Abstract
Elastic properties of shales are important for quantitative interpretation of seismic response, detecting high pore pressure before drilling and understanding overburden response during production. Modelling shale properties is difficult however as elastic properties of individual clay minerals are hard to measure directly. We use a transversely isotropic differential effective medium approach to calculate elastic constants of shales with different silt fractions. Increasing silt fraction from 0 to 25% results in an increase of elastic constants C11, C33, C13, C44 and C66 by 15%, 25%, -0.5%, 33% and 75%, respectively, whereas a 50% increase of silt fraction increases the elastic constants by 36%, 70%, -7%, 83% and 220%, respectively, in comparison with the constants of pure clay. These non-uniform alterations of elastic constants might lead to changes in elastic anisotropy. Thomsen?s anisotropy parameters e, ?, and d which describe the variation of P- and SH-wave velocities as a function of polar angle with respect to symmetry axis are also calculated. e decreases by 18% and 43% with increasing silt fraction from 0 to 25% and 0 to 50%, respectively. ? decreases by 15% and 36% by adding 25% and 50% of silt, respectively. d decreases by 60% with increasing silt fraction from 0 to 25% and changes sign when silt fraction reaches 42%. The results show that the presence of silt in shales cannot be neglected as it substantially increases compressional and shear velocities and reduces anisotropy. Elastic moduli of shales are predicted using known silt fractions and elastic moduli of clays and compared with the results of laboratory measurements.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.