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Experimental investigation of gas hydrate formation, plugging and transportability in partially dispersed and water continuous systems.

机译：部分分散和连续水系统中天然气水合物形成，堵塞和运移性的实验研究。

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摘要

As oil/gas subsea fields mature, the amount of water produced increases significantly due to the production methods employed to enhance the recovery of oil. This is true especially in the case of oil reservoirs. This increase in the water hold up increases the risk of hydrate plug formation in the pipelines, thereby resulting in higher inhibition cost strategies. A major industry concern is to reduce the severe safety risks associated with hydrate plug formation, and significantly extending subsea tieback distances by providing a cost effective flow assurance management/safety tool for mature fields. Developing fundamental understanding of the key mechanistic steps towards hydrate plug formation for different multiphase flow conditions is a key challenge to the flow assurance community. Such understanding can ultimately provide new insight and hydrate management guidelines to diminish the safety risks due to hydrate formation and accumulation in deepwater flowlines and facilities. The transportability of hydrates in pipelines is a function of the operating parameters, such as temperature, pressure, fluid mixture velocity, liquid loading, and fluid system characteristics. Specifically, the hydrate formation rate and plugging onset characteristics can be significantly different for water continuous, oil continuous, and partially dispersed systems. The latter is defined as a system containing oil/gas/water, where the water is present both as a free phase and partially dispersed in the oil phase (i.e., entrained water in the oil). Since hydrate formation from oil dispersed in water systems and partially dispersed water systems is an area which is poorly understood, this thesis aims to address some key questions in these systems.;Selected experiments have been performed at the University of Tulsa flowloop to study the hydrate formation and plugging characteristics for the partially dispersed water/oil/gas systems as well as systems where the oil is completely dispersed in water. These experiments indicate that the partially dispersed systems tend to be problematic and are more severe cases with respect to flow assurance when compared to systems where the water is completely dispersed in oil. We have found that the partially dispersed systems are distinct, and are not an intermediate case between water dominated, and water-in-oil emulsified systems. Instead the experiments indicate that the hydrate formation and plugging mechanism for these systems are very complex. Hydrate growth is very rapid for such systems when compared to 100% water cut systems. The plugging mechanism for these systems is a combination of various phenomena (wall growth, agglomeration, bedding/settling, etc). Three different oils with different viscosities have been used to investigate the transportability of hydrates with respect to oil properties. The experiments indicate that the transportability of hydrates increases with increase in oil viscosity. The data from the tests performed provide the basis for a mechanistic model for hydrate formation and plugging in partially dispersed systems. It is found that in systems that were in stratified flow regime before hydrate onset, the hydrates eventually settled on the pipe walls thereby decreasing the flow area for the flow of fluids. In systems that were in the slug flow regime before hydrate formation, moving beds of hydrates were the main cause for plugging. In both the flow regimes, the systems studied entered a plugging regime beyond a certain hydrate concentration. This is termed as &phis;plugging onset and can be used as an indicator to calculate the amount of hydrates that can be transported safely without requiring any additional treatment for a given set of flow characteristics. A correlation to calculate this hydrate concentration based on easily accessible parameters is developed in terms of flow characteristics and oil properties.;The work performed in this thesis has enhanced the understanding of the hydrate plug mechanism in pipelines having high amounts of water. This work has also shown the effect of hydrate formation in different flow regimes thereby shedding light on the effects of hydrates on multiphase flow and vice versa. Lessons resulting from this work could be incorporated into flow assurance models, as well as operating company production strategies to reduce or mitigate hydrate plugging risks in complex multiphase systems.
机译：随着油气海底油田的成熟，由于用于提高石油采收率的生产方法，产生的水量显着增加。尤其是在储油柜中。持水量的增加会增加管道中形成水合物塞的风险，从而导致更高的抑制成本策略。业界主要关注的问题是，通过为成熟油田提供经济有效的流量保证管理/安全工具，来减少与水合物塞形成有关的严重安全风险，并显着延长海底回馈距离。对不同的多相流动条件下形成水合物塞的关键机械步骤的基本理解是对流动保证界的主要挑战。这种了解最终可以提供新的见识和水合物管理指南，以减少由于水合物在深水流水线和设施中形成和积累而造成的安全风险。管道中水合物的可运输性是操作参数的函数，例如温度，压力，流体混合物速度，液体负荷和流体系统特性。具体而言，对于水连续，油连续和部分分散的系统，水合物的形成速率和堵塞开始特性可能会显着不同。后者定义为包含油/气/水的系统，其中水既以游离相形式存在，又部分分散在油相中（即油中夹带的水）。由于分散在水系统和部分分散的水系统中的油形成水合物的领域尚不为人所知，因此本文旨在解决这些系统中的一些关键问题。;塔尔萨大学flowloop实验室进行了精选实验研究水合物部分分散的水/油/气系统以及油完全分散在水中的系统的形成和堵塞特性。这些实验表明，与水完全分散在油中的系统相比，部分分散的系统往往存在问题，并且在流量保证方面更为严峻。我们已经发现，部分分散的体系是不同的，并且不是水为主的体系和油包水乳化体系之间的中间情况。相反，实验表明这些系统的水合物形成和堵塞机理非常复杂。与100％含水的系统相比，此类系统的水合物生长非常迅速。这些系统的堵塞机制是多种现象（壁增长，结块，铺垫/沉降等）的组合。已使用三种具有不同粘度的不同油来研究水合物相对于油性的可运输性。实验表明，水合物的运输性随油粘度的增加而增加。来自执行的测试的数据为部分分散系统中水合物形成和堵塞的机理模型提供了基础。发现在水合物开始之前处于分层流动状态的系统中，水合物最终沉降在管壁上，从而减小了流体流动的流动面积。在水合物形成之前处于段塞流状态的系统中，水合物的移动床是造成堵塞的主要原因。在两种流动方式下，研究的系统都进入了超过一定水合物浓度的堵塞状态。这被称为＆堵塞开始，并且可以用作指示器来计算可以安全地运输的水合物的量，而对于给定的一组流动特性无需任何额外的处理。在流动特性和油性方面，建立了一种基于易于获取的参数来计算水合物浓度的相关性。本论文的工作增强了对含大量水的管道中水合物堵塞机理的理解。这项工作还显示了水合物在不同流态下的形成作用，从而揭示了水合物对多相流的影响，反之亦然。这项工作所产生的经验教训可以纳入流量保证模型，以及运营公司的生产策略，以减少或减轻复杂多相系统中水合物堵塞的风险。

著录项

  • 作者

    Vijayamohan, Prithvi.;

  • 作者单位

    Colorado School of Mines.;

  • 授予单位 Colorado School of Mines.;
  • 学科 Petroleum engineering.;Engineering.;Energy.
  • 学位 Ph.D.
  • 年度 2016
  • 页码 231 p.
  • 总页数 231
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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