MEASUREMENT OF OIL AND WATER-FLOW RATES IN A HORIZONTAL WELL WITH CHEMICAL MARKERS AND A PULSED-NEUTRON TOOL

A new approach to obtaining oil and water flow rates in producing hori zontal wells has been developed with a pulsed-neutron tool (PNT). This approach uses separate measurements of oil and water velocities in co mbination with separate holdup measurements to obtain the flow rates. The velocity measurement uses water-soluble and oil-soluble chemical m arkers, both of which are insoluble in the other fluid phase for the m easurement. The markers are injected into the borehole by a logging to ol at one location and detected by a PNT at a second location. The tra nsit lime between injection and detection of the marker gives a measur ement of the fluid velocity. Because the markers are soluble in only o ne phase, the velocity of each phase can be measured separately. This measurement has been made under both laboratory and field conditions t o measure velocities from 10 to 500 ft/min at horizontal and several d egrees deviation from horizontal. The results of these tests show good linearity and repeatability of the measurement. The holdup measuremen t is performed with the inelastic data from a PNT With these data, it is possible to obtain quantitatively the holdup of all three phases by combining information from the inelastic near/far (N/F) ratio with th e near and far carbon/oxygen (C/O) ratios. This approach to the holdup measurement has been demonstrated by use of a combination of laborato ry data, Monte Carlo modeling, and field data. The results of this stu dy have demonstrated that the root-mean-square (RMS) accuracy of this measurement is about 6% on each of the three phases.