Feasibility of borehole ambient noise interferometry for permanent reservoir monitoring

Abstract

The analysis of seismic ambient noise acquired during temporary or permanent microseismic monitoring campaigns (e.g., improved/enhanced oil recovery monitoring, surveillance of induced seismicity) is potentially well suited for time‐lapse studies based on seismic interferometry. No additional data acquisition required, ambient noise processing can be automatized to a high degree, and seismic interferometry is very sensitive to small medium changes. Thus there is an opportunity for detection and monitoring of velocity variations in a reservoir at negligible additional cost and effort. Data and results are presented from an ambient noise interferometry study applied to two wells in a producing oil field in Romania. Borehole microseismic monitoring on three component geophones was performed for four weeks, concurrent with a water‐flooding phase for improved oil recovery from a reservoir in ca. 1 km depth. Both low‐frequency (2 Hz–50 Hz) P‐ and S‐waves propagating through the vertical borehole arrays were reconstructed from ambient noise by the virtual source method. The obtained interferograms clearly indicate an origin of the ambient seismic energy from above the arrays, thus suggesting surface activities as sources. It is shown that ambient noise from time periods as short as 30 seconds is sufficient to obtain robust interferograms. Sonic log data confirm that the vertical and horizontal components comprise first arrivals of P‐wave and S‐waves, respectively. The consistency and high quality of the interferograms throughout the entire observation period further indicate that the high‐frequency part (up to 100 Hz) represents the scattered wave field. The temporal variation of apparent velocities based on first‐arrival times partly correlates with the water injection rate and occurrence of microseismic events. It is concluded that borehole ambient noise interferometry in production settings is a potentially useful method for permanent reservoir monitoring due to its high sensitivity and robustness.

Passive processing of active nodal seismic data: Estimation of V<sub>P</sub> / V<sub>S</sub>-ratios to characterize structure and hydrology of an alpine valley infill

“…Body waves caused by surface noise sources are also more likely to be detected in boreholes (Behm, 2017;Zhuo and Paulssen, 15 2017) or inside mines (Olivier et al, 2015).…”

P and S Velocity Structure in the Groningen Gas Reservoir From Noise Interferometry

“…This indicates that the fluctuations are due to variations in anthropogenic noise. Previous studies by Grechka and Zhao (), Vaezi and Van der Baan () and Behm () have shown that surface activity can indeed be the dominant noise source up to 2 km depth. Our results confirm their observation, extending it to a depth of 3 km.…”

“…We did not succeed to identify temporal variations of the medium within the 33 day time span because the cross correlations appeared to be dominated by fluctuations in anthropogenic noise (Figures and S4 in the supporting information). Nevertheless, it should be possible to identify temporal medium variations at locations with more stable noise environments, as shown by Behm ().…”

“…They retrieved downgoing P waves at 1,800 m depth and in some cases also more weakly upgoing P waves at frequencies lower than 60 Hz. Recently, Behm () found downgoing P and S waves up to 50 Hz at around 1,000 m depth and suggested that velocity changes may be monitored from the high‐frequency (> 50 Hz) part of the cross correlations.…”

Brief communication: Post-seismic landslides, the tough lesson of a catastrophe

“…anisotropy, sets of directional discontinuities; Di Giulio et al, 2009) and their changes with time (e.g. shear wave velocity decrease due to crack opening or water level rise; Daskalakis et al, 2016;Behm, 2016), potentially providing an indirect assessment of strength degradation or stress changes. Furthermore, monitoring of acoustic emissions, i.e.…”