the invention will be implemented the surface installation includes a hoisting gear 1 comprising a hoisting tower 2 a winch 3 allowing displacement of a pipe hook 4 driving means 5 for driving the whole of the drill string 6 placed in well 7 into rotation are suspended below the pipe hook these driving means can be of the kelly type coupled with a rotary table 8 and mechanical motive means or of the power swivel type directly suspended from the hook and longitudinally guided in the tower drill string 6 is conventionally made up of drill rods 10 of a part 11 commonly referred to as bha for bottom hole assembly mainly comprising drill collars a drill bit 12 in contact with the ground during drilling well 7 is filled with a fluid referred to as drilling fluid which circulates from the surface to the bottom through the inner channel of the drill string and flows back up to the surface through the annular space between the walls of the well and the drill string to implement the invention a sub 13 equipped with instruments can be interposed between the driving means and the top of the string this.