Image Logs on the Ogbon-1 Well
Learning objectives
- Read an image, GR, and tadpole track together as one panel
- See the same plane as a sinusoid on the image and a tadpole beside it
- Walk a structural story, bedding, foresets, drag, a fault, a fracture
- Tie image features to the lithology the GR shows
The Whole Chapter on One Well
Every idea in the chapter comes together the way an interpreter actually works, three tracks side by side over the Ogbon-1 reservoir. The GR is the lithology spine, sand light and shale dark. The image is the unrolled wall, lithology bands crossed by bedding sinusoids, a fault, and a fracture. The tadpoles beside it carry the dip and azimuth of every plane. The image and the tadpoles are the same picks drawn two ways, so the two displays always agree.
Reading the Story
Scrub the depth cursor and the panel tells a story. The upper sand carries cross-bed foresets dipping to the southwest, a paleocurrent. Lower down the bedding steepens into a fault, drag bending it over, and below the fault the regional azimuth has rotated. Near the base a steep dark sinusoid cuts the beds, a conductive open fracture, a flow path that does not care about the bedding at all.
The Tool Behind the Picture
Switch the image between the resistivity pad tool, with its blind stripes where the pads do not touch the wall, and the full coverage of the acoustic tool. The choice changes what you can see and at what resolution. An image log is the richest single picture petrophysics offers, and reading it well is reading the rock, the structure, and the stress all at once.
References
- Rider, M. and Kennedy, M. (2011). The Geological Interpretation of Well Logs, 3rd ed. Rider-French.
- Luthi, S. M. (2001). Geological Well Logs: Their Use in Reservoir Modeling. Springer.