Statistical Evaluation of Reservoir Rock Type in a Carbonate Reservoir

Abstract

Abstract Reservoir rock type determination is one of the main parameters for simulation and prediction of the hydrocarbon reservoir behavior. Hence, it is of great importance to use a method which is capable of determining the rock type accurately. In this study, some of the most useful methods such as capillary pressure, Leverett dimensionless J-function, Winland R35 method, Flow Zone Indicator (FZI) and Discrete Rock Type (DRT) were applied to samples from a carbonate reservoir to determine the various reservoir rock types. The sample set consisted of 265 routine core data and 18 data sets of capillary pressure versus initial water saturation; all were analyzed using the aforementioned determination methods. Results of this study showed that both capillary pressure and Winland R35 were not accurate enough to determine rock types for this carbonate reservoir, mainly because of the high heterogeneity in the reservoir rock properties. For the same reason, the Leverett J-function method was found to be problematic in normalizing all the capillary data into one unique curve. However, FZI and DRT methods successfully classified all data into four discrete rock types while satisfying the relationships between permeability and porosity for each of them. The calculated permeability data for each rock type classified by FZI and DRT methods were in good agreement with core permeability data.