In this project, SLB and IFE invented the next generation simulation technology to capture the hydrodynamic slug flow evolution in oil and gas pipelines The technology is implemented in the transient multiphase pipe flow simulator Olga. A novel modeling approach was taken by coupling a new slug evolution model with the conservation equations of slug flow. The invention is called the Slug Field model. The approach enables a significant reduction in computational cost compared to existing simulation technology for developing slug flow.
Slug flow is a very common flow regime in oil and gas production. In slug flow, liquid slugs and large gas pockets flow alternately. Due to the flow development, slugs in long pipes can grow much longer than those in short pipes. These long slugs may lead to issues such as overfilling of vessel and equipment damage. The issues are more critical for long pipelines and for pipelines linked to reservoirs in tail-end production, where slug flow is more likely to be present. Such pipelines are common on for instance the Norwegian Continental Shelf.
Slug development is very difficult to predict. The target is to predict 80% of measured slug length and frequency data within a factor of two. Additional heuristic models are furthermore needed on top of the conservation equations to close the problem. Advances were made to several such closure models as part of the project. They improve Olga’s performance in predicting relevant parameters.
The Slug Field model predicts slug frequency development within the accuracy target. The model generally over-predicts slug length by a slightly larger margin than this target. However, it is fair to note that this discrepancy means that the model tends to err on the conservative side. We have identified several avenues that can improve the slug length prediction and work continues.
Increased simulation execution speed and improved accuracy allows designers and operators to reach answers faster or to consider more design and operational options within a given time frame. The Slug Field model has demonstrated measurable speed-up over the fastest dynamic developing slug flow model available in the market. This speed-up is attributed to being able to take larger integration time steps and to more efficient numerical methods within each time step.
The initial accuracy and computational speed performance for the Slug Field model is very promising, and there are several avenues to continue improving it. With these improvements, the new Slug Field simulator technology contributes to safer, more environmentally sound, and more economic hydrocarbon production from remote and deep offshore reservoirs.
Actual outcomes and impacts:
- the Slug Field model was developed to a pre-commercial state.
- collaboration between IFE and SLB was strengthened as a result of the project, contributing to new project opportunities.
- the new simulation technology was reviewed with some of the key adopters of this technology during the project execution.
Potential outcomes and impacts:
- the unparalleled combination of functionality, accuracy, and speed of the Slug Field model will help maintain the leading position of SLB's principal multiphase flow simulator (Olga).
- the computational speed of the Slug Field model will allow developers and operators of oil and gas transport pipelines the ability to simulate additional design scenarios and operational conditions, leading to increased safety, optimized fluid transport, and cost efficient solutions.
In this project, SLB and IFE aim to invent the next generation flow model to simulate spatially developing slug flow in long pipelines, with unprecedented computational speed and accuracy. Dynamic multiphase flow conservation equations will be coupled with a novel slug evolution model to achieve this purpose.
In multiphase flow, gas and liquid can exist in various arrangements, or flow regimes. Slug flow is a very common flow regime in oil and gas production, especially in mature fields, as well as in CO2 transport systems. It features alternating liquid slugs and gas pockets. Slug flow tends to evolve dramatically throughout pipelines. For example, liquid slugs in long and large pipes can grow to far greater lengths than those in short pipes, leading to operational risks such as separator flooding. This behavior poses significant challenges for long pipeline operations which allow more slug development.
Slug developments are very difficult to predict. The most common slug flow modeling technique (unit cell model) assumes no spatial development and is mostly tuned to laboratory data from short pipes. Thus, extrapolating this model to field applications may introduce large uncertainty. There are more exhaustive models that can predict the slug flow development. However, they are computationally much slower than the unit cell model and often impractical for field applications.
The enhanced functionality, accuracy, and speed of the new model, called the Slug Field model, will make it suitable for long distance multiphase pipelines, such as many of the subsea lines on the Norwegian Continental Shelf. The model can help operators to reduce uncertainties, leading to more efficient, safe, and environmentally friendly operations. This model will be embedded into the OLGA multiphase simulator. Expertise and data from the OVIP JIP will be leveraged for technology qualification, assuring impactful innovation.
