Seismic Efficiency and Overshoot of Fractures Associated with Stimulation in Heavy Oil Reservoirs

To better understand the different fracturing process of two passive seismic datasets collected over a 30 month period for two heavy oil reservoirs, utilizing steam injection and water flooding, we investigate radiated energy and seismic efficiency. We calculate the Savage-Wood Efficiency (ŋsw) and overshoot of microseismic events recorded in two reservoirs with different stimulations and find under similar geological conditions and time period, the seismic efficiency, for steam injection compared to water flooding are unique across the datasets implying that temperature and fluid pressure has a different impact on the fracturing dynamics. Reservoir A (stream injection), has 4069 events (Mw = −2.2 top −0.2) with low efficiency (ŋsw=0.01 to 0.48) and considered in overshoot (ε=0.1 to 0.5). Reservoir B (water flooding), has, 1763 events, but higher magnitude range (Mw = −1.4 to 1.8); with a combination of low efficiency (overshoot ε=0.002 to 0.49) and high efficiency (undershoot ε=−415 to 0.49) events. Overshoot occurs when the dynamic strength of the fault is relatively higher than the final stress acting on the fault and less energy is radiated; where undershoot occurs when the dynamic strength is relatively lower than the final stress on the fault and in a state of dynamic weakening.