Preliminary physical and geochemical study on a sedimentary rock series of the Pannonian Basin for CCS (Hungary)

摘要

One of the largest storage potential for CCS is in the deep saline aquifers because their pore water cannot be used for drinking and for agricultural activities. In the Pannonian Basin (Hungary) there are sedimentary sub-basins filled up by sedimentary rock sequences containing such aquifers, which have the main potential for CCS in Hungary. Our chosen study area in the Pannonian Basin was the Jaszsag Subbasin, well known by numerous seismics and hydrocarbon exploration wells. As Hungary is situated in the middle of the Pannonian Basin, its emissions could be significantly reduced by CCS. That is the main reason to find a suitable place for CCS. The process filling up the basin resulted in a sedimentary system from deep-water to deltaic sediments, including thick facies units of reservoir quality as well as thick facies units acting as seals above it. During the evolution of the basin, large rivers brought huge amounts of sediments from the NE and NW towards the deeper parts of Lake Pannon, forming huge deltas on the river mouths. The potential reservoir formations now form a hidrogeologically coherent regional system, indicating a large potential for storage capacity. Furthermore, the saline aquifer system is large enough to ensure its long-term industrial usage for CCS, because the injection does not cause critical increase in the pressure. However, the system is not homogenous: there are siltstone interbeddings both in the Algyo (clayey cover formation), and the Szolnok Formations (dominantly sandstone), as we could see on well-logs of HC exploration wells. The siltstone in these formations does not have porosity high enough to be the storage rock, whereas the permeability is not low enough to be a good cap rock. That is why we try to avoid sampling siltstone-rich regions in the whole Jaszsag Basin. On the other places, and depth intervals we have used drilling cores to get a realistic quality and representative quantity of the tested formations. Our detailed studies deal with the sandy Szolnok Formation, and the clayey Algyo Formation. The Szolnok Fm. is mainly formed by sandstone, its bottom is nearly 1000 to 3500 m deep under the surface, thus it would be used as a storage rock. Its cap rock (seal) is the Algyo Fm. with more than 1000 m thickness, and a clayey composition. These potential rock associations are examined in detail in our ongoing research. We will do ex situ tests observing the behavior of the rocks when injecting supercritical CO_2 in the saline pore water on pressure and temperature representing the depth of planned injection conditions.