Abstract

The production of full wellstream natural gas over long distances presents a number of novel flow assurance challenges. Among these challenges is a need to predict the amount of time required for injected chemicals to progress through a pipeline, predict the concentration of injected chemicals as a function of length in a pipeline during both steady state and transient operations, and the development of chemical injection operating philosophies to accommodate the potential creation of variations of concentration of the chemical as a function of length during transient operations.

ExxonMobil and the Qatar Liquefied Gas Company (II) Ltd (QGII) have successfully implemented the use of the transient multiphase simulator OLGA2000 to predict both the amount of time required for injected chemicals to progress through a pipeline and the concentration of these chemicals as a function of length under both steady state and transient conditions for a number of projects. Similarly, ExxonMobil and QGII have used the results from these analyses to successfully develop and implement operating practices.

This paper will discuss the methodology employed in the development of these simulations, interpretation of their results, and the development and implementation of pertinent operating philosophies.

Introduction

The distribution of chemicals such as corrosion and hydrate inhibitors during normal and transient operations is an integral part of the operational integrity and reliability of an upstream production system. Inadequate inhibition due to maldistribution of chemical inhibitors may cause corrosion, solids deposition, and ultimately line abandonment or replacement.

The issue of chemical distribution becomes exceptionally challenging in large diameter gas condensate fields due to the multiple forms of liquid phase transport and uncertainty surrounding the mechanics and prediction of these forms of transport.

The transportation and concentrations of liquids and chemicals in gas condensate systems can be modeled using transient multiphase hydraulic simulators such as OLGA 2000 and the results of these simulations can then be used to develop operating practices that ensure adequate chemical distribution during all modes of operation. Care, however, must be taken to ensure that calculation and compositional uncertainties are accounted for during the development of operating practices.

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