Water injection is an essential part of many modern oilfield development plans. The high costs and often tight economic margins associated with offshore developments require that the chosen waterflood design not only provides an optimum sweep efficiency and reservoir pressure support, to maximise the oil production revenue, but also carries an acceptable level of risk in terms of the project costs and technical uncertainties. The objective of this paper is to show how an optimisation process can be used to maximise the value of the injection water. This paper describes a holistic approach for an economic evaluation of the water injection process, integrating the key technical and economical elements.

A six–stage process to evaluate the "Value of Injection Water" is presented. For illustrative purposes, this process is applied to show how a holistic technical–economic evaluation of the water injection operational option for a North Sea field case can be carried out. The study concludes that the injection of a mixture of produced and aquifer water is the preferred source for injection water when applying a matrix injection process into a high quality formation. However, this introduction of the produced water increases significantly the uncertainty in the eventual economic outcome.

This process for developing an integrated technical and economic comparison of the options available is a tool by which the operator can decide on a decision on future water injection strategy. It can also assign a quantitative value to each volume of injection water - providing a quantitative framework for making day-to-day operational decisions..

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