Abstract
The study focused on investigating the effectiveness of functional acrylic polymer (AP) in improving the ability of airfoamed sodium silicate-activated calcium aluminate/Class F fly ash cement (slurry density of ￡1.3 g/cm3) to mitigate the corrosion of carbon steel (CS) after exposure to hydrothermal environment at 200?C or 300?C. Hydrothermally-initiated interactions between the AP and cement generated the formation of Ca-, Al-, or Na-complexed carboxylate derivatives that improved the AP’s hydrothermal stability. A porous microstructure comprising numerous defect-free, evenly distributed, discrete voids formed in the presence of this hydrothermally stable AP, resulting in the increase in compresive strength of cement. The foamed cement with advanced properties conferred by AP greatly protected the CS against brine-caused corrosion. Four major factors governed this protection by AP-incorporated foamed cements: 1) Reducing the extents of infiltration and transportation of corrosive electrolytes through the cement layer deposited on the underlying CS surface; 2) Inhibiting the cathodic reactions at the corrosion site of CS; 3) Extending the coverage of CS by the cement; and 4) Improving the adherence of the cement to CS surface.
Highlights
The major thrust in assembling and constructing Enhanced Geothermal Systems (EGSs) lies in creating a hydrothermal reservoir in a hot dry rock stratum ≥200 ̊C, located at ~ 3 - 10 km below the ground surface
We identified two major factors that significantly contributed to inhibiting the corrosion of carbon steel (CS) in such hydrothermal environment: One was the hydrothermally stable products formed by the interactions between acrylic polymer and cement; the other was the development of a dense microstructure by the combination of well-formed calcite and boehmite crystals with polymer-cement reaction products
When acrylic polymer (AP) additive was incorporated into non-foamed and foamed slurries, their densities gradually declined with an increasing content of AP; adding 2 wt% AP reduced the density to 1.82 g/cm3 for non-foamed and to 1.2 g/cm3 for foamed slurry, suggesting that AP has air-entraining properties in slurry during mixing
Summary
The major thrust in assembling and constructing Enhanced Geothermal Systems (EGSs) lies in creating a hydrothermal reservoir in a hot dry rock stratum ≥200 ̊C, located at ~ 3 - 10 km below the ground surface. We identified two major factors that significantly contributed to inhibiting the corrosion of CS in such hydrothermal environment: One was the hydrothermally stable products formed by the interactions between acrylic polymer and cement; the other was the development of a dense microstructure by the combination of well-formed calcite and boehmite crystals with polymer-cement reaction products Based upon this information, the CAC/Class F fly ash/ sodium silicate blend cements, formulated as the thermal shock-resistant cement (TSRC), would be required to possess two indispensable properties: First, the slurry density must be lowered; and, second, the ability of hydrothermally cured TSRC to protect the CS casing against corrosion must be assured. Integrating all the data obtained from the objectives described above would clarify the potential of the APmodified foamed TSRC as corrosion-alleviating well cement for CS casings in EGS environment at 200 ̊C and 300 ̊C
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