Synthesis and characterization of grafted nano-silica copolymerized fluid loss additive for oil well cement at ultra-high temperature of 240 °C

The exploitation of oil and gas resources is progressing towards deeper strata, and the high-temperature environment underground readily gives rise to the difficulty in controlling the fluid loss of cement slurry. An organic/inorganic copolymerized fluid loss additive (FLA) CAF-1 used for ultra-high temperature was synthesized and characterized by Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TG), Nuclear Magnetic Resonance (NMR), Gel Permeation Chromatography (GPC), etc. CAF-1 was composed of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), N, N-dimethyl acrylamide (DMAA), itaconic acid (IA), 4-acryloyl morpholine (ACMO) copolymerized with surface modified nano-silica (KNS). It exhibits excellent thermal-resistance and structure stability within 322°C due to the unique spatial reticulation structure. The fluid loss of oil well cement slurry containing CAF-1 could be controlled less than 50 mL/30 min× 6.9 MPa (1000 psi) at 240°C, even in the semi-saline slurry. CAF-1 could adsorb Ca^2 + and generate more calcium silicate hydrated (C-S-H) by consuming Ca(OH)₂. The “Pozzolanic Reaction” and “Nucleation Effect" accelerated the hydration of cement slurry. Ultimately, CAF-1 reduced fluid loss at high temperatures by optimizing the spatial structure of the filter cake.