Incorporating the Effects of Diagenesis in Geomechanical Models of Fracture Pattern Development

Jon Olson
Department of Petroleum and Geosystems Engineering, The University of Texas at Austin, Austin, Texas

Geomechanical models have proven successful in generating realistic fracture patterns. Subcritical crack propagation properties, which can be measured in the laboratory on core or outcrop samples, control fracture length and spacing distributions. Fracture connectivity as controlled by multiple fracture sets or hooking versus straight en echelon overlaps can be related to loading boundary conditions. Predicted fracture apertures under propagation conditions are dependent on rock stiffness, in situ stresses, fracture spatial arrangement and mechanical layer thickness. However, elastic models predict that when propagation stresses are relaxed with time, the fractures will close. The presence of open, partially mineralized fractures in the subsurface, where they exist under net compressive stress, suggests that diagenesis occurred simultaneously with fracture propagation. Contemporaneous fracture propagation and rock diagenesis provides a mechanism for preserving crack opening through mineral bridging from one fracture wall to the other. It also implies that rock properties are changing while fractures are propagating and rock strain may be locked into the matrix via intergranular, pore-filling cementation. The implications of these factors are explored in the context of elastic and non-elastic geomechanical models.

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