Three-dimensional deformation over Shuguang oilfield in Liaohe River Delta, China, from multi-track InSAR and its impacts on flood inundation

Land subsidence has a great impact on coastal plains near sea level, leading to permanent inundation. The Shuguang oilfield, located in Liaohe River Delta (LRD), northeastern China, is one of the most significant subsidence areas as a direct consequence of oil production. We studied the production-induced deformation in the LRD region by Sentinel-1 radar images. Images from two ascending and two descending tracks are processed by an Interferometric Synthetic Aperture Radar (InSAR) time series analysis over the 2017 to 2021 period, providing deformation rate maps and time series in the radar line-of-sight (LOS) direction.

Previous researches carried out in this area assumed the oil production-induced deformation corresponds only to vertical deformation. Here, we proposed a method to retrieve the three-dimensional (3D) displacement field over the oilfield. We retrieved the vertical and east-west deformation components by combining the multiple InSAR geometries LOS observations and retrieved the north-south component based on the assumption of a physical relationship between the horizontal and vertical displacement.

The derived 3D displacement fields over Shuguang oilfield exhibit a circular subsidence bowl with a maximum subsiding rate reaching 212 mm/year, accompanied by a centripetal pattern of horizontal displacements with maximum rates up to 50-60 mm/year moving towards the subsidence center. The retrieved-3D displacements are in good agreement with predictions from the geomechanical modeling by assuming a disk-shaped reservoir subject to a uniform reduction in pore fluid pressure. Finally, we show the importance of knowing both the vertical and horizontal displacement in characterizing the lateral boundary of the subsurface reservoir.

The Liaohe River Delta region is often affected by heavy rainfall and storm surge in flood season, and flood disasters occur frequently in this low-lying coastal area. This deltaic region is vulnerable to floods not only from the extreme heavy rainfall, but also the land subsidence related to oil production. By spatial overlay analysis of the land subsidence distribution and the inundation extent of a flood event in August 2022, we reveal the impacts of land subsidence on flood inundation in this region. Our findings provide scientific support for oil production-related subsidence control and flood planning and designing in this deltaic region.