3D hydrostratigraphic modelling of the Paleozoic bedrock of southern Ontario

The Geological Survey of Canada, the Ontario Geological Survey, the Ministry of Natural Resources and Forestry and the Ontario Oil, Gas and Salt Resources (OGSR) Library have initiated a cooperative project to create a regional 3D model of the layered Paleozoic bedrock strata of southern Ontario, and the occurrence of water within these strata. A wealth of data are available, including digital records from 400,000 water wells that penetrate the bedrock, nearly 27,000 petroleum wells records, and approximately 300 stratigraphic boreholes in shallow bedrock formations completed by the Ontario Geological Survey. Petroleum well records are the key data source for the model, with data already coded in an Oracle relational database with geographic coordinates and elevation data for all wells. There are depth and elevation values for nearly 600,000 formation tops and over 35,000 water interval records with information on water type, depth interval and static level. A significant number of QC edits has greatly improved accuracy and reliability of this data set since 2001, with further improvements to be funded by the GSC as part of this project. Also available are compositional analyses for over 1000 samples of produced water from petroleum wells, isotopic and compositional analyses for 130 samples of deep to intermediate groundwater, 89 water type maps and 17 static level maps for deep groundwater aquifers, and field observations from springs, quarries, road cuts, outcrops, well testing, and drill core examinations. The model will incorporate and build on a published regional 2D conceptual model of groundwater systems in the bedrock of southern Ontario, documenting a hydrochemical zonation of water by depth into a shallow fresh water system, an intermediate sulphur water system and a deep brine system. Hydrostratigraphic units in the southern Ontario bedrock are known to cross formational boundaries. Hydrostratigraphic units also change character laterally, within the same formation, due to facies changes, diagenetic modification, faulting and, of particular significance in southern Ontario, karstification of carbonate or evaporite strata at unconformities. Paleokarst horizons are known to be a key geological control on aquifers in the bedrock. Modelling of this inhomogeneity is a complex technical and conceptual task and will comprise an iterative process of modelling, QA/QC data review and editing, and critical geological appraisal. Final products will be co-released by GSC and the OGS with access via the OGSR Library website, and will include a 3D model in both Leapfrog and ESRI ArcGIS formats, a 2D conceptual hydrostratigraphic model, and improvements in data quality and accuracy in the petroleum well database. Numeric groundwater flow modelling is beyond the scope of this project but the static model will support dynamic modelling. Target date for project completion is mid to late 2018.