ABSTRACT
Indentation experiments were performed on Berea sandstone, Indiana limestone and highly porous refractory brick specimens using axisymmetrical indenters. The process of rock compaction in the region beneath the indenter was found to be of primordial importance in the indentation of these porous materials. The extent of the compaction zone was found to be controlled largely by the porosity of the rock and the strength of its pore structure. The refractory brick specimens failed exclusively by pore collapse and consequently were used to visualize the development of the compacted zone isolated from influences of other modes of failure. We infer from our results that rock compaction under the teeth of roller cone bits suppresses chip generation and consequently reduces the rate of penetration. In addition, a considerable amount of indentation energy is used during compaction, thus reducing the efficiency of the overall process during drilling. This problem is thought to be specifically acute in the case of deep drilling of porous rocks for gas and oil using roller cone bits.
