PR-015-08605-R02 Assessment of Orifice Meter Flow Measurements with Low Differential Pressures

Abstract

Measurement of natural gas flow with an orifice meter is a well-established methodology; however, orifice measurement accuracy is of concern when flow rates are low and the differential pressure (DP) across the orifice is at the extreme low end of common DP transmitter ranges. This research evaluated the performance of multiple types of transmitters in 10-inch and 4-inch orifice meter runs at differential pressures approaching 1 inch of water column (1� H2O), simulating low flow transmission meter stations and depleted production well stations. The results were analyzed to characterize and better understand the uncertainties and measurement errors associated with orifice meters operating with small bore diameters and low DPs. Transmitters tested included typical DP transmitters with stated accuracies of 0.1% of full scale, DP transmitters with stated accuracies as a percent of reading; and high-frequency-response DP transmitters. Data acquisition methods, transmitter technologies, and various calibrated measurement spans were studied for their potential to improve orifice meter accuracy at low DP conditions. This is an blinded report.