Predicting Wet-Steam Flow Regime in Horizontal Pipes

Abstract

Summary Knowing or predicting the flow regime for a wet steam flowing in asteam-distributing network is important to the engineering, management, andeconomics of steamflood EOR projects. The flow-regime data of steam inhorizontal pipes were compiled and analyzed with Taitel and Dukler's model ofpredicting flow regimes for two-phase flow. These data were used to constructsteam flow charts, to determine the effect of operating variables on thetransitions of flow regimes, and to establish transition criteria for steamflow in horizontal pipes. Introduction All steam EOR projects involve a steam-distribution system. Most steam usedin oilfield steam stimulation and steamflood operations is a wet steam, withvarious levels of quality. It is classified as a two-phase fluid. Many aspectsof two-phase flow behavior - such as frictional pressure loss, liquid holdup, and phase splitting at piping tees - are affected by the flow regime existingin the distribution system. Predicting the flow regime is important to theefficient and effective operation of oil recovery projects. However, the flowregimes are much more complicated for two-phase fluids. To date, no method orchart has been published specifically for the prediction of wet-steam flowregimes. This problem can be addressed either through experiments or byadapting a general flow-regime prediction technique developed for two-phaseflow. The latter approach is used in this study. After several techniques 1–3for predicting flow regimes of two-phase flow were reviewed and compared, Taitel and Dukler's Model was selected for steam flow. The flow regimes of wetsteam flowing in horizontal pipes are presented here. To facilitate thecomputation of the flow regimes, a two-phase-flow computer program based onTaitel and Dukler's model was used. These flow-regime data are then used toconstruct steam flow charts, to determine the effect of steam quality andoperating variables on flow-regime transitions, and to establish criteria forthese transitions. This study covers steam pressure ranging from 200 to 2,000psia [1.38 to 13.8 MPa]; steam quality, from 2 to 90%; pipe size, from 2 to 24in. [5 to 61 cm] (Schedule 80); and steam flow rate, from 50 to 620,000 B/D [8to 98 600 m3 /d] cold water equivalent (CWE). A pipe roughness of 0.001 in.[0.025 mm] was used for all pipes except where specified. Steam properties arebased on those listed in the steam tables. Taitel and Dukler's Theoretical Model Taitel and Dukler classified horizontal two-phase flow into five flowregimes: stratified smooth. stratified wavy, intermittent, annular, anddispersed bubble (Fig. 1). In stratified smooth flow, the liquid phase flowsalong the bottom of the pipe, the gas phase flows along the top, and theinterface is smooth. In stratified wavy flow, the two phases are separated inthe same manner, except the interface is wavy. In intermittent flow, the liquidphase in the pipe is distributed nonuniformly along the flow direction. Plugsor slugs of liquid are separated by gas bubbles or vice versa. In annular flow, sometimes also called annular dispersed or annular/mist flow. the liquid phaseflows as a film on the pipe wall surrounding a core of high-velocity gas phasecontaining various degrees of entrained liquid. Finally, in dispersed bubbleflow, the gas phase is distributed as discrete bubbles within a continuousliquid phase. Using physical mechanisms associated with the instability of asolitary wave, Taitel and Dukler developed a theoretical and empirical model topredict the transitions between flow regimes and presented those regimes in theform of a flow-regime map (Fig. 2).