# Experimental assessment of chemical solvents for asphaltic sludge removal to mitigate formation damage in oil reservoirs

## TL;DR

This study tests solvents for removing asphaltic sludge in oil reservoirs, finding THF and xylene most effective under various conditions.

## Contribution

The study experimentally evaluates solvent efficiency for asphaltic sludge removal, a previously understudied issue in oil reservoir acidizing.

## Key findings

- THF and xylene achieved 70% and 60% solubility, respectively, for asphaltic sludge.
- Kerosene-diesel mixture showed nearly 0% solubility due to lack of suitable compounds.
- Rock powders reduced THF and xylene solubility to 30% and 39% by deactivating H⁺ ions.

## Abstract

The reaction between acid and crude oil during oil well acidizing results in the formation of asphaltic sludge, a protonated complex enriched with H⁺ ions that forms within oil reservoirs. Its intricate structure and limited solubility make removal challenging, distinguishing it from asphaltene precipitation. This study aims to address the research gap regarding the effectiveness of solvents in asphaltic sludge removal. Three solvents, namely xylene, tetrahydrofuran (THF), and a kerosene-diesel mixture, were tested to evaluate their dissolution efficiency compared with the solubility of different asphaltene types. The results indicated that THF and xylene were the most effective solvents, with solubility rates of 70% and 60%, respectively. In contrast, the kerosene-diesel mixture exhibited nearly 0% solubility due to the absence of aliphatic and nonpolar compounds in the sludge required for effective dissolution. Analysis of influencing parameters revealed that increasing solvent volume to 20 mL/g improved solubility by 20%. In reservoir conditions, rock particle deposition is likely. The presence of 0.5 g of rock powders reduced THF and xylene solubility to 30% and 39%, respectively, due to H⁺ ion deactivation. Increasing contact time to 60 min and mixing speed to 1800 RPM further improved solubility by up to 10% and 20%, respectively.