Overpressure

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

Near‐seafloor overpressure in the deepwater Mississippi Canyon, northern Gulf of Mexico

Abstract: [1] Laboratory experiments constrain overpressure (25–50% of hydrostatic effective stress) above 30 mbsf at two sites in the Mississippi Canyon region, northern Gulf of Mexico. Overpressure at site 2562 is less than that at site 2567; however site 2562 has accumulated faster. One-dimensional sedimentation-consolidation models cannot recreate the overpressure without external fluid sources. A fluid source (specific discharge, q = 2–7 mm/yr) is required for site 2567, whereas a fluid sink (q = 10–12 mm/yr) is required for site 2562 to simulate the constrained overpressure. Although basal conditions differ, specific discharge of 2.1–4.2 mm/yr occurs at the sea floor. Shallow upward flow at each site, deep upward flow at site 2567 and deep downward flow at site 2562 is consistent with a two-dimensional flow field where sites 2562 and 2567 are hydrologically connected at depth by a regional aquifer.

Gas generation and overpressure: Effects on seismic attributes

Abstract: Drilling of deep gas resources is hampered by high risk associated with unexpected overpressure zones. Knowledge of pore pressure using seismic data, as for instance from seismic-while-drilling techniques, will help producers plan the drilling process in real time to control potentially dangerous abnormal pressures. We assume a simple basin-evolution model with a constant sedimentation rate and a constant geothermal gradient. Oil/gas conversion starts at a given depth in a reservoir volume sealed with faults whose permeability is sufficiently low so that the increase in pressure caused by gas generation greatly exceeds the dissipation of pressure by flow. Assuming a first-order kinetic reaction, with a reaction rate satisfying the Arrhenius equation, the oil/gas conversion fraction is calculated. Balancing mass and volume fractions in the pore space yields the excess pore pressure and the fluid saturations. This excess pore pressure determines the effective pressure, which in turn determines the skeleton bulk moduli. If the generated gas goes into solution in the oil, this effect does not greatly change the depth and oil/gas conversion fraction for which the hydrostatic pressure approaches the lithostatic pressure. The seismic velocities versus pore pressure and differential pressure are computed by using a model for wave propagation in a porous medium saturated with oil and gas. Moreover, the velocities and attenuation factors versus frequency are obtained by including rock-frame/fluid viscoelastic effects to match ultrasonic experimental velocities. For the basin-evolution model used here, pore pressure is seismically visible when the effective pressure is less than about 15 MPa and the oil/gas conversion is about 2.5% percent.

Methane–air explosion characteristics with different obstacle configurations

Abstract: To investigate the flame and overpressure characteristics of methane–air explosion with different obstacle configurations, an experimental study has been conducted, taking account of the number of obstacles, obstacle distance from ignition source, and stream-wise and cross-wise obstacle positions. The results show that the flame speed and peak overpressure increase with the increasing number of obstacles, while the time to reach the peak is not fully determined by it. And the configuration having the farthest obstacle produces a higher overpressure and takes a longer time to reach the peak, but a slower flame propagation speed is obtained. Similar explosion characteristics are also observed in the configurations with two obstacles fixed at different stream-wise positions. Furthermore, the experimental results demonstrate that the peak overpressures and flame speeds in configurations with central or staggered obstacles are relatively higher, which should to be avoided in practical processes to minimize the risk associated with methane–air explosion.

Enhancement effects of methane/air explosion caused by water spraying in a sealed vessel

Abstract: Experiments about the influence of ultrafine water mist on the methane/air explosion were carried out in a fully sealed visual vessel with methane concentrations of 8%, 9.5%, 11% and 12.5%. Water mists were generated by two nozzles and the droplets' Sauter Mean Diameters (SMD) were 28.2 μm and 43.3 μm respectively which were measured by Phase Doppler Particle Anemometer (PDPA). A high speed camera was used to record the flame propagation processes. The results show that the maximum explosion overpressure, pressure rising rate and flame propagation velocity of methane explosions in various concentrations increased significantly after spraying. Furthermore, the brightness of explosion flame got much higher after spraying. Besides, the mist with a larger diameter had a stronger turbulent effect and could lead to a more violent explosion reaction.