Simplified Flow Assurance Review for Offshore Pipelines in Operation Stage

Improper fluid flow and unexpected composition could lead to integrity and operational issues in subsea pipelines, e.g., liquid hold-up in a gas pipeline promotes microbial-induced corrosion (MIC) and wax an oil pipeline causing back pressure or even plugging. Flow assurance review is carried out to address and resolve issues commonly assisted by software. In an operating pipeline, the abundance of operating and maintenance data allows flow assurance to be carried out in a simplified manner. This paper introduces the application of simplified and comprehensive flow assurance reviews for operating pipelines. The methodology uses 20 parameters as the basis for the flow assurance review. These parameters are the brainstorming result on the causal factors contributing to pipeline issues. The parameters are classified into 2 categories normal operating issue, and pigging operating issue. The ideal range for the parameters is defined through literature review. Some of the ideal condition definitions require technical calculation. The actual operating conditions and maintenance data are compared with this ideal operating range and assign the status whether it is acceptable or not. Mitigation measures can be assigned to improve the pipeline operating condition. One of the pipelines that have been reviewed is a 14″ subsea pipeline, spanning 30 km transporting crude oil and water mixture with 97% water cut. The liquid holdup issue is not applicable, as it is a crude oil pipeline. Key parameters for normal operation are deposits, sand, wax, high pour point, high viscosity, pipeline integrity status, leak history, maximum allowable operating pressure, flow patterns, Slugging potential, and near-future developments. The results are pipeline flow rate of 27,000 barrel fluid per day (BFPD) is below the ideal range of 43,000–72,000 BFPD which increases the risk of wax deposition, while the current oil-water flow pattern suggests potential microbial growth in the water phase, leading to (MIC). This concern is already mitigated using wax inhibitor and biocide injection. Additional parameters for pigging operation are pigging pressure, potential back pressure, subsea tie-in, liquid handling, low velocity, and regular pigging. However, no pigging issue is found. In conclusion, this 14″ pipeline has concerns in MIC, and wax deposit, but has been successfully mitigated with chemical injection, and regular pigging. This flow assurance methodology has been successfully applied to 25 main pipelines in PHE ONWJ. It provides a clear reference to determine the status of each parameter to be used as guidance for operation and setting the focus of maintenance activities.