Determining injection flow profiles for various injected fluids was part of the surveillance program for monitoring the performance of Exxon's surfactant flood pilot test recently conducted in the Loudon Field, Fayette County, Illinois. Injection profiles for brine, microemulsion, and polymer drive water were measured using a radioactive tracer flow log. Profiles measured for brine injected prior to the microemulsion flood were in reasonable agreement with absolute permeability profiles determined by core analysis. However, for microemulsion injected in these same intervals, the profiles were found to be erroneous and completely misleading. For the viscous microemulsion, the profiles consistently indicated that all injected fluid was entering the upper one foot of the 13-foot-thick open-hole sandstone interval, thus suggesting the existence of horizontal fractures.

Poor dispersion of the radioactive tracer in the viscous microemulsion was believed to be responsible for the anomalous responses. To study the performance of the tracer flow log tool in water and in viscous solutions containing polymer, tests were performed in a visual flow loop using colored dye as a substitute for the radioactive tracer. Results confirmed that the tracer ejection system of the conventional tool usually ejected the tracer directly onto the casing wall where the velocity was substantially less than the average fluid velocity in the casing-tool annulus. When the flowing fluid was water, the turbulent jet of ejected tracer rebounded from the casing wall and was dispersed. However, when the fluid contained polymer, viscous laminar flow dampened dispersion of the tracer and retained it near the pipe wall, thus causing the interpreted flow rate to be essentially near zero.

To mitigate this problem, the ejection system of the tool was modified to allow tracer to be ejected closer to the center of the casing-tool annulus where the tracer velocity would be in better agreement with the average fluid velocity. A modified tracer flow log was subsequently used to redetermine injection profiles for microemulsion and polymer drive fluid in the Loudon pilot wells. Profiles measured by this modified tool were in reasonable agreement with profiles measured earlier for brine injection and with profiles of absolute permeability from core data.

Results of these experiments therefore show that injection profiles for viscous fluids measured by a conventional radioactive tracer flow log are likely to be unreliable. However, the log tool can be modified to provide reasonable results.

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