Screening and evaluation of a saline aquifer for CO 2 storage: Central Bohemian Basin, Czech Republic

Abstract

This work is a preliminary screening and evaluation of one of the most promising geological structures for CO 2 storage in the Czech Republic, namely the deep saline aquifers of the Central Bohemian Permian–Carboniferous Basin. Archived and new mineralogical, petrophysical, lithological, geochemical, sequence-stratigraphic, thermal history, core analyses, hydrogeological testing, and seismic data for both the reservoir formation and seal rocks were used to build an initial static geological model of the Central Bohemian Basin. Using this static geological model, a sector of the Basin was identified as meeting the basic geological requirements for CO 2 storage; a preliminary reservoir model of this sector was created and used to perform several simulation runs to further evaluate the suitability and potential of the selected formation for storing captured CO 2 from industrial emissions. The initial sensitivity analyses performed using a mechanistic model indicated that while the storage capacity of the structure (based on rock porosity and net-to-gross ratio) may be sufficient, the critical factor was the CO 2 injectivity. The CO 2 injectivity was found to be controlled mainly by the formation heterogeneities, rock permeability, reservoir connectivity, storage formation pore volume, as well as the injection wells type, location and completion scheme. Therefore, based on the current geological model these parameters were the most influential ones defining a potential success of a CO 2 geological storage project. Full-scale sector simulations confirmed the findings of the mechanistic model. The current reservoir model and simulation results have also shown that it would be unlikely to be possible to inject the required target volume of 2 million tonnes of CO 2 per year within a single storage project in the Central Bohemian Basin. The target CO 2 volume could be achieved only for a reservoir scenario that contains an optimistic absolute permeability field, sealing faults in the northern part of the site and the presence of two water production wells. These two production wells could be viewed as actual pressure relief wells or a way of (partially) reflecting pressure communication of the simulated aquifer region to adjacent pore volumes in the geological basin. At present, the available geological data does not allow a detailed formation characterization (there is a lack of reliable permeability and porosity data, sufficient and effective description of reservoir heterogeneities such as existence of faults, fault conductivity, presence of low or high permeability zones, sealing efficiency, etc.). Hence, crucial issues such as CO 2 injectivity, and CO 2 migration and containment in the reservoir rock currently remain uncertain. There is a potential to quantify these parameters more accurately only after additional and reliable seismic, core, and testing data from actual reservoir depths become available. A reduction of the existing uncertainties related to formation characterization is a prerequisite for more accurate predictions of the available reservoir volumes, the required number of wells, the well type, position and completion, CO 2 injection operational issues, and finally the amount of CO 2 that could potentially be stored.