HR: 08:45h
AN: H31L-04    [Abstracts]
TI: Radar Interferometry Measures Underground Salt Leaching of Anthropogenic Origin in a Saharan Oilfield
AU: * Feigl, K L
EM: feigl@wisc.edu
AF: Dept. Geology & Geophysics, University of Wisconsin-Madison 1215 West Dayton Street, Madison, 53706, United States
AU: Aryal, A
EM: aryal@hawaii.edu
AF: SOEST, University of Hawaii, Honolulu, 96822, United States
AU: Calais, E
EM: ecalais@purdue.edu
AF: Earth Atmospheric Sciences, Purdue University, W. Lafayette, 47907, United States
AU: Haase, J
EM: jhaase@purdue.edu
AF: Earth Atmospheric Sciences, Purdue University, W. Lafayette, 47907, United States
AU: Thurber, C
EM: clifft@geology.wisc.edu
AF: Dept. Geology & Geophysics, University of Wisconsin-Madison 1215 West Dayton Street, Madison, 53706, United States
AB: Remote sensing by satellite radar interferometry can identify and monitor subsidence caused by underground disturbances of anthropogenic origin, such as oil or water pumping or mine collapse. 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 led 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 have 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 aim at quantifying the size of the underground cavity and whether or not it is still continuing 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 slows to a stop around that date, suggesting that the process has healed at depth. Preliminary calculations indicate that a volume of the order of 80,000 cubic meters of salt have been leached and transported to the shallow aquifer.
DE: 1211 Non-tectonic deformation
DE: 1294 Instruments and techniques
DE: 1834 Human impacts
DE: 1855 Remote sensing (1640)
SC: Hydrology [H]
MN: 2007 Fall Meeting