Rethinking lateral side forces in PDC bit drilling: a comparative review of slide vs rotary evidence

Lateral side forces acting on polycrystalline diamond compact (PDC) drill bits affect borehole quality, trajectory control, and bit durability. Published studies report conflicting slide- and rotary-dominant behaviour because they rely on heterogeneous evidence, including direct downhole measurements, laboratory observations, modelling, and operational proxies. This review compares these evidence types without assuming quantitative equivalence between different observables. The synthesis indicates that slide-dominant lateral loading is most consistently associated with high-bend motor assemblies in aggressive build and turn intervals. Conversely, rotary drilling may sustain higher time-averaged lateral loading in moderate-bend assemblies, rotary-steerable laterals, geothermal hard-rock drilling, and high-temperature environments because of persistent gauge–wall interaction and dynamic excitation. The resulting context-dependent framework supports bit and BHA selection, gauge-design strategy, and drilling-risk mitigation in Australian onshore, geothermal, and carbon-storage applications. Because heterogeneous metrics cannot be physically normalised to a common force scale, the comparison remains qualitative and evidence-weighted.