Hydraulic design of a pipeline system typically rely on operating conditions, including flows and temperatures, to provide a capacity margin or safety factor in its design and operation. This marginal capacity is intended to ensure the pipeline operation will be robust over the range of conditions the pipeline will actually experience. However, these traditional design practices, which are largely based on experience, can sometimes provide too much or too little reserve that could result in either over-building of facilities or service shortfalls and disruptions, respectively. Tools or processes that would allow a designer to evaluate the robustness of a design in light of the variability and uncertainties in assumed parameters have not been generally available or communicated. At TransCanada, a number of statistical models based on the Monte Carlo simulation technique have been developed and are routinely used to assist in evaluating the effects of operating variables and uncertainties on the design and operation of the pipeline system. The specific models used provide the ability to characterize:

  • Demand and load characteristics on the pipeline system,

  • Seasonal or annual capability ranges based on the variability of operating conditions such as ambient

  • temperatures and load, and

  • The effects of unit and fleet compressor reliability on available capacity.

This paper will provide a description of the concepts behind and resulting development of the statistical models. Examples of where and how the models have been used will also be presented along with a discussion of other applications where the models could provide a benefit through the insight they can provide.

TransCanada Pipeline System Overview

TransCanada Pipelines owns and operates one of the largest pipeline system in North America (Figure 1), connecting the Western Canadian Sedimentary Basin to the major markets in Canada as well as the Northern Tier and West Coast of the United States. At the end of 2001, the TransCanada System consisted of almost 24,000 miles (38,300 km) of pipe with over 49.85 million HP (3716 MW) of compression available from 295 units at 113 different sites. During 2001, receipts onto the pipeline system averaged approximately 11.4 bcfd (322 e6m3/d) with peak receipts exceeding 13 bcfd (370 e3m3/d). The Alberta portion of the TransCanada Pipeline system, Nova Gas Transmission Ltd (NGTL), primarily serves to aggregate supply from the WCSB for delivery to markets within Alberta as well as markets connected elsewhere to the TransCanada system or other interconnecting pipeline. The supply on the NGTL system is collected at about 950 meter stations located throughout the province and then delivered at almost 175 stations within Alberta in addition to downstream pipelines. Given the obvious size and complexity of the NGT system, it is easy to understand the challenges presented in its design and operation.

NGTL Design Methodology

The Mainline Design process for the NGTL system evaluates facilities required in order to provide customers access to the transportation services to which they have contractually committed.

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