QUANTIFYING DISPERSIVITY IN BIOTURBATED LIMESTONES

Burrow-associated, selective dolomitization is observed in many Paleozoic limestones. The fabric is commonly characterized by distinct textural heterogeneity. Physical parameters such as permeability, porosity, tortuosity, and dispersivity are therefore difficult to assess. This study uses laboratory flow experiments bolstered with MRI and numerical modeling to compare the permeability fabrics and relative dispersivities of 3 different types of geological media: homogeneous sandstone, fractured limestone and burrowed dolomitic limestone. The results show that the flow paths present in burrow-associated dolomite are tortuous, and that the interaction between the flow paths and the matrix is extensive. Similar rocks therefore act as dual permeability systems in the subsurface and are conceptually similar to fractured media. This is pertinent to the problem of contaminant transport and storage or sequesterization. Also, resource extraction from such deposits will be strongly influenced by burrow-related heterogeneity; the influence of bioturbation should be carefully considered before extraction or recovery schemes are implemented.