Avery Island Salt Research Articles

Very Slow Creep Tests on Salt Samples

The objective of this paper is to assess the creep law of natural salt in a small deviatoric stress range. In this range, creep is suspected to be much faster than what is predicted by most constitutive laws used in the cavern and mining industries. Five 2-year, multistage creep tests were performed with creep-testing devices set in a gallery of the Altaussee mine in Austria to take advantage of the very stable temperature and humidity conditions in this salt mine. Each stage was 8-month long. Dead loads were applied, and vertical displacements were measured through gages that had a resolution of 12.5 nm. Loading steps were 0.2, 0.4, and 0.6 MPa, which are much smaller than the loads that are usually applied during creep tests (5–20 MPa). Five salt samples were used: two samples were cored from the Avery Island salt mine in Louisiana, United States; two samples were cored from the Gorleben salt mine in Germany; and one sample was cored from a deep borehole at Hauterives in Drome, France. During these tests, transient creep is relatively long (6–10 months). Measured steady-state strain rates ( $$\dot {\varepsilon }$$ = 10−13–10−12 s−1) are much faster (by 7–8 orders of magnitude) than those extrapolated from relatively high-stress tests (σ = 5–20 MPa). When compared to n = 5 within the high-stress domain for Gorleben and Avery Island salts, a power-law stress exponent within the low-stress domain appears to be close to n = 1. These results suggest that the pressure solution may be the dominant deformation mechanism in the steady-state regime reached by the tested samples and will have important consequences for the computation of caverns or mines behavior. This project was funded by the Solution-Mining Research Institute.

Micromechanical processes in consolidated granular salt

Granular salt is likely to be used as backfill material and a seal system component within geologic salt formations serving as a repository for long-term isolation of nuclear waste. Pressure from closure of the surrounding salt formation will promote consolidation of granular salt, eventually resulting in properties comparable to native salt. Understanding dependence of consolidation processes on stress state, moisture availability, temperature, and time is important for demonstrating sealing functions and long-term repository performance. This study characterizes laboratory-consolidated granular salt by means of microstructural observations. Granular salt material from mining operations was obtained from the bedded Salado Formation hosting the Waste Isolation Pilot Plant and the Avery Island salt dome. Laboratory test conditions included hydrostatic consolidation of jacketed granular salt with varying conditions of confining isochoric stress to 38 MPa, temperature to 250 °C, moisture additions of 1% by weight, time duration, and vented and non-vented states. Resultant porosities ranged between 1% and 22%. Optical and scanning electron microscopic techniques were used to ascertain consolidation mechanisms. From these investigations, samples with 1% added moisture or unvented during consolidation, exhibit clear pressure solution processes with tightly cohered grain boundaries and occluded fluid pores. Samples with only natural moisture content consolidated by a combination of brittle, cataclastic, and crystal plastic deformation. Recrystallization at 250 °C irrespective of moisture conditions was also observed. The range and variability of conditions applied in this study, combined with the techniques used to display microstructural features, are unique, and provide insight into an important area of governing deformation mechanism(s) occurring within salt repository applications.

A Very Slow Creep Test on an Avery Island Salt Sample

The applied deviatoric stress during most creep tests performed on salt samples is in the 3.5–20 MPa range. However, the stresses actually experienced in the vicinity of a salt cavern are much smaller. Any extrapolation is difficult to vindicate, as the dominant micro-mechanisms are strongly suspected to be very different in the low-stress and medium-stress domains. To answer this concern, a very slow creep test was performed on an Avery Island salt sample. To minimize the influence of even the smallest of temperature deviations during the test, the testing apparatus was placed in a remote gallery of the Varangeville salt mine, taking advantage of the very stable temperature conditions offered in an underground environment. The test was performed in multiple stages and lasted 42 months. The successive loads of 0.1, 0.2, 0.3, and 0.5 MPa were applied. Measured steady-state strain rates were of the order of 10−12 s−1, which are significantly faster than that extrapolated from creep tests performed at loads ranging between 3.5 and 20 MPa.

