Hot fluid injection and production operations require heat transfer between the hot fluids and adjacent wellbore areas (reservoir and upper layers). This results in heat loss to the surroundings as steam (or any hot fluid) moves through the pipelines from the surface to the bottom of the wellbore.
Calculating these losses is important when designing surface facilities and completing production systems. For the surface pipeline section, these values are determined under continuous or stationary flow conditions. For the internal section of the wellbore, losses are determined under semi-continuous or semi-stationary flow conditions.
There are four basic heat transfer mechanisms involved in hot fluid injection processes:
- Conduction through pipe walls on the journey from the steam generator to the wellhead.
- Radiation from the pipe network’s surface to the atmosphere.
- Conduction from the pipe’s outer surface through the surrounding air film.
- Convection by air movement, either natural (temperature difference), forced (wind), or both.
The rate of heat loss at the surface depends heavily upon the temperature difference between the hot fluid and surrounding air, atmospheric conditions (wind, velocity, etc.), surface line diameter and length, and type and thickness of insulation covering the lines.
Heat transfer mechanisms in the reservoir
When steam flows into the formation through the centralized injection tubing inside the casing, heat loss mechanisms and their quantification depend on the fluid in the annular space between the two.
If the injection tubing is not insulated, then the temperature outside the injection tubing will be approximately equal to the steam temperature. Heat transfer to the casing occurs by conduction, convection, and radiation when the annular space is filled with gas or even an insulating fluid.
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