A New Method for Measuring Vented Gas

Abstract

Because of the necessity for taking regularly occurring open-flow tests inprorated high-pressure oil fields, much gas is turned to atmosphere by way ofvertical vent lines leading away from the oil and gas separator. In the past, measurement of such gas has been accomplished by several methods, usually byuse of the open-flow Pitot tube. The use of the closed-flow Pitot tube has beenavoided apparently chiefly because the ordinary vent-line hook-up makes itnecessary to apply the instrument closer to a bend, valve, or obstruction inthe pipe than is recommended by rules of good practice. The many advantages that would result from the application of the closed-flowPitot tube prompted investigation of the actual effect upon quantity rate offlow measurements computed from data obtained with the tube in a normal workingposition, which is closer to the tee at the base of the vent riser than isusually considered as giving highly accurate results. An effort was first madeto compare the results thus obtained to those under ideal conditions and athigh velocities. To make this comparison, knowledge of the characteristics of gas flowing atvery high velocities is essential. Research for such information indicated thatlittle or no work had been done that would give data necessary for such acomparison, therefore the problem was changed to a test designed to determinethe relationship between quantity rates of flow as measured by an orifice meterand a Pitot tube placed at the center of a pipe eight diameters from a tee orell at the base of a vent riser, through which gas is flowing under lowpressures at very high velocities. To determine this relationship, a series of tests was run on a number of 8-in.iron-pipe vent risers in which the Pitot tube data were taken at the positionas stated above. Gas from a wet-gas gathering system was passed through anorifice meter setting and thence to atmosphere by way of the vents. Data were taken simultaneously from the orifice meter and Pitot tube from whichcomputations for comparisons were made. The actual method of comparison isdiscussed later in this paper.