Effective evaluation of fractured reservoirs involves both qualitative and quantitative data of various levels of complexity. This paper attempts to describe those geological and petrophysical data necessary in making an early evaluation of a fractured reservoir, during either exploration or early development phases. As such, prediction rather than detection will be emphasized.

Early in the evaluation of a fractured reservoir the majority of predictions are based on direct observations of a combination of geological and rock data. Those observations are generally made by geologists and/or petrophysicists, and are used to determine: (1) fracture origin and distribution, (2) the reservoir characteristics of the fracture system, (3) the interaction of the fracture and matrix porosity systems, and (4) the type of fractured reservoir, based on the contribution of the fracture system to overall reservoir quality. Each of these determinations is discussed, including the general types of geological interpretations

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and rock property analysis required.

Subsequent to those early determinations and predictions by geologists, larger scale, more quantitative data detecting the effect of reservoir fractures are made by the reservoir engineers. Techniques such as pressure transient analyses and interference testing allow the extrapolation of small scale geological and petrophysical data to larger scale reservoir flow predictions using large mathematical reservoir flow models.

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