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Deepwater gas field development with long tieback poses flow assurance challenges due to the liquid dropout, causing high backpressure and extensive compression and pumping energy requirements, leading to high OPEX, CAPEX, and CO2 emission. A novel Pseudo Dry Gas (PDG) concept has been developed as an inline gas-liquid separator (liquid removal system) which separates liquids into a dedicated liquid line from the gas to induce hydraulically ‘dry gas’ behavior within a wet gas pipeline over the operating envelope. The work aims to demonstrate the techno-economic benefits of a field development study undertaken jointly between oil and gas operators and service companies; with particular focus on the integrated life cycle CO2 assessment showing the ‘energy intensity’ of the technology in comparison with various well-established concepts. A widely accepted industry design software has been used to generate data for a range of various development concepts based on deepwater (2,000m of water depth) gas field data with 140km tieback. An advanced flow assurance design technique is developed to evaluate the number of PDG units required along the pipeline and to select the most optimum section to locate the PDG unit(s) for effective separation. The performance of the PDG units are predicted by linking the field data with PDG test data. The test has been conducted on a 6″ flow loop with 6″ PDG prototype and pilot scale unit, covering the operational pressure, temperature and anticipated fluid properties. The CO2 emission assessment is undertaken in accordance with ISO 14044, linking the reservoir production to the power demand of pumps and compressors when they are required to support production. The power demand is then converted into the equivalent CO2 emission based on the generation type. Finally, the carbon intensity (CO2 tonnes/ MMScf) for various development concepts is calculated by combining the accumulative production and total CO2 emissions over the field life. The results show a significant reduction in carbon intensity for PDG concept, in excess of 75% when compared to other potential concepts. Moreover, this gain in carbon intensity reduction is accompanied by other economic benefits i.e., without loss of recoverable reserves, enhanced ability to mitigate production risks associated with long-distance subsea gas tiebacks leading to lower life cycle cost and higher Net Present Value (NPV) as well as Internal Rate of Return (IRR). These observations are the net result of changing the internal resistance curve of the gas tieback from a quadradic function to a linear function, enabling the more efficient use of downhole pressure to reduce the overall carbon intensity (CO2 tonnes/ MMScf) of upstream gas production.
Deepwater gas field development with long tieback poses flow assurance challenges due to the liquid dropout, causing high backpressure and extensive compression and pumping energy requirements, leading to high OPEX, CAPEX, and CO2 emission. A novel Pseudo Dry Gas (PDG) concept has been developed as an inline gas-liquid separator (liquid removal system) which separates liquids into a dedicated liquid line from the gas to induce hydraulically ‘dry gas’ behavior within a wet gas pipeline over the operating envelope. The work aims to demonstrate the techno-economic benefits of a field development study undertaken jointly between oil and gas operators and service companies; with particular focus on the integrated life cycle CO2 assessment showing the ‘energy intensity’ of the technology in comparison with various well-established concepts. A widely accepted industry design software has been used to generate data for a range of various development concepts based on deepwater (2,000m of water depth) gas field data with 140km tieback. An advanced flow assurance design technique is developed to evaluate the number of PDG units required along the pipeline and to select the most optimum section to locate the PDG unit(s) for effective separation. The performance of the PDG units are predicted by linking the field data with PDG test data. The test has been conducted on a 6″ flow loop with 6″ PDG prototype and pilot scale unit, covering the operational pressure, temperature and anticipated fluid properties. The CO2 emission assessment is undertaken in accordance with ISO 14044, linking the reservoir production to the power demand of pumps and compressors when they are required to support production. The power demand is then converted into the equivalent CO2 emission based on the generation type. Finally, the carbon intensity (CO2 tonnes/ MMScf) for various development concepts is calculated by combining the accumulative production and total CO2 emissions over the field life. The results show a significant reduction in carbon intensity for PDG concept, in excess of 75% when compared to other potential concepts. Moreover, this gain in carbon intensity reduction is accompanied by other economic benefits i.e., without loss of recoverable reserves, enhanced ability to mitigate production risks associated with long-distance subsea gas tiebacks leading to lower life cycle cost and higher Net Present Value (NPV) as well as Internal Rate of Return (IRR). These observations are the net result of changing the internal resistance curve of the gas tieback from a quadradic function to a linear function, enabling the more efficient use of downhole pressure to reduce the overall carbon intensity (CO2 tonnes/ MMScf) of upstream gas production.
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.
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