The Krechba field is part of a multi-field gas development in central Algeria where CO2 is being injected rather than vented to develop carbon storage techniques within an active gas producing reservoir. Surface deformation monitoring has thus far proven to be one of the more useful of a wide array monitoring methods deployed at the site. Using differential interferometric synthetic aperture radar (InSAR), Pinnacle and MDA Geospatial services produced a high-resolution deformation time series of the Krechba field area over a 5 year period between 2004 and 2009. While the deformation measurements provide a qualitative visual assessment of the injection performance, the real goal of surface deformation monitoring is to determine the location of subsurface strain changes induced by the injected fluid. A geomechanical model is needed to determine the surface response to a given subsurface strain. An inversion routine modifies the strain source or sources to find a system that produces theoretical surface motion that best matches the measured deformation. This paper uses the example at injection well KB-501 to explore how the solution and associated uncertainty is affected by the choice of geomechanical model at this location. The best fit solution and sensitivity of that solution is derived from homogeneous and layered models of varying complexity using both linear and non-linear inversion techniques. The results place boundaries on the possible subsurface pressure distribution associated with CO2 injection and also quantify the possible benefit obtained from more complex geomechanical modelling for inversion of surface deformation data. The solutions suggest that the injected fluid at KB-501 remains near the intended depth and is spreading primarily along a northwest-southeast trajectory as anticipated.

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