Fabien Cens

Optical detection of gas in producing oil wells

A new production logging device has been field tested that uses innovative sensing technology to enable the direct detection and quantification of gas in multiphase flows. Four optical probes, deployed 90 degrees apart on the arms of a centralizer-like tool, measure the optical reflectance of the surrounding fluid. The probes are evenly spaced in the pipe cross section, and their orientation in space is accurately known through use of an integrated relative- bearing sensor. In gas-liquid mixtures, the optical signal reflected by the probe is used to determine gas holdup and a gas bubble count, which is related to gas flow rate. In addition, the individual sensor measurements are used to build an image of the gas flow in the well. These images are particularly useful in deviated and horizontal wells for better understanding the multiphase flow patterns and interpreting their inherent phase segregation occurring at such deviations. The new tool has been successfully field tested in wells throughout the world and the tools capabilities are illustrated by example form both field and laboratory data sets. The new tool has been designed to detect the presence of gas, and hence its major application is to identify gas entries in oil/water wells or water/oil/condensate in gas wells. Because of its high sensitivity to minute amounts of gas, the tool can also be used to locate the bubble point when logging in the tubing. The introduction of optical sensing technology in this new tool represents an innovation in production logging. The provided data enable the direct detection and quantification of gas or liquid in multiphase mixtures, allowing the precise diagnosis of well problems and helping design of production enhancement interventions.