This data release contains hydraulic head data used to create a hydraulic head map of the Clearwater hydrostratigraphic unit (HSU). The Wabiskaw Member was not included in the Clearwater HSU. The data were acquired from the following sources:
1. Alberta Environment and Parks' Alberta Water Well Information Database (AWWID)
2. Pressure data from drillstem tests (DSTs) from oil and gas wells
Data have been processed, relevant records selected, and outliers removed to compile this dataset.
Any errors in the original data were carried into this dataset and no systematic checking of attributes from original data sources was undertaken. Some obvious errors in the AWWID were corrected. For example, reversed top and bottom of the screened/perforated intervals were corrected.
Water well locations from the AWWID may be up to approximately 1131 m from their correct locations where the well is located to the centre of a section. As the 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 as well as the hydraulic head values, as the land surface elevation was used to calculate the mid-screen elevation and corresponding hydraulic head from measured “depth to” values.
Static water level data used in this dataset from the AWWID have been collected over decades, by different parties, and using different methods.
There is only one record for each "Source_ID", although 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.
Drillstem test data from oil and gas wells used in this dataset 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 Clearwater HSU study area with sufficient head/pressure information were selected from both the described sources.
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 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 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 10s of metres in areas where there are large changes in elevation within a 566 m or 1131 m radius of the well. Additionally, most wells have a casing which sticks up above the land surface from which measurements of water level are usually recorded. The calculation of hydraulic head does not take into account the elevation difference between the top of the casing and the land surface because this number is not always recorded in the AWWID. 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 screened interval is also 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 DST intervals 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 useful water well records:
1. Water well records that include screen completion interval and/or total depth information, and static water levels were selected;
2. The screen completion interval was constrained to less than or equal to 15 m;
3. Static water levels were allocated to the Clearwater HSU based on the completion intervall, or the total depth of the well if completion interval information was not available.
4. Static water levels from wells with completion intervals straddling the top or bottom of the Clearwater 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. Outliers were manually removed during the interpolation of potentiometric surfaces if the outlier’s static water level was significantly different from surrounding wells and these differences could not be explained or corrected, or the water well was interpreted to be incorrectly located and caused significant discrepancies in hydraulic data measured from the land surface.
Process steps for selection of pressure data from DSTs:
1. Records containing depth of tested interval, recovery information, and recovered water were selected;
2. The tested interval was constrained to less than or equal to 50 m;
3. DSTs were allocated to the Clearwater HSU based on the depth information of the tested interval;
4. DSTs from intervals straddling the top or bottom of the Clearwater 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. DST pressure values were considered potentially valid if there was evidence of a mechanically sound test (no misruns), pressures had stabilized or were close to stabilization (tests must have Pmax), and flow and shut-in times were reported.
DSTs were individually examined to remove any remaining non-representative fluid pressures. Outliers were manually removed during the mapping process based on the following conditions:
1. Final shut-in and final flow times less than 30 minutes
2. Final shut-in time less than the final flow time
3. Difference between final and initial shut-in pressures is more than 25% (may be indicative of supercharging)
4. Substantial gas flow or significant oil recovery
Regional potentiometric surfaces were created using static water levels from water wells and pressure data from DSTs. Pressure data were converted to equivalent freshwater hydraulic heads using the relationship: Hydraulic Head = Completion Mid Point Elevation + Pressure / ρg, where ρ = fluid density (1000 kg/m3 for freshwater), and g = gravitational acceleration (9.81 m2/s), pressure is measured in kPa (kg/ms2), and hydraulic head and mid point elevation are measured in metres above sea level (m asl).
This dataset includes only those wells that were used in the production of final potentiometric surfaces. 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].