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M+'. Max Kamey <br />,Irene 17, 2003 <br />Page 6 <br />shale was 7407 psi; this was reduced to 2553 psi for the [rock mass strength. This ambient <br />temperature rock mass strength was further reduced to 1000 psi when [he temperature was over <br />300°F. The rock mass strength reduction accounts for inhomogeneities associated with bedding, <br />suatigraphy and jointing, and sample size. The effect of bedding weaknesses and jointing is <br />quantified using the Rock Quality Designation (RQD). The rock quality in the crown pillar area <br />and through the height of the caverns is excellent with an average RQD from the Dissolution <br />Surface to the base of the Saline Zone of 94.4% for the six core holes cored in 1999. Very few <br />joints or weakness planes were evident in the core below the Dissolution Surface. <br />Cavern Integrity <br />The caverns have demonstrated the integrity of the crown pillar over the past 3 years of <br />operation with no leakage to the Dissolution Surface and no evidence of collapse above the <br />nominal top of cavern (the location of the cement basket and the cemented short string of 7-inch <br />casing). The caverns have operated with surface injection pressures of over 700 psi. Tracer <br />testing has indicated that leakage from caverns has been limited to the ore zone There has heen <br />no damage reported to the tabulars or casingstn any wells. Comparison of the gamma logs <br />completed on the six caverns that have each produced more than of 85,000 tons of nahcolite and <br />the logs completed before mining do not indicate any caving or collapse of the cavern roof. <br />Faults could also influence the stability of the crown pillar above the caverns. No faults <br />have been definitively identified in the mining area. The cavern characterization test will be <br />completed on Well 29-24, located near the middle of the well field, and no faults are evident near <br />this well. <br />]n considering die potential of developing caverns of diameter greater than ?00 11, the <br />variability of the rock mass and the potential for leakage from the cavern must be assessed. A <br />design criteria established during the planning of the well field was to maintain 50 ft of intact <br />rock between caverns and 100 ft of intact rock in the crown pillar. The first criterion was to <br />prevent leakage between caverns, the second, to prevent [eakage from the cavern to the <br />groundwater above the Dissolution Surface. In this study, we are concerned only with the latter. <br />The rock mass strength parameter's used were selected in 1998 based on the best available site- <br />specific data and no new data is available to suggest that the data and methodology are not <br />conservative. <br />Cyclic Loading <br />The effect of cyclic loading on the stability of the caverns has been modeled by allowing <br />the internal pressure to first drop from hydrostatic pressure to a uniform gas pressutY of 900 psi, <br />and then drop in 100-psi increments down to 100 psi. The pressure is then increased in similar <br />fashion to 900 psi for one complete pressure cycle. Cycling was analyzed foe a 200-ft-diameter <br />cavity subject to ten pressure cycles. The duration of each cycle was set at 6 months. <br />[^ the analysis of the influence of cavern cycling, both fixed and Flee cavern temperatures <br />were considered. The fixed temperature scenario reflects a situation where the cavern <br />Agapito Associates, Inc. <br />