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SUMMARY:MEchanics GAthering -MEGA- Seminar: Stress preconditioning in Enha
 nced Geothermal Systems
DTSTART:20200305T161500
DTEND:20200305T173000
DTSTAMP:20260916T063414Z
UID:3e45384b36f1c3b6afe655942f379a094218070b17bd16b08de02fb5
CATEGORIES:Conferences - Seminars
DESCRIPTION:Barnaby Padraig Fryer\, Laboratory of Soil Mechanics (LMS)\, 
 EPFL\nGeothermal energy is a renewable source of energy that would be capa
 ble of providing baseload power to large parts of the world were it not fo
 r a few key issues. Notably\, Enhanced Geothermal Systems (EGSs)\, which c
 ould pave the way for geothermal electricity production even in regions wi
 th moderately low geothermal gradients\, still struggle with their tendenc
 y to induce damaging seismicity when stimulated. It is therefore essential
  that methodologies are developed that mitigate the seismic risk associate
 d with EGS.\n\nUnfortunately\, the mechanism by which stimulation occurs i
 n many EGS stimulations is essentially the same as that in induced earthqu
 akes\, shear failure. Recently there has been an increased focus on soft s
 timulation\, whereby an effort is made to encourage the shear failure requ
 ired for reservoir stimulation and avoid the shear failure associated with
  large magnitude induced seismicity\; however\, so far these techniques ha
 ve been unable to prevent large earthquakes. In this sense\, a stimulation
  technique which lends itself to the induction of small seismic events and
  not large ones would represent a major step forward for the EGS industry.
 \n\nIt is suggested here that it is possible to design a stimulation treat
 ment that begins with a long period of injection-induced temperature chang
 e with the goal of reducing the differential stress in the reservoir\, pre
 conditioning the stress. During this stress-preconditioning phase\, the po
 re pressure increase is limited such that shear failure is avoided. Then\,
  after this period of temperature change\, a short period of high rate inj
 ection occurs with the goal of increasing the pore pressure. This second p
 hase induces shear failure on the optimally oriented faults/fractures in t
 he reservoir. Importantly\, the shear failure that occurs on faults/fractu
 res when following this methodology occurs on shear planes that are suppor
 ting less differential stress than they would have been had the reservoir 
 been stimulated without the first phase of temperature change. The advant
 age of maintaining a low differential stress comes from the connection see
 n between differential stress and the Gutenberg– Richter b-value. This c
 onnection implies that\, by maintaining a low differential stress\, a high
  b-value will be seen during stimulation. A high b-value results in more l
 ow magnitude seismic events and relatively few large magnitude events that
  might pose a nuisance to the public\, or even cause damage. In this way\,
  EGS reservoir stimulation can still be performed\, inducing shear failure
  on pre-existing planes of weakness\, with a lower risk of inducing large 
 events. The development and potential implications of this stimulation tec
 hnique will be addressed here.
LOCATION:MED 2 2423 https://plan.epfl.ch/?room==MED%202%202423
STATUS:CONFIRMED
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