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Fracture threshold in the real world (view source)
Revision as of 20:18, 15 April 2014
, 20:18, 15 April 2014no edit summary
Theoretically, fracturing occurs when the pore pressure reaches P<sub>f</sub>. However, P<sub>f</sub> increases as pore pressure increases. Although the theory generally is described in terms of the pore pressure needed to overcome the horizontal stress keeping the fractures closed, in practice the pore pressure must approach the lithostatic pressure for brittle failure to occur.<ref name=ch10r52>Lorenz, J., C., Teufel, L., W., Warpinski, N., R., 1991, [http://archives.datapages.com/data/bulletns/1990-91/data/pg/0075/0011/0000/1714.htm Regional fractures: a mechanism for the formation of regional fractures at depth in flat-lying reservoirs]: AAPG Bulletin, vol. 75, no. 11, p. 1714–1737.</ref>
Theoretically, fracturing occurs when the pore pressure reaches P<sub>f</sub>. However, P<sub>f</sub> increases as pore pressure increases. Although the theory generally is described in terms of the pore pressure needed to overcome the horizontal stress keeping the fractures closed, in practice the pore pressure must approach the lithostatic pressure for brittle failure to occur.<ref name=ch10r52>Lorenz, J., C., Teufel, L., W., Warpinski, N., R., 1991, [http://archives.datapages.com/data/bulletns/1990-91/data/pg/0075/0011/0000/1714.htm Regional fractures: a mechanism for the formation of regional fractures at depth in flat-lying reservoirs]: AAPG Bulletin, vol. 75, no. 11, p. 1714–1737.</ref>
[[:file:evaluating-top-and-fault-seal_fig10-42.png|figure 1]] charts P<sub>f</sub> vs. pore pressure for a range of overburden stress gradients (0.5–1.0). The pore pressure equals or exceeds P<sub>f</sub> only when the pore pressure is equal to or greater than the lithostatic stress. Fracture occurs when P<sub>f</sub> equals the pore pressure.
[[:file:evaluating-top-and-fault-seal_fig10-42.png|Figure 1]] charts P<sub>f</sub> vs. pore pressure for a range of overburden stress gradients (0.5–1.0). The pore pressure equals or exceeds P<sub>f</sub> only when the pore pressure is equal to or greater than the lithostatic stress. Fracture occurs when P<sub>f</sub> equals the pore pressure.
[[file:evaluating-top-and-fault-seal_fig10-42.png|thumb|{{figure number|1}}See text for explanation.]]
[[file:evaluating-top-and-fault-seal_fig10-42.png|thumb|{{figure number|1}}Chart of P<sub>f</sub> vs. pore pressure for a range of overburden stress gradients (0.5–1.0).]]
==Stress and poisson's ratio variation==
==Stress and poisson's ratio variation==