MULTIPHASE FLOW IN VERTICAL AND DEVIATED PIPES

该方案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。立管本质上是一根垂直或近垂直的管道，将海床收集管网（管线）连接到海面装置，通常是浮动的接收和处理船。在石油和天然气勘探和生产的早期，石油和天然气公司选择了最大和最容易获得的海上油田进行优先开发。在这些系统中，立管相对较短，直径适中。然而，随着这些油田逐渐枯竭，石油和天然气公司被迫将目光投向更远的地方，寻找能够经济开发的替代储量。因此，人们对更深的水域、更恶劣和更偏远的环境越来越感兴趣，尤其是在墨西哥湾、巴西Campos盆地、设得兰群岛西部和安哥拉Aptian盆地。许多大型深水开发项目位于水深超过1公里的区域（例如，Elf的Girassol位于1300米，巴西石油公司的Roncador位于1500-2000米）。为了利用现有的压力驱动力在这样的系统中输送产出的流体，自然导致了比以前使用的立管（通常为75毫米）直径大得多的规格（通常为300毫米）。对这类系统的投资已经并且将继续是巨大的（到2005年约为350亿美元），其中立管系统约占成本的20%。多相流提升管系统的性能预测是至关重要的，但不幸的是，现有的预测方法的有效性值得怀疑。造成这种情况的主要原因是，现有的数据和方法都是基于对直径较小的管道（通常为25- 75mm）的测量，以及根据这些管道中发生的流动模式对这些测量结果的解释。这些流型通常是气泡流、段塞流、搅拌流和环空流。有限的可用数据表明，较大的管道中的流型可能非常不同，并且在给定的流型内，详细的现象也可能不同。例如，有理由相信，在大型管道中可能不存在正常类型的段塞流（由经典形状的泰勒气泡分隔的液体段塞流）。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，有信心地预测这种流动的方法将得到显著改善，这将涉及更大规模的调查，以及在更密切的范围内对特定现象的调查，以及建模研究。诺丁汉和克兰菲尔德的大型设施将用于实验，其中将使用可以处理一系列流体的新型仪器测量管道横截面的相分布。克兰菲尔德试验将在非常大的直径（250毫米）上进行，但仅限于垂直的空气/水研究，特别强调大气泡的行为。相比之下，诺丁汉的测试将采用略小的管径（125毫米），但将使用新建的设施，可以系统地使用各种流体来改变物理性质，并可以利用垂直和微倾斜的测试管道。在帝国理工学院进行的工作将是实验性和数值性的。前者将侧重于研究搅拌波的时空演变和环空几何中的环形流；后者将使用界面跟踪方法来模拟两相流中的气泡，并将重点放在能够可靠地预测大直径管道中的流动行为的计算机代码的开发上。这段代码将使用从其他工作包中提取的关于管道上各种流动状态的信息作为输入。

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.