A study of flow-wetted surface area in a single fracture as a function of its hydraulic conductivity distribution

• Published in: Water resources research 2012-01, Vol.48 (1), p.W01508-n/a
• Main Authors: Larsson, Martin, Niemi, Auli, Tsang, Chin-Fu
• Format: Article
• Language: English
• Subjects: Channeling; Flow; flow wetted surface; Groundwater; Heterogeneity; Hydrology; Interfaces; Mass transport; particle tracking; Random variables; Rocks; single fracture; solute transport; Standard deviation
• ISSN: 0043-1397; 1944-7973; 1944-7973
• DOI: 10.1029/2011WR010686

The contact area between flowing water and rock—the flow‐wetted surface (FWS)—is a main factor controlling the rock‐matrix diffusion and sorption of flowing solute in a rock fracture. Flow channeling, therefore, has a strong effect on the retardation of mass transport due to the resulting lower contact area. This work presents a systematic study of the dependency between fracture aperture statistics and FWS in strongly heterogeneous fractures. Particle tracking is used to determine the transversal width of the particle flow lines, FWS, and β factor, where β is a variable that has been proposed as controlling tracer retention. The conductivity distribution over the fracture is assumed to be lognormal with standard deviation (σln K) ranging from 0.23 to 4.61, with correlation lengths from 2% to 18% of the width of the flow domain. Results show a clear dependency between the specific flow‐wetted surface (sFWS), defined as FWS divided by the total fracture area, and the standard deviation of the logarithm of fracture conductivity. The behavior is independent of the correlation length for the range of correlation lengths tested. The results are presented in the form of type curves and an empirical equation that provide a simple way to determine the sFWS as a function of σln K. This information can then be used to adjust the results of large‐scale fracture network simulations by taking into account the effect of single fracture heterogeneity, an effect that is in practice infeasible to directly take into account in large‐scale fracture network simulations. Key Points Fracture sFWS systematically decreases with increasing variance of conductivity Type curves are presented linking sFWS to standarad deviation of conductivity Results can be used to include heterogeneity in large‐scale fracture models