Novel sensing materials for harsh environment subsurface pH sensing applications

Robust pH sensors that can operate under harsh environmental conditions are valuable for a variety of applications, such as oil and gas production, geological CO2 sequestration, etc. However, despite the significant advance in pH measurement technology, reliable pH sensing at elevated pressures (up to 30,000 psi) and high temperatures (up to 350 degrees C) remains challenging. We describe an optical pH sensor based on optical fiber technology. A sensing layer that is comprised of metal nanoparticles incorporated in a silica matrix coated on an optical fiber exhibits strong and reversible optical response to pH variation at 80 degrees C and in solutions with different salt concentrations. The same robust response is also observed at elevated pressures up to 2,000 psi. The optical fiber pH sensor is made of materials with high stability at temperatures at least up to similar to 600 degrees C. Therefore, this approach provides a new potential means to enable optical pH sensing for extreme environment applications.