Partitioning Tracers and ln-Situ Fluid-Saturation Measurements

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Abstract
Summary: This paper reviews applications of partitioning tracers in the petroleum industry. Partitioning between phases slows the partitioning tracers in a phenomenon known as chromatographic retardation, from which fluid saturations and surface properties can be deduced. Single-well tracer testing (SWTT) to determine residual oil saturation to waterflood, Sorw, is the most common application of partitioning tracers. More than 200 tests have been run since its invention in 1971. In addition to development of new simulators, a mass-balance method and an internally calibrated method were proposed for direct calculation of Sorw from the tracer reaction rates. With the introduction of the chromatographic transformation technique, several successful interwell tests to determine residual oil saturations in watered-out and gas-saturated reservoirs have been reported. The technique involves direct comparison of the partitioning and nonpartitioning tracer profiles with no need for simulation. In a different approach, full-field simulation of a multiwell test has also been used to estimate oil saturation distribution. Other interesting applications include in-situ miscibility measurement, determining trapped gas saturation during a foam flood, relative permeability ratio measurement, and direct logging of gamma-emitting partitioning tracers through casing to determine residual oil saturation, Sor, vertical distribution.

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