The influence of rock-mechanical properties on fracture characteristics in finely-layered reservoirs

Abstract

Heterogeneities in finely-layered reservoirs complicate predictions on the fracture behavior. Understanding the controls on fracture behavior in these unconventional reservoirs is important for their successful production. This research examines the influence of rock-mechanical properties on fracture characteristics in finely-layered reservoirs. Rock-mechanical laboratory experiments have been performed on layered shale-sandstone samples and layered granite-sandstone samples, in order to investigate the rock-mechanical parameters and fracture geometry. Fracture characterization, including fracture initiation, propagation, orientation, and interaction between the multiple layers was performed using X-ray micro-computed tomography scans. Predictions of the rock-mechanical properties of a layered material can be made using the Reuss-bound averaging each individual layer. The strength, however, cannot be averaged. Fracture initiation is highly dependent on rock strength: Fractures initiate at the failure point of the weakest layer, after which they do propagate at low average stress levels through stronger layers due to local stress amplification at the fracture tip. The fractures change their orientation through layers with different mechanical properties. The results show that the variability in rock-mechanical properties influences the fracture behavior in a finely-layered reservoir.