Abstract

Cyclic Steam Stimulation (CSS) can significantly change the volume of the bitumen-bearing reservoir. Uneven uplift of overburden caused by such volume change induces noticeable stress perturbation in the structure providing containment for the steam/bitumen emulsion and may lead to material yielding in subsurface structure. To study the impact and mechanism of such a phenomenon, InSAR images of surface deformation were collected between 2010 and 2011 at a CSS operation site. These interferograms were processed to 14 snapshots of surface deformation within that period of time. We observed that heave and subsidence can occur simultaneously across one operation site, as the heated steam front moves through the reservoir. A brief review of the production history of the site indicates that the surface deformation is directly related to fluid injection and extraction. In the first step of our modelling, we invert the surface deformation to assess the extent of reservoir expansion/compaction and induced subsurface deformation. Due to the highly non-uniqueness nature of the inversion results, we carefully benchmarked the mathematical and geomechanical parameters used in the inversion process. The results from the selected inversion parameters are compared with forward modeling results to increase the confidence of the inversion scheme. Subsurface deformation is modelled sequentially through Finite Element forward modelling. The computed reservoir deformation is channeled into the commercial FEM simulation software Abaqus to assess the stress and strain of the overburden. We load the deformation computed from inversion at the reservoir/overburden interface and then simulate the corresponding stress and strain alteration of the overburden. Simulation results show that uneven uplift from reservoir expansion and compaction can alter the stress state of the overburden significantly. This study shows that with proper knowledge of in-situ geomechanical characteristics, InSAR coupled with geomechanical modelling can be a useful tool to understand injection/production monitoring data and identify possible effects of CSS operations on the structural integrity of subsurface.

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