In 1989 Valero Energy Corporation and Stoner Associates, Inc. entered into a partnership to create an On-Line Modeling System for a large natural gas pipeline system in Texas. The On-Line Modeling System combines both real-time estimation of the current pipeline conditions and a predictive capability for near term future analysis. The original intent for installing the On-Line Modeling System was to extend the SCADA system into areas where no telemetry exists and to provide a continuous overview of the pipeline making it easier to operate. But the main reason for installing the On-Line Model was to use the current state of the pipeline as the starting point for predictive modeling. Predictive modeling provides the vehicle to identify market opportunities and to discover operating problems before they arise. The project encountered and solved all of the usual problems associated with installing an On-Line Model. However, during the implementation of the system, it became apparent that the real-time state estimation had a significant number of benefits that had not been considered, in this sense it became our "Diamond in the Rough". The benefits that have been identified to date include: Pinpoint false telemetry information and allow Gas Controllers to act upon model generated corrected data. Find anomalies in the pipeline and within stations (e.g. leaking check valves and flow restrictions). Identify inefficient compressor operations. Identify poor field operating practices (e.g. pinched valves). Locate faulty regulators that do not properly control the flow of gas. Provide Gas Control with a tool to determine when to run scrapers. Accurately determine ownership of gas within a pipeline owned by more than one company. Display the quality of gas within the pipeline to aid Gas Control with their decisions on operating the system. Minimize the bypassing of rich gas around gas plants. Provide accurate flow calculations and therefore eliminate the need for in-line flow meters. Provide Gas Control (using a Graphical Interface) with assistance in configuring stations. Compute operating costs. Compute any pipeline's gas capacity and determine its current usage of that capacity. Assist in operating the pipeline safely during field work. The purpose of this paper is to discuss how theValero On-Line System has evolved over the past six years to its current configuration. Where possible quantitative benefits of the System will be presented. The planned future of the On-Line System will also be presented.

Valero Pipeline System

Valero Transmission owns and operates the largest intrastate pipeline system in the State of Texas, Its 6000 miles of pipeline and three (3) billion cubic foot daily throughput are not large by major interstate standards, but the nature of its system and the many localized demands put upon it make for an extremely complicated pipeline to model. It is not a simple "from here to there" type of system.

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