Abstract
This paper briefly summarizes that during the depressurization operation in subsea pipeline for maintenance or prevention of hydrate formation, because the flare knock-out drum pump is designed for ambient temperature, and cannot deal with the low temperature fluid in the depressurization process. Therefore, the low temperature fluid needs to be heated in the knock-out drum to meet the temperature requirement of pump. In order to avoid the volume of low temperature fluid exceeding the surge volume of the flare knock-out drum, the concept of multi stage depressurization is innovatively proposed in this paper, which meets both the requirements of pump temperature and the surge volume of flare drum. Taking a gas field project in the South China Sea as an example, the simulation analysis of depressurization temperature and pressure is carried out by using different size of the blowdown valve. It provides a good reference for the similar project in future.
Highlights
Subsea production systems(SPS) are widely used in deep-water and marginal oilfield development[1]
The surge volume of the flare knock-out drum is taken as the limit condition, and the pressure of the subsea pipeline is reduced by multi stage depressurization, so as to provide the operator with enough time for low temperature fluid treatment, that is, to dissolve the hydrate generated
The depressurization analysis for regular project, the high pressure fluid in the subsea pipeline is simulated with directly discharged by blowdown valve
Summary
Subsea production systems(SPS) are widely used in deep-water and marginal oilfield development[1]. The water depth of a gas field project in the South China Sea is 1500m, using the subsea production system and semisubmersible platform (SEMI) development program, the natural gas is exported after drying and dehydration treatment in SEMI, and the condensate oil is stored in SEMI for regular export after qualified dehydration treatment. The SPS consists of seven production wells (W1-W7), with relatively scattered well locations, using three subsea manifold (E1~E3) and double subsea pipeline development scheme. Oil & gas wells output pipelines are connected to subsea manifold through jumpers, and production fluid are connected to SEMI for processing[2]. When hydrate is generated in the subsea pipeline and SPS will block pipelines and affect production, depressurization operation should be carried out on the platform to reduce the operating pressure in the subsea pipeline and make it lower than the hydrate dissolution pressure, so as to ensure the safety of production and operation
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