DOWNHOLE ENTHALPY MEASUREMENT WITH FIBER OPTICS
Studies investigating ways to measure enthalpy down hole have been in progress at Stanford University for the last three years. So far, the void fraction and the dispersed-phase velocity, which are the two essential factors required for calculation of flowing enthalpy, were determined by using resistivity and photosensors. Currently, research efforts have been oriented toward measuring down hole enthalpy by fiber optics. After discussing the applicability of using horizontal or vertical fiber tips, this paper describes the usage of normal reflection probe with the tip surface cut at a right angle to the fiber axis to investigate the void fraction initially in water-air flow then in water-steam flow. The calibration curve was obtained by correlating the void fraction given by the fractional flow ratio detector (FFRD) and the calculated local void fraction. Successful results were obtained for the slow bubble flow case. Future work includes determining the bubble velocity, and testing the device in a model wellbore.
Optical fiber probe to measure local void fraction profiles.
A fiber optic probe for measuring the local void fraction in a two-phase (air-water) flow has been developed. The liquid-gas and gas-liquid interfaces are detected by the normal reflections of IR laser light at the tip of a multimode fiber. The probe and its associated electronic circuitry were calibrated by using the averaged void fraction measured by a quick closing valve system. The void profiles obtained by this method were compared with those obtained by a conductivity local probe. The proposed optical system shows a better sensitivity at high void fractions.
Structure of air-water bubbly flow in a vertical pipe—I. liquid mean velocity and turbulence measurements
Abstract The liquid-phase turbulent structure of an air water, bubbly upflow in a circular pipe has been investigated experimentally. Liquid-phase local velocities and turbulent stresses were simultaneously measured, using both one- and two-dimensional hot-film anemometer probes. A highly-accurate digital process method, based on threshold combinations of level and slope, was developed to identify the phases. Systematic measurements were conducted under 48 flow conditions covering a range of local void fraction from 0 to 50%. The important experimental results and parametric trends are summarized and discussed. Finally, the present data are compared with some other data sources and existing models.