The reservoir can be divided into two sections (1)Rocks (2)Fluids, whole reservoir engineering revolves around these two elements and their interaction at different pressure (P) and sometimes temperature (T) conditions. These interactions are further complicated by injecting different fluids to pump-out residual (stubborn) hydrocarbon molecules (EOR techniques).
Rock properties mainly consist of fundamental questions on Mineralogy, Porosity, Permeability, and saturation (big brother of porosity) determination. While fluid properties are mainly determination of fluid thermodynamic behaviour at different P&T conditions. This is achieved, first by measuring the fluid composition and then using equation of state (EOS) models to predict behaviour at different pressure/temperature conditions.
Finally, rocks and fluids are combined to determine their interactions, as properties of both of them can change when they are combined and the world becomes more complex/interesting once rocks & fluids are combined. For example: when flow occurs in nanopores due to variation in density near the walls critical points of fluid changes. Similarly, relative permeability changes due to slippage of molecules on the pore walls or consider unconsolidated sands rock compressibility which changes drastically (Ekofisk, Norway) with production causing man-made subsidence. Along with the change in individual characteristics of the elements (rock/fluid), the combination results in the definition of newer properties like relative permeability, surface tension, capillary pressure, different types of compressibilities (Cpp,Cpc,Cpb,Cbp).
Engineers have three different methods to “MEASURE” these properties at different scales (a) Core analysis (b) Well-logs (c) Well-Tests (WFT/DST/RTA). But, countless empirical correlations & Methods/Models (generally, adopted from other science disciplines (even Darcy was a civil engineer!) exists to “CALCULATE” combined properties of rocks, hydrocarbons & their interactions. Once enough data is available about the system reservoir modelling is done using geostatistical techniques and mathematical simulations are used to predict future behaviour of the reservoir.
This site deals with newer methods and models which can be envisioned so measure/calculate these properties using laboratory experiments/theoretical laws.
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