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Advances in carbon capture and storage technologies published
The potential reactivity of Portland cement in wellbores is one of the key issues in assessing the long-term viability of storage of CO2 in geologic formations. CO2 is known to react with Portland cement, and the possibility of deleterious reactions leading to leakage of CO2 is a serious concern.
Figure 2. The polished surface of a sample of wellbore cement recovered from the SACROC CO2-enhanced oil recovery field (about 5 cm in height). The orange-altered cement reflects reactions with CO2 and is separated from unaltered gray cement by a translucent deposit of silica. This is the first sample of cement ever recovered for studies of long-term CO2 interactions and the security of geological storage of CO2.
Carey and Lichtner conducted innovative experiments on simulated wellbore systems involving flow of high pressure CO2-brine mixtures through composite cement-caprock and cement-casing systems. The scientists used the results of these experiments to guide their modeling efforts. They found that they needed to significantly enhance existing reactive transport codes to handle solid solution. The researchers published the first reactive transport code capable of handling arbitrarily complex solutions, allowing them to handle both major compositional variation as well as trace contaminants in cement system. Reference: Lichtner, P. C. and Carey, J. W. (2006) “Incorporating Solid Solutions in Geochemical Reactive Transport Equations using a Kinetic Discrete-composition Approach”. Geochimica Cosmochimica Acta 70: 1356-1378.
Using this theoretical foundation, the Carey and Lichtner developed a numerical model for wellbore cements exposed to CO2. They employed this model to predict long-term performance of Portland cement and have thus made significant contributions to the development of Carbon Capture and Storage technologies. These successes have made LANL a recognized leader in wellbore issues. Reference: Carey, J. W. and Lichtner, P. C. (2007) “Calcium Silicate Hydrate (C-S-H) Solid Solution Model Applied to Cement Degradation using the Continuum Reactive Transport Model FLOTRAN”. In Mobasher, B. and Skalny, J., editors, Transport Properties and Concrete Quality: Materials Science of Concrete, Special Volume, pp. 73-106. American Ceramic Society; John Wiley & Sons, Inc. LANL researchers organized the international Wellbore Integrity Network and hosted the most recent meeting of the Network in March.
Figure 3. Primary Plot: Numerical simulation of CO2-cement reactions occurring within the wellbore environment. The simulations reproduce the key features of the sample of cement recovered from the SACROC site including a 0.5 cm zone of intense carbonation, a region of non-altered cement, and a barrier between the two that impedes further reaction.