Fremgangsmåter for prøvetakning samt anordning for bruk i borehull

The invention concerns a method of sampling the formation fluids in an earth formation surrounding a borehole, the region of the formation immediately surrounding the borehole being at least partially invaded by borehole fluids, and an apparatus for carrying out such a method. According to the invention, a borehole tool is adapted to be lowered into the borehole and is provided with a sampling probe device and means for urging the sampling probe device into contact with the borehole wall, the sampling probe device comprising an inner probe and an outer probe surrounding the inner probe for withdrawing respective fluid samples from the formation, wherein the ratio between the respective flow areas of the inner and outer probes is selected so as to tend to reduce the time taken to obtain via the inner probe a sample of the formation fluids having a given level of contamination by borehole fluids.