Well Plugging Study from Inorganic Scale Viewpoint for an Offshore Seawater-Flooded Oilfield

A seawater-flooded offshore oilfield has experienced well plugging issues causing production decline. Fines migration was the assumed cause for plugging for many years. A comprehensive study was initiated to review the initial completions, fines migration, and scaling as causal mechanisms. The study concluded further evaluation of inorganic scaling and organic deposits was appropriate, and a flow assurance study was commissioned to evaluate these possible plugging mechanisms. This paper focuses on inorganic scale evaluation. Calcite (CaCO3) and/or barite (BaSO4) scales were observed in wells and production system in seemingly random ways, which correlated to the varying effectiveness of stimulation jobs. Historical water chemistry data was not considered suitable to investigate scale risks and patterns by scale modeling. An innovative approach was taken to analyze all available chemistry data and field information, which guided further investigation. A study was designed to sample and analyze produced water from 42 wells distributed across the field. Scale modeling with the new water chemistry data confirmed the trends suggested in the historic data with considerations to geochemical non-uniformity in the reservoir. The scale study successfully identified the scaling pattern in the field and confirmed scaling has contributed to well plugging and production decline. The study can now inform scale risk for new wells, plugging remediation and stimulation operations. Additionally, a complete review of incumbent scale control program was recommended for well plugging control and production improvement.