VALIDATING LABORATORY MEASURED ARCHIE SATURATION EXPONENTS USING NON-RESISTIVITY BASED METHODS

Archie’s second law has considerable impact on calculated water saturation, especially in the low to intermediate water saturation range. Despite this fact, Resistivity Index (RI) measurements for our limestone reservoirs were sparse and performed at non-reservoir representative conditions. Our lack of knowledge of the proper saturation exponent to apply forced us to use the industry standard value of two. To rectify the situation, reservoir condition RI experiments were carried out using different techniques on separate reservoir units. The first experiment employed the traditional porous plate with continuous scanning, live crude and hot toluene cleaned core plugs. The second experiment used fresh state core, dead crude oil, and the Fast Resistivity Index Measurement (FRIM) technique. The third technique employed “as received” single point RI measurements on plugs drilled from an oil base core. All three methods were performed at reservoir temperature and simulated overburden pressure. To give us confidence in the “correctness” of the saturation exponents measured, we compared water saturation obtained with non-resistivity based methods to water saturation calculated with our new Archie parameters.