SIMULATING HETEROGENEITY IN CHANNEL-BELT DEPOSITS - GEOMETRIC SIMULATION APPROACH

We developed a code that simulates the hierarchical stratal architecture formed by braided rivers. The code first creates a geometric model of the stratal architecture. The stratal units are created at each hierarchical level, and a level N unit is the bounding surface for an assemblage of level N-1 unit types. For a given level, creating an occurrence of a unit type starts with an archetypal geometry. The archetypal geometry is a polyhedron defined by piecewise planar elements. A parsimonious number of geometric lengths are used to define the size and shape of a polyhedron. The polyhedron is then transformed by mapping its axis onto a curve, created in the coordinate system of the level N+1 unit in which it will reside. The algorithm is repeated to create other level N units until the level N+1 unit is filled. The same process is used to create smaller-scale level N-1 unit types and fill, in turn, the level N unit. The code then creates a digital model as a 3-D cubic lattice by sampling the geometric model. Each voxel in the lattice is considered individually and assigned a unit type at each hierarchical level. At each level, the voxel is assigned to one polyhedron in the final model, based on rules consistent with knowledge of depositional processes and whether boundaries represent erosional or conforming surfaces. In this manner, the algorithm assigns only one unit type for each hierarchical level to a voxel. The digital model is then populated with permeability values defined by the mean and variance of permeability for unit types at only the lowest level (smallest scale) of the hierarchy. The assignment of unit types and permeability to one voxel is independent of another voxel, and thus this algorithm is highly scalable when executed on supercomputing platforms. The code has been written for both serial and parallel execution. The metrics for unit types at each level compare well against those observed in an abandoned channel-belt of the Sagavanirktok River. The digital model is intended for use as high-resolution base cases in various areas of computational research on multiscale flow and transport processes, including the testing of upscaling theories.