Tight oil reservoirs present a unique opportunity fordielectric dispersion logging. Dielectric logging issensitive to the water content and provides water-filledporosity without having to know Archie’s empiricalparameters or water salinities, as is required withresistivity log interpretation. Moreover, because of theextremely low permeability of the shale reservoirs, thereis effectively no invasion of the borehole fluids into theformation. Thus, in these reservoirs, dielectric dispersionlogging directly provides the water-filled porosity of theundisturbed zone.In this paper, we investigate the interpretation of thedielectric dispersion measurements in tight oilformations. A representative core collection wasobtained from two intervals in a field. The core materialwas characterized in terms of lithology and total organiccarbon (TOC) content. The cores were cleaned andsaturated with brines that match the formation watersalinities. Next, the dielectric dispersion measurementson cores were obtained under controlled laboratoryconditions of pressure, temperature, and brine salinity.On the basis of the analysis we conducted on these data,we have developed a new method for the interpretationof multifrequency dielectric logs in tight oil reservoirs.The new method has a significant advantage over theexisting approaches because it does not require an inputfor either matrix or hydrocarbon permittivities, includingkerogen permittivity, to derive water-filled porosity as isthe case with the existing approaches. The new methodenables the elimination of all associated uncertaintieswith formation mineral models in complex lithologies,unknown mineral permittivity endpoints, and, mostimportantly, the poorly defined permittivity of kerogen.The new method requires only the relatively well-knowninput of formation temperature. Thus, the new methodprovides a more robust, streamlined, and consistent interpretation of the dielectric dispersion logs in tight oiland reduces the uncertainty on the estimate ofhydrocarbon in place.
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