Research Article Open Access FA Abija et al., J Earth Sci Clim Change 2020 2020, 11:9 Review Article Open Access Journal of Earth Science & Climatic Change Volume 11 • Issue 9 J Earth Sci Clim Change , an open access journal ISSN: 2157-7617 Keywords: Subsidence, Symmetric and wide area lateral depressions, Flood vulnerability Introduction Ground subsidence is a form of mechanical deformation of the crustal materials resulting in the sinking of the ground surface such as ground level or sea foor into its surrounding environ- ment relative to a stable reference point [1]. It is a gradual, slow and subtle mass movement of the earth’s surface under gravi- tational loading as a consequence of lowering of the ground- water table due to aquifer overdraf, decreased porosity and or permeability, aquifer undersaturation and reduction in the wa- ter holding capacity [2]. Ground subsidence can be caused by heavy withdrawal of ground water in densely populated cities [3], hydro-compaction of recent sedimentary deposits, pressure depletion, porosity reduction and compaction of oil and gas res- ervoir [4-6]. Other causative factors include extraction of coal, sulphur, and other solids through mining; oxidation and shrink- age of organic deposits; catastrophic development of sinkholes in karst terrains, natural consolidation of sedimentary deposits, earthquake induced liquefaction, associated consolidation and reduction in pore spaces, secondary consolidation and compac- tion of organic materials; and coseismic and aseismic natural or regional plate tectonics movement above active faults [7]. Signifcant subsurface compaction in oil/gas felds can produce measurable ground subsidence [4] due to reservoir depletion in weakly cemented sandstones, porosity loss with hydrostatic pressure and shear enhanced compaction [5]. Te degree and spatio-temporal development of the bowl of subsidence depends on reservoir geometry, surface area, depth, production rates and the mechanical properties of the reservoir, overburden, under- burden and side-burden [1,8]. Te lateral extent of the vertical displacement of the ground surface also depends on the mate- rial properties of the overburden and depth of the compacting formation. Ground subsidence could produce catastrophic damages to the environment and infrastructures and efects could range from relative rise in sea level in coastal areas, fooding, loss of wet- lands, coastal erosion, salinization of fresh ground water aqui- fers, formation of karst and sinkholes, foundation failures in civil engineering infrastructures, wellbore casing collapse and sand production in completed oil wells. Ground subsidence above producing oilfelds was frst reported in the Goose Creek field in Texas in the late 1910 s and in the 1920 s and the Bolivar oil field in Venezuela [9]. Another well- known case is the Wilmington field in Long Beach, California, with about 9 m between 1932 and 1965 [10]. Te Ekofisk and Valhall reservoirs in the Norwegian sector of the North Sea, and the Groningen gas field onshore and ofshore the Netherlands have been reported. Over 50 areas of contemporary subsidence are known, some with as much as 10 meters in countries such as Mexico, Japan and the United States. In the San Joachim valley, * Corresponding author: FA Abija, Department of Geomechanics, Energy and Environmental Sustainability, Port Harcourt, Nigeria, Tel: +2348038962622; E-mail: Fidelabija@yahoo.co.uk Received date: 16-10-2020; Accepted date: 30-10-2020; Published date: 12- 12-2020 Copyright: © 2020 FA Abija, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Abstract Oil and gas production leads to formation pressure depletion, porosity loss and compaction causing sinking of the ground surface above the producing zone that extends to hundreds of kilometers in lateral extent. Ground subsidence is noticeable as protrusion of wellheads and casings in oilfelds, encroachment and submergence of previously dry lands at the coastal zone, loss of air gap above the high wave and bottom deck in offshore platforms and sinking of surface structures and facilities in inland deltas. In this paper, ground elevations measured at wellhead locations in 1982 have been integrated with ground elevations extracted from ASTER-digital elevation models of 2000 and 2018 at the same wellhead locations to calculate the rate and magnitude of ground surface displacement above the producing feld. Results indicate a mean subsidence rate of 0.555 m/year ranging from 0.033-0.558 m/ year. Ground rebound suspected to be due to water injection to sweep the hydrocarbons in enhanced oil recovery occurred between 1982 and 2000 in well 10 at a rate of 0.933 m/year which was followed by subsidence at a rate of 0.556 m/year depicting the average ground subsidence due to reservoir compaction in the oilfeld. Symmetric and wide area lateral bowls of subsidence above wells forms intermontane topographic depressions flled with quaternary clastic materials that serves as runoff collection and detention points increasing food vulnerability and risk of damage to surface facilities and infrastructures. Ground Subsidence and Intermontane Topographic Depressions above a Producing Oilfeld: A Link to Flood Vulnerability in the Niger Delta Basin, Nigeria FA Abija 1,2* , TKS Abam 2 , SC Teme 2 and CL Eze 2 1 Department of Geomechanics, Energy and Environmental Sustainability, Port Harcourt, Nigeria 2 Department of Geosciences and Space Technology, Rivers State University, Port Harcourt, Nigeria