WellCAD Basics - Advanced Logic Technology

Balanced Tangential: Coordinates of point B’
are calculated by moving one half of a sample
rate (dL) along the tangent calculated from
Azimuth and Tilt at the former position (A)
and next moving one half of a sample rate into
the direction calculated from Azimuth and Tilt
measured at B.
Radius Of Curvature: The coordinates of B’
are calculated by incrementally approaching the
Azimuth and Tilt angles beginning with the
values measured at A and ending with the
values measured at B – it is an integration along
the well path.
BOOK 1 - WELLCAD BASICS - 151
Detailed information about the algorithm can be found in Walstrom, J.E. et al.: “A
Comparison of Various Directional Survey Models and an Approach To Model
Error Analysis”. Journal of Petroleum, Technology 24, August 1972
Azimuth Correction:
The value set in the edit box for a magnetic declination correction will be subtracted
from the incoming azimuth values. Assumed the azimuth channel provides an
azimuth with respect to magnetic north the computed Northing and Easting
coordinates use True North as reference. Magnetic declination must be inserted as
clockwise measured angle from Magnetic North to True North. E.g. let us assume a
magnetic declination of 10 deg West (sometimes given as –10 degrees). The value
that must be inserted into the edit box is 10.
Estimation of uncertainty:
If you check this option and set the values for the accuracy of the azimuth and tilt
recordings, two additional Well Logs will be output. The uncertainty at each point
can be depicted as ellipse, with the most probable value being the mid point of the
ellipse. The amount of uncertainty is reflected by the size of the ellipse – the
extension of the long and short axis defining the ellipse. The two Well Logs will
contain the computed length of the two axis of the error ellipse for each
measurement point. As the algorithm is based on a probabilistic approach you will
get less uncertainty the more orientation measurements have been made.