Well SP-4D has undergone three workovers because of formation of calcite blockages at its flash point depth at around 800-850 mMD. The calcite inhibition trials conducted in 1999 failed to inhibit the formation of calcite primarily because of the inability to reach proper inhibition point due to liner problems encountered prior to the set-up of the inhibition system.

During the workovers, obstructions were also encountered at deeper sections of the wellbore (>1250 m) while undergoing reaming operations. These obstructions were believed to be calcite, formed when calcium-rich low temperature fluids (220?C) from deeper feed zones (1300 mMD to bottom) were heated by hotter fluids (240?C) from the major feed zone (1200 mMD) of the well. This wellbore phenomenon in SP-4D presented two possibilities for the setting depth of the inhibition system, namely, (1) near well bottom at 1400 mMD or (2) at a shallower portion of the well thus letting the deeper but relatively colder section of the well to be totally blocked by calcite deposition.

An optimization study was performed using wellbore simulation to determine the setting depth of the inhibition system for SP-4D. Results show that the inhibition system should be set at shallower levels (around 1100 mMD), allowing the deeper colder sections to be naturally blocked by calcite deposition.
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