Previous publications discussing the shallower portions of the Eagle Ford shale have demonstrated the engineering worth of combining the results of multiple fracture diagnostics, such as microdeformation and downhole microseismic. This paper extends previous work by incorporating results from a surface microseismic mapping study. Moment Tensor Microseismic Imaging™ (MTMI™) was performed to help provide a better understanding of the nature of microseismic failure mechanisms associated with the hydraulic fracture process and its interaction with the natural rock fabric.
The study region is within the Eagle Ford shale in an area where previous microseismic mapping has indicated that the magnitude of the overburden stress is less than the magnitude of one or both of the two principal horizontal stresses (Walser and Roadarmel 2012). The source mechanisms derived from the surface imaging were assessed for two very different groups of microseismic events also observed during downhole microseismic mapping.
Debate continues regarding the technical, practical, and fiscal value of understanding source mechanisms associated with microseismic activity (Baig and Urbancic 2010; Warpinski et al. 2010; Warpinski 2014;). This work demonstrates one situation where MTMI provided a deeper understanding of the fundamental geomechanical mechanisms occurring during hydraulic fracturing and highlights that, when examining the seismicity generated by a hydraulic fracture, one should always consider the fabric of the rock within which that stimulation occurred.
This case study relates to a horizontal stimulation where monitoring observed evidence of interaction between the hydraulic fracture and several subvertical or subhorizontal pre-stressed natural features. This paper discusses the value of source mechanism information provided by MTMI and how it can be used with other fracture mapping technologies to help impact future exploration and production decisions.