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

Abstract

In Salah Gas Project in Algeria has been injecting 0.5-1 million tonnes CO 2 per year over the past five 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 an ongoing research project we use field data and coupled reservoir-geomechanical numerical modeling to assess the effectiveness of this approach and to investigate monitoring techniques to evaluate the performance of a CO 2 -injection operation in relatively low permeability formations. Among the field data used are ground surface deformations evaluated from recently acquired satellite-based inferrometry (InSAR). The InSAR 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. In this paper we use the observed surface uplift to constrain our coupled reservoir-geomechanical model and conduct sensitivity studies to investigate potential causes and mechanisms of the observed uplift.The results of our analysis indicates that most of the observed uplift magnitude can be explained by pressure-induced, poro-elastic expansion of the 20 m thick injection zone, but there could also be a significant contribution from pressure-induced deformations within a 100 m thick zone of shaly sands immediately above the injection zone.

Long-term thermal effects on injectivity evolution during CO2 storage

“…Simulation results showed that such ground uplift rate could be reproduced by considering pressure increase and volumetric expansion of both the injection zone and the overlying caprock (Rutqvist et al, 2010). This uplift rate would require the caprock permeability to be two orders of magnitude higher than the initially estimated value from core samples (Rutqvist et al, 2010). Furthermore, a double lobe uplift pattern appeared on top of KB-502 injection well, which was explained by the opening of a fracture zone at depth .…”

“…A ground uplift of around 5 mm/yr was measured on top of the three horizontal injection wells using satellite geodetic data (Vasco et al, 2008;Mathieson et al, 2009;Onuma and Okhawa, 2009). Simulation results showed that such ground uplift rate could be reproduced by considering pressure increase and volumetric expansion of both the injection zone and the overlying caprock (Rutqvist et al, 2010). This uplift rate would require the caprock permeability to be two orders of magnitude higher than the initially estimated value from core samples (Rutqvist et al, 2010).…”

A hydromechanical approach to assess CO2 injection-induced surface uplift and caprock deflection

“…[7][8][9][10] Although these approaches can address the problem, significant efforts and costs are required to construct numerical models for each potential candidate site and for uncertainty studies of geometric, geological and material parameters. Analytical solutions or semianalytical approaches may be more suitable because of their computational efficiency and ability to identify driving mechanisms.…”

“…5,6,28 Because highly accurate measurements are available, the surface heave at In Salah is considered an ideal benchmark problem for geomechanical modelling. Using these data, Rutqvist et al 8 and Preisig and Prévost 7 investigated the surface uplift around injection well KB501 using 3D and 2D numerical models, respectively. The results are in good agreement with the field measurements.…”

“…The results are in good agreement with the field measurements. Here, we apply our semi-analytical solutions to the same data set used by Rutqvist et al 8 to assess the same problem. Instead of a three-dimensional analysis, we perform our analytical modelling in a 2D axisymmetric configuration.…”