Modelling DAS signals for hydraulic fracturing and caprock monitoring

Matthew Eaid, Kristopher A. Innanen

Passive seismic technologies are indispensable tools for monitoring hydraulic fracture growth, caprock integrity during cyclic steam stimulation (CSS) and CO₂ sequestration, and borehole casing integrity. Mature fields use a combination of permanent arrays and temporary wireline tools to monitor the reservoir and optimize production. Conventionally, passive seismic monitoring consists of large arrays of surface and downhole geophones. This can result in the drilling of dedicated monitor wells, and well shut-in during wireline monitoring, resulting in elevated costs. Distributed acoustic sensing (DAS) uses non-invasive optical fibres that can be cemented behind casing in producing and injecting wells, offering an opportunity for the dual purposing of wells and reduced monitoring costs. DAS has the potential to be a powerful reservoir monitoring technology. To better understand the capabilities of DAS for reservoir monitoring, we develop an analytic modeling tool for DAS signals from moment tensor sources, providing data like that expected from hydraulic fracturing and CSS treatments. This tool provides an efficient means of examining DAS signals from various moment tensor sources. In this paper this tool is used to investigate the diagnostic characteristics in the DAS signals from different moment tensor sources and gain an enhanced understanding of the effect of source mechanics on DAS signals.