Topic
Pore water pressure
About: Pore water pressure is a research topic. Over the lifetime, 11455 publications have been published within this topic receiving 247670 citations. The topic is also known as: pwp.
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TL;DR: A coherent oil-migration model based on geomechanical considerations includes both the high-molecular kerogen structure and the capillary properties of source rocks was proposed in this paper.
Abstract: A coherent oil-migration model based on geomechanical considerations includes both the high-molecular kerogen structure and the capillary properties of source rocks. Oil is squeezed from kerogen by compaction following oil generation. This squeezing effect should be created by the differential stress (maximum compressive stress minus least compressive stress) acting on the kerogen which has been chemically broken up by oil formation. In sedimentary bodies whose water is at hydrostatic pressure, the migration of oil seems to involve two processes: (1) lateral transfer, by channeling into the more coarsely microporous layers of the source rocks, from the oil generation site toward the geologic structure or lower pressured zone; and (2) vertical transfer from source rock to eservoir by the opening or reopening of vertical fractures in the few areas, such as structural tops, where the least compressive stress is slightly greater than or equal to the pore pressure, and where the capillary pressure increment (2^ggr/R) of oil in the microporosity exceeds the tensile strength of the rock. In sedimentary bodies whose water is overpressured, the pore pressure should be governed by the least compressive stress and thus migration should begin by oil transfers in a system of small open fractures, and eventually in larger fractures. The theory demonstrates the impossibility of oil being transferred to the reservoir under true tensile conditions (negative effective compressive stress) and thus explains the large asphaltic veins of southeastern Turkey and the well-known bitumen veins of the Uinta basin.
123 citations
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TL;DR: In this paper, the effects of undrained cyclic loading on clay behavior were investigated using triaxial tests, and the authors presented concepts and methods for predicting both behaviours during and after cyclic loadings.
123 citations
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TL;DR: In this paper, the authors model the evolution of regional stress following the 1992 Landers earthquake in order to test the importance of pore fluid flow in producing aftershocks and find that regions of rising postseismic poroelastic Coulomb stress overlap considerably with regions of positive coseismic Coulomb stresses.
Abstract: [1] We model the evolution of regional stress following the 1992 Landers earthquake in order to test the importance of pore fluid flow in producing aftershocks. Rising fluid pressure due to pore fluid flow and the resulting Coulomb stress changes were found to be strongly correlated with the time and location of aftershock events. Regional aftershock frequencies computed by integrating pore pressure decay rates also agreed quite well with aftershock data. Calculations show that regions of rising postseismic poroelastic Coulomb stress overlap considerably with regions of positive coseismic Coulomb stress. Thus pore fluid flow, which affects pore pressure within faults and causes regional poroelastic stress evolution following earthquakes, gradually evolves the initial coseismic stress changes. Together these changes provide a reasonable physical mechanism for aftershock triggering which agrees with data for the 1992 Landers earthquake.
123 citations
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TL;DR: In this article, the authors studied the mechanical behavior of serpentinite under conditions of dehydration to olivine + talc + water, at temperatures ranging between 300° and 600° and at total pressures from 100 to 300 MPa.
Abstract: We have studied the mechanical behavior of serpentinite under conditions favouring dehydration to olivine + talc + water, at temperatures ranging between 300° and 600° and at total pressures from 100 to 300 MPa. Constant stress, stress relaxation and constant displacement rate testing techniques permitted a wide range of deformation rates and paths to be accessed. Effective confining pressure was held constant during the dehydration process by means of a controlled pore water pressure system. Stress supported by the samples was almost independent of deformation rate at temperatures below those required for the onset of the breakdown reaction. At 500° and 600°C, however, the strength was linearly dependent on the inverse of the deformation rate, and independent of effective confining pressure over the range investigated. Microstructural studies revealed that the weakening was associated with sliding in narrow shear zones containing ultrafine-grained (0.1 µm olivine produced in the breakdown reaction. The enhanced deformability is interpreted in terms of flow of the olivine in these shear zones by diffusion-accommodated grain boundary sliding. These experimental results suggest that metamorphic transformations affect the deformability of rocks, and demonstrate enhancement of deformability through the transient existence of fine-grained reaction products. The results may also be applicable to the mechanics of deformation processes in oceanic transform faults and give some indication of the degree of weakening that might be expected from grain-size reduction by dynamic recrystallization in plastically deforming rocks.
123 citations
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TL;DR: In this article, the authors hypothesize that depression of pore pressure resulting from rebound during erosional unloading also may occur in certain geologic settings, such as some shales.
Abstract: When rocks deform in response to changes in stress, the small variations in pore volume that occur affect the pore fluid pressure. The changes in fluid pressure can be significant if the rate of change of stress is large relative to the rate at which pressure perturbations are dissipated by flow. It has been proposed previously that the gradually increasing loads on sediments undergoing burial can cause excess fluid pressures. We hypothesize that the opposite effect, depression of pore pressure resulting from rebound during erosional unloading, also may occur in certain geologic settings. Simple theoretical treatment of the problem indicates that rocks with small hydraulic diffusivity, such as some shales, could experience significant pore pressure decreases when unloaded by moderate rates of erosion. The analysis further indicates that decreases sufficient to produce negative pressures can occur. No theoretical bar to this condition exists, and it has been achieved in the laboratory. However, in subsurfa...
123 citations