Rock Mechanics of Shale

Zunyi Xia, Carl H. Sondergeld, Chandra S. Rai, and Richard Sigal
University of Oklahoma, Norman, OK

The geotechnical properties of shale are required for stimulation and production of gas from shale gas reservoirs. A limited number of studies are available in the literature on the rock mechanics of shales. We performed dynamic and static tests simultaneously on shale samples in directions - parallel and perpendicular to the bedding. More than half of the samples showed less than 10% difference between the static and dynamic Young’s modulus. Several shale samples have static Poisson’s ratio larger than 0.5 because of the anisotropy. The Young’s moduli of the vertical samples are more stress dependent than the horizontal samples. The failure stress of the horizontal and vertical shale samples range from 7 to more 31 kpsi and 14 to 33 kpsi, respectively. The correlation between modulus and the lithology facies has been examined.

Our shale samples displayed a wide variation in mineralogy. Our shales are dominated by clays, illite and smectite constitute almost 22% by weight. The two other minerals of consequence are Calcite and Quartz ranging respectively from 0 to 21% and 0 to 19% by weight.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas