Study of the Imbibition Behavior of Hydrophilic Tight Sandstone Reservoirs Based on Nuclear Magnetic Resonance

Hydraulic fracturing is one of the key technologies to enhance the oil recovery from tight sandstone reservoirs. The study on the behavior of imbibition for tight sandstone reservoir is of great significance to increase oil production after fracturing. In this paper, nuclear magnetic resonance (NMR) and high-pressure mercury injection were implemented on the samples taken from the Yanchang Formation of the Ordos Basin. The NMR T 2 curves of the core at the state of 100% water saturated were converted to pore-throat radius distribution curves. On this basis, the experiments of imbibition and displacement were conducted and the changes of fluid distribution, imbibition quantity, and imbibition rate with different scale pores and different imbibition times were analyzed. Moreover, the results of imbibition and displacement were compared to assess the distribution of the recoverable and remaining oil under two exploitation modes and the contribution of imbibition made to displacement in pores at different scales. The result shows that imbibition is a relatively slow process. The entire imbibition process is mainly affected by nanopores, which are widely distributed in cores, and the imbibition rate of total pores constantly decreases as the imbibition time increases. Moreover, the relative recovery in pores at different scales shows a huge difference under the two exploitation modes of imbibition and displacement. During imbibition, smaller pores produced higher degrees of oil, while during displacement, larger pores have higher relative recovery. The contribution of imbibition made to displacement in nanopores was the highest and decreased with the increase of the pore-throat size.