Cerro Fortunoso is one of the main fields of YPF Mendoza Business Unit. Itcurrently produces more than 7,500 bbl fluid/d from a hundred wells, most of them on sucker rod pumping. The field is located 80 miles from the nearest town, near the Andes Mountains and the environment is quite hostile windy, cold and with frequent snowfalls). Besides the field is very near a National Park.

Produced fluids are usually a problem. The oil is heavy (14.7 API) and viscous (more than 3,000 cp at ambient conditions). It tends to form emulsions with production water and behaves as a non newtonian fluid below 120 F.

The produced gas contains about 95 % of CO2 and has been vented up to now. In late 1996 a decision was made to reinject the produced gas in order to maintain pressure and prevent environmental damage.

A small technical team used a complex network simulator to model both the current field oil gathering and the future gas reinjection systems. Although the model fitted experimental data successfully and proved to be a powerful design tool some limitations to the simulator were found.

Due to the fact that commercial simulators do not take into account non-newtonian performance. a parallel study was conducted to analyze the effect of this behavior on predicted pressure drop. The team concluded that although deviation was found to be slight, non- newtonian effect should be properly included on design calculations.

As the gas will be reinjected at field conditions near its critical point. thermodynamics becomes extremely important. Five different thermodynamic software packages were run to predict gas phase envelope. Important differences between some models were detected.

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