Systems and methods for using Stoneley waves for bottom-hole proximity detection

A method comprising:

• emitting, from a downhole tool in a bottom-hole assembly comprising a drill bit, a plurality of Stoneley waves into a borehole in a pulse sequence, while the drill bit is off a bottom of the borehole and is being lowered to the bottom of the borehole;
• detecting, via a plurality of sensors, the plurality of Stoneley waves traveling in the borehole;
• and
• calculating, via a processor, a distance from the downhole tool to the bottom of the borehole based at least in part on the speed of the plurality of Stoneley waves in the borehole and a time between detections of the plurality of Stoneley waves.

Machine-executable instructions stored on a tangible, non-transitory machine readable storage medium, which, when executed by a machine, causes the machine to perform a method, the method comprising:

• controlling an emission of one or more Stoneley waves at a plurality of locations in a borehole;
• processing signals received from one or more Stoneley wave sensors, wherein the signals are representative of the one or more Stoneley waves sensed within the borehole;
• calculating a direction of travel of the one or more Stoneley waves;
• calculating a roundtrip time of the one or more Stoneley waves propagating down the borehole and reflecting back to the one or more Stoneley wave sensors based at least in part on the direction of travel of the one or more Stoneley waves;
• calculating a distance from a bottom-hole assembly to the bottom of the borehole based at least in part on the roundtrip time of the one or more Stoneley waves;
• calculating a first speed of Stoneley waves corresponding to the one or more Stoneley waves propagating adjacent to the bottom-hole assembly;
• and
• calculating a second speed of Stoneley waves corresponding to the one or more Stoneley waves propagating in a section of the borehole not adjacent to the bottom-hole assembly.