| Oil-based drilling fluids have the advantages of good high temperature stability,strong anti-collapse ability and good lubricity,and have become the first choice for drilling shale gas formations.Due to the development of pores and micro-fractures in shale formations,oil-based drilling fluids have been leaking seriously and drilling costs have increased significantly.Commonly used hydrophilic plugging materials have poor compatibility with oil-based drilling fluids,resulting in low plugging success rate and weak pressure bearing capacity after plugging.Therefore,there is an urgent need to carry out research on new materials for leakage prevention and plugging of oil-based drilling fluids in shale gas formations.Regarding present problems,A new type of high oil-absorbing resin leakage while drilling plugging agent was prepared by the suspension polymerization method.Through orthogonal experiments and single factor analysis,the effects of soft branch monomers,hard branch monomers,initiators,crosslinkers,dispersants,tougheners,polymerization temperature and polymerization time on the oil absorption rate and crosslinking degree of the resin are studied.influences.The best synthesis conditions are as follows:the ratio of soft branched chain monomer A: monomer B is 2:1,the amount of hard branched chain monomer accounts for 1% of the monomer mass,and the amount of initiator accounts for 0.3% of the monomer mass,cross-linking The dosage of the agent accounts for 0.16% of the monomer,the dispersant accounts for 2% of the monomer mass,the toughening material concentration is0.8%,the optimal polymerization temperature is 85°C,and the optimal polymerization time is5 h.The molecular structure,microstructure,oil absorption swelling experiment,rheological properties and compatibility properties of the plugging agent were studied by infrared spectroscopy,electron microscope scanning,oil absorption swelling test,rheological analysis and compatibility experiments.Experiments show that the plugging agent has good oil absorption and expansion performance.The filling of inert materials increases the spatial network structure of the resin plugging agent,and the toughness is stronger.The plugging agent has good shear performance,G’ > G’’,and G’ can reach up to 80 kpa.The performance is stable at high temperature,does not react with the components of the drilling fluid,and has little effect on the rheology of the base slurry.Through sand bed filtration experiment,high temperature and high pressure filtration experiment,fracture module plugging experiment and high temperature and high pressure displacement experiment,the pressure-bearing plugging of the plugging agent was studied.In the sand bed loss experiment and high temperature and high pressure filter loss experiment,the filter loss is used as the evaluation standard,and resin plugging particles of different concentrations and different particle sizes are selected,and the optimal addition of the oil-based drilling fluid while drilling plugging agent is optimized.Under the condition of120 ℃,the resin particle plugging agent compound is used for the crack plugging experiment with a crack width of 1 to 3 mm,and the pressure bearing capacity can reach 7.6 MPa.The process of particle migration,filling,plugging and instability in fractures is studied through visual models.Based on the macro-scale and micro-scale,the process of particle migration in fractures is revealed,including particle entry and particle bridging.,Particle aggregation and particle deformation and extrusion.It is found that the bridging of particles in the cracks is mainly affected by physical trapping.In addition,settlement,accumulation,and accumulation in the cracks are also important forms of crack plugging,so as to achieve effective plugging.The instability mechanism of the accumulation layer was studied,including the failure modes of particle shear dislocation instability,frictional sliding instability,and crushing instability. |
