BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:Why fracking works and why not well enough - Zdeněk P. Bažant\, 
 McCormick Institute Professor and Walter P. Murphy Professor of Civil and 
 Environmental Engineering\, Mechanical Engineering and Material Science an
 d Engineering\, Northwestern University
DTSTART:20150611T130000Z
DTEND:20150611T140000Z
UID:TALK58026@talks.cam.ac.uk
CONTACT:Ms Helen Gardner
DESCRIPTION:The astonishing success of the U.S. industry with horizontal d
 rilling and hydraulic fracturing\, aka fracking or frac\, drastically impr
 oves the energy prospects of the U.S. Many aspects of fracking\, including
  the propagation of a single crack with the flow of pressurized incompress
 ible fluid through the crack\, are well understood by now. However\, the t
 opology\, geometry and evolution of the crack system still remains an enig
 ma. This makes mechanicians wonder: Why fracking works? The answer must be
  sought in the stability of interacting hydraulic cracks. Based on: 1) the
  known gas permeability of shale\, 2) the known percentage of gas extracti
 on from shale stratum\, 3) the observed time to peak flux of gas at the we
 llhead  and 4) the observed halftime of flux decay\, it is shown that the 
 crack spacing must be only about 10 cm. This roughly coincides with rock j
 oint spacing and implies about 106 vertical cracks per frac stage. Attainm
 ent of such a small spacing requires preventing localization in parallel c
 rack systems. This is a stability problem analogous to a system of paralle
 l cooling or shrinkage cracks studied at Northwestern in 1970s. Formulated
  is a hydro-thermal analogy which makes it possible to transfer solutions 
 from cooling to hydraulic cracks. From this analogy\, and from new numeric
 al solutions of stability of a system of pressurized circular equidistant 
 vertical cracks\, it is concluded that\, at slow flow\, the localization i
 nstability can be avoided if the hydraulic pressure profile along the crac
 ks can be made almost uniform. How it depends on the rate and history of p
 umping of viscous frac water\, and on the proppants\, gellants and acids i
 n the water\, is being studied. Preventing localization in a vast system o
 f growing cracks interacting with the flow of frac water through the crack
 s (or open rock joints) is\, from the fracture mechanics viewpoint\, what 
 makes fracking work. But not well enough\, since currently only 5-15% of g
 as gets extracted from the shale strata. More extensive suppression of fra
 cture localization will be one way to increase the gas extraction percenta
 ge. It will also reduce the amount of frac water per unit amount of extrac
 ted gas and diminish the potential for seismicity since narrower and dense
 r cracks make smaller dynamic jumps at inhomogeneities. This will mitigate
  the environmental footprint. Finally\, similarities with deep sequestrati
 on of waste water and CO2 are pointed out. \nReferences:  ♦ Bažant\, Z.
 P.\, Salviato\, M.\, Chau\, Viet T.\, Viswanathan\, H. and Zubelewicz\, A.
  (2014). "Why fracking works." ASME J. of Appl. Mech. 81\, 101010-1---1010
 10-10. ♦ Bažant\, Z.P.\, and Ohtsubo\, H. (1977). ``Stability condition
 s for propagation of a system of cracks in a brittle solid." {\\em Mech. R
 es. Communications} 4\, 353--366.\nBio: Born and educated in Prague (Ph.D.
  1963 at CTU)\, Bažant joined Northwestern in 1969\, where he has been WP
  Murphy Professor since 1990 and simultaneously McCormick Institute Profes
 sor since 2002\; and Director of Center for Geomaterials (1981-87).  He wa
 s inducted to NAS\, NAE\, Am. Acad. of Arts & Sci. and Royal Soc. London\;
  to the national academies of Italy\, Austria\, Spain\, Czech Rep. and Lom
 bardy\; to Academia Europaea and Eur. Acad. of Sci. & Arts. Honorary Membe
 r: ASCE\, ASME\, ACI\, RILEM. Received 7 honorary doctorates (Prague\, Kar
 lsruhe\, UC Boulder\, Milan\, Lyon\, Vienna\, Ohio State)\; Honors: ASME T
 imoshenko\, Nadai and Warner Medals\; ASCE von Karman\, Newmark\, Biot\, M
 indlin and Croes Medals and Lifetime Achievement Award\; SES Prager Medal\
 ; RILEM L'Hermite Medal\; Exner Medal (Austria)\; Torroja Medal (Madrid)\;
  Šolín Medal (Prague)\, etc.\; was President of SES\, founding pres. of 
 IA-FRAMCOS & IA-CONCREEP\; was editor (in Chief) of JEM\, ASCE. He is Illi
 nois Registered Structural Engineer. Authored six books: Scaling of Struct
 ural Strength\, Inelastic Analysis\, Fracture and Size Effect\, Stability 
 of Structures\, Concrete at High Temperatures\, and Concrete Creep. Citati
 ons: 43\,000\, H-index: 101 (Google Apr 2015\, incl. self-cit.)\, i10 inde
 x: 479. He is one of the original top 100 ISI Highly Cited Scientists in E
 ngineering (of all fields)\; www.ISIhighlycited.com.      Home: http://cee
 .northwestern.edu/people/bazant/.\n
LOCATION:Oatley Seminar Room\, Department of Engineering
END:VEVENT
END:VCALENDAR