More Microseismic Events are Not Always Better

We examine a case study in a North American shale play where a number of wells were stimulated. Because the completions were monitored with two whip arrays, we were able to perform seismic moment tensor inversion on many of the detected events. For the first well, we say many sub-vertical failures following two dominant orientations while the second well showed a predominance of sub-horizontal fractures, with a lower overall event count. The initial predictions indicated that the first well would have better production due to the larger volumes of more complicated stimulated volumes. However, when the production data was acquired, it was the second well that had the higher production. We resolved this paradox through examining the apparent stress of the events: the first well had higher apparent stresses more characteristic of fault activation; the second well had lower apparent stress values more characteristic of fluid induced events. Our interpretation is that the fluids allowed for bedding planes to slip and stimulate a larger volume whereas the first well did not succeed in transferring fluids to the seismically active volumes.