Porosity-permeability relationship in dual-porosity carbonate analogs

We have investigated the effect of micrite content and macroporosity on the porosity-permeability relationship of dualporosity carbonates using analog samples created in the laboratory. Specifically, we control the micrite-to-coarse-grains ratio to produce samples in which the micrite content is the only parameter changing. We also introduce into the microstructures controlled volumes of an acetone-soluble solid material (camphor) at the expense of the micrite aggregates, which functions as macropores after being dissolved. With regard to the effect of micrite on the porosity-permeability relationship, our results indicated that adding micrite to samples exhibiting a grain-supported microstructure reduces porosity and permeability drastically. By increasing the micrite content up to approximately 30%, the sample becomes micrite supported, at which point adding more micrite increases the porosity but no longer affects the permeability significantly. Samples characterized by a high micrite content were found to have lower permeability at any given porosity. When macropores are introduced at the expense of micrite aggregates, permeability increases drastically with porosity. The rate of increase in permeability decreases, however, as themicrite content of the original microstructure increases. Additionally, at any given micrite content, the permeability increases as the percentage of macropores increases because such pores do contribute more significantly to fluid flow as compared with the micropores characterizing micrite aggregates. We used the varying micrite-to-coarse-grains ratio and its effect on the porosity-permeability relationship to inform the Kozeny-Carman relation for a pack of spheres. Our analysis determined that micrite affects the porosity- permeability relationship of carbonates by reducing the effective particle size and increasing the percolation porosity. Additionally, incorporating the content of micrite and macropores into the analysis of the porosity- permeability relationship increased the coefficient of determination (R2) from 0.24 to 0.78. We concluded that knowledge of micrite content and macroporosity is of paramount importance to interpret andmodel porosity- permeability relationships in carbonates.