In March 2020, C&C Reservoirs unveiled a new Fractured Reservoir Classification that will enable DAKS™ users to find global examples of producing fractured reservoirs, better understand the production behaviour of their fractured reservoirs of interest and identify appropriate recovery strategies and reservoir management techniques. C&C Reservoirs’ new classification is simple, pragmatic and based on empirical evidence, underpinned by a solid understanding of fractured reservoir science.

A fractured reservoir is defined as one whose bulk permeability and permeability are significantly affected by the presence of naturally occurring fractures which are essential for the delivery of commercial petroleum production. In other words, a rock that without natural fractures would not flow oil and gas at commercial rates, with or without hydraulic fracturing interventions.

The new classification recognises three Fractured Reservoir Types:

Fracture classification types

Note: The classification is not of the type of fracturing, but of the reservoir as a whole, its fluid storage and flow characteristics. And while C&C Reservoirs’ Fractured Reservoir Type Classification bears some similarities to existing industry-known versions (for example, Nelson (2001)) it differs in its greater simplicity and objectivity, lack of reliance on arbitrary poroperm cut-offs and focus on fractures as fluid conduits rather than flow barriers.

Fractured Reservoir Example Collage

An understanding of the main porosity type is the key to determining the Fractured Reservoir Type. In essence, this boils down to Type I fractured reservoirs being dominated by fracture, cavernous, channel and breccia porosity, Type III by microporosity (defined as having pore diameters of <20 µm) and Type II by other porosity types, such as interparticle, intergranular, intercrystalline, mouldic and vuggy. In addition, whereas Type I are characterised by negligible matrix permeability and porosity, Types II and III may have somewhat higher matrix porosities but nonetheless have relatively low matrix permeabilities and rely on natural fractures to flow at commercial rates.