Thixotropy and gelation characteristics of thermosensitive polymer nanofluids at high temperature

High thixotropic polymer fluids are less prone to gravity collapse and leakage after injected into large-scale space, facilitating complete three-dimensional filling in the annulus of horizontal wells. Therefore, thixotropy is crucial for effective water plugging. To address the limitations of weakened stacking interactions among polymer chains and reduced hydrogen bonding of nanoparticles at high temperatures, a high-temperature thixotropic polymer nanofluid was developed using a composite of nano laponite and thermosensitive polymer poly(acrylamide-acrylamidomorpholine-2-acrylamide-2-methylpropanesulfonic acid) (P(AM-ACMO-AMPS)). The study focused on the structure-activity relationship and gelation properties of the gel at 120℃. The gel exhibited good thixotropy at 120℃, increasing with higher concentrations of polymer and nano laponite. At 1 wt% polymer concentration, the thixotropy value reached 1.445. The scanning electron microscopy (SEM) images indicated that the gel formed a dense three-dimensional network structure of interlaced interpenetration after shearing, enabling smooth and complete annulus filling without gravity collapse. The gel showed a shear thinning coefficient inversely related to solvent dispersion forces and a shear recovery time proportional to solvent polar forces. Gelation time was controllable from 1 to 12 hours, with an elastic modulus reaching 93.9 Pa after gelation. It showed good temperature and salt resistance stability with high quality retention rates. The radial and axial slip pressure gradients at 120℃ were 4.38 MPa/m and 7.34 MPa/m, maintaining 3.96 MPa/m and 6.16 MPa/m after two months, demonstrating excellent compressive strength. The breakthrough pressure gradient reached 18.5 MPa/m, sustaining a plugging rate over 95 %, indicating excellent plugging performance and erosion resistance.