Simulation of episodic rainwater infiltration into fractured aquifers
Although one can readily observe infiltration of rainwater into rocks fractured by natural processes, getting a quantitative understanding of this process is challenging: observations made in physical experiments are rich and to date, have not been reproduced by numerical simulations. Even infiltration into single vertical fractures is intricate and non-linear unstable flow regimes have been documented (Nicholl and Glass, 2005). In porous fractured rocks, some of the infiltrating water spontaneously imbibes into the adjacent rock. How much, depends on time. It is therefore, difficult to assess the seepage fraction that reaches the groundwater table.
Fracture seepage is important because it controls aquifer recharge and groundwater contamination from the earth's surface by agents like fertilizer, pesticides or bacteria. Understanding this process also matters because it underpins the natural and engineered barrier concept that underpins the design of the high-level nuclear waste repository planned at Yucca Mountain, Nevada, USA. Consequently, fracture infiltration has been the subject of much research, but system simulation has largely been restricted to dual continuum models, which are not predictive (see Long and Ewing, 2004).
In this project, an alternative simulation approach will be used to simulate and better constrain fracture infiltration and its dynamics. We will use discrete representations of fractures and the rock matrix in a DFM approach (Matthai and Bazrafkan, 2013, Bazrafkan et al., 2014), and a hybrid finite-element, finite volume method to carry out the simulations. The aim is to quantify fracture seepage in idealised and realistic models, highlighting implications for the aforementioned processes and related engineering measures.
S. Bazrafkan, S.K. Matthai and J.E. Mindel, The Finite-element-centered Finite-Volume Discretization Method (FECFVM) for Multiphase Transport in Porous Media with Sharp Material Discontinuities. (EAGE) ECMOR XIV - 14th European Conference on the Mathematics of Oil Recovery. DOI: 10.3997/2214-4609.20141841, 17 p. (Sept. 2014).
Long, J. C. S. and Ewing, R. C., “Yucca Mountain: earth-science issues at a geologic repository for high-level nuclear waste.”Annual Review of Earth and Planetary Science 32, 263-401, doi: 10.1146/annurev.earth.32.092203.122444 (2004).
Nicholl, M. J. and Glass, R. J., “Infiltration into an Analog Fracture: Experimental Observations of Gravity-Driven Fingering.”Vadose Zone Journal 4, 1123-51 (2005).
Matthai, S. K., Bazr-Afkan, S., “Simulation of gas-oil-gravity drainage: comparison of the dual continuum with the discrete fracture and matrix approach.” 2nd EAGE Workshop on Naturally Fractured Reservoirs, Muscat, Oman, 8-12 December 2013.
Leader: Stephan Matthai
Staff: Giorgio Urso, Andrew Western
Students: Mohammad Sedhagat
Optimisation of resources and infrastructure
civil engineering; complex systems