Abstract
Changes in subsurface pore pressures and stresses due to the extraction of hydrocarbons often cause deformation over oil and gas fields. This can have significant consequences, including ground subsidence, induced seismicity and well failures. Geodynamic monitoring is an important requirement in recognising potential threats in sufficient time for remedial measures to be implemented. Differential interferometric synthetic aperture radar (DInSAR) is increasingly utilised for monitoring ground deformation over oil and gas reservoirs, achieving greater spatial coverage than traditional field-based surveying techniques. However, ground deformation over oil and gas fields can extend regionally into the surrounding rural landscape, where many conventional DInSAR techniques are of limited use due to the dynamic nature of the land cover. The Intermittent Small Baseline Subset (ISBAS) method is an advanced DInSAR technique, which considers the intermittent nature of coherence over dynamic land cover types to obtain markedly more ground motion measurements in non-urban regions. In this study, the ISBAS technique is used to delineate deformation over the super-giant Tengiz oil field in rural Kazakhstan. Analysis of ENVISAT data for 2004-2009 reveals a well-defined bowl subsiding with a maximum rate of -15.7 mm/year, corroborated by independent DInSAR studies and traditional levelling data. Subsequent application of ISBAS to Sentinel-1 data reveals significant evolution of deformation over the field in 2016-2017, with subsidence increasing dramatically to a maximum of -79.3 mm/year. The increased density of measurements obtained using the ISBAS technique enables accurate and comprehensive delineation and characterisation of ground deformation in this rural landscape, without the need for corner reflectors. This enhanced information could ultimately aid reservoir characterisation and management, and improve understanding of the risk posed by ground subsidence and fault reactivation.
NSTL
Elsevier