Slug Catchers in Natural Gas Production - NTNU

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Karam – Slug Catchers in Natural Gas Production suitability of the current design. However, it should be noticed that when simulating multiphase flow in pipelines, results can be undependable due to the difficulty of an accurate representation. Page 2 of 56
Karam – Slug Catchers in Natural Gas Production CHAPTER 2 MULTIPHASE FLOW AND SLUGS 2.1 Multiphase flow and flow patterns Multiphase flow is the mostly common and dominating flow in pipelines. A single phase flow is rarely found in the oil industry as the high pressure in the reservoir will cause a portion of the gas from the gas cap to get dissolved in the oil or water to be dissolved in the gas. As the pressure is reduced due to production, the gas will come out of solution; similarly, water will come out of solution in the form of water droplets. In a more general description, two different sets of simultaneous flows constitute the multiphase flow. Simultaneous flow of materials of two different states such as liquid, solid or gas occurring at the same time in the same mixture is classified as multiphase flow. On the other hand, simultaneous flow of materials of different chemical properties belonging to the same state or phase such as oil droplets in water is also considered as a multiphase flow (Bakker, 2005). As for the nomenclature of the phases, the continuous one is considered primary while the second phase(s) is considered secondary as it is dispersed in the first. Several multiphase flow regimes take place in horizontal pipelines. The two-phase gas-liquid flow is considered in the section below. Phase separation usually occurs when the gravity effect is perpendicular to the pipe axis. Six different patterns can appear in the horizontal pipe and are represented in Figure 1. The following flow regimes are mentioned as a function of increasing flow rate velocities. Stratified smooth (SS) pattern is the flow regime that is taking place more frequently in pipes as both gas and liquid streams are being separated and parallel due to gravity. The gas overlies the liquid and the interface is smooth. Stratified wavy (SW) pattern occurs as the gas velocity increases slightly and causes waves to form on the gas-liquid interface. The considerable increase in gas velocity in the pipes leads to more complicated flow regimes. Elongated bubble flow (EB), also known as plug flow, shows elongated gas bubbles that separate the liquid plugs. The elongated bubbles have a large diameter so that the liquid phase is lying continuously at the bottom of the pipe. The elongated bubbles will grow in size with increasing flow velocity until they reach a diameter similar to that of the channel leaving behind some liquid slugs. This is known as the slug flow (I). The latter bubbles are known as the Taylor bubbles which will be coated by a liquid film. Dispersed bubble (DB) flow takes place where the gas phase is extensively distributed in the Page 3 of 56
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Slug Catchers in Natural Gas Production - NTNU

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