Onshore drilling is going more and more to multiwell pads with (relative) close well to well spacing. They face the same problem with magnetic interference that offshore wells have always had when drilling near existing casing. MWD surveys will fail their Field Acceptance Criteria because of this interference. A work-around is to allow higher FAC values with the trade-off of larger Ellipses of Uncertainty.
The International Association of Directional Drilling had a forum on Multiwell pad drilling in Midland Sept 2017. The presentations for this and other IADD events are on the iadd-intl.org website under >events >past event presentations.
My presentation on magnetic MWD near existing casing is at https://www.iadd-intl.org/files/1021/
. Questions and feedback would be appreciated.