Abstract

A new-generation production logging toolstring is being introduced with a sensor that can measure fullbore gas holdup. Unlike previous center-sampling holdup sensors (whether radioactive fluid-density or capacitance holdup), this new sensor responds to the entire cross-sectional area of the production tubulars (casing, tubing or slotted liner) occupied by gas and liquid. From this response, the holdup fractions for liquid and gas (Y₁ and Y_g) can be determined.

The fullbore measurement eliminates previous uncertainties in holdup fractions that can occur when flowing conditions are nonuniform or when water cut is high. This new capability is shown by flow loop comparisons between measurements taken with the fullbore gas-holdup tool and those taken with previous center-sampling holdup sensors in horizontal stratified flowing conditions. The new production logging toolstring includes a high-speed, bi-directional, monocable digital telemetry system. This system permits simultaneous logging with additional tools such as pulsed neutron tools, oxygen-activation water-flow tools, or other radioactive fluid-velocity tools. The combination of production logging sensors with oxygen activation measurements are important for the evaluation in complex well completions where there are flow paths both inside and outside of the production tubulars, such as with slotted liners. An interactive wellsite production logging analysis package has been developed to utilize the improved data. Both flow-loop based and conventional slip-velocity interpretation methods are available for determining the flow rates of the individual phases. A new method for determining the downhole flow regime is presented which utilizes both the center-sample holdup and the fullbore holdup measurements.