A new and extended Sleipner Benchmark model for CO2 storage simulations in the Utsira Formation

Abstract

Abstract This paper introduces a new benchmark model for the Sleipner CO2 storage site. The new Sleipner Benchmark has the same aerial coverage of the original benchmark, but is extended in depth to include the CO2 layer trapped beneath a thick shale interval. The Sleipner Benchmark is a numerical mesh and geological description of the upper part of the storage site, based on high-resolution 4D seismic mapping of the uppermost layers of CO2 over the period 1999-2008. This allows for calibrated simulations of a decade of plume dynamics, and prediction of both the free- phase and dissolved CO2 distributions. Calibrated modeling results from the first Benchmark are presented and discussed with respect to the dynamic equilibrium behavior of the uppermost layer of the plume. The results indicate that the plume is much closer to a stable distribution than previously predicted by modeling, and is likely to further stabilize as a result of significant dissolution in the decades immediately following injection. Benchmark results support a capillary-dominated (layering) and gravity-segregated (flat gas-water contact) interpretation of the Sleipner plume beneath the caprock. The new Benchmark addresses the multi-layered distribution of the entire plume. A conceptual model is presented that clearly distinguishes between Darcy flow and buoyant capillary flow. The stratigraphic alternation of high and low permeability rocks is commonly found in storage formations; however, the baffled nature of stacked CO2 layering is inherently challenging for reservoir simulation. The new Benchmark will allow modelers to address this challenge by attempting to match the observed CO2 distribution in the uppermost two layers. This will provide insights into the entire plume dynamics, as well as the nature of CO2 migration when stored in formations that are characterized by thin shale or siltstone baffles.