This data release contains water chemistry data used to create a total dissolved solids (TDS) map of the Horseshoe Canyon / St. Mary River hydrostratigraphic unit (HSU). The data were acquired from the following public sources:
1. Alberta Environment and Parks' (AEP) Alberta Water Well Information Database (AWWID)
2. Alberta Health Services (AHS)
3. Alberta Energy Research Institute (AERI)
4. Baseline Water Well Test Database (BWWT)
5. Data submissions by industry as required by Alberta Energy Regulator (AER) Directive 044: Requirements for Surveillance of Water Production in Hydrocarbon Wells Completed Above the Base of Groundwater Protection
6. Formation water chemistry data from oil and gas well drillstem tests (DSTs) and production fluids.
Data have been processed, relevant records selected, and outliers removed to compile this dataset.
Water chemistry data used in this dataset from the AWWID and other compiled sources have been collected over decades, by different parties, and using different methods. There may be more than one record for a Source_ID if the water well was sampled more than once. This will be reflected in the ChemAnal_ID field. Geographic coordinates (latitude/longitude) may be the same for different wells, often because the AWWID wells have been located as being in the middle of a quarter section or section.
Formation water analysis from oil and gas wells have been collected over decades, by different parties, and using different methods.
A majority of the AWWID wells are located to the middle of the Alberta Township System (ATS) quarter section (occasionally to the middle of the section). Therefore, there can be up to approximately 566 m (or up to approximately 1131 m if the well is located in the middle of a section) of error in the well location and subsequent maps derived from the well records. These sources of error are not unique to this study and are encountered in any hydrogeological study that uses the AWWID, unless further refinement of well locations is undertaken.
The locations of the oil and gas wells may be accurate to within millimetres depending on surveying standards at the time of drilling.
The potential for up to approximately 566 m (sometimes approximately 1131 m) of horizontal accuracy error for water wells may also introduce errors in the surface elevation, which is derived from the provincial 25 m DEM, based on the location of the well. This error is likely on the order of plus/minus 5 m, but may be 10's of metres in areas where there are large changes in elevation. Any error in elevation may influence the allocation of the well as well as sampling location. These sources of error are not unique to this study and are encountered in any hydrogeological study that uses the AWWID, unless further refinement of well locations is undertaken.
The mid-point of the sampled interval is a calculated value and its accuracy is dependent on the accuracy of the measured depths and elevations provided in the well header. These values are somewhat inconsistent for the water wells because many of them are not surveyed. For the oil and gas wells, the well elevations and locations are surveyed in, so accuracy will be to the same significant digits provided by the source, even though there may be considerable uncertainty as to where the sample actually came from.
The location of the sampled interval in oil and gas wells may be accurate to within millimetres in accordance with surveying standards at the time of drilling.
Process steps for selection of chemical analysis from water wells:
1. Water well records with completion interval and/or total depth information, and complete chemical analysis, were selected;
2. Chemical analyses from completion intervals longer than 15 m were excluded;
3. Chemical analyses were allocated to the Horseshoe Canyon / St. Mary River HSU based on the completion interval, or the total depth of the well if completion interval was not available;
4. Chemical analyses from wells with completion intervals straddling the top or bottom of the Horseshoe Canyon / St. Mary River HSU were excluded, unless they were from wells in data-poor areas and it was verified that less than 30% of the completion interval extended into the formation directly above or below the HSU, but not into any other formation;
5. The acceptable charge balance error was constrained to ±10%;
6. Chemical analyses which reported CO3 and pH <8.3 were excluded;
7. The concentration of total dissolved solids (TDS) was determined either by summing the concentration of major constituents (if available), or by using the TDS values as reported in the source dataset (if major constituents were not available);
8. Outliers were manually removed during the mapping process based on substantial difference in screen depth, and unexplained anomalous values.
Process steps for selection of formation water analyses from oil and gas wells:
1. Records containing depth of tested interval information were selected;
2. The tested interval length was constrained to less than or equal to 50 m;
3. The acceptable charge balance error was constrained to ±10%;
4. Samples labelled as “incomplete analysis" were excluded;
5. Records were allocated to the Horseshoe Canyon / St. Mary River HSU based on the depth information for the tested interval;
6. Records with tested intervals straddling the top or bottom of the Horseshoe Canyon / St. Mary River HSU were excluded, unless they were from wells in data-poor areas and it was verified that less than 30% of the tested interval extended into the formation directly above or below the HSU, but not into any other formation;
7. In case of collocated data, the most representative sample was selected, or averaging of TDS values was done;
8. The concentration of total dissolved solids (TDS) was determined either by summing the concentration of major constituents (if available), or by using the TDS values as reported in the source dataset (if major constituents were not available)
The remaining formation water analyses were subjected to additional screening to identify potential contamination of the formation water by drilling fluids such as acid water, corrosion inhibitors, mud filtrates, and alcohols.
Process steps for selection of formation water analyses from compiled sources:
1. Any records where the sampled interval was identified as the Horseshoe Canyon / St. Mary River HSU were included in the initial dataset.
The final dataset includes only those records that were used in the production of the final TDS surface.
Details about the screening process can be found in the following reference: Jensen, G.K.S., Rostron, B., Palombi, D., and Melnik, A. (2013): Saskatchewan Phanerozoic Fluids and Petroleum Systems project: hydrogeological mapping framework; in Summary of investigations 2013, Volume 1, Saskatchewan Geological Survey, Sask. Ministry of the Economy, Misc. Rep. 2013-4.1, Paper A5, 10 p. URL http://publications.gov.sk.ca/details.cfm?p=80100 [October 2014].