2010-12-17_REVISION - C1981019 (140)

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Model calibration D R A F T 4.3 Transient calibration 20 A transient calibration was performed on a sub-region of the regional model defined in the area of the pilot dewatering test by using the hydraulic response measured during the pilot test as a target. The pilot test caused a wide area of drawdown in the F/G sequence indicating that the coal seams are relatively permeable and that there are no lateral barriers to flow in the test vicinity. Analysis of the pilot test indicated that vertical leakage occurring from underlying and overlying units into the F/G sequence was very low, demonstrating that the interbedded mudstone and siltstone units above (from the top of the Fa coal to the bottom of the E2 coal) and below (from the bottom of the Gc coal to the top of the I coals) have a very low hydraulic conductivity, especially in the vertical direction. The hydraulic response to the dewatering test in these interbedded materials above and below the F/G was minimal, and was only observed very near to the pilot well. The response in the F/G sequence from the pilot test also indicated some horizontal anisotropy with drawdown spreading more in the direction of the N66W fracture sets than perpendicular to these fractures. The transient sub-region model and the regional model were adjusted to reflect this horizontal anisotropy. Because of the requirements of the FEFLOW code, this was achieved by rotating the model until the N66W fracture set was parallel to the east-west direction in the model coordinate system. During the transient calibration, hydraulic parameters such as the horizontal and vertical conductivity and confined storage coefficient of the bedrock units were adjusted to synthesize the observed hydraulic response. The calibrated parameters are listed in Table 4.2. Table 4.2 Calibrated hydraulic parameters from transient calibration Model Kx Ky Kz Specific Drainable layer no. (along main (perpendicular (vertical) storage porosity fracture to main direction) fracture direction) (ft/day) (ft/day) (ft/day) /m) (%) 1 and 2 65 65 65 N/A 20 3 41 20 4.1 2 x 10-7 20 4 and 5 3,287 1,641 329 2 x 10-7 5 6 and 7 41 20 0.4 1 x 10-6 5 8 3,939 1,967 3,939 2 x 10-7 5 9 952 476 95 2 x 10-7 5 10 and 11 68 34 0.7 1 x 10-6 5 12 819 411 82 2 x 10-7 5 13 0.01 0.01 0.01 2 x 10-7 5 14 309 154 31 2 x 10-7 5 15 and 16 615 309 61 2 x 10-7 5 2572-R3 Colowyo Coal Company, L.P. Water Management Consultants