Overpressure development

The peak overpressure developed immediately after a burst is an important parameter for evaluating pressure vessel explosions. At that instant, waves are generated at the edge of the sphere. The wave system consists of a shock, a contact surface, and rarefaction waves. As this wave system is established, pressure at the contact surface drops from the pressure within the sphere to a pressure within the shock wave. 

Note that the venting design may not necessarily prevent a deflagration, but is intended to relieve the overpressure developed (see reference [72]). 

Outlets should not be provided in constantly recirculating systems, particularly where close control of humidity is required. The overpressure developed is far less than that exerted by the wind, and for this reason any system which does have both intake and discharge ducts should have them on the same face of the building. While care is necessary to prevent short-circuiting, this alleviates problems arising from the considerable wind pressure difference that can develop on opposite sides of a building. 

Figure 7.19 Chronpes 25 overpressure development chamber for forced-flow TLC. The configuration shown is for on-line detection. 

The overpressure developed in semi-confined explosions depends on the following key parameters ... 

Fertl, W.H. and G.V. Chilingarian, 1987. Abnormal formation pressures and their detection by pulsed neutron capture logs. Journal of Petroleum Science and Engineering 1, pp. 23-38 Forbes, P.L., Ungerer, P. and B.S. Mudford, 1992. A two-dimensional model of overpressure development and gas accumulation in Venture Field, Eastern Canada. The American Association of Petroleum Geologists Bulletin, Vol. 76, no. 3, pp. 318-338... 

Fig. 6. Lack of pressure-leakage results in overpressure development in the terminal trap in this diagram. Leakage from the terminal structure acts to preserve petroleum in the deeper structures. Partly leaking thin caprocks, permeable for gas (dynamic trap), or superthick tight and strong caprocks in deep prospects (static trap) where advanced diagenesis has occurred, represent two other configurations able to retain petroleum for...

In this model the reduced permeability at faults is caused by advanced quartz diagenesis which is exponential in temperature (cf. Fig. 9), leading to constrained fluid flow and thereby overpressure development. Traps which earlier contained oil will, in the normal case of continued communication with a subsiding basin, eventually receive high GOR petroleum in the form of a condensate, i.e. a gas phase, from the subsiding deep source rocks. The replacement of the oil with the low density gas phase, in shallower... 

The additional overpressure development in shallow and intermediately deeply buried traps, caused by the influx of a high API gravity gas phase, may have resulted in catastrophic leakage from traps with thick tight caprocks which lacks a pressure valve (cf. Figs 6 7) like those in Halten Vest. 

Fluid communication across faults and within faults may thus be genetically linked to both petroleum migration and overpressure development (cf. Figs 8 10). In particular, palaeo-migration of petroleum from the Are source... 

Palaeo-leakage from Smorbukk and the time for leakage and overpressure development in Halten Vest... 

Vik et a/. (1991) suggested that hydraulic fracturing caused gas to escape from reservoirs in the Halten Vest region, and used the coinciding overlap between overpressured regions and the regions where the Are Formation coals today are overmature, to tentatively indicate this assumed Are derived gas to be responsible for the overpressure development. Vik et al. (1991) did not have data available to indicate that several of these stmctures they report to be dry... 

It is thus a likely interpretation that this migration event from Garn in Smorbukk into the Cretaceous strata occurred before the onset of overpressure development. 

Sandstone porosity loss versus depth in Haltenbanken is similar to trends seen for the North Sea, especially between 1.4 and 2.6 km (Bjorlykke et al. 1989). This could suggest that overpressure does not influence the porosity depth trends in these basins. It is possible, accordingly, that the lack of correlation between overpressure and shale porosity reported at Haltenbanken by Hermanrud et al. (1998) is a manifestation of disequilibrium in the sense that the shales did not have time to respond chemically to the overpressure development. This suggests that mechanical models for compaction cannot adequately explain porosity loss in deep shales and that a time/temperature... 

The fact that the shales have not had time to re-equilibrate to the new pressure regime must imply that overpressure development in Halten Vest is very recent, underlined by the fact that the strata today are at maximum burial depth and that relevant mineral reactions are exponential in temperature. 

Diagenesis on the fault planes is believed to be the main cause of overpressure development in Halten Vest, as the region was effectively sealed off from pressure leakage towards the east. 

Fast turbulent deflagrations often transit spontaneously to detonations. For fully developed self-sustained detonation, boundary conditions and confinement play minor roles. The Chapman-Jouguet velocity and overpressure are based on the energetics of the mixture and can be evaluated from equilibrium thermodynamic computations. During the onset of detonation, the transient peak overpressures developed can be much higher than the equilibrium detonation pressures. Transition from deflagration to detonation is to be avoided whenever possible because of this extremely high pressure transient at the onset of detonation. 

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