Study On Internal Rigid And External Flexible Plugging Agent For Drilling Fluid

Due to the heterogeneity of the formation and the different sizes of pores and fractures,the single size plugging agent can not achieve the effective plugging effect.At present,the strength of rigid plugging agent is high,so it is difficult to adaptively plug micro cracks with different sizes and shapes;Flexible plugging agent has strong adaptability,but its bearing strength is low,so it is difficult to form effective plugging.Therefore,combining the advantages of high strength of rigid plugging agent and strong adaptability of flexible plugging agent,a kind of internal rigid and external soft plugging agent with particle size of micron and a soft plugging agent with diameter of 100 micro meters are prepared.Through the combination of two kinds of plugging agents,the effective plugging of pore and fracture formations with different sizes can be realized,the purpose of stabilizing wellbore in drilling process can be achieved,and the theoretical and technical support for efficient drilling can be provided.Nano silica was used as rigid core.Acrylamide and N-vinyl-2-pyrrolidone were applied as main polymerizing monomers with methylene-bis-acrylamide used as crosslinking agent.In addition,ammonium persulfate sodium bisulfite redox system was used as initiator.An internal rigid external plugging agent PANS with a median particle size of 10.5 microns was prepared by inverse emulsion polymerization.It was evaluated by thermogravimetry,infrared spectroscopy,scanning electron microscopy,rheology,fluid loss reduction,sand bed plugging,nuclear magnetic resonance and other experiments.The results show that the plugging agent has good temperature resistance of 180 ℃,salt resistance and calcium resistance,and can effectively block 80-120 mesh sand bed.Calcium carbonate was used as the rigid core.Acrylamide and 2-acrylamido-2-methylpropane sulfonic acid were applied as the main polymerizing monomers with methylenebis-acrylamide used as crosslinking agent.In addition,ammonium persulfate sodium bisulfite redox system was used as initiator.A kind of soft plugging agent aan with a median particle size of about 600 microns was prepared by solution polymerization.It was evaluated by thermogravimetry,compressive strength,water swelling,rheology,fluid loss reduction and sand bed plugging experiments.The results show that the plugging agent has low expansion ratio,high compressive strength,little influence on drilling fluid rheology,and better fluid loss reduction and sand bed plugging performance than flexible plugging agent.Finally,AAN-1with the best performance was selected.With PANS and AAN-1 as the core treatment agents,a water-based drilling fluid suitable for plugging formation pores and fractures was constructed through the combination of two plugging agents with different particle sizes.The drilling fluid has good properties of rheology,fluid loss reduction and bentonite expansion inhibition,and has strong temperature resistance of 150 ℃ and resistance to bentonite,drilling cuttings and Na Cl pollution.