Understanding out of zone frac growth can lead to designing stimulation programs that can effectively enhance production from adjacent horizons. The effectiveness of the stimulation program can be assessed by incorporating monitoring programs that include instrumentation to detect seismic events over a broad range of magnitudes from the smallest detectable events with magnitudes below zero (microseismic) to larger events with magnitudes above zero (induced seismic), typically related to larger pre-existing fractures or faults. Stimulating these larger structures could lead to loss of fluid from the reservoir and affect estimates of stimulated volume. In this study, we examine data recorded using a typical downhole microseismic wireline supplemented with a near surface array designed to record induced seismic events. In this study, two horizons were stimulated. The intent of the program was to stimulate both zones by stimulating wells in the lower horizon by increasing pressure rates both early and late into the injection program in the upper horizon. About 4500 microseismic events and 28 induced seismic events were observed. These larger events represent approximately 83% of the total seismic energy released during the stimulation, which, if only using standard recording, would have been mis-interpreted as microseismic events and thereby would not have contributed to the overall energy dissipation levels. The larger events were associated with fractures with lengths varying from about 40 m to over 110 m, whereas the microseismic fracture lengths varied from ~5 m up to ~ 35m. The microseismic and induced seismic events could be used to identify growth from the upper to lower horizon at different pressure rates. The occurrences of larger magnitude events appeared to precede pressure increases in the program, suggesting that larger structures were activated as a result of the injection program even before pressures were increased. This observed process sets the foundation to better control stimulation programs.
Identifying Frac Growth in Multiple Horizons Using Integrated Microseismic and Induced Seismic Monitoring Approaches
Urbancic, T.I. , Cochrane, A. , Bowman, S. , and A. Baig. "Identifying Frac Growth in Multiple Horizons Using Integrated Microseismic and Induced Seismic Monitoring Approaches." Paper presented at the SPE/AAPG/SEG Unconventional Resources Technology Conference, Denver, Colorado, USA, August 2014. doi: https://doi.org/10.15530/URTEC-2014-1922826
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