Linking preferred orientations to elastic anisotropy in Muderong Shale, Australia

Abstract

The significance of shales for unconventional hydrocarbon reservoirs, nuclear waste repositories, and geologic carbon storage has opened new research frontiers in geophysics. Among many of its unique physical properties, elastic anisotropy had long been investigated by experimental and computational approaches. Here, we calculated elastic properties of Cretaceous Muderong Shale from Australia with a self-consistent averaging method based on microstructural information. The volume fraction and crystallographic preferred orientation distributions of constituent minerals were based on synchrotron x-ray diffraction experiments. Aspect ratios of minerals and pores, determined 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 [Formula: see text]. The shape of clay platelets displayed an average aspect ratio of 0.05. These platelets were aligned parallel to the bedding plane with a high degree of preferred orientation. The estimated porosity at ambient pressure was [Formula: see text] 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.

Seismic properties and anisotropy of the continental crust: Predictions based on mineral texture and rock microstructure

“…[] and Kanitpanyacharoen et al . [] indicate that purely CPO‐based models are not appropriate for modeling the seismic properties of shale, and microstructural and porosity factors need to be considered.…”

“…Kanitpanyacharoen et al . [] have provided further insight into elastic anisotropy of shale, from a microstructural and CPO point of view. They studied the Muderong Shale from Australia, using two different effective medium models, (1) a combined self‐consistent modeling scheme (GeoMIXself) [ Matthies , ] that takes into consideration both CPO, as well as grain and pore aspect ratios, and (2) a differential effective medium model.…”

“…They studied the Muderong Shale from Australia, using two different effective medium models, (1) a combined self-consistent modeling scheme (GeoMIXself) [Matthies, 2010] that takes into consideration both CPO, as well as grain and pore aspect ratios, and (2) a differential effective medium model. The studies of Vasin et al [2013] and Kanitpanyacharoen et al [2015] indicate that purely CPO-based models are not appropriate for modeling the seismic properties of shale, and microstructural and porosity factors need to be considered.…”

Deformation mechanisms and evolution of the microstructure of gouge in the Main Fault in Opalinus Clay in the Mont Terri rock laboratory (CH)

“…10e) and bent (e.g., Fig. 14a) clay particles, although elastic deformation may also cause this Kanitpanyacharoen et al, 2015). In a nano-indentation test to determine the elasticity of single phyllosilicate minerals, Zhang et al (2010) suggest measurement artifacts caused by intracrystalline plasticity beneath the indenter tip.…”

Texture Development of Clay‐Rich Sediments Across the Costa Rica Subduction Zone

“…By rotating the sample 180° in 5° steps, we achieve full pole figure coverage with a 5° grid, as we extract diffraction patterns every 5° from the plate detector images. This is a higher resolution as, for example, used by Lonardelli et al (), Wenk et al (), or Kanitpanyacharoen et al (), who rotated their samples about 60–90° by measuring every 10–15° and did not get full pole figure coverage. According to a large grain size variability, number of different mineral phases, weak preferred orientations, and a generally high microstructural heterogeneity, it is important to reach a good pole figure coverage, which represents the fabric adequately.…”