Abstract
Reservoir Quality can be defined as a qualitative estimate of a rock’s ability 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 which may affect reservoir quality include fines migration (Messla Field Sandstone), acid sensitivity (Khalifa Formation), 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 is 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 which do not contribute to permeability (Khalifa and Zelten Formations). It is important to determine the proportion of effective vs non-effective porosity.
Drill cuttings can be small pieces of a prospective reservoir, though the information available from this material is not often 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, for example, framework mineralogy, diagenetic mineral suite, pore types, etc. In many cases, permeability and core analysis porosity can be empirically derived from cuttings.
The use of petrographic techniques in the determination of reservoir quality is illustrated using examples from the Khalifa and Zelten Formations plus the Messla Field Sandstone.