Title: Mine-induced sinkholes over the U.S. Strategic Petroleum Reserve (SPR) storge facility

Abstract

The initial sinkhole at the Weeks Island SPR site that was first observed in May 1992 gradually enlarged and deepened, concurrent with the increasing dissolution of salt over the mined oil storage area below. Beginning in 1994 and continuing to the present, the injection of saturated brine directly into the sinkhole throat some 76 in (250 ft) beneath the surface essentially arrested further dissolution, buying time to make adequate preparation for the safe and orderly transfer of crude oil to other storage facilities. A second and much smaller sinkhole was first noticed in early 1995 on an opposite edge of the SPR mine, but with a very similar geological and mine mechanics setting. Both sinkholes occur where the edges of upper-152 in (-500 ft) and lower-213 m (-700 ft) storage levels are nearly vertically aligned. Such coincidence maximizes the tensional stress development leading to fracturing in the salt. Such cracking takes years to develop, perhaps 20 or more. The cracks then become flowpaths for brine incursion, wherein after time it is released into mined openings. Undersaturated ground water gradually enlarges the cracks in salt, leading to further dissolution and eventual collapse of the overlying sand to form sinkholes. Other geologicmore » conditions may have been secondary factors in controlling both mining extent and sinkhole location. An en echelon alignment of sinkholes over other mine edges has been observed. Thus most likely areas of future occurrence at Weeks Island are adjacent to the existing sinkholes; surface inspections are now concentrated at those locations. Although neither timing nor location is predictable with precision, the study of numerous sinkholes elsewhere shows that progression is inevitable, provided that relevant conditions and enough time exists for development. These principles should provide mine designers and operators the knowledge to minimize the occurrence of sinkholes, and to plan for their progression when they occur.« less

Authors:

Neal, J T; Bauer, S J; Ehgartner, B L

Publication Date:

1995-12-31

Research Org.:

Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

Sponsoring Org.:

USDOE, Washington, DC (United States)

OSTI Identifier:

167192

Report Number(s):

SAND-95-1661C; CONF-9510268-1
ON: DE96003697; TRN: 96:000870

DOE Contract Number:  

AC04-94AL85000

Resource Type:

Conference

Resource Relation:

Conference: Joseph F. Poland symposium on land subsidence, Sacramento, CA (United States), 4-5 Oct 1995; Other Information: PBD: 1995

Country of Publication:

United States

Language:

English

Subject:

02 PETROLEUM; 58 GEOSCIENCES; SALT DEPOSITS; DISSOLUTION; BRINES; INJECTION; CRACKS; STRATEGIC PETROLEUM RESERVE; STORAGE FACILITIES; GEOLOGY; UNDERGROUND STORAGE