Model Based Multiphase Metering and Production Allocation

Abstract

It is irrefutable that subsea operation is one of the most critical operations for Oil & Gas industry. To meet the growing demand of energy in the coming years, upstream oil and gas industry will develop even marginal fields which would tie-back to existing infrastructure and require more complex subsea network. Subsea production monitoring, back allocation and fiscal allocation are an essential part of any field development, as inaccurate tracking of production will negatively impact management and recovery from a reservoir. The need for allocation is due to the fact of unavailable quality measurements of oil, gas, condensate and water produced and injected at all nodes in a subsea distribution system. Contrary to easily monitored downstream onshore operation, subsea offshore operations cannot be easily monitored due to low reliability and high cost of subsea sensors. From industry experience, the currently available physical subsea flow meters, instrumentation and associated measurements are subject to deficiency, inconsistency and failure and results in low accuracy, and reliability. Due to these facts, there is a high demand for an alternative and accurate method of flow metering and condition monitoring for offshore operation and processing. In the past few years the use of Virtual Flow Metering systems as a backup or validation system for MPFMs or Wet Gas Meters has become more common. There are various options available depending on the vendor; statistical analysis of measurements (steady state solution), high fidelity online flow simulation models (dynamic solution) or a mix of both (nodal analysis). While VFM is maturing it has not been fully accepted as a viable alternative to good physical metering. Driving the dynamic model with real time measurements from the plant opens a new world of information for the operator in terms of model estimated data and enables him to take better decisions. This paper will present a case study whereby a virtual flow metering system has fully replaced a multiphase flow meter for flow metering and allocation purposes.