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Kotalna dleta se množično uporabljajo pri izdelavi hidroloških, naftnih, plinskih in drugih vrtin, za katere pridobivanje jedra ni bistvenega pomena. Odpoved delovanja dleta med vrtanjem ima za posledico zmanjšanje napredka vrtanja, zaradi česar je potrebno poškodovano ali izrabljeno kotalno dleto odstraniti iz vrtine. Zaradi tega dejstva se znanstveniki in inženirji v čedalje večji meri posvečajo raziskavam, katerih rezultati bi pripeljali k podaljšanju efektivnega časa delovanja dleta in k povečanju napredka v efektivnem času delovanja dleta. V doktorski disertaciji so bile izvedene "in situ" spremljave vrtalnih parametrov med izvajanjem vrtalnih del s kotalnima dletoma Smith SB117PS premera 215.9 mm in proizvajalca Baker Hughes J3 136 premera 155.57 mm, ki sta namenjena za vrtanje v mehkejših hribinah. Po izvedenem vrtanju sta bili dleti temeljito preiskani za ugotovitev poškodb in obrabe, ki je nastala med vrtanjem. Pri preiskavah smo uporabili naslednje sodobne in standardizirane preiskovalne metode: analizo mikro in makrostrukture hribine in materialov kotalnih dlet, ki je bila izvedena z optično in elektronsko mikroskopijo, simultano termično analizo materialov kotalnih dlet, analizo kemijske sestave hribine in materialov kotalnih dlet ter določitev geomehanskih parametrov hribine. Nastalo obrabo, lokalne porušitve in razpoke smo kvantitativno in kvalitativno opredelili in povezali z režimom vrtanja in mineraloško sestavo hribine. Na podlagi metalografskega pregleda kotalnih dlet in geofizikalnih lastnosti kamnin so se ugotovile strukturne spremembe materiala kotalnih dlet ter način in potek njihove obrabe. Izdelan je bil model predstavitve obrabe dleta v odvisnosti od hribinskih in vrtalnih parametrov s pomočjo KDV diagramov, na podlagi katerih se je ocenila pravilnost izbire uporabljenih kotalnih dlet v nastopajočih hribinah. Roller cone drill bits are widely used for drilling the hydrogeological, oil, gas and other wells, for which the acquisition of the core is not essential. The breakdown of the drill bit or rapidly decreasing of rate of penetration during the drilling process results in a reduction in the progress of the drilling, which makes it necessary to remove the damaged or worn roller cone bit from the well. Due to this fact, scientists and engineers are increasingly focusing on research, the results of which would lead to an extension of the effective time of the bit and to increase the progress and the effective time of the bit. In the doctoral dissertation, was monitored "in situ" drilling parameters during the drilling process with the Smith SB117PS 215.9 mm diameter roller cone drill bit and the Baker Hughes J3 136, diameter 155.57 mm roller cone drill bit, intended for drilling in soft rock materials. After drilling, the bits were thoroughly examined to determine the damage and wear that occurred during drilling. The following modern and standardized investigative methods were used: analysis of the micro and macrostructure of rock materials and materials of roller cone bits carried out by optical and electron microscopy, simultaneous thermal analysis of materials of drill bits, analysis of the chemical composition of rock materials and materials of drill bits, and determination of geomechanical parameters of rock materials. The resulting wear, local bursts and cracks were quantitatively and qualitatively defined and linked to the drilling regime and the mineralogical composition of the rock material. On the basis of the metallographic examination of materials of drill bits and geophysical properties of rocks, the structural changes in the material of the drill bits and the manner and course of their wear have been identified. A model for the presentation of wear in relation to the rock and drilling parameters was created using KDV diagrams, on the basis of which the correctness of the choice of the used bits in the performing rock materials was evaluated.