Mechanical insights into the development of fracture corridors in layered rocks

Abstract

Fracture corridors are ubiquitous features formed by closely-spaced sub-parallel fractures, typically occurring in brittle mechanical units. They are important because they can form drains for fluids in hydrocarbon reservoirs and aquifers. Their development is sometimes associated with local structural or sedimentary heterogeneities but other situations exist where their mechanical origin remains obscure. In this paper, we investigate the combined role of contrasts in mechanical properties of consecutive layers and pre-existing fracturing in the formation of fracture corridors in sedimentary rocks, using 2D elastic finite element models.Our models contain five bonded layers with contrasted elastic properties and two pre-existing open fractures in the central layer. Firstly, we compute stress fields in the models submitted to biaxial compression and compression-extension plane strain loading. We identify favorable stress conditions supporting further fracturing in both situations. Secondly, we investigate fracture clustering mechanisms by means of quasi-static fracture propagations in identified areas of tensile stress. We characterize three situations leading to the development of incipient fracture corridors and discuss their geological implications. Finally, we propose a new conceptual model for the formation of these features in the subsurface, with important consequences for the characterization and modeling of fractured reservoirs.