Preparation and Performance Evaluation of Novel Organoclay for Oil-based Drilling Fluids

To improve the rheological performance of oil-based drilling fluids at high temperatures, bentonite was used as the matrix to comparatively investigate the effects of head-group structures, including quaternary ammonium, pyridine, and imidazole groups, and alkyl chain length on the microstructure and high-temperature rheological performance of organoclays. FT-IR, XRD, and thermogravimetric analyses showed that the modifiers were intercalated into the bentonite interlayers through electrostatic adsorption of the head groups and hydrophobic interactions among the tail chains, while some were physically adsorbed onto the surface. The maximum physical adsorption/electrostatic intercalation loadings of CTAC, OPB, CPB, OMB, and CMB on bentonite were 0.37/0.56 mmol/g, 0.021/0.63 mmol/g, 0.44/0.28 mmol/g, 0.016/0.54 mmol/g, and 0.17/0.48 mmol/g, respectively. Molecular dynamics simulations indicated that the absolute value of the electrostatic energy of CPB increased from 87.42 kcal/mol to 88.17 kcal/mol under high-temperature conditions, suggesting enhanced electrostatic interactions between CPB and bentonite. Rheological experiments showed that, with respect to head-group structures, heterocyclic-group-modified organoclays exhibited better high-temperature rheological performance, with the AV and YP of OBen-3 reaching 19 mPa·s and 3 Pa, respectively, after hot rolling at 240 ℃. As the alkyl chain length increased, the rheological performance of the organoclays improved markedly. After hot rolling at 240 ℃ in the all-oil-based drilling fluid system, OBen-3 exhibited AV, PV, and YP values of 90 mPa·s, 85 mPa·s, and 5 Pa, respectively, demonstrating good compatibility and high-temperature rheological performance. Moreover, the high-temperature and high-pressure filtration loss of OBen-3 was only 3.2 mL, indicating good filtration-loss control performance. In addition, OBen-3 exhibited favorable high-temperature rheological performance and effective high-temperature and high-pressure filtration-loss control in the water-in-oil system. This study suggests that introducing rigid structures with long alkyl chains can enhance intermolecular and interfacial interactions within the organoclay structure, thus significantly improving the high-temperature rheological performance of organoclays. These findings provide insights into the development of organoclays for high-temperature-resistant oil-based drilling fluids.