ABSTRACT

This paper discusses the challenges in simulating the Dampier to Bunbury Natural Gas Pipeline (DBNGP) which has capacity transportation services defined by probability of supply with specific interruption limits. There are two main types of capacity services, namely, Firm and Non Firm. The Firm Capacity Service has a 98% probability of supply and it may not be interrupted for more than 2% of the time. For Non Firm Capacity Service, up to 10% of the total contracted capacity could be interrupted per year. These types of capacity services require a different flow modelling approach - the model must be able to simulate thousands of steady state runs under different pipeline operating configurations in order to derive each of the different capacity service levels. This specific modelling requirement has resulted in the development of a modelling tool that offers: A robust spreadsheet-based model with full pipeline simulation capability The ability to carry out thousands of simulations unattended The capability to process and statistically analyse simulation results Error checking, data validation and reporting In summary, a versatile pipeline modelling tool has been developed for the determination of the DBNGP's unique capacity services. This model can be used in both steady state and transient simulations. In addition, day to day capacity forecasting for both short and long term planning can also be performed using the same model.

INTRODUCTION

The DBNGP pipeline connects the gas processing plants located near Dampier in the North West of Western Australia to the customers in the state's South West. It has a total of ten compressor stations situated approximately 93miles (150km) apart from each other. All the gas inlets are located at the start of the pipeline and most of the outlets are located at the southern end of the pipeline. Interconnections with other pipelines are fairly limited. By world standards, it is a relatively small and simple pipeline. However, operationally this pipeline differs from most other pipelines - Capacity Services are contracted by levels of firmness and probability of supply. It is easy to model the physical and flow characteristic of this pipeline but it is both time consuming and challenging to model the capacity services for this "probabilistic" pipeline. This paper presents: An overview of the pipeline Definition of the different capacity services and the challenges in modelling these services An example of how the services are determined and modelled Discussion on the experience and methodology used to model this pipeline

Pipeline Capacity and Operation

Capacity is measured by the energy rate in Terajoules per day. Hence, energy content is an important measure of gas quality that will impact on the pipeline's capability to deliver the contracted capacity. Contractually pipeline full-haul capacity and throughput are measured by the quantity of gas leaving the last mainline compressor station at CS9. Mainline compressor stations (CS1 to CS9) are installed with two 15000 hp gas turbo compressor units in series operation. Five of the stations are also installed with older generation LM500 units that are operated very infrequently.

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