Using regional datasets of isotope geochemistry to resolve complex groundwater flow and formation connectivity in northeastern Alberta, Canada

摘要

In the southern Athabasca Oil Sands (SAOS) Region, located in Alberta Canada, individual in-situ oil sands operators have conducted local geochemical and isotope groundwater studies to establish baseline characteristics and to improve understanding of the connectivity of water supply and disposal formations within individual leases. Canada's Oil Sands Innovation Alliance (COSIA) initiated this study to combine the data from these individual studies along with public information into a comprehensive unified dataset to evaluate conceptual models of regional groundwater flow and the degree of interaction and separation between important water supply and disposal aquifers. The unified dataset comprised over 293 groundwater samples from the main water source and disposal hydrostratigraphic units and included geochemical and isotopic tracers that can be used to identify sources (delta O-18 and d2H) and age of water (H-3) and associated solutes (C-14(DIC), Cl-36), as well as the sources of salinity and diagenetic processes (delta C-13(DIC), delta S-34(SO4), Sr-87/Sr-86, delta B-11, delta Cl-37 and delta Br-81) and dissolved organics (delta C-13(DOC)). The TDS and stable isotope composition (delta O-18 and delta H-2) of groundwater from several Cretaceous formations were used to identify three main mixing controls. i) Areas where locally recharged groundwater mixes with glaciogenic water were identified by lower delta O-18 and delta O-18 values, high TDS, Cl:Br and delta S-34(SO4), Sr-87/Sr-86, and delta Cl-37 values consistent with dissolution of evaporites. These areas were situated where vertical pathways through otherwise competent formations are likely to occur. ii) Mixing with paleo-waters characterized by high TDS and higher delta O-18 and delta H-2 signatures indicating groundwater recharged under warmer climate periods and/or evaporative enrichment were identified in the south, and southwestern portions of the study area. The presence of these paleo-waters indicate