Microfractures in Tengiz and Korolev rocks are obscure or invisible using TL petrography. However, they are clearly visible in high-resolution (0.2 m/pixel) laser-scanning confocal images. In decreasing order of abundance, we observed the following microfracture types: (1) dissolution-enlarged microfractures, (2) mosaic microfractures, (3) sealed and partially sealed microfractures lined with carbonate cement and/or bitumen, (4) intercrystalline microfractures in echinoderm fragments and coarse blocky calcite cements, (5) en echelon microfractures, (6) sediment-filled microfractures, (7) microfaults and deformation bands, (8) microfracture ganglia, and (9) reaction halos in the matrix near open microfractures. All microfracture types are interpreted to be natural, as opposed to induced features.

Microfracture quantification, used here to determine the amount of open microfracture porosity in 2-D confocal images, has been applied to more than 300 samples. Microfracture porosity typically ranges from 0.2 to 1.0 pu (porosity units). Aperture widths are generally on the order of 0.2-10 μm.

A unique feature of this study is the relationship between dynamic properties and the amounts and types of microfractures observed in the rocks. Specifically, microfracture abundance relates to the effect of variable confining pressure on porosity and permeability in core plugs. Samples in which total confocal porosity is dominated (> 80%) by microfractures, mainly upper-slope boundstones, showed moderate decreases in porosity and major decreases in permeability as a function of increased confining pressure. Samples in which microfractures are a relatively minor component (