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Reservoir pressures within the Bullwinkle minibasin (Green Canyon 65, Gulf of Mexico continental slope) increase at a hydrostatic gradient whereas pressures predicted from porosity within mudstones bounding these reservoirs increase at a lithostatic gradient: they are equal at a depth 1/3 of the way down from the crest of the structure. Two- and three-dimensional steady-state flow models demonstrate that bowl-shaped structures will have lower pressures than equivalent two-dimensional structures and that if a low permeability salt layer underlies the basin, the pressure is reduced. We conclude that at Bullwinkle, pressure is reduced due to an underlying salt body and the bowl-shape of the basin. A geometric approach to predict sandstone pressure is to assume that the reservoir pressure equals the area-weighted average of the mudstone pressure. When the mudstone pressure gradient is constant, as at Bullwinkle, the reservoir pressure equals the mudstone pressure at the average depth (centroid) of the reservoir. 相似文献
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Generation of overpressure and compaction-driven fluid flow in a Plio-Pleistocene growth-faulted basin, Eugene Island 330, offshore Louisiana 总被引：2，自引：0，他引：2
The complex pressure and porosity fields observed in the Eugene Island (EI) 330 field (offshore Louisiana) are thought to result from sediment loading of low-permeability strata. In this field, fluid pressures rise with depth from hydrostatic to nearly lithostatic, iso-pressure surfaces closely follow stratigraphic surfaces which are sharply offset by growth-faulting, and porosity declines with effective stress. A one-dimensional hydrodynamic model simulates the evolution of pressure and porosity in this system. If reversible (elastic) compaction is assumed, sediment loading is the dominant source of overpressure (94%). If irreversible (inelastic) compaction and permeability reduction due to clay diagenesis are assumed, then thermal expansion of pore fluids and clay dehydration provide a significant component of overpressure (>20%). The model is applied to wells on the upthrown and downthrown sides of the major growth fault in the EI 330 field. Assuming that sediment loading is the only pressure source and that permeability is a function of lithology and porosity, the observed pressure and porosity profiles are reproduced. Observation and theory support a conceptual model where hydrodynamic evolution is intimately tied to the structural and stratigraphic evolution of this progradational deltaic system. 相似文献
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Mahdi Heidari Maria A. Nikolinakou Peter B. Flemings Michael R. Hudec 《Basin Research》2017,29(3):363-376
We use a simple analytical model to estimate the stress field in density‐driven, rising salt domes and adjacent sediments, and to describe the evolution of these domes. We show that the pressure exerted by the salt pushing out against its wall rocks (the salt pressure) decreases linearly up the flank of the dome, but is always greater than the overburden stress. In fact, the salt pressure normal to the dome boundary is everywhere the maximum principal stress, whereas the hoop stress parallel to the circumference of the dome is the minimum stress. In addition, we quantitatively describe the critical stages of salt dome evolution (initiation, upbuilding, and downbuilding), relating these stages to sedimentation rate and basin thickness. This analysis also shows that even the highest sedimentation rates are unlikely to accumulate enough sediments to bury downbuilding domes as long as the salt supply is unrestricted. Despite the simplicity of the model, its predictions are in good agreement with field observations near salt domes. Overall, our analytical model can provide critical insight into the stress field perturbation in and near rising salt domes and can be used to assess the accuracy of numerical models and field measurements near these domes. 相似文献
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Roozbeh Foroozan Derek Elsworth Peter Flemings Frank Bilotti Sankar Muhuri 《Marine and Petroleum Geology》2012,29(1):143-151
We examine the role of basin-shortening on the development of structural compartments in passive margin basins. A coupled flow-deformation model is used to follow the evolution of an idealized prismatic basin during lateral shortening. This includes the deformation-induced generation (lateral compaction) and dissipation (hydraulic fracturing) of pore fluid pressures and the resulting natural evolution of an underlying décollement and subsidiary fault structures. This model is used to examine the influence of strata stiffnesses, strain softening, permeability-strain dependence, permeability contrast between layers, and deformation rate on the resulting basin structure and to infer fluid charge within these structures. For a geometry with a permeability contrast at the base of the basin a basal décollement forms as the basin initially shortens, excess pore pressures build from the impeded drainage and hydrofracturing releases fluid mass and resets effective stresses. As shortening continues, thrust faults form, nucleating at the décollement. Elevated pore pressures approaching the lithostat are localized at the hanging wall boundary of the faults. Faults extend to bound blocks that are vertically offset to yield graben-like structural highs and lows and evolve with distinctive surface topography and separate pore pressure signatures. Up-thrust blocks have elevated fluid pressures and reduced effective stresses at their core, and down-thrust blocks the converse. The development of increased permeability on localized fault structures is a necessary condition to yield this up-thrust and down-thrust geometry. In the anti-physical case where evolution of permeability with shear strain is artificially suppressed, pervasive shear develops throughout the basin depth as fluid pressures are stabilized everywhere to the lithostat. Correspondingly, permeability evolution with shear is an important, likely crucial, feedback in promoting localization. 相似文献
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