title: Determination of diffusion profiles in altered wellbore cement using X-ray computed tomography methods.
abstract: The development of accurate, predictive models for use in determining wellbore integrity requires detailed information about the chemical and mechanical changes occurring in hardened Portland cements. X-ray computed tomography (XRCT) provides a method that can nondestructively probe these changes in three dimensions. Here, we describe a method for extracting subvoxel mineralogical and chemical information from synchrotron XRCT images by combining advanced image segmentation with geochemical models of cement alteration. The method relies on determining "effective linear activity coefficients" (ELAC) for the white light source to generate calibration curves that relate the image grayscales to material composition. The resulting data set supports the modeling of cement alteration by CO2-rich brine with discrete increases in calcium concentration at reaction boundaries. The results of these XRCT analyses can be used to further improve coupled geochemical and mechanical models of cement alteration in the wellbore environment.
authors.affiliation: Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory , Livermore, California 94559, United States.
authors.forename: Harris E
authors.initials: HE
authors.lastname: Mason
authors.forename: Stuart D C
authors.initials: SD
authors.lastname: Walsh
authors.forename: Wyatt L
authors.initials: WL
authors.lastname: DuFrane
authors.forename: Susan A
authors.initials: SA
authors.lastname: Carroll
mesh_terms: D002118:Calcium / Q000737:chemistry; D002138:Calibration; D002254:Carbonates / Q000737:chemistry; D003252:Construction Materials / Q000032:analysis*; D004058:Diffusion; D008962:Models, Theoretical; D012492:Salts / Q000737:chemistry; D013052:Spectrometry, X-Ray Emission; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D002254:Carbonates; D012492:Salts; C017082:brine; D002118:Calcium