This data release contains water chemistry data used to create a total dissolved solids (TDS) map of the Wapiti / Belly River hydrostratigraphic unit (HSU) as part of the Alberta Geological Survey’s (AGS) Provincial Groundwater Inventory Program. The source datasets are water well chemistry data from Alberta Environment and Parks' Alberta Water Well Information Database (AWWID) and 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.
All attributes for both the water wells and oil and gas wells are as received from the data source. The total dissolved solids (TDS) values are calculated from other fields and do not contain any decimal places. Calculation of TDS is dependent on the measurement of the availability of specific ions at the time of testing and the generally accepted standard for displaying TDS is a whole number.
The mid-point of the sampled interval is also a calculated value and its accuracy is dependent on the accuracy of the measured depths and elevations provided from 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, 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.
Water chemistry data used in this dataset from the AWWID 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.
Fluid chemistry data from oil and gas wells used in this data set have been collected over decades, by different parties, and using different methods.
Null values were assigned where attributes were not present.
All data records within the Wapiti / Belly River study area with sufficient chemistry information were selected from both the AWWID and oil and gas well data.
Null values are reported as -9999.
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 400 m (or up to 800 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.
The locations of the oil and gas wells may be accurate to within millimetres depending on surveying standards at the time of drilling.
Because water well elevation is derived from the provincial 25 m digital elevation model (DEM), based on surface location, elevation accuracy is affected by the variability of the local topography and the potential locational inaccuracy. Any error in elevation may influence the allocation of the well into the modelled HSU. This is especially true where there are large changes in elevation within a quarter section or section, such as along the banks of rivers or in hilly areas. Error is likely on the order of plus/minus 5 m, but may be 10s of metres in areas where there are large changes in elevation (e.g., Porcupine Hills, hills south of Calgary, along river valleys).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 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.
Data containing chemical analyses were obtained from two sources: the AWWID, and formation water analyses from oil and gas wells (from DSTs and production fluids).
AWWID data, current up to 2014 (records ranging in time from 1961-2000), provided water chemistry information in the Wapiti / Belly River HSU. Data in feet were converted to metres.
Selection criteria for AWWID wells were as follows:
Chemical analyses that included major-ion chemistry were exported from the AWWID;
Chemical analyses from wells with no screen interval information, with multiple screen intervals, with screen intervals longer than 15 m, and with erroneous or incomplete chemical analyses were excluded;
The concentration of total dissolved solids (TDS) was determined for each analysis by summing the concentration of major constituents;
Acceptable charge balance error was constrained to ±10%;
Analyses which reported CO3 and pH < 8.3 were excluded;
Outliers were manually removed during the mapping process based on substantial difference in screen depth, and unexplained anomalous values.
This dataset includes only those wells that were used in the production of the final TDS surface.
DST and production well data, current up to March, 2013 (test dates ranging from 1977-2013), were used to provide chemical information for the deeper groundwater system.
Process steps for selection of chemical analysis from oil and gas wells:
1. Records that have values for interval top and bottom were selected.
2. The screen interval was constrained to less than or equal to 50 m.
3. Acceptable charge balance error was constrained within plus or minus 10%.
4. Samples labelled as “incomplete analysis" were removed.
5. Records were allocated, and selected if they were within the Wapiti / Belly River HSU.
6. The most representative sample was taken in case of duplicate samples at one location or at locations closer than 1 km horizontal distance.
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.
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, 10p. URL http://publications.gov.sk.ca/details.cfm?p=80100 [October 2014]