Understanding of the carbon dioxide sequestration in extremely low-permeability saline aquifers in the Ordos Basin

Abstract:

A full-chain CCS demonstration project was started in 2010 by capturing and injecting around 100,000 tons of CO₂ per annum into extremely low-permeability sandstone formations in the northeastern Ordos basin, Inner Mongonia, China. It is the first demonstration project in China for the purpose of public interests by sequestrating in the deep saline aquifers massive amount of CO₂ captured from a coal liquefaction company. The injection takes place in overall five brine-bearing geological units that are composed of four sandstones and one carbonate, which are interbedded with various mudstone caprocks. A single vertical well was drilled to the depth of 2826m. Injection screens are opened to more than 20 thin aquifers distributed between the depth 1690m-2453m with a total of 88 m injecting thickness. The permeability for all the storage formations is less 10 md and porosity is in the range of 1-12%. Hydraulic fracturing and formation acidizing were conducted at 10 layers for reservoir improvement. Up to present, total injection of CO₂ is about 280,000 tons. Injection pressure drops from around 8.5 MP at the beginning to less than 5MP at present and most CO₂ goes to shallowest injection formation at the depth interval 1690-1699 m, which has not been conducted any reservoir improvement. We intend to understand the improving injectivity of such low permeability reservoirs with numerical simulations. The modeling results reasonably describe the spreading of the CO₂ plume. After 3 years of injection of CO₂, the maximum migrating distance of CO₂ plume is about 500 m and the pore pressure build-up is slightly less than 15 MPa. The major storage reservoir at the depth interval 1690-1699 m contributes over 80% of the storage capacity of the entire reservoir system.