Lithological and Petrophysical Core-Log Interpretation in CO2SINK, the European CO2 Onshore Research Storage and Verification Project

Abstract

The storage of carbon dioxide (CO 2 ) in saline aquifers is one of the most promising options for Europe to reduce emissions of greenhouse gases from power plants to the atmosphere and to mitigate global climate change. The CO 2 SINK (CO 2 Storage by Injection into a saline aquifer at Ketzin) project is a research and development (R&D) project, mainly supported by the European Commission, the German Federal Ministry of Education and Research, and the German Federal Ministry of Economics and Technology, targeted at developing an in-situ laboratory for CO 2 storage.The preparatory phase of the project involved a baseline geological-site exploration and the drilling of one injection and two observation wells, as well as the acquisition of a geophysical baseline and geochemical monitoring, in Ketzin, located near Berlin. The target saline aquifer is the lithologically heterogeneous Triassic Stuttgart formation, situated at approximately 630-to 710-m (2,070-to 2,330-ft) depth. A comprehensive borehole-logging program was performed consisting of routine well logging complemented with an enhanced logging program for one well that recorded nuclear-magnetic-resonance (NMR) and boreholeresistivity images, to characterize the storage formation better. A core analysis program carried out on reservoir rock and caprock included measurements of helium porosity, nitrogen permeability, and brine permeability at different pressure conditions.The saline aquifer at Ketzin shows a variable porosity/permeability distribution, which is related to grain size, facies variation, and rock cementation with values in the range from 5 to > 35% and 0.02 to > 5,000 md for porosity and permeability, respectively. On the basis of core analysis and logging data, an elemental loganalysis model for the target formation was established for all three wells. In addition, permeability was estimated using the Coates equation and compared with core data and NMR log-derived permeability, which seems to provide meaningful permeability estimates for the Ketzin reservoir. On the basis of the good core control that guided the petrophysical well-log interpretation in the first two CO 2 SINK wells, a porosity and permeability prediction by analogy for the third well is appropriate and applicable. The availability of cores was crucial for a sophisticated formation evaluation at borehole scale that characterizes the real subsurface conditions.

Hydraulic characterisation of the Stuttgart formation at the pilot test site for CO2 storage, Ketzin, Germany

“…The discrepancy is not a systematic effect from core expansion. Compared to atmospheric pressure, a confining pressure between 50 and 85 bar does not affect the results (Norden et al 2010). We therefore conclude that the discrepancy is not a measurement error.…”

“…The circles represent values which are determined with core samples, the green line represents the Coates permeability, and the blue line represents the NMR permeability. The second column is the geological profile (Förster et al submitted), the third column presents the caliber log, and the fourth column shows the measured permeabilities (Norden et al 2010). Table 4: Calibrated aquifer parameters for single-hole and cross-hole evaluations.…”

“…The wells Ktzi 200, Ktzi 201 and Ktzi 202 form a right-angled triangle with leg lengths of 50 m and 100 m. At these wells, the sandstone is divided into aquifer layers with thicknesses of 5 m to 8 m (Figure 1). The core analyses and borehole logs show an effective aquifer porosity of about 20% (Norden et al 2010). The layer's average horizontal core permeabilities range between 500 mD and 1,100 mD ( Table 1).…”

“…Thin layers of sandstone and siltstone exist below the main aquifers (Figure 1). They belong to overbank facies and are probably not connected to the flow system (Förster et al, submitted).The mudstone shows a permeability in the microdarcy range (Norden et al 2010). Although the distribution of the sandstone is not well-predicted on the regional scale (Frykman 2006), the sandstone structure in Ktzi 200 and Ktzi 201 is very similar, suggesting that they belong to the same channel (Norden et al, personal communication).…”

Advanced and Integrated Petrophysical Characterization for CO2Storage: Application to the Ketzin Site

“…For NMR, we computed the T 2 distribution using an in-house software, which was also used for analyzing laboratory data. Unlike the NMR distribution presented by Norden et al (2010), no data averaging is performed in order to have a better vertical resolution. Therefore, the distribution is shown at the highest possible vertical resolution (about 0.25 m).…”