Patent ID: 6786086
Filing Date: 2004-09-07
Classification: E21B

Abstract:
A method for determining the average in situ permeability of a formation layer traversed by a borehole, the steps comprising:a) selecting a set of locations in the formation layer; b) selecting from the set a first location; c) lowering a formation test tool in the borehole to the location, the tool comprising a central conduit having an inlet and being provided with a pressure sensor, a fluid receptacle in fluid communication with the central conduit, a optical fluid analyzer, a fluid sample chamber in fluid communication with the central conduit, and means for discharging fluid; d) establishing an exclusive fluid communication between the formation layer and the inlet of the central conduit; e) inducing formation fluid to flow from the formation layer through the central conduit, entering the fluid receptacle, and measuring formation fluid pressure build-up; f) determining formation permeability and formation fluid mobility from the pressure build-up; g) positioning the tool near a next location in the set and repeating steps d) through f), determining the formation fluid mobility at of the locations in the set; h) determining the location in the set having the highest mobility, the effective mobility, calculating the permeability for this location based on viscosity of the uncontaminated formation fluid and effective mobility, and determining viscosity of contaminated formation fluid using the permeability and the effective mobility for that location; and i) recalculating the permeabilities for the other locations in the set using the viscosity of the contaminated formation fluid and the mobility measured in step f), for that location and calculating the average of the permeabilities.