The distribution of trace water around brine leaks in the avery island salt mine: Implications for the natural migration of water in salt

The natural distribution of water in the Avery Island domal salt has been investigated by performing trace water content analysis on 64 samples collected systematically at the 210 and 270 meter levels of the International Salt Compan mine. Specific attention was given to salt near an internal shear zone which is the apparent source of several mine leaks. No discernible migration of brine into the adjacent salt was observed from the meteoric leak at the 210 m level. Extensive water enrichment (>1000 mg/kg) was limited to 30 meters from the formation water leak at the 270 m level. The water contents of coexisting samples near the formation water leak are highly variable. If water is moving from; this leak into the adjacent normal salt it is not doing so by way of a uniform diffusion process. Petrographic examination of polished salt samples reveals that fluid inclusions occur mainly in healed fractures. The water content of a sample depends on the density of such fractures. Natural movement of water in the salt appears to occur mainly through microfractures and possibly along crystal boundaries rather than by the diffusion of brine through crystals. One possible zone of enhanced water content may occur along a possible bedding plane which intersects a mine leak. This suggests that any natural movement of fluid not associated with fractured salt may occur preferentially along bedding planes. The method of brine migration under natural conditions, the occurrence of fluid inclusions (i.e., fracture vs. nonfracture-fill inclusions), and the water content of salt will be helpful in evaluating the migration of brine in response to the thermal and/or pressure gradient which will be created by the emplacement of radioactive waste.

Room convergence monitoring with an EDM in the Avery Island Salt Mine : Thoms, R L; Gehle, R M Proc 24th US Symposium on Rock Mechanics, College Station, Texas, 20–23 June 1983P849–856. Publ: AEG, 1983

Room convergence monitoring with an EDM in the Avery Island Salt Mine : Thoms, R L; Gehle, R M Proc 24th US Symposium on Rock Mechanics, College Station, Texas, 20–23 June 1983P849–856. Publ: AEG, 1983

Isotopic character and origin of brine leaks in the Avery Island salt mine, south Louisiana, U.S.A.

Twelve brine leaks in the Avery Island salt mine have the isotopic signature of meteoric waters and are isotopically similar to shallow wells around the salt dome. The mine leaks are interpreted as meteoric waters which have penetrated the salt. One leak at the 275 m (∼ 900 ft.) level is drastically enriched in 18O relative to the other waters. This water is similar to 18O-rich waters in other Gulf (of Mexico) coast salt domes and is interpreted as formation water which became incorporated in the salt during diapiric rise of the dome. While water encounterd in other salt domes is primarily formation water, the water encountered in the Avery Island salt is primarily meteoric. This may be related to the shallow depth of the mine, close proximity of the salt top to the surface, absence of caprock, and/or duration and technique of mining.

Effect of pressure and temperature on the thermal properties of a salt and a quartz monzonite : Durham, W B; Abey, A E Proc 22nd US Symposium on Rock Mechanics, Cambridge, Mass: MIT, 1981

Measurements have been made of thermal conductivity, diffusivity, and linear expansion as a function of temperature (to 573 K) and hydrostatic pressure (to 50 MPa) on two rocks, Avery Island domal salt and Climax Stock quartz monzonite. For Avery Island salt the thermal properties do not show any pressure dependence and are approximately the same values as for single crystal halite at 0.1 MPa. The lack of pressure dependence is attributed to the high symmetry of halite (cubic) and to its low strength, both of which inhibit brittle fracturing. For Climax Stock quartz monzonite no pressure dependence of thermal diffusivity has been resolved, but conductivity does show a drop of approximately 10% with decreasing pressure from 50 to 3 MPa. The pressure dependence is not measurably altered by heating the rock to as high as 473 K under 50 MPa. Our measurements so far on the thermal conductivity of quartz monzonite vs temperature and pressure are in agreement with predictions of the Walsh and Decker (1966) model of thermal conductivity vs crack porosity based on independent measurements of crack porosity vs temperature and pressure for the same quartz monzonite. Heating to temperatures greater than 473 K at 50 MPa, ormore » heating to lower temperatures at lower pressures, should substantially reduce thermal conductivity of the quart monzonite.« less

Geology of Avery Island Salt Dome, Iberia Parish, Louisiana

Two important papers on the geology of Avery Island Dome (one of the often mentioned Five Islands of South Louisiana) were published in 1899 and 1931. The present study reports the findings since the discovery of oil in 1942. The history of salt-mine operations is reviewed, present mining practices explained briefly, and the configuration of the salt mass as it is now known is described. Oil sands have been found ranging in depth from 4,500 feet to 15,600 feet; 16,456 feet is the greatest depth to date drilled. The bulk of the proved reserves ranges from about 8,500 to 9,500 feet in depth and is located on the southwest flank. Present drilling is mainly to define new deep reserves on the east flank, or explore for new reserves on the southeast flank. Accumulative produc ion totals about 34 million barrels of oil with minor volumes of gas as of May 1, 1958. The total proved reserve is probably about half depleted, with good possibilities for new reserves being discovered on untested or deeper flanks. The structure of the drilled flanks has been found to be a complex of radial faults, salt overhang, and steeply dipping sediments with updip terminations against the shallow piercement-type salt mass. The age of formations penetrated ranges from Recent to the Discorbis zone of the middle Miocene.