Tapered-Bean Steam Chokes Revisited

Abstract

Controlling and monitoring flow rates at continuous and cyclic steam 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-inch outer diameter (O.D.) by 6-inch long bean with 6° tapered-bore inserted in a 2-inch O.D. 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 cost-cutting 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 taperedbean lengths are presented. A modified Thornhill-Craver flow rate equation is provided for critical and subcritical flow regions. Calculated and measured rates are compared and their relative uncertainties are assessed.