As field development continues to move further into the offshore deepwater arena, the options available to deliver produced hydrocarbons become constrained. Pipelines may not be available in or near the producing locations. Additionally, the presence of rich gas streams and the resulting retrograde condensates requires that two-phase systems be employed. Companies wishing to attract and attach these deepwater streams to their pipelines must consider the impact to existing two-phase systems and the possible conversion of singlephase systems to two-phase systems. Several questions must also be addressed in this conversion process. This paper presents the methodology adopted in addressing the questions concerning the delivery of rich gas streams from the deepwater areas to onshore receiving stations and on to processing facilities. The answers to these questions impact daily operations of pipelines as well as the design and location of liquid dropout facilities. Simulations are performed to address the following questions:
How much liquid condensate will be held up in the pipeline system?
How much liquid condensate will be swept through the pipeline system into onshore facilities?
What potential is there for these liquid condensates to cause slugging in the pipeline system?
Is it necessary to increase the pigging frequency in the pipeline system?
What is the peak volume of liquid condensate that would be swept in during a shut down and start up of the system brought on by a hurricane, freeze-off, or other similar event?
El Paso Corporation (El Paso) owns and operates a pipeline system that transports natural gas from the South Pass region in the Gulf of Mexico to onshore facilties in southeast Louisiana. This system currently runs in single-phase gas mode. Additional third party pipeline systems from the deepwater Gulf of Mexico will eventually be tied into this El Paso system. These deepwater systems will deliver rich gas into the pipeline resulting in liquid condensate dropout along the length of the pipeline.
34th Annual Meeting - Portland, Oregon Pipeline Simulation Interest Group Page 2 of 15
To gain an understanding of the impact of incremental liquid condensates, El Paso brought in Knowledge Reservoir to simulate their pipeline system and to quantify the expected liquids. The results of these studies would then be utilized to design separation and stabilization facilties needed to remove the liquids from the pipeline. El Paso's 60-mile pipeline system comprises of a 17-mile 36" sub-sea section and 43- mile 26" onshore section. A pipeline system map is shown in Figure 1. The sub-sea section begins in South Pass 55 (SP 55) on the Gulf of Mexico shelf and terminates at a valve platform onshore. The onshore system begins at this valve platform and proceeds to a separation facility and compressor station near Port Sulphur, LA (Port Sulphur). The system incorporates a fairly jagged profile as the pipeline traverses bayou and valve station locations.
The dynamic modeling of two-phase flow systems has, over recent years, become commonplace.