A Century of Extraction
The ground in and around Dibrugarh, Assam, is sinking. This gradual lowering of the earth's surface is a direct consequence of more than a century of oil and gas production in the region. The area is part of India's oldest petroleum-producing zone, with the first commercially successful well in the country struck at nearby Digboi in 1889. This long history of extraction has had a profound effect on the local geology.
The mechanism causing the subsidence is a matter of geophysics. Crude oil and natural gas are held within the tiny pores of subterranean rock formations. The pressure of these fluids helps support the weight of the overlying rock layers. When oil, gas, and associated water are pumped out, this subsurface pressure decreases. Without the support of the fluid pressure, the porous rock structure compacts under the immense weight from above. This compaction at depth manifests on the surface as subsidence. The main hydrocarbon-bearing geological formations in Upper Assam are the Barail Group (Upper Eocene to Lower Oligocene) and the Tipam Group (Upper Miocene). It is the compaction of these layers that leads to the sinking land.
measuring a sinking area
Satellite-based radar studies provide precise measurements of the ground deformation. A recent study using Sentinel-1A satellite data between 2015 and 2022 confirmed the ongoing subsidence. The analysis revealed that the Dibrugarh area is subsiding at an average rate of approximately 5 millimeters per year. The nearby Digboi region, with its even longer history of extraction, is deforming at a much faster rate of around 22 millimeters per year.
The consequences of this slow-motion sinking are visible across the area. The cumulative effect over decades results in significant drops in elevation, altering the local topography. This change disrupts the delicate balance of the Brahmaputra river floodplain. Natural drainage patterns can be altered or even reversed, leading to waterlogging and increased flood risk. Infrastructure pays a heavy price. Roads develop cracks, building foundations shift, and pipelines are put under stress. The 2020 gas blowout and fire at the Baghjan oil field, near Dibrugarh, showed the environmental risks associated with the industry in this ecologically sensitive area. That incident caused extensive damage to the nearby Maguri-Motapung wetland, killing wildlife and affecting local livelihoods.