Azimuth Reference Systems
For directional surveying there are three azimuth reference systems:
• Magnetic North
• True (Geographic) North
• Grid North
All “magnetic-type” tools give an azimuth (hole direction) referenced to
Magnetic North. However, the final calculated coordinates are always
referenced to either True North or Grid North.
True (Geographic) North
This is the direction of the geographic North Pole which lies on the Earth’s
axis of rotation. Direction is shown on maps using meridians of longitude.
Grid North
Drilling operations occur on a curved surface (i.e, the surface of the Earth)
but when calculating horizontal plane coordinates a flat surface is assumed.
Since it is not possible to exactly represent part of the surface of a sphere
on a flat well plan, corrections must be applied to the measurements. To do
this, different projection systems which can be used.
UTM System
One example of a grid system is the Universal Transverse Mercator (UTM)
System. In transverse mercator projection, the surface of the spheroid
chosen to represent the Earth is wrapped in a cylinder which touches the
spheroid along a chosen meridian. (A meridian is a circle running around
the Earth passing through both North and South geographic poles.)
These meridians of longitude converge towards the North Pole and do not
produce a rectangular grid system. The grid lines on a map form the
rectangular grid system, the Northerly direction of which is determined by
one specified meridian of longitude. This “Grid North” direction will only
be identical to “True North” on a specified meridian.
For directional surveying there are three azimuth reference systems:
• Magnetic North
• True (Geographic) North
• Grid North
All “magnetic-type” tools give an azimuth (hole direction) referenced to
Magnetic North. However, the final calculated coordinates are always
referenced to either True North or Grid North.
True (Geographic) North
This is the direction of the geographic North Pole which lies on the Earth’s
axis of rotation. Direction is shown on maps using meridians of longitude.
Grid North
Drilling operations occur on a curved surface (i.e, the surface of the Earth)
but when calculating horizontal plane coordinates a flat surface is assumed.
Since it is not possible to exactly represent part of the surface of a sphere
on a flat well plan, corrections must be applied to the measurements. To do
this, different projection systems which can be used.
UTM System
One example of a grid system is the Universal Transverse Mercator (UTM)
System. In transverse mercator projection, the surface of the spheroid
chosen to represent the Earth is wrapped in a cylinder which touches the
spheroid along a chosen meridian. (A meridian is a circle running around
the Earth passing through both North and South geographic poles.)
These meridians of longitude converge towards the North Pole and do not
produce a rectangular grid system. The grid lines on a map form the
rectangular grid system, the Northerly direction of which is determined by
one specified meridian of longitude. This “Grid North” direction will only
be identical to “True North” on a specified meridian.
