On some remarkable observations of laboratory dispersion using computed tomography
- Texas A&M Univ., College Station, TX (United States)
This work re-examines the applicability of Fickian dispersion theory to predict tracer performance in Berea sandstone core samples. Elution history and mixing zone growth behavior are examined. The mixing zone data is obtained from CT experiments. CT has the unique ability to visualize fluid flow within a sample without disturbing displacement progress. Fickian dispersion laws predict a mixing zone which growns with the square root of time. This type of behavior has been observed in bead and sand pack experiments. The analysis shows the effluent history data from Berea sandstone agree well with Fickian dispersion theory; however, the mixing zone data do not agree with Fickian predictions. The mixing zone is shown to grow more nearly proportional to time, indicating non-Fickian flow. Although the Berea sandstone is relatively homogeneous, CT measurements reveal that small scale permeability contrasts which follow a nearly Gaussian distribution may be responsible for this non-Fickian mixing zone growth. These results show that elution history data is non-unique to the dispersion mechanism and non-Fickian flow can produce elution history data which is representative of an indistinguishable from Fickian flow. To provide a deeper understanding, the authors propose a new, more general dispersion model that includes Fickian and non-Fickian dispersion caused by spatial permeability variations. The permeability heterogeneity is described by applying probability density functions. Analytical solutions are developed. The new model is shown to correctly predict and explain the Berea sandstone tracer behavior. This agreement confirms that flow in Berea sandstone at the laboratory scale is indeed non-Fickian. The authors demonstrate that the applicable dispersion mechanism cannot be positively identified by observing only elution history data, more correctly, mixing zone data is also needed. The analyses leads to a new and improved understanding of dispersion in porous media.
- OSTI ID:
- 141369
- Report Number(s):
- CONF-930304-; TRN: 93:003688-1046
- Resource Relation:
- Conference: 205. American Chemical Society national meeting, Denver, CO (United States), 28 Mar - 2 Apr 1993; Other Information: PBD: 1993; Related Information: Is Part Of 205th ACS national meeting; PB: 1951 p.
- Country of Publication:
- United States
- Language:
- English
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