Testing the Untestable
Delivering Flowrate Measurements with High Accuracy on a Remote ESP Well
Flow rate testing is the most fundamental form of reservoir surveillance
and is typically performed on a monthly basis using a test separator.
Unfortunately, in some remote locations, the logistical challenges are so
onerous that testing cannot be conducted. This case study demonstrates the
novel use of gauge data for obtaining accurate liquid rate and water cut trends
for such a well equipped with an ESP in an unmanned desert location.
The liquid flow rate calculation was based on the principle that the
power absorbed by the pump is equal to that generated by the motor, which
provides a linear equation which can be resolved for rate. Water cut was
calculated by measuring the production tubing differential pressure, which
provides the average fluid density, which is subsequently converted to a water
cut. Analytical equations are used throughout the process ensuring that the
physics are respected at all times, which yields greater repeatability and
confidence than analogous methods, which are based on correlations and
The algorithms used real-time data from existing permanent downhole
gauges and ESP surface controllers, which provided the necessary measurement
metrology to capture well performance transients and provide a full production
history. This method also has the advantage that there is no need to mobilize
testing equipment to the well site, thereby minimizing cost as well as
eliminating flaring and HSE risks associated with remote location operations.
This case study demonstrates a new technique for providing continuous
calibration of the flow rate models without any physical measurement of flow rate
or fluid specific gravity, while taking into consideration changing well and
ESP performance over time. This novel calibration method is also based on
analytical equations and derived from first principles. After one year of
production, a test separator was specially mobilized to the well site to
validate the liquid rate and water cut calculations and associated calibration
technique to consider the method for fieldwide application.
This case study demonstrates that the proposed real-time algorithm
provides the necessary metrology and data frequency to determine the production
index as well as a trend of drainage area reservoir pressure over time. Finally,
it enables a reduction in physical testing frequency while providing liquid
rate and water cut with high frequency, repeatability, and resolution, thereby
delivering both cost savings and improvements in information quality.