Applications of Ichnology to Fluid and Gas Production in Hydrocarbon Reservoirs

Biogenically modified sedimentary flow media can occur as well-defined, highly contrasting permeability fields (i.e., dual-permeability networks), or slightly contrasting permeability fields (i.e., dual-porosity networks). Dual porosity reduces the resource quality of a sedimentary rock, in that although the entire rock contributes to fluid flow, the presence of more than one fluid phase can induce preferential flow along tortuous permeability pathways. Additionally, fluid moves via diffusion and advection, making the pathways difficult to model. Dual-permeability flow media have even poorer resource characteristics because the higher permeability portions of the rock provide the only transmissive conduits, and fluid resources may be absent in the tighter (unburrowed) rock. Secondary recovery attempts in dual permeability media can isolate large parts of the active flow network, which may contain resource fluids or gasses.

The presence of a dual porosity versus a dual permeability network, and the stratigraphic configuration of burrow-enhanced permeability are the primary considerations when classifying the type of biogenic flow media encountered. These parameters define the five flow-media types: 1) surface-constrained textural heterogeneities; 2) non-constrained, discretely packaged textural heterogeneities; 3) selectively sorted, weakly defined textural heterogeneities; 4) cryptically bioturbated sandstone; and 5) diagenetic heterogeneities. Other factors that influence the quality and behavior of the flow media are burrow density, burrow connectivity and burrow/matrix permeability contrast, burrow surface area, and burrow architecture.

With respect to permeability fabrics, 3-D imaging techniques are an essential component of burrow-fabric analysis. Computer Tomography (CT) scans, Micro-CTscans, and MRI techniques have the most potential in burrow-reservoir analysis. These techniques can be used collaboratively to fully assess the nature of burrow-modified flow media.