Compartmentalization of Formation Waters, Prince Colliery, Cape Breton, Nova Scotia
Kennedy, Angela Marie
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The Prince Colliery is located offshore of Point Aconi, Cape Breton , Nova Scotia. The colliery is presently extracting coal from the Hub seam of the Marien Group, part of the Carboniferous Sydney Basin. Directly overlying the Hub seam is a channel sandstone body which contains formation water. Water was sampled directly from the roof before mining as well as from collapsed areas (gob areas) after mining. Two formation waters were identified, (1) a low salinity formation water with Na/Cl ratios between 0.87 and 0. 72 and chloride concentrations up to 11 200 mg!L, (2) a high salinity formation water with Na/Cl ratios between 0.6 and 0.7 and chloride concentrations between 24 400 and 30 000 mg!L. Gob water samples have chemistries similar to the high salinity formation water even at sampling depths similar to the low salinity formation water. Gob water samples have Na/Cl ratios between 0.6 and 0.7 and chloride concentrations up to 28 000 mg!L. The high salinity formation water and the gob waters are enriched in Br. A 24 cm mudstone divides the channel sandstone body overlying the Hub coal seam into two sandstone units. The upper sandstone (8.56 m thick) has vertical permeabilities up to 20.9 mD and the lower sandstone (1.56 m thick) has vertical permeabilities up to 1.33 mD. A vertical salinity profile constructed from geophysical data for drill hole P6 reveals the more saline formation water overlies the low salinity formation water. The channel sandstone body or aquifer overlying the Hub coal seam is compartmentalized by an area of low permeability which separates two distinct formation waters. The chemistry of the high salinity formation water suggests that it is related to lower basinal brines. The low salinity formation water is a mixture of the high salinity formation water and a dilute ocean water end member. Mixing probably took place during geologic time. The gob waters are shown to be a mixture of these two formation waters and not sourced by the overlying modem seawater. Mixing models completed for the gob water samples support this conclusion. Key Words: Compartmentalized, Formation Waters, Brine, Aquifer, Permeability, Chloride, Bromide, Na/Cl ratio, Salinity, Colliery, Gob.