The Long-term Corrosion Behavior of Abandoned Wells Under CO2 Geological Storage Conditions: (3) Assessment of Long-term (1,000-year) Performance of Abandoned Wells for Geological CO2 Storage

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A hypothetical CO2 storage site that has some abandoned wells located near the injection well is considered. Generally, cement plugs are set to cover or isolate porous or productive formations and to isolate usable groundwater from hydrocarbons. When CO2 is injected into a reservoir, supercritical CO2 or dissolved CO2 spreads out in the reservoir. This dissolved CO2 can react chemically with cement seals (plugs and casing cement) in abandoned wells. As a result, minerals in the cement seals (plugs and casing cement) may alter to form other minerals or mineral phases.The first simulations concerning migration of supercritical CO2 and dissolved CO2 in a saline aquifer and a depleted gas field reservoir, were carried out using TOUGH2. The following temperatures and depths of reservoir were selected: 50°C at E.L.-1,000 m, 60°C at E.L.-1,500 m and 70°C at E.L.-2,000 m.Secondly, geochemical reactions of cement seals (plugs and casing cement) were simulated. The results of reservoir simulations were used as boundary conditions for the geochemical calculation of cement seals. Geochemical simulation of the reactions yielded the extent (length) of alteration of cement seals (plugs and casing cement) after long time periods; for example, the alteration length of cement seals after 1,000 years was about one meter. This length is short enough so that the usable cement seals (plugs and casing cement) of abandoned well are able to continue to isolate CO2 in the reservoir from the upper aquifer.