Hydraulic flow zone unit characterisation and mapping for Australian geological depositional environments

Abstract

Prediction of reservoir productivity and petroleum recovery efficiency requires detailed analysis of various reservoir properties and their interrelationship. Among fundamental data used in such analysis, core data occupies a significant place in characterizing reservoirs. Core data is used in laboratory measurements to obtain basic and special formation parameters and plays a vital role in terms of understanding geological depositional environments and subsequent alteration (diagenesis). Geoscientists have traditionally classified rocks according to porosity, grain parameters (size, sorting and distribution) whereas reservoir engineers tend to emphasize the dynamic behaviour of multiphase flow in rock formations (relative permeability and capillary pressure). To bridge such differing views, the Carman-Kozeny (C-K) equation based Hydraulic Flow Zone Unit (HU or FZIJ) methodology, which considers variation in flow behaviour properties as a function of geological facies, has been found ideal in characterizing very diverse Australian reservoirs. Compared to previous studies, which tended to classify formations firstly by rock parameters, this research work shows the advantages of classifying formations firstly according to geological deposition and secondly by rock parameters. For this purpose, the concept of 'Global Characteristic Envelopes' (GCEs) has been introduced which groups data by specific geological environments. Several such envelopes can be created for different fields, where the internal structure of each envelope is a function of rock parameters, influenced by variation in deposition and subsequent diagenetic effects, such as compaction, cementation and mineralization (e.g. formation of clays). As a specific application that uses the above methodology, laboratory derived capillary pressure data, for a number of Australian offshore fields, has been reviewed for the purpose of establishing water saturation-height relationships as a function of rock type, forming part of a comprehensive petrophysical analysis. A modified 'FZI-λ' method, capable of giving improved estimates of reservoir fluid distributions, has been proposed. The new methodology is particularly well suited for interpolating among different lithologies and diverse rock types as evident from comparison with other methods reported in the literature. In conclusion, this work demonstrates the multidisciplinary approach to reservoir characterisation, a requirement for a more comprehensive understanding of reservoirs. This systematic approach, utilizing FZIJs, has resulted in an overall improved methodology that is able to integrate geological, petrophysical and engineering aspects.