Study of Subcritical Flow Through Multiple-Orifice Valves

Summary Increased oil and gas production from offshore areas and hostile environments has led to a greater use of multiple- orifice-valve (MOV) wellhead chokes. Unlike conventional wellhead chokes, MOV's can be adjusted to any given choke area while under pressure, allowing wells in remote locations to be controlled from a central site. Data on the behavior of multiphase flow through MOV chokes have not been available in the past. This study investigated high-pressure (400 to 800 psia [2.8 to 5.5 iMPa]), two-phase air/water flow through a 2-in. [5.1-cm] MOV choke. Single-phase air and water data were obtained to determine the valve-sizing coefficient, Cv. A correlating parameter was determined with two-phase data to predict the subcritical two-phase pressure drop. This parameter was found to be a function of the gas/liquid ratio, upstream pressure, and choke opening. A mathematical model based on experimental observations was developed to predict the subcritical pressure drop across the choke for single-phase liquid flow.