MULTIPHASE FLOW IN VERTICAL AND DEVIATED PIPES

Lead Research Organisation: Imperial College London
Department Name: Department of Chemical Engineering

Abstract

This proposal addresses the vital issue of prediction of multiphase flows in large diameter risers in off-shore hydrocarbon recovery. The riser is essentially a vertical or near-vertical pipe connecting the sea-bed collection pipe network (the flowlines) to a sea-surface installation, typically a floating receiving and processing vessel. In the early years of oil and gas exploration and production, the oil and gas companies selected the largest and most accessible off-shore fields to develop first. In these systems, the risers were relatively short and had modest diameters. However, as these fields are being depleted, the oil and gas companies are being forced to look further afield for replacement reserves capable of being developed economically. This, then, has led to increased interest in deeper waters, and harsher and more remote environments, most notably in the Gulf of Mexico, the Brazilian Campos basin, West of Shetlands and the Angolan Aptian basin. Many of the major deepwater developments are located in water depths exceeding 1km (e.g. Elf's Girassol at 1300m or Petrobras' Roncador at 1500-2000m). To transport the produced fluids in such systems with the available pressure driving forces has led naturally to the specification of risers of much greater diameter (typically 300 mm) than those used previously (typically 75 mm). Investments in such systems have been, and will continue to be, huge (around $35 billion up to 2005) with the riser systems accounting for around 20% of the costs. Prediction of the performance of the multiphase flow riser systems is of vital importance but, very unfortunately, available methods for such prediction are of doubtful validity. The main reason for this is that the available data and methods have been based on measurements on smaller diameter tubes (typically 25-75 mm) and on the interpretation of these measurements in terms of the flow patterns occurring in such tubes. These flow patterns are typically bubble, slug, churn and annular flows. The limited amount of data available shows that the flow patterns in larger tubes may be quite different and that, within a given flow pattern, the detailed phenomena may also be different. For instance, there are reasons to believe that slug flow of the normal type (with liquid slugs separated by Taylor bubbles of classical shape) may not exist in large pipes. Methods to predict such flows with confidence will be improved significantly by means of an integrated programme of work at three universities (Nottingham, Cranfield and Imperial College) which will involve both larger scale investigations as well as investigations into specific phenomena at a more intimate scale together with modelling studies. Large facilities at Nottingham and Cranfield will be used for experiments in which the phase distribution about the pipe cross section will be measured using novel instrumentation which can handle a range of fluids. The Cranfield tests will be at a very large diameter (250 mm) but will be confined to vertical, air/water studies with special emphasis on large bubbles behaviour. In contrast those at Nottingham will employ a slightly smaller pipe diameter (125 mm) but will use newly built facilities in which a variety of fluids can be employed to vary physical properties systematically and can utilise vertical and slightly inclined test pipes. The work to be carried out at Imperial College will be experimental and numerical. The former will focus on examining the spatio-temporal evolution of waves in churn and annular flows in annulus geometries; the latter will use interface-tracking methods to perform simulations of bubbles in two-phase flow and will also focus on the development of a computer code capable of predicting reliably the flow behaviour in large diameter pipes. This code will use as input the information distilled from the other work-packages regarding the various flow regimes along the pipe.

Publications

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Kaji R (2010) The effect of pipe diameter on the structure of gas/liquid flow in vertical pipes in International Journal of Multiphase Flow

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Kaji R (2009) Investigation of flow development of co-current gas-liquid vertical slug flow in International Journal of Multiphase Flow

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Kaji R (2009) EXTRACTING INFORMATION FROM TIME SERIES DATA IN VERTICAL UPFLOW in Multiphase Science and Technology

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Omebere-Iyari N (2008) The characteristics of gas/liquid flow in large risers at high pressures in International Journal of Multiphase Flow

