Article on Orientation of Borehole Data

Discontinuity measurements on oriented cores are in terms of alpha and beta angles measured with respect to the core axis.  The beta angle is measured with respect to a reference line scribed along the length of the core.  The position of this reference line is measured with respect to the TOP of the core.  

Orientation parameters for borehole data (left); Definition of alpha angle (centre); Definition of beta angle (right)

 

For example:

  • if the reference line is coincident with the TOP of the core, then Orientation 1 = 0
  • if the reference line is at the bottom of the core, then Orientation 1 = 180

 Typically, the reference line is either at the top or the bottom of the core, so Orientation 1 = 0 or 180.

However, Dips allows for a general definition of the position of the reference line, so Orientation 1 can be any angle between 0 and 359.

Also, note that the direction of drilling must also be accounted for.  As stated in the Online Help, Orientation 1 is defined as:

The angle from the top of the core to the reference line (measured clockwise looking in the down-core direction).  Use 0 if the borehole is vertical.

To summarize:

  • the alpha and beta angles of discontinuities are measured with respect to the core itself
  • Dips then uses the Orientation 1, 2, and 3 values of the borehole to convert the local alpha and beta angles into true dip and dip direction

In order to process your data correctly, you will have to enter all of the data in the exact format required by Dips.  If you have used slightly different conventions for any of the measurements, make sure that they are converted to the format described in the Dips Online Help for Borehole Traverse Orientation and Borehole Orientation Data Pairs.

 

Descriptions of Orientations: 

Orientation 1:

For a non-vertical borehole, the TOP of the core is a line along the topmost point of the core, as it was insitu.  You need this line in order to relate the orientation of the core to the borehole.  For a vertical borehole, there is no "top" of the core, since the hole is vertical.  In this case, you can simply enter zero for Orientation 1, and the Orientation 3 value then serves two purposes:

  1. To define the position of the core within the borehole, and
  2. The direction of north.

Orientation 1

 

Orientation 2:

Inclination of the borehole axis from the zenith.  For example, if the borehole is drilled 20 degrees from vertical, Orientation 2 = 160.

Orientation 2

 

Orientation 3:

This is the direction of drilling with respect to north.

Orientation 3