000			02004nab a2200193 4500
005			20260520001839.0
008			260224s2010 xxu
245	0	0	_aViscous creep in room-dried unconsolidated Gulf of Mexico shale (II) _bDevelopment of a viscoplasticity model
260			_a _b _cmayo 2010
270			_a03/08/2010 ; 02/08/2010
300			_a6 p. ; 50-55
520			_aTranscripción del resumen del autor. Laboratory creep experiments show that compaction of dry Gulf of Mexico shale is a permanent irrecoverable process associated with viscoplastic deformation. In order to find a relatively simple model that can describe such viscoplastic behavior of the dry frame of the shale, we combined the Perzyna viscoplasticity constitutive law with a modified Cambridge clay plastic yield model. The constitutive equation for this model is a power-law function that relates strain rate to the ratio of dynamic and static yield surfaces defined by the modified Cam-clay model. By incorporating the effect of strain hardening on the static yield pressure, we derived an equation relating volumetric creep strain at a constant hydrostatic pressure level to the logarithm of time, which is in good agreement with experimental results. We determined the model parameters by fitting experimental data of creep strain as a function of time. The determined parameters indicate that the yield stress of the hydrostatically loaded shale increases by 6–7% as strain rate rises by an order of magnitude. This demonstrates that the laboratory-based prediction of yield stress (as well as porosity) may be significantly overestimated. Thus, strain-rate calibration is required for weak shales such as those studied here to appropriately estimate physical properties under in situ conditions.
581			_a1-2
773	0		_tJournal of Petroleum Science & Engineering _g72
942			_cARTICULO
100	1		_aChang, Chandong _942910
100	1		_aZoback, Mark D. _921228
999			_c175667 _d175667