Pipelines transporting multiphase products (i.e. mixtures of liquids and gas) are common in the upstream oil and gas industry. However, there are numerous flow assurance challenges to the operation of multiphase pipelines, particularly in hilly terrain. For multi-phase pipelines the flow pattern, pressure drop, and associated liquid hold-up within the pipeline is highly dependent on the elevation profile, the gas to liquid ratio, the fluid properties, and the rate of flow. It is desirable to consider how multiphase pipelines can be routed to minimize these operational challenges.
Variation from project to project and the complex nature of multi-phase flow can create challenges to developing common rules of thumb to be used in pipeline routing. There are commercially available software programs that model steady-state and transient flow conditions for multiphase flow, but these programs accept only one set of inputs for a particular routing scenario and the process of finding an optimal pipeline profile through the landscape can become tedious. Consequently, in the author’s experience, it is still common practice to develop pipeline routes for multiphase pipelines using traditional pipeline routing methods that are biased towards pipeline construction rather than operational factors. However, operational cost-savings can be realized through the application of multi-phase flow optimization in early pipeline routing and facility siting.
This paper proposes an alternate method to routing multiphase pipelines using Geographic Information Systems (GIS) based design tools to simultaneously evaluate route options at a landscape level and model the hydraulic behavior of the multiphase flow to identify optimal pipeline routes that minimize the challenges related to multiphase flow. This method allows for proper consideration of the potential construction and operational challenges of multiphase pipelines to be integrated into the pipeline design and balance against various other factors which includes land use, construction methods, terrain challenges and environmental or social impacts. Considering these challenges early in the conceptual design process will help operators realize capital and operational cost savings while allowing for safer and more reliable pipeline operations.
The method uses a multi-criteria approach coupled with a hydraulic model with the ability to balance the influence each factor has on the calculated “least cost path” to route options that improve the flow assurance aspects by strategically navigating the terrain while respecting the host of other factors that contribute or influence the final chosen pipeline route. Using this method, operators can be assured that where opportunities exist to improve the hydraulic performance of a pipeline through route selection, these opportunities will be presented as outputs of the model and expert judgment can be used to determine the final pipeline alignment.