1.0 INTRODUCTION

Interprovincial Pipe tine Inc. (IPL) and Lakehead Pipe Line Company, Inc. (LPL) are currently upgrading existing computational pipeline monitoring systems. The purpose of this work is to enhance pipeline monitoring capabilities and to meet the guidelines set out in the recommended practice of the standard CAN/CSA-Z183-M90 "Oil Pipeline Systems". This standard defines material balance as "a mathematical procedure based on the laws of conservation of matter and fluid mechanics which is used to determine whether a leak has developed in a pipeline system". Real-time, model based, material balance systems are being implemented. In-house expertise is being developed to build, tune and maintain these pipeline monitoring systems. The simplest material balance system is based on injection and delivery volumetric flow rate measurements only. Mainline volumetric flow rates at intermediate points along the pipeline may also be used. These flow measurements are used to calculate the, difference in incoming and outgoing fluid volumes for a ficed section of a pipeline. A more sophisticated material balance system is volume balance with linepack correction. This system uses flow measurements the same way as the simple material balance and in addition accounts for changes in the volume of fluid in the pipeline due to pressure and temperature changes. Material balance systems are referred to as volume balance systems hereafter. The mass contained in a volume of a particular fluid at reference conditions is referred to as the volume. Volume balance systems are Pipeline Operator tools that can be used to identify leaks in pipelines. A leak is detectable when the volume imbalance due to the leak in a given time period exceeds the system's volume uncertainties. The volume uncertainties and hence, the sensitivity of the volume balance system, depend on the uncertainty of the receipt and delivery volume measurements and on the uncertainty of the linepack calculation. The following four factors have been identified as affecting the accuracy of the linepack calculations:

  • software (the numerical technique); including stability characteristics and order of accuracy of the numerical technique used,

  • the physical pipeline parameters; pipeline characteristics including length, diameter, wall thickness, and elevation profile,

  • fluid properties; viscosity, reference mass density, bulk modulus and temperature modulus data and

  • instrumentation; the values of measured process variables such as temperature, pressure, density and flow rate, including time skew from data sampling.

Qualitative analyses of the uncertainties introduced by the variables in th8s8 four areas are done for three different volume balance methods:

  • volume balance with no linepack correction,

  • volume balance with linepack correction using a single, representative fluid and

  • volume balance with linepack correction using on-line fluid property measurements and real-time batch tracking.

These qualitative analyses are presented in sections 2, 3 and 4 for volume balance methods (i), (ii) and (iii), respectively. Methods of identifying and minimizing these errors are discussed in section 5.

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