| Popis: |
ABSTRACT: Stimulation of lab-scale boreholes was studied using small explosives for improving the development of fracture networks in engineered rock surrogates. The experimental series examines the confluence of initial stress states, orientation of induced discontinuities, and their interaction with source generated fracture growth. Density and stress response to the energetic was measured using high-speed schlieren imaging through the transparent polymethyl methacrylate (PMMA) sample. Outer surfaces were instrumented with an acoustic emissions array to detect 3D location of fracture evolution between wellbores. Prior to testing, the experiments were simulated to predict the generation of a shock-induced fracture network between single and multiple wellbores in a variety of stress states. The quantification of wave arrivals, fracture growth, and development of the fracture network in transparent PMMA material is used as further validation against computational models. Understanding the conditions under which fractures propagate in the multivariate environment with small energetics results in improved modeling capability of larger scale wellbores and sources. The present work is part of a broader effort to improve the accuracy of computational models necessary to predict formation interconnectivity established with energetics in low permeability reservoirs typical of enhanced geothermal systems. 1. INTRODUCTION Acoustic emission (AE) sensing has become a pertinent technology to observe flaws in a variety of media. Investigators can use arrays of omni-directional probes to observe energy radiating in the form of compression waves released from fracture tips, voids or features as they are distorted under load. Patterns in radiated energy may be correlated to spatial-temporal formation of microfractures. This method has been applied to the field of geomechanics where fractures grow due to an induced stress state, or when energy is radiated from an existing feature such as a slip plane. In this study, stress was induced for the purposes of studying lab-scale stimulation of geothermal wellbores using energetic sources so that computational models could be further informed by the acoustic emissions of fractures driven by energetics. |
