Oil and gas reserve estimates based on measurements by downhole electrical tools require input data such as the cementation factor m and saturation exponent n obtained from core measurements in the laboratory. Thus,the quality of both the laboratory measurement and downhole measurement determines the overall uncertainty of the data interpretation. The uncertainty associated with the laboratory measurement can be minimized by designing an adequate special core analysis(SCAL)program and taking care of quality assurance. There are several parameters to be controlled to ensure good data quality during a porous plate test with resistivity measurements,such as representative applied net confining stress,equilibrium criteria,corrections of sleeve conformance and brine squeeze off,pore volume compressibility,resistance contribution of the porous plate,excess of conductivity due to clay,temperature variation,or even saturation derived from the material balance. Moreover,comprehensive quality control of these tests requires knowledge of rock characteristics,such as mineral composition and routine core analysis data. This paper presents a description of the porous plate experiment combined with measurement of the rock resistivity at capillary equilibrium. A sensitivity analysis of the resistivity measurement with respect to the various parameters evaluates the degree of impact on the cementation factor and the saturation exponent. Some parameters have a small effect on data quality whereas others can lead to significant error in the calculation of the Archie’s exponents m and n. Precautions are necessary in the laboratory to obtain good data quality and avoid large errors in water saturation calculated from electrical logging techniques.
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