Testing the Untestable… Delivering Flowrate Measurements with High Accuracy on a Remote ESP Well

Abstract

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 with sufficient frequency and, in some cases, testing is only performed once per year. This case study demonstrates the novel use of ESP gauge data for obtaining accurate liquid rate and water cut trends in an unmanned desert location without the need for mobilizing surface well testing hardware. 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 artificial intelligence. 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 mobilise 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 demonstrated a new technique for providing continuous calibration of the flowrate models without any physical measurement of flowrate 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 field wide 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. 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.