This data release contains pressure data used to create a hydraulic head 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 head data from Alberta Environment and Parks' Alberta Water Well Information Database (AWWID) and 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, we corrected the records that had the top and bottom of the screened/perforated interval reversed in the original database.
Water well locations from the AWWID may be up to 800 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.
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 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.
Hydraulic head data used in this dataset from the AWWID have been collected over decades, by different parties, and using different methods. GOWN wells are included in the AWWID.
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.
A majority of the AWWID wells are located to the middle of the Alberta Township System 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.
The potential for up to 400 m (sometimes 800 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 10's of metres in areas where there are large changes in elevation. 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 location of the DST intervals in oil and gas wells may be accurate to within millimeters in accordance with surveying standards at the time of drilling.
Data for the mapping were obtained from three sources: 1. the Alberta Water Well Information Database (AWWID) from Alberta Environment and Parks, 2. the Groundwater Observation Well Network (GOWN), 3. pressure data from drillstem tests (DSTs) from oil and gas wells.
AWWID data, current up to March 2013 (records ranging in time from 1912-2013), provided hydraulic information in the upper approximately 200 m of the subsurface. Data in feet were converted to metres. Selection criteria for AWWID wells were as follows.
First, wells were selected that had only one well record, a single screened interval, a single static water level, and that were not under flowing artesian conditions.
Second, outliers were manually removed during the interpolation of potentiometric surfaces where
1) the static water level was significantly different from surrounding wells and these differences could not be rectified;
2) the water well was interpreted to be incorrectly located and caused significant discrepancies in hydraulic data measured from the land surface;
Finally, only the deepest well within a given 5 km grid spacing was selected. This is intended to provide uniform data distribution.
For the GOWN wells the SWL was averaged for the active duration and no culling steps were implemented (all allocated wells were included in the final dataset).
For the oil and gas well DSTs, an automated culling process with the following criteria was implemented:
1) The tested interval must have a top and bottom depth value
2) Test was conducted over a defined and resonable interval (< 50 m)
3) Tested interval does not straddle multiple formations
4) Complete recovery information is provided and the test includes water recovery information;
5) Evidence exists of a mechanically sound test (no misruns)
6) Pressures have stabilized or were close to stabilization (tests must have PMax)
7) Flow and shut-in times are 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 oil and gas well DSTs. Pressure data were converted to equivalent freshwater hydraulic heads using the relationship: Hydraulic Head( masl)=(Pressure (kpa))/ρg+Elevation (masl), where ρ = fluid density (1000 kg/m3 for freshwater) and g = gravitational acceleration (9.81m2/s) and masl = metres above sea level.
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]