Variable-aperture Fractures Research Articles

Two‐phase flow in a variable aperture fracture

In this paper a dynamic two‐dimensional two‐phase flow model for a single variable aperture fracture is developed. The model is based on a finite volume implementation of the cubic law and the conservation of mass for each liquid. The two‐phase fracture flow system is represented by incompressible parallel plate flow within two‐dimensional subregions of constant aperture. The fluid phase distribution is represented by an explicit definition of the phase presence at each location within the domain. To achieve this definition, a phase distribution is assigned to each fracture subregion. Knowledge of the phase distribution allows calculation of interface capillary pressure based on the fracture aperture. One‐dimensional analytic solutions for two‐phase flow are developed and used to verify the model's behavior in one dimension. The model is verified against the Sandia Waste‐Isolation Flow and Transport III model for the case of two‐dimensional single‐phase flow. Two‐dimensional two‐phase flow verification is performed qualitatively because no suitable analytic or physical model is currently available. Two‐dimensional flow phenomena are investigated for variable aperture fractures generated using geostatistical methods. Results from these simulations illustrate the flow processes of phase isolation, pinching off of nonwetting phase globules, nonwetting phase refusal at the edges of tight regions, and downslope migration of a fluid countercurrent to flow of a less dense fluid.

Variable-aperture fracture network model for flow and transport in fractured rocks at different scales : Nordqvist, AW; Tang, YW; Tang, CF; Dverstorp B. Andersson J. Proc Conference on Fractured and Jointed Rock Masses, Lake Tahoe, 3–5 June 1992P579–586. Publ California; Lawrence Berkeley Laboratory, 1992

Variable-aperture fracture network model for flow and transport in fractured rocks at different scales : Nordqvist, AW; Tang, YW; Tang, CF; Dverstorp B. Andersson J. Proc Conference on Fractured and Jointed Rock Masses, Lake Tahoe, 3–5 June 1992P579–586. Publ California; Lawrence Berkeley Laboratory, 1992

Variable aperture fracture network model for flow and transport in fractured rocks : Nordqvist, A W; Tsang, Y W; Tsang, C F; Dverstorp, B; Andersson, J Water Resour ResV28, N6, June 1992, P1703–1713

Variable aperture fracture network model for flow and transport in fractured rocks : Nordqvist, A W; Tsang, Y W; Tsang, C F; Dverstorp, B; Andersson, J Water Resour ResV28, N6, June 1992, P1703–1713

Permeability and dispersivity of variable-aperture fracture systems : Tsang, Y W; Tsang, C F Proc 1st Annual Topical Meeting on High Level Radioactive Waste Management, Las Vegas, 8–12 April 1990V1, P544–550. Publ ANS/ASCE: La Grange Park, 1990

A number of recent experiments have pointed out the need of including the effects of aperture variation within each fracture in predicting flow and transport properties of fractured media. This paper introduces a new approach in which medium properties, such as the permeability to flow and dispersivity in tracer transport, are correlated to only three statistical parameters describing the fracture aperture probability distribution and the aperture spatial correlation. We demonstrate how saturated permeability and relative permeabilities for flow, as well as dispersion for solute transport in fractures may be calculated. We are in the process of examining the applicability of these concepts to field problems. Results from the evaluation and analysis of the recent Stripa-3D field data are presented.

A variable aperture fracture network model for flow and transport in fractured rocks

A three‐dimensional variable aperture fracture network model for flow and transport in fractured rocks was developed. The model generates both the network of fractures and the variable aperture distribution of individual fractures in the network. Before solving for the flow and transport of the whole network, a library of single‐fracture permeabilities and particle transport residence time spectra is first established. The spatially varying aperture field within an individual fracture plane is constructed by geostatistical methods. Then the flow pattern, the fracture transmissivity, and the residence times for transport of particles through each fracture are calculated. The library of transmissivities and frequency distributions of residence times is used for all fractures in the network by a random selection procedure. The solution of flow through the fracture network and the particle‐tracking calculation of solute transport for the whole network are derived from one side of the network to the other. The model thus developed can handle flow and transport from the single‐fracture scale to the multiple‐fracture scale. The single‐fracture part of the model is consistent with earlier laboratory tests and field observations. The multiple‐fracture aspect of the model was verified in the constant aperture fracture limit with an earlier code. The simulated breakthrough curves obtained from the model display dispersion on two different scales as has been reported from field experiments.

Hydrological characterization of variable-aperture fractures : Tsang, Y W; Tsang, C F Proc International Symposium on Rock Joints, Loen, 4–6 June 1990P423–431. Publ Rotterdam: A A Balkema, 1990

Hydrological characterization of variable-aperture fractures : Tsang, Y W; Tsang, C F Proc International Symposium on Rock Joints, Loen, 4–6 June 1990P423–431. Publ Rotterdam: A A Balkema, 1990

Comment on “Flow and tracer transport in a single fracture: A stochastic model and its relation to some field observations” by L. Moreno et al.

This paper briefly comments on a previous paper written on the use of a solute transport model in a variable-aperture planar fracture. The authors present evidence to demonstrate that this model is not very accurate for field application and give examples of errors induced by the application of the node-to-node routing scheme. While this may be appropriate when these fractures are part of a network of discrete fractures, it only allows movement along the lines connecting nodes. The paper goes on to make recommendations of other solute transport models which are more applicable to fracture flow analysis.