Resistance of rocks to crushing during well drilling

The paper presents properties of the rocks according to their resistance to drilling. The effects of differential pressure on the rock drillability and changes in rocks strength depending on the depth of their occurrence and crushing conditions are examined. The interlinkage between technological processes for rock crushing at the borehole bottom and breaking stresses has been analyzed. The interlinkage between the breaking loads and deformations of rocks with account of their structural changes and rate of loading has been assessed. The relevance and applicability of identified regularities between stresses, deformations and differential pressure for solving practical tasks of efficient rock crushing in the course of drilling have been assessed. Issues of providing theoretical evidence for the rock breakage with the rock cutting tools in the bottom-hole conditions have been reviewed. It is proven that the rock destruction effect of drilling depends not only on the value of the breaking load but also on the rate of its application.