Summary
The gas transport system on the Norwegian continental shelf (NCS) consists
of 7800 km of pipelines and is the largest offshore network of its kind in the
world. Natural gas is processed at treatment plants in Norway, and dry gas is
exported through pipelines to customers in the UK and continental Europe. These
customers have the opportunity to make varying gas delivery nominations, and
meeting such sales gas commitments is important.
A major challenge is to operate the network at minimum cost, with minimum
environmental emissions, fulfilling variations in contractual nominations and
maintaining a sufficient pipeline inventory to provide operational
flexibility.
Optimum pipeline inventory and optimum operation of export compressors have
been analyzed in earlier studies.
The scope of the work presented in this paper is to establish a model for
optimum operation of a gas export system, including customer nominations and
operation of pipelines and compressor stations. That implies improving system
energy efficiency, reducing environmental emissions, and maintaining sufficient
availability and export deliverability. The model will provide guidelines which
will be implemented in planning and operation of the gas export system.
This model is based on analyzes of operational data from the gas export
system on the NCS. The data are analyzed using statistical and simulation
software.
The paper describes the established model for optimum operation of the
system, where specific power consumption is minimized. A case study which
illustrates the use of the model is also presented. Furthermore, the paper
reports on a cost-benefit analysis based on the established model.
Introduction
Problem Statement. Context. The gas export system on the
Norwegian continental shelf (NCS) consists of 7800 km of pipelines and is the
largest offshore network of its kind worldwide (Fig. 1). The system is operated
at very high pipeline pressure, up to 210 bar, and few booster stations are
installed along the way. Pipelines on the NCS are up to 1200 km long. As much
as approximately 100–150 Mstd m3/d of gas can be stored in the
pipelines. Dry gas exports from the NCS totaled 82.5 billion std m3
in 2005, making Norway the third-largest gas exporter on a world basis.
Norway’s gas export system also includes land-based and offshore treatment
plants which process natural gas. Dry gas is exported from these plants through
pipelines to customers in the UK and continental Europe.
Customers have the opportunity to make varying gas delivery nominations.
Meeting these sales gas commitments is important. Failure to do so would result
in gas sale losses, as well as reducing regularity and hurting the reputation
of the gas shippers.
A major challenge is to operate the network at minimum cost, with minimum
environmental emissions, fulfilling variations in contractual nominations and
maintaining a sufficient pipeline inventory to provide operational flexibility.
This requires striking a delicate balance between high pressure and associated
energy consumption for compressors on the one hand, and lower pressure and the
risk of losing gas sales on the other. It also calls for detailed knowledge of
network integration and the relationship between customer nominations, pipeline
flow and inventory, compressor station operation, and operational flexibility
of the network.
This paper uses the existing gas export system on the NCS, comprising
customer nominations, pipelines, and compressor stations, to develop a model
for optimum operation. The stated operational values and capacities in the
paper are typical.
Focus. The paper establishes a model for optimum operation of
gas export systems. Optimum operation implies increasing system energy
efficiency by minimising operational network costs and environmental emissions,
while fulfilling contractual nominations and maintaining operational
flexibility and availability. System energy efficiency is measured by relating
pipeline inventories and gas deliveries to specific compressor power.
Guidelines based on the model will be applicable to an actual gas export
system.
© 2008. Society of Petroleum Engineers
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History
- Original manuscript received:
19 July 2007
- Meeting paper published:
4 December 2007
- Revised manuscript received:
11 April 2008
- Manuscript approved:
17 June 2008
- Version of record:
15 December 2008
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