SAGD Vacuum Insulated Tubing vs. Bare Tubing – Concentric and Eccentric Configurations: A Comparative Thermal Computational Fluid Dynamics Study

Abstract

In a typical injector string in SAGD operation, steam is injected through tubing placed inside a casing. Heat losses through the string and casing can result in lower quality steam being injected into the formation, and hence reduce the productivity of a SAGD operation. An ideal SAGD operation would be one where no heat losses happen inside the tubing and all the latent heat is released inside the formation to heat up the heavy oil. Several methods have been used to reduce heat losses in the injector tubing. One of the methods is the usage of a vacuum insulated tubing (VIT) placed inside the casing. VIT consists of specially manufactured tubing with a getter coating to maintain vacuum between ID and the OD of the tube. This helps in preventing heat losses compared to normal bare steel tubing. In an effort to demonstrate the benefits of VIT compared to bare tubing injector string, a comparative 3D Computational Fluid Dynamics (CFD) study was carried out. The objective of the study is to provide a comparison of heat loss in both VIT and bare tubing concentric and eccentric configurations. The simulation accounts for frictional and heat losses throughout the tubing and most importantly, condensation of steam inside the tubing as result of heat loss. The consideration of condensation inside the tubing is a critical component of the simulation as it in turn affects the heat loss through the tubing. The other significant aspect of the study is the consideration of eccentric and concentric placement of tubing string inside the casing and its effect on heat loss. This study uses an Euler-Euler Multiphase flow based approach which accounts for the fluid-fluid interactions such as drag, turbulent dispersion etc. between steam and water inside the tubing. The thermal phase change model in ANSYS CFD accounts for the condensation of steam into water. The computed results successfully demonstrate the benefits of vacuum insulated tubing over bare tubing in maintaining steam quality in the vertical section of the wellbore. Also, the study shows reduction in steam quality for eccentric position of the bare tubing compared to concentric position. Most importantly this study demonstrates the capability of CFD to solve industrial scale complex problems and provide engineers with an insight into some of the challenging physics associated with a SAGD operation in the field.

A Review of Research Status and Prospect of Vacuum Insulated Tubing Insulation System

“…In comparing concentric and eccentric configurations of VIT and bare tubing, ANSYS Canada and ZEroCor Pipeline Company studied three different formation temperatures (253.15K, 313.15K and 423.15K), two different tubing types (bare tubing and VIT tubing) and two different tubing configurations (concentric tubing and eccentric tubing). 12 simulations of were carried out [23]. On the other hand, the steam quality of VIT tubing is minimized at different formation temperatures.…”

A CFD study of steam injection tubing heat losses

“…• Input (x = 0 in Figure 4): steam injection rate q in = 1.2 kg/s and 3.3 kg/s [39], steam temperature T in = 595.59 o C [32], steam quality φ in = 80% [8]; • Output (x = L in Figure 4): steam pressure P out = 11.7 MPa [37]; and • External border (y = well radius in Figure 3):…”

“…In addition, the gas blanket is stagnant and does not present heat transfer by convection. The tubing inner diameter d ic is 7.6 cm (2.99 in); the casing inner diameter d ir is 22.6 cm (8.9 in) [39]. In this study, the cemented region between the casing outer surface and the wall of the drilled well is not included in the analysis.…”

“…It can be observed from Figure 6 that the most refined meshes did not show sufficient discrepancy with the Table 3. Materials properties [39,40].…”

Heat Transfer Modeling of Wellbore with Vacuum-Insulated-Tubing (VIT)

“…Over the past three decades, VIT has proven to be an effective thermal isolation management tool in increasingly challenging environments, including deepwater challenges, steam challenges, and onshore challenges (Purdy and Cheyne 1991;Azzola et al 2007;Bradford et al 2004;Ellis et al 2004;Ellis et al 2004;Ferreira et al 2012;Li et al 2010;Singh et al 2007;Pattillo et al 2004;Lively 2002;Feeney 1999;Karra et al 2014;Kutzak and Gunn 1989;Nowinka et al 2005;Gonzales and Bajwa 2010).…”