Fracture Imaging Using DAS-Recorded Microseismic Events

Abstract

Hydraulic fracturing enables hydrocarbon production from unconventional reservoirs. Mapping induced seismicity around newly created fractures is crucial for understanding the reservoir response and increasing the efficiency of operations. Distributed acoustic sensing (DAS) provides a large amount of high spatial resolution microseismic data acquired along the entire length of horizontal wells. We focus on the observed reflected S-waves and develop a new methodology using microseismic events as sources of energy to image induced fractures acting as reflectors in the media surrounding the events and monitoring fiber. The workflow consists of DAS data preprocessing, event location, wavefield separation, raytracing-based imaging, and image post-processing. The comparison of the resulting images with low-frequency DAS signals of fracture hits corroborates that the reflections are from fractures created by stimulation. The proposed algorithm can be used for real-time mapping of fractures and tracking fracture changes in space and time. Fracture imaging leads to a better understanding of the reservoir response to hydraulic fracturing stimulation.

Strain-based forward modeling and inversion of seismic moment tensors using distributed acoustic sensing (DAS) observations

“…The successive arrivals of the P-and S-waves are clearly visible but are followed by secondary arrivals due to reflections from the horizontal layers of the Montney Formation (Karrenbach et al, 2017). In addition, where the primary and secondary arrivals cross fault planes, they generate reflected waves that propagate in a direction opposite to that of the direct waves, which makes them noticeable in a time-distance diagram (Ma et al, 2022;Staněk et al, 2022). To the right of the apex, the first arrivals propagated rightward and leftward to the left of the apex.…”

Multiwell Fiber Optic Sensing Reveals Effects of CO2 Flow on Triggered Seismicity

“…Distributed acoustic sensing (DAS) systems have great potential to become such a monitoring tool. Downholedeployed DAS provides relatively inexpensive receiver array that is sensitive to the microearthquakes in a wide frequency range, as is evident from applications to enhanced geothermal systems (Lellouch et al, 2020) or stimulation of unconventional reservoirs (Luo et al, 2021;Staněk et al, 2022). A 15,000 tonnes CO 2 injection during the Stage 3 CO2CRC Otway Project in the Australian state of Victoria (Jenkins et al, 2017) (referred to simply as Stage 3 subsequently) presented a unique opportunity to quantitatively characterize the seismicity triggered by two successive CO 2 injections using five deep boreholes instrumented with enhanced DAS systems (Pevzner et al 2021).…”