The Impact of Shale Barriers and Injection Strategy on CO2-Flooding and Sequestration Performance

摘要

In this paper the impact of stochastic shale barriers and injection-strategy on recovery-factor and sequestration capacity have been investigated for secondary CO2-floods in horizontal oil reservoirs. Permeability fields, shale size and shale fraction have been varied in several numerical simulations and the calculated oil recovery factors have been correlated to a dimensionless number relating the viscous to gravity forces. The results show that for relatively homogeneous reservoirs the impact of shale barriers can be accounted for using an upscaled vertical permeability and that a unique relationship can be found between recovery factor and ratio of viscous to gravity forces. For layered reservoirs the impact of shales depends very much on the vertical layer permeability arrangement, pressure drop ratio, and optimisation of injection strategy. Based on the best field characterisation (permeability and shale barriers), injection strategies aim at simulating an overall CO2 injection in all layers, followed by an analysis of the flooding mechanisms, and ending with an optimisation of the vertical conformance. This is recommended especially for low to intermediate pressure drop ratio.