Well-control fluids were used during a routine overbalanced workover operation in an offshore well completed in high permeability sandstone. As expected, a fluid loss control pill was used to control the excessive losses encountered during this operation. However, due to the high permeability of the reservoir and the absence of sized particles in the pumped pill; large amount of fluids were lost to the formation before losses were controlled. The deep invasion of fluids laden with high concentration of polymer had inevitably resulted in severe formation damage and impaired production. Several attempts to clean out the wellbore and revive the well flow were unsuccessful with no injectivity either. The well was consequently suspended while a multidisciplinary team was formed to identify the cause of the impairment and recommend a treatment plan.
A comprehensive review of detailed field operation and data related to the fluid losses accompanied with laboratory work to identify the damaging mechanism and formulate an optimized remedial treatment was conducted. The lab work included jar testing to assess compatibility and emulsion tendency when different wellbore fluids are mixed with each other and with formation fluids. Analysis of the samples collected from the wellbore was carried out and different treatment fluid options were evaluated using actual field samples. Core flood experiments were also conducted to assess the impact of high-viscosity pills on permeability and ability of remedial treatment in restoring the original permeability.
Experimental results revealed partial removal of the polymer invading the core using organic acid. The designed pre-flush composed of mutual solvent with surfactant package was effective in breaking the emulsion from field samples and laboratory-prepared emulsions. A significant improvement in production from this well was realized by application of a cost effective formic acid-based chemical treatment. Proper treatment design with effective displacement technique were also attributed to the successful damage removal and regained well productivity.