Wednesday, February 13, 2013

Highlights—Unraveling Sediment Mixing

Mixed carbonate-siliciclastic sediments can provide unique interpretive challenges, as the two types of sediments are controlled by different parameters.  In this paper, Chiarella and Longhitano describe the application of a new technique for describing and interpreting sediments of mixed systems.  The application of this method to a succession of Plio-Pleistocene deposits facilitated the reconstruction of the depositional framework and stratigraphic evolution, revealing otherwise ambiguous patterns.  These techniques and results illustrate a new means to evaluate mixed carbonate-siliciclastic systems and their dynamics.  

Tuesday, February 12, 2013

Highlights—Dolomite: It’s the Fault’s Fault

A unique aspect of carbonate platforms is their ability to develop flanks with gradients that exceed the angle of repose due to early cementation and binding.  Frost et al. document a Permian example of an oversteepened carbonate platform margin that was impacted by early syndepositional deformation.  A suite of field, petrographic, and stable isotopic data reveal that these early fractures and faults also facilitated the flow of early dolomitizing fluids.  These results are interpreted to reveal a spatially and temporally complex alteration of host limestone that led to bed-scale heterogeneity in dolomite patterns and petrophysical properties.

Thursday, February 7, 2013

Highlights—Don’t Underestimate Perms (with apologies to Charles Nessler)

Predicting the permeability of subsurface sandstone bodies is a major challenge for petroleum production and ground water management. In this study, Walderhaug et al. test several methods of permeability prediction using almost 1900 samples from the Norwegian continental shelf and the Fontainebleau Sandstone.  The data indicate that for clay-free and very clay-poor sandstone, permeability can be calculated with the Kozeny equation.  In contrast, for sandstones containing more than ~ 3% clay, a modified Kozeny equation that accounts for pore system geometry provides more accurate results for sandstone with higher clay contents.  These results emphasize the hazards of predicting permeability from grain size and porosity alone, and illustrate the complexity of permeability-porosity relations in sandstones with clays.