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Microstructural and microchemical consequences of fluid flow in deforming rocks
66A
PROPERTIES:PERMEABILITY & CAPILLARITY
952157 Application of the Pi theorem to the wear rate of gouge formation in frictional sliding of rocks H. Nagahama & N. Nakamura, Pure & Applied Geophysics, 142(3-4), 1994, pp 795-808. A simple law of wear rate is examined for the process of gouge generation during the frictional sliding of simulated faults in rocks, by use of the Pi theorem method (dimensional analysis) and existing experimental data. The relationship between wear rate (t/d) and the applied stress can be expressed by the power-law relations: t/d = Coo~'', t/d = C ~ , where t is the thickness of the gouge generated on the frictional surfaces, d is the fault displacement, ~ and ~ are normal stress and shear stress, respectively, and Co, C,, mo and m, are constants. These results indicate that the exponent coefficients, mo and m~ and the coefficients Co and C~ depend on the material hardness of the frictional surfaces. By using the wear rates of natural faults, these power-law relationships may prove to be an acceptable palaeopiezometer of natural faults and the lithosphere. (Authors)
Physico-chemical properties 952158 Methods for estimating the properties of soils as geochemical barriers for heavy metals V. I. Sergeev, ITC Journal, 1994-1, 1994, pp 29-33. Groundwater pollution caused by heavy metals in industrial wastes affects both industrialized and industrializing countries. Experimental data confirm that a foundation layer of clay in the aeration zone can act as a geochemical barrier to the downward migration of heavy metals. It is also possible to predict the life-spans of these clay layers as effective pollution screens, and thus to predict the useful life of waste disposal sites. (Author)
Permeability and capillarity 952159 Fluid flow in actively deforming sediments: 'dynamic permeability' in accretionary prisms E. L. Stephenson, A. J. Maltman & R. J. Knipe, in:
Geofluids: origin, migration and evolution of fluids in sedimentary basins, ed J. Parnell, (Geoleogical Society, London; Special Publication, 78), 1994, pp 113-125. Experimental data are presented which show that permeability during accumulating strain, here called the dynamic permeability, is not a static value but is highly variable. Moreover, microstructural analysis and precise determination of permeant volume reveal that this dynamic permeability is not solely the varying capacity of the deforming medium to transmit fluid, a quantity here called the Darcyan permeability, but includes a contribution to the amount of permcant from the medium itself. In the laboratory experiments this additional contribution, called the dynamic component, arises from pore-volume fluctuations associated with microstrucrural changes, but in nature there may be further mechanical and chemical effects. (from Authors)
952160 Microstrueturai and mierochemical consequences of fluid flow in deforming rocks R. J. Knipe & A. M. McCaig, in: Geofluids: origin, migration and evolution of fluids in sedimentary basins, ed J. Parnell, (Geological Society, London: Special Publication, 78), 1994, pp 99-111.
A critical factor in the efficiency of fluid flow in deformed rocks is the competition between the processes which maintain the connectivity of the high permeability pathways and those which close such pathways. The range of deformation processes which are involved in this competition will be different depending on the tectonic settings, the deformation conditions and the rock types involved. A brief review of the processes which interact to control fluid flow during deformation in sedimentary basins, crystalline basement under low to moderate grade metamorphism and during prograde metamorphism at moderate to high grades is given. (from Authors)
952161 An integrated approach to the study of primary petroleum migration U. Mann, in: Geofluids: origin, migration and evolution of fluids in sedimentary basins, ed J. Parnell, (Geological Society, London; Special Publication, 78), 1994, pp 233-260. There is more than one mechanism, and the pathways and efficiencies of individual mechanisms vary from case history to case history due to the variable abundances of micropores, macropores and fractures in source rocks as well as different sources for the build-up of a pressure gradient. Primary migration probably proceeds as diffusion through source rock micropores via mesopores to macropores and fractures. From there, a petroleum bulk phase develops, and moves along the macropores and fracture system, possibly together with aqueous solutions. In fact, many parameters influence petroleum transport out of a source rock, and all of them have seldom been checked by exploration geologists as most mature source rocks are inaccessible. (from Author)
952162 The role of geopressure zones in the formation of hydrothermal Pb-Zn Mississippi Valley-type mineralization in sedimentary basins A. D. Fowler, in: Geofluids: origin, migration and evolution of fluids in sedimentary basins, ed J. Parnell, (Geological Society, London; Special Publication, 78), 1994, pp 293-300. Geopressure zones immediately subjecent to platform carbonate rocks can be modelled to serve as proximal sources of hydrothermal fluids for epigenetic Pb-Zn deposits in sedimentary basins. In some geopressure zones of the Gulf of Mexico, geothermal gradients can be as high as 10°C I00 m "l. This arises because the water-saturated gcopressured shale masses act as thermal insulators. C-eopressure zones may have sufficient fluid pressure to rupture overlying strata, providing a vertical conduit for hot mineralized brine to migrate directly into carbonate host rocks. (Author)
952163 Dual-porosity behaviour of naturally fractured reservoirs M. Bai, Q. Ma & J.-C. Roegiers, International Journal for Numerical & Analytical Methods in Geomechanics, 18(6), 1994, pp 359-376. A dual-porosity model for a finite naturally fractured reservoir subjected to a constant outer boundary pressure is obtained using the Hankel transform technique, taking into account the transient flow in the matrix blocks. Both solution accuracy and efficiency are achieved utilizing an optimized algorithm when solving the inherent Bessel functions. This research indicates that the transient fluid pressure profiles in naturally fractured reservoirs are critically controlled by the permeability ratio between matrix and fractures, and by the compressibilities of fluid, fractures and solid grains. Fluid pressure change is shown to be substantially delayed if the permeability ratio becomes increasingly smaller. (from Authors)
