The dataset includes lithostratigraphic picks made from wireline logs for the Paleozoic succession in northeastern Alberta (Townships 59-104, Ranges 1-19, west of the fourth meridian. The dataset comprises group-, formation-, member-, and unit-level stratigraphy, including: 1) Cambrian System: Cambrian Basal Sandstone unit and Earlie Formation, 2) Devonian Elk Point Group: La Loche Formation, Basal Red Beds unit of the Lotsberg Formation, lower and upper Lotsberg Formation and intervening Middle Red Beds unit, Ernestina Lake Formation, Cold Lake Formation, Contact Rapids Formation, Keg River Formation, Prairie Evaporite Formation including Whitkow, Shell Lake, and Leofnard members, including the White Bear and Conklin marker beds of the Leofnard Member, including the "remnant Prairie Evaporite unit" (insoluble breccias east of the Prairie Evaporite halite dissolution scarp where all halite and sulphates are dissolved), and Watt Mountain Formation, 3) Beaverhill Lake Group: Fort Vermilion Formation, Slave Point Formation, Waterways Formation including Firebag, Calumet, Christina, Moberly, and Mildred members, 4) Woodbend Group: Cooking Lake Formation, Leduc Formation, lower and upper Ireton Formation, Grosmont Formation including lower Grosmont, upper Grosmont 1, upper Grosmont 2, and upper Grosmont 3 units, 5) Winterburn Group: Nisku Formation, Calmar Formation, and Graminia Formation, 6) undifferentiated Wabamun Group, and 7) sub-Cretaceous unconformity.
Where a formation-, member-, or unit-level pick corresponds to the top of a group, both stratigrapic picks are included in the dataset.
A stratigraphic pick in a well is a point defined in three dimensions (X, Y and Z).
The accuracy of the pick depth, either in measured depth from the kelly bushing or with respect to sea level, is difficult to quantify and includes (but is not necessarily limited to) errors in
- well surface or bottom-hole latitude and longitude (X and Y);
- well ground elevation (Z);
- well kelly bushing elevation (Z);
- human error resulting from errors in picking the incorrect stratigraphic top (Z);
- data entry or data transfer (X, Y, and/or Z); and
- incorrect well log depth calibration (Z).
The data are tabular (point data with X, Y, and Z values).
The author made all of the stratigraphic picks. All picks are the same quality.
As the dataset includes vertical and deviated wells, the location data and well identifier data (UWI) are not unique. In non-vertical wells, surface and bottom-hole latitude and longitude should be different. Picks from non-vertical wells are derived from the deviation survey within IHS Petra. The deviation survey uses the measurements of depth, inclination, and azimuth, and a minimum curvature method to interpolate the position of the stratigraphic pick along the non-vertical well path. The position of the stratigraphic pick on a non-vertical well path is therefore dependent upon the number of measurements of inclination and azimuth at depth during the time of drilling. In this dataset, the X, Y location for a stratigraphic pick in a non-vertical well is the X, Y location of that pick at depth along the deviated well path (i.e., not the surface hole X, Y location).
The data are from the Alberta Plains where deformation of the Devonian sedimentary succession is relatively minor. All points are east of the deformation front at a given latitude. Thus, rocks should not be thrusted or structurally duplicated. Therefore, the pick should only occur once in any given vertical well.
The horizontal datum for the well locations is the North American Datum of 1983 (NAD83).
The X and Y coordinates for stratigraphic pick locations are in 10TM (Forest) from IHS (Petra software). The horizontal positional accuracy is unknown.
The vertical datum for elevations in this data set is the Canadian Geodetic Vertical Datum of 1928 (CGVD28).
In vertical wells, the subsurface elevation of a pick in a well, measured with respect to sea level, is calculated by taking the elevation of the kelly bushing (on the drilling platform) and subtracting the measured depth of the pick on the geophysical well log.
Some uncertainty in the vertical depth of the pick will result if the borehole is not entirely vertical. In general, the amount of vertical depth due to deviations from the vertical in boreholes is deemed negligible with respect to other potential sources of vertical error in this study. In the case of non-vertical wells, the deviation survey from IHS Petra was used to calculate the position of the stratigraphic pick along the well path. The deviation survey uses the measurements of depth, inclination, and azimuth, and a minimum curvature method to interpolate the position of the stratigraphic pick along the non-vertical well path. The position of the stratigraphic pick on a non-vertical well path is therefore dependent upon the number of measurements of inclination and azimuth at depth during the time of drilling.
Perhaps the greatest source of vertical uncertainty in this study is potential error in the elevation of the kelly bushing (KB). Any errors in surveying the ground elevation of the well site can result in vertical error. In addition, once the ground elevation is determined, the site is usually prepared for the drilling rig. If the original survey marker is disturbed or moved, this can result in potential vertical errors. The KB elevation is usually derived from adding the height of the drilling platform above the ground surface to the survey ground elevation. If this is not done correctly, it can introduce vertical error in the KB elevation, which is then propagated in the measured depth to the pick and the pick elevation.
Although incorrect KB elevation data can be difficult to detect, the data were screened by comparing the ground elevation and the KB elevation (derrick height) for each well. An acceptable range of derrick height (calculated by subtracting ground elevation from KB elevation) of zero to eight metres was used. Wells with derrick heights outside this range were excluded.
Vertical error in the pick elevation value can also result from human error resulting from uncertainty or incorrect placement of the pick on the well logs. The occurrence and magnitude of this error is difficult to identify, but comparison with existing published pick datasets and checks for internal consistency (such as identification of global and local outliers using statistical methods and gridding data while picking) minimized this source of error as much as possible.
Stratigraphic picks were made within the IHS Petra software application using well logging data from IHS.
Attribute values were checked to ensure reasonable values. For instance, the well locations were plotted on a map and no obvious anomalous locations were seen. A quality control process was used to test the quality of the deviation survey in non-vertical wells. Structural and isopach mapping were employed to check for anomalies in the stratigraphic picks in this dataset.
The data were also screened by comparing the ground elevation and the KB elevation (derrick height) for each well. An acceptable range of derrick height (calculated by subtracting ground elevation from KB elevation) of zero to eight metres was used. Wells with derrick heights outside this range were excluded.