UTILIZATION OF OBSERVATIONS OF WELL BORE FAILURE TO CONSTRAIN THE ORIENTATION AND MAGNITUDE OF CRUSTAL STRESSES - APPLICATION TO CONTINENTAL, DEEP-SEA DRILLING PROJECT, AND OCEAN DRILLING PROGRAM BOREHOLES

The conditions necessary for compressive and tensile failure of well bores drilled into crystalline rock can be adequately represented by simple elastic failure criteria, and analysis of well bore failure can provide constraints on the magnitudes of in situ stresses if the strength of the rock is known. When applied to several boreholes drilled into continental crust where there is relatively complete knowledge of stress magnitudes, these criteria enable us to predict the depth at which compressive failure of the well bores is observed. In oceanic crust, breakouts have been observed at depths below 700m below sea floor in Deep Sea Drilling Project (DSDP) hole 504B, drilled into 5.9Ma crust south of the Costa Rica Rift, and near the botton of DSDP hole 395A, drilled into 7.3Ma crust west of the Mid-Atlantic Ridge. As ridge push forces are relatively small in young oceanic crust, we concur with previous suggestions that the high horizontal compressive stresses result from the thermoelastic effects of a convectively cooled upper crustal layer overlying a conductively cooling lithosphere. -from Authors