Stanford Geothermal WorkshopFebruary 9-11, 2026

Drilling-induced features identified from borehole image logs provide direct constraints on in-situ stress orientations and serve as a basis for stress magnitude estimation. Classic features such as drilling-induced tensile fractures and borehole breakouts have been extensively documented since the 1980s, predominantly in sedimentary rocks within hydrocarbon reservoirs. More recently, petal-centreline fractures have also been recognised. Their formation has been modelled as functions of stress state, borehole trajectory, rock properties, and drilling fluid parameters. In the high-temperature geothermal wells of the rifted Taupo Volcanic Zone, Aotearoa New Zealand, typical drilling-induced features are commonly observed in borehole image logs. These geothermal systems are hosted in a diverse lithological sequence of silicic to andesitic volcanic and volcaniclastic rocks, as well as metasedimentary basement. Alongside typical features, we also identify a range of non-typical drilling-induced features, which we hypothesise arise from the interaction of drilling with complex rock textures, mechanical anisotropy, natural fractures and veins, fault density, thermal stress, and variations in hydrothermal alteration. Globally, recent studies have modelled these non-typical features on a well-by-well basis to derive stress constraints. With the increasing availability of borehole image data in geothermal environments, we aim to engage the broader geoscience community in recognising and interpreting these non-typical features. They hold promise for refining stress and permeability models—critical for drilling stable and productive geothermal wells. This understanding is vital for optimising conventional geothermal development and advancing next-generation systems such as superhot and Enhanced Geothermal Systems.

Topic: Geology