Hydraulic Conductivity Characterisation and Effects of Scale in Fractured Rock. James R. Kunkel

Transcription

1 Hydraulic Conductivity Characterisation and Effects of Scale in Fractured Rock James R. Kunkel

2 Outline Hydraulic Conductivity Measurement Scale of Hydraulic Conductivity Conclusions Questions 2

3 Hydraulic Conductivity Measurement Methods Source: USEPA, 1998 and 2001; Burbey and Murdoch, 2010 and Burbey et al.,

4 Hydraulic Conductivity Measurement Scale of Measurement 4

5 Hydraulic Conductivity Measurement Fractured Rock Characterization Issues LEGEND CFZ = Conductive Fractures Zone PFN = Primary Fracture Network SFN = Secondary Fracture Network HSFN = Horizontal Fractures of SFN VSFN = Subvertical Fractures of SFN K x = Hydraulic Conductivity in x-type of fracture/material S x = Storativity in x-type of fracture/material After Maréchal, Dewandel and Subrahmanyam,

6 Depth (m-bgs) Hydraulic Conductivity Measurement E E E-05 Hydraulic Conductivity (cm/s) Lugeon Tests (Various Fractured Rock Types) Marmato Mine, Colombia 1.00E-06 Dacite Porphyry (P1*) Dacite Porphyry (P2) Andesite Porphyry (P4*) Diorite Porphyry Schist Unidentified Dacite Porphyry (P1) Basalt Linear (Trend) 1.00E-07 6

7 Normalized Head Normalized Head Normalized Head Hydraulic Conductivity Measurement Time (sec) Falling Head Tests (Fractured Gneiss) Edgar Experimental Mine, Colorado USA (GEGN 581) 7

8 Hydraulic Conductivity (m/s) Depth (mbgs) Depth (mbgs) Hydraulic Conductivity Measurement E E E E E E-05 Hydraulic Conductivity (m/s) Seismic Velocity (m/s) 1.00E E-05 Downhole Seismic Surveys Source: Urban and Pasquarell, E Seismic Velocity (m/s) 8

9 Drawdown (ft) Hydraulic Conductivity Measurement 100 Pumping Tests (Fractured Basalt) Source: Paschis, Kunkel and Koenig, Time Since Pumping Started (min) Pumping Well Y-2 Observation Well Y-1 Observation Well T-1 Observation Well T-2 Observation Well T-3 9

10 Hydraulic Conductivity Measurement Tracer Test (Fractured Basalt) Source: Kunkel and Way,

11 INCREASING SCALE Hydraulic Conductivity Measurement Scale of Hydraulic Conductivity by Measurement Method METHOD LABORATORY TESTING SLUG/LUGEON TESTS BOREHOLE GEOPHYSICS DOWNHOLE SEISMIC SURVEYS STRAIN-DEFORMATION SURVEYS PUMPING TESTS TRACER TESTS COMPUTER MODELS 11

12 Scale of Hydraulic Conductivity What is SCALE? Source: Kunkel, Way and McKee, 1988 REV = Representative Elementary Volume (of fractured rock) 12

13 Scale of Hydraulic Conductivity What is SCALE? A common scale measure is distance (m) Valid for dispersivity and perhaps storativity A better scale measure for K is volume (m 3 ) Volume measures eliminate the issues of length between field and laboratory testing for slug tests vs. laboratory core test Source: Schulze-Makuch and Cherkauer,

14 Scale of Hydraulic Conductivity PFN = Primary Fracture Network SFN = Secondary Fracture Network Source: Maréchal, Dewandel and Subrahmanyam,

15 Scale of Hydraulic Conductivity Source: Schulze-Makuch and Cherkauer,

16 Scale of Hydraulic Conductivity Source: Kunkel, Way and McKee, 1988 C o n c e p t u a l l y K = al n where: K = hydraulic conductivity in appropriate units L = a characteristic length (volume) in appropriate units a = a fit parameter whose physical meaning is a measure of the medium-characteristic (log hydraulic conductivity of fractured rock, for example) n = the scale coefficient 16

17 Scale of Hydraulic Conductivity Scale as a Volume Formation Type Scale Coefficient n (1) Medium Characteristic a (2) L Lower Bound (3) L Upper Bound (3) Porous Flow >1 100,000 Fracture Flow < Double Porosity > (1) Average scale coefficient of all data. (2) Average medium-characteristic parameter given as log value (m/s) (3) Upper and lower bound of the average relationships in m 3 of tested formation Source: Schulze-Makuch and others,

18 Scale of Hydraulic Conductivity Marmato Mine, Colombia 18

19 Hydraulic Conductivity in Fractured Rock Characterisation and Scale Hydraulic conductivity measurement in fractured rock can include direct and indirect methods, as well as methods which measure at various scales The most common methods are direct measurement using pumping tests for far-field results and slug/lugeon tests for near-field results Hydraulic conductivity in fractured rock may involve identification of various flow boundaries, heterogeneities, and directional issues 19

20 Hydraulic Conductivity in Fractured Rock Characterisation and Scale Use the characterization method appropriate for the scale of the problem Typically, an order of magnitude change in the characteristic length scale results in about an order of magnitude change in hydraulic conductivity A REV may not exist if large-scale features such as fracture zones or barrier boundaries exist. Additionally, several REVs may be necessary to adequately characterize a mine site. 20

21 Hydraulic Conductivity in Fractured Rock FIN?? 21