Microseismic Monitoring and Geomechanical Modelling of CO2 - bris

5.4. RESULTS
0
500
1000
Depth (m)
1500
2000
2500
3000
Reservoir
Overburden
3500
0 0.1 0.2 0.3 0.4 0.5
Porosity
Figure 5.6: Porosity as a function of depth for the reservoir and overburden materials.
Reservoir Overburden Ratio (Eres/E 0 over)
0
7GPa 20GPa 0.35
20GPa 20GPa 1
35GPa 7GPa 5
Table 5.3: Initial Young’s moduli for the range of stiff and soft reservoir models.
The Young’s modulus is dependent on porosity as per equation 5.15. Assuming e=0 makes A and
B immaterial. As a result, the Young’s modulus is given by
E = E 0 Φ −0.372 (5.18)
in the overburden and
E = E 0 Φ −0.4 , (5.19)
in the reservoir. In order to test the sensitivity of the stress path to the relative stiffness of the reservoir
and overburden, the reference Young’s modulus is varied for both the reservoir and overburden. Segura
et al. (2010) have shown that the key material property with first order control on the stress path is
the ratio of Young’s modulus between the reservoir and the side- and overburden. Therefore I have
developed models with a stiff reservoir and soft overburden (referred to as the stiff model), with a soft
reservoir and stiff overburden (soft model) and with similar stiffnesses (medium model). The initial
Young’s moduli are listed in Table 5.3, and the resulting Young’s moduli, and reservoir:overburden
Young’s modulus ratios, as a function of depth are shown in Figure 5.7.
5.4 Results
I will show the results from the 9 models described above (3 geometries × 3 stiffnesses). For each of
these I will analyse the stress evolution in 5 locations: (1) in the centre of the reservoir; (2) at the edge
of the reservoir; (3) at the corner of the reservoir; (4) in the overburden at the first node above the
centre of the reservoir; and (5) in the sideburden (see Figure 5.8). For the 3 cells inside the reservoir
I will consider the stress path parameters described above. Outside the reservoir there is little pore
93