Reading Dip from a Sinusoid
Learning objectives
- Read the dip from the sinusoid amplitude (tan dip = height/diameter)
- Read the dip azimuth from the low point of the sine
- Recognize a flat bed as a straight line, a steep one as a tall sine
- See the dip and azimuth as the single measurement a tadpole records
Drawing the Sine in Reverse
A planar feature on a borehole image is a sine wave, and reading its dip is the inverse of drawing it. Two numbers come straight off the curve. Fit the moving sine to the bed boundary on the image and watch them appear.
Amplitude Is Dip, Phase Is Azimuth
The amplitude, the peak-to-peak height , gives the dip through
so a tall sine is a steep dip and a flat line is a horizontal bed. The phase, the azimuth of the low point of the sine, is the downdip direction, the way water would run down the bedding plane.
One Measurement
When the moving sine locks onto the boundary, the dip and the dip azimuth are the single measurement a dipmeter records, the dot at the dip magnitude with its tail pointing downdip, the tadpole of the next section. Modern image interpretation auto-picks thousands of these down a well, but every one is this same two-number read off a sine.
References
- Serra, O. (1989). Formation MicroScanner Image Interpretation. Schlumberger.
- Rider, M. and Kennedy, M. (2011). The Geological Interpretation of Well Logs, 3rd ed. Rider-French.