Sensitivity and Uncertainty Analysis of a Downhole Flow Metering System for an ESP

Abstract

Downhole flow meters are needed in oil field applications to measure the amount of fluid produced from a well. One of their advantages over surface flow meters is measurement of in situ pressure and temperature, which provides additional wellbore information to reservoir and production engineers. This work involves performing uncertainty analysis on a downhole flow meter tested for use in oil field operations. It is an important step to determine acceptable measurement limits of the metering system. To quantify the measurement uncertainty, the analysis was performed on a downhole, oil-water flow meter with an inlet pipe diameter of 0.076 m. The analysis covered differential pressures with corresponding flow rates from 0.0036 m3/s up to the maximum flow meter capacity of 0.0224 m3/s. The operating fluid temperatures varied from 32°C to 40°C, which consequently changed the oil and water densities and kinematic viscosities during the flow meter tests. For a given operating flow rate and temperature, the uncertainty in the individual measurement components of the meter were determined, and the overall metering system uncertainty established. The results indicate that as the operating flow rate increased, the uncertainty in the flow rate reduced substantially. The increase in temperature had the effect of increasing the magnitude of the flow rate measured by the flow meter. The variation in the flow meter inlet pipe diameter introduced the largest uncertainty in the flow meter measurement. The uncertainty was in the order of a factor of two and higher compared to the next lower uncertainty contributor. These observations suggest the importance of ensuring accurate control of flow meter geometry and flow parameters, to ensure reliable measurements of fluid flow from the wellbore. Installing downhole flow meters in oil field applications is an important step in gaining additional knowledge of reservoir conditions at the flow measurement location. It is vital to ensure that measurements obtained from these flow meters are accurate in field operations for good production decision making. This paper highlights the flow meter parameters contributing to its uncertainty and also provides recommendations to maintain its reliability in the field.