Scalable and Robust Fiber-Optic Sensor Array System for Injected CO2 3D Mapping Using Active Micro-Acoustics

Underground carbon dioxide (CO2) storage is increasingly seen as a promising tool in the fight against climate effects. Subsurface CO2 is stored in a supercritical fluid state, which requires deep insertion into porous basement rock. If the CO2 works its way towards the surface (moving into lower pressure areas), it can quickly return to a gaseous state and escape back into the atmosphere. The DOE seeks innovative methods of mapping pressure in CO2 storage applications to detect potentially harmful CO2 leakages. IFOS proposes the development of an innovative, fiber-optic-based 3D imaging product – InjectSense™ - to improve characterization of CO2 reservoirs both during and after injection operations. This cost effective, robust, scalable, high-speed, precision characterization tool will target two major injected CO2 monitoring challenges: low signal-to-noise ratio (SNR) of conventional acoustic measurement, and massive data storage requirements required by conventional acoustic sensing systems’ reliance on extensive time averaging. The InjectSense™ system will overcome the low SNR of existing distributed acoustic systems by two innovative methods. First, InjectSense™ is enabled by the innovative use of multiplexed fiber Bragg grating (FBG) sensors configured in a novel quasi-distributed sensing configuration, or Q-DAS. FBGs provide higher SNR at the expense of measurement distance. IFOS has developed an innovative configuration to mitigate this tradeoff. The back-end data processing burden is reduced and the need for data-intensive time averaging is eliminated. The second IFOS innovation in boosting SNR is in InjectSense™’s ability to be operated as an ‘active’ system by deploying acoustic micro emitter (AME) technology. The AMEs will be conveyed through formation pores before emitting an acoustic signal at a predetermined time. This staggered acoustic wave will be measured by the FBGs and interpreted by InjectSense™’s supporting optoelectronics signal processing interrogator to develop a 3D image of the formation. In Phase I IFOS will demonstrate the feasibility of its innovative CO2 injection imaging system before proceeding to field validation of an integrated engineering prototype in Phase II.The intelligence provided by IFOS’ InjectSense™ system will increase the safety and efficiency of carbon storage by giving operators greater understanding of the injection process, enabling better operations decisions and reducing environmental impacts of injections. The system has numerous spin-off applications in geothermal energy and in structural health monitoring.