The effects of a bimodal pore distribution on matrix diffusion in a fractured porous medium

Technical Report · Sat Aug 01 00:00:00 EDT 1987

OSTI ID:5916850

Tomasko, D

Three models are developed for predicting the concentration of a conservative (nonreactive) solute during transport through a fractured porous medium consisting of two materials with different physical properties. The materials are assumed to be arranged in series along the fracture, so that the advecting fluid sequentially passes through two different matrix environments. In all cases, the matrices are assumed to be infinite in a direction perpendicular to the orientation of the fracture. The first model predicts the time-dependent solute concentration using two one-dimensional transport equations for the fracture and two one-dimensional diffusion equations for the rock matrices. Longitudinal dispersion in the fracture is assumed to be negligible. The fracture equations are coupled by assuming a constant concentration at the boundary between the two materials, and the fractures are coupled to the matrices by appropriate flux terms. In the second model, the number of equations required to predict the concentration of the solute in the fracture is reduced by a factor of 2 by developing simple, analytic expressions for a single, effective porosity and matrix-diffusion coefficient. The third model incorporates longtitudinal dispersion in the fracture transport equations. This model was developed and used to investigate the effects of axial dispersion on the predicted concentrations and to determine when the simpler models are appropriate. Comprisons between the three models indicate that the predicted solute concentrations in a fracture for a constant source input are very similar except near the boundary between the two materials, where the maximum differences are approx.20%. Even better results are obtained when the duration of the injection is short compared to the total time of the test. 32 refs., 18 figs., 2 tabs.

• Research Organization: Sandia National Labs., Albuquerque, NM (USA)
• DOE Contract Number: AC04-76DP00789
• OSTI ID: 5916850
• Report Number(s): SAND-87-0265; ON: DE88000258
• Resource Relation: Other Information: Portions of this document are illegible in microfiche products. Original copy available until stock is exhausted
• Country of Publication: United States
• Language: English

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