Thaw-Front Dynamics of Super-Insulated Wells in Cold Environments
Abstract/Contents
- Abstract
- Steam injection is often used to recover heavy oil. In cold environments such as the Arctic, wellbore heat losses from the steam to the surrounding rock thaw permafrost and then damage the well. Therefore, it is indispensable to insulate the well. Amongst the various insulation techniques, the use of fibrous insulations is attractive due to cost and versatility. An analytical and numerical model based on a well configuration using various insulation layers was developed to calculate wellbore heat losses, wellbore temperature and permafrost temperature. Well failure/stability was inferred from the study of thaw-front propagation. Different processes were simulated: one modeling an injector well with constant fluid temperature and the other a well used for cyclic steam injection. A key parameter is the insulation thermal conductivity, a datum often inaccurately or only partially given by the manufacturers. Our companion experimental investigation determined thermal conductivity versus temperature of various materials. Measurements use heat-flux sensors and thermal conductivity is assumed to be a linear function of temperature. A simplistic qualitative experimental study simulating mechanical stress due to thermal cycles was also conducted. The materials tested were white and black aerogels (silica based substance composed of 90- 99.8% air), fiberglass, thermolastic insulation, and carbon fibers. Experiments show a reasonable agreement of thermal conductivity with literature values at ambient temperature. Aerogels (0.012 – 0.025 W.m-1.K-1) are half as conductive as fiberglass (0.03 – 0.045 W.m-1.K-1) and three to four times less conductive than thermolastic insulation and carbon fibers (0.04 – 0.067 W.m-1.K-1) for temperatures between 40°C and 140°C. Moreover, aerogels and carbon fibers have good mechanical resistance in comparison to fiberglass. The wellbore heat loss and thaw-front propagation model indicates that aerogels alone or aerogels associated with more conductive insulation meet the requirements to avoid well failure, even for very high temperature fluids and long periods of hot fluid injection. Thus, in combination with active subcooling of the permafrost, aerogels appear to provide effective thermal insulation to insure the integrity of permafrost. Although aerogel insulations alone they are not as effective as active refrigeration, their moderate cost and their ease of use encourage further investigation.
Description
| Type of resource | text |
|---|---|
| Date created | June 2007 |
Creators/Contributors
| Author | Marques, Cristovao |
|---|---|
| Primary advisor | Kovscek, Anthony R. |
| Advisor | Castanier, Louis M. |
| Degree granting institution | Stanford University, Department of Energy Resources Engineering |
Subjects
| Subject | School of Earth Energy & Environmental Sciences |
|---|---|
| Genre | Thesis |
Bibliographic information
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Preferred citation
- Preferred Citation
- Marques, Cristovao. (2007). Thaw-Front Dynamics of Super-Insulated Wells in Cold Environments. Stanford Digital Repository. Available at: https://purl.stanford.edu/cy080rh3308
Collection
Master's Theses, Doerr School of Sustainability
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