Evaluation of Two-Phase Steam Flow Through an Orifice

Abstract

ABSTRACT Proper management of steamflood projects requires accurate information about heat input to the petroleum reservoir. The first logical step toward obtaining this information is to meter the steam flow rate and quality directly at the injection wellhead. However, this is not an easy task. The need for reliable, cost effective wellhead steam metering methods has existed for many years. Recently, methods using an orifice or nozzle in series with a second device, such as a critical flow choke or densitometer, have been introduced for metering wellhead steam quality and flow rate. Although orifices are commonly used to monitor superheated or high quality saturated steam exiting an oil or gas-fired boiler, little is known about the reliability and accuracy of using orifice meters over the wide range of pressures, flow rates, and qualities that exist at injection wells. Of primary concern is whether or not there is a strong correlation between the pressure drop across the orifice and changes in steam quality and/or mass flow rate. The effects of two-phase flow regime on pressure drop are also important and must be considered. This paper presents results of field testing and evaluation of two-phase steam flow through an orifice over an extended range of flow rates, qualities, and pressures. Overall accuracy and reliability of orifice meter data are discussed and compared to published studies. An overview of the fundamental aspects of steam flow through an orifice is given and reasons for the variation in existing empirical correlations are discussed. Finally, the problems encountered when using an orifice or nozzle in conjunction with other metering devices to determine wellhead steam quality and flow rate are examined.