Coupled reservoir-geomechanical analysis of CO2 injection at In Salah, Algeria

In Salah Gas Project in Algeria has been injecting nearly one million tonnes CO(2) per year over the past four years into a water-filled strata at a depth of about 1,800 to 1,900 m. Unlike most CO(2) storage sites, the permeability of the storage formation is relatively low and comparatively thin with a thickness of about 20 m. To ensure adequate CO(2) flow-rates across the low-permeability sand-face, the In Salah Gas Project decided to use long-reach (about 1 to 1.5 km) horizontal injection wells. In this study we are using field data and coupled reservoir-geomechanical numerical modeling of CO(2) injection to analyze geomechanical responses and to assess the effectiveness of this approach for CO(2) storage in relatively low permeability formations. Among the field data used are surface deformations evaluated from recently acquired satellite-based inferrometry (In SAR). The In SAR data shows a surface uplift on the order of 5 mm per year above active CO(2) injection wells and the uplift pattern extends several km from the injection wells. We use the observed surface uplift to constrain our coupled reservoir-geomechanical model. We conduct sensitivity studies to investigate potential causes and mechanisms of the observed uplift. Preliminary results of our analysis presented in this paper indicates that most of the observed uplift magnitude can be explained by poro-elastic expansion of the 20 m thick injection zone, but there could also be a significant contribution from pressure changes within the adjacent caprock. Moreover, we show that surface deformations from In SAR can be useful for tracking the fluid pressure and for detection of a permeable leakage path (e.g. in a permeable fault) through the overlying caprock layers. (C) 2008 Elsevier Ltd. All rights reserved.