Abstract

Recent research shows that ichnology has significant application to production geology. As such, permeability enhancement in bioturbated media has been recognized in five interrelated scenarios: (1) surface-constrained textural heterogeneities; (2) nonconstrained textural heterogeneities; (3) weakly defined textural heterogeneities; (4) diagenetic textural heterogeneities; and (5) cryptic bioturbation.

Our data demonstrate that substrate-controlled ichnofossil assemblages can enhance the permeability and vertical transmissivity of an otherwise relatively impermeable matrix. Permeability enhancement develops when burrows excavated into a firm ground are filled with a contrasting sediment from the overlying strata. Fill contrasting with the encasing firm-ground substrate leads to anisotropic porosity and permeability. The same concept can be applied to carbonate reservoirs, where burrow fills are subjected to different diagenetic phases. This may also lead to anisotropic porosity and permeability that can have dramatic effects on reserve calculations.

If the burrow fills have enhanced permeability but burrow effects are not recognized, reserve calculations will be too low. Likewise, if the burrow fills have reduced permeability, the reserve calculations may be too high. Understanding the flow dynamics of the resulting anisotropic permeability provides a potentially powerful reservoir-development tool. The implications are far reaching, particularly pertaining to calculations of reserves and their deliverability.

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