EVALUATION OF CO2 GEOLOGICAL STORAGE CAPACITY IN THE PALEOZOIC FORMATIONS OF THE ORDOS BASIN, CHINA

The Ordos Basin in China produces large amounts of fossil energy including coal, oil and natural gas. As the result of numerous co-located power generation and coal-to-liquids facilities massive CO₂ emission sources exist in the basin. Geologic storage (GS) resource in the basin was evaluated as a potential method to reduce CO₂ emission. Based on the geographic distribution of potential storage reservoirs and burial depth, several Paleozoic formations were identified as potential GS reservoirs.

In Paleozoic units, two independent gas systems provide effective reservoir-seal assemblages. In Ordovician, the major depositional environments were shallow marine and tidal flat. The potential reservoirs include karst reservoir in the Fifth Majiagou (Ma5) member, the Fourth Majiagou (Ma4) dolomite reservoir and subsalt reservoir in Mizhi Depression. In late Paleozoic, the continental depositional facies gradually replaced the marine environments, including fluvial, delta and lacustrine systems. The potential storage reservoirs include sandstones in the First and Second Shanxi (Shan1, Shan2) and the Eighth Shihezi (He8) units and Shiqianfeng Group. Paleozoic coal beds could function as both potential reservoirs and caprocks. The thick shale in Shangshihezi Group provides a regional caprock. The shale in Shiqianfeng Group is effective caprock for Shiqianfeng reservoirs.

To evaluate potential geologic storage resources, reservoirs were classified into three types: gas fields, saline aquifers and coal beds. The gas fields possess large storage resource with reliable caprocks. However, most gas fields still produce and are not available. In the Ordos basin, saline aquifers appear to be the best near-term option to store CO₂. Saline aquifers are widely distributed in the basin, possess significant storage capacity and have effective caprocks. The coal beds are also good reservoirs for GS with the additional possibility of CO₂-ECBM. We screened all potential storage reservoir using criteria for pressure and temperature and minimum depth. Potential reservoirs that met minimum screening criteria were evaluated for technical CO₂ storage capacity and geologic and engineering factors contributing to the risk of CO₂ leakage.