2013-03-01_HYDROLOGY - P2010026 - Laserfiche WebLink

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Shell has defined the boundary of the project area (Figure 1), which also shows the area of review and placement of their wells in the pilot area. To allow for wells to be easily accessible for workovers and yet maintain the hexagonal geometry necessary to optimize heating for oil shale recovery, Shell will achieve both these objectives by utilizing deviated wells. Figure 2 shows the placement of the wells at the surface as well as their corresponding positions in the subsurface. The proposed H01 well will be located In the center of the hexagon (subsurface location) to leach the nahcolite. it is . expected for the dissolution to progress most rapidly In the rich disseminated nahcolite zones of the T1 bed, Greeno bed, and other unnamed rich disseminated nahcollte units. In these most readily leachable beds, an approximately 20 feet radius circular region around the H01 well is expected to develop. Along the rest of the 153 feet vertical column, the horizontal extent of leaching will vary depending upon the leachability of the zone, but to a lesser extent than the rich disseminated nahcollte zones. In the event that the dissolution does not occur uniformly in a radial manner outward from the H01, Shell will request the addition of OB01 and/or OB03 wells to the area permit to initiate leaching through these wells. These wells will initially be used as observation or monitoring wells and when needed can be converted to an injection well to redirect the leach front to achieve a more symmetrical lateral leach pattern. A conversion plan Is included in the permit in anticipation of these additional wells. After the nahcolite leaching phase is completed, the H01 will be converted to a heater well, and if used for leaching, the OB01 and 0B03 will be converted back to observation wells. Well Operation Initially, fresh potable water at ambient surface air temperature will be injected to establish circulation within the injection zone. Once circulation has been established, the injection water will be gradually heated to a maximum of 400 deg F at the surface. However, the designed surface operational temperature is 350 deg F. The heated fluid will be circulated so that the targeted temperature in the Injection zone of 300 deg F is achieved. When the fluids have neared saturation, the recovery of the pregnant solution will begin. The concentration of the recovered fluid will be maintained at a high level, yet preclude the cooling- induced precipitation of the nahcolite as the fluid moves up the production tubing for recovery. The most efficient dissolution of nahcolite occurs when the solution is below the saturation limit for the salt. The targeted sodium bicarbonate concentration of the Injection water is 3 -4 weight% NaHCO3. Therefore, part of the produced brine (pregnant solution) will be combined with fresh, heated make -up water for reinjection. No additional additives will be part of the injection stream. The proposed injection zone Is into the R3, L2, and R2 stratigraphic units in the Creek member of the Green River formation. A USDW is defined by its water quality (less than 1.0,000 mg /L total dissolved solids (TDS)) - and ability to supply a public drinking water system (at least 1 gal/min, James R. Elder EPA memo, 1993). The proposed injection zone for the East RDD Project is within the regional Saline Zone, which is a saline - mineral cemented zone of mixed oil shale, maristone, and nahcolite. The Saline Zone is dry (i.e. water will not flow from pores within the saline zone.) Shell has provided several lines of evidence to show that the saline zone is dry. These include knowledge of the geology and mineralogy, geophysical logs, conditions at the Horse Draw Mine, which is approximately 5 miles northeast of the project area. Saline minerals fill the pore spaces between mineral grains in the saline zone to such an extent that porosity is occluded and permeability is too low to admit groundwater. Regionally, the saline minerals include nahcolite and dawsonite, with significant halite only in the upper part of the Saline Zone. In the East RDD area, the most abundant saline mineral is nahcollte. Because nahcolite is readily soluble, the saline zone must be inferred to be dry, lest the nahcolite minerals would have been dissolved away by groundwater. Geophysical logs, principally gamma ray /density logs, also show that porosity and permeability are extremely low in the saline zone. Permeability is less than 0.1 millidarcys in more than 95 percent of the saline zone in the OB04(SAW) well, and less than 1 Permit CO32210-00000 3 . FINAL PERMIT Statement of Basis