Sinkhole progression at the Weeks Island, Louisiana, Strategic Petroleum Reserve (SPR) site Page: 9 of 20
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The construction of a freezewall to arrest the flow of ground water into primary Sinkhole
#1 began in mid 1995 and was completed by the end of the year. This involved the construction
of 56 wells in three circumferential rings around the sinkhole which were used for circulating the
refrigerant. Testing of the wall in late 1995 was expected to provide reasonable confirmation that
a hydrologic barrier had been achieved.
Unlike other mines where leaks can be observed underground, SPR must rely on indirect
evidence such as fluctuations in the oil/water or oil/air interfaces, increased pressure, or changed
isotopic composition of the contained water (~750,000 barrels or 1.19 x 105 m3), about one per-
cent of the total volume. The diagnostics were complicated by salt creep closure, which gradually
reduces the storage volume by one-fifth of one percent per year (~160,000 barrels; 2.54 x 104
m3), a very small amount overall, but a very large amount relative to the few gallons per minute
leaks that could explain the sinkhole.
Water inflow into the mine was suggested by increasing amounts of brine which were
measurable in the fill hole sump, a by product of the initial oil fill operations. While not a precise
measurement, in early 1994 the inflow trend increased from one to nearly three gallons per min-
ute. This increase was noticed almost immediately following filling of the sinkhole with sand;
continued deepening of the sinkhole began occurring, at a rate of about 1.5 m3 (2 yds3) per day,
requiring new fill weekly. This suggested that dissolution was ongoing, and there was reasonable
correlation with the amount of increasing brine that was observed in the fill holes and the increas-
ing sinkhole volume.
Brine hydrochemistry is frequently analyzed in salt mines to distinguish meteoric water
from connate water. At Weeks Island a decided change in isotopic composition was evident in
comparing 1993 water from the fillhole sump with that obtained in late 1991, about the same time
postulated for the sinkhole origin (Knauth, 1994). Although inconclusive, earlier data suggested
that a smaller leak may have existed as early as 1987.
Magorian (Acres, 1987) mapped a shear zone just south of the mine edge, based on exter-
nal dome structure, surface topography, and gas outbursts experienced during mining. Recent
coring in salt during construction of a freezewall around Sinkhole #1 also showed shearing and
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Neal, J.T.; Bauer, S.J. & Ehgartner, B.L. Sinkhole progression at the Weeks Island, Louisiana, Strategic Petroleum Reserve (SPR) site, article, November 1, 1995; Albuquerque, New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc620914/m1/9/: accessed May 26, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.