| Title | Distributed Acoustic Sensing Monitoring at the First EGS Collab Testbed |
|---|---|
| Authors | David LI, Lianjie HUANG, Benxin CHI, Jonathan AJO-FRANKLIN, Veronica RODRIGUEZ TRIBALDOS, Martin SCHOENBALL, Timothy KNEAFSEY, and EGS Collab Team |
| Year | 2020 |
| Conference | Stanford Geothermal Workshop |
| Keywords | DAS, EGS Collab, monitoring, fracture, borehole, stimulation |
| Abstract | Distributed Acoustic Sensing (DAS) employs a fiber-optic cable as a seismic sensor. In a DAS survey, a fiber optic cable is either cemented in a borehole or buried at the surface of the survey area. An interrogator unit is attached to one end of the cable and sends laser pulses down the length of the fiber to measure deformations in the fiber caused by passing seismic waves. The EGS Collab project is to study the fracture stimulation and monitoring for enhanced geothermal systems (EGS). The first testbed is located at 4850 ft. beneath the surface at the Sanford Underground Research Facility in South Dakota. The testbed consists of a stimulation well, a production well, and six monitoring wells drilled around a fracture stimulation zone. A length of optic fiber was deployed along the monitoring wells to continuously monitor during hydraulic stimulations. The gauge length for data collection was set to 10 m. We analyze the DAS data and compare the signal changes before, during, and after the hydraulic stimulations. We then compare the time-lapse monitoring results obtained from DAS data with results obtained from continuous active-source seismic monitoring (CASSM) data to study the feasibility of DAS for monitoring hydraulic fracturing in EGS reservoirs. In our preliminary results, we do not observe any scattered signal on the DAS data which may be caused by the large (10 m) gauge length used during data acquisition. |