Reservoir Management of CO2 Injection: Pressure Control and Capacity Enhancement

Abstract

The transition to large-scale CO2 storage as part of a low Carbon-fuels energy mix will require intelligent use of reservoir management methods, and can draw from many decades of experience from Enhanced Oil Recovery (EOR) projects. CO2 EOR is also proposed as an important CO2 storage option, but has not yet been optimized for CO2 storage. We focus here on the application of reservoir management methods for optimizing CO2 storage.In hydrocarbon production, high recovery factors normally relate to good volumetric sweep of the injected phase, as has been demonstrated by 4D seismic monitoring for a number of fields. The volumetric sweep in turn depends on the sweep efficiency at the pore scale as well as the macroscopic areal and vertical sweep. Flexible drainage strategies that can be adapted over time have also proven to be a key to successful enhanced recovery measures.In order to translate this reservoir management perspective to CO2 storage in saline aquifers, we simulate a number of cases using Sleipner-based and Snøhvit-based reservoir models. The Sleipner case involves CO2 injection close to the critical point in a high permeability sandstone reservoir while the Snøhvit case involves deeper, high- pressure injection into a moderate permeability fluvial reservoir. Our simulation results indicate that the sweep efficiency during the injection period has a critical effect on the long-term storage behavior. Therefore, the injection period is an important time-window where it is possible to actively design the injected phase composition, injection pressure and temperature, the injection strategy, and the flooding pattern in order to manage the CO2 plume development.Careful design of the injection wells is critical for successful delivery of the overall injection plan. For large-scale CO2 injection projects alternative well configurations are required to increase injectivity. Our simulated cases with long-reach and/or multilateral injection wells give significant improvements in injectivity. Such well designs combined with methods for enhancing the sweep efficiency result in increased overall storage efficiency and effective use of the available pore space.