HR: 0800h
AN: G51B-0088    [Abstracts]
TI: Radar Interferometry Reveals Underground Salt Leaching of Anthropogenic Origin in a Saharan Oilfield
AU: * Aryal, A
EM: aaryal@purdue.edu
AF: Purdue University, EAS Dpt., West Lafayette, IN 47907 United States
AU: Calais, E
EM: ecalais@purdue.edu
AF: Purdue University, EAS Dpt., West Lafayette, IN 47907 United States
AU: Haase, J
EM: jhaase@purdue.edu
AF: Purdue University, EAS Dpt., West Lafayette, IN 47907 United States
AU: Feigl, K
EM: Kurt.Feigl@cnes.fr
AF: CNRS UMR 5562, 14 ave. E. Belin, Toulouse, 31400 France
AB: Local to regional-scale ground subsidence due to underground disturbances of anthropogenic origin, such as oil or water pumping or mine collapse, represent significant environmental hazards. Radar interferometry has proven to be an essential tool for identifying and monitoring such processes. Here, we report on a case of ground subsidence at an oil field in Algeria (Ouargla area) following a well accident. In 1986, a 250 m-wide ground collapse appeared at the abandoned OKN32 oil-well near the town of Ouargla in the Sahara desert. It is hypothesized that a break in the well casing allowed for deep artesian water to reach a subsurface salt layer, which lead to salt dissolution, the formation of an underground cavity, and intense pollution of a shallow aquifer used by the local population for irrigation and drinking. We used 22 ERS images spanning from 1992 to 2000 to investigate the temporal and spatial evolution of the ground subsidence associated with this process. In particular, we aimed at quantifying the size of the underground cavity and whether or not it still continues to grow. Although no information was available on the location of the accident (or on any of its characteristics), we found a circular subsidence area clearly correlated with the OKN32 oil field. Its diameter spreads from 900 m in 1993 to about 1300 m in 1996, with a total subsidence of up to 20 cm over that time period. The subsidence rate decreases gradually from 1993 to 1996 and stops after that date, suggesting that the process has healed at depth. Preliminary calculations indicate that about 80,000 cubic meters of salt have been leached and transported to the shallow aquifer.
DE: 1709 Geodesy
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting