Enhancing the Synergistic Performance of CAPB-Modified SPAM/Silica Drilling Fluid System in High Calcium and Magnesium Brine Environments: Towards Advanced Fluid Loss Control for Challenging Wells

Abstract

Abstract The increasing complexity of oil and gas drilling requires drilling fluids that offer improved fluid loss control and brine stability, especially in deep wells known for their high salinity and formations rich in divalent ions. Salt-free fluids (SFBF) can cause high fluid loss, form denser filter cakes, and jeopardize wellbore integrity when subjected to high levels of calcium (Ca2+) and magnesium (Mg2+) cations. This study evaluates the effect of nanocomposite drilling fluids based on sulfonated polyacrylamide (SPAM) and cocamidopropyl betaine (CAPB)-modified nanosilica (SiO2/CAPB), in a prepared brine condition designed to mimic a challenging wellbore drilled at 180 °C. The nanocomposite fluid systems were carefully synthesized, and the rheological and filtration parameters of SFDF at 180 °C temperature with 8.0 wt.% concentrations of both CaCl2 and MgCl2 were evaluated. Incorporating 0.5 wt.% of SPAM/SiO2 (unmodified) and SPAM-CPAB/SiO2 (modified) into 350 mL of the drilling fluid was done to improve the characteristics of the base fluid system in saline conditions. The findings showed that SPAM/SiO2−CAPB fluids surpassed SFBF and SPAM/SiO2, demonstrating enhanced yield point (YP), apparent viscosity, 10-minute gel strength, and plastic viscosity (PV), while efficiently managing the filtration parameters. The SPAM/SiO2−CAPB system demonstrated a reduction of only 7.0% in PV and 10% in YP. In contrast, the SPAM/SiO2 system experienced a more significant decline of 19.4% in PV and 22.2% in YP when subjected to combined CaCl2/MgCl2 concentrations at 180°C. The SFBF contaminated with salts showed a decreased PV by 61.5% and YP by 62.5%. The filtrate loss with SPAM/SiO2 and SPAM/SiO2−CAPB under CaCl2/MgCl2 contamination was minimal, recorded at 5.3 mL and 5.0 mL, respectively, in contrast to a notable increase of 42.2 mL for SCBF. This behavior supports the efficient salt inhibition capability demonstrated by the nanocomposites, especially when paired with zwitterionic CAPB molecules. The combined impact of CAPB, SPAM, and SiO2 enhances the quality of the filter cake, optimizes SiO2 dispersion, and strengthens salt resistance at higher temperatures. The importance of these characteristics lies in their ability to improve borehole stability and increase efficiency in challenging deep-well-drilling environments.