Modeling and interpretation of scattered waves in interstage distributed acoustic sensing vertical seismic profiling survey

Abstract

Optimization of well spacings and completions are key topics in research related to the development of unconventional reservoirs. In 2017, a vertical seismic profiling (VSP) survey using fiber-optic-based distributed acoustic sensing (DAS) technology was acquired. The data include a series of VSP surveys taken before and immediately following the hydraulic fracturing of each of 78 stages. Scattered seismic waves associated with hydraulic fractures are observed in the seismic waveforms. Kinematic traveltime analysis and full-wavefield modeling results indicate these scattered events are converted PS-waves. We tested three different models of fracture-induced velocity inhomogeneities that can cause scattering of seismic waves: single hydraulic fracture, low-velocity zone, and tip diffractors. We compare the results with the field observations and conclude that the low-velocity zone model has the best fit for the data. In this model, the low-velocity zone represents a stimulated rock volume (SRV). We propose a new approach that uses PS-waves converted by SRV to estimate the half-height of the SRV and the closure time of hydraulic fractures. This active seismic source approach has the potential for cost-effective real-time monitoring of hydraulic fracturing operations and can provide critical constraints on the optimization of unconventional field development.

Convolutional neural network‐based classification of microseismic events originating in a stimulated reservoir from distributed acoustic sensing data

“…and velocity correction steps that require extensive and time‐consuming parameter testing (e.g. Consolvo & Thornton, 2020; Liang et al ., 2009; Titov et al ., 2021). Algorithms such as the bandpass filter, median filter and non‐local means filter, however, are very simple and quick to implement.…”

From Fluid Flow to Coupled Processes in Fractured Rock: Recent Advances and New Frontiers

“…In the context of unconventional reservoirs, strain measured by DAS has quickly revolutionized the detection of fracture propagation to offset wells, crucial for understanding induced fracture architecture after stimulation (e.g., Jin & Roy, 2017); this has been enabled by the low noise floor (sub‐nanostrain) of modern DAS interrogators which will only improve with advances in optical technology and engineered fibers. Higher frequency recordings using the same DAS systems can also be utilized for microseismic event location (e.g., Verdon et al., 2020), relevant for understanding the stimulated rock volume, as well as active source seismic imaging to detect elastic perturbations induced by fractures (e.g., Binder et al., 2020; Titov et al., 2021).…”

Seismic Applications of Downhole DAS

“…Seismic properties may vary due to the stimulation of unconventional reservoirs [ 89 , 90 , 91 ] and production, primarily important in conventional ones [ 36 ]. For example, [ 91 , 92 ] show how 4-D DAS-VSP acquired in a deviated well can delineate seismic signatures related to fractures opening during stimulation. The kinematic and dynamic properties of these signals can be used to infer the vertical fracture geometry and their temporal behavior.…”