Preparation and characterization of new expansible composite microspheres for use with water-based drilling fluids

In the process of drilling, the filtration of water-based drilling fluid causes the hydration and expansion of the rock near the borehole wall, thus bringing some hidden dangers to the borehole stability. In this work, new expansible composite microspheres (NECMs) are prepared by inverse suspension polymerization using vinyltrimethoxysilane, acrylamide, and 2-acrylamido-2-methyl propane sulfonic acid as raw materials. The results of laser particle size and scanning electron microscopy investigations showed that NECMs are spherical particles with smooth surface, and the particle size was concentrated between 0.2 and 1.78 mu m. The water absorption test shows that the amount absorbed reaches 16.4 g/g in fresh water and 13.03 g/g in 10 g/L NaCl solution. Through the drilling fluid plugging performance test, the results show that when the amount of the composite microspheres added is 0.6 wt%, the American Petroleum Institute filtration loss (FLAPI) value is 8.6 mL at room temperature, the cumulative water loss is 12.6 mL in 2 hours, and the FL(API)is only 13 mL after aging at 150 degrees C for 16 hours. When the addition of NECMs is 1.2 wt%, the average plugging rate of cores is 94.32%. It is indicated that the NECMs have good high-temperature resistance and salt resistance. The soft shell of the composite microspheres has a deformation effect at high temperature, which produces a good deformation plugging effect on the irregular pores. These results show that the microsphere has a good application prospect as a plugging agent for water-based drilling fluid.