The Mapping of Hydraulic Flow Zone Units and Characterisation of Australian Geological Depositional Environments

Abstract

The Carman-Kozeny formulation has been used as a basis to provide a new perspective of flow zone units (FZUs), by mapping similar rocks in terms of "Characteristic Envelopes", for different geological depositional environments. A large amount of data, covering several fields and different Australian basins, has been analysed. The methodology has been used for well-to-well correlation, reverse modelling for better identification of depositional trends, diagenetic affects and grain characteristics. It is also shown how photomicrographs, scanning electron micrographs (SEM), and log shapes can be incorporated in a detailed analysis. The method is ideal for validating plug samples used in special core analysis. It is shown how various data types, geological attributes and engineering parameters can be integrated. Results from such analysis can then be used in consistent model preparation and better quantification of petroleum recovery efficiency. Introduction Prediction of recovery efficiency and petroleum reservoir productivity is an important task for petroleum engineers, requiring detailed analysis of various reservoir properties and their interrelationship. To be successful, such reservoir description and analysis requires the integration of geological and engineering parameters. Core description and analysis gives information about pore structure and their characteristics, where the geometry is the end result of a long geological process involving deposition and diagenesis. Geoscientists have traditionally classified rocks according to porosity, grain size and distribution, grain sorting, mineralogy and petrophysical parameters, whereas reservoir engineers tend to emphasize the flow behaviour of rocks. The Carman-Kozeny (C-K) equation may be used to bridge this gap, considering variation in flow behaviour as a function of geological facies, the correlation parameter being the hydraulic radius. For a particular reservoir, various layers or facies may be grouped together to form Hydraulic Flow Zone Units (FZUs) or Hydraulic Units (HUs). This paper provides a new perspective of FZUs, by mapping regions or envelopes in the C-K space, for different geological depositional environments, analysing a large amount of data from a number of fields and covering several Australian basins. "Characteristic Envelopes" may be seen as a key feature in FZU modelling and they can be defined for very specific situations, with envelope boundaries covering a limited or entire depth range, including diagenetic variation. HU composition inside each envelope may thus reflect sorting, compaction, variation in grain characteristics, pore structure, and energy of deposition for the particular depositional environment under consideration. More generally, major depositional environments, for example channel environments, have been grouped for comparison, covering different parts of the C-K domain and demonstrating individual quality. The definition of each envelope has been derived by analysing similar depositional sequences for several fields, showing good agreement. To further verify and validate this approach, particularly for non-uniform intervals, use has also been made of log shapes and petrographic (also SEM) images and several of these are given to demonstrate the concepts. Finally, the outlined methodology may be used as a prediction tool for the case of a new geological province, where a particular geological environment has a certain chance of occurrence. In this case, a specific envelope may be considered, to predict possible formation characteristics, and related porosity, permeability and other property values. Study results may be used in prediction of recovery efficiency and reservoir/well productivity. The described methodology is also compared to other methodologies.

An Integrated Method for Modeling Fluid Saturation Profiles and Characterising Geological Environments Using a Modified FZI Approach: Australian Fields Case Study

“…Water saturation and permeability relationship can be approximated by straight lines on a log-log plot and can be represented by reduced major axis regression analysis as described by the equations: ….………….……….. (7) …………..……... (8) Equation 8 represents the empirical correlation used by Johnson, correlating capillary pressure and height above Free Water Level (FWL) with water saturation and core permeability. The constants A, B and C are derived from a series of capillary pressure plots.…”

“…While natural edge water has been effective, resulting in a high recovery factor for the generally good quality Zeepaard formation, a number of shale and low permeability barriers have resulted in uneven displacement. By contrast, the overlying Birdrong formation shows much more heterogeneity and facies variation, where average formation characteristics are relatively poor (8,25) .…”

“…Biniwale and Behrenbruch (8) report the comparison, and describe the analysis, of a large data set covering several Australian offshore basins. Therefore, GCEs may be seen as an aid in FZU modeling, by mapping regions or envelopes in the C-K space as a function of geological depositional environments.…”

“…Validation is the most important step before processing conventional core analysis data, in order to generate reliable results (24) . For every well in the Griffin area, the core analysis data validation step was carried out, and all data is categorised into various classes, as explained in previous publications (6,8) .…”

Tight-Gas-Sand Permeability Estimation From Nuclear-Magnetic-Resonance (NMR) Logs Based on the Hydraulic-Flow-Unit (HFU) Approach

“…Though varying among flow units, K T is constant within a given unit (Amaefule et al 1993;Biniwale and Behrenbruch 2004;Tiab and Donaldson 2012). If permeability is expressed in millidarcies, then the following formula can be obtained by dividing both sides of Eq.…”