A Transient Flow Analysis of a Real System

Abstract

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. This paper was prepared for the 49th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Houston, Texas, Oct. 6–9, 1974. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Introduction The Transient Problem In the past, gas transmission systems have been built with little consideration for system dynamics. All that was necessary for a satisfactory design was to determine line size and compressor horsepower required to move the gas using steady-state conditions. As system loads increase and deliverability becomes more dependent upon installed horsepower, the planning for transient flow is mandatory. This planning for transient flow is mandatory. This has been the case with the Exxon Gas System, an intrastate transmission system serving the industrial markets in the Texas Gulf Coast and the northeast Texas areas. An unexpected compressor station shutdown can cause pressure transients at the source gas plant that are potentially damaging. Sudden changes in plant potentially damaging. Sudden changes in plant pressure and flow can cause severe process pressure and flow can cause severe process instability resulting in vessel overpressuring, flaring, and even total plant shutdown unless preventive measures are taken. preventive measures are taken. Transient flow studies have been made with each new compressor addition to the Exxon Gas System. A primary objective has been to quantify the transient effects of various compressor upsets on the King Ranch Gas Plant, the major supply source, to determine the rate, magnitude, and duration of plant tailgate pressure changes. These calculations have been pressure changes. These calculations have been used to develop corrective procedures for operating personnel to use when compressors shut down. This paper will encompass three major areas:method of analysis,comparison of model to actual data, andresults of a simple case study. Description of the Exxon Gas System The Exxon Gas System is an intrastate gas transmission system with approximately 60,000 hp at nine compressor stations. It transports gas from Exxon-operated gas plants to industrial customers on the Texas Gulf Coast and northeast Texas areas (see Fig. 1). The system consists of 200 miles of parallel 30- and 36-in lines from the King Ranch Gas Plant in south Texas to the Houston metropolitan area. From Houston eastward 90 miles to Beaumont, there is a 30-in. line, and from Houston northward to the Longview area a 26, 20-in. combination line. The parallel 30–36-in. lines from the King Ranch Gas Plant to the Houston area is referred to as the mainline and is the segment of interest for this study. It is powered by three remotely operated compressor stations, each consisting of approximately 12,000 BHP.