Accurate multiphase flow predictions for long tiebacks and subsea developments

IPN ACCURATE: Accurate multiphase flow predictions for long tiebacks and subsea developments. To limit costs and environmental impact associated with new offshore oil/gas field developments, the gas, oil and water are transported as multiphase flow from the reservoir in one single pipe. The pipes can be laid all the way from the well-head to an onshore receiving facility or as a subsea tieback to the nearest production facility on a platform or a floater. This ultimately means that the flow must be transported together over large distances, in many cases more than 50-100 km and even further. Good design decisions must be made to avoid operational problems and accidents associated with long-distance multiphase flow transport, and a key prerequisite is access to accurate simulation tools. A major challenge the industry currently faces is related to "slugging" where the liquid flows as a series of liquid plugs, or slugs, separated by large gas bubbles. Slugging causes mass fluctuations and subsequent vibrations in the pipe, and possibly also separator flooding. Vibrations cause prolonged mechanical stresses in the pipe system that eventually can compromise the integrity of pipe joints. This can cause pollutive leakages of production fluids such as crude oil from offshore installations. Deep-water risers are particularly susceptible to mechanical failure caused by the slugging-induced fatigue, and designers of such systems depend on reliable tools for accurately predicting the lifetime of the riser components. Research in ACCURATE has improved the accuracy of the LedaFlow "Slug Capturing model", a model that targets prediction of slugging. The work has proved to be successful, yielding significant advances in the model's predictive capabilities, especially with respect to estimating slug length and frequency. Two oil companies are already using the latest R&D version of LedaFlow Slug Capturing in the design of deep-water risers, reflecting the high demand and importance of this research. The design work is specifically aimed at forecasting the slug-induced mechanical stresses on new deep-water pipeline-riser systems and requires reliable predictions to ensure the integrity of the installations. The new slug capturing model is planned to be commercially released in 2021. ACCURATE aims is to make LedaFlow Slug Capturing a world leading technology on slugging predictions, providing a tool that will help oil field operators to prevent oil spill accidents as well as other serious operational and safety issues at affordable development cost. In addition to the work on slugging predictions, there have been three modelling activities in the project: Wall-wetting in three-phase gas dominated flow: Using multi-phase data from experiments mainly performed at SINTEF's multiphase laboratory, a new model for predicting wall wetting in gas-dominated flow is developed. Wall wetting leads to an increase in pressure drop, because the liquid film covering the wall increases the flow resistance. The new model was released in the commercial LedaFlow code in 2019. It reduces the uncertainty in the pressure drop predictions for long gas pipes, thereby reducing the design margin on pipe size and other cost-driving investments. This is important for the development of long tiebacks associated with new gas fields. Oil-water interaction: A new model has been developed to predict the regime transition between separated oil-water to fully dispersed oil-water in three-phase flow. This is important for predicting the flow resistance in liquid dominated systems, which depends critically on the oil/water flow regime. It will be commercially released in LedaFlow in 2021. Another model for predicting the interfacial shear stress between oil and water was developed and included in the commercial LedaFlow release in 2020. The model significantly improves prediction of water accumulation, especially in oil/water systems with inclined pipes. Water accumulation can lead to severe corrosion problems that threaten the integrity of the installation, potentially leading to oil leakages. By enabling prediction of where and when water accumulation will occur, pipeline operators can make sound decisions related to possible mitigation strategies. Vertical three-phase flow: Measurements conducted by SINTEF indicate that the presence of oil/water droplets reduces the gas bubble capacity of the liquid mixture. This ultimately leads to lower concentrations of gas bubbles in three-phase flows compared to two-phase gas/liquid flows, and the reduction leads to an overall increase in pressure drop for three-phase flows. LedaFlow's gas entrainment model for near-vertical flows is improved to account for the presence of oil/water droplets and is planned to be commercially released in 2021. ACCURATE is owned by LedaFlow Technologies DA and is implemented in close collaboration with SINTEF and Kongsberg Digital.

The majority of future field developments on the Norwegian Continental Shelf will likely be in subsea tiebacks, due to lower costs and a reduced CO2 footprint. The innovation project ACCURATE has delivered three key achievements for more accurate simulations of transport of unprocessed well stream over large distances: The Slug Capturing 2 model for slug prediction, already in use by major operators for optimal design of deep-water risers, enabling cost reductions while maintaining operational safety. A new LedaFlow model reducing uncertainty in the pressure drop predictions for long pipes with gas-dominated flow, thereby reducing the design margins and energy use. Significant improvements in LedaFlow's ability to simulate oil water interaction, enabling accurate prediction of flow resistance in liquid dominated systems and water accumulation. Two models resulting from ACCURATE are released in the commercial "Ledaflow 1D Engineering" software.Three more will follow in 2021.

Long tiebacks will be a key technology for the resources to be developed in the future in the NCS as they can: (a) Make economically viable marginal or small oil and gas developments (b) Extend the life of existing production installations and infrastructures (c) Maintain production levels. The proposed project represents a step change in the design of safe and cost-efficient tiebacks and subsea systems through accurate prediction of multiphase flow systems in the transient simulator LedaFlow. In this project, new and improved predictive multiphase flow models will be developed and validated using unique three-phase flow experimental datasets. Most existing experimental datasets only cover two-phase gas-liquid flows, and have a fundamental lack of detailed measurements. Access to high-quality three-phase data with detailed measurements paves the way for more advanced models and subsequently more accurate and reliable predictions. At present, no commercial tool can provide the models planned to be developed in this project and it can be a substantial market differentiator for LedaFlow. The ACCURATE project is organized in 5 work packages (H1-H5): H1:New wall film model to improve pressure drop predictions at high USG and low USL H2: New models for oil-water dispersions and oil-water flow regimes in three-phase flows H3: New closure laws to improve the predictions in unsteady flows H4: Continuous closing of modelling gaps based on new acquired data H5:LedaFlow software releases and case models for demonstrating new functionality. The new models will be incorporated in the commercial releases, after thorough testing of the implementation. The rapid path from advanced multiphase modelling at the research forefront to commercial implementation to the benefit of operators and others using LedaFlow is a strong quality of the consortium and ensures value creation from scientific progress at an earliest possible time.