We will never cease to be interested in how fluids flow in the subsurface.
The same reservoir and simulation technologies which have been developed and honed in the pursuit of oil and gas resources will continue to be required in the future, for a declining production of hydrocarbons, continuing interest in geothermal energy, increasing disposal of CO2 and storage of energy itself. This is in addition to the long-standing needs to manage water, understand earthquakes and predict hydrothermal systems and even volcanic plumbing. All of these require a technical understanding of fluid flow in the subsurface and draw on the skills discussed in this text, and more. Hence we have emphasised in this second edition the use of modelling technologies for carbon storage, an issue of immediate urgency to meet the challenge of managing climate change. Perilous as it is to predict the future, and at the risk of dating this book as soon as it is written, it is worth closing with comments on possible ways ahead. In this last chapter we summarise our current position, draw together some of the developments which may become standard tools in the future and close with a thought on the purpose of modelling itself: understanding.