Self-healing, Re-adhering and Carbon-Steel Corrosion-Mitigating Inorganic Cement Composites for Geothermal Wells at 300degC

Abstract

The work discusses factors affecting self-healing behavior (strength recovery and cracks’ sealing), carbon steel (CS) corrosion protection and cement-steel bond-recovery, thermal shock and acid resistance of various cementitious materials under high-temperature (300°C) hydrothermal conditions. Experimental results are presented for formulations based on Ordinary Portland Cement chemistry modified with pozzolanic materials, slag, chemical and hydraulic calcium-aluminate cement-based blends and combinations of different types of fly ash at early ages (up to 28 days of the initial curing) after repeated compressive damage and short-term (5 days) exposure to the original curing conditions. Effect of environmental fluids compositions, curing conditions, physical-chemical constrains such as where the healing takes place (matrix vs. interface) on the healing process are discussed. Among the tested systems Thermal Shock Resistant Cement composed of calcium-aluminate cement, fly ash, type F, and sodium meta-silicate activator met all the target material criteria including: 1) thermal and hydrothermal stability at 300°C; 2) Compressive strength of more than 1000 psi (6.9 MPa), bond strength of 80 psi (0.55 MPa) based upon non-confined tests of sheath samples surrounding CS tube; 5) compressive strength recovery of more than 80% and bond strength recovery of more than 40% of the original strength after self-healing for 5 days under the initial curing conditions; 6) ≥30% higher sheath shear bond strength than that of OPC/SiO2 after 6 cycles of thermal shock (one cycle, 350°C heating and 25°C water cooling by passing water through CS casing); 7) ≥30% higher lap-shear bond strength than that of OPC/SiO2 after exposure to pH 0.2 H2SO4/brine for 30 days at 90°C; 8) ≥50% lower corrosion rate of CS protected by adhered and re-adhered cement to CS than that of OPC/SiO2 after autoclaving for up to 30 days at 300°C.