The pressure impact of CO2 storage on neighbouring sites

In this paper, we present a saline aquifer showcase model from the North German Basin, predicting the regional pressure impact of a small industrial scale CO2 storage operation on its surroundings. The static model is based on real geology while the injection program is fictitious. We simulated a rate controlled injection of 2.5 Million tons CO2 per year through a single vertical well into the structural top of a dome shaped anticline, over a period of 10 years. The target is a 20 m thick sandstone layer intercalated in low permeability claystone sequences. We used ECLIPSE300 with its CO2 storage module and MUFTE-UG to predict pressure at the top of the target sandstone layer in 1, 5, 10, and roughly 31 km distance to the injection point. The farthest point represents the structural top of a neighbouring anticlinal dome, another favourable potential storage site. We varied the model's boundary conditions, permeability, permeability anisotropy, rock compressibility, and injection temperature. A total of nine model scenarios were run, five with MUFTE-UG and another four with ECLIPSE. Comparison of reference scenarios showed that the results of both simulators match well. In the open boundary model, pressure increase is lowest and dissipates back to the pre-injection state within 30 years after injection shutdown. In the fully closed models, pressure peaks are high, equilibrating to a remnant, model-wide overpressure several decades after the end of injection. In the distance, this equilibrated, model-wide overpressure is the actual maximum pressure. In the model scenarios which are laterally half open, half closed, pressure relief is seriously retarded in comparison to the fully open model. In all cases, the pressure maximum arrives at the neighbouring structure ( 31 km distance) years after the actual injection shutdown. Rock compressibility impacts both the peak pressure and the speed of the pressure build-up and relief. High permeabilities are more important in the immediate injection area than for the regional footprint. In all of our fully closed (i.e. the most pressurized) models, the remnant regional overpressure amounted to about 9 bars. If 10 bars are taken as the maximum tolerable overpressure, then the volumetric storage capacity of the target structure itself is not affected. However, injection into the target structure does affect the storage capacity of the neighbouring site. While a purely volumetric approach yields a cumulative storage capacity of roughly 175 Mt for both structures, a tolerable regional overpressure of 10 bars lowers the joint storage capacity to about 32 Mt CO2. Exactly what regional pressures are tolerable for a given aquifer, however, needs to be determined on a site specific base. (C) 2010 Published by Elsevier Ltd.