A new method for evaluating the oil mobility based on the relationship between pore structure and state of oil

An accurate evaluation of the shale oil mobility is crucial to its cost-effective exploitation. This study presents a method to assess shale oil mobility by integrating the pore structure and oil states distributions. First, a set of three discrete organic extracts (EOM-A, B and C) were obtained by sequential extraction. The relationships among the EOMs and the oil states were inferred from the group compositions and fluorescence properties of the produced shale oil (free state). The results showed that EOMs A and B represent free oil in the open and closed pores, respectively, while the EOM-C represents adsorbed oil. Then, NMR T₁-T₂ map is used to determine the T_2-cutoff values that indicate the pore size ranges of different oil states. Free oil resides mainly in larger pore space (T₂ > 0.5 ms), while the adsorbed oil in smaller pore space (0.2 ms < T₂ < 0.5 ms). Finally, the ratio of free to adsorbed oil (F/A) > 0.5 and T_2-cutoff > 1.0 ms suggest that the free oil in connected pores has the highest mobility. This work can provide a reference for evaluating the shale oil potential and prospectivity in other regions.