Cause of the 1985 Ross Store Explosion and Other Gas Ventings, Fairfax District, Los Angeles

Cause of the 1985 Ross Store Explosion and Other Gas Ventings, Fairfax District, Los Angeles by Douglas H. Hamilton and Richard L. Meehan, in Engineering Geology Practice in Southern California, Association of Engineering Geologists, Special Publication No. 4, 1992.
Despite its own initial interest in abandoned wells as a potential source of the gas and the mandated purpose of the Roberti Bill to study such wells, the Task Force’s surprising conclusion was that neither the existence of dozens of such abandoned wells, nor even the presence of underlying oil and gas field which had been venting to surface for hundreds of millennia, had anything to do with the gas venting accidents. In fact, the oil field operation was not even mentioned as a possible agent in the Task Force report. Instead a chemical analysis of a sample of the venting gas led the Task Force to conclude that the gas was of “biogenic” origin, presumably derived from near surface decaying of organic matter in the alluvial soil, rather than being of petrogenic of thermogenic origin, i.e. derived from rock-source hydrocarbon (oil field type) accumulations. The Task Force then went on to present a scenario of shallow “biogenic” methane being displaced and pressurized by a rising water table in the perched fresh-water aquifer beneath the Ross Store. It was an imaginative explanation…. Troublesome legal issues were eliminated by this conclusion, the implication being that the methane hazard could exist virtually anywhere, so no human agency was at fault for its workings. The abandoned wells, the filled sumps, or anything else having to do with the past and current exploitation of the Salt Lake oil field evidently was considered no more than coincidence. … Although Task Force Report II explicitly “exonerated” past and present oil field operations from any role in the 1985 and 1989 gas ventings, it did, unlike the 1985 report, at least mention them. But, even this was evidently regarded as stepping outside of some kind of bounds by the Task Force member representing the C.D.O.G., since that member wrote a letter providing comments regarding the second draft of the Task Force Report II which seemed to generally take his fellow members to task for even mentioning oil field operations (Baker, 1989). … Neglecting this, we believe that beyond this particular coincidence of a gas blowout occurring directly over a pressurized gas field but being completely unrelated to that field, the dubious conclusion of the Roberti Investigation, that the “vast majority” of gas above oil-gas fields in the Los Angeles Basin is unrelated to underlying fields, effectively destroys the credibility of these “biogenic source” interpretations. … Conclusion Our analysis indicates that the raise of well head pressures at Gilmore #16, sanctioned by the C.D.O.G., from 200 to 700 psi was sufficient to fracture the formation at the nearby fault. This possibility is not recognized in the current C.D.O.G. review of oil field operations, though the analytical techniques necessary for its consideration are certainly available in the oil industry. Moreover, there is evidence suggestive that additional injection, unreported in C.D.O.G. records, was taking place at the time of the disaster. It seems to us that future studies of the Los Angeles gas problem can hardly be considered complete without full investigation of these issues. Finally, our analysis suggests that the criteria currently employed by C.D.O.G. and industry may not adequately protect against formation fracturing and escape of formational or injected fluids and gas to the surface environment, resulting in disastrous consequences comparable to the Ross Store explosion.

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