Abstract. Hydraulic properties and upscaling characteristics of low-permeability fractured rock are analyzed based on systematic well test data from three different measurement scales. First, tests are simulated in a large number of geological fracture network realizations, and the acceptable fracture transmissivity distribution parameters that produce the observed statistics of the two smallest measurement scales, i.e., 2-m and 10-m scales, are defined. Instead of a single value, a range of acceptable parameter values can be found to produce the observed result. Second, upscaling simulations are carried out with the calibrated networks. These indicate that the investigated system cannot be properly modeled by means of a continuum tensor presentation but would better be represented by means of "equivalent fracture" statistics. Third, the conductive characteristics of the calibrated 30-m network blocks are compared to well test results from the same scale. The results from this preliminary analysis indicate that onedimensional borehole observations interpreted with standard continuum-based methods may considerably underestimate the three-dimensional conductive characteristics of heterogeneous, noncontinuum fractured media. ]. The modeling approaches for field-scale fractured media can be divided into three basic categories: (1) deterministic porous medium approaches, (2) fracture network approaches, and (3) stochastic continuum approaches. As the relative significance of local heterogeneities decreases with increasing scale, the range of applicability of these approaches depends on the scale of interest. Because of computational constraints, fracture network models can usually be applied for a scale of at most a few hundreds of meters. In deterministic porous medium approaches the medium properties are assumed fixed and known; major fracture zones are imbedded deterministically, and the remaining part of the rock is assigned averaged properties. These approaches are applicable in the largest of scales when, for example, the effect of major fracture zones is investigated and the effect of local heterogeneities is not of interest. The range of applicability of the stochastic continuum approaches falls between these two, that is, scales too large for fracture network models but small enough so that heterogeneity of rock outside the major deterministic fracture zones is still of interest. The range of applicability of each approach, especially the transition from fracture network-based approaches to continuum-based approaches, also depends on the characteristics of the rock in question. Continuum behavior is more likely to occur in densely fractured, well-connected fracture networks with mixed fracture orientations than in sparsely fractured, poorly connected, and/or strongly anisotropic systems [e.g., Long et al., 1982].The support scale and the related conductivity statistics of stochastic continuum models can be determined either directly from hydraulic well test data or by means of fracture network modeling. In t...
We examine the possibility of using the flow dimension identified from constant pressure injection tests as a tool for characterizing the hydraulic conditions of fractured media. The data comes from a low-conductivity crystalline rock site, from depths of up to 450 m, and is obtained with 2 m and 10 m measurement scales. In the analysis, the general solution for n-dimensional flow by Barker (1988) is applied. The results show that the most prominent characteristics of the medium can be identified; that is, linear and sublinear flow dimensions as distinguished from dimensions higher than two. In many cases, however, there is significant difficulty in distinguishing the dimensions n = 2, 2.5, and 3 from each other. This is usually because of the experimental difficulties in achieving the ideal conditions required by the theory during the early part of the experiment. In such cases, a full flow curve is not available for the type-curve fitting. In the nonunique cases the higher dimensions typically correspond to higher, sometimes unrealistically high, values of specific storage and to the less reliable and less representative early part of the experiment. Therefore, most of the dimensions in categories n = 3 can be excluded, thus leaving the majority observations in the categories of n = 2 and n = 2-2.5. The dominance of dimension n = 2 is more pronounced for data related to fracture zones in comparison to that related to "average" rock, in particular in the 2 m scale data. The proportion of low (n < 1.5) flow dimensions is small, but for the 10 m scale data it is relatively higher at greater depths and corresponds to lower conductivities. For the smaller 2 m scale data, the low dimensions are not linked to greater depths or systematically smaller conductivities, giving preliminary indication of different flow dimension behavior for the two different scales.
Abstract. The water retention behaviour of partially saturated MX-80 bentonite with pure water is relatively well investigated. However, in practical cases, the water contains a number of chemical compounds which affects the bentonite behaviour. In particular, bentonite is used in buffer applications of geological repositories for spent nuclear fuel, where the concentration of total dissolved solids in groundwater is expected to increase significantly with time. This paper investigates water retention behaviour of MX-80 type bentonite partially saturated with deionised water as well as 1M NaCl solution. In the experiments the specific volume of bentonite has been kept approximately constant.
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