Expedition 308 synthesis: overpressure, consolidation, and slope stability on the continental slope of the Gulf of Mexico

Integrated Ocean Drilling Program Expedition 308 quantified the coupling between sedimentation, consolidation, overpressure, fluid flow, and slope instability in continental margin settings. We summarize and synthesize peer-reviewed hydrogeologic studies published since the end of Expedition 308 that focus on Expedition 308 sites drilled in Ursa Basin: Sites U1322, U1323, and U1324. There is a rich stratigraphic complexity in the Ursa Basin, deepwater Gulf of Mexico. The sandstone-prone Blue Unit is a permeable aquifer overlain by mudstone-prone leveed-channel deposition. Multiple mass transport deposits, each densified relative to surrounding material, are present. Eight coeval surfaces mapped across the drilling transect span ~70 ka to present. Sedimentation rates were >10 mm/y at Site U1324. In situ penetrometer measurements document severe overpressures that begin at or near the seafloor and extend to the base of the drilled holes. Uniaxial consolidation experiments quantified the compression behavior of the sediments and provided an approach to predict pressure from porosity. Laboratory analysis of permeability and compressibility document that the coefficient of consolidation (hydraulic diffusivity) of Ursa Basin mudstones is 10–8 m2/s over the effective stresses encountered during drilling at Ursa Basin (0.1 to 5 MPa). This low and constant value for the coefficient of consolidation is responsible for the presence of high overpressure very near the seafloor. Although permeability is very high, the sediments are also highly compressible. Forward modeling of Ursa Basin sediments shows that overpressure near the seafloor is reasonable given the rock properties and sedimentation rates that are observed. Modeling also illustrates that flow is driven laterally along an underlying aquifer, the Blue Unit. Soon after Blue Unit deposition, lateral flow induced submarine landslides. Later in the evolution of this system, overpressure may have preconditioned the slope to failure by earthquakes of magnitude 5.0

Scientific basis for safely shutting in the Macondo Well after the April 20, 2010 Deepwater Horizon blowout

As part of the government response to the Deepwater Horizon blowout, a Well Integrity Team evaluated the geologic hazards of shutting in the Macondo Well at the seafloor and determined the conditions under which it could safely be undertaken. Of particular concern was the possibility that, under the anticipated high shut-in pressures, oil could leak out of the well casing below the seafloor. Such a leak could lead to new geologic pathways for hydrocarbon release to the Gulf of Mexico. Evaluating this hazard required analyses of 2D and 3D seismic surveys, seafloor bathymetry, sediment properties, geophysical well logs, and drilling data to assess the geological, hydrological, and geomechanical conditions around the Macondo Well. After the well was successfully capped and shut in on July 15, 2010, a variety of monitoring activities were used to assess subsurface well integrity. These activities included acquisition of wellhead pressure data, marine multichannel seismic pro- files, seafloor and water-column sonar surveys, and wellhead visual/acoustic monitoring. These data showed that the Macondo Well was not leaking after shut in, and therefore, it could remain safely shut until reservoir pressures were suppressed (killed) with heavy drilling mud and the well was sealed with cement

Электронный компас

Разработка электронного компаса на основе датчиков: магнитометра, акселерометра и гироскопа. Данное устройство будет определять направление на северный магнитный полюс как при горизонтальном положении, так и при отклонениях от горизонтальной плоскостиDevelopment of electronic compass based on sensors: magnetometer, accelerometer and gyroscope. This device will determine the direction to the North magnetic pole both in the horizontal position and in deviations from the horizontal plan

The Effect of Convection on Disorder in Primary Cellular and Dendritic Arrays

Directional solidification studies have been carried out to characterize the spatial disorder in the arrays of cells and dendrites. Different factors that cause array disorder are investigated experimentally and analyzed numerically. In addition to the disorder resulting from the fundamental selection of a range of primary spacings under given experimental conditions, a significant variation in primary spacings is shown to occur in bulk samples due to convection effects, especially at low growth velocities. The effect of convection on array disorder is examined through directional solidification studies in two different alloy systems, Pb-Sn and Al-Cu. A detailed analysis of the spacing distribution is carried out, which shows that the disorder in the spacing distribution is greater in the Al-Cu system than in Pb-Sn system. Numerical models are developed which show that fluid motion can occur in both these systems due to the negative axial density gradient or due the radial temperature gradient which is always present in Bridgman growth. The modes of convection have been found to be significantly different in these systems, due to the solute being heavier than the solvent in the Al-Cu system and lighter than it in the Pb-Sn system. The results of the model have been shown to explain experimental observations of higher disorder and greater solute segregation in a weakly convective Al-Cu system than those in a highly convective Pb-Sn system

Rapid sedimentation, overpressure, fluid flow and slope instability at the Gulf of Mexico continental margin

Integrated Ocean Drilling Programme (IODP) Expedition 308 studied overpressure and fluid flow on the Gulf of Mexico continental slope. The scientific program examined how sedimentation, overpressure, fluid flow, and deformation are coupled in a passive continental margin setting. The expedition investigated the model of how extremely rapid deposition of finegrained mud leads to rapid build-up of pore pressure in excess of hydrostatic (overpressure), underconsolidation and continental slope instability. Expedition 308 tested this model by examining how physical properties, pressure, temperature, and pore fluid compositions vary within low-permeability mudstones that overlie a permeable, overpressured aquifer. Three sites were drilled in the Ursa Basin off the Mississippi Delta, using the research drillship R/V JOIDES RESOLUTION (Fig. 1). In the Ursa Basin rapid, late Pleistocene sedimentation was known to be present. Drilling documented severe overpressure in the mudstones overlying the aquifer. The most important achievement of IODP Expedition 308 is to have successfully recorded in situ formation pressure and temperature in an overpressured basin. This is the first time that a coherent data set of such measurements has been obtained

Strength-ductility behaviour of Al-Si-Cu-Mg casting alloys in T6 temper

A comparative study of the mechanical properties of 20 experimental alloys has been carried out. The effect of different contents of Si, Cu, Mg, Fe and Mn, as well as solidification rate, has been assessed using a strength-ductility chart and a quality index-strength chart developed for the alloys. The charts show that the strength generally increases and the ductility decreases with an increasing content of Cu and Mg. Increased Fe (at Fe/Mn ratio 0.5) dramatically lowers the ductility and strength of low Si alloys. Increased Si content generally increases the strength and the ductility. The increase in ductility with increased Si is particularly significant when the Fe content is high. The charts are used to show that the cracking of second phase particles imposes a limit to the maximum achievable strength by limiting the ductility of strong alloys. The (Cu + Mg) content (at.%), which determines the precipitation strengthening and the volume fraction of Cu-rich and Mg-rich intermetallics, can be used to select the alloys for given strength and ductility, provided the Fe content stays below the Si-dependent critical level for the formation of pre-eutectic alpha-phase particles or beta-phase plates