Real Time Microseismic Feedback of Hydraulic Fracture Effectiveness and Barriers
Microseismic monitoring of hydraulic fracture stimulations of unconventional reservoirs can effectively delineate treatment volumes and fracture geometries with appropriate considerations about which events represent the progression of the hydraulic fracture versus events that represent stress-induced slip on nearby fractures that do not necessarily contribute to production. As the technology matures, operators expect the microseismic interpretation over shorter timelines, approaching real-time delivery such that decisions can be made based on the feedback of microseismic signatures can then be applied to subsequent treatments. Augmenting the real-time analysis is the determination of source parameters such as magnitude and apparent stress for events related to the treatment. The distribution of magnitudes is characterized through the b-value, which describes the proportion of large events to small events. In areas dominated by a response to stress, for each magnitude unit increase, there is a 10-fold decrease in the frequency of events, corresponding to b-values of 1 whereas fluid-induced events show notably higher b-values (up to 2 meaning a much larger proportion of small events to large events). Such analyses can effectively identify fracture barriers in the formation, as events that occur in a frac barrier will have notably lower b-values than where fracturing is most intense. Apparent stress offers a complementary way to use the source parameter data. High apparent stress is characteristic of shear-dominant events that occur in highly stressed regions that are close to failure. Lower apparent stress values describes events that need to invest more energy into deformation processes in areas that are not as highly stressed; these areas are potentially where fluid-induced fracturing is most vigorous. Because source parameter estimation involves looking at the spectral content of the signals, not only do the algorithms need to be in place to rapidly and accurately estimate the spectra, but consideration of needs to be paid to the particulars of signal acquisition (i.e. instruments that are well-coupled to the Earth and not introducing spurious resonance frequencies, and the dominant frequencies from the microseismic sources need to be within the bandwidth of the instrumentation). We shall discuss the monitoring of a completion where this source parameter estimates were used to assess the effectiveness of the treatment real-time in the field.
AAPG Datapages/Search and Discovery Article #90189 © 2014 AAPG Annual Convention and Exhibition, Houston, Texas, USA, April 6–9, 2014