Environmental hazards posed by the Los Angeles Basin urban oilfields

Environmental hazards posed by the Los Angeles Basin urban oilfields: an historical perspective of lessons learned by G.V. Ghillingar and B. Endres, received November 28, 2003, Accepted August 9, 2004, Published online October 26, 2004 in Environmental Geology (2005) 47:302-317
These hazards are caused by gas migration along faults, subsidence caused by the fluid removal with consequent formation of faults and fractures, and by improperly maintained wellbores. … Four aspects of these environmental hazards are presented: 1. Oilfield gas migration into the near-surface deposits and aquifers 2. Soil and groundwater contamination from upward migration of oilfields fluids, mainly gases 3. Subsidence caused by oilfield fluid withdrawal and declining reservoir pressures 4. Outgassing and release of air toxics from the oil-and-gas-field operations. These issues are interactive and must be evaluated in combination. Ignoring these issues could result in substantial legal liability upon oilfield operator and upon those responsible for the public safety. Subsidence also results in the formation of faults and fracture zones, which are avenue for the migration of gases. … Eventually, well records were obtained that revealed that the well casing had developed leaks as a result of corrosion holes located at a depth beginning at approximately 366 m, and extending deeper…. Gas fingerprinting has confirmed that the gas seeps at the La Brea Tar Pits match the leaking gases that caused the Ross Department Store explosion (Jenden 1985). … The near disaster of February 7, 1989 … There is overwhelming scientific evidence that the gas accumulations were the direct result of oil and gas production and leaking oil wells. Well records clearly demonstrate that the Metropolitan No. 5 well had developed serious corrosion leaks in the well casing. These leaks were ongoing, and caused large quantities of oilfield gases to leak into secondary collector zones below both the explosion site and under the Hancock Park Elementary School. The gas fingerprinting experts (Schoell and others 1993, Jenden 1985) showed the match between the field production gases and the gas from seeps at the surface…. Virtually all well leaks can be traced to poor well completion and/or abandonment procedures (e.g., poor cementing practices). … Tests showed that even when the most up-to date cement types and techniques are used, leakage can and will occur in a significant number of cases (Marlow 1989 pp. 1147, 1148). For example, in a study of 250 casing jobs over a 15-month period with new cements, 15% of the wells leaked (Watters and Sabins 1980). Accordingly, the poor cementing and completion practices in the Los Angeles Basin, are giving rise to very serious environmental problems associated with gas leakage to the surface…. Numerous fields have accumulations of hydrogen sulfide that will eventually destroy the integrity of both the steel and cement relied upon to provide protection against gas migration…. The corrosive conditions of hydrogen sulfide are well known, and have defied engineering solutions (Craig 1993). … In January 2003, serious gas leakage problems were discovered in the South Salt Lake Oilfield, located in a residential area…. The oilfield operator had been injecting natural gas into the South Salt Lake Oilfield for approximately two years, under elevated pressures to enhance recovery. … These examples indicate the importance of a systematic examination of how wells leak, and the dangers posed by allowing residential construction to occur directly over old wells. … The gas leakage was traced to a leaking storage gas reservoir about 7 miles from town. … Approximately 75% of the wells were found to be leaking. The waterflooding for enhanced oilfield recovery can be a dangerous practice due to hydraulic fracturing which would create avenues for the migration of gas to the surface creating an explosive hazard.

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