Preparation, characterization and properties of SiO2 expansible composite microspheres for water-based drilling fluid

In the process of drilling for oil and gas, plugging materials are used to effectively plug the formation pores and microfractures and thus ensure the stability of the wellbore. In this work, SiO2 expansible composite microspheres (SECMs) were prepared by inverse suspension polymerization using SiO2, vinyltrimethoxysilane, acrylamide, and 2-acrylamido-2-methyl propane sulfonic acid as raw materials. The results of infrared spectroscopy, laser particle size, thermogravimetric analysis, and scanning electron microscopy investigations show that the SECMs are homogeneous. They are spherical in shape with a median particle size of 19.38 μm and a particle size distribution that is relatively uniform. They also have good water absorption and expansion capacity. After 24 h, the average particle size of the SECMs was 34.4 μm, which was 77% higher than the average particle size before water absorption. The SECMs were further investigated by adding them to a low-solid water-based drilling fluid containing 4 wt% bentonite. Plugging tests carried out using the drilling fluid showed that the SECMs can significantly reduce the filtration rate of the drilling fluid. A 0.6 wt% dose of the SECMs led to a FLAPI value of 13 mL. This dropped to 11 mL after aging at 150 °C for 16 h. This shows that the SECMs have a good resistance to high temperatures and that the soft shells of the microspheres deform at high temperature which improves the sealing effect in irregularly shaped pores.