Overpressure

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

Distribution and Generation of the Overpressure System, Eastern Delaware Basin, Western Texas and Southern New Mexico

Abstract: Three subsurface pressure systems have been identified in the Delaware basin: an upper normal pressure system, a middle overpressure system, and a lower normal pressure system. The overpressure system occurs in the eastern Delaware basin, covering six Texas and New Mexico counties. The depth of the overpressure system ranges from 3100 to 5400 m. The normal fluid pressure gradient is 0.0103 MPa/m in the eastern Delaware basin. The highest overpressure gradient, however, approaches 0.02 MPa/m, which is close to the lithostatic gradient of 0.0231 MPa/m. The overpressure system has a relatively flat top and a downwarped bottom. The maximum thickness of the overpressure system reaches about 2300 m at the depocenter and pinches out toward the edges. An area of excess pressure o curs within the system where the highest excess pressure reaches 60 MPa. Local underpressured areas due to production are found in the lower normal pressure system in the War-Wink field area. Overpressure in the eastern Delaware basin is mainly associated with Mississippian, Pennsylvanian, and Permian (Wolfcampian) shale sequences, which also are major source rocks in the basin. Initial sedimentation rates within the overpressure system range from 17 to 90 m/m.y. Corrected bottom-hole temperature measurements indicate that the geothermal gradient within the overpressure zone is 25.1°C/km, which is higher than the basin's average geothermal gradient of 21°C/km. Temperatures at the top and bottom of the overpressure system are about 80 and 115°C, respectively. This temperature range approximates the temperature of the average clay dehydration zone. The oil window in the War-Wink field is coincident with the overpressure system, which implies that hydrocarbon g neration and migration are active in the overpressure system. A two-stage overpressure model is proposed. Hydrocarbon maturation combined with mechanical compaction disequilibrium and clay dehydration are the initial causes for overpressure generation due to an abnormal increase of fluid volume and pore space. Subsequently, the increase in temperature due to a decrease of thermal conductivity and fluid migration within the preexisting overpressure system would reinforce further overpressuring due to the fluid thermal expansion.

Propagation of medium strength shock waves through the atmosphere

Abstract: The rise times and overpressures for shock waves from supersonic projectiles have been measured under a variety of atmospheric conditions. These measurements extend the overpressure for which weak shock theory adequately predicts measured values to 3 kPa. Predicted shock rise times agree reasonably well with theory for shock overpressures between 0.04 and 0.5 kPa with differences increasing at higher overpressures. At overpressures greater than 0.5 kPa, measured rise times might be limited by the experimental apparatus. No correlation between measured rise times and atmospheric turbulence was observed.

Geological Characteristics and Controlling Factors of Deep Shale Gas Enrichment of the Wufeng-Longmaxi Formation in the Southern Sichuan Basin, China

Abstract: Abstract To identify the factors controlling high-quality deep shale gas reservoirs and the exploration and development potential of the Lower Paleozoic marine shale in the Sichuan Basin, the sedimentary environment of deep shale was comprehensively analysed using core thin sections, scanning electron microscopy, gamma ray spectrometry logging, and elemental logging data. In addition, the geological conditions of deep shale gas accumulation and the effect of tectonic processes on the preservation conditions are discussed based on the experimental data of mineral composition analysis, geochemical features, and reservoir spatial characteristics. (1) The sedimentary environment changes from an anoxic water environment to an oxygen-rich oxidizing environment from bottom to top in the Wufeng-Longmaxi Formation in southern Sichuan. The deep shale gas reservoir shows overpressure and rich gas characteristics, namely, high formation pressure (2.0~2.2), high porosity (20%~55%), and high gas content (4.0~5.0 m3/t). (2) The favourable sedimentary environment has a higher hydrocarbon generation potential and deposits of rich organic matter and siliceous particles. During the hydrocarbon generation process, the rich organic matter generates a large number of organic pores and a large specific surface area, which provides the main reservoir and adsorption space for free and adsorbed shale gas. A large number of biogenic siliceous particles provide a solid rock support framework for the shale reservoir, thereby maintaining excellent reservoir physical properties. (3) Late and small stratigraphic uplifts result in a short shale gas escape time and favourable preservation conditions. Additionally, the small-scale faults and a high-angle intersection between the fracture strike and the geostress direction are conducive to the preservation of shale gas. (4) A high formation pressure coefficient, a sedimentary environment rich in organic siliceous deep-water continental shelf microfacies, and a relatively stable tectonic structure are conducive to the accumulation of deep shale gas.