Challenge: An electric submersible pump (ESP) was set in a 7-in casing inside a 5 1/2-in shroud at about 1,676 m [5,500 ft] in a vertical, cased wellbore. As the intake pressure increased, the motor temperature rose slightly and production began to decline.
Solution: The multisensor of the Phoenix™ artificial lift downhole monitoring systems data showed that the motor temperature had risen because of an increased pump load on the motor, caused by progressive scaling of the pump.
Results: Acid was used to dislodge the scale. Both the intake pressure and the motor temperature then fell significantly, returning to normal operating conditions and resulting in higher drawdown and increased production.
An ESP was set in a 7-in casing inside a 5 1/2-in shroud at about 1,676 m [5,500 ft] in a vertical, cased wellbore. The production rate was approximately 80 m3/d [500 bbl/d]. The Phoenix artificial lift downhole monitoring system showed the pump slowly drawing down the reservoir. Initial production tests from the well yielded flow rates consistent with ESP design.
On June 10, 2004, the intake pressure began to increase. No apparent change in the production rate was found to explain the increase, so the ESP motor temperature alarms were set to monitor and protect the system against overheating.
Scale inside a pump can plug the stages, and plugged stages cannot impart the dynamic head needed to produce the wellbore fluid to the surface at the expected rate. As the intake pressure continued to increase, the motor temperature rose gradually, setting off the alarm. After further evaluation, production tests indicated a decline in flow rate. Then on June 20, when the motor temperature increase triggered the alarm, the decision was made to dissolve the scale by treating the well with acid.
Acid was placed inside the annulus and run through the shroud and pump to dislodge the scale. After the acid treatment, both the intake pressure and the motor temperature fell significantly, resulting in higher drawdown and increased production.
