UC Berkeley

The significance of shales for unconventional hydrocarbon reservoirs, nuclear waste repositories, and geologic carbon stor- age has opened new research frontiers in geophysics. Among many of its unique physical properties, elastic anisotropy had long been investigated by experimental and computational ap- proaches. Here, we calculated elastic properties of Cretaceous Muderong Shale from Australia with a self-consistent averaging method based on microstructural information. The volume frac- tion and crystallographic preferred orientation distributions of constituent minerals were based on synchrotron x-ray diffrac- tion experiments. Aspect ratios of minerals and pores, deter- mined from scanning electron microscopy, were introduced in the self-consistent averaging. Our analysis suggested that phyllosilicates (i.e., illite-mica, illite-smectite, kaolinite, and chlorite) were dominant with ~70 vol:%. The shape of clay platelets displayed an average aspect ratio of 0.05. These plate- lets were aligned parallel to the bedding plane with a high degree of preferred orientation. The estimated porosity at am- bient pressure was ~17 vol:% and was divided into equiaxial pores and flat pores with an average aspect ratio of 0.01. Our model gave results that compared satisfactorily with values derived from ultrasonic velocity measurements, confirming the validity and reliability of our approximations and averaging approach.