Acoustic communication through well-head for an untethered autonomous well logging tool

Untethered autonomous well logging tools have recently been introduced to oilfields. Once deployed into a well, the tools autonomously travel in the well to collect data and return to surface after the mission is completed. A service operator needs to travel to the well-site and open the well cap to check if the tool has returned. This increases the operational time and cost. This can be addressed by implementing a return detector and notifying the operator. Steel well-head construction leaves acoustics as the most viable option for such detection. We demonstrated a proof of concept of acoustic based simplex communication system through well-head. A pair of identical transducers were used as transmitter and receiver that operates at 155 kHz. Transmitter piezo was positioned at the center of a water filled steel wellhead with 7-inch diameter and 0.25-in. wall thickness, while the receiver was taped outside the wellhead with grease to increase acoustic coupling. Transmission loss was measured as -57 dB which was partially compensated by using a receiver amplifier stage with a gain of 1000. Next, the transmitter will be incorporated on a miniaturized untethered well logging tool.