The Alberta Township System is a land survey system used in Western Canada to divide land in 1 square mile sections. Initially used to define land for agriculture purposes, the system was later adopted in land sales and leases for hydrocarbon exploration rights.
Provincial governments in Western Canada regulate the naming of oil and gas wells, by assigning unique well identifiers(UWID) to each drilled hole. This nomenclature is based on the Alberta Township System for wells in Manitoba, Saskatchewan, Alberta and the Peace Country in north-western British Columbia. Furthermore, the surface and bottom coordinates of a well are defined as distances from the closest sectionboundary.
The land survey system was introduced in 1910 and was based on the Dominion Land Survey algorithm. It is used to this day, in spite of abounding inaccuracies and errors stemming from early topographic measurements.
Understanding the Alberta Townhip System
The surface is referenced firstly to a Meridian: The first (or Prime) meridian is defined at approximately 97º West, the second meridian overlays the 102º West longitude, the third meridian at 106º West, the fourth at 110º West, the fifth meridian at 114º West, the sixth meridian at 118º West. Locations are specified as west of a meridian (ex: W5 refers to a location west of 114º and east of 118º West. Locations east of the prime meridian are epressed as east of Prime Meridian (ex. EPM or EM).
Townships are approximately 6 miles by 6 miles in area, and are defined between range lines and township lines. A Township is defined by a Township line number, a Range line number and a Meridian (ex. “92-10W5”).
Township lines are east-west lines parallel to latitude lines. Numbering starts from the first baseline, located at latitude 49º North (along the United States/Canada border). Township lines are numbered from south to north at every 6.0375 miles (9.7164 km), allowing six rows of sections of one mile each between each two township lines, as well as space for three road allowances of 1 chain (approximately 20 meters) each. A total of 127 township lines are defined between latitude 49º North (first baseline) and latitude 60º North (36th baseline).
Range lines run south-north and are parallel to the meridians. Numbering starts at 1 at the intersection of a meridian and a baseline and progresses west until the next meridian. Numbering (and marking) is re-set at every baseline in order to compensate for meridian convergence and variable of earth circumference at different latitudes. There are 30 range lines intersecting the first baseline (49º North), and only 23 range lines intersecting the 32nd baseline (60º North). The townships east of each Meridian have various widths due to re-setting of the range line number along baselines. The result of re-setting range numbering along baselines is westward jogging at correction lines.
A Section is a sub-division of a Township. A Township is divided into 36 sections, each approximately one mile wide and one mile long. From north to south, each section measures exactly one mile. From east to west, a section can measure more or less than one mile, depending how wide a township is at a specific latitude. A section is exactly 6 miles wide along a baseline, less then 6 miles north of the baseline and south of a correction line, and more than 6 miles wide south of a baseline and north of a correction line. Sections are less than 6 miles wide if they are directly east of a Meridian. Sections are numbered in sinusoidal progression starting with 1 in the SE corner of a township and ending with 36 in the NE corner. A section is defined by the section number and the Township (ex. Section 22 of Township 92-10W5 is named “22-92-10W5”).
| Section numbering in a township | |||||
|---|---|---|---|---|---|
| 31 | 32 | 33 | 34 | 35 | 36 |
| 30 | 29 | 28 | 27 | 26 | 25 |
| 19 | 20 | 21 | 22 | 23 | 24 |
| 18 | 17 | 16 | 15 | 14 | 13 |
| 7 | 8 | 9 | 10 | 11 | 12 |
| 6 | 5 | 4 | 3 | 2 | 1 |
Legal Sub-divisions (LSD’s) are defined within a section. A section is divided into 16 LSD’s. LSD’s are approximately ¼ by ¼ miles in area (approximately 400 by 400 meters, or 40 acres). The surface and bottom coordinates of a well are not referenced to LSD boundaries, but rather to section boundaries. However, the LSD is part of the well name and UWID. LSD’s are numbered in sinusoidal progression starting with 1 in the SE corner of a section and ending with 16 in the NE corner. LSD’s are named with the LSD number and section name (ex. LSD 4 of section 22-92-10W5 is named “4-22-92-10W5”).
| LSD numbering in a section | |||
|---|---|---|---|
| 13 | 14 | 15 | 16 |
| 12 | 11 | 10 | 9 |
| 5 | 6 | 7 | 8 |
| 4 | 3 | 2 | 1 |
Legal Subdivisions (LSD’s) can be further divided in four (A, B, C, D) if well spacing is tighter than 400 meters.
Calculating well coordinates
Well coordinates are specified relative to the closest Section boundaries (ex. ” 128.0m N and 543.5m E from exterior boundaries of section 22-92-10W5″, meaning 128m north of the south boundary and 543 m east of the west boundary of the section).
Bottomhole coordinates are calculated by taking in account the surface coordinates and the position of the bottom relative to well centre. The position relative to well centre is expressed as Northing and Easting (see Directional drilling glossary).
Start by subtracting or adding northing to the north/south surface coordinate, and by subtracting or adding the easting to the east/west surface coordinate (ex. a well bottom located at -99.30m north and 793.15m east from well centre was drilled towards south and east). Adding the (negative) northing to the north-south coordinate results in 128.0 +(-99.30)=28.7m north of south. Adding the easting to the east-west coordinate results in 543.5+793.15=1336.65m east of west).
Next, determine which section boundaries are closest to the bottomhole location. Re-calculate the distances to the closest boundary, taking in account that a section is 1 mile (1609.34 meters) long and wide. As all coordinates are calculated from the closest boundary, any coordinate number must not be larger than half a mile or 804.67 meters (ex. 1336 meters east of west should be expressed as 1609.34-1336.65=272.69 meters west of east boundary. The bottom coordinate would read ” 28.70m N and 272.69m W from exterior boundaries of section 22-92-10W5″).
If the well passes into another township, take in account road allowance as well. (subtract 20 meters from the coordinate if a road allowance was crossed). Road allowances can also be present inside townships, between sections (a topographic survey would show this).
© April, 2011, Chinook Consulting Services
References:
- Alberta Geological Survey. Alberta Township System (ATS) and Universal Transverse Mercator (UTM) Map Conversion Tools
- Alberta Geological Survey. Alberta Township System (ATS)