Computer modeling bioturbation: The creation of porous and permeable fluid-flow pathways

Abstract

Computer modeling of trace fossils (Skolithos, Thalassinoides, Planolites, Zoophycos, and Phycosiphon) and ichnofacies (Skolithos, Cruziana, and Zoophycos ichnofacies) is undertaken to assess the impact of bioturbation on porosity and permeability trends in sedimentary media. Model volumes are randomly populated with the digitally modeled trace fossils to test for connectivity between burrows. The probability of vertical and lateral interconnections is compared with bioturbation intensity. The results of the simulations indicate that biogenic flow networks develop at low bioturbation intensity, between 10 and 27.5% bioturbation (BI-2). However, the efficiency of connectivity is controlled by the architecture of the burrows. For all trace-fossil and ichnofacies models, regardless of trace-fossil orientation, continuous horizontal and vertical connectivity across the sediment volume is achieved within a 0 to 10% range in bioturbation. In subsurface aquifers and petroleum reservoirs, the presence of bioturbation can significantly influence fluid flow. In particular, for marine sedimentary rocks, where burrows are more permeable than the surrounding matrix, a greater degree of three-dimensional burrow connectivity can produce preferred fluid-flow pathways through the rock. Recognizing these flow conduits may enable optimization of resource exploitation or may contribute to increasing reserve estimates from previously interpreted nonreservoir rock.