Quantitative characterization of bound and movable fluid microdistribution in porous rocks using nuclear magnetic resonance

Porous rocks are the source of important energy resources such as oil and gas that support development worldwide. The quantitative characterization of bound and movable fluid microdistribution is important for reservoir evaluation, productivity prediction, and petroleum recovery. However, due to the complexity of the fluid microdistribution in porous rocks, there is currently no effective method to achieve the continuous and quantitative characterization of the downhole or subsurface bound and movable fluid microdistribution. In this study, a method is proposed for the continuous and quantitative characterization of bound and movable fluid microdistribution in porous rocks based on nuclear magnetic resonance (NMR) measurements. First, 19 conventional sandstone samples collected from the Songliao Basin and 19 tight sandstone samples from the Ordos basin in China were evaluated using NMR experiments under fully water-saturated and bound water conditions and the transverse relaxation time (T2) distributions of the saturated, bound, and movable water were obtained. Based on the findings from the NMR experiments, two exponential functions were proposed to quantitatively characterize the proportional coefficient distribution of the bound and movable fluids in pores of different sizes and to obtain the corresponding T2 distributions of the bound and movable fluids. The effectiveness of the proposed method was verified by comparing the prediction results with the experimental results. Finally, the proposed method was extended into field applications in a tight sandstone reservoir in the Ordos Basin, China. The results of this study provide practical guidance for the exploration and development of oil and gas resources. •A fluid microdistribution characterization method in porous rocks was proposed.•Two exponential functions were used to characterize fluid proportions in pores.•The results are intuitive display of the bound and movable fluid microdistribution.•The proposed method provides guidance for further pore structure and seepage study.