ABSTRACT

The eastern province of the Troll field is a hugh gas field located some 40 miles offshore the western coast of Norway, northwest of the city of Bergen. The recoverable reserves are estimated to be some 44 000 x 10' SCF (1250 x 10' Sm3). The production lifetime will be some 50 years. The production facilities, comprising an offshore concrete gravity base platform in 995 ft waterdepth, two 36" multiphase carbon steel pipelines and an onshore plant for wet gas reception, processing and dry gas export, will have a capacity of some 3000 MMSCFD (84 x 106 Sm3/day). This paper describes the strategies behind and the benefits from using dynamic production system computer simulations in the Troll Phase I concept development and engineering phases. Furthermore, the strategies and principles for development and use of online and offline dynamic simulation models in support of Troll Phase I operations are explained.

INTRODUCTION

The Troll Phase I development represents several technical challenges, both wrt. design and operations. This paper will highlight the assessment of the impacts of the multiphase flow phenomena on the design and operations of the production system, especially the dynamic simulations of the interactions between the pipelines and the onshore plant. Already in the concept definition phase, dynamic multiphase flow simulations were carried out for the pipelines and the slugcatcher, to evaluate the feasibility of the concept and to define the slugcatching requirements. As a part of the preengineering work, dynamic process simulation models were developed for the offshore topside process facilities, the two parallel multiphase pipelines and the onshore plant. Also a combined model, for the total production system were developed to be able to investigate the dynamic interactions between the abovementioned production system elements. These models were used successfully to verify the process design and control ability. Several findings were, however, made. These findings were grouped into "modification proposals" and "operational guidelines". The first category items were handed over to the detail engineering contrator, whereas the latter category were built into to the operation philosophy document. A new simulation study is scheduled later in the detail engineering phase. The operators of the Troll Phase I production system will have to respond rather quickly to requests from the gas buyers wrt. changes in the gas export rate. Due to the hydraulic characteristics of the multiphase flow pipelines, the optimum set of actions will depend on the production history the past days, the current state of the pipelines, the slugcatcher liquid level and the expectations wrt. future short term gas demands. In support of the operations, it is currently planned to use an online dynamic production system model. A dedicated project has been initiated to develop this model, together with models for operator training and engineering studies (modifications/debottlenecking etc.). This paper outlines the principles selected for these Troll Phase I simulators.

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