Burrowing organisms displace and mix sedimentary grains by burrowing, feeding and relocating. Their activity within the substrate can add to sedimentary heterogeneity, but more importantly alters horizontal and vertical permeability. Understanding the subtle changes in permeability that result from biogenic structures within sediments is an important concern for operators working IOR and EOR projects, such as steam-assisted gravity drainage and CO2 sequestration.
A geologic process-oriented stochastic method was used to model the wave-dominated shoreface outcrop and biogenic structures of the Spring Canyon Member (Upper Cretaceous), Blackhawk Formation, Utah. Outcrop sedimentologic studies, modern and ancient analogs and probe permeameter provided input for these process-oriented stochastic models. This stratigraphic interval was chosen because it contains heterolithic shoreface-transition facies exhibiting abundant burrowing trace fossils (Ophiomorpha, Asterosoma, and Chondrites). Biogenic structures were modeled as 3D objects of varying dimensions and orientations, and superimposed on process-oriented stochastic models. Permeability was assigned to primary burrows, burrow rims and host lithologies. Multiple realizations were generated to adequately quantify parameter variability.
This study documents the impact of biogenic structures on estimates of effective directional permeability by varying model parameters like orientation, abundance, diversity, and permeability in burrow and burrow rims. These simulation models underwent flow-based upscaling to calculate the effective directional permeabilites for each uncertainty realization.
Les B. Dabek and Rex Knepp, Geomodeling.
Presented at the AAPG Annual Convention and Exhibition, Houston, Texas, USA, April 10-13, 2011
