This paper presents test cases, methodologies, and test results from the extensive testing and qualification program that have been conducted with LedaFlow ® . This new transient multiphase flowline simulator has been built with focus on multiphase flow challenges in the oil and gas industry, and the resulting software includes both transient 1D and quasi 3D multiphase models. Development has been based both on existing and new large-scale experimental data from the SINTEF multiphase laboratory, taken over a nearly ten-year period. The focus of this paper is the transient 1D model.The transient three-phase 1D simulator offers new modeling capabilities as it is based on a model concept conserving mass for 9 fields (bubbles, droplets, and continuous fluids), using three momentum equations, and solving for the enthalpy and temperature of the three individual fluid zones. Improved closure relations have been built from a combination of new largescale multiphase flow experiments and sub-models which represents the distribution of droplets over the pipe cross section.

LedaFlow ® is a new transient multiphase flow simulator which includes 1D multi-fluid models consisting of mass, momentum and energy conservation equations for each field (continuous, bubble and droplet), as well as compositional tracking. In this paper, a new method called Slug Capturing is employed for slug flow, and the results analyzed and compared with the field data of two different fields. Additionally, for some cases, differences between the new simulator and another commercially available transient code results are compared and analyzed.The first case corresponds to the production of a TOTAL-operated field in the UK. Produced fluids from the wells are transported through a 21 km long, 16-inch multiphase flowline from the well platforms to the central receiving facilities. The multiphase line (gas/oil/water) must be operated in a narrow range of pressure and flow rate conditions in order to avoid severe slugging issues. Flow patterns are compared for various water cuts and superficial gas velocities. When severe slugging is observed, slug characteristics (frequency, length) are analyzed and compared to simulator predictions.The second case is from a CONOCOPHILLIPS-operated North Sea asset. The 3-phase, 18-inch ID oil flow line runs 3.7 km from a wellhead platform to a central processing platform. The line drops approximately 6 m over the last 3 km before flowing up a 130 m riser. The pipeline exhibits severe riser slugging which is not adequately modeled by conventional transient models, due to the complex interplay between hydrodynamic and riser slugging, as well as 3-phase effects. Slug frequencies and lengths are analyzed and compared to predictions.

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.