Estimating the Geological Structure and Transport Properties of Denied and Limited Access Sites

Onsite measurements are the standard for establishing geological conditions and related transport properties. However, making direct measurements is not always possible, either because a location is too remote, too vast, or access is outright denied. The latter is typically the case at nuclear test sites, or military installations. Here we describe a systematic method to characterize geology and estimate fracture width, spacing, tortuosity, permeability, and porosity at locations where direct measurements cannot be made. Fractures are treated as fractals with their respective fractal dimensions determined using surface images. Tortuosity in the geological matrix (i.e., bulk media) is determined using rock class with the latter also being used to determine distributions for permeability and porosity. The approach is tested using areal images and rock class for the Nevada Test Site and validated by comparison to field and core measurements. Past work has shown that testing a nuclear weapon underground can affect not only the migration time for gases to the surface but also their isotopic ratios. Accurately modeling gas transport and isotopic fractionation requires knowledge of the geology. However, suspected tests are typically conducted at sites to which the international community has no access.