METHOD AND APPARATUS FOR DETERMINING A CHARACTERISTIC OF THE MOVEMENT OF A DRILL STRING

摘要

METHOD AND APPARATUS FOR DETERMINING A CHARACTERISTIC OF THE MOVEMENT OF A DRILL STRING The invention is related to a method of determining the instantaneous rotation speed of a drill string or a drill bit in a borehole or the lateral shocks applied to the string or bit. The centripetal acceleration of the drill string is measured at at least two opposite ends of a drill string diameter so as to obtain two centripetal acceleration signals acl and ac2: the signals acl and ac2 are combined and the instantaneous rotation speed or the lateral shocks are derived from said combined signal. The accelerometers must be of the type delivering a signal with a DC component. An important application of the invention is to transform drill string rotation speed dependent data acquired versus time with a constant sampling time increment Tc separating successive data, into compensated data which would be obtained for a substantially constant drill string rotation speed Sc. The compensated data are obtained either by adjusting the constant sampling time interval Tc into a variable sampling time increment TV, using the measured instantaneous rotation speed S, or by selecting the data which have been acquired during periods of time during which the instantaneous rotation speed of the drill string varied within predetermined limits only.