Selectedgaspulsetestsoninitiallysaturatedclaystonesamplesunderisotropicconfinement pressure aresimulated usinga3DTHMcode.The constitutive model considers the hydro- mechanical anisotropyof argillaceous rocks. Cross anisotropic linear elastic law is assumed for the mechanical behaviour. An embedded fracture permeability model is adopted for the hydraulic problem.Permeabilityandretentioncurvedependonstrainsthroughafractureaperture. Both hydraulicand mechanicalpartsarecoherentlylinkedtroughtwobeddingangles.Small scale heterogeneity is consideredin orderto enhancetheinitiation of flowthrough preferential paths, following thedirection ofthebeddingplanes.HM simulations are carried out considering differentbeddingorientations,parallelandnormaltotheimposedflowinthetest.Two tests simulationarepresented,thefirstwiththesamplebeddinginverticalpositionandthesecond with thebeddinghorizontal.Simulations are in agreement with recorded upstream and downstream pressures in the test. Flow patterns in each case are compared.
Fine grained sedimentary rocks such as claystones are foreseen asgeologicalbarrierinradioactivewaste disposal as well as sealing cap rocks in CO2 underground storage due to its low permeability. In the first case, most of research work concerning gas migration process in the past decadeshasbeenfocusedonthebentonitebased engineered barrier, while more attention is being recently putinthestudyofgasflow in hostrock, mainlyinfull scale tests,but smallamountofinformationisavailable at thelaboratoryscale(e.g. Rummeland Weber, 1997). In the field of CO2 storage several laboratory studies concerning thesealingefficiencyoffinegrained sedimentary rockshavebeendeveloped(Hildebrandet al., 2002; Hildebrand et al., 2004; Li et al., 2005). These works mainlyconsistofgaspulsetestsonpreviously saturated rock samples of small dimensions,from which the permeabilityto gas can be derived from Darcy’s law for compressible fluid.
In this paper, the modelling of two tests performed by Hildebrand et al.(2002)is presented.The constitutive modelfortherocktakesintoaccountitsnaturalcross anisotropy givenbythebeddingclaystoneplanes.This anisotropy isconsideredbothinitsmechanicaland hydraulic properties.
2 MODELLING APPROACH
The constitutive model for the rock is based on the cross anisotropy ofargillaceousrocks,bothinits mechanical and hydraulic behaviour. This is achieved by the use of two angles describing the orientation of the rock bedding. Bedding has an important effect on the behaviour of such type ofrockssinceitcontrolsbothitsmechanical behaviour (e.g.,highestcompressibilityindirection perpendicular to