Severe Slugging In a Catenary-shaped Riser: Experimental and Simulation Studies

Abstract:

A series of experiments on two-phase, air-water flow in a flowline-riser geometry have been made. The riser has a catenary-shaped form (10.5 m high), and the flowline has a 2-degree downward inclination toward the riser-base (10.16 cm ID). Experimental data were used to characterize the severe slugging and unstable flows in terms of pressure cycling and fluid production characteristics. A model to study dynamic behavior of severe slugging flow in a pipeline-riser system was also developed under the environment of the OLGA2000 code, and experimental test results were compared with the OLGA model predictions. The motive for this work was to identify areas that pose substantial difficultly to the code for the simulation of severe slugging in a catenary-shaped riser. In addition, numerical experiments, exploring some of the reasons for difference between experimental and simulation results, have been presented in this article.     

Severe Slugging in a Free-Standing Riser

A series of experiments on air/water two-phase flow in a flowline riser have been performed. The riser has a free-standing form (7 m high) with the flowline of a 2° downward inclination toward the riser-base. Severe slugging flows are described in the free-standing riser (FSR). Then, experimental pressure comparison between the FSR and L-shaped riser is presented, and three differences are analyzed. Finally, the behavior of severe slugging flow in the FSR was simulated with OLGA software. In conclusion, it is difficult to do the theoretical simulation of severe slugging in a FSR.     

Severe Slugging in Flexible Risers: Review of Experimental Investigations and OLGA Predictions

Flexible risers are key components of floating production systems, particularly in harsh environmental conditions where the riser must deal with substantial vessel motion. Liquid slugging in flexible risers often causes severe operational problems for the downstream production system. To avoid such costly delays, it would be desirable to predict severe slugging behavior in flexible risers using experiments and transient codes. This article details the basic mechanisms and general characteristics of severe slugging in a pipeline-riser system. It also tries to present the research studies that have been carried out on severe slugging in flexible risers in two parts; experiments on different flexible riser configurations, and existing OLGA code predictions.     

Severe Slugging in Flexible Risers: Review of Experimental Investigations and OLGA Predictions

Abstract

Flexible risers are key components of floating production systems, particularly in harsh environmental conditions where the riser must deal with substantial vessel motion. Liquid slugging in flexible risers often causes severe operational problems for the downstream production system. To avoid such costly delays, it would be desirable to predict severe slugging behavior in flexible risers using experiments and transient codes. This article details the basic mechanisms and general characteristics of severe slugging in a pipeline-riser system. It also tries to present the research studies that have been carried out on severe slugging in flexible risers in two parts; experiments on different flexible riser configurations, and existing OLGA code predictions.     

海底混输立管段瞬态流动规律及其敏感性分析

利用OLGA 2000软件对某海底混输管道系统立管段瞬态流动规律及其敏感性进行了数值模拟分析,在立管底部、顶部以及管道入口、出口处压力波动很大,容易形成段塞流;采取适当减小立管管径、管道出口节流阀开度、多相流含水率以及增大管道出口压力、降低立管高度和增大多相流气油比等措施,可以在一定程度上减弱或消除立管中严重段塞流的影响。今后应加强数值模拟、试验模拟和理论计算等方法的综合研究,深入探讨海底混输管道立管段严重段塞流的形成机理,并探索经济、有效地控制和消除严重段塞流影响的措施。     

深水立管严重段塞流控制方法及其模拟分析

深水立管中常会出现严重段塞流,如果不加以控制,会带来严重的流动安全问题。为此,对国内外深水立管严重段塞流控制方法进行了全面调研和分析,总结了每种控制方法的优缺点、现场应用情况和适用范围。在此基础上利用某深水油气田的海管和立管资料,采用多相流瞬态模拟软件OLGA模拟了典型年份的流动状况,对段塞流最严重年份分别采用节流法、气举法、节流和气举结合法等方法进行了模拟,并探讨了管径与段塞流的关系。结论认为：该油气田生产后期会出现严重段塞流;在管径优化和设计阶段要充分考虑严重段塞流的影响;不同的段塞流控制方法适用于不同的工况,针对具体深水工程项目,应在开展软件模拟分析时综合考虑各种因素,最终选取经济、有效的段塞流控制方法。     

