Environmentally Friendly Rosin-Modified Silica Nanocomposite as High-Performance Plugging Agent for Drilling in Nano-Microporous Formations

Summary The increasingly severe wellbore instability problem and the intensified environmental requirements necessitate the development of high-performance and environmentally friendly plugging materials for drilling fluid. In this work, a novel core-shell nanocomposite (PDSA) with nano-silica (nano-SiO2) as the rigid core and hydrophobic resin derived from dehydroabietic acid (DHAA) of pine rosin and crosslinked hydrophilic layer of 2-acrylamido-2-methyl-1-propanesulfonic acid and N, N-dimethylacrylamide (DMA) as the polymer shell was synthesized through semi-continuous emulsion polymerization. The molecular structure of PDSA was confirmed by proton nuclear magnetic resonance and Fourier transform infrared spectra analysis. Particle-size distribution and morphology measured by dynamic light scattering, scanning electron microscopy, and transmission electron microscopy revealed that PDSA was a monodisperse nanosphere with a particle size of around 98 nm, with a core-shell structure and possessed excellent long-term colloidal dispersion stability. The nano-microporous plugging performance of PDSA was evaluated using tight sandstone cores, shale cuttings, and filter membranes (200–400 nm) as plugging media. The results showed that PDSA could form effective aggregated plugging zones in nano-micropores and fractures in sandstone core and shale samples, lowering the core permeability by 78% and improving the shale recovery to above 80%, superior to conventional plugging agents of nano-polyester (NP) and sulfonated asphalt. PDSA also effectively minimized the nano-micropore fluid loss for filter membranes under high-temperature and high-pressure (HTHP) conditions. Furthermore, based on the response surface methodology (RSM) design, the established statistical significant prediction model for HTHP nano-microporous fluid loss indicated the main controlling factor of temperature and its interactive effects with PDSA dosage and membrane size. The high-temperature-induced deformation of PDSA in conjunction with the rigid core was conducive to enhancing and maintaining the HTHP plugging effect within 180°C. The plugging mechanism of PDSA was revealed to be the core-shell synergistic plugging effects of the interparticle bridging and gap filling of the rigid core and the adhesive film forming of the rosin resin shell. The study might provide a novel strategy for preparing high-performance and eco-friendly nano-plugging agents from natural rosin to maintain wellbore stability and relieve environmental pressure, especially for applications in the deep shale and tight formations associated with high-temperature and nano-microporous harsh conditions and the environmentally sensitive areas.