The classic Nelson plot (Nelson, 2001) has been widely used to illustrate the geologic characteristics of various NFR types ranging from matrix dominated flow with some fracture enhancement to purely fracture dominated systems (e.g. basement reservoirs). However, for many reservoirs, there is significant overlap in model types and different parts of the reservoirs may fit into different classifications. In fact, the choice of characterization and modeling approaches depends on other considerations such as the fluid system, matrix geologic characteristics, and recovery processes. For example, for gas-oil gravity drainage processes, the rate of vertical oil drainage in the matrix may dominate oil recovery and dual-permeability may be the desired modeling approach even in a highly fractured reservoir. Alternatively in pure depletion processes, we might be able to model a highly fractured system with an effective single-porosity representation because of rapid matrix-fracture pressure equilibration. However, in all fractured reservoirs, of special concern is the rate of matrix-fracture fluid transfer which is directly related to the fracture intensity of the open connected fractures.

In this paper we present a new classification plot that highlights the importance of fracture-matrix fluid transfer. This consideration is not directly incorporated in the Nelson plot. Our new classification concept can be used to understand differences in dynamic performance of NFR for purposes of analogue selection or screening of potential recovery processes. In this paper, several characterized NFR reservoirs (including unconventional systems) are compared via the new classification plot and their differences and performance are discussed. Additionally we provide some discussion of naturally fractured reservoir (NFR) characteristics for the purpose of illustrating the controls on matrix-fracture fluid transfer.

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