High Angle and Horizontal Wells

In previous chapters it was assumed, unless otherwise mentioned, that the borehole was vertical and the formation layers horizontal. Most discussions of the physics of borehole measurements do the same. The assumptions are natural and mainly historical, since it was not until the 1980s that highly deviated wells became common, and not until the 1990s that horizontal wells were drilled in numbers. On the other hand, highly dipping formations are rare, and only affect the deeper reading resistivity devices significantly.