Texture and anisotropy analysis of Qusaiba shales

Abstract

A B S T R A C TScanning and transmission electron microscopy, synchrotron X-ray diffraction, microtomography and ultrasonic velocity measurements were used to characterize microstructures and anisotropy of three deeply buried Qusaiba shales from the Rub'alKhali basin, Saudi Arabia. Kaolinite, illite-smectite, illite-mica and chlorite show strong preferred orientation with (001) pole figure maxima perpendicular to the bedding plane ranging from 2.4-6.8 multiples of a random distribution (m.r.d.). Quartz, feldspars and pyrite crystals have a random orientation distribution. Elastic properties of the polyphase aggregate are calculated by averaging the single crystal elastic properties over the orientation distribution, assuming a nonporous material. The average calculated bulk P-wave velocities are 6.2 km/s (maximum) and 5.5 km/s (minimum), resulting in a P-wave anisotropy of 12%. The calculated velocities are compared with those determined from ultrasonic velocity measurements on a similar sample. In the ultrasonic experiment, which measures the effects of the shale matrix as well as the effects of porosity, velocities are smaller (P-wave maximum 5.3 km/s and minimum 4.1 km/s). The difference between calculated and measured velocities is attributed to the effects of anisotropic pore structure and to microfractures present in the sample, which have not been taken into account in the matrix averaging.

Linking preferred orientations to elastic anisotropy in Muderong Shale, Australia

“…Kaolinite and chlorite are also present with a relatively minor amounts of 14.4 vol.% and 4.1 vol.%, respectively. Illite-mica and chlorite show the highest degrees of preferred orientation, and illite-smectite, probably authigenic, exhibits relatively weaker degrees of preferred orientation (Figures 3 and 4), which is consistent with previous studies on shales (e.g., Wenk et al, 2008Wenk et al, , 2010Kanitpanyacharoen et al, 2011Kanitpanyacharoen et al, , 2012.…”

“…In addition, flat pores and cracks also tend to align subparallel to the bedding plane and amplify the elastic anisotropy of shale (e.g., Jones and Wang, 1981;Sayers, 2008;Keller et al, 2011). Several studies have characterized pore types and pore shapes from microto nano-scale (e.g., Loucks et al, 2009Loucks et al, , 2012Kanitpanyacharoen et al, 2011;Keller et al, 2011Keller et al, , 2013Kuila and Prasad, 2013) to describe their influence on elastic properties.…”

A comparative study of X-ray tomographic microscopy on shales at different synchrotron facilities: ALS, APS and SLS

“…SRXTM methods may be complemented with nanoscale approaches such as focused-ion-beam scanning electron microscopy (Keller et al, 2011;Bera et al, 2011), transmission electron microscopy (Kanitpanyacharoen et al, 2011) and X-ray nanotomography (Nelson et al, 2011;Grew et al, 2010). Overall, this round-robin experiment of SRXTM documented that all three beamlines produce similar results with microstructural resolution of approximately 2 mm.…”

“…With its growing importance in the geological field, SRXTM has been applied to various geomaterials such as sandstone (Lindquist et al, 2000), mylonite (Fusseis et al, 2009), peridotite , volcanic rock (Voltolini et al, 2011), meteorites (Friedrich et al, 2008), gypsum (Fusseis et al, 2012) and shale (Lenoir et al, 2007;Kanitpanyacharoen et al, 2011Kanitpanyacharoen et al, , 2012. Shales are of interest owing to the low porosity and permeability, which allow them to serve as cap rocks for hydrocarbon reservoirs (Best & Katsube, 1995), repository sites for nuclear wastes (Mallants et al, 2001;Bossart & Thury, 2007), and storehouses for carbon sequestration (Chadwick et al, 2004;Busch et al, 2008).…”

Fabric Development and Pore-Throat Reduction in a Mass-Transport Deposit in the Jubilee Gas Field, Eastern Gulf of Mexico: Consequences for the Sealing Capacity of MTDs

“…The degree of preferred orientation or texture can be expressed as the maximum pole densities in multiples of random distribution -m.r.d. -in which a value of 1 corresponds to a random or isotropic distribution and higher values reflect higher degrees of preferred orientation or fabric (Weiss and Wenk, 1985;Wenk, 1985;Kanitpanyacharoen et al, 2011). Typically, the pole densities are displayed in pole figure diagrams; more highly aligned textures or fabrics yield pole figures that can be contoured as concentric rings, whereas random or isotropic fabrics yield figures that have no poles.…”