Process simulation can be used for allocation when fluids from multiple fields are commingled in a terminal or processing facility. It allows a more accurate method of allocation that is suitable when the simpler approach of allocating exports pro rata according to input volumes is not sufficiently precise. 

Axis determines mass by component of metered streams, including the input streams from each field and the separated export streams, using sample compositions or chromatograph data and passes this data to a process simulation package. The process simulation uses an equation of state (EOS) to estimate the proportion of each component that will be in the liquid and vapour states in each separation vessel. By considering each field’s molecules separately, it calculates the contribution of each field to the separated export streams. The results of the simulation are passed back to Axis and used to determine final product allocations. 

Process Simulation Results

Axis can be integrated with external process simulation packages including HYSYS from AspenTech, and CHARM from Accord ESL. Axis also contains a built-in module that implements the Peng Robinson EOS, which allows simple process simulations to be carried out without the need for an external package.  

Integrating the process simulation with Axis means that each run of the calculation is audited, and also that inputs and results data are version controlled and subject to approval. The entire allocation process, including the interface to the external package is implemented using Axis modular calculations, which means the process can be easily adapted to match specific requirements. In addition, the automated scheduling and notification functionality of Axis can be used to implement a highly efficient process with minimal user interaction. 

Extract of Calculation Log

The benefits of using Axis for process simulation based allocation include:

•  A more accurate allocation method, which may be required when fluids from multiple fields are commingled in a single processing train; 
• An efficient process for gathering input data, executing the process simulation and finalising results;
   
• A flexible solution which can be adapted to support highly specific requirements; 
• Comprehensive functionality for auditing, version control and approval, which ensures each run of the process is fully documented, controlled and repeatable. 

Configuration of modular process step which calls process simulation package

You can read more on this topic here.