Preparation and performance study of nano styrene-acrylate emulsion plugging agent for drilling fluid

Abstract:

To address the wellbore instability caused by nano-micro-scale pores and fractures in deep shale formations， a nano styrene-acrylate emulsion plugging agent was synthesized via semi-continuous seed emulsion polymerization using styrene， butyl acrylate， acrylic acid， acrylamide， and 2-acrylamido-2-methylpropanesulfonic acid as monomers， and its structural characterization and performance evaluation were carried out. The results show that the emulsion has a median particle size （D₅₀） of 174.5 nm with a unimodal distribution； the particles are spherical or nearly spherical and stably dispersed， and the solid content is higher than 80%. After hot-rolling aging at 180 ℃ for 16 h， the high-temperature and high-pressure （HTHP） fluid loss of the drilling fluid decreases with increasing emulsion dosage， while the API fluid loss reaches its minimum at a dosage of 2.5%. Considering both fluid loss control performance and economic efficiency， the optimal dosage is determined to be 2.5%， under which a thinner and denser filter cake is formed and the reduction rate of clear-water fluid loss of the filter cake reaches 41.7%. The emulsion exhibits favorable compatibility with conventional drilling fluid additives. After aging at 150 ℃， compared with the blank system， the HTHP fluid loss of the nano-emulsion-containing system decreases from 15.3 mL to 13.2 mL， and the 10 μm sand-disk fluid loss decreases from 7.2 mL to 5.6 mL， indicating good plugging performance for micron-sized fractures， improved filter-cake quality， and beneficial effects on wellbore stability.