Flow Zone Unit Analysis for Bayu-Undan Field
Morsidi, Mohamad Asdee
Engineering Honours Degree, 2006
University of Adelaide
A study of flow zone unit of Bayu-Undan Field was conducted over the course of March – October 2006. The objective of this study is to perform Flow Zone Unit (FZU) analysis on the Bayu-Undan Field, one of the largest gas fields in Australia in interest to identify hydraulic groups in each Bayu-Undan depositional environments. These hydraulic groups can be very helpful in categorizing lithofacies and sub-intervals within a depositional environment or a reservoir unit. A hydraulic unit represents a homogeneous sub-unit that share similarity characteristics in term of porosity, grain size and distribution, grain sorting and mineralogy and its behaviour of flow. By identifying the hydraulic units and be aware of their locality, a more cautious and accurate upscaled reservoir simulation could be pursued to yield an enhanced, better reservoir models. It is also important to keep in mind that a hydraulic unit could also hint the reservoir quality.
This FZU analysis is done by applying Carman-Kozeny formulation. The Carman-Kozeny equation is used to link the disciplines of geology and engineering by integrating hydraulic units as a correlation device which controls the flow behaviour however at the same time honours geological features of the rocks in term of facies, depositional environment and diagenesis. Hence, another objective of this project is to integrate the geological quality of the reservoir rocks with the technical dynamic flow characteristics. The FZU analysis methodology in this project considers depositional environment as the highest level of categorization and integrates rock type as a secondary categorization.
The FZU analysis is performed in two major steps. First approach is to analyse a number of wells individually. Each well is analysed by its reservoir units and hydraulic groups are then identified in each of these depositional environments. By doing so, a very basic overview can be obtained concerning the levels of heterogeneity or homogeneity of the layers that are contained in a particular depositional environment. The next step is to correlate the findings of each well for each reservoir units. By doing this, the reservoir quality distributions could be made for each depositional environment based on the locations of the wells.
This HU group could be identified by plotting a log-log graph of Reservoir Quality Index and Porosity Group. A proposed Carman-Kozeny 45°-slope straight line would be the indicator of reservoir quality of the HU. A result of a cluster of data points that sits on the Carman-Kozeny line reflects a HU group and they have similar dynamic flow behaviour.
The Bayu-Undan FZU study included 6 wells namely Bayu-2, Bayu-3, Bayu-4, Undan-1, Undan-2 and Undan-3 available for evaluation. The potential hydrocarbon-bearing reservoir section at Bayu-Undan spans over several thousands true vertical feet with 7 genetic units subdivided further into 17 sub units. The reservoir is made up of both fluvial and marine sedimentary sequences. A further investigation needs to be done in order to predict the fluid flow in the reservoir considering Bayu-Undan Field has known to have a high degree of reservoir heterogeneity.
Although FZU analyses have been done on the 6 wells available for evaluation, thorough and detailed results are only presented for Bayu-2, Bayu-4 and Undan-1 in the Result and Discussion section. This is due to the constraint of the length of the report.