FIELD-SCALE EXPERIMENTS FOR DEVELOPING SOLUTIONS TO SUBSURFACE ENERGY CHALLENGES

Scale is the single most important element common to all of the crosscutting challenges facing the nation and the world to improve the utilization of subsurface energy resources. From enhanced geothermal systems, to unconventional oil and gas, and from geologic carbon sequestration to nuclear waste disposal, useful and practical subsurface energy systems are large, typically on the order of kilometers or more on a side, extending to depths of a few to several kilometers. A common configuration for carbon sequestration and oil and gas systems comprises a reservoir rock, into which fluids can be injected and/or withdrawn through an array of deep wells spread out over the landscape, and a cap rock or seal on top of the reservoir. When reservoir and cap-rock systems reach useful dimensions (e.g., greater than 100 m in size), faults and possibly large variations in properties may be encountered. These heterogeneities can make the systems behave fundamentally differently from smaller systems (e.g., less than 10 m) and may require innovative permeability control for optimal utilization.

In order to reduce uncertainties and develop robust designs and optimal procedures for operating large-scale energy systems, we need to undertake field tests on scales greater than 100 m. Without such tests, researchers and engineers must extrapolate their laboratory and small-scale field results to large-scales, a process known as upscaling that is fraught with uncertainty. The goal of large-scale field testing is to (1) observe performance over similar length scales to those over which the technology will need to be applied to be a useful solution to our energy needs, (2) validate models and concepts needed to design and optimize the technology, (3) develop and test monitoring strategies applicable to large length scales, and (4) develop and confirm upscaling approaches to exploit the existing knowledge base and data that have been measured in the lab or from previous smaller scale testing. Building upon a variety of previous field tests, researchers and innovative companies need to now expand field-scale testing to larger scales to develop crosscutting capabilities in controlling permeability and fluid flow through carefully controlled and monitored stimulation and fluid injection/withdrawal processes.