--> Reassessment of the Nuclear Magnetic Resonance (NMR) Fluid Typing Methods in Shale

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Reassessment of the Nuclear Magnetic Resonance (NMR) Fluid Typing Methods in Shale

Abstract

The emergence of shale reservoirs as a potential resource for energy supply directs research to analyze these reservoirs. Nuclear Magnetic Resonance is one of the used tools for prospect evaluation which proved its applicability in both conventional and unconventional reservoirs. However, Shale reservoirs characteristics including pore size, organic matter, clay content, wettability, adsorption, and mineralogy add complexity to the interpretation methods. Different challenges are noticed during the analysis process including the inapplicability of the controlling equations that were derived assuming fast relaxation mechanisms, the overlap among the fluid peaks and the lack of robust correlation to estimate fluid properties in shale. Consequently, an experimental and theoretical re-evaluation was important to compare the different existing fluid typing methods and correlations. The study involves one-dimension and two-dimension methods along with the doping agent's applications. Furthermore, fluid properties estimation such as density, viscosity, and the gas-oil ratio is included. The abundance of different typing methods should boost the identification process, however, unfortunately, shale heterogeneity limit the applicability of most of them. The T1-T2 method is the most appropriate method for fluid typing in shale. As, the high internal gradients confronted in shale would limit the applicability of most of diffusion based methods. Moreover, the accuracy of the fluid properties estimated will tied to the efficiency of extracting the bulk relaxation response. Although most current correlations were derived for pure alkane components, the mixing rules proposed in the literature could extend their applicability to the multicomponent systems. The fluid properties estimation from NMR measurements in shale is challenging and needs more experimental work to develop reliable correlations and properly calibrate the devices. The fluid typing in shale is a complicated process, but it would be better performed by well-understanding of the shale system on one side and developing robust identification methods on the other side.