Controlling and monitoring steam injection into heavy oil reservoirs are important elements of heat management. Static chokes with tapered-bean inserts are the most reliable and cost-effective means of controlling wellhead steam injection rates. However, adjustable steam chokes are often used because 1. Rate changes can be made without interruption of steam supply to the well.2. An inventory of bean inserts is not required.Adjustable or multiple orifice valve (MOV) chokes have two disks, each with a pair of holes (orifices). The size of the choke opening is adjusted by rotating one disk causing the two pairs of holes on each disk to overlap by differing amounts. This paper presents the results of field tests conducted to assess the flow control and monitoring capability of MOV steam chokes. Topics include adjustment precision and reproducibility, critical and subcritical flow conditions, and comparison of calculated and measured flow rates.

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.

Controlling and monitoring flow rates at continuous-and 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 critical-and subcritical-flow regions. Calculated and measured rates are compared, and their relative uncertainties are assessed. *The basic gas-flow-rate equation for Thornhill-Craver chokes was first published by Cook and Dotterweich (1946).