13th International Conference on Fracture June 16–21, 2013, Beijing, China -70.0 5.0x105 1.0x106 1.5x106 2.0x106 2.5x106 3.0x106 1.0 1.2 1.4 1.6 1.8 2.0 0 A single crack with b/a →∞ H0 = 3500 m H0 = 5000 m H0 = 4000 m a/a0 Tim e (year) 0.0 5.0x105 1.0x106 1.5x106 2.0x106 2.5x106 3.0x106 3.2 3.6 4.0 4.4 4.8 0 A single crack with b/a →∞ H0 = 3500 m H0 = 5000 m H0 = 4000 m Δ P (M Pa) Tim e (year) 0.0 5.0x105 1.0x106 1.5x106 2.0x106 2.5x106 3.0x106 3.5x106 1.0 1.2 1.4 1.6 1.8 2.0 C olinearcracks with b/a0 = 3 H0 = 3500 m H0 = 5000 m H0 = 4000 m a/a0 Tim e (year) 0.0 5.0x105 1.0x106 1.5x106 2.0x106 2.5x106 3.0x106 3.5x106 2.5 3.0 3.5 4.0 4.5 5.0 C olinearcracks with b/a0 = 3 H0 = 3500 m H0 = 5000 m H0 = 4000 m Δ P (M Pa) Tim e (year) 3.2 Collinear cracks case The effects of initial burial depth on crack propagation distance and excess pressure evolution for b/a0=3 are shown in Figures 4 and 5, respectively. The general trends in the variation of crack propagation distance and excess pressure with time corresponding to different H0 are quite similar to those observed in Figures 2 and 3, respectively. A particularly noteworthy feature is sharp differences on the crack propagation duration between a single crack and collinear cracks at shallow burial depth. For example, Figure 2 shows that it takes about 2.74 million years for the single crack to grow to 1.97 times its original length when all the oil within the crack converts to gas completely. For collinear cracks, it takes about 2.42 million years to grow to 1.98 times its original length and the microcracks are almost to coalesces (b/a0=3 and h/a0=2) to form macroscopic cracks. The Figure 2. Crack propagation distance versus time for a single crack corresponding to different initial depths of burial Figure 3. Excess pressure evolution over time for a single crack corresponding to different initial depths of burial Figure 4. Effect of initial depth of burial on the crack propagation distance for collinear cracks with initial crack spacing b/a0 = 3 Figure 5. Effect of initial depth of burial on the excess pressure for collinear cracks with initial crack spacing b/a0 = 3
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