Imbibition Replacement Rules of Bedding Shale in Lucaogou Formation in Jimsar Sag,Junggar Basin
In order to investigate the production of crude oil during the imbibition period after hydraulic fracturing of the bedding shale in the Permian Lucaogou formation in the Jimsar sag,core imbibition replacement experiments and nuclear magnetic resonance(NMR)tech-nology were combined to quantitatively describe the relative content of crude oil in different pores.Cores from the upper sweet spot in Jim-sar sag were used in the experiments to identify the impacts of gravity,anisotropy,gravity differentiation,and hydraulic fracture width on imbibition replacement and quantitative characterization was conducted.The results show that during the spontaneous imbibition process of bedding shale,gravity plays a dynamic role,and the recovery of top imbibition is higher than that of horizontal imbibition.Anisotropy has a significant impact on imbibition of bedding shale,with a larger imbibition displacement of fracturing fluid into parallel bedding and a short-er period to reach imbibition equilibrium compared to vertical bedding,and imbibition recovery of parallel bedding is higher than that of vertical bedding.Gravity differentiation means that during the imbibition at the bottom of the core,the crude oil is displaced by imbibition and stays on the surface of the core to form an oil film,which prevents the fracturing fluid from further entering the matrix,deteriorating the imbibition effect.The recovery of imbibition at the bottom differs by 14.12%from the recovery of imbibition at the top.Given a simulated hydraulic fracture width of 2 mm,the volume of liquid involved in imbibition replacement is limited,causing a rapid decline of water satura-tion within the simulated fracture,which restricts further imbibition.Therefore,the fracture height should be oriented to pass through paral-lel bedding,so that the fracture width and the stimulated reservoir volume can be increased.
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