Retrieving surface deformation by PSInSAR™ technology: A powerful tool in reservoir monitoring

Reservoir monitoring improves our understanding of reservoir behaviour and helps achieve more effective reservoir management and prediction of future performance with obvious economic benefits. It relies on an integrated approach involving both surveillance (well or surface based; seismic, electrical, leakage, flow and deformation measurements, etc.) and modelling. Surface deformation monitoring can provide valuable constraints on the dynamic behaviour of a reservoir enabling the evaluation of volumetric changes in the reservoir through time. Levelling campaigns, tiltmeters, GPS permanent stations and Permanent Scatterer SAR Interferometry (PSInSAR™) are the techniques most widely used to determine surface displacements. Whatever the surveying technique, the detection of millimetre-level surface deformation is required to monitor small surface displacement rates that could impact risk evaluation and land use planning. Depending on depth and reservoir/overburden rheology, volumetric changes in reservoirs due to fluid extraction and injection can induce either subsidence or uplift that could trigger fault reactivation and threaten well integrity; deformation may also be detectable at the surface. Mapping surface effects accurately requires hundreds of observation points per km² which cannot be delivered by traditional monitoring methods without unacceptably large expenditure. PSInSAR™ is one of the most promising and cost-effective techniques capable of providing high precision and high areal density displacement measurements over long periods of time. Moreover, the availability of PS data for both ascending and descending orbits enables the estimation of both vertical and E–W horizontal displacement fields. Two case histories will be presented to illustrate the advantages of PSInSAR™ technology for the detection of surface deformation induced by reservoir exploitation and monitoring of its evolution though time.