Characterizing the ambient noise wavefield at hydrocarbon reservoir scale and some implications in hydraulic fracturing monitoring

Abstract:

There is an increasing interest in hydrocarbon reservoir imaging with ambient noise interferometry technique, as well as time-lapse monitoring of transient deformation associated with hydraulic stimulation operations or production activities. One general challenge of noise-based monitoring approaches is the spurious measurements ascribe to the sporadic nature of the excitation pattern, especially for the anthropogenic noise at the intermediate frequencies (a few Hz). Thus, it is imperative to characterize the spatiotemporal distribution of the ambient seismic wavefield at the field scale. A massive multi-stage hydraulic fracturing treatment was conducted in the Weiyuan shale play, located at the center of Sichuan basin in China during the period from 25 October to 10 November 2014. As part of the microseismic monitoring experiments, we deployed a small temporary array, which is composed of 22 broadband seismic stations and is centered at the wellhead of the treatment well with an aperture of ~3 km. With the continuous records for about 15 days, we statistically analyzed the time-dependent properties of the ambient seismic wavefield between 0.1 and 10 Hz. The preliminary analysis showed that the passive records are dominated by surface wave energy that exhibits a moderate daily variation. Daily beamforming results also reveal that there is a persistent ring of maximum amplitude with a slowness around ~0.55 s/km between 1 and 3 Hz. As a consequence, the daily noise cross-correlation functions within this frequency range appear to be remarkably symmetric and stable. With the ambient noise interferometry technique, we plan to detect the potential velocity changes in the regions surrounding the injection zone, and explore its possible correlation with the spatial distribution of the microseismic events.