Tapered-Bean Steam Chokes Revisited

Abstract

This paper (SPE 144615) was accepted for presentation at the SPE Western North American Regional Meeting, Anchorage, 7–11 May 2011, and revised for publication. Original manuscript received for review 5 July 2011. Paper peer approved 31 August 2011. Summary Controlling and monitoring flow rates at continuousand cyclicsteam-injection wells are important elements of reservoir-heat management. For nearly 30 years, critical flow chokes have proven to be the most reliable and cost-effective means of controlling steam injection into heavy-oil reservoirs. Flow-control efficiency has been further improved with tapered-bore bean inserts to achieve critical flow, with only 10 to 15% pressure loss across the choke. For the past 10 years, the standard steam-choke assembly has consisted of a 1-in.-outer-diameter (OD) and 6-in.-long bean with a 6° tapered bore inserted inside a 2-in.-OD cage nipple or housing. Larger-diameter cage nipples and bean inserts have been required for steam-injection rates exceeding 500 B/D. More recently, a costcutting practice has been employed using shorter tapered beans inserted in standard choke assemblies. This paper presents the results of field tests conducted to evaluate the effectiveness of shorter tapered-bean length for controlling steam-injection rates. Transition from subcritical to critical flow and overall pressure loss for different tapered-bean lengths are presented. A modified Thornhill-Craver flow-rate equation is provided for criticaland subcritical-flow regions. Calculated and measured rates are compared, and their relative uncertainties are assessed.