Low temperatures challenge ESP elastomers
An operator in a North Sea field faced the challenge of scale buildup in
its wells, a common occurrence for the area. The buildup would slow production
in affected wells, so the operator would pump inhibitor downhole as a
preventive measure. From 2006 to the end of 2014, the operator performed
approximately 630 scale squeezes on about 50 wells in the field, 10 of which
had ESP failure within 1 month of a scale squeeze. Although a 0.02% failure
rate seems low, the cost of each workover is USD 2 million, which is a
significant cost when multiplied by 10 wells.
The Schlumberger dismantle, inspection, and failure analysis (DIFA) team
determined that the 10 ESPs that failed experienced electrical failures
immediately after the scale squeezes. The DIFA team discovered that the problem
was fluid ingress past the AFLAS elastomers. AFLAS elastomers have
temperature limitations and are compromised if the temperature reaches below 50
degC [122 degF]. The operator asked Schlumberger for a solution that would help
maintain a minimum downhole temperature during scale squeezes to avoid leakage
past the seals.
Lift IQ services analyze pumps remotely
Schlumberger recommended implementing Lift IQ services. The Lift IQ
service delivers 'round-the-clock remote surveillance of all artificial lift
systems, preventing or resolving ESP downtime, misuse, or failure. Experienced
engineers monitor alarms and analyze data transmitted from multiple wells
across fields simultaneously in real time, up to 24/7/365 at one of many
Schlumberger Artificial Lift Surveillance Centers (ALSCs).
When ALSC engineers receive alarms and alerts, they use their expertise,
experience, data resources, and Schlumberger best practices to identify
possible causes and remediation options. Some recommendations can be
implemented remotely, enabling immediate intervention to prevent shutdowns or
restart pumps; others are relayed to field personnel, who can rapidly complete
the necessary action because they know the most likely diagnosis before they
arrive on the location.
Real-time monitoring and onsite intervention eliminate ESP failure
For the wells in the field, Schlumberger engineers used a proactive
surveillance plan to remotely monitor downhole temperature data from gauges on
the ESPs. ALSC engineers monitored the wells during all scale squeeze
operations. If the well temperature dropped below 70 degC [158 degF], the ALSC
engineers advised Schlumberger engineers at their offshore
control room to reduce the injection rate of the scale squeeze by 15%. If the
well temperature hit 50 degC—the low limit threshold of the
elastomers—the ALSC engineers would notify Schlumberger to pause the
operation until the temperature stabilized to maintain the elastomer integrity
and prevent ESP failure.
In the 2 years since the operator began using the Lift IQ service, 54
wells have had 157 scale squeezes with no subsequent ESP failures. Using the
averages from 2006 to 2015, at least two ESP failures would be expected.
Because of the Lift IQ surveillance and coordination with Schlumberger
operations, however, no well has dipped below the minimum acceptable
temperature. Every ESP for the operator in the field has started successfully
after a scale squeeze since the Lift IQ service was implemented.