Mechanical and Chemical Durability of a Fly Ash–Epoxy Composite Cement for Extreme Oil and Gas Well Conditions

Oil and gas well cement is routinely exposed to aggressive chemical and mechanical environments that can compromise long-term zonal isolation. Conventional Portland cement systems, which rely on hydration products such as calcium silicate hydrate (C–S–H), are particularly vulnerable to acid attack, carbonation, high salinity, and thermal stress. This study investigates a polymer–mineral composite cement in which Class F fly ash is incorporated into an epoxy resin matrix at 0, 25, and 50 weight percent (wt%) loading. The composite samples were exposed for ten days to harsh downhole-representative environments, including hydrochloric acid (HCl, 15–28 wt%), sodium hydroxide (NaOH, 15–28 wt%), sodium chloride (NaCl) brines (20 wt%), crude oil, elevated temperatures up to 100 °C, and high-pressure carbon dioxide (CO2). Compressive strength was evaluated using a universal testing machine, capturing both deformation strength and ultimate failure strength to assess elastic and structural performance. Across most conditions, the composite maintained strengths exceeding 5000 psi, demonstrating strong chemical resistance. Acidic and CO2 exposures primarily reduced elastic deformation rather than ultimate strength, suggesting localized interaction with the polymer matrix. Elevated temperature reduced strength to ~2800 psi and diminished elasticity, marking the material’s upper thermal limit. Acetone exposure progressively degraded the polymer network, highlighting potential controlled removability. These findings indicate that embedding industrial fly ash in a polymer matrix produces a mechanically resilient and chemically robust cement alternative with up to 50 wt% industrial waste incorporation. This hybrid system offers a promising approach for wells exposed to acidic, CO2-rich, or high-salinity environments, where conventional Portland cement may fail.