Storing CO_2 underneath the Siberian Permafrost: A win-win solution for long-term trapping of CO_2 and heavy oil upgrading

摘要

A two-year project entitled "Assessment of the Feasibility of CO_2 Storage in the Russian Permafrost" was carried out in Russia in collaboration with the Siberian branch of the Russian Academy of Sciences. This project delivers new conclusions about the safety role of the permafrost and specific conditions of storage in an area of abnormal geothermal gradient in Western Siberia. One of the specific issues of the project was the potential formation of carbon dioxide hydrates from the injected CO_2 and the possible reaction between the existing methane hydrates and the injected CO_2. Maps have been constructed showing the areas of CO_2 hydrate stability. A second specific issue was the compatibility of CO_2 storage in the permafrost with oil production. Pilot tests of EOR technologies, involving either the injection of CO_2 or the generation of CO_2 in situ, proved very efficiency for highviscosity oil pools. Therefore, we propose to inject CO_2 in West Siberia into high-viscosity oil fields. High-viscosity oil fields are mainly located in the centre of the Western Siberian Basin in Khanty-Mansijsk autonomous okrug (KMAO). An alternative or complementary solution is storage in aquifers. Deep aquifers, such as the Pokur formation overlain could also be storage targets, but their potential is unknown because they have not been explored in detail. The inventory of major CO_2 sources in Western Siberia has shown that the major CO_2 emission in the power sector comes from the KMAO, where power stations in Surgut and Nizhnevartovsk are large CO_2 sources. GIS mapping of the permafrost depth and thickness, and the associated stability domain of the CO_2 hydrates, has shown that a good overlap could exist between these industrial areas and the stability domain of the gas hydrates, underneath the permafrost. Storage beneath the permafrost as CO_2 hydrate is not suitable due to the probable rapid plugging of the porosity by solid gas hydrates. But, the CO_2 should be stored at supercritical state in the hydrocarbon fields, with added value of heavy oil upgrading, and trapped underneath a classical cap rock. In addition, the permafrost would act as a secondary cap-rock by trapping the CO_2 as hydrates if the primary caprock should fail.