Modeling of DNAPL migration, entrapment and dissolution in single and intersecting variable aperture fractures
2009 (English)In: Eos Trans. American Geophysical Union, 90(52), Fall Meet. Suppl.American Geophysical Union, Fall Meeting 2009, abstract #H13C-0964, 2009Conference paper (Other academic)
Predicting the dissolved mass flux generation that contributes to subsurface water contamination from dense non-aqueous phase liquids (DNAPLs) entrapped in highly heterogeneous fractured rocks is important yet challenging. How a DNAPL infiltrates and becomes entrapped within an individual fracture and within a fracture network formed by such fractures affects the subsequent dissolution and longevity of the DNAPL. As fracture networks are formed by fractures intersecting with each other, it is important to understand how the fracture intersections influence the DNAPL migration and entrapment. It is known from fundamental studies elsewhere that fracture intersections may have distinct hydraulic properties, and e.g. high permeability pathways can exist at the intersection. How this will influence a multiphase flow system is presently not understood and is addressed in the present study. Both individual single fractures and intersecting variable aperture fractures are considered. Log-normally distributed aperture fields with local fracture transmissivities following the cubic law for laminar flow are assumed and DNAPL migration, entrapment and dissolution are modeled. The effects of different hydraulic characteristics at fracture intersections are examined. Multiple realizations with different sets of aperture statistics and fracture inclination angles are considered. For the modeling iTOUGH2/T2VOC/ TMVOC codes are used.
Preliminary results suggest that the entrapment geometries of DNAPL in single heterogeneous fractures are highly sensitive to the statistics of the aperture field. Larger correlation length or standard deviation produces a wider range of total entrapped DNAPL volume in individual fractures. Modeling of different fracture inclination angles reveals that gravity plays an important role as well. Subsequent dissolution modeling shows that mass transfer will also be strongly influenced by the different DNAPL entrapment architectures corresponding to the different aperture correlation lengths and standard deviations. Based on the simulations with two intersecting factures remarkably different results are obtained for different properties (e.g. permeabilities and heterogeneity) of the intersections. Furthermore, understanding is gained concerning how the fracture intersections should be treated when upscaling DNAPL migration, entrapment and dissolution from single fracture scale to the scale of fracture networks. In the light of the modeling results a laboratory experimental design is also being carried out to investigate the issue of DNAPL entrapment and dissolution in fractures.
Place, publisher, year, edition, pages
Earth and Related Environmental Sciences
Research subject Hydrology
IdentifiersURN: urn:nbn:se:uu:diva-120406OAI: oai:DiVA.org:uu-120406DiVA: diva2:303287
American Geophysical Union, fall meeting 2009 14–18 December San Francisco, California, USA