Abstract

This paper addresses the application of a single phase simulation software to Gassco's wet gas pipelines. To meet their on-line pipeline modelling and simulation requirements Gassco carried out a thorough review of both multi-phase and single-phase simulation software solutions in the market. To help with their evaluations, a single-phase software was configured and implemented on three wet gas networks. For these pipelines and operations the simulation results were surprisingly close to actual measured flow and pressure values. To provide liquid build up estimations, an additional module has been developed. With this enhancement accurate gas and liquid estimates have become possible for on-line and offline simulations.

Introduction

The accurate simulation of a wet gas pipeline is a challenging problem. Under many operational conditions the fluid in the pipeline separates into gas, condensate and water/MEG phases. This means that a full simulation of the pipeline dynamics involves tracking these 3 elements separately, along with their interactions and the transfer of mass between them as the pressure and temperature change. In addition the various processes all operate on different time scales.

Gassco supplies Norwegian natural gas to the European market through nearly 8,000 km (5000 miles) of large-diameter high-pressure subsea pipelines. The Norwegian export pipelines are between 300 and 900 km (200-560 miles) long, and have diameters up to 44 inches. Pressure transmitters, flow meters and temperature measurements are only located at the inlet and outlet. The state of the gas between those two points can only be predicted by computer models and simulators, which are very important in order to obtain optimal operation of the pipelines.

Following the successful implementation of the new pipeline management system on the single phase pipelines [1], Gassco wanted to replace their existing multiphase Pipeline Management System. After a comprehensive research of different options, they decided to explore the application and benefit of re-using the single phase Pipeline Management System on their wet gas pipelines.

Gassco Wet Gas Pipelines

Most of the pipelines Gassco operate are single-phase gas pipelines, but Gassco also run five wet gas pipelines. These five wet gas pipelines are detailed below:

Pipeline A consists of a 147 km (91 miles) mainline pipe of 30 inch with a 35 km (22 miles), 20 inch pipe branch that supplies gas to the main pipeline 2 km (1.2 miles) downstream of the platform. Metering is only available at the inlet and the outlet of the pipeline.

Pipeline B is a 22 inch diameter pipeline and is 176 km (109 miles) in length. The pipeline goes from one platform to another and has a relatively flat profile with a riser at each end, with the deepest point at 136 m (445 feet) below sea level. Metering is only available at the inlet and the outlet of the pipeline.

The third pipeline system consists of three parallel pipes which will be considered as pipelines C, D and E. Each pipe is 36 inch in diameter and 67 km (41 miles) long. All three parallel pipes have an inclination from 340 m (1115 feet) below sea level to the onshore terminal. Metering is only available at the inlet and the outlet of the pipeline.

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