Separators have a proven track record and are widely used in well testing operations. However, their range of applications is relatively narrow and they can encounter limitations with fluids for which separation is an issue. For example, in wet gas wells, when the liquid volume is small compared to the gas, or the gas and liquid are foaming, it is difficult to separate properly the phases, especially at high flow rates where the retention time in the separator vessel may be too short. Inefficient separation results in wrong measurements, which can not only have significant consequences for the assessment of commerciality of a new field, but also have a negative environmental impact if the burning process is also adversely affected, resulting, for example, in production of black smoke or imperfect burning leading to hydrocarbon discharge in the environment.This paper describes a well test in a deepwater well offshore Brazil. To be able to accommodate different production scenarios, two separators and a multiphase meter were used to measure the flow rates. During the test, the comparison of the flow rates from the multiphase flow meter and those reported by the separator made possible the identification of some carryover in the separator at high choke setting. When the choke size was increased, the separator gas rate increased while the liquid rate dropped at the separator, resulting in a very low condensate to gas ratio (CGR). The multiphase meter on the other hand, reported a constant CGR. At the end of the test, the same choke setting was used for a short period of time to confirm the behavior. The same observations could be made on the rates and a small amount of liquid could be seen in the gas flare. The final proof came from the analysis of the downhole samples which confirmed the CGR measured with the multiphase meter.The consistent results from the multiphase meter make it ideal to validate the flow rate measurements from the reservoir and improve the burning efficiency reducing the HSE risks associated with well test operations.

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.