Determination of Reservoir Permeability Based on Irreducible Water Saturation and Porosity from Log Data and FZI (Flow Zone Indicator) from Core Data

Abstract

Abstract The Flow Zone Indicator (FZI) core analysis method is an accurate approach for defining different Hydraulic Units (HUs) in a well with core data, and finding accurate k-f relations for each HU according to k = Cn fxn. Determining HUs in un-cored wells from logs or geological information is the main challenge for the FZI method. Several methods have been proposed for finding HUs in un-cored wells. In many approaches, HUs are correlated with log attributes in cored wells, and this relationship is applied to un-cored wells. However, since a persistent relationship between log attributes and FZI does not exist in all litho-facies, this does not always give reliable results. Based on a study of core and log data from several carbonate reservoirs, a practical, straightforward technique designated as the FZI-SWPHI (Flow Zone Indicator - Irreducible Water Saturation and Porosity) method is proposed. A theoretically sound relationship between FZI and Swir fe exists for a sedimentary environment. To find this relationship, FZI values from cores of the well are statistically related to the irreducible water saturation and porosity values from log data. The resulting equation, similar to the Wyllie and Rose, Tixier, Timur, and Coates equations, relates permeability directly to effective porosity and irreducible water saturation. Unlike these general equations, however, this new equation is specific to the reservoir under investigation because constants are defined for the reservoir. The derived equation can be directly applied to wells or reservoir model grid blocks, where water saturation and porosity are known. This method is more straightforward to use and generates more precise permeability estimates with higher vertical resolution. Several examples demonstrate the accuracy and practical applications of this technique. Introduction The Flow Zone Indicator (FZI) method for classifying core data into Hydraulic Units (HUs) with specific FZI was introduced by Amaefule et al. (1993) and is one of the best techniques for reservoir description. This method provides accurate correlations between permeability and porosity when FZI of the reservoir rock is known. FZI is determined from core data in the cored wells and it is often applied to wells without cores through correlations with log attributes. However, existing correlation methods do not always generate accurate permeability values for wells without core data.