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Stang er Brune site
The Stang er Brune experimental site consists of 4 unscreened boreholes: B1 borehole (83 m deep), B2 and B3 boreholes (100 m deep) and F22 borehole (70 m deep). B1, B2 and B3 form a triangle within the radius of 10 m and F22 is 30 m from this triangle (Figure 3.5). The boreholes B1, B2 and B3 were drilled by the University of Birmingham during the European project ALIANCE in collaboration with the University of Montpellier. The objective was to develop an experimental site in fractured rock. The upper part of the boreholes is in mica-schists, while below 30 − 40 m is granite. All boreholes are open below 24 m. Several studies were conducted at the site in order to characterize connected fracture networks.
Ploemeur field site
Le Borgne et al. [2007] used borehole geophysical measurements along with single- and cross-borehole flowmeter tests in order to characterize flowing frac-tures that intersect the boreholes and identify those that are hydraulically con-nected. Each borehole was found to be intersected by 3 −5 flowing fractures with overall hydraulic transmissivities on the order of 10−3 m2/s over the borehole length. The cluster of fracture connected all over the site is composed of several of these fractures Le Borgne et al. [2007].
Vertical borehole flow velocities, measured at all boreholes under the ambient and pumping conditions, and caliper logs are presented in Figure 3.6 (B1), Fig-ure 3.7 (B2) and (Figure 3.8 (B3). For each borehole we measured an ambient vertical upward flow of 0.2 − 5 L/min. Pumping flowmeter profiles were mea-sured for 2 different flowrates using heat-pulse flowmeter and impeller flowmeter [Le Borgne et al., 2007; Paillet, 2004]. Using flow model, presented in Chapter 2, we interpret these data to infer transmissivities of fractures intersecting the borehole. Results are presented in Table 3.11. Moreover, step-drawdown single packer tests, performed for some borehole intervals in the site [Le Borgne et al., 2007], were also interpreted in terms of fracture transmissivity and reported in Table 3.11. Step-drawdown tests were analyzed by applying Bierschenk & Wilson method based on Jacob’s equation [Clark, 1977]. Finally, all estimations are in a relatively good agreement.
Figure 3.6: Flowmeter and caliper logs in B1. (a) Ambient vertical velocity (positive values correspond to upward flow), (b) vertical velocity measured while pumping in the cased part of the well at a rate of 19 l/min. The steady state drawdown observed was 55 cm, (c) vertical velocity measured while pumping in the cased part of the well at a rate of 82 l/min. The steady state drawdown observed was 6.76 m and (d) caliper log.
Figure 3.7: Flowmeter and caliper logs in B2. (a) Ambient vertical velocity (positive values correspond to upward flow), (b) vertical velocity measured while pumping in the cased part of the well at a rate of 42 l/min. The steady state drawdown observed was 21 cm, (c) vertical velocity measured while pumping in the cased part of the well at a rate of 140 l/min. The steady state drawdown observed was 1.9 m and (d) caliper log.
Figure 3.8: Flowmeter and caliper logs in B3. (a) Ambient vertical velocity (positive values correspond to upward flow), (b) vertical velocity measured while pumping in the cased part of the well at a rate of 19 l/min. The steady state drawdown observed was 3 cm, (c) vertical velocity measured while pumping in the cased part of the well at a rate of 145 l/min. The steady state drawdown observed was 63 cm and (d) caliper log.
Figure 3.9: Extracts of the migrated multioffset single-hole GPR sections of B1 and B2 with superimposed interpretations of tracer pathways fromDorn et al. [2012]. Red circles indicate the tracer injection points, while red and blue arrow-heads locate saline and unaffected groundwater inflow into the pumping bore-hole, respectively. Light red regions highlight fractures through which the in-jected tracer is interpreted to move, whereas blue regions highlight reflections from other boreholes. Light blue letters refer to transmissive fractures identified in the boreholes using optical logs and flowmeter tests with corresponding blue lines indicating their corresponding dips [Le Borgne et al., 2007]. (d) Dip angles corresponding to the axis aspect ratio r : z of 2 : 1 [Dorn et al., 2012](Appendix1).
These tracer tests were mainly conducted with injection taking place in B1-2 (50.9 m depth) and B1-4 (78.7 m depth) fractures [Le Borgne et al., 2007]. Figure 3.10 shows the optical images of these fractures, obtained by Montpelier University.
Figure 3.10: Optical images of B1-2 (50.9 m depth) and B1-4 (78.7 m depth) fractures [Le Borgne et al., 2007].
Analysis of thermal properties
In this thesis temperature data were used to characterize fracture hydraulic prop-erties. In order to reduce uncertainty we performed laboratory measurements of the specific heat, thermal diffusivity and bulk density of the rock. The B1 bore-hole at the Stang er Brune field site have been fully cored. Thus, thermal analysis were conducted on the core samples. 10 samples were chosen, including 3 sam-ples in mica-schists and 7 samples in granite. Table 3.11 synthesizes the obtained results. According to this analysis the mean bulk density, thermal diffusivity, spe-cific heat and thermal conductivity can be given as followings: ρm = 2520 kg/m3, ρg = 2470 kg/m3, αm = 1.4 • 10−6 m2/s, αg = 1.8 • 10−6 m2/s, cm = cg = 738 J/kgK, λm = 2.59 W/mK, λg = 3.31 W/mK.
Table of contents :
1 General introduction
1.1 Flow in fractured media
1.1.1 Single fracture
1.1.2 Fracture networks
1.2 Transport in fractured media
1.3 Flow and transport modeling in fractured media
1.4 Imaging of hydraulic and transport properties of fractured media
1.4.1 Hydraulic tomography
1.4.2 Flowmeter tests
1.4.2.1 Single-borehole flowmeter test
1.4.2.2 Cross- borehole flowmeter test
1.4.3 Temperature
1.4.3.1 Heat tracer test
1.5 Approaches proposed in thesis
2 Inverse framework for flow tomography experiment
2.1 Introduction
2.2 Paper: Inverse modelling of flow tomography experiments in fractured media (Klepikova et al., submitted for possible publication in Water Resources Research)
2.3 Conclusions
3 Ploemeur field site
3.1 Introduction
3.2 Site localization
3.3 Hydrogeological context
3.4 Stang er Brune site
3.4.1 Analysis of thermal properties
3.5 Conclusions
4 Using borehole temperature profiles to estimate borehole flow velocities
4.1 Introduction
4.2 Paper: A methodology for using borehole temperature-depth profiles under ambient, single and cross-borehole pumping conditions to estimate fracture hydraulic properties (Klepikova et al., Journal of Hydrology, 2011)
4.3 Conclusions
5 Temperature tomography experiment in fractured media
5.1 Introduction
5.2 Paper: Temperature tomography experiment in fractured media (Klepikova et al., in preparation)
5.3 Conclusions
6 Heat and solute transport in fractured media
6.1 Introduction
6.2 Heat transport: numerical modeling
6.2.1 Sensitivity analysis
6.2.1.1 Sensitivity of temperature recovery to push time
6.2.1.2 Sensitivity of temperature recovery to flow rate and geometry
6.2.1.3 Sensitivity of temperature recovery to the fracture aperture
6.3 Heat transport: push-pull heat tracer tests
6.4 Discussion and Conclusions
7 Conclusions and perspectives
7.1 Conclusions
7.2 Perspectives
7.2.1 Tomography approaches
7.2.2 Temperature and flow heterogeneity
7.2.3 Heat as a tracer .
