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Experimental study of the evolution of permeability in rocks under simulated crustal stress conditions

Keaney, Gemma Maria Jacinta; (2000) Experimental study of the evolution of permeability in rocks under simulated crustal stress conditions. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

The fluid permeability of rocks is a complex rock physical property, in general dependent on such factors as effective pressure, stress history and anisotropy. Very little experimental data exist that describe the changes in permeability and poro-elastic properties (specific storage) that occur during loading to brittle failure, particularly in low porosity rocks. In this experimental programme the permeability evolution in three different porosity-permeability evolutionary situations has been compared; isotropic increases in crack damage, hydrostatic compaction (pore closure) and non-hydrostatic deformation (anisotropic pore closure and anisotropic pore opening). A methodology has been newly-developed in order to measure permeability and specific storage in a low permeability sandstone undergoing hydrostatic and non-hydrostatic deformation. Under hydrostatic stress conditions, permeability has been shown to be sensitive to effective pressure and effective pressure history. An empirical effective pressure law for permeability and specific storage in Tennessee sandstone has been determined. The evolution of permeability parallel to the direction of the maximum compressive stress (O-1) has been investigated as a function of increasing magnitudes of O-1 in triaxial compression deformation experiments and a unique integrated analysis of the stress-strain, pore volume, permeability and specific storage evolution has been undertaken. All rocks were deformed within the brittle faulting regime, allowing investigation of changes in permeability, specific storage and pore volume during compaction, dilatancy, brittle faulting and stable frictional sliding. Over the range of effective pressures investigated (20 MPa - 250 MPa) permeability shows a consistent pattern of evolution up to brittle failure. Upon initial loading permeability reduces to 0.5 of the starting permeability during compaction, and increases by up to an order of magnitude during dilatancy from the permeability 'minimum' measured during compaction. During stable sliding permeability decreases steadily, possibly reflecting the development of a relatively impermeable seal to fluids. An assessment is made of the roles of hydrostatic and non-hydrostatic stresses in controlling permeability and specific storage, and stress path dependence of permeability and specific storage under non-hydrostatic stress conditions is demonstrated.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Experimental study of the evolution of permeability in rocks under simulated crustal stress conditions
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Applied sciences; Fluid permeability
URI: https://discovery.ucl.ac.uk/id/eprint/10100899
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