Experimental Research of Imbibition Law in the Continental Shale in Sichuan Basin in China

Marine shale has been developed successfully in China, however, the exploration and development of the continental shale is still limited. Study about imbibition and influence factors of the continental shale is insufficient. The objective of the proposed paper is to design and conduct an imbibition experiment to research imbibition rate, imbibed volume, induced crack and influence factors in the Jurassic continental shale in Sichuan basin in China. The imbibition experiment is developed based on the low field Nuclear Magnetic Resonance(NMR) and accurate weighting. The permeability, porosity and mineral composition of shale samples of LU Formation and DD Formation are measured and the differences are analyzed. The change of permeability and porosity before and after the imbibition process is set as the evaluation index and the influence factors of imbibition in the continental shale are analyzed. The influence factors include lithology, imbibition fluid, imbibition pressure and clay content. Besides, the wettability of the continental shale is estimated in the experiment. The experimental results show that the imbibition capacity of the limestone sample is weaker than that of shale samples, and the shell limestone interlayer in the continental shale reservoir may inhibit the imbibition and crack propagation in the shale. Oil phase may enhance the crack propagation after the shale samples induced crack in aqueous phase, and the complicated phase imbibition in the continental shale reservoir may be beneficial to the permeability improvement. The forced imbibition has weaker capacity of crack induction and permeability improvement compared to the spontaneous imbibition, and the influence of the reservoir confining pressure on the imbibition should be considered during the well shut-in process after hydraulic fracturing. The higher clay content shale sample has stronger capacity of crack induction and permeability improvement compared to the lower clay content shale sample. The wettability of the continental shale sample is water-wet. The imbibition experiment reveals the imbibition law and the induced crack character of the continental shale samples, whose results fill the gap in existing studies and have a theoretical guidance for the shut-in and flowback design in the continental shale reservoir.