Experimental Approach To Elucidating Damage Mechanisms In Cement-Well Casting-Host Rock Settings For Underground Storage of CO2

Tuesday, 16 December 2014: 2:40 PM
Chang Li1, Vahid Jafari Azad1, David Rodriguez1, Jason Ideker1, Burkan Isgor1 and Circe Verba2, (1)Oregon State University, School of Civil and Construction Engineering, Corvallis, OR, United States, (2)National Energy Technology Laboratory Pittsburgh, Pittsburgh, PA, United States
During CO2 sequestration, wellbore cement could be vulnerable to high temperature and high pressure in underground storage settings. Wellbore alteration has been observed under supercritical CO2 exposure condition in previous experimental and field studies. One such study also showed that a reduction in both tensile and compressive strength when specimens were exposed to CO2-O2 gases at 50°C and 85°C as compared to specimens only exposed to CO2 gases; secondary mineral precipitation (SMP) and high temperature was speculated as the causes. In this study, experiments were designed to justify how different variables influenced SMP, and to quantify its effect on mechanical properties of Class H Portland cement. Chemical and mechanical alterations of Class H cement were investigated to verify the impact of SMP during this process. Cement prisms were investigated under different scenarios including influence of brine composition (simulated Mt. Simon basin), high temperature (up to 85 °C); high pressure (up to 4200psi); CO2 sequestration; CO2-O2 co-sequestration. Modulus of rupture and compressive strength of the cement prisms were tested under each scenario and several exposure durations. Initial results indicated that high temperature and synthetic brine composition had a negative influence on compressive strength. Pore solution analysis was conducted to examine the ionic exchange and geochemical alteration between the cement and brine. Specimens decreased in sodium and potassium, significantly increased in calcium, and slightly increased in sulfate after CO2 injected into system. Scanning electronic microscopy visually identified SMP and the alteration depth of specimens exposed to CO2 gas and CO2-O2 gases with time of exposure, respectively. The predicted degree of SMP, change of pore solution, and mechanic strength based on temperature, pressure, brine composition, and gas exposure conditions will be presented.