Connectivity mapping for flow and transport models in heterogeneous fluvial deposits using lidar and optical imaging

Connectivity of heterogeneities within fluvial aquifers has a strong influence on groundwater flow and solute transport. Addressing the effects of heterogeneities, popular modeling tools use geostatistical methods that produce multiple realizations faithful to a chosen statistical framework, but usually with minimal correlation or resemblance to real geologic formations. These typically include pixel-based approaches and object-based approaches. More recently applied to this problem, multiple-point approaches have become popular for addressing the heterogeneities and connectivity of the geometries of aquifer facies. This is due to their greater ability to handle the complexities and three-dimensionality of these systems; yet still rely on training images statistically derived from abstract geometries. Taking a step closer to models based on true geological structures, we are developing a measurement approach using ground-based lidar and optical imaging data obtained from extended, rugose outcrops. The varying spatial orientations of these extended outcrops allow the reconstruction of more complete 3D descriptions of the facies. These outcrops provide multiple cross-sections of facies (or realizations) that are continuous through a single geological unit. We use these data to measure the minimum possible extension in 3D space of the high and low transmissivity facies, which characterize the key components of the heterogeneities and their connectivity. That is, for a given facies, using the outcrop data, we are able to identify the lengths of the facies in multiple directions within the extent of the available outcrops; effectively providing a minimum length of the facies in each direction. This yields minimum limits, and in cases where facies terminate, maximum limits on the characteristic lengths of the facies. Where possible, their orientation with respect to the direction of the paleocurrent is also recorded. Because the facies of this particular geological unit may be classified as bimodal, it is reasonable to represent them as either high or low K material. This allows us to develop the model as high K heterogeneities as connected groups of facies that are separated by measurable distances between them through low K material. We are looking at these distances or lengths in multiple orientations, allowing us to construct a model of connectivity that may be related to gradients in any direction. These measurements will be used to provide a real-world geological basis for modeling flow and transport in aquifers.