A new method for characterizing dynamic reservoir quality: Implications for quality maps in reservoir simulation and rock type classification

Abstract

Determining reservoir quality is vital in order to efficiently produce hydrocarbon and/or inject fluids for secondary/tertiary recovery and carbon sequestration. In this study, we introduce a new approach and present dynamic reservoir quality index (DRQI). A high-quality reservoir would have high displacement (recovery) rate and displaceable (recoverable) saturation of oil. A modified true effective mobility (TEM) function is developed representing displacement rate of oil by an injected fluid (e.g., water or CO2). DRQI is defined as the area under modified TEM curve of oil and includes the well-known reservoir quality index (RQI) as its special case. A large dataset composed of 220 water displacing oil relative permeability experiments, conducted on limestone and dolomite rocks from three Iranian carbonate reservoirs, was used to investigate the potential relationships between DRQI and other reservoir characteristics (e.g., irreducible water saturation, bulk irreducible water, maximum movable oil saturation, and bulk maximum movable oil) as well as quality indicators of RQI, flow zone indicator (FZI), and Winland r35. Results showed that irreducible water saturation and maximum movable oil saturation as well as their bulk variants may not be appropriate for characterizing multiphase quality of reservoirs. Furthermore, the frequently-used single-phase rock quality indicators RQI, FZI, and Winland r35 were not found to be very accurate in characterization of dynamic reservoir quality. DRQI can be used in reservoir simulation studies as a criterion for defining quality maps, and in petrophysical tasks for rock typing and comparing between dynamic qualities (in terms of displacement rate and displaceable saturation of oil) of rock samples.