Slug Tracking in Pipelines: Part I - Experiments and Analysis

Abstract

Abstract A large-scale multiphase flow experimental facility is used to study slug tracking behavior in pipelines. The description of the flow loop, testing procedure, analyses of data, and development of closure terms for a slug tracking model are the focus of this paper. Pressure, temperature, and liquid holdup were collected for 286 tests. Each test was characterized by a superficial liquid velocity, superficial gas velocity, length of pipeline, diameter of pipeline, and length and angle of the inclined sections of the pipeline in a hilly terrain configuration. Data collected in flow tests were analyzed to yield;slug translational velocity,liquid holdup in slug and film, andslug length distribution. Correlations were derived for the slug translational velocity in the inclined sections. These correlations have been compared with an existing relation. It is the intent to use the correlations in a slug tracking model under development and validate the numerical simulator with the processed data. Introduction The slug structure is a common and complex flow pattern which occurs in a pipeline transporting a multiphase mixture. It consists of a region of liquid with entrained gases, referred to as the liquid slug body, a gas bubble or pocket, and a liquid film. Figure 1 shows a slug flow in a horizontal pipe. The case of slug flow in a vertical pipe is shown in Figure 2. An example of the flow situation in the case of a hilly terrain pipeline is illustrated in Figure 3. In the multiphase pipelines, slugs can be further differentiated according to the mode of formation. The slug flow structure may be initiated by flow instabilities, such as the Kelvin-Helmholtz instability. These are termed hydrodynamic slugs. In other cases, the geometry of the pipeline plays an important role in the slug formation. An example of this is a pipeline-riser pipe system. At low fluid flow rates, there is blockage at the base of the riser leading to an intermittent flow behavior termed severe slugging. Slugs formed as a result of the geometry are commonly referred to as terrain induced slugs. An initiated slug can grow or decay as it moves along a pipeline due to expansion, wake, and terrain induced effects. Slug tracking is the process whereby the development of the slug is traced from the initiation point to the point of decay or to the exit of the pipeline. An understanding and knowledge of the slug flow characteristics are necessary to permit,a design of downstream process equipment such as slug catchers and separators,an analysis of the impact of the pressure and flow transients created by this complex flow on the reservoir,an analysis of the impact of the pressure and flow transients created by this complex flow on equipment and structures, andthe effect of slugging on corrosion rates. The following sections describe an experimental study of slug flow in a hilly terrain pipeline. The main intention of the experiments is to obtain data on slug growth and slug dissipation in a hilly terrain configuration. The data obtained on tracking the slugs are to be used in the validation of a mathematical and numerical simulator currently under development. Details of the latter are to be presented in a paper at a later date.