Passive seismic imaging of subsurface natural fractures: application to Marcellus shale microseismic data

Abstract

S U M M A R Y Imaging and characterizing subsurface natural fractures that are common in the Earth crust has been a long-sought goal in seismology. We present an application of a 3-D passive seismic fracture imaging method applied to Marcellus shale microseismic data for mapping natural fractures. Unlike conventional seismic imaging methods that need source information, the proposed imaging method does not require source information and is flexible enough to apply to any passive seismic data where the source location is unknown or inaccurate. We first test our imaging approach using surface microseismic monitoring array data in 3D synthetic examples. The finite-aperture fractures are designed by an open-source discrete fracture network software. Compared to conventional source-dependent fracture imaging, the proposed source-independent imaging approach produces superior images of fractures with less ambiguity. These tests also illustrate that the proposed method is less sensitive to the accuracy of background velocity and less affected by the sparse and irregular acquisition geometry which often cause acquisition-footprint issues in convention imaging methods. The final test in the field microseismic data from the Marcellus Shale (Pennsylvania) demonstrates the applicability of the proposed imaging method. Field data results indicate two clusters of east-northeast fractures existed above and below the hydraulic fracturing zone, which corroborates previous work that found two main types of faults in the study area.