BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Memento EPFL// BEGIN:VEVENT SUMMARY:MEchanics GAthering -MEGA- Seminar: Talk1 - A semi-infinite hydrau lic fracture driven by a shear-thinning fluid\; Talk2 - Evolution of asei smic and seismic slip on a pressurized dilatant fault with frictional weak ening properties DTSTART:20181206T161500 DTEND:20181206T173000 DTSTAMP:20260924T163604Z UID:f55f15bbb4da4bc4bc9409e4678bc23d54541c2a13d60f7515af5cb3 CATEGORIES:Conferences - Seminars DESCRIPTION: Fatima-Ezzahra Moukhtari and Federico Ciardo\, GEL\, EPFL \nA semi-infinite hydraulic fracture driven by a shear-thinning fluid by  Fatima-Ezzahra Moukhtari\, GEL\, EPFL\nAbstract Complex fluids are often used in hydraulic fracturing practice due to their interesting shear thin ning properties that notably minimize pressure losses when pumped down the wellbore while allowing for large fracture width during hydraulic fractur e propagation. We focus here on the near-tip region of a hydraulic fractur e where most of the solid-fluid non-linearities reside. We solve the coupl ed problem of a semi-infinite hydraulic fracture propagating at a constant velocity in an impermeable linearly elastic material. We allow for the oc currence of a region without fluid of a-priori unknown length at the fract ure tip. We use the Carreau rheological model - which we compare with simp ler rheological models - in order to properly account for the shear thinni ng of fracturing fluid between the low and large shear rates Newtonian lim its. The solution exhibits a complex structure with up to four distinct as ymptotic regions: a region governed by the classical linear elastic fractu re mechanics behaviour near the tip\, a high shear rate viscosity asymptot ic and power-law asymptotic regions in the intermediate field and a low sh ear rate viscosity asymptote far away from the fracture tip. The occurrenc e and order of magnitude of the extent of these different asymptotic regio ns are obtained analytically via scaling arguments. Our results quantify h ow shear thinning drastically reduces the size of the fluid lag compared t o a Newtonian fluid.\nF. E. Moukhtari and B. Lecampion. A semi-infinite hy draulic fracture driven by a shear thinning fluid. Journal of Fluid Mecha nics\, 838:573–605\, 2018.\n\nEvolution of aseismic and seismic slip on a pressurized dilatant fault with frictional weakening properties by Fed erico Ciardo\, GEL\, EPFL\nAbstract Aseismic slip associated with shear crack activation on a pressurized fault may or may not turn into seismic s lip depending on in situ conditions\, frictional properties\, value of inj ection over-pressure and dilatant compliance fault behavior. By focusing o n a “young” fault\, for which the mechanically weak gouge unit accommo dating slip is also the most permeable\, we develop a planar bi-dimensiona l fault hydro-mechanical model accounting for weakening of frictional prop erties with slip. Specifically\, we study the effect of fault dilatancy on the fluid driven shear crack propagation\, when the in-situ background sh ear stress to is both larger and lower than residual frictional strength  tr (i.e. unstable and ultimately stable fault\, respectively). The undr ained pore pressure drop associated with dilatancy induces a shear fault s trengthening near the propagating crack tips. An undrained residual fault shear strength tur is thus introduced. Under small scale yielding condit ion\, we show theoretically that an otherwise unstable fault never exhibit transition to seismic slip when tur is larger than to. \nThe numerica l solutions of the fully coupled hydro-mechanical problem confirm such sta bilization. Finally\, we show that if the fault longitudinal permeability increases considerably during the dilatant process\, the aseismic crack gr owth accelerates but never diverges. In other words\, the undrained fault stabilization due to dilatancy still holds for large increase of permeabil ity.  \n  LOCATION:MED 2 2423 https://plan.epfl.ch/?room=MED22423 STATUS:CONFIRMED END:VEVENT END:VCALENDAR