Fluid-flow pathways in actively deforming sediments: the role of pore fluid pressures and volume change

doi:10.1016/S0264-8172(98)00025-7

Marine and Petroleum Geology

Volume 15, Issue 4, June 1998, Pages 281-297

https://doi.org/10.1016/S0264-8172(98)00025-7 Get rights and content

Abstract

The manner in which sediments respond to burial and shear depends largely on the ease with which fluids can escape. Rapid increase of overburden pressure or shear prevents efficient dewatering and can lead to the generation of excess pore fluid pressures. A principal control on the development of overpressure and hence mechanical strength is the sediments permeability. Observations from modern plate-margin accretionary prisms indicate that many faults are associated with both overpressuring and efficient fluid flow that operates in pulses, indicative of permeability that is constantly changing. We present the results of laboratory experiments exploring how the permeability of sediment retrieved from the Barbados accretionary prism and laboratory analogues varies with progressive strain. Volume changes are linked to permeability fluctuations and the drainage capacity of the material. We investigate the importance of the previous stress history imparted on the sediment and quantify the extent to which different deformation structures can acts as conduits for fluid flow under conditions of fluctuating effective stress. Material that has been initially consolidated and then subjected to reduction of effective stress, either by raised fluid pressure, or reduction of load (inducing overconsolidation) dilates during shear zone formation and displays an increase in permeability during strain. Shear fabrics can localise flow further where the principal mode of deformation is intensely localised and brittle, and effective stress approaches zero. Conversely, normally consolidated sediments deform by bulk volume loss without generating discrete fabrics, and hence do not enhance flow under reduced effective stress conditions. Permeability can increase during strain by up to one order of magnitude when deformation results in sudden porosity collapse and pore water expulsion. Microstructural analysis and permeability testing before, during, and after shear have helped constrain the principal factors that control the evolution of flow conduits in fine-grained low permeability sediments.

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Citation Excerpt :
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PaperFluid-flow pathways in actively deforming sediments: the role of pore fluid pressures and volume change

Abstract

Computers and Geotechnics

Marine and Pet. Geol.

J. Struct. Geol.

Anisotropic permeability and tortuosity in deformed wet sediments

J. Geophys. Res.

Evaluation of the flow pump and constant head techniques for permeability measurement

Géotechnique

An Introduction to the Mechanics of Soils and Foundations

Seismic modeling of the décollement zone at the base of the Barbados Ridge accretionary complex

J. Geophys. Res.

Episodic and constant flow models for the origin of low-chloride waters in a modern accretionary complex

Water Res. Res.

A numerical model of compaction driven groundwater flow and heat transfer and its application to the palaeohydrology of intracratonic basins

J. Geophys. Res.

Heterogeneous hydrofracture development and accretionary fault dynamics

Geology

Fabric and hydraulic conductivity of sheared clays

Géotechnique

Relation between permeability and effective stress along a plate boundary fault, Barbados accretionary complex

Geology

Paleohydrogeology of the Gulf of Mexico basin

Am. J. Science

The relationship between the effective stresses and water content in saturated clays

Géotechnique

The role of fluid pressure in mechanics of overthrust faulting

Geol. Soc. Am. Bull.

Fluids in convergent margins; What do we know about their composition, origin, role in diagenesis and importance for oceanic fluxes

Phil. Trans. Royal Soc. London

Paper
Fluid-flow pathways in actively deforming sediments: the role of pore fluid pressures and volume change