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1 Luca Baratelli 863472 MSc. EXAMINATION 2015 Exercise 1: material balance for a gas field (i) GAS CONDENSATE FIELD: it is a field that produces oil inside the reservoir as the pressure drops. Hence, the difference with respect to a wet gas field, where oil is produced only at the surface, is that the fluid in the reservoir actually expands with a phase transition. It is possible to plot a phase diagram for a hydrocarbon mixture in the reservoir for different pressures and temperatures in order to better understand the behaviour of a gas condensate field during production. As we can see, considering that temperature in the reservoir remains constant during production, the process that takes place in the reservoir can be represented by a vertical line starting from the point (above the dome) of the initial conditions of the field and reaching surface conditions point. A gas condensate field is characterized by an expansion line which intercept the dome to the right of the critical point and then enters the 2 phase region. The second phase to appear is denser than the majority phase and so it’s defined as oil. The point where the first drop of oil is formed is called “dew point”. 2 Condensate liquid saturation can build up near a well ultimately restricting the flow of gas: the near-well choking can reduce the productivity of a well by a factor of two or more. DRY GAS: it is a particular physical state of fluid that can be produced at the surface, characterized by the complete absence of liquid phase. In the p-T phase behaviour diagram, a dry gas is a point located outside the dome on the right hand side of the critical point. There are only two types of field that can produce a dry gas at the surface: obviously a dry gas field, but also the particular case of a gas…