2011-08-17_HYDROLOGY - P2008046 - Laserfiche WebLink

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Mr. Travis Marshall Mr. Kent Walter Ms. Wendy Cheung Page 3 of 4 An evaluation of the porosity and resistivity measurements within the interval extending from the top of the L3 hydrostratigraphic unit (the nearest Underground Source of Drinking Water [USDW]) through the confining zone (L2, R2, and L1) and to the base of the injection zone (R1, LO, and RO) is discussed below. At the AMSO site, the L3 hydrostratigraphic unit generally extends from the upper to middle portion of the L3 lithologic zone to near the dissolution surface within the middle to lower portion of the R3 lithologic zone. At well BH -1, the top of the L3 lithologic zone is 1,726 ft bgs and the dissolution surface is located at approximately 1,835 ft bgs. The logs show that resistivity measurements through this interval are generally lower than the values shown for the overlying R4 zone or underlying R3 zone below the dissolution surface. The lower resistivity measurements in the L3 may indicate higher salinity formation water compared to adjacent units. The lower resistivity measurements could also be related to a lower kerogen content and /or a greater proportional volume of shale in the total rock composition. The porosity logs indicate low porosity for the L3 zone and increasing porosity in the underlying R3 zone probably due to increased kerogen content in the R3 zone. The prevalent voids observed in video logs in the L3 hydrostratigraphic unit may affect both resistivity and porosity measurements. Just above the dissolution surface, located at approximately 1,835 ft, is a fairly thick (25 ft) zone of rock that exhibits a relatively low and somewhat constant resistivity compared to surrounding strata and a low porosity (approximately 0.06). The dissolution surface exhibits erratic, moderate resistivity measurements with a local increase in porosity. Porosity again decreases in the underlying L2 zone. An apparent void in the borehole at 1,885 ft causes a significant deviation in both resistivity and porosity readings. The lower L2 zone and the upper R2 zone, an interval of approximately 22 ft, exhibits a distinct high resistivity with values approaching 2000 ohms. This zone shows an initial increase in density porosity (0.1) and neutron porosity (0.18) in the upper part of the unit underlain by several swings from moderately high to very low values. This high resistivity zone may be associated with increased kerogen content as porosity values are not distinctively low. Resistivity begins to decrease in the lower R2 zone and is characteristically low from the top of the L 1 through the LO zone compared to overlying strata. The lower part (approximately 16 ft) of the L 1 zone exhibits the lowest resistivity in the strata logged below the L3 zone and a low density porosity (near zero) and neutron porosity less than 0.10. Illitic strata are prevalent below approximately 1,950 ft, a boundary that closely matches the marked decrease in resistivity at the top of the L 1 zone. The decrease in resistivity is likely related to higher water salinity in the illitic shale. This interpretation is supported by magnetic resonance and dielectric log data (Seleznev and others 2011). The low resistivity may also be related to the greater clay content in this interval (clay /shale is more conductive). Porosity in the L 1 through RO zone is quite variable with many neutron porosity peaks attaining 0.2 or greater and only a few density porosity peaks greater than 0.2. The log shows a positive correlation between local resistivity peaks and porosity peaks. However, it cannot be said with confidence that zones of less saline formation water are the cause of the higher porosity values observed. This relationship may be complicated by local zones of higher kerogen content in the illitic shale. In general, porosity variability in this interval is likely related to normal variability in kerogen content and primary matrix porosity. If you have any questions regarding the step rate test conducted at well TM -1 or the resistivity and porosity logs performed at well BH -1, please contact me at (970) 625 -2227 or by email at Roger.Day@amso.net.