Acidification as a produced water treatment for WSO removal – A review

Removing water-soluble organics (WSO) from oilfield-produced water (OPW) has become a primary challenge for the offshore industry, driven by regulatory updates that now include WSOs in Total Oil and Grease (TOG) measurements. This review investigates acidification before three-phase separation as a strategic solution compatible with existing offshore equipment, such as hydrocyclones and flotation units. Over the last four decades, there has been a transition from the use of mineral acids to organic acids, which are less aggressive to processing equipment and less harmful to the marine environment. Presently, acetic and glycolic acids are the most used options. While the fundamental partitioning behavior of naphthenic acids between aqueous and organic phases is well-documented, the operational performance and practical implications of acidification in continuous-flow OPW treatment remains under-explored. This study highlights the need for novel phase transfer agents to enhance WSO removal efficiency while reducing chemical consumption and associated costs. By consolidating fragmented literature and patent data, this review identifies critical pathways for technological optimization in the treatment of oilfield-produced water. • Acidification before separation shifts naphthenic acids into the oil phase. • Protonation of naphthenic acids reduces WSO and, thus, TOG concentrations. • Mineral acids (HCl, H₃PO₄, H₂SO₄) were replaced by milder organic acids. • Acetic and glycolic acids are currently the primary options for OPW acidification. • Future research should develop novel agents to lower acid volume and cost.