A new report by an independent panel recommends that the Energy Department take a leading role in understanding subsurface systems to better address the nation’s energy and security issues. JASON – a group of scientific thought leaders that has provided independent consultation to the U.S. government for over 50 years – undertook the study on behalf of the new crosscutting Subsurface Technology and Engineering Research, Development, & Demonstration (SubTER) Tech Team in the Office of the Under Secretary for Science and Energy. SubTER is an integrated platform across DOE offices to address crosscutting grand challenges associated with the use of the subsurface for energy extraction and storage purposes.
The 2014 JASON subsurface report was developed during a summer study period that began with a day-long briefing series in La Jolla, CA, where members of the subsurface research and development community were invited to present the state-of-the-art in and key challenges to assessing the state of stress at depth. JASON study members also visited the La Jolla cliffs to study the Eocene marine sedimentary rocks and assess stress-induced geologic structures and heterogeneity in the field. These interactions provided the background that the JASON group built on during a month of study and writing, culminating in the finished report.
In the new report the JASON group recommends that “DOE take a leadership role in the science and technology for improved measurement, characterization, and understanding of the state of stress of engineered subsurface systems in order to address major energy and security challenges of the nation.” Successful utilization of the vast majority of U.S. energy resources fundamentally hinges on understanding and controlling the state of stress and mechanical deformation of rocks in the upper crust. Examples include creating and sustaining fracture networks in enhanced geothermal systems (EGS) and unconventional oil and gas reservoirs; predicting and controlling geomechanical stability of reservoir rocks and seals in CO2 storage reservoirs; and predicting geomechanical evolution at the interface between geologic media and engineered materials in nuclear waste storage and disposal settings. New insights into characterizing the state of stress at key scales are needed to understand, predict, simulate, and monitor the dynamic response of the subsurface to changing stresses (e.g., fracture initiation and propagation, induced seismicity).
The report reviews the key length scales controlling stress changes that precipitate fracture nucleation and propagation, and considers existing methods and new opportunities for resolving the subsurface stress field. JASON recommends coordinated research and technology development at dedicated field sites to connect insights from laboratory scales and models to operational environments. The group proposes “dense arrays of micro-boreholes … and sensor networks” and implies “a focus on rapid/inexpensive drilling as well as development of small, inexpensive sensors” deployed at “re-occupied existing structures (e.g., abandoned boreholes, mines, existing field sites) or newly developed sites.“ Complementary expansions in laboratory analyses and advanced theory, modeling and simulation should leverage DOE expertise and national laboratory user facilities.