Reservoir Fluid Properties Required for Low Permeability Oil Reservoir Analysis

Matt Mavor
Sr. Technical Advisor, Apache Corporation

Quantifying fluid flow through porous media requires accurate fluid property estimates. This is especially important for low permeability oil reservoirs which will produce gas, oil, and water in time-dependent proportions due to hydraulic fracture stimulation and production pressures below oil bubble point pressure. Gas and oil properties are required to properly quantify flowing properties such as the effective permeability to each phase, to determine the oil and gas volumes in place, to predict future production rates and recovery, and to evaluate open-hole log data.

Reservoir fluid systems are classified based upon the phase behavior relative to the critical point of a multicomponent hydrocarbon mixture. The fluid system phase behavior PVT (pressure-volume-temperature) analysis depends on the fluid type. Representative fluid samples are required for the analysis. These samples are best acquired by recombining separator oil and gas samples collected under relatively stable production conditions very early in the life of a reservoir. The samples are recombined at the separator gas-oil rate ratio to serve as the reservoir fluid sample.

Oil production behavior is strongly dependent upon the oil gravity and the original solution gas-oil ratio. The differences in behavior for three actual Permian oil reservoirs will be demonstrated with reservoir simulation models. An example PVT analysis of one of the fluid systems will be discussed.

AAPG Search and Discovery Article #90186 © AAPG Geoscience Technology Workshop, Hydrocarbon Charge Considerations in Liquid-Rich Unconventional Petroleum Systems, November 5, 2013, Vancouver, BC, Canada