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.

Monitoring the amount of steam distributed to individual injectors is an important part of steamflood management. For many years, attempts have been made to employ orifice meters at injectors to measure steam quality or rate. However, published orifice meter correlations for two-phase steam vary significantly. Of primary concern is whether or not there is a strong correlation between the pressure drop across the orifice plate and changes in steam quality and/or flow rate. It is also important to understand the impact of two-phase flow regime (e.g., slug flow, annular-mist flow, stratified flow, &) on pressure drop across the orifice plate and how it affects the reliability and accuracy of the orifice meter. This paper discusses the basic principles of steam flow through orifice meters and presents a straightforward analysis of the reliability and accuracy of orifice meters for measuring steam qualities or rates at injectors. Additionally, the problems encountered when using two orifice meters or orifice meter and critical flow choke in series to simultaneously measure injector steam quality and rate are examined. Introduction Orifice meters are commonly used to measure feedwater and fuel gas rates at steam generators because they are relatively inexpensive, durable, and, if installed properly, can provide accurate, reliable measurements.1 In addition, orifice meters are often used to measure generator output quality because they can withstand the requisite high pressures and temperatures. In this second application, the steam is considered to be "dry", with very little liquid volume present. Steam quality and rate can vary significantly throughout a steamflood project as the liquid and vapor phases are split through large, often complex piping systems. Because of the high cost of generating and supplying steam, monitoring rates and qualities at injectors is an integral part of the steamflood management process. Orifice meters have been installed at steam injectors to monitor rate or quality because they are relatively inexpensive and easy to install. Various empirical correlations have been developed to adapt orifice meters for 'wet’ or two-phase steam flow.2–5 However, the primary concern has always been the reliability and accuracy of orifice meters over the range of two-phase steam conditions at most steamflood injectors. In fact, a comprehensive evaluation of commonly used two-phase orifice meter correlations has shown them to be inadequate for the range of flow conditions present in typical steamflood projects.6 Despite these findings, some operating companies have continued to employ orifice meters for injector monitoring. Apparently, some confusion remains about the effectiveness of orifice meters for measuring steam rate or quality at injectors. The purpose of this paper is to reiterate the basic operating principles and guidelines for orifice meters and to clearly establish whether or not two-phase steam rate and quality measurements can be reliably and accurately obtained with orifice meters. Fundamental Concepts The orifice meter measures differential pressure across an opening or restriction as fluid flows through it. Other types of differential pressure flow meters include venturi tube, nozzles, segmental wedge, and V-cone. The main advantage of these types of meters is that they have no moving parts and can be constructed of materials that can withstand high operating temperatures and pressures. The main disadvantage is that they have a very limited flow rate range, typically around 3:1 or 4:1, create a permanent pressure loss and are sensitive to installation effects.7