L2M NSERC - Fibre Optic Technology Innovation for Subsurface Fracture Characterization

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During resource exploration, monitoring induced microseismicity and imaging the subsurface has typically been undertaken using geophones. Recently, fibre optic technology (e.g., Distributed Acoustic Sensing (DAS), Distributed Temperature Sensing (DTS)) has shown advantages over geophones, such as the ability to monitor the entire fibre (enhanced spatial resolution) and over broad frequencies. DAS/DTS therefore provides an effective solution for subsurface imaging, detecting microseismicity and slow slip using the same instrumentation. In most instances, a fibre optic cable is installed into a single horizontal well adjacent to others at a multi-well pad. A single fibre can detect microseismic events but, unlike multicomponent geophones, it cannot unambiguously determine source locations since it records only one direction of ground motion. Determination of event locations is essential for fracture mapping and characterization as well as determining operational success and for risk management. We have created novel methods that use recorded reflected waves on fibre optic cables to better determine locations of microseismic events, and to characterize fracture aperture and proppant distribution. Using the standard practice of picking the direct wave arrivals, locating microseismic events with a single fibre optic cable lacks depth resolution. Like scanning a bar code, our approach decodes event depth based on the detected pattern of reflections from horizontal layer boundaries, which are typically discarded. We also use subtle amplitude variations of reflections from vertical hydraulic fractures to determine critical characteristics such as fracture aperture and proppant, which are otherwise unknown. Integrating these calculations into a workflow focusing on the identification and location of microseismicity would be transformative, enabling industry to gain a better understanding of the extent and characteristics of fractures in the subsurface. We aim to enhance our technology to account for evolving demands, allowing integration of our technology by many different clients.