TOUGH2 SIMULATION OF THE PUMPING TESTS AT KETZIN SITE: HETEROGENEITY EFFECTS AND MODEL CALIBRATION

ABSTRACT
The Stuttgart Formation used for CO2 injection at the Ketzin pilot site in Germany is highly heterogeneous. The characterization data, including 3D seismic amplitude image, the regional geology data, and the core measurements and geophysical logs of the wells, show a lithologically heterogeneous formation composed of permeable sandstone channels of varying thickness and length embedded in less permeable mudstones. At the storage site, most of the sandstone channels are located in the upper 20 m of the formation, with only a few sparsely distributed sandstone channels in the lower part of the about 70-80 m thick formation. Due to the low channel thicknesses, the explicit spatial pattern of these channels could not be obtained from the 3D amplitude image. Heterogeneity has a large effect on the pressure propagation measured during a suite of pumping tests conducted in 2007-2008 and also impacts strongly the CO2 arrival times observed during the ongoing CO2 injection experiment. To understand the varying effects of heterogeneity at the Ketzin pilot site and calibrate the spatial variability of permeability and porosity using the field monitoring data, we developed a TOUGH2 model for modeling the hydraulic pumping tests. A geological model calibrated against downhole pressure of two wells and the CO2 arrival times was used in the simulations discussed here. Our modeling results show that the simulated pressure responses to the pumping tests were significantly different in magnitude from the measured data. A systematic increase or decrease of permeability fails to improve the matches to the pressure data in all observation wells. Further work is needed on the calibration of the geological model against the pumping test results using inverse modeling approaches.