Well log NMR T_2 measurements of bitumen appear tobe significantly longer than the laboratory results. Thisis likely due to the dissolved gas in bitumen. The T_2distribution depends on oil viscosity and dissolved gassaturation, which may vary throughout the field.Therefore, a method to determine the solution gas andthe in-situ viscosity from NMR logs would be veryuseful in heavy oil and bitumen reservoir development.The viscosity and laboratory NMR measurements weremade on the recombined live bitumen sample and theBrookfield oil (synthetic oil, 100% Poly-Alpha-Olefin)as a function of dissolved gas concentrations. Theeffects of three major reservoir gases (CH_4, CO_2, C_2H_6)on the viscosity and T_2 response of these two heavy oilsat different saturation pressures were investigated.The measured T_2 of live heavy oil is significantly largerthan the T_2 of dead oil, even at the lowest pressure levelin this work (～ 100 psia). The live oil T_2 is found tohave a linear correlation with both saturation pressureand gas concentration on semi-log scale for all threegases. Our calculations show that, at same saturationpressure, CO2 generally has the largest solubility amongthe three gases especially at the lower pressures, whileCH4 appears to be the least soluble. However,considering the efficiency of these three gases onchanging the oil T_2, the effect of C_2H_6 or CH_4 on the T_2change are close to each other, while CO_2 has a muchless significant impact for the same amount of dissolvedgas (in moles).The investigations on live oil viscosity show that,regardless of the gas type used for saturation, the liveoil T_2 correlates with viscosity/temperature ratio on loglogscale. More importantly, the changes of T_2 andviscosity/temperature ratio caused by solution gasfollows the same trend of those caused by temperaturevariations on the dead oil. This conclusion holds forboth bitumen and the synthetic Brookfield oil. Thisinteresting finding on the relationship between the oilT_2 and its corresponding viscosity/temperature ratiocreates a way for in-situ viscosity evaluation of heavyoil through NMR well logging.
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