Key Takeaways from Implementing a Successful Downhole Scale Mitigation & Prevention Job in an Indian Western Offshore ESP Well

Abstract

Multiple ESP wells in an Indian Offshore Carbonate reservoir were afflicted with inorganic scale deposition chronically. Analysis of recovered deposit samples was carried out and the root cause of deposition established. This was followed by successfully carrying out remedial operations for scale removal and prevention. The experience gained from the same has been elaborated in the paper. Inorganic scale deposition in Electrical Submersible Pumps has been a big cause of concern in many wells of a carbonate reservoir in Indian Offshore. Scale deposition in ESPs causes decrease in pump efficiency and sometimes, complete choking and ultimate failure. As part of this study, a detailed Compositional Analysis of recovered samples retrieved from inside the ESP was carried out. Based on the analysis, custom job plans were formulated to clear the scale from within the ESPs and its vicinity. This was followed by a continuous inhibitor injection program from a downhole chemical injection mandrel after the selection of the appropriate chemical. The results of the compositional analysis of the recovered debris showed that despite the well operating in a carbonate reservoir, the majority of the sample was acid-insoluble sulphate scale. Further probing elucidated the fact that multiple acid washes had been performed in the well, which while dissolving the carbonates, left behind insoluble sulphates as residual scale. The operating conditions inside the pump were also especially conducive for sulphate deposition. As such, tailored job plans consisting of a formulation of a chelating agent in an alkaline solution were designed and executed. Implementation of the job plans resulted in significant oil gain from the affected wells and the continuous inhibitor injection has further improved the efficiency of the ESPs and reduced the frequency of cleaning jobs required. The paper aims at providing an insight into inorganic scale deposition in ESPs. After analysing the scaling problem and establishing the root cause, mitigating measures have been devised and implemented. The paper provides a holistic approach towards tackling the problem of existing inorganic scale and preventing future deposition from taking place. The experiences gained during the entire exercise have been deliberated in the paper.