Degradation of Abandonment Cement Plugs Under Prolonged Exposure to Completion Fluids: A Multi-Technique Evaluation

This study investigates the durability of abandonment cement plugs applied in decommissioned oil wells in Brazil. The objective is to analyze the integrity of cement barriers over time to ensure the permanent sealing of wells and prevent leaks that could compromise the environment. The research involves the analysis of four cement slurry formulations: two without additives (with densities of 14.0 lb/gal and 15.8 lb/gal) and two with additives, including antifoaming agents, dispersants, fluid loss control, aiming to evaluate their physical and chemical resistance after exposure to completion fluids for 24 h, 30, 60, 90, and 180 days. The test specimens were aged at a temperature of 38°C and ambient pressure. The samples were subjected to compressive strength (CS) tests, x-ray diffraction (XRD), thermogravimetry (TG), scanning electron microscopy (SEM), and energy-dispersive x-ray spectroscopy (EDS). The results revealed significant concerns regarding well safety. The samples exposed to saline completion fluid for 180 days exhibited a decrease in CS, highlighting a critical issue. One of the hypotheses for this reduction in mechanical strength is the leaching of calcite from the cementitious matrix and the formation of hydrocalumite. This study raises a discussion on the importance of continuous safety monitoring for decommissioned wells.