HR: 0830h
AN: T41D-0253    [PDF]
TI: Development of Discrete Compaction Bands in Two Porous Sandstones
AU: * Tembe, S
EM: stembe@ic.sunysb.edu
AF: Dept of Geosciences, SUNY, Stony Brook, NY 11794-2100 United States
AU: Baud, P
EM: Patrick.Baud@eost.u-strasbg.fr
AF: Universite de Louis Pasteur, IPG, 5 rue Rene Descartes, Strasbourg, 67084 France
AU: Wong, T
EM: Teng-fong.Wong@stonybrook.edu
AF: Dept of Geosciences, SUNY, Stony Brook, NY 11794-2100 United States
AB: Compaction band formation has been documented by recent field and laboratory studies as a localized failure mode occurring in porous sandstones. The coupling of compaction and localization may significantly alter the stress field and strain partitioning, and act as barriers within reservoirs. Two end-members of this failure mode that develop subperpendicular to the maximum principal stress have been identified: numerous discrete compaction bands with a thickness of only several grains, or a few diffuse bands that are significantly thicker. Much of what is known about discrete compaction bands derives from laboratory experiments performed on the relatively homogeneous Bentheim sandstone with 23% porosity. In this study we observe similar compaction localization behavior in the Diemelstadt sandstone, that has an initial porosity of 24.4% and a modal composition of 68% quartz, 26% feldspar, 4% oxides, and 2% micas. CT scans of the Diemelstadt sandstone indicate bedding corresponding to low porosity laminae. Saturated samples cored perpendicular to bedding were deformed at room temperature under drained conditions at a constant pore pressure of 10 MPa and a confining pressure range of 20-175 MPa. Acoustic emission activity and pore volume change were recorded continuously. Samples were deformed to axial strains of 1-4% and recovered from the triaxial cell for microstructural analysis. The mechanical data map the transition in failure mode from brittle faulting to compactive cataclastic flow. The brittle regime occurred at effective pressures up to 40 MPa, associated with failure by conjugate shear bands. At an effective pressure range of 60-175 MPa strain hardening and shear-enhanced compaction were accompanied by the development of discrete compaction bands, that was manifested by episodic surges of acoustic emission. Preliminary microstructural observations of the failed samples suggest that bedding influenced the band orientations which varies between 75-90\deg relative to the maximum principle stress. Our study demonstrates that despite their different mineralogy, failure modes and development of the compaction localization are similar in the Diemelstadt and Benthiem sandstones.
DE: 5104 Fracture and flow
DE: 5112 Microstructure
DE: 5114 Permeability and porosity
DE: 8030 Microstructures
SC: Tectonophysics [T]
MN: 2003 Fall Meeting