Tuning interphase behavior of thermo-responsive block polymer assemblies for enhanced filter cake performance

Abstract

Fluid loss in deep drilling formations poses a persistent challenge, necessitating advanced synthetic polymer additives to ensure efficient filter cake formation. Conventional additives often fail to maintain thermal stability and compact filter cake under high-temperature and high-salt conditions. In this study, a low molecular weight thermo-responsive block polymer (DAMP) was synthesized via in-situ polymerization with unique interphase transition responses above its lower critical solution temperature (LCST). The molecular architecture of DAMP consisted of N,N-diethylacrylamide for thermo-responsiveness, 2-acrylamido-2-methyl-1-propanesulfonic acid and acrylamide for stability, and a chain transfer agent for molecular control, enabling controlled thermally-triggered end-chain assemblies to dynamically regulate filter cake properties in water-based drilling fluids (WDFs). Experimental results reveal that DAMP exhibits an LCST of 85 °C, exceptional thermal stability up to 362 °C, and retains around 80 % of its rheological properties after aging at 220 °C, surpassing conventional polyacrylonitrile (PAN) homopolymers. Additionally, X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirm the formation of entangled structural assemblies and a thin, compact filter cake microstructure post-aging. In 15 % NaCl at 220 °C, 2 % DAMP formulation significantly mitigates fluid loss, achieving API fluid loss (FL_API) and high-temperature high-pressure fluid loss (FL_HTHP) values of only 4.7 mL and 19.7 mL, respectively. Environmental assessments using earthworms demonstrated that DAMP-fluid filtrate possesses low toxicity, with earthworm survival rate exceeding 89 % at 8 % after 7 days of incubation. These findings highlight DAMP innovative molecular design and interphase behavior for optimizing drilling fluid performance under hostile environmental conditions.