The Critical Factors Causing Casing Corrosion in Aqueous Drilling Fluids

Abstract

Abstract Understanding the corrosivity of aqueous drilling fluids is essential for more efficient and safer drilling operations. The main factors causing the corrosion of typical aqueous drilling fluids were investigated under laboratory conditions using American Iron and Steel Institute (AISI) 1018 mild carbon steel at 70 degC dynamic flow. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), X-ray fluorescence (XRF), and X-ray photoelectron spectroscopy (XPS) analyses were used to characterize the metal microstructure of AISI 1018 steel rotating cylinder electrodes (RCE) and study the changes that occurred during corrosion. The effects of fluid composition, barite weighting agent, and clay contaminant were investigated using RCE to simulate the effect of flow velocity on mild carbon steel corrosion and the effect of dissolved oxygen. Starting with a low salinity chloride-brine base fluid (3% NaCl), the effect of adding various components such as amine-based shale inhibitors, polymeric viscosifiers, and suspended solids on the corrosion of RCE was investigated using various electrochemical techniques such as linear polarization resistance, Tafel analysis, and weight loss measurements. Three additional corrosion factors and chemical additives affecting the corrosion of AISI 1018 mild carbon steel were identified: (1) polymeric viscosifiers, (2) the formation of a mud solids skin on the metal surface, and (3) galvanic corrosion. These factors improve the understanding of the corrosion mechanisms occurring in aqueous drilling fluids and provide valuable insights for the development of effective strategies to reduce corrosion in drilling operations.