Estimating the recovery factor

Section 8.2 indicated the ranges of recovery factors which can be anticipated for different drive mechanisms, but these were too broad to use when trying to establish a range of recovery factors for a specifio field. The main techniques for estimating the recovery factor are 

These are listed in order of increasing complexity, reliability, data input requirements and effort required. 

Analytical models using classical reservoir engineering techniques such as material balance, aquifer modelling and displacement calculations can be used in combination with field and laboratory data to estimate recovery factors for specific situations. These methods are most applicable when there is limited data, time and resources, and would be sufficient for most exploration and early appraisal decisions. However, when the development planning stage is reached, it is becoming common practice to build a reservoir simulation model, which allows more sensitivities to be considered in a shorter time frame. The typical sorts of questions addressed by reservoir simulations are listed in Section 8.5. 

When estimating the recovery factor, it is important to remember that a range of estimates should be provided as input to the calculation of ultimate recovery, to reflect the uncertainty in the value. 

The production profile for oil or gas is the only source ofrevenueior most projects, and making a production forecast is of key importance for the economic analysis of a proposal (e.g. field development plan, incremental project). Typical shapes of production profile for the main drive mechanisms were discussed in Section 8.2, but this section will provide some guidelines on how to derive the rate of build-up, the magnitude and duration of the plateau, the rate of decline, and the abandonment rate. 

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This section will consider the behaviour of the reservoir fluids in the bulk of the reservoir, away from the wells, to describe what controls the displacement of fluids towards the wells. Understanding this behaviour is important when estimating the recovery factor for hydrocarbons, and the production forecast for both hydrocarbons and water. In Section 9.0, the behaviour of fluid flow at the wellbore will be considered this will influence the number of wells required for development, and the positioning of the wells. 

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