Calcium based brine has regularly been used during workover operations on naturally completed wells without any sign of formation damage, in gravel packed wells which have seen severe losses of Ca based brine production decline was observed.

For some of the gravel packed wells the production decline occurred when bringing the well on production after completion, whilst in others, the loss in productivity occurred after sea water breakthrough.'

In order to increase productivity and confirm the relationship between productivity decline and formation of CaSO4 scale due to losses of completion brine, scale dissolver treatments were carried out.

The use of dissolver chemicals resulted in mobilization and removal of several hundred kilograms of solids from the near wellbore area.

A post-evaluation strategy to provide information about the nature, origin and location of scale was successfully implemented. More importantly, the dissolver treatments resulted in increased oil production.

The findings and lessons learned have had several important implications for gravel pack completions and well treatments in Statoil.

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