Certain classes of oil-based drilling fluids develop a mudcake that has a propensity to lose fluid (desiccate) and fracture under tension (c.f. synaeresis cracking). These fractures are sharp, narrow, commonly regularly spaced and very resistive. They are often discontinuous across the borehole and can occur on two opposed pads. Inclinations typically range from 15º to 85º. These artefacts often visually dominate an image and if they occur alongside real natural resistive fractures, they can be difficult to interpret. In addition, they can be readily confused with drilling induced tension fractures. Automatic dips through affected zones can track these features. We consider that their formation is controlled by a range of variables which include, in no particular order: mud type, lithology, formation tilt, hole orientation and in-situ stress.
See also drilling induced tension fractures, mud, mudcake.