Oil shale anisotropy measurement and sensitivity analysis

Abstract

We have measured velocity anisotropy on 13 core samples from an organic shale oil reservoir with differential pressure up to 3000 psi. The pressure effect on velocities is generally stronger in direction normal to the bedding than along the bedding, and thus the anisotropy decreases with increasing differential pressure. P-wave anisotropy and vertical Vp/Vs ratio have good correlation with TOC content: the higher is the TOC content, the stronger is Pwave anisotropy and the lower is Vp/Vs ratio. The measured P-wave anisotropy is generally greater than Swave anisotropy. Sensitivity of c 13 and  to errors in

Physical constraints on c13 and δ for transversely isotropic hydrocarbon source rocks

“…where is the phase velocity. As Yan, Han, and Yao () pointed out, this small angle error can have significant effect on estimation of c 13 and δ. In Fig.…”

Practical and robust experimental determination of c13 and Thomsen parameter δ

“…The angle error does not cause significant difference in the estimation of δ for this sample, but as shown by Yan et al (2012), a 5°angle error can cause greater error in c 13 and δ in some cases. V P90°i s not shifted because it is measured on the axial direction of the horizontal plug.…”

“…Yan, Han and Yao (2012) showed that 1% error in estimating of 45°P-wave phase velocity can cause significant error in estimating c 13 and δ. For this sample, the scalar difference between the 45°group velocity and the 45°phase velocity is about 6%.…”

“…We did not repeat the measurement on the axial direction because the samples under study were first measured for velocity anisotropy half a year ago on our five-component (V P0°, V P90°, V SV90°, V SH90°, and V Pϕ45°) , single-horizontal-plug velocity anisotropy measurement system (Wang 2002a;Yan et al 2012). The ultrasonic velocity measurement on a cylindrical sample is usually conducted on the axial direction because the coupling between the transducer and the end surface of the sample is much better than the coupling in the radial direction.…”

“…This difference can cause significant error in estimating c 13 and δ and lead to erroneous interpretation of the deformation behaviour of the TI medium. Yan, Han and Yao (2012) showed that 1% error in estimating of 45°P-wave phase velocity can cause significant error in estimating c 13 and δ. Therefore, for reliable estimation of c 13 and δ, maximum effort should be made to ensure that genuine phase velocity or group velocity is measured with minimum uncertainty.…”