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 carry-over 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.