Overpressure

About: Overpressure is a research topic. Over the lifetime, 3236 publications have been published within this topic receiving 34648 citations.

Influence of water thermal history and overpressure on CO2-hydrate nucleation and morphology

Abstract: The onset of gas hydrate nucleation is greatly affected by the thermal history of the water that forms its lattice structure. Hydrate formation experiments were performed in a 72 L pressure vessel by injecting bubbles of carbon dioxide through a 1 L tube at hydrate formation pressures (1.4 to 3.7 MPa) and temperatures (2 to 5 °C). The results revealed that when even a small fraction (e.g., 5–35%) of the water in which the hydrate formed was recently thawed the overpressure for nucleation was reduced by an average of 50% as compared to untreated distilled water. This observation was confirmed by an analysis of variance (ANOVA) test that indicated that recently thawed water required a significantly lower overpressure compared to the untreated distilled water. In experiments where hydrate nucleated at low overpressure (e.g., 0.75 MPa), hydrate formed at the vapor-liquid interface, encrusting the bubbles with less than 1 g of hydrate accumulation in the first minute. When a higher overpressure was required for nucleation (e.g., 1.3 MPa), hydrate was observed to form abruptly not only on bubbles but also from the bulk liquid phase, typically accumulating a mass of more than 100 g in the first few seconds. Our results show that initiation of hydrate formation is strongly influenced by temperature-dependent pre-structuring of water molecules prior to their contact with gas. Although as little as a 5% volume fraction of pre-structured water may decrease the required overpressure, once hydrate formation commences the mass of hydrate accumulation is dependent on the overpressure.

Nanopowders explosion : influence of the dispersion characteristics

Abstract: With the publication of NFPA 68 (2013); a major change is in progress in venting area calculation methods for gas explosions. Old methods referring to the Kg parameter proved to be inappropriate for real applications. The present work provides new data to correlate real gas concentration and initial turbulence conditions to flame propagation and explosion overpressure during a vented gas explosion. Explosion tests were performed in a 4 m3 rectangular chamber equipped with transparent walls and vented (0.49 m2 square vent) on one side. The chamber is filled with a turbulent or quiescent hydrogen-air mixture with a purposely built injection system that allows to vary the turbulence intensity and the length scale. Gas concentration and turbulence parameters are measured with concentration gauges and Pitot probes distributed in the chamber (Duclos, 2017). Then the flame propagation is fully characterized with high speed video and explosion overpressure is measured inside and outside the chamber. The paper presents the parametric study performed by varying the initial turbulence and focuses on its influence on the inside explosion overpressure. Then physics of vented gas explosion is discussed, results are compared to developing phenomenological model.

Simplified modeling of blast waves from metalized heterogeneous explosives

Abstract: The detonation of a metalized explosive generates a complex multiphase flow field. Modeling the subsequent propagation of the blast front requires a detailed knowledge of the metal particle dynamics and reaction rate. Given the uncertainties in modeling these phenomena, a much simpler, 1D compressible flow model is used to illustrate the general effects of secondary energy release due to particle reaction on the blast front properties. If the total energy release is held constant, the blast pressure and impulse are primarily dependent on the following parameters: the proportion of secondary energy released due to afterburning, the rate of energy release, the location the secondary energy release begins, and the range over which it occurs. Releasing the total energy over a longer time period in general reduces the peak blast overpressure at a given distance. However, secondary energy release reduces the rate of decay of the shock pressure, increases the local gas temperature and hence increases the velocity of the secondary shock front. As a result, for certain values of the above parameters, the peak blast impulse may be increased by a factor of about two in a region near the charge. The largest augmentation to the near-field peak impulse results when the secondary energy is released immediately behind the shock front rather than uniformly within the combustion products.

The generation and continued existence of overpressure in the Delaware Basin, Texas

Abstract: The Delaware Basin, part of the larger Permian Basin, contains important hydrocarbon plays. Permian strata contain 71% of in-place oil and 53% of in-place gas, with the remainder hosted in the Lower Palaeozoic. Excessive pore fluid pressures (up to 〜 8000 psi above hydrostatic) are found within Early Permian and Pennsylvanian strata, which account for 30-35% of the hydrocarbon producing zones. This study has utilised an array of basin analysis techniques to analyse the pressure history of the Delaware basin. To fully appreciate the geopressure history in the Delaware Basin, a rigorous quantitative approach has been applied using advanced thermochronology techniques. This has enabled for the first time an accurate burial history curve to be established for the basin. The results show that maximum burial occurred in the basin at 55 Ma as a consequence of an additional 6890 ft of Mesozoic and Cenozoic sediment. The basin then underwent two major tectonic uplift events during the Cenozoic. The Laramide orogeny (55-50 Ma) uplifted and eroded off 3890 ft of sediment, then during the Eocene and Oligocene the basin subsided and accumulated a further 600 ft of sediment. The Basin and Range event (25-10 Ma) then uplifted and tilted the basin further, eroding off 3600 ft of sediment from the centre of the basin. The new burial history curve has been integrated with wireline logs and basin modelling software to evaluate the mechanism of overpressure generation and its maintenance through geological time. This study has shown that the main mechanism for overpressure generation in the Delaware Basin was disequilibrium compaction. Analysis of the sonic log using the Equivalent Depth Method and the Eaton Ratio Method, combined with velocity I density cross-plots, indicate that compaction is driven by vertical loading, and undercompaction seen in the basin is a consequence of the sediments' inability to dewater. Basin modelling shows that it was the rapid deposition of the Permian sediments that enabled disequilibrium compaction to generate overpressure. These techniques have also shown that a secondary cause of overpressure due to unloading mechanisms (e.g. gas generation or expansion with uplift, lateral transfer and hydrocarbon buoyancy) may be occurring within localised horizons below the Wolfcampian Series. Overpressure has been maintained within the basin for more than 250 Myr. Basin modelling and wireline logs have shown that numerous intercalated tight limestones (Mississippian to Late Permian) acted as pressure seals to maintain overpressure. In addition, low permeability mudstones (l0 (^-6) mD) have contributed to the inability of the Delaware Basin to reach pressure equilibrium.