Major sources of uncertainty in the subsurface environment include variable lithology, structure, and in situ stresses and the resulting variations in fracture initiation and growth processes, geochemical reactions and multi-phase flow at a variety of scales. These processes occur in the deep subsurface accessible only by wells.

To realize the full potential of subsurface resources, improvements are needed in characterization, monitoring, prediction and ultimately control of fracture and flow processes over scales ranging from nanometers to kilometers.

DOE established the SubTER Tech Team to address crosscutting grand challenges associated with the use of the subsurface for energy extraction and storage purposes. This Tech Team includes representatives of DOE applied technology offices that are active in the subsurface, as well as representatives of the Office of Science, Office of Energy Policy and Systems Analysis, EIA, CI, OE, and ARPA-E. Functions of the DOE SubTER Tech Team include:

• Identify subsurface challenges and advocate solutions;
• Identify potential cross-cutting subsurface initiatives;
• Facilitate both intra-departmental and interagency collaboration of cross-cutting subsurface R&D activities; and
• Engage industry stakeholders operating in the subsurface.

The RFI. DOE is seeking specific information in four technical areas that have been identified as priorities based on the DOE’s strategies and technology roadmaps as well as on results from an internal workshop held to gather input from the National Labs: (1) intelligent wellbores; (2) induced seismicity; (3) control of fractures and subsurface fluid flow; and (4) new subsurface signals.

Intelligent Wellbores. DOE is interested in enhancing the ability of stakeholders to construct, maintain, remediate, and abandon wellbores across a wide range of geologic environments to meet application specific performance requirements. Key research, development and demonstration focus areas that are being considered include:

• New materials and enhancements to existing materials for casing, cements, centralizers, downhole equipment or tools; lost circulation mitigation materials, and drilling fluids, that are tailored to specific application and subsurface environments. Specific areas of interest include:

  • Self-healing or adaptive casing and cement materials that respond to mechanical or chemical damage.

  • Empirical and computational studies of material fatigue under various operating and deployment conditions.

  • Case-studies of existing legacy wells to better understand common failure mechanisms and material limitation over long time periods (50+ years).

  • Better annulus preparation and quality assurance (e.g. centralizers and annulus cleaning) to improvement cement placement, cement uniformity, and seal quality.

• Diagnostic and monitoring technologies that deliver to decision makers better transient (logging) or real-time data on wellbore/system health and performance. Specific areas of interest include:

  • Technologies that permanently integrate sensors and electronics into wellbores for continuous in-situ monitoring, including the integration of sensors and electronics into casing strings, joints/couplings, cements, and other element of wellbores especially for inter-casing strings.

  • Data telemetry methods for transmission of downhole information to the surface continuously, over long time durations (years).

  • Methods to harvest downhole energy sources to power sensor(s) and telemetry systems continuously, over long time durations (years).

• Remediation technology and techniques that are non-intrusive and non-destructive, that can selectively target/perforate problem sections and deliver fit-for-purpose remediation materials.

Induced seismicity. Naturally-occurring seismicity is a phenomenon common on plate margins and in regions of intra-plate strain accumulation, and provides critical information about the structure, composition and behavior of the subsurface. Similarly, seismicity resulting from subsurface engineering for energy applications provides critical information for characterizing the in situ stress state and its response to applied stresses. Recent increases in the number and frequency of earthquakes in areas that have not been historically seismically active have been correlated to local fluid injection, elevating induced seismicity as a topic of public interest.

DOE is interested in exploring the nature of and controls on induced seismicity; the information induced seismicity can provide on changing in situ stress conditions and critical stress states in the subsurface; the potential for developing accurate, real-time stress state monitoring; and the possibilities for predicting, avoiding and/or mitigating felt seismicity.

Control of fractures and subsurface fluid flow. Real-time or near real-time control of induced fracturing and subsurface fluid control would greatly improve efficient and environmentally safe use of the subsurface. A major goal that DOE is interested in supporting is the ability to adaptively control fractures and fluid flow in response to the evolving conditions of engineered subsurface environments.

DOE is interested in focusing on several fundamental science and applied technology areas that promote novel concepts, technologies, and/or materials for controlling fracture formation and fluid flow. Some energy applications require enhancement of flow paths, while others require reducing or eliminating fluid flow. Major advances in understanding of fracture mechanics and the coupled physical and chemical processes that influence fracture generation and propagation are necessary in order to make such real-time control possible.

Novel stimulation methods may provide alternative methods to hydraulic fracturing to enhance flow paths. These methods, which could include energetic and/or chemical approaches, have the potential to be both more effective and more environmentally sustainable than hydraulic fracturing.

For reducing or eliminating flow, new materials that change properties (solidify or dramatically change viscosity) in response to their environment could be deployed to block flow paths. Materials that impede flow for different lengths of time and under different conditions could be valuable for a variety of applications. All of these new technologies would need to be developed through computational and laboratory studies and eventually tested at field scale.

New subsurface signals. DOE is interested in the potential to dynamically control and manage subsurface fractures, associated flow, and reactions. A major obstacle to adaptive control of subsurface fractures, reactions and flow is the limited ability to clearly characterize and monitor critical subsurface features.

Although the energy industry has developed sophisticated tools to characterize the subsurface using both surface and wellbore methods, an entirely new class of capabilities are needed to characterize fractures and associated processes at sufficiently high spatial resolution and over large enough volumes to guide subsurface operations. The challenge is complicated by the range of relevant scales and by the coupled nature of thermal-hydrological-mechanical-chemical processes.

DOE is interested in transforming the ability to characterize subsurface systems by focusing on four areas of research: new signals, integration of multiple datasets, identification of critical system transitions, and automation.

Potential approaches include both the use of multiple dataset to co-characterize physical, geochemical, and mechanical properties and the leveraging of advances in material science, nano-manufacturing, and high-performance computing. Success in addressing this challenge is needed to master the subsurface, enabling highly efficient and environmentally sound use of subsurface systems.