MULTIPHASE FLOW IN VERTICAL AND DEVIATED PIPES

这一建议解决了海上油气开采中大直径立管多相流预测的关键问题。立管基本上是一条垂直或近乎垂直的管道，将海底收集管网(输油管)连接到海面设施，通常是一艘浮动的接收和处理船。在油气勘探和生产的早期，油气公司首先选择最大、最容易获得的海上气田进行开发。在这些系统中，立管相对较短，直径适中。然而，随着这些油田的枯竭，石油和天然气公司正被迫将目光投向更远的地方，寻找能够在经济上开发的替代储量。因此，这导致人们对更深的水域以及更恶劣和更偏远的环境的兴趣增加，最明显的是在墨西哥湾、巴西坎波斯盆地、设得兰西部和安哥拉阿普提安盆地。许多主要的深水开发项目位于超过1千米的水深(例如1300米处的精灵吉拉索尔或1500-2000米处的巴西国家石油公司的龙卡多)。在这样的系统中利用可用的压力驱动力输送产出的流体，自然会产生比以前使用的直径(通常为75 mm)大得多的立管直径(通常为300 mm)的规格。对这类系统的投资一直是巨大的，而且将继续是巨大的(到2005年约为350亿美元)，立管系统约占成本的20%。多相流提升管系统的性能预测是非常重要的，但非常不幸的是，现有的预测方法的有效性令人怀疑。这主要是因为现有的数据和方法是基于对较小直径的管子(通常为25-75 mm)的测量，并根据这些管子中出现的流动模式来解释这些测量结果。这些流型通常是气泡流、弹状流、搅拌流和环状流。有限的现有数据表明，较大管内的流型可能会有很大的不同，在给定的流型内，详细的现象也可能不同。例如，有理由相信正常类型的弹状流(由经典形状的泰勒气泡隔开的液体段塞流)可能不存在于大管道中。通过三所大学(诺丁汉大学、克兰菲尔德大学和帝国理工学院)的综合工作计划，将大大改进有信心地预测这种流动的方法，该计划将涉及更大规模的调查以及在更密切的范围内对具体现象的调查，同时还将进行模型研究。诺丁汉和克兰菲尔德的大型设施将用于实验，其中将使用可处理一系列流体的新型仪器测量管道横截面上的相分布。克兰菲尔德试验的直径将非常大(250毫米)，但将限于垂直的空气/水研究，特别强调大气泡的行为。相比之下，诺丁汉的那些将使用略小的管径(125毫米)，但将使用新建的设施，在这些设施中，可以使用各种流体来系统地改变物理性质，并可以使用垂直和略有倾斜的测试管道。将在帝国理工学院进行的工作将是试验性的和数值的。前者将重点研究环形几何形状的搅动和环状流中波的时空演变；后者将使用界面跟踪方法来模拟两相流中的气泡，并将重点放在开发能够可靠地预测大口径管道中流动行为的计算机代码上。该代码将使用从其他工作包中提取的有关沿管道的各种流型的信息作为输入。

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.