Final Report Summary - CO2SINK (In-situ R&D Laboratory for Geological Storage of CO2) The CO2SINK pilot project aimed for a better understanding of geological CO2 storage in a saline aquifer. The main focus of the project was the development and testing of monitoring techniques. Furthermore, CO2SINK served as a test site for CO2 injection and safety measures. Through the European project CO2SINK the most advanced monitoring project of the subsurface worldwide was established. It triggered a broad variety of national and international activities, which contributed greatly to the success of the storage operation.Food-grade CO2 was injected into upper triassic sandstones (Stuttgart formation) of a double-anticline structure. The Stuttgart formation represents a fluvial environment composed of sandstone channels and silty to muddy deposits. Undisturbed, initial reservoir conditions are approximately 35 degrees Celsius and 62 bar at depth of injection at 650 m below surface. The initial reservoir fluid was highly saline with about 235 g/l total dissolved solids primarily composed of sodium chloride with notable amounts of calcium chloride. The initial pH value was 6.6. Hydraulic tests revealed permeability between 50 and 100 mDarcy for the sand channels of the storage formation.CO2 injection started on 30 June 2008 and by end March 2010 - after 21 months a total of 33 000 tons of CO2 has been injected. This is slightly more than half of the original target of up to 60 000 tons. The injection was operated successfully and safely. The mean injection rates were around 67 tons of CO2 per day when in service. The monitored wellhead pressure was almost constant at 63 to 64 bar and the calculated flow pressure at reservoir depth was 77 to 78 bar. The effects of CO2 injection were observed with surface and downhole measurements. A long-term field monitoring of natural diffusive CO2 soil gas emissions, gas fluxes along faults and fissures as well as CO2 dissolved in regional ground waters at shallow levels with different commercially available geochemical sensors has been conducted over the whole life time of the project.Spreading of the CO2 plume in the reservoir was monitored by a broad range of geophysical and geochemical techniques. Three wells (one injection and two observation wells) were equipped with 'smart casings' containing electrodes for electrical resistivity tomography (ERT) behind casing, facing the rocks and a distributed temperature sensing (DTS). Changes in borehole temperatures were continuously monitored since the start of CO2 injection with permanently installed downhole fibre-optic sensor cables using DTS. A newly developed gas membrane sensor (GMS), enabling a continuous monitoring of the gas composition in the observation wells (OWs), observed the arrival of CO2 and gaseous tracers at the observation wells.The seismic monitoring included crosshole seismic experiments, vertical seismic profiling (VSP) and moving source profiling (MSP), star seismic experiments and 4-D seismics. Seismic measurements for structural interpretation and baseline characterization were carried out in 2005 and 2007 using different methods in order to cover the near-injection to the regional scale. Time-lapse crosshole seismics showed no considerable changes in seismic velocity between the two observation wells within the first two repeats after injection of 660 tons and 1 700 tons of CO2, respectively. However, after injection of 18 000 tons CO2 all time-lapse surveys showed a clearly observable signature of the CO2 propagating in the Stuttgart formation.ERT proved to be sensitive to saturation changes caused by propagation of supercritical CO2 within the reservoir. Forward modelling indicated an increase of electrical resistivity of about 200 % caused by CO2 injection, which is verifiable in the field data from geoelectrical cross-hole and surface-downhole measurements, respectively.Data used for history matching were injection pressure and CO2 arrival times at both OWs. CO2 arrival at the first OW was in good agreement with the predictions made by different modelling approaches. However, the arrival of CO2 at the second OW was notably later than predicted. Downhole sampling revealed quantitative and qualitative changes after CO2 arrival in the first OW. An increase of the iron content and shifts in the microbial community from chemo-organotrophic to chemolithotrophic populations were observed, as evidenced by the temporarily outcompetition of sulphatereducing bacteria by methanogenic archaea. Additionally, an enhanced activity of the microbial population after five months CO2 storage indicated that the microbial community was able to adapt to the changes in environmental conditions (e.g. pH decrease, pressure increase).Long-term CO2-fluid exchange experiments under simulated reservoir conditions (p,T) were performed to study petrophysical, mineralogical, geochemical and microbiological changes induced by CO2 exposure in detail. Ca2+ and Mg2+ concentrations in the sampled fluid exceeded Ketzin reservoir fluid concentrations by 15 % and 8 %, respectively, which may reflect mineral dissolution in response to CO2 exposure. This is consistent with the dissolution of Ca-rich feldspar observed. The majority of the microbes were able to adapt to the changed conditions, since only minor changes in the composition of the microbial community were observed. Extraction experiments with CO2 at supercritical conditions showed a preferred extraction of formate, acetate, chloride and nitrate. Considerable efforts were made to inform the wider community about the project and CCS in general. There have been many visits to the site where a small visitor's centre and a tour of the site have been available. Press coverage following several open events has been quite extensive, ranging from local, national, European and international journalists. More than 1 000 new articles were printed in newspapers and weekly journals, all big TV stations of Germany and from several European countries (e.g. France, Denmark) and beyond (e.g. Japan) put CO2SINK into the media. The visit of Andris Piebalgs, the European Commissioner for Energy, was one of the highlights of public communication. The communication activity was focused on the local acceptance by educating, informing and involving the local public. Little if any adverse reaction has been received from the local inhabitants.Following the CO2SINK project and further national funded projects for Ketzin the aim is to continue and complement the research activities at the CO2 storage site for a second period. For this reason, the GFZ German Research Centre for Geosciences coordinates the two proposals CO2MAN and CO2CARE. Documenti correlati Final Report - CO2SINK (In-situ R&D Laboratory for Geological Storage of CO2)
