Open Access

ARTICLE

Molecular Design of a Hyperbranched Polymer Wetting Agent for Superior Barite Sag Control in Ultra-Low Oil-to-Water Ratio Drilling Fluids

Dapeng Zou^1,2, Jun Wang^1,*

1 College of Chemistry and Chemical Engineering, Northeast Petroleum University, Daqing, China
2 Drilling Fluid Company, Daqing Drilling & Exploration Engineering Corporation, Daqing, China

* Corresponding Author: Jun Wang. Email:

Journal of Polymer Materials 2026, 43(2), 16 https://doi.org/10.32604/jpm.2026.081141

Received 24 February 2026; Accepted 13 May 2026; Issue published 30 June 2026

Abstract

Reducing the oil-to-water ratio (OWR) of oil-based drilling fluids (OBDFs) to ultra-low levels (e.g., 55:45) exacerbates barite sag—a failure mode driven by barite’s inherent hydrophilicity and the weakened suspending capacity of the oil phase. Conventional low-molecular-weight wetting agents fail under these demanding conditions due to weak adsorption and thermal instability. In direct response to the solid-phase control challenge described above, we designed and synthesized a new hyperbranched polymeric wetting agent (HP-Wet) via a deliberate molecular topology strategy. The HP-Wet architecture incorporates phosphonate groups for robust anchoring onto barite surfaces and long alkyl chains to confer oleophilicity. By optimizing the amine-to-anhydride molar ratio, HP-Wet-1.05 was obtained, exhibiting a well-defined hyperbranched structure with a moderate molecular weight (M_w = 31,021 g/mol) and narrow dispersity (PDI = 1.96). This agent demonstrated exceptional efficiency in barite wettability reversal, increasing the water contact angle from 21.9° to over 117.1°. In an ultra-low OWR (55:45) OBDF formulated with the synergistic cetyltrimethylammonium bromide (CTAB) system, the HP-Wet delivered outstanding comprehensive performance after dynamic aging at 180°C: superior sag resistance (sag factor = 0.505), high electrical stability (demulsification voltage > 1000 V), and low high-temperature/high-pressure fluid loss (1.5 mL), significantly outperforming a commercial wetting agent (X-407). The enhanced performance is attributed to a multi-scale stabilization mechanism distinct from interfacial emulsification: strong multi-point anchoring on barite at the molecular level; formation of a dense, thermally self-reinforcing composite hydrophobic layer with CTAB at the solid-oil interface; and establishment of a weak three-dimensional network in the continuous phase for uniform particle suspension. This work not only presents a high-performance and environmentally compatible additive but, more importantly, establishes a distinct molecular design paradigm focused on solid-phase wettability control and sag prevention for stabilizing ultra-low OWR drilling fluids.

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