Elastic rock properties
The main reservoir strata of Olituoz area was originally formed at the surface or near surface (less than 1km, Gu, et al., 2002) during Es3, Which later on were overlaid by Dongying Formation and the up-layers. Thus the up-layers were peeled in order to obtain the corrected depth for these strata till the end of Dongying Formation time with normal temperature conditions. After depth calculation, rock samples collected from the intact well cores are subjected to tri-axial compression tests to gain the mechanical parameters of these rocks (Table 1 and Table 2) for the simulation of stress field and prediction of fractures.
Table 1. Rock Mechanic Parameters Obtained Through Triaxial Compression Tests
| Sample Number | Lithology | Depth (m) | Diameter (mm) | Height (mm) | Confining Pressure σ3(Mpa) | Axial Crack Stress σ1(Mpa) | Young's Modulus E (GPa) | Poisson's Ratio ν | Form of Crack |
|---|---|---|---|---|---|---|---|---|---|
| O11-1 | Basalt | 2411.4 | 25 | 50 | 31.52 | 244.34 | 28.73 | 0.232 | Tension |
| O15-1 | Trachyte | 2303.7 | 25 | 50 | 26.1 | 167.52 | 18.78 | 0.252 | Shear |
| O15-4 | Trachyte | 2313.1 | 25 | 50 | 26.33 | 176 | 41.09 | 0.189 | Shear |
| O15-8 | Trachyte | 2405.6 | 25 | 50 | 28.6 | 302.51 | 37.17 | 0.33 | Shear |
| O19-4 | Trachy-breccia | 2369.1 | 25 | 50 | 25.95 | 141.28 | 15.58 | 0.143 | Tension |
| O27-1 | Trachyte | 2401.1 | 25 | 50 | 28.2 | 153.83 | 20.58 | 0.206 | Shear |
| O27-4 | Trachyte | 2525.3 | 25 | 50 | 31.24 | 233.76 | 37.47 | 0.253 | Shear |
| O28-2 | Tuff | 2341.2 | 25 | 50 | 26 | 93.82 | 10.41 | 0.232 | Shear |
| O29-4 | Trachy-breccia | 2218.5 | 25 | 50 | 23.48 | 115.47 | 16.88 | 0.268 | Shear |
| O29-5 | Trachy-breccia | 2223 | 25 | 50 | 23.52 | 151.9 | 20.35 | 0.23 | Shear |
| O30-1 | Basalt | 2515.4 | 25 | 50 | 29.41 | 111.79 | 45.57 | 0.179 | Tension |
Table 2. Evaluation of Shear Strength Parameters Based on Triaxial Compression Tests
| Number | Sample Number | Lithology | σ0(MPa) | K | C(MPa) | φ(°) |
|---|---|---|---|---|---|---|
| 1 | O11-1 | Basalt | 92.83 | 4.807 | 21.17 | 40.96 |
| 2 | O15-1 | Trachyte | 67.61 | 3.828 | 17.28 | 35.86 |
| 3 | O15-4 | Trachyte | 81.56 | 3.587 | 21.53 | 34.33 |
| 4 | O15-8 | Trachyte | 61.91 | 8.413 | 10.67 | 51.95 |
| 5 | O19-4 | Trachybreccia | 68.22 | 2.815 | 20.33 | 28.41 |
| 6 | O27-1 | Trachyte | 66.37 | 3.101 | 18.84 | 30.82 |
| 7 | O27-4 | Trachyte | 38.1 | 6.263 | 7.61 | 46.44 |
| 8 | O28-2 | Tuff | 24.95 | 2.649 | 7.67 | 26.86 |
| 9 | O29-4 | Trachybreccia | 49.1 | 2.827 | 14.6 | 28.51 |
| 10 | O29-5 | Trachybreccia | 38.9 | 4.804 | 8.87 | 40.95 |
| 11 | O30-1 | Basalt | 72.17 | 1.347 | 31.09 | 8.51 |