Real-time Transient ModeM For Batch Tracking, Line Balance And Leak Detection
Authors: Huber Dennis W. 
Published: March 2010

Project Summary

The Cochin Pipeline System was drawn together by Dome Petroleum Limited as joint-venture project, with Dome assuming responsibilities for design and engineering and now as pipeline operator. This 1900-mile, 12-inch-diameter pipeline traverses Canada and the U. S.A. to transport light hydrocarbon liquids such as ethylene, ethane and propane, in a multi-batch mode of operation. The Cochin System operates as a common carrier pipeline system under the jurisdiction of the National Energy Board in Canada and the Federal Energy Regulatory Commission in the United States of America. Ethane shipments were initiated in mid-1978. In October 1978, ethane and propane shipments commenced on an uninterrupted basis. Ethylene movements began with the first shipment to Dow"s facilities in Sarnia. Ontario in November 1979.

The batched system, with its compressible products and long transit distance has unique operating requirements for control, surveillance and measurement. Asa prime outcome, a computer based pipeline "model" or simulator has been installed in the central control office in Calgary, Alberta, to meet some of the requirements for on-line, real-time surveillance of the line. The resulting model is capable of determining pressure, temperature, density and flow profiles for the entire line and, thus, establishes for Cochin the ability to batch-track and perform line balance and leak detection on a mass format. This system is supported in Calgary by a multi-level, computer-based telecontrol system which provides the data gathering and handoff, the display function and the capability for control. Measurement in the field is facilitated with mass metering, which eases the task of custody transfer.

Currently, all systems are in operation and at various stages of final acceptance. Levels of monitoring and control are much improved over those achieved with previous systems similar to Cochin, and the potential for many future enhancements is quite evident.

Description of the Cochin Pipeline System

Figure 1 shows the geographic route of Cochin and the locations of the pump stations and laterals. The pipeline begins in Fort Saskatchewan, Alberta, traverses two provinces and seven states, and ends in Sarnia, Ontario, with several injection and delivery terminals along the route. The present pipeline network consists of thirty-three pumping/metering stations and nine injection/delivery points. The stations are at 51- to 65-mile spacings, depending on the hydraulic gradient required along the line, resulting in a total of thirteen stations being located m Canada and the remainder in the U.S.A.

Currently, the liquid ethylene, ethane and propane being shipped are serially batched through the pipeline, with each batch moving at an average daily flow rate in the vicinity of 4 mph (72,000 BPD) or greater. The pipeline has a maximum operating pressure of 1440 psig, with minimum operating pressures dependent on the various vapour pressures of each product and allowances for maintaining safe margins above these values.

A typical field installation consists of a centrifugal pump driven by a 2000-HP electric motor via a variable-speed fluid coupling. Pump speed is automatically adjusted by a programmable digital controller which directs a control signal on the variable-speed drive.