Synthesis and Characterization of Salt Tolerant Ternary Polyampholyte as Rheology Enhancer and Fluid Loss Additive for Water-Based Drilling Fluids
Abstract
A novel ternary polyampholyte (TPA) was synthesized via free radical copolymerization in deionized water using ammonium persulfate as an initiator. The TPA composition included 80 mol.% acrylamide (AAm), 10 mol.% 2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt (AMPS), and 10 mol.% (3-acrylamidopropyl) trime-thylammonium chloride (APTAC). TPA was used as an alternative to low viscosity polyanionic cellulose (PAC-LV) to prepare bentonite based drilling fluids with different concentrations of NaCl (1-35 wt.%). Gel strength (GS) measurements demonstrated that, at a 6:1 [initiator]:[catalyst] ratio, even in high salinity brines (25-35 wt.%), the GS values exceeded industry standards, highlighting the superior performance of ben-tonite/ternary polyampholyte (BT/TPA) in high salinity media. Notably, TPA addition significantly reduced the filter cake thickness to 0.09 cm, outperforming BT/PAC-LV (0.18 cm) and bentonite alone (0.41 cm). Furthermore, the BT/TPA drilling fluid exhibited the lowest permeability/thickness ratio at 13 mD/cm, indicating its potential as a rheology enhancer and fluid loss additive for salt-resistant Water-Based Drilling Fluids (WBDF) applications. The filtration performance of bentonite and bentonite/polymer dispersions showed a clear trend in fluid loss values: BT/TPA < BT/PAC-LV < Base flu-id. The high-salinity BT/TPA drilling fluid had remarkably low fluid loss, measuring just 3.5 ml, well below the API standard limit of 12 ml.