Overpressure

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

Paleohydrology of the Delaware Basin, Western Texas: Overpressure Development, Hydrocarbon Migration, and Ore Genesis

Abstract: This study integrates quantitative modeling techniques with field observations to establish a paleohydrologic framework of the Delaware basin, western Texas. The reconstructed paleohydrologic models allow for a better understanding of the development and maintenance of anomalous overpressures, hydro carbon generation and migration, and ore genesis in the basin. Results of numerical modeling show that disequilibrium compaction and oil generation might generate excess fluid pressures during the Late Permian in response to the rapid deposition of evaporite beds. The preservation of this overpressure to the present, however, requires the presence of an extremely low-permeability (<10-11 d) top seal. Most shaly sediments, with permeability ranging from 10-4 to 10-8 d, thus may be too permeable, by several orders of magnitude, to preserve overpressure for more than 250 m.y. The predicted present-day gas window is located within the overpressure zone, suggesting that the volume increase associated with the oil-to-gas conversion may be attributed to present overpressures. The native sulfur deposits likely formed in a fluid mixing zone resulting from the Laramide uplift of the western basin during the Tertiary. In our model, meteoric water recharged along the basin's uplifted western margin and discharged basinward. Hydrocarbons migrated landward by pressure gradients and buoyancy and discharged upward along faults in the western basin, where they mixed with meteoric water. Many oil and mineral reservoirs may have formed in the fluid mixing zone, where extensive chemical reactions take place. In the Culberson sulfur ore district, for example, fluids including hydrocarbons and meteoric water migrated upward through faults from underlying carrier beds, into the Permian Salado limestone. There, the mixture of fluid drives biochemical reactions that precipitate native sulfur.

Offshore sediment overpressures of passive margins: Mechanisms, measurement, and models

Abstract: [1] Fluid pressure in excess of hydrostatic equilibrium, or overpressure, in offshore environments is a widespread phenomenon that contributes to the migration and storage of fluids, solutes, and energy and to the potential mechanical instability of these sediments. Overpressure exists in deep and shallow systems and is most likely to be found where low-permeability ( mm/yr), tectonic loading, and lateral fluid transfer) and thermal and chemical processes (e.g., aquathermal expansion, hydrocarbon generation, mineral diagenesis, and organic maturation). In systems where near-lithostatic overpressures are generated, potentially unstable sediments are created. Failures of these sediments can create large-scale natural disasters, generate fractures, and damage seafloor and subseafloor infrastructure. Detailed characterization of overpressured systems has been accomplished through geological and geotechnical analyses, including investigation of physical-mechanical properties (mainly porosity, consolidation state, and shear strength), inversion of geophysical data (e.g., compressional and/or shear velocities), measurement of in situ properties, and postevent analyses. Process-based models have been developed to explain the origin of overpressure in terms of rate of overpressure genesis. This allows identification of potentially unstable zones and assessment of the potential for failure. Future development in measurements and in coupling of models will lead to more accurate analysis and prediction of fluid pressure in offshore sediments, which in turn will facilitate better hazard analyses and will enable safer and more cost-effective offshore drilling practices and other offshore infrastructure development.

Submarine slope failures due to pipe structure formation.

Abstract: There is a strong spatial correlation between submarine slope failures and the occurrence of gas hydrates. This has been attributed to the dynamic nature of gas hydrate systems and the potential reduction of slope stability due to bottom water warming or sea level drop. However, 30 years of research into this process found no solid supporting evidence. Here we present new reflection seismic data from the Arctic Ocean and numerical modelling results supporting a different link between hydrates and slope stability. Hydrates reduce sediment permeability and cause build-up of overpressure at the base of the gas hydrate stability zone. Resulting hydro-fracturing forms pipe structures as pathways for overpressured fluids to migrate upward. Where these pipe structures reach shallow permeable beds, this overpressure transfers laterally and destabilises the slope. This process reconciles the spatial correlation of submarine landslides and gas hydrate, and it is independent of environmental change and water depth.

A volcanic degassing event at the explosive-effusive transition

Abstract: [1] A sequence of five Vulcanian explosions followed a lava dome collapse in July 2003 at Soufriere Hills Volcano. Each explosion occurred at ∼t = 190 n4.3 where n = 1–5 and t is the time (s) since the decompression rate peak during the collapse. Instead of a sixth explosion at the predicted time, a rapid emission of 97 × 103 kg SO2 was observed by a spectrometer network. This event represents the transition from explosive to effusive activity. After the last explosion, high magma ascent rates were maintained, but the critical overpressure explosion criterion was not reached. Instead, degassing and crystallisation in the upper conduit caused horizontal gradients in viscosity and flow rate, and brittle failure at the walls when the rate of shear strain exceeded a critical value. Development of a permeable shear zone allowed gas release, relief of overpressure and a return to effusive lava-dome building.