Borehole stability: A new challenge for an old problem

During the 2nd century A.D., Hadrien ordered the excavation of a tunnel to provide water supply to Athens. His engineers must have long argued about the stability of the excavation. Anazingly enough and as far as we know, the tunnel is still in use. Since then, many tunnels have been excavated and many progress made in the quantification of the rock/support interaction. However, in the area of oil well drilling, the problem of the stability of the open hole(i.e. uncased wellbore) is of crucial importance because of economical factors. The assessment of predictive models and the definition of the key parameters governing stability are the essential issues of this new challenge. The environment of oil well drilling Imposes boundary conditions such as the role of the drilling fluid, or mud, and of temperature effects which are Seldomly studied In civil or mining engineering. Another problem linked with wellbore stability is that the parameters required for an analysis are very difficult to gather. This imposes the need for parametric studies and easy-to-use representations have to be found in order to facilitate these studies.