Abstract: Laojunmiao oilfield in Yumen is the oldest field in China developed with modern technologies and by waterflooding process. Since 1967, several methods such as well logging, reservoir engineering, core analysis, numerical simulation and water salinity analysis have been adopted for study the residual oil distribution in reservoirs in different periods or stages of development. However, the studies have shown that each of these methods has both peculiarity and limitation of its own. It is indicated that isotopic tracer injection is more suitable for revealing in-situ oil-water distribution and residual oil status. The principle of this technique includes that two isotopic tracers are injected into injection wells. The peak concentration change and the time-difference of the tracers produced from opposite oil wells will be shown on their curves. Then, the injection-production relations analysis, the reservoir heterogeneous parameters determination and the residual oil saturation evaluation are conducted using the tracer interpretation software in terms of chromatographic fractionation theory and convection-diffusion theory. Such an isotopic tracer technique has been used to Wellgroup-4252 of M pool in Laojunmiao oilfield. It is indicated that it is a simple, visual and effective method for study of the residual oil distribution in this old oilfield by waterflooding process.

Key words: Yumen oilfield, Mpool, isotopic tracer, injection-production performance, reservoir parameter, residual oil saturation