Exploiting Acoustics for Subsurface Communication

Reliable, safe, and robust storage of CO2 beneath the surface is important today and is expected to become even more critical in the coming decades. Safe storage requires knowledge regarding the dynamics and evolution of subsurface CO2 reservoirs. Temperature, pressure, and potentially other sensors are used to monitor important subsurface zones at various depths. An effective and relatively convenient way to accomplish this is with sensors mounted within the cemented annulus residing outside of a borehole casing. A telemetry system for the retrieval of sensor data that is free of cables and wires is advantageous. In this Phase-I STTR, advanced acoustic modes of propagation within the casing will be studied to quantify opportunities for acoustic telemetry specific to the CO2 monitoring environment. Communication while drilling is not an issue, and indeed the drill is absent during the long-term monitoring environment. The specific waveguide environment is therefore the cement annulus itself, the metal casing, and the gas or fluid comprising the interior of the casing. This structure may present desirable acoustic propagation modes that permit high bit-rate communication. The acoustical physics of the channel will be rigorously and comprehensively studied in Phase I to reveal such opportunities. Should suitable designs be discovered in Phase I, Phase II will focus on the demonstration of such designs.