Flow Assurance in Multiphase Environments
Authors: Forsdyke I.N. 
Published: December 2007

Future oil and gas discoveries will be, increasingly, produced through multiphase flowlines from remote satellite facilities in deepwater environments. Much of the technology needed to design and install these facilities exists. However, our current inability to reliably predict and control the behaviour of the fluids could result in plugged lines and premature abandonments. This has lead to the high levels of conservatism seen in current designs and could ultimately result in some field deferral. Through unprecedented industry co-operation in areas such as wax and hydrates, significant progress has been made in both their prediction and control. To meet future challenges we will need to develop new predictive tools and different ways of working. Cost effective solutions will not just rely upon ongoing chemical cures but must be linked to design. "Fast track" developments have lead the way with new technologies readily being applied. This has been achieved through improved working relationships within the project design teams, with facility and production engineers working closely with production chemists, fluid specialists and reservoir engineers to "get it right first time".

This paper sets out to review current and future production challenges, technical progress to date and to identify areas where further effort is required.

Introduction

The design strategy of most new oil/condensate discoveries has been governed predominately by reserves, reservoir performance, environment (i.e. subsea vs. onshore) and the pay-back period. However, as new discoveries are increasingly in hostile environments especially deepwater, and new technologies such as subsea completions make marginal fields more attractive, another factor "Flow Assurance" or operability is impacting design. Here the ability of the produced fluids to present a multitude of problems, from minor upsets to major shutdowns or even early abandonment, is being addressed at the design stage.

Until recently traditional designs afforded us the luxury of easy access to wellheads and both ends of flow/pipelines. If the fluids presented production problems such as waxes or scales, intervention remediation was relatively easy and cost effective to achieve. As we move into remote subsea production, access into the system will become increasingly expensive and hence limited. The combination of multiphase flow and limited remediation now makes it necessary for us to have a detailed understanding of how the fluids will behave in our production system. The risks associated with not understanding fluid behaviour and its impact on system operability have all too painfully been demonstrated through flowline replacements and even early abandonments. It is through these bad experiences that the "scare factor" associated with produced fluid problems results in the high level of conservatism in design. Systems are therefore designed to either totally avoid potential fluid problems through super insulation for example, or to give us the ability to reliable intervene on a regular basis such as using round trip pigs or Through Flowline tools (TFL). Both the conservatism and potential for lost production and reserves have substantial cost implications, that, in the current economic climate we can ill afford.

In order to achieve our design goals of a cost effective fit for purpose system we must be able to reliably predict and control our fluids behaviour over the production lifetime.

Produced Fluid Issues

The use of multiphase systems to produce and transport fluids long distances is becoming increasingly common. The fluids, a combination of gas, oil/condensate and water together with solids such as scales and sand, have the potential to cause many problems including:

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