Abstract
Other investigations have shown that rock cylinders exposed to hydrostatic pressures of 10,000 atm and loaded axially in compression behave in a ductile fashion as contrasted with their brittle behavior when tested in axial compression at atmospheric pressure. Similar tests were made by the author on rock cylinders in the pressure range 0 to 15,000 psi, which is equivalent to pressures exerted by drilling muds upon the face of formations exposed to the cutting action of rock-bit teeth. Results indicated that many formations commonly encountered in drilling operations undergo a brittle-to-ductile behavior transition in the range 0 to 15,000-psi hydrostatic pressure. The great majority of tests were made on samples which were dry and which were protected from the surrounding fluid with a plastic jacket. At atmospheric pressure, all formations so tested were brittle. The compressive strength of all formations tested in this condition increased with increasing confining pressure.
