Study of Mechanical and Flow Properties of Weakly Cemented and Uncemented Sands Using a Discrete Element Method

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dc.contributor.advisorOlson, Jon E.
dc.creatorLikrama, Fatmir
dc.date.accessioned2020-04-21T20:10:54Z
dc.date.available2020-04-21T20:10:54Z
dc.date.issued2008-12
dc.description.abstractMany natural gas and oil reserves are situated in uncemented and weakly cemented formations. These formations exhibit different mechanical and transport properties compared to cemented, consolidated ones. Phenomena such as sand production, wellbore stability, subsidence and permeability alteration during production have been reported in field experience and in numerous experimental results. Our work is intended to analyze these issues. A two dimensional discrete element method is developed using the commercial software PFC-2D, with the aim of studying the mechanical and transport properties of uncemented and poorly cemented sandstones. Unconfined compressive tests of poorly cemented sands, triaxial, hydrostatic compressive and radial extension tests of cemented and uncemented materials were simulated. Failure modes under different conditions and the effect of micromechanical properties of the rock’s constituents on the macroscopic behavior were studied. Comparison of our simulations to the experimental data was used to reaffirm the validity of the DEM method we are using. Pore collapse is observed in hydrostatic compression tests of wekly bonded sands with a critical pressure of 17 MPa. The failure mechanism of weakly cemented sands during triaxial tests changes at a critical confining pressure of about 4 MPa from brittle failure to strain thickening ductile failure. Using a pore network fluid flow model which takes into account the mechanics of the material from a microscopic point of view, permeability variation with deformation during triaxial, radial extension and hydrostatic compression tests was simulated and the results shown. The permeability of uncemented and weakly cemented sands is dependent on the stress state of the system and the stress path followed. Permeability of uncemented sands decreases by 55% at 5.4 MPa hydrostatic stress and by 35% before shear failure in triaxial tests of 1.0 MPa confining pressure. It increases up to 200% of the initial value during shear failure in 0.35 MPa confining stress triaxial tests and up to 200% during radial expansion tests. Weakly cemented sands’ permeability drops by 60% at 19 MPa hydrostatic pressure. Pore collapse which occurs at 17 MPa hydrostatic pressure speeds up the irrecoverable reduction in permeability. A 60% reduction in permeability of weakly cemented sands is also observed during 1.5 MPa confining pressure triaxial tests. Weakly bonded samples’ vertical permeability increases by 200% during radial expansion tests with an initial hydrostatic pressure of 5.0 MPa. A strong coupling between permeability evolution and stress-deformation state of the system exists and is confirmed in the results of all tests simulated.en_US
dc.description.departmentPetroleum and Geosystems Engineeringen_US
dc.format.mediumelectronicen_US
dc.identifier.urihttps://hdl.handle.net/2152/80760
dc.identifier.urihttp://dx.doi.org/10.26153/tsw/7775
dc.language.isoengen_US
dc.relation.ispartofUT Electronic Theses and Dissertationsen_US
dc.rightsCopyright © is held by the author. Presentation of this material on the Libraries' web site by University Libraries, The University of Texas at Austin was made possible under a limited license grant from the author who has retained all copyrights in the works.en_US
dc.rights.restrictionRestricteden_US
dc.subjectSandsen_US
dc.subjectCementeden_US
dc.titleStudy of Mechanical and Flow Properties of Weakly Cemented and Uncemented Sands Using a Discrete Element Methoden_US
dc.typeThesisen_US
dc.type.genreThesisen_US
thesis.degree.departmentPetroleum and Geosystems Engineeringen_US
thesis.degree.disciplinePetroleum Engineeringen_US
thesis.degree.grantorUniversity of Texas at Austinen_US
thesis.degree.levelMastersen_US
thesis.degree.nameMasters of Science in Engineeringen_US

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