Benchmark Calibration and Prediction of the Sleipner CO2 Plume from 2006 to 2012

Abstract

The Sleipner Benchmark, released in 2011 by Statoil, allows for high-resolution flow simulations of the world's largest offshore CO2 storage site. While benchmarks already exist for CO2 storage, they are unconstrained by observational data. The Sleipner Benchmark is unusual in being a real case study with data of sufficient detail and duration to calibrate key uncertainties. At Sleipner, CO2 has been injected since 1996 into a shallow marine sandstone formation. The model measures 3×6km2 directly above the injection location, and includes the subtle caprock topography that appears to control the plume development. This paper presents simulation results that (a) match the plume over the period 1999 to 2008, and (b) predict the plume for 2010 (seismic not yet released) and 2012 (seismic acquired last year), using the 2006 and 2008 observations as calibration points. A combination of modeling techniques indicates that the best match is derived from a black oil reservoir simulator, but only when adapted to approximate the near-equilibrium pressure conditions of a migration simulator for flow beneath the caprock. This strongly favors a gravity-segregated/capillary-dominated interpretation of the plume behavior at a relatively short distance from the injection location. The black oil simulation approach also allows for an estimate of the plume dissolution behavior - a poorly constrained phenomenon. The simulation results imply: (1) a rapid approach to equilibrium for the buoyant CO2 within years; and (2) a significant local dissolution effect within decades. This combination of near-equilibrium conditions and subsequent dissolution suggests that the risk associated with the Sleipner plume is currently low and likely to diminish in the immediate post-operational phase.