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Summary This paper presents general guidelines to determine the feasibility of offshore petroleum projects in terms of field appraisal, subsurface development planning, and facilities options. It also illustrates the multidisciplinary nature of various tasks and includes examples for illustration. The emphasis is on oil fields, particularly marginal fields. Introduction The life of every oil and gas field begins with its discovery. Almost immediately, we want to know what its potential is (in terms of reserves and monetary value) and what the development options are in terms of subsurface plan and facilities. To answer these questions, a systematic approach is required to evaluate the discovery, to forecast the reservoir behavior under expected producing conditions, and to design the optimum facilities to meet forecasted production. This paper outlines the required process for studying the feasibility of developing offshore petroleum fields. A petroleum development project typically is divided into a number of major phases: exploration (including permit acquisition), field appraisal (primary and possibly secondary), feasibility study, project implementation (construction), and field production (operation and maintenance, management, and facilities upgrades, including secondary development phases). Different technical departments, each with specific aims, usually manage these phases (Fig. 1). While the development sequence is similar for all fields, there are notable differences between onshore and offshore projects. Most significantly, the engineering requirements and capital expenditure tend to be one or two orders of magnitude greater for offshore projects than onshore developments. Furthermore, offshore developments tend to have a much longer development schedule before they come on stream. Reserves and well productivity need to be substantially greater for offshore projects to cover the greater capital expenditure and operating cost, respectively.

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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.