Impact of large-scale structures on fracture network connectivity: Insights into the Vaca Muerta unconventional play, Neuquén basin, Argentina

Abstract

Understanding natural fracture networks in rock masses is crucial due to their significant impact on mechanical behavior and fluid flow dynamics. Discrete Fracture Network (DFN) models provide a robust framework for representing these networks and assessing their role as pathways for fluid migration. They also allow the study of the relationship between fracturing and large-scale geological features such as faults, lineaments, and fracture corridors, all of which influence fracture-network connectivity. This last feature is critical for defining the geometry of the stimulated rock volume in low-permeability shale oil reservoirs and predicting well interference problems. In this study, 2D DFN models were developed using a dataset that integrates field measurements of fractures with interpretations derived from a georeferenced orthomosaic generated through an Unmanned Aerial Vehicle (UAV) survey. The Mallín de los Caballos site, where the Los Catutos Member within the Vaca Muerta Formation outcrops, was selected as the natural prototype. This carbonate-dominated membe provides notable exposures, enabling a detailed survey. Lateral connectivity analyses of the constructed models reveal a poorly connected background system. However, when larger-scale ENE-WSW-oriented structures are introduced, connectivity and resulting anisotropy of permeability increase substantially, transforming the spatial distribution and local fluid flow potential. At the reservoir scale, these structures correspond to subvertical strike-slip faults identified in 3D seismic data of the Neuqu´en Embayment, though their full characterization is limited by seismic resolution. This work proposes improved parametrization of these structural lineaments identified in the outcropping upper section of the Tordillo Formation. These findings highlight the importance of integrating geological data of various scales to comprehensively understand the behavior of fluid flow in unconventional reservoirs such as the Vaca Muerta Formation.