2011-08-04_HYDROLOGY - P2008046 - Laserfiche WebLink

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Mr. Travis Marshall Mr. Kent Walter Ms. Wendy Cheung Page 5 of 6 bond is rated as good through the confining zone; the bond is rated as fair through the confining zone in well TM -2. Although the CAST log does not extend to the casing point in most wells, it is reasonable to assume that the cement to pipe bond rating within the interval between the bottom of the log and the casing point is at least as good as the interval immediately above the bottom of the log. Therefore, no cross -hole communication is expected through the confining zone in any of the wells. Isolation of Hydrostratigraphic Units Exploration work conducted to date at the AMSO site has shown that the shallowest water - bearing unit is generally encountered within the transition zone between the Uinta Formation and the underlying R8 at a depth of approximately 650 ft bgs. The transition zone contains Green River Formation shale (R8 zone) and interbedded tongues of Uinta Formation sandstone, the water - yielding strata. Below the transition zone, the R8 characteristically exhibits low permeability, yielding very little water compared to Uinta Formation sandstone. Once the water - bearing zone is penetrated, the water level rises in the well bore, indicating that the unit is under confined pressure. This water - bearing zone is referred to as the Uinta hydrostratigraphic unit. The hydrostratigraphic units identified at the TM Pad between the ground surface and the AMSO retort test interval are as follows: • Uinta (Uinta Formation/R8 transition zone beginning at about 600 ft bgs) • A- Groove (962 — 974 ft bgs) • B- Groove (1,113 —1,133 ft bgs) • L5 (1,269 —1,337 ft bgs) • L4 (1,529 — 1,570 ft bgs) • L3 (1,726 —1,774 ft bgs) The CAST logs and associated ACE reports demonstrate that the cement to pipe bond in each well is adequate, with a reported Halliburton rating of "good" or "fair ", for the interval extending from the bottom of the of the log to at least the upper R8 (at least 236 ft above the top of the A- Groove hydrostratigraphic unit). These findings indicate adequate isolation of hydrostratigraphic units underlying the Uinta hydrostratigraphic unit as well as isolation of the Uinta hydrostratigraphic unit from the underlying hydrostratigraphic units. The cement to pipe bond in all of the wells is rated as "poor" through some portions of the Uinta Formation. Except for well TM -3 and TM -4, the interval of adequate cement to pipe bond extends to well above the Uinta hydrostratigraphic unit. The adequate bond interval extends to slightly above the Uinta hydrostratigraphic unit in well TM -3. At TM -4, the top of cement was estimated at a depth of approximately 700 ft bgs. The interval above the top of cement in well TM -4 includes the Uinta Formation, Uinta Formation/R8 transition zone, and possibly a portion of the upper R8. Therefore, the Uinta hydrostratigraphic unit is not isolated from the overlying Uinta Formation strata and possibly the underlying upper R8 at well TM -4. The possible lack of isolation from the underlying R8 poses little threat hydrologically or with respect to water quality since the R8 is characterized as a low - permeability zone with very little groundwater yield. The lack of isolation from the overlying strata within the Uinta Formation also poses little threat either hydrologically or with respect to water quality. The Uinta hydrostratigraphic unit is regionally known to produce groundwater of good quality, and any flow from the unit to overlying unsaturated strata would be limited by the relatively short duration of the