By September 2009, MTBF (defined as cumulative number of run days/number
of failures) was 794 days. While more than satisfactory for some applications,
in this case the combination of some ESPs below this level, high workover costs
in the offshore environment, and declining production from the mature field
made the total cost of ownership (TCO) for ESPs uneconomical. To reduce lifting
costs, the operator tendered the entire work scope and mandated a minimum
guaranteed run life (GRL) of 2 years (730 days). Schlumberger was awarded the
work and in 2014, the GRL for Maximus and MaxFORTE systems was further
increased to 2.5 and 4 years (913 and 1,460 days), respectively.
Surveillance and engineered ESP systems enhance performance
To meet the challenge Schlumberger adopted a holistic approach,
combining root cause failure analysis, advanced hardware engineering, and 24/7
real-time surveillance with the Lift IQ production life cycle management
Level 2 Lift IQ service uses experienced surveillance engineers to
monitor artificial lift performance with real-time data delivered from each
well to a Schlumberger Artificial Lift Surveillance Center (ALSC). The data
includes alarms for critical events—conditions that require immediate
action to avert an ESP failure—including deadhead events, blockages,
pumpoff conditions, and subminimal speeds.
When ESPs did fail, the combination of historical remediation data and
dismantle inspection failure analysis (DIFA) enabled development of customized
operating procedures and hardware designs specific to that well or section of
the field. ESPs were replaced with more robust Maximus and MaxFORTE systems
designed specifically to survive the failure mechanism for that well, whether
corrosion, abrasion, scale, or something else.
Improvements incorporated into the new systems included
- 5530 alloy stage material to improve corrosion and erosion resistance
- silicon carbide sleeves and bushings to increase hardness and resist abrasive wear
- full-bearing housing configuration to increase shaft stability
- sand shedders and retainers to mitigate sand fallback damage
- advanced protector technology to improve and protect the shaft seal and drain abrasives
- improved motor bearing design to maintain operation even under poor lubrication
- mine-duty motors with increased insulation thickness and low-stress winding design to handle high-horsepower applications at 95 degC and operating motor winding temperatures of up to 140 degC [284 degF]
- high-viscosity oil, thicker wiring insulation, fully varnished motor stator, high-temperature stator laminations, and a low-stress winding process to improve motor reliability.
Holistic approach surpasses minimum GRL mandate
From 2009 through 2017, ALSC engineers responded to 400 critical ESP
events, making immediate recommendations for remedial actions to prevent damage
or failure. Not only were critical events rapidly resolved, but the lessons
learned helped the operator's field staff avoid recurrence. As a result, the
frequency of these events decreased from 1.4 per well year in 2012 to less than
0.5 in 2017, an improvement of 64%.
MTBF for Schlumberger ESPs installed since 2009 was 2,335 days (>6
years) at the end of 2017, nearly three times the 2009 MTBF for all ESPs in
this field. In addition, MaxFORTE systems in the field have more than 12 years
of cumulative installed days with zero failures to date. Proactive monitoring
and the changes in ESP system designs have significantly improved the lifting
performance of the entire field.