Preparation Of Expandable Composite Microspheres And Their Application In Drilling Fluids

In the process of drilling,the filtration of drilling fluid causes the hydration and expansion of the rock near the wellbore,which brings certain hidden trouble to the stability of the wellbore.In recent years,scholars at home and abroad have done some research on this issue and made some achievements,but the irregular pore in rocks and mud cakes cannot be sealed.In this paper,expansible composite microspheres are used as plugging agent for water-based drilling fluid,and their structure and performance are also discussed.Silica was modified by Vinyl trimethoxysilane(VTMS),the improvement conditions were optimized by single factor experiment.The SiO2 expansible composite microspheres(SECMs)were synthesized from modified SiO2,acrylamide(AM)and 2-acrylamide-2-methylpropionic sulfonic acid(AMPS)by reverse phase suspension polymerization,and the synthesis conditions were optimized.The Infrared spectroscopy(FT-IR)showed that the SECMs were synthesized by polymerization reaction between modified SiO2,AM and AMPS.Thermo-gravimetric analysis showed that SECMs had great heat temperature resistance.SEM and particle size analysis showed that SECMs were spherical with good regularity and dispersion,and its particle size(d0.5)was 19.38μm.The water absorption ratio test showed that SECMs had certain water absorption expansion performance,and the water absorption ratio was 45.3g/g after 24 hours.Polyhedral oligomeric silsesquioxanes(POSS)was synthesized by silane coupling agent VTMS,then POSS expandable composite microspheres(PECMs)were synthesize from POSS,AM and AMPS by reverse suspension polymerization.The synthesis conditions were optimized by orthogonal experiment.Infrared spectroscopy(FT-IR)showed that the PECMs were synthesized.Thermal gravimetric analysis showed that the synthesized PECMs had good temperature resistance.SEM and particle size analysis showed that PECMs were spherical with good regularity and dispersion,and its particle size(d0.5)was 0.485μm.The water absorption ratio test shows that PECMs had certain water absorption expansion performance,and the water absorption ratio was 16.4g/g after 24 hours.Through testing rheological properties,filtration performance test,high temperature aging test,the cumulative filtration experiment,scanning electron microscopy(SEM)test of mud cake and expansible composite microspheres compounding test,the plugging performance of expansible composite microspheres was evaluated.The results showed that the filtration loss of drilling fluid decreases with the increase of the mass fraction of expansible composite microspheres.When the mass fraction of SECMs was 0.9%,the API loss of drilling fluid was 12 mL,and the cumulative loss was 23 mL in 2 hours.The API loss of drilling fluid was only 8 mL after aging at 180℃ for 16 hours.When the mass fraction of PECMs was 0.9%,the API filtration capacity was 7.2 mL,the cumulative filtration capacity was 10.9 mL in 2 hours,and 13 mL after aging at 180℃ for 16 hours.SECMs and PECMs were micron and nano-sized particles respectively.The two kinds of composite microspheres were compounded in different proportions.The microspheres can physically plug the pore of mud cake after water absorption and expansion,and seal the irregular pore with different pore sizes through synergistic action.The results showed that when the ratio of the two microspheres was 1:1,the rheological properties and filtration capacity of drilling fluid were better before and after aging.Through the optimization,compounding and evaluation of other drilling fluid additives,a set of drilling fluid system with good performance was finally established:4%bentonite+0.2%Na2C03+0.45%SECMs+0.45%PECMs+I%SMP-1+2.5%FA367+barite powder,The comprehensive test of drilling fluid showed that the system had excellent rheological property,filtration loss reduction,temperature and salt resistance,and had a good application prospect.