 
Description In this project, axial view photography was used to show for the first time that the gas core in churn flow is continuous though with extensive droplet entrainment. An advanced interface-tracking scheme has also been developed for the simulation of large bubbles rising in vertical pipes. Codes have also been developed for single large bubbles that are tracked in a frame moving with the bubble, and for trains of large bubbles, validated against steady state results in the literature. The results have revealed how bubbles break up due, mainly due to gas entrainment at the tail of a bubble after amplification of oscillations in the "skirt" (or tail) of the bubble, or direct breakup before a skirt is formed, although a stable bubble was possible in some cases wherein breakup was followed by coalescence. It was also established also that there exists a maximum pipe diameter even for laminar flow conditions, before a Rayleigh-Taylor instability would be expected. The investigation of the bubble flow/slug flow transition in small and large diameter pipes using the void wave growth model . was shown to give excellent predictions when compared with previously unpublished data on bubble/slug transition in a 32 mm diameter pipe showing that the transition to slug flow was dependent only on the phase flow rates. Transient analysis of the large diameter data obtained in the Nottingham experiments (Nottingham were partners in this research) showed that void wave growth leading to slug flow did not occur. A new correlation was developed for liquid entrainment in churn flow (based on data for 32 mm tubes) and this was found to give reasonable predictions of the entrained fraction in the larger diameter tubes when the variability of interfacial stress was accounted for. A simplified model was also developed to model bubbly flows in large-diameter pipes which considered the gas phase to consist of small bubbles of a fixed size (typically with a diameter around 3 mm) and spherical cap bubbles. Approximate calculations revealed that this model was consistent with the observations.
Exploitation Route The technological output of the research programme, backed by the outcomes of the scientific objectives can provide highly reliable design methods which would be of tremendous value to engineers designing wells and (near) vertical risers in hydrocarbon production. This would ensure the definition of more effective and cost efficient riser systems. The industrial partners involved in our Transient Multiphase Flow joint-industry programme, TMF, supported this work by funding two project studentships. The large amount of data and understanding produced in this work are of tremendous interest to researchers in academia working in the areas of multiphase fluid mechanics, numerical methods and applied mathematics. The data generated will provide a testbed for newly developed models and validating computer codes.
Sectors Energy

 
Description The findings of this project have gone a long way towards elucidating the mechanisms underlying the flow regime transitions in risers. This knowledge, which is essential for the design of risers, has been passed on to the oil-and-gas companies through the Transient Multiphase Flow consortium, led by Omar Matar, which comprises 14 major operators, and software and design houses.
First Year Of Impact 2009
Sector Energy,Environment
Impact Types Economic

 
Description Sponsoring TMF project (Chevron)
Amount £22,500 (GBP)
Organisation Chevron Corporation 
Sector Private
Country United States
Start 10/2012 
End 10/2015
 
Description Sponsoring TMF project (Schlumberger)
Amount £42,000 (GBP)
Organisation Schlumberger Limited 
Sector Private
Country United States
Start 10/2014 
End 10/2017
 
Title TMF database 
Description Database for multiphase flow data (e.g. flow regimes and their transitions for various flows as a function of system parameters). The data are collected as part of the TMF consortium, which compromises 14 oil-and-gas companies and design and software houses, led by Omar Matar. 
Type Of Material Database/Collection of data 
Provided To Others? Yes  
Impact TMF sponsors have access to the database and they have used it to improve their understanding of multiphase flows, which improves their design capabilities. The software houses that sponsor TMF use the data to validate the predictions of their codes. 
 
Description Next generation predictive tools for multiphase flows (BHRG) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Type Of Presentation keynote/invited speaker
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Presented the next-generation predictive tools produced by the MEMPHIS Programme Grant to industrialists in the oil-and-gas sector at the BHRG conference in Cannes, June 2013. There was a lot of discussion following the presentation about the potential use of the MEMPHIS codes in providing solutions to flow assurance problems in the oil-and-gas industry.

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Year(s) Of Engagement Activity 2013
 
Description TMF meetings 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Meetings of the Transient Multiphase Flow consortium, led by Omar Matar, are instrumental in facilitating tech. transfer. There are 14 companies within TMF (e.g. BP, Shell, Chevron, Petrobras, Statoil, TOTAL, Schlumberger, ENI, Cameron, etc.) and we have semi-annual sponsors' meetings in which sponsored students present their findings.

Continued funding of our multiphase flow activities.
Year(s) Of Engagement Activity Pre-2006,2006,2007,2008,