--> Abstract: The Mudstone-Dominated Caprock System of the CO2-Storage Site at Ketzin, Germany; #90063 (2007)

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The Mudstone-Dominated Caprock System of the CO2-Storage Site at Ketzin, Germany

 

Förster, Andrea1, Niels Springer2, Gerhard Beutler3, Joachim Luckert4, Ben Norden5, Holger Lindgren2 (1) GFZ Potsdam, Potsdam, Germany (2) GEUS, Denmark (3) Martin Luther University Halle-Wittenberg, Germany (4) LBGR, Germany (5) GFZ Potsdam, Germany

 

Critical evaluation of the top seal properties constitutes an integral part in Europe's first onshore pilot storage of CO2 to be performed in 2007 at Ketzin, in the Northeast German Basin. We report facies and physical and mineralogical properties of the Upper Triassic (Middle Keuper) caprock above the Stuttgart Formation serving as a CO2 reservoir. The Ketzin caprock sediments are of continental playa type, consisting mainly of fine-grained clastics (clayey and sandy siltstone) that alternate with thin-bedded lacustrine sediments (carbonates), and evaporates. The playa-type succession is of basin-wide uniformity permitting marker horizons to be traced over great distances. The caprock characterization involved the study of outcrop analogues and analysis of well logs and cores. Surface exposures offered a unique perspective on the stratigraphic relationships and are crucial in gaining a better appreciation of factors that affect the sealing behavior. Analysis by XRD, XRF, EMPA, SEM, AFM, MICP, DTA, and TG of a selection of core samples from the Ktzi 38 borehole provided a first insight into the expected sealing properties. The samples, mostly classified as clayey siltstone cemented by dolomite, exhibit an average porosity of 10% and a gas-permeability in the nanoDarcy range or below. The rocks contain illite (42-74 wt%), quartz (4-20 wt%), and dolomite (4-35 wt%), in addition to small fractions of plagioclase (2-8 wt%), chlorite (1-3 wt%), amorphous phases, K-feldspar, halite, and hematite. Pore bodies and pore throats are small (<500 nm and 10-36 nm, respectively), and the pore space is usually unconnected. The high clay-mineral content and the observed pore-space geometry attest good sealing properties.  

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California