Rapid Distributed Sensing of Subsurface In situ Stress

The earth’s subsurface possesses great potential for energy production, energy storage, and the safe disposal of CO2 and hazardous materials. Presently, there is insufficient understanding of subsurface stress, human-induced seismicity, and their combined effects on permeability. Higher fidelity sensing of the subsurface is necessary to develop a geomechanical model that can guide geothermal and well design to minimize cost and maximize safety. A recent report by the JASON advisory group emphasized the need for new ways to measure the in-situ stress state over a wide range of scales (10-6 to 102 m) and at significant depth (up to 5 km). According to the DOE’s SubTER group, in-situ stress measurement techniques are currently “woefully inadequate”. Advances in stress sensing technology are critical to improving our understanding and mastery of the subsurface. The nation’s energy, security, and environmental needs all hang in the balance. Luna will leverage its expertise in high definition distributed fiber-optic sensing to develop an innovative new sensor design for actively measuring in-situ subsurface stress in near real-time. Luna’s core technology lies in Optical Frequency Domain Reflectometry (OFDR) utilizing the Rayleigh backscatter within optical fiber. The OFDR technique provides higher spatial resolution than Optical Time Domain Reflectometry (OTDR) and Fiber Bragg Grating (FBG) based systems. This high spatial resolution will be utilized to measure stress at a much finer resolution than ever before, yielding new data for modeling and prediction methods. Sensing lengths between 1 m and 1000 m could be possible with this approach, yielding continuous data all along the fiber sensor in a single instrument reading. Compared to existing technologies, this new innovation would provide critical stress data in higher resolution and in less time. This innovation would directly address a large portion (10-3 to 102 m) of the scales of interest to the DOE. Novel fiber optic sensor to measure stress in underground rock to support energy generation markets. Commercial Applications and Other Benefits: Numerous sectors within the energy industry will benefit from accurate in-situ stress measurements. Oil and gas – enabling risk-driven adaptive controls on injection rate, volumes, pressures, and well locations. Hydraulic fracturing – prediction and control of hydraulic induced fractures and the activation/reopening of faults. Geothermal – develop theoretical and experimental models relating stress and induced seismicity. Waste disposal – improved understanding of stresses that will act on deep disposal facilities for energy related waste products.