A field test of bare 2.375-in and insulated 4.500-in tubulars has been conducted using heat flux sensors and thermocouples to evaluate bare and insulated tubular performance, annulus heat transfer, and overall wellbore heat loss in a cooperative effort between Sandia National Laboratories and Husky oil operations, Ltd. The well is part of a steam flood pilot in the Aberfeldy Field near Lloydminster, Saskatchewan.
Insulation thermal conductivity was observed to vary by a factor of four between competing designs. Couplings and internal structures (e.g., centralizers) were seen to account for up to half the string heat loss Idth the annulus dry. For a wet annulus, the typical field case, steam generated at the hot couplings refluxed in the vented annulus and maintained the casing temperature constant at 212F at all points. Thus wellbore heat loss was 3–6 times higher than expected, the same opposite the highest and lowest quality insulated tubings and only 30–40 percent less than bare tubing.
Shutting-in the annulus increased the partial pressure and temperature of the steam in the annulus and increased the wellbore heat loss. Heat loss for a shut-in annulus with steam and nitrogen was about 5 times higher than for the wet r vented annulus (15–30 times higher than for a dry annulus and the most effective insulated tubing). Operating the well with the annulus shut-in and filled with liquid water and boiling at the couplings increased the casing temperature and heat loss still further.
Steamflood operators are using insulated tubing in an increasing number of steam injection wells to reduce heat loss or in some cases to protect low grade casing from excessive thermal stress. Wells in Canada the United States and Venezuela are now equipped with over 400,OOO feet of insulated tubing.
Sandia National Laboratories as part of Project DEEP STEAM, and Husky Oil Operations started this program in 1980. Husky drilled and operated the test well. Sandia instrumented the well, and performed the data analysis. Program supervision was shared.
The primary objectives of the program were (1) to evaluate commercially-available insulated tUbing under typical field conditions, and (2) to observe heat loss rates for better calibration of computer models used to estimate wellbore heat loss. In addition, we hoped to develop suitable instrumentation for steam inJection test wells; and to suggest improvements in insulated tubing manufacture and injection well operation. There are essentially no data in the literature on field performance ot insulated tUbing, and very limited data on bare tubing heat loss.l General Electric, at Tacoma, Washington, has evaluated several types of insulated tubing in Sandia's test tower.2 Their results showed that the heat loss is much higher at the coupling, and generally confirmed performance estimated from insulation properties. However, the test tower does not simulate all aspects of an actual injection well, nor can it be used to assess long term tubular reliability in the field.
Insulated tubing is at present considered to be cheaper and easier to operate than a downhole steam generator.