State of the art Test Method to Quantify Progression Rate of Carbonation of Wellbore Sealing Materials

Abstract The primary objective of this paper is to demonstrate an effective approach for mapping and quantifying progression rate of CO2 induced carbonation on wellbore cements. The method involves four steps: 1. molding and curing the sealant, 2. exposing axially to CO2, either super-critical CO2 saturated with H2O or H2O saturated with CO2, at a high differential pressure while measuring flow rates, 3. mapping reacted versus unreacted areas radially and axially by measuring matrix hardness with an indentation method and 4, comparing pre-, post- and reference exposure results for various mechanical properties and permeability. Permeability and conventional mechanical properties are measured before and after exposure and then compared with reference samples. The method provides a quantitative and illustrative map of the carbonation progression axially through the exposed sample, and it helps build a map of the exposed area in terms of actual changes to the mechanical properties. It further provides data that shows the effect of the carbonation in terms of hardening, softening and change in permeability. This reveals changes in the materials taking place beyond the initial carbonation of Ca(OH)2 normally mapped by the phenolphthalein method and helps when evaluating sealants for which mapping methods like phenolphthalein are not available. The method was applied to a wide variety of sealant compositions with consistent results. A high axial differential pressure is applied to accelerate progression, so that more predictive data can be gathered in a relatively short time, from which long-term effects can be extrapolated. The method has shown highly applicable for quantifying physical effects of carbonation and can be performed without highly advanced and expensive equipment by using equipment that most technology centers have access. It provides a valuable quantification of progression rate of affected as well as damaged matrix which can be used to assess usable lifetime of barrier materials in well-defined and semi-confined geometries such as plugs or annular barriers for CCUS wells.