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Abstract:
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After the injection of CO₂ into a subsurface formation , various storage mechanisms help immobilize the CO₂ . Injection strategies that promote the buoyant movement of CO₂ during the post -injection period can increase immobilization by the mechanisms of dissolution and residual phase trapping . In this work , we argue that the heterogeneity intrinsic to sedimentary rocks gives rise to another category of trapping , which we call local capillary trapping . In a heterogeneous storage formation where capillary entry pressure of the rock is correlated with other petrophysical properties , numerous local capillary barriers exist and can trap rising CO₂ below them . The size of barriers depends on the correlation length , i .e . , the characteristic size of regions having similar values of capillary entry pressure . This dissertation evaluates the dynamics of the local capillary trapping and its effectiveness to add an element of increased capacity and containment security in carbon storage in heterogeneous permeable media . The overall objective is to obtain the rigorous assessment of the amount and extent of local capillary trapping expected to occur in typical storage formations . A series of detailed numerical simulations are used to quantify the amount of local capillary trapping and to study the effect of local capillary barriers on CO₂ leakage from the storage formation . Also , a research code is developed for finding clusters of local capillary trapping from capillary entry pressure field based on the assumption that in post -injection period the viscous forces are negligible and the process is governed solely by capillary forces . The code is used to make a quantitative assessment of an upper bound for local capillary trapping capacity in heterogeneous domains using the geologic data , which is especially useful for field projects since it is very fast compared to flow simulation . The results show that capillary heterogeneity decreases the threshold capacity for non -leakable storage of CO₂ . However , in cases where the injected volume is more than threshold capacity , capillary heterogeneity adds an element of security to the structural seal , regardless of how CO₂ is accumulated under the seal , either by injection or by buoyancy . In other words , ignoring heterogeneity gives the worst -case estimate of the risk . Nevertheless , during a potential leakage through failed seals , a range of CO₂ leakage amounts may occur depending on heterogeneity and the location of the leak . In geologic CO₂ storage in typical saline aquifers , the local capillary trapping can result in large volumes that are sufficiently trapped and immobilized . In fact , this behavior has significant implications for estimates of permanence of storage , for assessments of leakage rates , and for predicting ultimate consequences of leakage . |