Acid-Induced Emulsion and Sludge Mitigation: A Lab Study

Acid matrix stimulation is a widely used method to improve well productivity by removing and/or bypassing damage in the near wellbore area and creating channels for hydrocarbon flow. Hydrochloric (HCl) and organic acids are commonly used to design fluid recipes utilized in these treatments. However, these acids can cause formation damage by forming stable emulsions and sludge upon contact with formation crude if the treatment and/or stimulation fluid are not designed carefully. It is well reported that acid in contact with crude oil can destabilize asphaltenes either by neutralizing asphaltene or dissolution of resins. Therefore, acid recipe chemical additives must be selected and examined carefully to ensure effective acidizing treatments. In this study, the interaction of different HCl-based recipes with oil was investigated using different lab techniques and analysis including acid/oil separation tests, sludging tendency testing, and SARA analysis. The influence of several factors including acid concentration, acid type, and dissolved iron content were investigated. Experiments were conducted with varying acid blends, demulsifier and anti-sludge type and concentration. To simulate dissolving corrosion products by acids in downhole environment, ferric chloride was incorporated in acid recipes. The results showed an increase in temperature enhanced emulsion/sludge breaking tendency. The addition of demulsifier/anti-sludge agents in acid recipes was necessary to avoid creating stable emulsions and sludge that can damage reservoir permeability. Higher amounts of dissolved iron in the acid solution resulted in a more stable emulsion and enhanced sludge formation. Asphaltene problematic oil, as determined from the asphaltene colloidal instability index, showed severe sludging tendency. Lastly, the use of HCl/organic acid blends may be necessary for some oil types to avoid formation of sludge. This paper showcases a comprehensive testing method to mitigate formation damage from acidizing treatments. The testing can be expanded to design an acid stimulation fluid recipe to minimize acid-induced formation damage and maximize well productivity enhancement.