Application of NMR core experimental analysis in evaluation of low-porosity and low-permeability sandstone reservoirs

Nuclear magnetic resonance (NMR) core experimental analysis is a new developing technique in experi-mental geology. Based on the principles and methods of NMR core experimental analysis, as well as some improved parametric models, a series of reservoir parameters of Chang6 low-porosity and low-permeability oil-bearing sandstone core samples from well 3062 in the ZC Oil Field in the eastern Ordos Basin were systematically measured by NMR. Additionally, the accuracy and relative error of the NMR analysis were calculated and discussed by means of recognized exact method of conventional core experimental analysis as control group. It is revealed that the Chang6 oil-bearing sandstones are typical low-porosity and low-permeability reservoirs, with porosity ranging from 8.6% to 13.0%, and permeability from 0.07×10^-3 to 1.27×10^-3 μm². NMR core experimental analysis has advantages of convenience, high efficiency and accepted accuracy with a smaller relative error for testing the low-porosity and low-permeability reservoir parameters of porosity, microscopic pore structure and irreducible water saturation. However, compared with the results of conventional core analysis, there is a larger relative error in NMR prediction for the permeability parameters, which is most probably due to some uncertainty of the reservoir permeability predictive models.