Making sense of carbonate pore systems

The most widely used pore-type classification systems for carbonate reservoirs are limited by the fact that the relation between porosity and permeability is poorly defined. Existing classification schemes for porosity-permeability data do not, in many cases, optimally integrate sedimentology, diagenesis, and flow-related properties. In many carbonate reservoirs, it is therefore difficult to generate predictive models for reservoir-quality distribution, resulting in significant uncertainty in hydrocarbon reserve calculations. Based on empirical data, mostly from Europe and the Middle East, a new pore-type classification system has been developed. The new system not only uses elements from existing pore-type classification systems, but also introduces many new elements. The new pore-type system includes 20 pore-type classes that show a predictable relation between porosity and permeability. It combines sedimentologic and diagenetic features with flow-related properties, and reservoir-critical parameters can thus be predicted using sedimentologic and diagenetic models. A practical example based on data from a Devonian hydrocarbon field shows that pore-type variations may account for several-hundred-percent differences in calculated hydrocarbon reserves.