Correlation of Acoustic Velocity, Stress, Rock Composition, Organic Matter and Rock Lamination in Organic-Rich Shales

摘要

Organic-rich shale formations have unique properties that significantly differ from conventional formations because of low permeability, anisotropy and multiscale heterogeneity. These properties are the results of lithology variation, depositional process, diagenesis, fabric and thin lamination, pore structure as well as the distribution and maturity of the organic matter which influence the rock properties and wave velocities. In this paper, the influence of rock composition, organic matter (TOC) and orientation of formation lamination on acoustic velocity in organic-rich shales was experimentally evaluated. A correlation was developed describing the dependence of the compressional wave velocity on stress, rock composition, organic matter, rock lamination orientation as well as the fluid composition. After its development using core-scale measurements of the preserved shale core samples in the laboratory, the correlation was modified to include the fluid saturation using well log data in order to obtain more accurate in situ estimation of the compressional velocity. The correlation presented here can be utilized to predict velocity, TOC, and orientation of the formation lamination or potentially the in-situ pore pressure when one of the variables are unknown. The results of this study can be utilized in economic planning and optimization of the field development for organic-rich shale source rocks. Further study is in progress to verify the validity of the correlation in other shale formation field applications as the correlation presented here is specifically developed and customized for Eagle Ford shale formation.