Large-Scale Experimental Investigation of Fracture Propagation Using OFDR-Based Distributed Fiber-Optic Strain Sensing

Abstract

Abstract Distributed fiber-optic strain sensing has been used as cutting-edge technology for real-time hydraulic fracturing monitoring. To better understand the fiber-measured strain response to the fracture propagation, we conducted a large-scale experimental investigation in a poly-triaxial testing site with OFDR-based fiber-optic sensors. The objective of this study is to measure the strain variations due to fracture propagation by time, estimate the fracture geometry and provide insights into the quantitative interpretation of the field-measured strain data. The experiments were conducted in a large-scale poly-triaxial testing site with a testing concrete sample of 30in×30in×36in dimension. The fiber-optic sensing cable was "Hairpin turn" shape embedded in different locations inside the sample with varying distances to the injection side. The fiber-measured strain data was recorded and displayed on a waterfall plot during fracturing. We injected dyed fluid to generate the fracture so that we could cut the sample to investigate the fracture geometry. After the experiment, the treating pressure, injection, and fiber strain data are obtained. Eventually, we analyzed the measured data to characterize the fracture geometry over time. This research demonstrates the utilization of using OFDR-based distributed strain sensing to monitor fracture propagation and estimate the fracture geometry. The experiment results show significant insights. The vital function of OFDR-based fiber-optic sensing in extremely high precision and resolution shows its feasibility in monitoring the fracturing process in a laboratory-scale experiment. The results of the experiments validate the current understanding of interpreting featured patterns observed in fiber-optic monitoring plots as fracture propagation intersects the fiber cables.