This paper investigates the suitability of a virtual flow metering system for a subsea gas development offshore Tanzania. The field development is characterized by water depths of down to 2600 meters and tie-back distances to shore of around 100 km. The reservoir fluid is dry gas. The preliminary plan for the field is to install 20–30 subsea wellheads, and metering of the flow from each well is required for reservoir drainage planning. In addition, flow rate metering is required in order to predict the flowing conditions inside the 100 km long flowline. For this purpose, metering accuracy of within +/- 5% from the actually produced gas rate is considered sufficient.
Based on simulations of the planned production profile, well trajectories and fluid characterization the expected performance of virtual flow metering has been evaluated for five different type of wells with similar reservoir fluid. Virtual flow metering is a low-cost alternative compared to installation of multiphase meters on each well.
Virtual flow metering (VFM), sometimes referred to as model based metering, has been in use in online metering systems for two decades, ref /1/, /2/, /3/. Virtual metering historically emerged due to the lack of cost efficient and reliable multiphase flow meters.
In recent years, the reliability of multiphase flow meters has increased significantly. In parallel, the possibility to access data from well instrumentation from any location inside an operator's network is making virtual flow metering more attractive. New data management strategies allow for remote operational support and production optimization on fields by dedicated experts at any global location. The choice between virtual flow metering and multiphase flow meters in this perspective becomes a cost – benefit choice dependent on the type of field, accuracy requirements and the acceptable uncertainty for the operation.