Preparation and Performance Study of Plugging Agents for Deep Shale Based on Montmorillonite Modification
Natural fractures are developed in the deep shale,which are generally micro/nanoscale fractures.However,the existing micro/nanoparticle plugging agent is easy to agglomerate and usually used in a large amount,resulting in downhole failure and complex situations including wellbore instability and sticking.In order to solve this problem,nano-montmorillonite was prepared from layered montmorillonite,and then the surface of nano-montmorillonite was modified by atomic transfer radical polymerization.The hydrophobic nano-plugging agent N-MMT was synthesized.It was characterized by infrared spectrum,energy spectrum analysis,particle size analysis,and scanning electron microscope,etc.The plugging performance of N-MMT was evaluated by core imbibition experiment,microporous filtration membrane filtration test,and high-temperature aging test.The experimental results show that the nano-plugging agent N-MMT has a pre-designed group with an average size of 526 nm,which can significantly reduce the self-imbibition capacity of shale core,and the self-imbibition amount of shale core is decreased by 66.67%.N-MMT has good compatibility with conventional treatment agents for oil-based drilling fluid,which reduces the high-temperature and high-pressure filtration loss by 47%.In addition,it increases the emulsion-breaking voltage and enhances the stability of the system.Nano-plugging agent N-MMT can adhere to the surface of shale micro and nano pores to form a tight plugging film,preventing drilling filtrate from entering fractures in deep shale and protecting the borehole stability,and has certain application foreground.
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