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During the experimental pilot project up to six underground injection/production wells will be <br /> installed. At any one time it is expected that one to three cavities will be in production and <br /> used to solution mine the nahcolite. <br /> Each well will be cased and consist of an outer hanging injection string and a central <br /> production casing. Solution mining will involve injection of up to 350OF water down the outer <br /> hanging injection string and flowback to the surface with the pregnant nahcolite brine <br /> through the center production tubing. Flows may be reversed from time to time. The <br /> surface plant equipment will crystallize the nahcolite, recover most of the heat from the brine <br /> solution, and reinject the barren brine/water after reheating the injection fluid up to 350°F. <br /> The injection of hot water serves two purposes: <br /> 1. The hot water increases the dissolution rate of the nahcolite; and <br /> 2. The hot water causes the oil shale in which the nahcolite is distributed to rubblize <br /> which allows access to additional nahcolite ore. <br /> Based on rock mechanics testing and analysis, Hardy and Goodrich (July, 1996) determined <br /> that using this method of solution mining will result in good roof stability for cavern diameters <br /> up to 225 feet. <br /> D-3.2 SOLUTION MINING <br /> The proposed solution mining technique is similar to that demonstrated by the Shell Oil <br /> Company in the Piceance Creek Basin in the early 1970's. The technique has been revised <br /> and reengineered based on Shell's pilot facility experience (Prats et al, 1977), the <br /> experience of Denison Resources Ltd. Of Brisbane, Australia, and.the knowledge and <br /> experience of Kavernen Bau - Und Betriebs - GMBH (KBB) of Hanover, West Germany and <br /> PB-KBB of Houston, Texas. The primary solution mining technique is to initially drill a single <br /> vertical well. A hot, dilute (7 percent NaHCO3) bicarbonate solution will be injected into the <br /> cavity; allowed to dissolve the nahcolite under controlled conditions of temperature, <br /> pressure and flow rate, and then extracted as a nearly saturated solution. Once the nearly <br /> saturated solution is brought to the surface, it may be filtered to remove particulate <br /> contamination. The solution will be cooled, and the sodium bicarbonate crystallized. The <br /> solid crystals will be removed from the mother liquor, dried and screened into various size <br /> grades. More detailed solution mining and process descriptions are included later in this <br /> Section. The general solution mining operation is shown in Figure D-3.2. <br /> G:\LM=78545.002\Reclamation%Reclamexh.DOC D-16 <br />