Abstract
In Jurassic Nugget Formation sandstones in East Painter Reservoir in the Wyoming overthrust belt, open fractures have been identified as a key reservoir element. In this study, we document fracture spatial distribution from 13 horizontal image logs in the doubly plunging East Painter Reservoir anticline. New analysis methods allow identification of spatial arrangement patterns and tests of correlation of spatial arrangement with fracture abundance and fold curvature. We found that the steeply dipping forelimb of the anticline tends to host the highest overall fracture density, whereas the gently dipping backlimb has lower fracture density, but these values depend on which fractures are included in the analysis. Degree of fracture clustering varies. Despite high fracture intensity, fracture arrangement in the forelimb is mostly indistinguishable from random. On the gently dipping backlimb fractures are markedly more clustered than random arrangements. Hierarchical and regularly spaced clustered were detected.
Fractures are a mechanism of permanent strain in brittle rock. The abundance of fractures (intensity) and their spatial arrangement can have a profound effect on fluid flow and rock strength, but are exceedingly challenging to measure in the subsurface (Laubach et al., 2019). In fold-and-thrust belts, rocks undergo deformation as fold geometries evolve. Deformation may be accommodated by brittle fracturing (opening-mode fractures, reactivated opening-mode fractures, and faults). The amount and mode of deformation can vary depending on structural position, stratal curvature, and other factors. Some fractures in fold and thrust belts are commonly thought to form synchronously with folding and therefore their pattern variations may be expected to relate to structural position within a fold. Understanding the mode of fold formation and strain history and the timing and mode of fracture is critical for prediction of fracture attribute variations, which can be used in a range of applications, including fractured reservoir exploration, carbon capture and storage, aquifer characterization and civil and mining engineering.
