Research and Evaluation of a Nanometer Plugging Agent for Shale Gas Horizontal Wells

Due to the low permeability of shales, drilling fluid filtrate is very likely to intrude into the formation along the nanomicron pore joints of shale, leading to microfracture expansion and causing a well wall destabilization phenomenon. Based on the characteristics of the formation shale, a new nano plugging agent, styrene (St)/2-acrylamido-2-methylpropanesulfonic acid (AMPS)/ethyl acrylate (EA), was synthesized by emulsion polymerization using St, EA, and AMPS as reaction monomers. The analysis results using infrared spectroscopy and transmission electron microscopy showed that the product met the expected design. The particle size of the nano plugging agent St/AMPS/EA was mainly concentrated in the range of 50-130 nm. Thermogravimetric analysis revealed that the initial thermal decomposition temperature of St/AMPS/EA is 363.8 °C, indicating strong thermal stability. At a 3% concentration, the permeability of the mud cake decreased by 87.35%, and the maximum differential stress of the shale increased from 141.7 to 174.4 MPa. Stability analysis showed that the plugging agent maintained good plugging performance under various pH values and salinity conditions with fluid loss consistently around 3.2 mm. This nano plugging agent significantly improves wellbore stability, making it suitable for drilling in the Longmaxi Formation shale with developed microfractures, and provides valuable insights for similar formations.