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In deep well drilling, the filtration-loss reducer remarkably impacted the rheological property of water-based drilling fluids at high temperature and salinity, causing serious problems during the drilling process. In this work, a combination of low molecular weight amphoteric copolymer and bentonite clay was exploited to tackle these issues due to their relatively different thermal-saline-properties dependence. In detail, a novel amphoteric tetramer (AB-47) of N,N-dimethylacrylamide (DMAm), 2-acrylamide-2-methylpropanesulfonic acid (AMPS), diallyl dimethylammonium chloride (DMDAAC), and N-vinylpyrrolidone (NVP) was prepared by free-radical copolymerization technique under optimal conditions. And the molecular structure of AB-47 was evidenced by FT-IR, 1H NMR, and elemental analysis. The filtration and rheological performance of AB-47 in low solid-phase water-based mud (LSWBM) were examined in comparison with Driscal D before and after a 16 h aging at 230 °C according to the American Petroleum Institute (API) standard. Results indicated that, only 1% AB-47 could not only control an API filtration loss volume of 8.9 mL but also the change rate of main rheological parameters were found to be more stable while parameters of Driscal D containing mud not only varied dramatically but also an API filtration loss of 30 mL could be maintained under identical conditions. Although the contamination with NaCl affected both muds properties, AB-47 could still exhibit higher performance. Therefore, the relative stability of AB-47 containing mud with respect to the chemical environment could be achieved through the strong synergistic interactions between AB-47 and bentonite particles, which were examined through particle size distribution, zeta potential and scanning electron microscopic. [ABSTRACT FROM AUTHOR]

In this work, the effects of hot-aging on the rheological characteristics of acrylamide-based tetrapolymer modified bentonite drilling mud were examined. The dosage of the acrylamide-co-sodium 2-acrylamido-2-methylpropanesulfonate-co-N-vinyl pyrrolidone-co-N-butyl propenoate (ASAPB) in the drilling muds was varied from 0 to 1 wt.% under geothermal condition ranging from 25°C to 150°C. The rheological behaviour of ASAPB modified bentonite drilling mud were quantified using Vipulanandan model and compared with Herschel-Bulkley model. The Herschel-Bulkley model predicted satisfactorily the shear thinning relationship between the shear stress and shear strain rate. However, Vipulanandan has a maximum shear stress limit whereas the other did not. [ABSTRACT FROM AUTHOR]

ABSTRACT Aiming at good thickening ability and temperature resistance in water-based drilling fluid, a novel copolymer viscosifier (SDKP) of sodium 2-acrylamido-2-methylpropane sulfonate (NaAMPS) with N-vinylcaprolactam (NVCL) and cross-linking divinylbenzene (DVB) was prepared by micellar radical polymerization. The composition and molecular structure of optimal SDKP under the optimum reaction conditions was characterized by FT-IR, 1H-NMR, and elemental analysis, and the molecular weight was determined by GPC. Thermal gravimetric analysis showed that the SDKP was even stable when the temperature was not higher than 330 °C. The performance of SDKP as viscosifier for aqueous, brines, and saturated brine bentonite drilling fluid was evaluated before and after aging tests at 230 °C for 16 h. The evaluation results indicated that the SDKP had excellent thickening ability, thermal resistant, and salt tolerance. HTHP rheology test showed that the SDKP containing drilling fluids displayed a thermo-thickening effect in temperature range of 150 to 180 °C, which was beneficial to increase the viscosity and strength of fluids at high temperatures. Shear test showed that the SDKP illustrated a similar shear thinning to xanthan gum. ESEM observations demonstrated that the continuous three-dimensional network was formed in the SDKP aqueous and brines solution, which was probably the main reason for its excellent thickening properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44140. [ABSTRACT FROM AUTHOR]