Abstract

A recent field project [sponsored by APIGEC (Alberta Petroleum Industry Government Environmental Committee) assessed basic source characteristic assumptions relevant to modelling sour gas pipeline ruptures and well blowouts. This paper describes the project and conclusions. A 3.2 km, 168 mm diameter pipeline was ruptured 32 times under varied conditions. The experimental rupturing technique, the transient release rate, and the sensitivity to source configuration were evaluated. Parameters investigated included: overburden, windspeed, release angle, fracture length, rupture mode, and line pressure. A 7.1 km, 323 mm diameter pipeline was also ruptured. Results were photographically recorded. Analysis showed release rate simulations to be within experimental error; plume rise from vertical jets to be two to three times higher than present estimates; and a low level distributed line source or volume source to approximate most accurately a "worse case" pipeline rupture.

Introduction

In 1974, the Alberta Industry Government Sour Gas Environment Committee published a report on "Guidelines for Urban Development in Relation to the Sour Gas Industry". The recommendations, therein, resulted in legislation restricting both land subdivision in existing sour gas areas, and the placement of new sour gas facilities in relation to existing land developments.

From 1974 to February 1979, the H2S isopleth (a loci of points of equal ground-lever concentration) was utilized in administering the land development/sour gas policies. However, complications arose when the computer models developed eparately by industry and government were found to yield significantly different results.

The validity of basic assumptions and the accuracy of the different models were key items to be resolved to expedite the development of a workable land development/sour gas policy.

In July 1978, the Alberta Petroleum Industry Government Committee approved funding for two phases of a four-phase industry proposal to clarify and/or improve isopleth prediction techniques. Phase I investigated the sensitivity of input parameters for three computer models. Phase II2, discussed here, assessed basic source input parameter assumptions by means of a field verification program.

Plume rise (simulated release height), volume dilution (air entrainment) and rate of release were identified as some of the computer input parameters needing verification. The objectives were to:

  1. evaluate equipment and experimental techniques,

  2. record the source characteristics (plume rise, volume dilution) for pipeline ruptures by considering plume rise and volume dilution sensitivity to:

    • wind effects, using a tee release mechanism to obtain a consistent vertical jet source,

    • release angle-fractures initiated on top, side or bottom,

    • fracture length initiated, (3.05 m vs 0.61 m linear charge),

    • line pressure, (3450 kPa vs 6900 kPa),

    • overburden,

    • pipe diameter, (323 mm vs 168 mm), and

  3. obtaining measurement data with which to correlate data from existing transient release rate models.

Equipment and Experimental Technique

Test Sites

The test sites were located in the Waterton gas field in southwestern Alberta. The 3.2 km, 168 mm diameter test section was situated in a narrow mountain valley.

This content is only available via PDF.
You can access this article if you purchase or spend a download.