A laboratory procedure proposed for mechanical testing of shales
Vida Minaeian A , Vamegh Rasouli A and David Dewhurst BA Curtin University
B CSIRO Earth Science and Resource Engineering
The APPEA Journal 54(1) 337-344 https://doi.org/10.1071/AJ13034
Published: 2014
Abstract
The authors have developed a laboratory procedure that uses a true triaxial stress cell (TTSC) to test cubes of rock instead of cylindrical-shaped samples. In this approach, three independent stresses are applied on the rock sample, which makes it possible to simulate field-conditions. Estimation of rock failure strength and deformation properties, while applying three stresses—rather than two as in case of conventional triaxial tests—is closer to the in-situ conditions. This is specifically important for shales due to their complicated transverse isotropic structure. The present study investigates the effect of minimum and intermediate principal stresses on the strength and elastic properties of gas shales. True triaxial experiments have been carried out on cubic shale samples from the Perth Basin under constant levels of minimum stress (~3 and 6 MPa) and varying magnitudes of intermediate principal stress (~3–40 MPa). Both minimum and intermediate stresses affect the rock strength through a non-linear trend. The behaviour of shales elastic modulus (E) with respect to varying σ2 tends to be similar to that of rock compressive strength. Poisson’s ratio in two directions along minimum and intermediate principal stresses (V13 and V12) does not show a simple dependency on the intermediate stress over the applied stress range. Finally, the observation of post-failure specimens revealed a significant influence of stress anisotropy on the failure mode, which evolves from dual to multiple shear faults.
Vida Minaeian is a PhD candidate at Department of Petroleum Engineering at Curtin University in Australia. She received her Master Degree in Petroleum Engineering in 2008 after completion of her Bachelor in Mining Engineering in 2006 at Tehran Polytechnic. Vida joined Petroleum Geomechanics Group of Curtin University (CPGG) in 2011 and started her research on geomechanical characterization of gas shales under true triaxial stress conditions. She has been awarded Curtin International Postgraduate Research Scholarship (CIPRS) and MERIWA’s (The Minerals and Energy Research Institute of Western Australia) scholarship. vida.minaeian@postgrad.curtin.edu.au |
Vamegh Rasouli is an associate professor and head of department of Petroleum Engineering at Curtin University in WA. He is a Chartered Professional Engineer (CPEng) and is a registered engineer with the National Professional Engineers Register (NPER) of Australia. Vamegh received his PhD from Imperial College London in 2002. In 2006, after joining Curtin University, he established the Curtin Petroleum Geomechanics Group (CPGG) and the Curtin Drilling Research Group (CDRG) in 2010. Vamegh is supervising a number of PhD students and is involved in a number of research and consulting projects in the area of geomechanics and drilling. He has done several projects related to petroleum geomechanics for various companies and has also been a consulting engineer on various geomechanics related projects with Schlumberger’s Data and Consulting Services (DCS) in Perth. v.rasouli@curtin.edu.au |
David N. Dewhurst is a geologist by background with a BSc from the University of Sheffield and a PhD from the University of Newcastle, both in the UK. He has worked for over 20 years on microstructure and rock properties, with an emphasis on clay and shale behaviour. He did postdoctoral stints at the University of Birmingham, University of Newcastle, L’Institut Français du Pétrole and Imperial College before moving to CSIRO in 1998. There, he has worked on overpressure, fault and top seals and the links between geomechanics, rock physics and petrophysics in shales. David is the Research Programme Leader for Petroleum Geoscience at CSIRO, leading a team of 75 people and also is the head of the CSIRO Shale Research Centre, where he leads a consortium investigating gas shales. David.Dewhurst@csiro.au |
