Preparation And Properties Of Shale Nano-blocking Agent

Shale gas reserves of China are very abundant,but the shale formation is easily hydrated and expanded,and the reservoir geology is complex,which makes the exploration and development of shale gas in China have certain limitations.At present,China adopts oil-based drilling fluids for shale gas drilling which has good inhibition and lubricity.However,oil-based drilling fluids have high cost and high pollution.So,it is necessary to develop a high-performance water-based drilling fluid suitable for shale gas.One of the reasons for the instability of the well wall is that the water in the drilling fluid enters the shale,resulting the expansion of shale hydration.There are many micropores in shale formation,and the pore size is very small,so the nanometer plugging agent is used to block it and effectively stop water to enter shale.For this phenomenon,nano-shale plugging agent JH-1,JH-2,JH-3 and film-forming nano-microemulsion CMJ-1,CMJ-2,CMJ-3 have been developed,which have good compatibility with water-based drilling fluid.Nanometer polymer microspheres were composed of white oil as the dispersing medium,Span80/Tween80 as compound emulsifier,n-butyl alcohol as auxiliary emulsifier,respectively with AM and AA,cationic monomer DMDAAC,and anionic monomer AMPS as polymer monomers.N,N-methylene bisacrylamide as crosslinking agent,ammonium persulfate and sodium bisulfite as initiator,and prepared by inverse microemulsion polymerization method.Taking particle size,rheological property and API filtration as synthesis indexes,the influencing factors of its performance were studied,and the best synthesis process was finally obtained.The film-forming nano-microemulsion was composed of Span 80/Tween 80 as the composite emulsifier,n-butanol as the co-emulsifier,styrene?St?,methyl acrylate?MA?,butyl acrylate?BA?,acrylamide?AM?and cationic monomer DMDAAC as polymer monomers,azobisisobutyronitrile?AIBN?as initiator.Taking the particle size,rheology,and API fluid loss as the synthetic index,the influencing factors of its performance were studied,and the best synthesis process was finally obtained.An organic/inorganic composite shale plugging system with good rheological and plugging properties was prepared by adding nano plugging agent to drilling fluid formulations which is commonly used in mining site:water+0.2%NaOH+3%sodium formate+1%AP-1+3%?nanometer calcium carbonate+JH-3+CMJ-2?+3%ASP-1250+3%ASR-1+0.3%PAC-HV+0.3%XCD+baryte.It combines the advantages of inorganic nanomaterials and organic nanomaterials.The experimental results show that the drilling fluid formulation has excellent plugging performance,the FL_?HTHP30min?is only 2.9 mL,the rolling recovery rate is93.36%and the linear expansion rate of 24 hours is 9.85%.It can effectively restrain the hydration expansion of shale and effectively solve the problem of wellbore instability.