Issue 27

X. Ran et alii, Frattura ed Integrità Strutturale, 27 (2014) 74-82; DOI: 10.3221/IGF-ESIS.27.09 78 Parameter Ⅰ Value Parameter Ⅰ Value parameter Ⅱ Value parameter Ⅱ Value H /m 3500  0.95 E / GPa 2 m c / MPa 12 w r / mm 158  /(g/cm 3 ) 2.13  0.2  0.2 H  / MPa 75 m  /(g/cm 3 ) 1.60 e 0.25 h  / MPa 54 i P / MPa 55  / ° 25 v  / MPa 70 p P / MPa 45 0 k / (m/s) 3 × 10 -12 Table 1 : Model parameters. Setting mechanic parameters The mechanic parameters ( Ⅱ ) of undamaged shale are shown in Tab. 1. The parameter E is the elastic modulus;  is the Poisson ratio; e is the void ratio;  is the harden parameter; m c is the cohesion;  is the frictional angle; 0 k is the permeability. The mechanic parameters and hydraulic parameters of damaged rock is need to write in ABAQUS through software FORTRAN, which include c , E , d k and d n . Choose the equivalent plastic strain as damage variable and define the damage  is field variable according to Eq. (6). Define the c , E , d k and d n are state variables according to Eq. (2), (4), (7) and (8). It is too small to ignore the influence of damage on Poisson ratio. R ESULTS hen the drilling fluid m  = 1.6 g/cm 3 , the damage distribution and permeability change of wall rock is calculated. Additionally, the distribution of pore pressure, stress and displacement is obtained. - Damage and permeability. The distribution of damage is shown in Fig.3. In the non-uniform ground stress, most of wall rock is in elastic zone or protolith zone. The rock damage only occurred on the side of the minimum ground stress near the wall when m  = 1.6 g/cm 3 . The maximum value of damage is 0.59 on the wall. The depth of damage rock is about 0.4 w r and the value of damage is decreasing with the increase of distance far from the wall. Figure 3 : The distribution of damage. Figure 4 : The distribution of permeability. The permeability variation of rock is indicated in Fig.4. Compared with Fig.3, we can see that the distribution of permeability is corresponds with damage. The maximum permeability reach up to 1.76 × 10 -9 m/s in damaged area. The permeability has no change in undamaged area. W