engleski

Carbonation of Portland-Zeolite and geopolymer well-cement composites under geologic CO2 sequestration conditions

Degradation of Portland cement under supercritical CO2 conditions (scCO2) is one of the major concern in geological sequestration projects. This paper presents the research on two novel types of binders considered to display a CO2 corrosion resistance potential: (1) Portland cement partially replaced with 20, 30 and 40 wt % of zeolite and blended with Styrene-Butadiene (SB) Latex and (2) geopolymer based on lime-slag and lime-pozzolan blends. Specimens were placed in an autoclave, covered with water, heated up to 100°C and pressurized with 7 MPa CO2 in order to simulate CO2 environment in the Croatian wellbore. On behalf of tests on compressive strength, porosity, permeability and alkalinity, as well as thermogravimetry, X-ray diffraction and SEM microstructural analyses of samples at various penetration depths, carbonation mechanisms were discussed. Portland-Zeolite composites have been argued as potential CO2 resistant cement systems, with an replacement rate below the minimally tested addition of 20 wt %, as excessive replacement rates resulted in an increase in porosity and permeability. Geopolymer composites based on lime activation unfortunately haven’t exhibited required properties for application in well cementing of CO2 injection wells. Calcium carbonate polymorphs precipitated throughout the whole specimen thickness of all samples, but preferably in mixtures based on Ca-richer raw materials. A re-precipitation of calcium carbonate filled in the porosity preferentially at the 0.5 mm surface layer of PC-based specimens, due to the outward diffusion of calcium at the early stage of carbonation.

Wellbore cements ; zeolite ; SB Latex ; geopolymer ; geologic CO2 sequestration ; carbonation degradation

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