Natural fractures are common in several unconventional reservoirs in the U.S. and around the world and, even when sealed with cements, can facilitate the propagation of induced fractures during hydraulic fracturing. This study is focused on correlating fracture types and intensity to distinct petrophysically significant facies and to an established sequence stratigraphic framework in the unconventional carbonate reservoirs of the “Mississippian limestone” of the U.S. midcontinent region.

Four fracture types are observed: ptygmatic, vertical extension, shear, and mixed types of fractures. Most of the fractures have been completely sealed with predominantly calcite cement. Fractured zones are vertically heterogeneous at...