High Pressure Hydrocarbon Separation Performance for Variation in Operational Parameters – Pseudo Dry Gas Systems

Pseudo Dry Gas (PDG) technology is proposed as an alternative concept for transporting multiphase fluids (gas, condensate, and water) for long deep-water subsea tieback developments while delivering significant reductions in Scope 1 and 2 CO2 emissions by the mitigation of compression (Liebana, et al, 2021)). The basis of the PDG system is to remove the liquid from the main pipeline using piggable liquid removal unit(s). With the removal of the majority of liquid, the shape of the internal resistance curve of the tieback is changed from a quadratic function to a linear function over the operational envelope, allowing the pipeline to operate like a "pseudo" dry gas system. The original prototype of this design underwent low pressure flow loop testing (Thomas, et al 2021)). The current work involved the fabrication of a 180 bar rated PDG unit, a subsea magnetic drive pump and the supporting subsea control system for flow loop testing undertaken at TÜV SÜD National Engineering Laboratories (hereinafter NEL), UK. This development program is supported by operators in conjunction with the Net Zero Technology Center. The testing program is developed to encompass the expected operational envelope that the PDG units would see in service aligned to a broad range of asset-based study work and to consider critical non-dimensional flow assurance parameters to ensure scalability. The testing parameters considered are pressure (up to 125 bar), temperature (up to 40 C), and inclination (zero- and two-degrees). In addition, various liquids are considered e.g., two hydrocarbon fluids (representing oil and condensate), brine water, and hydrocarbon and brine water mixture. An extensive number of test points at different liquid and gas superficial velocities are included both with and without the PDG unit installed to allow for baseline comparisons, with entrainment samples being collected upstream and downstream of PDG unit aligned to the Tulsa University technique (Bhaskoro, et al 2024). This paper will focus on how varying certain parameters including superficial gas velocity, superficial liquid velocity, and pressure impacts the separation efficiency and liquid entrainment. Some examples of mapping actual study results onto the high-pressure testing results are included to allow a greater understanding of required versus actual performance. Results show comparable PDG separation performance at high pressure for all cases indicating negligible impact of higher pressures in relation to required performance as linked to the actual study cases.