PROPERTIES:PERMEABILITY & CAPILLARITY
952157 Application of the Pi theorem to the wear rate of gouge formation in frictional sliding of rocks H. Nagahama & N. Nakamura, Pure & Applied Geophysics, 142(3-4), 1994, pp 795-808. A simple law of wear rate is examined for the process of gouge generation during the frictional sliding of simulated faults in rocks, by use of the Pi theorem method (dimensional analysis) and existing experimental data. The relationship between wear rate (t/d) and the applied stress can be expressed by the power-law relations: t/d = Coo~'', t/d = C ~ , where t is the thickness of the gouge generated on the frictional surfaces, d is the fault displacement, ~ and ~ are normal stress and shear stress, respectively, and Co, C,, mo and m, are constants. These results indicate that the exponent coefficients, mo and m~ and the coefficients Co and C~ depend on the material hardness of the frictional surfaces. By using the wear rates of natural faults, these power-law relationships may prove to be an acceptable palaeopiezometer of natural faults and the lithosphere. (Authors)
Physico-chemical properties 952158 Methods for estimating the properties of soils as geochemical barriers for heavy metals V. I. Sergeev, ITC Journal, 1994-1, 1994, pp 29-33. Groundwater pollution caused by heavy metals in industrial wastes affects both industrialized and industrializing countries. Experimental data confirm that a foundation layer of clay in the aeration zone can act as a geochemical barrier to the downward migration of heavy metals. It is also possible to predict the life-spans of these clay layers as effective pollution screens, and thus to predict the useful life of waste disposal sites. (Author)
Permeability and capillarity 952159 Fluid flow in actively deforming sediments: 'dynamic permeability' in accretionary prisms E. L. Stephenson, A. J. Maltman & R. J. Knipe, in:
Geofluids: origin, migration and evolution of fluids in sedimentary basins, ed J. Parnell, (Geoleogical Society, London; Special Publication, 78), 1994, pp 113-125. Experimental data are presented which show that permeability during accumulating strain, here called the dynamic permeability, is not a static value but is highly variable. Moreover, microstructural analysis and precise determination of permeant volume reveal that this dynamic permeability is not solely the varying capacity of the deforming medium to transmit fluid, a quantity here called the Darcyan permeability, but includes a contribution to the amount of permcant from the medium itself. In the laboratory experiments this additional contribution, called the dynamic component, arises from pore-volume fluctuations associated with microstrucrural changes, but in nature there may be further mechanical and chemical effects. (from Authors)
952160 Microstrueturai and mierochemical consequences of fluid flow in deforming rocks R. J. Knipe & A. M. McCaig, in: Geofluids: origin, migration and evolution of fluids in sedimentary basins, ed J. Parnell, (Geological Society, London: Special Publication, 78), 1994, pp 99-111.
A critical factor in the efficiency of fluid flow in deformed rocks is the competition between the processes which maintain the connectivity of the high permeability pathways and those which close such pathways. The range of deformation processes which are involved in this competition will be different depending on the tectonic settings, the deformation conditions and the rock types involved. A brief review of the processes which interact to control fluid flow during deformation in sedimentary basins, crystalline basement under low to moderate grade metamorphism and during prograde metamorphism at moderate to high grades is given. (from Authors)
952161 An integrated approach to the study of primary petroleum migration U. Mann, in: Geofluids: origin, migration and evolution of fluids in sedimentary basins, ed J. Parnell, (Geological Society, London; Special Publication, 78), 1994, pp 233-260. There is more than one mechanism, and the pathways and efficiencies of individual mechanisms vary from case history to case history due to the variable abundances of micropores, macropores and fractures in source rocks as well as different sources for the build-up of a pressure gradient. Primary migration probably proceeds as diffusion through source rock micropores via mesopores to macropores and fractures. From there, a petroleum bulk phase develops, and moves along the macropores and fracture system, possibly together with aqueous solutions. In fact, many parameters influence petroleum transport out of a source rock, and all of them have seldom been checked by exploration geologists as most mature source rocks are inaccessible. (from Author)
952162 The role of geopressure zones in the formation of hydrothermal Pb-Zn Mississippi Valley-type mineralization in sedimentary basins A. D. Fowler, in: Geofluids: origin, migration and evolution of fluids in sedimentary basins, ed J. Parnell, (Geological Society, London; Special Publication, 78), 1994, pp 293-300. Geopressure zones immediately subjecent to platform carbonate rocks can be modelled to serve as proximal sources of hydrothermal fluids for epigenetic Pb-Zn deposits in sedimentary basins. In some geopressure zones of the Gulf of Mexico, geothermal gradients can be as high as 10°C I00 m "l. This arises because the water-saturated gcopressured shale masses act as thermal insulators. C-eopressure zones may have sufficient fluid pressure to rupture overlying strata, providing a vertical conduit for hot mineralized brine to migrate directly into carbonate host rocks. (Author)
952163 Dual-porosity behaviour of naturally fractured reservoirs M. Bai, Q. Ma & J.-C. Roegiers, International Journal for Numerical & Analytical Methods in Geomechanics, 18(6), 1994, pp 359-376. A dual-porosity model for a finite naturally fractured reservoir subjected to a constant outer boundary pressure is obtained using the Hankel transform technique, taking into account the transient flow in the matrix blocks. Both solution accuracy and efficiency are achieved utilizing an optimized algorithm when solving the inherent Bessel functions. This research indicates that the transient fluid pressure profiles in naturally fractured reservoirs are critically controlled by the permeability ratio between matrix and fractures, and by the compressibilities of fluid, fractures and solid grains. Fluid pressure change is shown to be substantially delayed if the permeability ratio becomes increasingly smaller. (from Authors)