Production logging detects gas, oil and water entry into the wellbore and also measures the flow rate and fluid holdup. A tool called the FlowScanner (by Schlumberger) is designed for use in horizontal and high-angle wells to analyze multiphase flow across the wellbore.
This tool uses a low-frequency electrical probe for water holdup measurement and an optical sensor probe for gas holdup measurement. The electrical probe tip senses the electrical impedance of the fluid touching it. It distinguishes water, which is low-impedance, from high-impedance oil and gas. The optical probe is sensitive to a fluid's index of refraction. Gas, having a low refractive index, is much more reflective than either oil or water. The video clip below demonstrates this measurement.
