Investigation Into the Mechanistic Insights and Performance Evaluation of Advanced Viscosity Reducing Agents for Heavy Oil Invaded Oil‐Based Drilling Fluids via Asphaltene Structure Disruption

To tackle the viscosity surge in oil‐based drilling fluids (OBDFs) due to heavy oil invasion, a novel tetrapolymer viscosity reducer (PVR) was synthesized from diisobutylene, isobutylene, isoprene, and maleic anhydride. FT‐IR, NMR, and TGA confirmed its structure and high thermal stability (decomposition at 398°C). Tests showed PVR reduced plastic viscosity of contaminated fluids by 21 mPa s and yield point by over 12.5 Pa, achieved by disrupting asphaltene π‐π stacking and hydrogen bonds, reducing aggregate size ( D 50 from 31.345 to 6.265 μm). At 2% dosage, it maintained emulsion stability (breakdown voltage 486 V, above 400 V threshold). After 72‐h 180°C aging, PVR performed better: plastic viscosity showed little change (72–71 mPa s), yield point dropped sharply (16–7 Pa), and density difference was 0.01 g/cm 3 (vs. 0.04 g/cm 3 for blank), indicating superior high‐temperature long‐term stability. This offers a reliable solution for optimizing deep‐well high‐temperature drilling fluids.