Floating LNG (FLNG) plant is one of the options to monetize remote and marginal gas field. A robust upstream facility design requirement should include flow a assurance assessment in order to achieve stable operations and protect the integrity of the LNG facility. In this case study for a specific FLNG project, flow assurance issues associated with the FLNG receiving dehydrated gas from a processing platform are explained. The aspects include hydrate management, flow stability and location of the pressure control system. For FLNG, the producing wells normally produced as wet gas to the processing facility via a relatively short pipeline.

A LNG plant requires constant pressure, flowrates and compositions to operate in a stable manner because most equipment such as refrigerant loops, compressor and distillation columns are sensitive to changes in inlet conditions. Consequently the location of the pressure control valve (PCV) and the impact of transient operations on the dehydrated gas were studies including the effect of the gas dehydration unit offline. For the pipeline, the location of the PCV at the upstream facility and FLNG facility affect the pipeline survival time in term of seconds versus minutes.

During normal operating condition, the dehydrated gas poses no major threat to operations as the inlet facility had been designed for, except for low temperature during the initial start-up and the gas turndown requirement during pigging operation. Sensitivity cases indicated that when the dehydration unit is offline, hydrate inhibition is required for shutdown, restart and depressurisation operations. The hydrate inhibition requirement depended on the mode of inhibition required i.e. continuous vs. intermittent or the availability of inhibition for the existing field. An integrated flow assurance study between departing upstream and inlet receiving facilities of FLNG enabled the design of a robust inlet facility suitable for the FLNG process.

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