Tightoil poses huge reservoir in many countries. Due to the poor reservoir properties, such as nanometer to micrometer pores, low permeability, energy deficiency, the oil recovery in tightoil reservoir is very low, even with horizontal drilling and hydraulic fracturing. The small pores are featuring large capillary pressure thus spontaneous imbibition. Surfactant would accelerate this process. However, due to the small amount of oil in core, the accurate recording of oil recovery is challenging, especially during dynamic imbibition within fracture matrix system. Nuclear Magnetic Resonance (NMR) T2 spectra was used to characterized the migration of oil and water in pores and throats during dynamic imbibition. Various phenomenons are revealed and proved by T2 spectra figure, such as: water imbibed into small pores, oil expelled from large pores, and oil film formed on fracture face. The oil recovery during dynamic imbibition was examined online during experiment from the peak area generated by T2 spectra. Before and after the dynamic imbibition, Magnetic Resonance Imaging (MRI) was used to compare the saturation and distribution of oil in the core sample. When the oil drop migrates out of the pores, it will emerge from the surface of rock sample. Its shape on top, lateral, and bottom of the sample was observed with a long distance microscope. Their growth in width and height was compared carefully. The growth rate was categorized into different stages, and quantitatively compared.

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