Pipeline Transportation of Offshore Condensate Gas

With the development of offshore oil and gas fields, the engineering of transporting condensate gas out of the fields through submarine pipelines is undertaking a unceasing upgrading. The development and transportation of condensate gas, which is a gas mixture of multicomponents with the principal being saturated hydrocarbon, are courses of condensation and anticondensation. The pipeline delivery of condensate gas, therefore, is different from that of single-phased gas or liquid, having two transport modes, gas-liquid mixed flow and gas-liquid separate flow. The two phase (gas-liquid) mixed flow, commonly adopted for its cost effectiveness and short construction time as one of two options of mixed flow, calls for solutions to flowability reduction and liquid sluggish, flow which result from the build up of condensated liquid; on the other hand, the other option, the dense phase gas flow with a single phase operation, suffers from high construction and operation costs. Gas-liquid separate flow involves condensate gas separation and separate delivery of natural gas and condensated liquid, leading to single phase flows either by using two separate pipelines or by means of batch tramsportation. Pressure drop, temperature drop and liquid holdup are three closely interacted parameters along pipeline. The paper describes the relationship between pressure drop, flow and liquid holdup in a condensate gas pipeline, and points out that it is a precondition for safe operation to predict the temperature drop along pipelime. For the purpose of developing Pinghu Oil/Gas Field in East China Sea, the paper makes a technoeconomical evaluation on the oil/gas mixed flow process by comparing different gas-liquid ratios, transport pressures and pipe diameters.