85 / 2023-04-17 17:23:36

Three-dimensional surface deformation in the Liaohe Oilfield, northeast China, observed from multi-track InSAR

Land subsidence, InSAR, three-dimensional deformation, oilfield

In unconsolidated or poorly consolidated reservoirs, displacement associated with oil and gas production can result in reservoir compaction, land subsidence, and potential fault activation, causing damage to oil production facilities and surface infrastructures. The induced surface displacement is predominantly vertical subsidence, which has a great impact on coastal plains and wetlands near sea level, and land elevation loss increases flood risk, leading to permanent inundation. The Liaohe oilfield, located in Liaohe River Delta (LRD), northeast of China, is one of the most significant subsidence areas in China as a direct consequence of oil extraction from the reservoir. In this work, we investigate the production-induced surface displacement in the LRD region by taking advantage of multiple viewing geometries of Sentinel-1 radar images. Images from two ascending and two descending tracks covering the area are processed by an Interferometric Synthetic Aperture Radar (InSAR) time series analysis over the 2017 to 2021 period, providing consistent displacement rate maps and displacement time series in the radar line-of-sight (LOS) direction.

The regional InSAR displacement fields reveal three surface subsidence features across the lower LRD related to oil production, with a maximum subsiding rate up to 177 mm/year, 69 mm/year, and 41 mm/year in the LOS direction for Shuguang, Huanxiling, Jinzhou oilfield, respectively. Results also reveal a land uplift at a depleted oilfield in Huanxiling, with a maximum uplifting rate of ~35 mm/year in the LOS direction, which is likely related to the natural gas storage within the depleted reservoir. A seasonal displacement pattern with an annual peak-to-peak amplitude of ~16 mm in response to the summer gas injection and winter gas extraction is embedded in the uplift trend at this oilfield.

Previous studies carried out in this area assumed that the oil production-induced displacement retrieved from InSAR corresponds only to vertical deformation. Horizontal motion can also occur, which can adversely affect pipes and other surface structures unless they are designed to accommodate the strain. Here, for the first time, we proposed a method to retrieve the full three-dimensional (3D) displacement field over the oilfield. We retrieved the vertical and east-west displacement components by combining the multiple InSAR viewing geometries (ascending and descending) 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 center of the subsidence bowl. The volume of the subsidence bowl is 1.0109×10⁴ km³, which is corresponding to a volume reduction of the compacting reservoir of 0.6739×10⁴ km³. 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. Our findings demonstrate that high spatiotemporal resolution of surface displacement data from InSAR can provide valuable information about reservoir geomechanics behavior and InSAR can be used as a tool for the optimized management of reservoir production.