Applied Concepts in Naturally Fractured Reservoirs

by John C. Lorenz

This course is designed to provide an appreciation of the significant differences in the effects on reservoir permeability of the most common extension and shear fracture types.  Extension fractures typically occur as sets of parallel fractures that produce a strong horizontal permeability anisotropy in a reservoir and limited, strata-bound vertical permeability.  In contrast, shear fractures commonly create an interconnected, more isotropic horizontal permeability system, with a higher probability of a fracture system that is vertically-connected across minor bedding contrasts.  However, some shear fracture types degrade reservoir permeability.

This course explores the different characteristics of extension and shear fractures so that they can be recognized in core and image logs.  The course also briefly describes the mechanics of creating fractures in the subsurface in order to provide a basis for predicting fracture types in a reservoir.  The course examines the effects of fractures on a reservoir, including the differences between extension and shear fractures due to their dissimilar orientations relative to the in situ stresses, and it explores the interactions between natural fractures and hydraulic stimulation fractures.

The course is designed to provide participants with an introductory working knowledge of fracture systems and their effects on reservoirs.  A small set of nine core hand samples illustrating natural shear and extension fractures, induced fractures, and coring artifacts will be set out on a table to demonstrate some of the differences between natural and induced fractures in core.