestone, Wisconsin Dolomite,
and Bonneterre Dolomite, which exhibit distinct mineralogical compositions
and structural characteristics, were analyzed. The samples were characterized
using X-ray diffraction (XRD), X-ray fluorescence (XRF), nuclear magnetic
resonance (NMR), and porosity measurements. Dissolution experiments
were conducted in a batch reactor, allowing the acquisition of kinetic
curves for the acid–rock reaction. The results showed that,
in the absence of additives, predominantly calcitic rocks exhibited
the highest dissolution rates (exceeding 1 g min–1), with dissolution kinetics primarily controlled by mass-transfer
limitations. In contrast, dolomitic rocks displayed lower reactivity,
with rates below 0.1 g min–1. The presence of additives
significantly retarded the reaction in all rock types, with the most
pronounced effect observed for calcitic samples, where the dissolution
time increased by more than 18-fold. This behavior can be attributed
to foam formation and the reduction of H+ availability
at the acid–rock interface caused by the surfactants contained
in the additives.