(345e) Applying Predictive Analytics to Detect and Diagnose Impending Problems in Electric Submersible Pumps Used for Lifting Oil from Wellbores

1. Objectives/Scope

The
electrical submersible pump (ESP) is currently the fastest growing
artificial-lift pumping technology.  Deployed across 15 to 20 percent of oil-wells
worldwide, ESPs are an efficient and reliable option at high production volumes
and greater depths. However, ESP performance is often observed to decline gradually
and reach the point of service interruption due to factors like high gas
volumes, high temperature, and corrosion.  The financial impact of ESP failure is
substantial, from both lost production and replacement costs.  Therefore, ESP
performance in extensively monitored, and numerous workflows exist to suggest
actions in case of breakdowns.  However, such workflows are reactive in
nature, i.e. action is taken after tripping or failure.   Furthermore,
the emerging trend in the E&P industry of using downhole sensors for
real-time surveillance of parameters impacting ESP performance there is an
opportunity for predicting and preventing ESP shutdowns using data analytics. Therefore,
a data-driven analytical framework is proposed to advance towards a proactive
approach to ESP health monitoring based on predictive analysis to detect impending
problems, diagnose their cause, and prescribe preventive action.  

2. Methods/Procedure
and Process

Data-driven techniques
employing multi-variate statistics are applied to detect and diagnose impending
problems with ESP operation.  To reach that goal, a three-stage workflow was
designed and mathematical models were built for each stage. 

The first stage of the workflow
involves prediction of failures in advance. Historical data is first used to
determine and evaluate key operational variables (decision variables) affecting
ESP performance. A hybrid approach (combination of first principles and close
to 20 decision variables) is then used to develop a robust principal component analysis
(Robust PCA) model. The model is then used to monitor subsequent operation.  An
alarm is issued if a corresponding index exceeds the normal operating range
established by the model, and diagnosis is offered based on the nature and
value of the index or indices exceeding their normal operating range.

The second stage involved
diagnostics of the potential cause leading to the failure. A mathematical model
was built to determine the contribution of the various decision variables towards
failures and ranking them according to these contributions. This ranking will
help the operator understand the root cause and take appropriate action.

The third stage involved
prescription of preventive action. It was modeled keeping in mind the operators
need for a remedial solution to fix the issue. Stable operating ranges were
determined for each decision variable. Operating within the stable range would
not lead to an alarming event. The values of the parameters during the failures
were compared against the stable operating ranges to understand which all
parameters were behaving outside the acceptable limits. Those parameters were
reset to values within the acceptable range.

3. Results,
Observations and Conclusion

In building the predictive
model based on normal operation data from an oilfield, it was demonstrated that
four principal components obtained from the model output were sufficient to
capture more than 80% of observed variance with 95% confidence limit.

Trends or patterns during
normal operation were identified and correlated to either satisfactory
operation or impending problems. This could be observed in the plot of Scores
of Principal component 1 and Principal Component 2 as seen in figure 1. In this
plot, the stable operating zone is clustered together as a green zone along the
(0,0). The failure data sets move away from the stable zone with increasing time
steps and fail at a point farther away as shown below. The increasing numbers
represent the increasing time steps. The Trip 1 happened at 1518 minute, therefore
the ESP was functioning abnormally for more than 24 hrs before it actually failed
at the 1518^th minute. With this kind of pattern plot, the failure
could have been detected much in advance and could have been prevented.

Figure
1: ESP Health Monitoring Plot

It was observed that the
Hotelling T-square distribution statistic monitored over time stays within the
95% confidence limit for stable operation and exceeds the limit during unstable
(transient) operation, long before an ESP trips or fails.  The actual value of
this statistic during a trip or failure shows an increase of more than two
orders of magnitude compared to its normal value.  The statistic successfully
identified all impending trips or failures a few hours before they actually
occurred.  Had this tool been used in the field, there would have been ample
time for preventive action that could mitigate or altogether avoid each problem.

Figure 2: A plot of Hotelling
T-square distribution for a Robust PCA Model

Prescription Plot in
Figure 3 shows the stable ranges in green bars and the behavior of the
parameters for two different events. It can be observed that some of the
parameters are away from the stable zone. They can be reset to the stable zone
and a failure event can be predicted in this manner.

                                                                                                             
Figure 3: Prescription Plot for parameter behavior identification

4.  Significance of the
Subject Matter

This real-time analytical
framework enables a shift towards proactive ESP monitoring to identify impending
problems long before they occur thereby safeguarding ESP operation, reducing
intervention costs and optimizing production. This approach creates
opportunities to increase pump uptime, extend the life expectancy of ESPs and
improve oilfield economics.