ABSTRACT
Distributed Acoustic Sensing (DAS) is an emerging fiber optic-based technology that has been utilized to monitor hydraulic fracturing treatments. DAS data in low-frequency bands monitored in offset wells is sensitive to strain variations induced by fracture propagation. However, the interpretation of real DAS data can be challenging because of complicated subsurface conditions. Thus, it is necessary to develop a physical model consistent with the downhole conditions to simulate LF-DAS signals. In this paper, we present a hydraulic fracturing model that generates dynamic fracture geometries and calculates fracture-induced strain variations during fracture propagation under various completion conditions. We investigate the geomechanical responses detected by the fibers attached to horizontal offset wells during simultaneous multi-fracture propagation. A typical strain-rate waterfall plot shows different signatures before and after the fractures hit the monitor well. A ‘heart-shape’ extending zone forms of each fracture as the fracture approaches the monitor well. After the fracture encounters the monitor well, the extending zone shrinks to a narrow band. And a two-wing compressing zone is observed on the sides of a fracture. We also investigate the impacts of fracture spacing, cluster number and perforation number on the strain-rate responses. Different fracture-hit times and interactions among fractures can be clearly identified using LF-DAS. This study provides critical insights into the strain and strain rate responses along offset monitor wells during hydraulic fracturing and enables better interpretation of real-time DAS data.
Plug-and-perf completion scheme is widely used for hydraulic fracturing treatments to economically develop unconventional reservoirs (Daneshy, 2011). Due to subsurface complexity, it is challenging to evaluate the stimulated fracture geometry that is critical for improving fracturing design and maximizing well production (Liu et al., 2018; 2019). Fiber-optic sensing (FOS) is an emerging technology that has been used recently in the oil and gas industry to monitor hydraulic fracturing treatments (Molenaar et al., 2012; Webster et al., 2014). Distributed Acoustic Sensing (DAS) is such a fiber-optic based dynamic strain sensing technique, which can provide valuable information on stimulated fracture geometry (Jin and Roy, 2017).
