Long-Term Study of CCUS Cement Designs Under Static and Cyclic CO2-Conditions

Abstract With the emerging focus of zonal isolation for underground storage projects, and the potential uncertainty of applicability of current barrier materials when exposed to a corrosive environment alongside added mechanical stressors a long-term exposure study was conducted. A base design known as a fit-for-purpose design for corrosive exposure was selected, with two additional permutations that would enhance the resistance towards the wellbore environmental risks. The study entailed a six-month long test schedule with intermittent sampling at one-three- and six-month intervals of the exposed plugs. Mechanical properties testing and complementary micro-CT scans were completed on the plugs in two separate laboratories and are detailed in this paper. Furthermore, the impact of constant pressure and temperature conditions in comparison to cyclic conditions was investigated. Aided by software simulations, a comparative discussion of the three designs was done to select the optimum design for a specific well scenario in the North Sea. Even though all considered cement systems showed an outstanding resistance towards CO2-saturated brines, minor differences based on the selection of additives could be observed. In addition, the choice of either static or cyclic test conditions also contributed to the degree of reaction during exposure. The realistic rather slow changes of the conditions given by the operational sequence for the well do not impose any impactful stress on the samples. Whereas the dominant factor appears to be the average partial pressure of CO2.