ABSTRACT

Reservoir quality can be defined as a qualitative estimate of the ability of a rock to produce fluid, preferably hydrocarbon. It is generally determined using thin section petrography, scanning electron microscopy (SEM), and X-ray diffraction (XRD) techniques.

Potential problems that may affect reservoir quality include fine fraction migration, acid sensitivity, and swelling clays. The type and quantity of potentially damaging minerals, plus the position and morphology of this material with respect to the pore system, are significant.

In addition, porosity and permeability are obviously important with respect to reservoir quality. In general, exploration and development geologists use log and core analysis derived porosity (i.e., total porosity). In many reservoirs, a significant proportion of the pore system consists of isolated pores that do not contribute to permeability. It is important to determine the proportion of effective versus noneffective porosity.

Drill cuttings can be small pieces of a prospective reservoir, though the information available from this material is not commonly incorporated into completion decisions. Most reservoir quality information that can be obtained from core samples can also be obtained from thin section and SEM examination of drill cuttings (e.g., framework mineralogy, diagenetic mineral suite, pore types, etc.) In many cases, permeability and core analysis porosity can be empirically derived from cuttings.

The value of reservoir quality analysis in the determination of porosity and permeability controls plus drill cuttings analysis is illustrated in two case studies.

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