Abstract: The present invention is a system and method for generating an alarm relative to effective longitudinal behavior of a drill bit fastened to the end of a drill string driven in rotation in a well by a driving device situated at the surface, using a physical model of the drilling process based on general mechanics equations. The following steps are carried out: the model is reduced so to retain only pertinent modes, at least two values Rf and Rwob are calculated, Rf being a function of the principal oscillation frequency of weight on hook WOH divided by the average instantaneous rotating speed at the surface, Rwob being a function of the standard deviation of the signal of the weight on bit WOB estimated by the reduced longitudinal model from measurement of the signal of the weight on hook WOH, divided by the average weight on bit WOB0, defined from the weight of the string and the average weight on hook. Any danger from the longitudinal behavior of the drill bit is determined from the values of Rf and Rwob.

Abstract: The present invention relates to a system and to a method designed to estimate the effective displacement of a drill bit fastened to the end of a drill string and driven into rotation in a well by surface driving means. A non-linear physical model of the drilling process based on general mechanics equations is used in the invention. The following stages are performed in the method:the parameters of said model are identified by talking account of the parameters of said well and of said string,said model is linearized about a working point,said linearized model is reduced while keeping only some of the specific modes of the state matrix of said model,the displacement of the drill bit is computed in real time by means of the reduced model and of at least one parameter measured at the surface.FIG. 4 to be published.

Abstract: The present invention relates to a system and to a method designed to estimate the effective behaviour of a drill bit fastened to the end of a drill string and driven into rotation in a well by surface driving means, wherein a non-linear physical model of the drilling process based on general mechanics equations is used. The following stages are performed in the method:the parameters of said model are identified and computed by taking account of the parameters of said well and of said string,said model is linearized about a working point,said linearized model is reduced while keeping only some of the specific modes of the state matrix of said model,the displacement of the drill bit or the stress applied to the bit is computed in real time by means of the reduced model and of at least one parameter measured at the surface.FIG. 4 to be published.