Enlargement of a borehole through the jetting action of a drill bit, resulting in an over-gauge hole. Often observed on dipmeter calipers as an over-gauge hole, with equal or sub-equal caliper sizes indicating a pseudo-circular well section. Boundaries to washouts are sometimes gradual, unlike borehole breakouts that appear more step-like in occurrence. Severe washouts degrade image quality and can sometimes be too large for caliper tool devices to compensate for.
See also calipers, rugose hole, borehole breakout and bit size.