Experimental Investigation and Numerical Simulation of Two-Phase Flow in a Large-Diameter Horizontal Flow Line Vertical Riser

Abstract

As oil and gas field development moves further into deep seas, maximizing hydrocarbon extraction at an acceptable cost is one of the greatest challenges facing the industry today. In this regard, considerable attention has been given to understanding the flow behavior in long and deep flow line risers of different topologies through transient multiphase simulation. However, the application of the large diameter to the above scenario is still an unresolved issue creating a great deal of uncertainty. This is mainly due to the limitation of the available experimental and field data being confined to much smaller diameters.

In view of the aforementioned, an experimental campaign to investigate the flow behavior in a 254-mm nominal-diameter horizontal flow line vertical riser has been performed. A numerical model to study the dynamic behavior of the large-diameter horizontal flow line vertical riser system is also developed using OLGA software with the intention of identifying the capability of this software. This article presents the comparison of the simulation and experimental data in terms of near riser base and flow line pressure variations along with flow regime predictions. The existence of the multiple roots in the OLGA code is also reported for the first time. Additionally, a review on the state-of-the-art application of the code and analysis of the numerical experiment performance of the code are included.     

气液混输组合管线系统严重段塞流特性实验

针对海洋油气传输中常见的水平一下倾一立管组合系统,在两种不同高度立管下,通过实验获得了3种严重段塞流现象(严重段塞流Ⅰ、Ⅱ和Ⅲ型)。研究高度变化与严重段塞流关系,对寻求相应预测方法有着重要意义。     

混合立管系统严重段塞流流动特性的实验研究

深海油气田开采过程中混合立管系统会出现严重段塞流,造成系统流动特性参数周期性剧烈波动,严重危害海洋开发系统。在混合立管系统的模拟装置上,实验研究了混合立管系统严重段塞流的流动特性。研究结果表明：混合立管严重段塞流的1个周期分为液塞形成、液塞生产、液气喷发和液体回流4个阶段,立管的垂直管段与U形柔性管段的流动特性稍有不同,U形柔性管段在液气喷发阶段产生剧烈抖动;严重段塞流周期随气液相折算速度的增大而减小;立管压力波动幅度随气相折算速度的增大先增大后减小;液塞长度随气相折算速度的增加而减小,且下倾管增加缓冲容积时液塞长度明显增大,减小出油管长度有利于抑制严重段塞流;在深水混合立管系统结构尺寸变化范围内,垂直管高度和U形柔性管尺寸对严重段塞流的发生范围及特性影响不大。该研究结果将为混合立管的设计提供一定的参考依据。     

柔性管段对立管严重段塞流特性的影响

严重段塞流是深海混输立管面临的流动安全问题之一,开展混输立管严重段塞流研究对立管的流动安全及实际生产具有重要意义。在中国石油大学（北京）原立管系统实验装置及改造后的混合立管系统实验装置上进行的不同工况下的严重段塞流特性实验结果表明,柔性管严重段塞流特性不同于垂直管段。在立管总高度相等条件下,利用L型立管和混合立管的流型图、压力、周期和液塞等数据分析了柔性管的存在与否对立管严重段塞特性的影响。相对于L型立管,柔性管存在会在一定程度上缩小严重段塞流I的范围,同时使立管底部最大压力增大约15%～20%,严重段塞周期减小约12.09%,液塞长度减小约1.38%,液塞速度增加约2.93%。在立管总高度等几何参数一定的情况下,对柔性管跨度和长度变化对严重段塞流特性的影响进行了分析。结果表明,柔性管跨度对严重段塞流特性的影响较小;柔性管长度增加,会同时增大严重段塞流的周期和立管底部最大压力。