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Collaborating Authors
Results
Dependence of Severe Slugging On the Orientation Angle of the Pipeline Upstream of the Riser Base
Malekzadeh, R. (The University of Tulsa) | Mudde, R.F. (Delft University of Technology) | Henkes, R.A.W.M. (Delft University of Technology, Shell Projects & Technology)
ABSTRACT: At constant inflow conditions, large-amplitude pressure and flow rate fluctuations may occur in a pipeline-riser system operating at relatively low liquid and gas flow rates. This periodic flow instability has been referred to as severe slugging. In this experimental study, three different orientation angles of the pipeline upstream of the riser base were investigated. The experiments were carried out in a downward inclined pipeline, in a horizontal pipeline and in a hilly-terrain pipeline followed by a vertical riser. Air and water were used as the experimental fluids. For each pipeline-riser configuration, different types of flow instability were found. 1 INTRODUCTION Pipeline-riser configurations in an offshore oil and gas production facility are required to transport multiphase hydrocarbons from a subsurface oil and gas reservoir to a central production platform. The diameter of the pipeline and the riser ranges from typically 0.1 to 0.8 m. The length of the pipeline can vary from a few kilometres to more than hundred kilometres. The height of the riser depends on the water depth, which can be more than two kilometres (in deepwater areas). At relatively low flow rates, liquid accumulates at the bottom of the riser, creating a blockage for the gas, until sufficient upstream pressure has been built up to flush the liquid slug out of the riser. After this liquid surge, and subsequent gas surge, part of the liquid in the riser falls back to the riser base to create a new blockage. This transient cyclic phenomenon is called severe slugging. Severe slugging can significantly reduce the production from the reservoir (due to an increased back pressure) and also can damage or even lead to a shut down of the platform facilities, downstream of the riser, like separators, pumps, and compressors.
A Lagrangian One-dimensional Three-phase Slug Tracking Model
Kjeldby, T.K. (Norwegian University of Science and Technology) | Henkes, R.A.W.M. (Delft University of Technology) | Nydal, O.J. (Norwegian University of Science and Technology)
ABSTRACT: A Lagrangian three-phase slug tracking model is demonstrated for a severe slugging case with gas, oil and water in an S-shaped riser. The model is an extension of a hybrid twophase flow scheme in which a two-fluid model formulation is used in the stratified flow region. In the slug body region, an incompressible flow model is applied. Mass and momentum conservation equations are solved for open and moving control volumes. This moving grid formulation allows for tracking of discontinuities within the flow, without numerical diffusion. A sub-grid two-fluid model in the bubble region allows for slug initiation directly from the two-fluid model in combination with a fine grid. Alternatively, a mechanistic slug initiation model may be used in combination with a coarse grid. The model is presented and applied to a severe slugging case in which oilwater separation occurs during slug build-up. The third phase is modeled with a mass conservation equation and an oil/water slip model in a mixture liquid momentum equation formulation. 1 INTRODUCTION The introduction of nuclear power generation in the mid 1950s increased the need for accurate and reliable methods to predict two-phase steam and water flows in pipe networks. This led to the development of several commercial codes for one-dimensional two-phase pipe simulation. Almost two decades later, a new field of application of the multiphase technology arose with the emergence of oil and gas production from deep water offshore fields. Several codes specifically designed for such systems were developed. These tools were to a large extent based on the modelling and simulation principles originally introduced with the nuclear technology, and were mainly suited for simulation of two-phase oil and gas flows. Here, an algebraic slip model for the relative velocity between the oil and the water was utilized.
- Reservoir Description and Dynamics > Reservoir Simulation (1.00)
- Reservoir Description and Dynamics > Fluid Characterization > Fluid modeling, equations of state (1.00)
- Production and Well Operations > Well & Reservoir Surveillance and Monitoring > Production logging (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Pipeline transient behavior (1.00)
A First Look At the Hydrodynamics of Air-water-foam Flow For Gas Well Deliquification
van Nimwegen, A.T. (Delft University of Technology) | Portela, L.M. (Delft University of Technology) | Henkes, R.A.W.M. (Shell Projects & Technology)
Experiments for air-water flow with and without added foamers were performed in a 50 mm diameter 12 m long vertical pipe at ambient pressure. It was observed that adding foamers to water will lead to a lower pressure drop at superficial gas velocities below the transition limit from annular flow to churn annular flow (which is around 15 m/s) and at superficial liquid velocities between 0.5 and 2 cm/s. Visualisation of the flow with a high speed camera indicates that the decrease in the pressure drop is due to the more regular nature of the flow when the water is foaming: churning of the flow is suppressed by the foam. This is confirmed by the decrease of the pressure oscillations in the presence of foamers. These experiments give insight into why and how liquid loading in gas wells is prevented by the addition of foamers. 1 INTRODUCTION In a gas well, both liquids โ in the form of water and gas condensate โ and gas are produced. If the reservoir pressure is high, the gas velocity in the well tubing is sufficient to drag the liquids to the surface. However, near the end of field life when the reservoir pressure has depleted, the gas velocity becomes too low to transport the liquids through the well. The minimum gas velocity required to lift the liquids is called the criticalvelocity. When the gas velocity becomes lower than the critical velocity, liquid will start accumulating at the bottom of the well. This will generate a large hydrostatic pressure in the well, which severely limits the gas production. This process is called liquid loading (1). Most foamers used in gas wells foam only the water (2), but there also exist some condensate foamers (3). In this work, only a water-based foamer has been considered.
Experiments And Modelling of Multiple Holdup States For Gas/liquid Flow In a Pipeline
Birvalski, M. (Delft University of Technology) | Henkes, R.A.W.M. (Delft University of Technology, Shell Projects & Technology)
In this study, the occurrence of multiple solutions in stratified flows was investigated. The model equations give multiple holdup solutions for certain flow regimes โ in small angle upflows with low liquid velocity (low liquid loading) and with low to moderate gas velocity. We applied a steady state as well as a transient flow model, supplied with different closures, verifying the structural stability of different solutions. We compared our model results to observations in our own experiments for zero net liquid flow, and also with two experimental cases by other authors, who investigated the occurrence of hysteresis or holdup discontinuities in stratified flows. 1 INTRODUCTION Long gas/condensate pipelines follow the natural terrain and thus have an undulating profile. Since they operate in the low liquid loading regime, the flow pattern is predominantly stratified flow. In those parts of the pipeline which are slightly upwardly inclined, a steep change in holdup can be observed when the gas velocity is decreased. Under these same conditions, the standard stratified two-phase flow models predict the occurrence of multiple holdup solutions. It is our goal to investigate if we can reliably predict which holdup solution is going to happen in reality, and at which conditions the sudden change in holdup will take place. One of the first studies to point out the occurrence of multiple solutions under certain conditions in the original two-phase stratified flow model presented by Taitel and Dukler (1) was done by Baker and Gravestock (2). Landman (3, 4) and Ullmann et al. (5) showed that this was also the case when laminar gas/liquid flow in rectangular ducts was solved exactly. Further, Landman (3, 4) parameterized the multi-valued solutions, and did a stability analysis and dynamic simulations in order to see which of the solutions is likely to happen in reality.