Integrated Study on Tensile Fracture Mechanics and Subsequent Flow in Naturally-Fractured Niobrara Shale

摘要

Natural fractures exist in shale plays. Whether these fractures contribute to flow, how they interact with hydraulic fractures, and how they are reactivated under in-situ stresses are three main questions in shale hydraulic fracturing. The objective of this paper is to integrate experimental results related to these questions. To this end, the permeability of cores with calcite-filled natural fractures and without natural fractures was measured. Next, the tensile strength and tensile fracture pattern of core plugs containing natural fractures at different orientations were examined by applying the Brazilian test method. Subsequently, the permeability of these tensile-failed samples was measured. The results of this study on Niobrara shale samples show that the calcite-filled fractures do not contribute to flow, yet they are planes of weakness for tensile failure depending on the orientation of the fracture. Once calcite-filled fractures are activated, they contribute to flow quite significantly even without proppant or shear displacement. The results of this study could be beneficial in other investigations related to complex fracture network.