New explicit solver for pipeline networks

The development of LedaFlow is linked to the needs of the oil and gas industry and it is validated against field data. A central aspect of the project is to gather industrial users of LedaFlow to identify relevant areas of further development, to collect relevant field data for benchmarking and use industry experts as advisors. Future oil and gas production assets will look more complex with larger networks as existing facilities will be connected to new deeper and farther fields using longer tiebacks. New approach using tiebacks can help reduce CO2 emissions via fewer new topside e.g. steel structures. Tiebacks and riser design challenges is where we would like to deploy predictive capabilities of Ledaflow. During production LedaFlow is used to keep the fields outside slugging conditions, or to handle slugging. Slug Capturing is a step change in the simulation of transient multiphase flows, and allows predicting the transient development of the flow, in particular slugs. In Slug Capturing, the slugs are resolved on the grid, hence slugs are an alternation of stratified and bubbly flow sections. This requires a much more accurate numerical solver than with the average correlations. An explicit solver has been chosen for its greatly reduced numerical diffusion, as well as its ability for parallelization to utilize cloud servers. We have already released this technology for single pipelines, and we will now extend and demonstrate the technology for pipeline networks. To consider the full range of possible fluid chemistry, the energy balance and composition tracking functionality need to be reimplemented in the new solver. Finally, all the devices that can be present on or in a pipe need to be made compatible. Previous attempts at Slug Capturing with the existing fully implicit solver showed that the meshing required to reduce numerical diffusion to an acceptable level was not realistically feasible. This would have resulted in simulations taking months. With the new, more explicit solver, we are able to use acceptable meshes (with a cell length in the order of 5 to 10 times the pipe diameter), representing a reduction by up to 10 times in terms of number of cells, and hence up to 100 times in terms of computation time. In the project, we have been able to add the support for pipeline networks, that is, implement junctions which keep the new solver’s performance while handling the complex flow phenomena involved in slug flow (e.g. intermittent, countercurrent flow of the different phases). In addition, the tracking functionality for production chemicals is ready to be released. Detailed profiling of Slug Capturing cases show that we have been able to attain a very good parallelisation of the most intensive parts of the algorithm (mainly the source terms), and that the non-parallelizable part (inversion of the global pressure matrix) is isolated in a relatively less intensive part. When the required functionalities are supported, simulation data will be verified against the field data collected from the project's industrial partners and used to identify gaps where the model is not performing well enough, and to guide further enhancements. The capability to model pipe networks was commercially released in April 2023 in LedaFlow 2.9, and energy equations and custom fluids tracking are ready for commercial release in 2025. Significant improvements on parallelization were released in LedaFlow 2.10 in April 2024 and additional improvements will be released in 2025. Composition tracking of chemicals has not yet been applied. However, testing using Slug Capturing and manual tuning has shown that the presence of chemicals – generally used to mitigate corrosion or hydrate formation – can significantly influence slugging behavior, making this functionality very useful in industrial applications. Following the commercial release of the network solver, an industrial partner ran a Slug Capturing case study which proved that the overall improvement to LedaFlow is significant for its users and that the new solver is meeting industrial needs in terms of accuracy, robustness and speed.

The project has made it possible to further develop a new explicit solver to enhance simulations using the Slug Capturing model and to allow for parallelization of the code. The Slug Capturing model is a predictive method that captures the initiation and growth of small-scale instabilities at the interface between liquid and gas. The previous solver, which was mainly implicit, required a very fine static grid to solve the equations, which was computationally costly. The explicit solver leads to improvements in terms of accuracy and robustness which have been verified, for the duration of the project, by the industry partners before it was commercially released in LedaFlow. Parallelization of the code has improved the speed of calculations with a factor between 2 and 4, depending on the degree of parallelization chosen. It is now possible to benefit from 8 or more CPU cores, instead of the 4 cores previously recommended. The new solver is being gradually released commercially. The capability to model pipe networks was released in April 2023 in LedaFlow 2.9, while the ability to solve energy equations and custom fluids tracking are ready for commercial release in 2025. Significant improvements on parallelization were released in LedaFlow 2.10 in April 2024. The Slug Capturing functionality is crucial for new O&G field developments. It is used to assess the flow stability of different design concepts enabling the development of low-carbon and cost-efficient designs (e.g. optimal tie-back solutions that minimize steel usage). It is also beneficial during operations. As the reservoir pressure decreases during the life of the field, flow rates decrease, and flow becomes unstable. Slug Capturing simulations can help identify methods to mitigate unstable flows, potentially reducing the need for flaring which may arise if slugs arrive at a receiving facility, which are larger than the capacity that the facility can handle. By providing more accurate results faster, the new solver supports the O&G industry in its decision making, as a better understanding of the flow behavior during production operations is essential for minimizing environmental impact, managing risks and selecting safe and cost-efficient technological designs. Following the commercial release of the network solver, an industrial partner ran a Slug Capturing case study which proved that the overall improvement to LedaFlow is significant for its users and that the new solver is meeting industrial needs in terms of accuracy, robustness and speed. The new explicit solver caters for more accurate results and faster decision making. Composition tracking of chemicals has not yet been applied. However, testing using Slug Capturing and manual tuning has showed that the presence of chemicals – generally used to mitigate corrosion or hydrate formation – can influence the slugging behaviour significantly, and hence this functionality will become very useful in industrial applications.

LedaFlow has already proven and demonstrated a new explicit solver for single pipe Slug Capturing 2 that improved speed and accuracy for multiphase flow simulations. However, for complex fields the new Slug Capturing 2 technology still falls short since we fail to match new field data received via an ongoing LedaFlow Demonstration JIP (LIFT III). One such failed application is calculation of fatigue contribution in deep-water risers due to slugging initiated in connected tiebacks. This has far-reaching consequences from oil leaks if not estimated properly and hence under-designed. We also see that the current limitation to single pipe falls short on comparison vs. field data since we are missing capability of addressing the entire system e.g. network of pipelines and wells. LedaFlow Technologies DA has financed a research activity to develop this functionality through Explicit Solver Project and we would like to combine the results of this project with the ongoing Demonstration JIP by expanding the scope to demonstrate new explicit solver for network of pipelines. This requires new type of numerical integration for our explicit solver that needs to be demonstrated by matching the new field data more accurately. This new explicit network solver for pipe-networks is unique amongst multiphase flow simulators in the market and can be used in several future applications as well. For example, it can be used in CCUS applications that may require the increased accuracy that is offered by explicit solvers compared to more common implicit solvers. We also intend to use the new capability as infrastructure to deploy results from another ongoing innovation project Chemflow IPN (Project Number 329658). Early indications are that results from Chemflow IPN together with explicit network solver could potentially help cover the gaps we mention above vs. field data. Investigation and demonstration of such improvement is an urgent need but is not in scope of any ongoing projects.