Diagenetic Controls on Spatial Arrangement of Fractures: an Example from the Cupido Fm., Sierra Madre Oriental, Mexico

Gomez, Leonel¹, Randall Marrett¹ (1) The University of Texas at Austin, Austin, TX

Although recent research has started to address the influence of diagenetic processes in fracture development using numerical modeling, little to none has been investigated on how diagenetic processes influence spatial arrangement of natural fractures.

We measured aperture and spacing of opening-mode fracture sets along 1D scanlines in dolostone layers of Cretaceous Cupido Fm. Fracture sets were diagenetically categorized from petrographic and SEM/CL observations: fracture trace morphology (irregular or straight), timing with respect to regional dolomitization (before, during or after), and fracture cement composition and texture (synkinematic dolomite, synkinematic and postkinematic quartz and postkinematic calcite). Independently, fracture sets were studied using normalized correlation count (NCC), a recently developed analytical technique that distinguishes five possible types of spatial arrangements: indistinguishable from random, fractal clusters, imposed clusters, periodically arranged clusters, or a combination of the previous four arrangements.

Proportion of fracture filled by synkinematic cement shows a strong correlation with spatial arrangement. Fracture sets with abundant (>60%) synkinematic cement exhibit periodically arranged clusters, clusters that in turn have internally a fractal arrangement. In contrast, fracture sets containing little (<40%) synkinematic cement have arrangements that are indistinguishable from random inside and in between clusters. Synkinematic cement produces mineral bridges that locally reestablish cohesion across fractures and that blunt fracture tips. We speculate how differences in the amount of synkinematic cement can systematically alter the interaction between the stress shadows of fractures that are growing simultaneously, resulting in different spatial arrangements.