The difficulties associated with producing heavy oil have discouraged operators from developing the Atlanta field in the Santos basin offshore Brazil, despite more than 1.5 billion bbl of oil in place. The water depth in the area is more than 1,500 m, which makes operations even more challenging. Because Brazil has set aggressive production targets for the next decade, new interest has been given to the field, and a consortium of E&P operators began to reassess the field.
Well deliverability and test data are crucial to field development planning. Well test operations were planned with a multienergy gamma ray and venturi multiphase flow meter used as contingency. During the well test operations, the foaming propensity of the produced oil made it almost impossible to distinguish an interface between liquid and gas in the separator or tank, rendering the standard equipment useless. Only in the second test were some tank measurements available. The measurement principle used in this multiphase flow meter, however, is not sensitive to foam or emulsion because they respond to the atomic-level composition of the different components of the mixture independently of their arrangement, providing accurate flow rate measurements.
We detail the behavior of the multiphase flow meter during the well tests in the Atlanta field and the challenges caused by foaming oil. In the case of standard oils, the measurements are not sensitive to the viscosity value. However, in the case of high viscosities which lead to low Reynolds numbers, the viscosity value can drastically affect the results. In this case, some solvents were injected during the well test to reduce the liquid viscosity, and we present the consequences on the multiphase flow meter. We also compare the multiphase flow meter results to the gas/oil ratio measured in the laboratory on downhole samples from the same reservoir, to the water cut measured manually during the operations and to the tank measurements. Finally, we present some recommendations on the use of multiphase flow meters for heavy oil well tests.