Enhanced amphoteric polymer filtration reducer with vinyl-functionalized nanosilica for high-salt and ultra-high temperature water-based drilling environments

Exploring deep oil and gas reservoirs presents significant challenges for conventional drilling fluids and their filter cakes due to high salinity and ultra-high temperatures. To address this, a highly effective amphoteric polymer nanocomposite (Nano-DAVD) was synthesized through controlled free-radical polymerization. NanoDAVD consisted of N,N-dimethylacrylamide, 2-acrylamido-2-methyl-1-propanesulfonic acid, acryloyloxyethyltrimethyl ammonium chloride, and N-vinylpyrrolidone as polymer chain units and vinyl-functionalized nanosilica (VMS) as nanofillers, optimized by a three-to-four factor orthogonal test design. VMS nanosilica exhibited a high specific surface area (SSA) of 302 m2/g, and the chemical structure and morphology of VMS and NanoDAVD was analyzed using FTIR, 1H NMR, TEM, XRD, BET, permeability, and SEM imaging. The incorporated VMS nanosilica in Nano-DAVD, promoted better alignment and chain packing through in-situ covalent binding, resulting in a more ordered and crystalline structure. At 15 wt% NaCl, Nano-DAVD exhibited remarkably low API and HTHP filtration volumes of 3.6 +/- 0.1 mL and 30 +/- 0.2 mL, respectively, at 240 degrees C. Additionally, the presence of VMS nanosilica significantly decreased the filter cake thickness from 7.44 to 1.01 mm and permeability from 14.7 to 5.55 x 10-4 mD. Nano-DAVD displayed excellent rheological properties with a slight decrease in AV and PV from 17.2 to 72.8 mPa s to 10.5 and 54.2 mPa s, respectively, while YP remained almost unchanged after aging at 240 degrees C. The Herschel-Bulkley flow model perfectly described the flow behavior with a high coefficient of determination (R2 = 0.999). The working mechanism was explained via polymer chain confinement and nucleation growth, adsorption, covalent bonding, and electrostatic interactions of Nano-DAVD onto bentonite platelets. The interactions reshaped the polymer-bentonite colloid 3D network, inducing tightchain entrapment for retention of solid particles on the filter cake to improve filtration inhibition. Consequently, Nano-DAVD exhibits improved filtration behaviors and rheological performance with environmentally friendly characteristics for practical applications in deep formations.