A new method of determining three phase holdups in horizontal wellbores using pulsed neutron tools has been field tested. A two variable, linear algorithm using the measured inelastic carbon/oxygen and near/far ratios is used to determine holdups. The measurement is fully characterized by Monte Carlo modeling. Laboratory data shows the accuracy of the holdup calculation to be approximately 10%. The method produces a continuous borehole image of the volume fractions of the water, oil, and gas in the borehole. Log examples demonstrate the use of the Pulsed Neutron Holdup Imager in horizontal well production logging and in production logging behind tubing.
Three phase hold-up data are essential for remedial action in wells that produce unwanted water and gas. The traditional production logging tool suit consisting of temperature, pressure, fluid capacitance, fluid density, spinner flowmeter and gradiomanometer sensors has proven its utility for production monitoring in vertical wells. In horizontal wells, however, the interpretation of the holdup measurements from conventional production logging instrumentation becomes unreliable due to the fluid segregation. Thus, there is a strong motivation for devising an alternate method of measuring holdups with improved accuracy in horizontal wellbores.
Nuclear measurements offer a method for measuring three phase holdups in horizontal wells with increased accuracy. In contrast to the traditional production logging tools which measure at a localized position in the borehole volume, nuclear measurements average over a larger volume and are relatively insensitive to the segregation and layering of the flow components in horizontal boreholes. Additionally, in single or dual string completions, nuclear measurements can measure nuclear responses through the tubing wall and, therefore, image the annular region of the wellbore that is physically inaccessible to direct measurement. Further, the nuclear measurement offers the possibility of imaging the holdups covering the whole borehole, including by-passed flow around slotted liners and screens.
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